In this book, we solve the heat equation partial differential equation by first transforming it into an integral equation. We use exponential temperature profiles which satisfy the boundary conditions and also the initial condition. We also look at cases where ther is natural convection and go ahead and solve for both the transient and steady state solution. We also go ahead an solve the heat equation in cylindrical coordinates. We explain alot of phenomena observed experimentally for example the melting of wax on the sides of a metal rod when heat is applied on one end. For updated information about heat flow, follow the link below:
https://www.slideshare.net/Wasswaderrick3/analytic-solutions-to-the-heat-equation-using-integral-methods-with-experimental-resultspdf
Integral method of the Analytic solutions to the heat equation With Experimen...Wasswaderrick3
In this book, we solve the partial differential equation of the heat equation by first transforming it into an integral equation. We use exponential temperature profiles which satisfy the boundary conditions and also the initial condition. We also look at cases where ther is natural convection and go ahead and solve for both the transient and steady state solution and compare the mathematical findings with those got from experiment. We also go ahead an solve the heat equation in cylindrical coordinates. We explain alot of phenomena observed experimentally for example the melting of wax on the sides of a metal rod when heat is applied on one end
This document discusses analytical solutions to the heat equation using an integral method for various scenarios involving heat flow through semi-infinite and finite metal rods and cylinders. It first presents the analytical solution for a semi-infinite wall and provides an alternative derivation. It then explains how the Fourier law of heat conduction applies in steady state for a semi-infinite rod. Subsequent sections generalize the solutions to scenarios involving rods of different materials arranged in series, natural convection, different boundary conditions, finite lengths, zero flux boundaries, cylindrical coordinates, and temperature-dependent initial conditions.
In this book, we look at the analytical integral approach used to solve the heat equation. We look at different cases of boundary and initial conditions and we solve the heat equation using exponential temperature profiles that satisfy the boundary and initial conditions. We go ahead to look at predictions made by the solutions we have calculated and verify them experimentally. We look at different geometries including rectangular coordinates, cylindrical cordinates and solve their governing equations analytically. We look at the predictions of the transient state made by the solutions and verify them experimentally. We look at scenarios of semi-infinite rods, finite rods including semi-infinite cylinders and finite cylinders. We go ahead to develop the governing equation for heat loss by convection for a liquid in a container.In all the above solutions, we used the integral approach to solve for the solutions. We compare the Fourier series solution to our solution and we realise that the Fourier solution is approximate since it involves summing terms to infinity yet we notice that our solution is exact. We look at cases where theres is both conduction and natural convection at the sides of the rod and solve the governing equations for given boundary and initial conditions. We realise that our method of approach can be used to solve the heat equation for any type of boundary conditions.
TRANSIENT AND STEADY STATE HEAT CONDUCTION WITH NO LATERAL CONVECTION SOLVED ...Wasswaderrick3
In this book we go ahead and solve for the transient and steady state heat conduction phenomena in one dimensional heat flow with no lateral convection. It is known that there exist a Fourier series method but the problem of this method is that it is an approximate method since it involves summing up to infinite number of terms which we can never achieve in practice without approximating. In this book we develop an analytic solution to the heat equation with no lateral convection by using the already derived hyperbolic temperature profile functions in literature and solve the heat equation using these functions and the integral equation method and get a solution of the time dependent parameter δ which we substitute in the temperature profile. We deal with different types of boundary conditions and get their solutions. In solving for the steady state temperatures, we use the L’hopital’s rule since we get undefined limits when we substitute for time tending to infinity in some cases. We realize that the steady state temperature profile agrees with theory.
RADIAL HEAT CONDUCTION SOLVED USING THE INTEGRAL EQUATION .pdfWasswaderrick3
We look at the case of radial heat flow. Again, in radial heat flow, the temperature profiles that satisfy the boundary and initial conditions are the exponential and hyperbolic functions as derived in literature of conduction in fins. We use the technique of transforming the PDE into an integral equation. But in the case of radial heat flow, we have to multiply through by r the heat equation and then introduce integrals. We do this to avoid introducing integrals of the form of the exponential integral whose solutions cannot be expressed in the form of a simple mathematical function. We look at the case of a semi-infinite hollow cylinder for both insulated and non-insulated cases and then find the solution. We also look at cases of finite radius hollow cylinders subject to given boundary conditions. We notice that the solutions got for finite radius hollow cylinders do not reduce to those of semi-infinite hollow cylinders. We conclude by saying that this same analysis can be extended to spherical co-ordinates heat conduction.
SEMI-INFINITE ROD SOLUTION FOR TRANSIENT AND STEADY STATE.pdfWasswaderrick3
For the case of conduction of semi-infinite metal rod in natural convection, we postulate that the temperature profile which satisfies the boundary conditions and the initial condition is the exponential temperature profile. We go ahead and solve the heat equation using this temperature profile and the integral approach and the solution got is used to explain what is observed in the transient and steady state. We notice that the prediction made by the theory is not exactly what is observed with an intercept term which comes in. To account for this intercept, we postulate that there’s convection at the hot end. This accounts for the observed intercept. This analysis can be extended to metal rods of finite length with given boundary conditions and different geometries.
GENERAL MATHEMATICAL THEORY OF HEAT CONDUCTION USING THE INTEGRAL HEAT EQUATI...Wasswaderrick3
In this book, we look at using the integral heat equation as the general method of solving the heat equation subject to given boundary conditions. We begin first by looking at x- directional heat conduction and look at the case of the insulated metal rod first. It is known from literature that the Fourier series yield a solution to this problem for given boundary conditions. But on analyzing the solution got, we notice that it is made up of an infinite number of terms and what this means is that we shall only have an approximate solution since we can’t in practice add up all the terms to infinity. To solve this problem, we solved the heat equation by first transforming it into an integral equation and then find an exact solution as shall be shown in the text later. In solving the heat equation, the temperature profiles that satisfy the heat equation are exponential temperature profiles and hyperbolic temperature profiles as derived in literature for heat conduction in fins. For this case of insulate metal rod, we invoke L’hopital’s rule to get the steady state temperature profile. We then extend this integral equation approach to the case where there is lateral convection along the metal rod and get also both the transient and steady state solution which agrees with theory for steady state heat conduction.
After that, we look at the case of radial heat flow. Again, in radial heat flow, the temperature profiles that satisfy the boundary and initial conditions are the exponential and hyperbolic functions as derived in literature of conduction in fins. We use the same technique of transforming the PDE into an integral equation. But in the case of radial heat flow, we have to multiply through by r the heat equation and then introduce integrals. We do this to avoid introducing integrals of the form of the exponential integral whose solutions cannot be expressed in the form of a simple mathematical function. We look at the case of a semi-infinite hollow cylinder for both insulated and non-insulated cases and then find the solution. We also look at cases of finite radius hollow cylinders subject to given boundary conditions. We notice that the solutions got for finite radius hollow cylinders do not reduce to those of semi-infinite hollow cylinders as was the case for x-directional heat flow. We conclude by saying that this same analysis can be extended to spherical co-ordinates heat conduction
THE TEMPERATURE PROFILE SOLUTION IN NATURAL CONVECTION SOLVED MATHEMATICALLY.pdfWasswaderrick3
In this book we derive the generalized cooling law in natural convection for all temperature excesses from empirical results using the fact that Newton's law of cooling is obeyed for temperature excesses less than 30C. We derive an equation from empirical results that predicts the rate of cooling for a given temperature excess and then integrate and solve this equation to give us a straight line that predicts the temperature at a given time for a cooling body in natural convection for all temperature excesses
Integral method of the Analytic solutions to the heat equation With Experimen...Wasswaderrick3
In this book, we solve the partial differential equation of the heat equation by first transforming it into an integral equation. We use exponential temperature profiles which satisfy the boundary conditions and also the initial condition. We also look at cases where ther is natural convection and go ahead and solve for both the transient and steady state solution and compare the mathematical findings with those got from experiment. We also go ahead an solve the heat equation in cylindrical coordinates. We explain alot of phenomena observed experimentally for example the melting of wax on the sides of a metal rod when heat is applied on one end
This document discusses analytical solutions to the heat equation using an integral method for various scenarios involving heat flow through semi-infinite and finite metal rods and cylinders. It first presents the analytical solution for a semi-infinite wall and provides an alternative derivation. It then explains how the Fourier law of heat conduction applies in steady state for a semi-infinite rod. Subsequent sections generalize the solutions to scenarios involving rods of different materials arranged in series, natural convection, different boundary conditions, finite lengths, zero flux boundaries, cylindrical coordinates, and temperature-dependent initial conditions.
In this book, we look at the analytical integral approach used to solve the heat equation. We look at different cases of boundary and initial conditions and we solve the heat equation using exponential temperature profiles that satisfy the boundary and initial conditions. We go ahead to look at predictions made by the solutions we have calculated and verify them experimentally. We look at different geometries including rectangular coordinates, cylindrical cordinates and solve their governing equations analytically. We look at the predictions of the transient state made by the solutions and verify them experimentally. We look at scenarios of semi-infinite rods, finite rods including semi-infinite cylinders and finite cylinders. We go ahead to develop the governing equation for heat loss by convection for a liquid in a container.In all the above solutions, we used the integral approach to solve for the solutions. We compare the Fourier series solution to our solution and we realise that the Fourier solution is approximate since it involves summing terms to infinity yet we notice that our solution is exact. We look at cases where theres is both conduction and natural convection at the sides of the rod and solve the governing equations for given boundary and initial conditions. We realise that our method of approach can be used to solve the heat equation for any type of boundary conditions.
TRANSIENT AND STEADY STATE HEAT CONDUCTION WITH NO LATERAL CONVECTION SOLVED ...Wasswaderrick3
In this book we go ahead and solve for the transient and steady state heat conduction phenomena in one dimensional heat flow with no lateral convection. It is known that there exist a Fourier series method but the problem of this method is that it is an approximate method since it involves summing up to infinite number of terms which we can never achieve in practice without approximating. In this book we develop an analytic solution to the heat equation with no lateral convection by using the already derived hyperbolic temperature profile functions in literature and solve the heat equation using these functions and the integral equation method and get a solution of the time dependent parameter δ which we substitute in the temperature profile. We deal with different types of boundary conditions and get their solutions. In solving for the steady state temperatures, we use the L’hopital’s rule since we get undefined limits when we substitute for time tending to infinity in some cases. We realize that the steady state temperature profile agrees with theory.
RADIAL HEAT CONDUCTION SOLVED USING THE INTEGRAL EQUATION .pdfWasswaderrick3
We look at the case of radial heat flow. Again, in radial heat flow, the temperature profiles that satisfy the boundary and initial conditions are the exponential and hyperbolic functions as derived in literature of conduction in fins. We use the technique of transforming the PDE into an integral equation. But in the case of radial heat flow, we have to multiply through by r the heat equation and then introduce integrals. We do this to avoid introducing integrals of the form of the exponential integral whose solutions cannot be expressed in the form of a simple mathematical function. We look at the case of a semi-infinite hollow cylinder for both insulated and non-insulated cases and then find the solution. We also look at cases of finite radius hollow cylinders subject to given boundary conditions. We notice that the solutions got for finite radius hollow cylinders do not reduce to those of semi-infinite hollow cylinders. We conclude by saying that this same analysis can be extended to spherical co-ordinates heat conduction.
SEMI-INFINITE ROD SOLUTION FOR TRANSIENT AND STEADY STATE.pdfWasswaderrick3
For the case of conduction of semi-infinite metal rod in natural convection, we postulate that the temperature profile which satisfies the boundary conditions and the initial condition is the exponential temperature profile. We go ahead and solve the heat equation using this temperature profile and the integral approach and the solution got is used to explain what is observed in the transient and steady state. We notice that the prediction made by the theory is not exactly what is observed with an intercept term which comes in. To account for this intercept, we postulate that there’s convection at the hot end. This accounts for the observed intercept. This analysis can be extended to metal rods of finite length with given boundary conditions and different geometries.
GENERAL MATHEMATICAL THEORY OF HEAT CONDUCTION USING THE INTEGRAL HEAT EQUATI...Wasswaderrick3
In this book, we look at using the integral heat equation as the general method of solving the heat equation subject to given boundary conditions. We begin first by looking at x- directional heat conduction and look at the case of the insulated metal rod first. It is known from literature that the Fourier series yield a solution to this problem for given boundary conditions. But on analyzing the solution got, we notice that it is made up of an infinite number of terms and what this means is that we shall only have an approximate solution since we can’t in practice add up all the terms to infinity. To solve this problem, we solved the heat equation by first transforming it into an integral equation and then find an exact solution as shall be shown in the text later. In solving the heat equation, the temperature profiles that satisfy the heat equation are exponential temperature profiles and hyperbolic temperature profiles as derived in literature for heat conduction in fins. For this case of insulate metal rod, we invoke L’hopital’s rule to get the steady state temperature profile. We then extend this integral equation approach to the case where there is lateral convection along the metal rod and get also both the transient and steady state solution which agrees with theory for steady state heat conduction.
After that, we look at the case of radial heat flow. Again, in radial heat flow, the temperature profiles that satisfy the boundary and initial conditions are the exponential and hyperbolic functions as derived in literature of conduction in fins. We use the same technique of transforming the PDE into an integral equation. But in the case of radial heat flow, we have to multiply through by r the heat equation and then introduce integrals. We do this to avoid introducing integrals of the form of the exponential integral whose solutions cannot be expressed in the form of a simple mathematical function. We look at the case of a semi-infinite hollow cylinder for both insulated and non-insulated cases and then find the solution. We also look at cases of finite radius hollow cylinders subject to given boundary conditions. We notice that the solutions got for finite radius hollow cylinders do not reduce to those of semi-infinite hollow cylinders as was the case for x-directional heat flow. We conclude by saying that this same analysis can be extended to spherical co-ordinates heat conduction
THE TEMPERATURE PROFILE SOLUTION IN NATURAL CONVECTION SOLVED MATHEMATICALLY.pdfWasswaderrick3
In this book we derive the generalized cooling law in natural convection for all temperature excesses from empirical results using the fact that Newton's law of cooling is obeyed for temperature excesses less than 30C. We derive an equation from empirical results that predicts the rate of cooling for a given temperature excess and then integrate and solve this equation to give us a straight line that predicts the temperature at a given time for a cooling body in natural convection for all temperature excesses
DERIVATION OF MODIFIED BERNOULLI EQUATION WITH VISCOUS EFFECTS AND TERMINAL V...Wasswaderrick3
In this book, we use conservation of energy techniques on a fluid element to derive the Modified Bernoulli equation of flow with viscous or friction effects. We derive the general equation of flow/ velocity and then from this we derive the Pouiselle flow equation, the transition flow equation and the turbulent flow equation. In the situations where there are no viscous effects , the equation reduces to the Bernoulli equation. From experimental results, we are able to include other terms in the Bernoulli equation. We also look at cases where pressure gradients exist. We use the Modified Bernoulli equation to derive equations of flow rate for pipes of different cross sectional areas connected together. We also extend our techniques of energy conservation to a sphere falling in a viscous medium under the effect of gravity. We demonstrate Stokes equation of terminal velocity and turbulent flow equation. We look at a way of calculating the time taken for a body to fall in a viscous medium. We also look at the general equation of terminal velocity.
FUNDAMENTALS OF FLUID FLOW 3rd Edition .pdfWasswaderrick3
In this book we use energy conservation techniques on a differential element and derive the governing equation from which we get the Toricelli , Pouiselle , transition and turbulent flow equations all from one equation. The most important value in using the energy conservation techniques is to first get the Friction factor by solving the corresponding Navier Stoke's equation for a given geometry of pipe for laminar flow and then find the Friction factor whose value we use to derive the Toricelli governing equation, the laminar flow equation, turbulent flow and transition flow equations. We note that in Toricelli flow the length of the pipe is reduced to zero and we go ahead to derive the governing equation. We go ahead to look at the head loss equations and derive the friction factors from them. we also go ahead to look at a spherical body falling under the influence of gravity alone and we derive the governing equations and terminal velocity equations. Other phenomena are explained too
n this book we use energy conservation techniques on a differential element and derive the governing equation from which we get the Toricelli , Pouiselle , transition and turbulent flow equations all from one equation. The most important value in using the energy conservation techniques is to first get the Friction factor by solving the corresponding Navier Stoke's equation for a given geometry of pipe for laminar flow and then find the Friction factor whose value we use to derive the Toricelli governing equation, the laminar flow equation, turbulent flow and transition flow equations. We note that in Toricelli flow the length of the pipe is reduced to zero and we go ahead to derive the governing equation. We go ahead to look at the head loss equations and derive the friction factors from them. we also go ahead to look at a spherical body falling under the influence of gravity alone and we derive the governing equations and terminal velocity equations. Other phenomena are explained too
FUNDAMENTALS OF FLUID FLOW 3rd Edition.pdfWasswaderrick3
In this book we use energy conservation techniques on a differential element and derive the governing equation from which we get the Toricelli , Pouiselle , transition and turbulent flow equations all from one equation. The most important value in using the energy conservation techniques is to first get the Friction factor by solving the corresponding Navier Stoke's equation for a given geometry of pipe for laminar flow and then find the Friction factor whose value we use to derive the Toricelli governing equation, the laminar flow equation, turbulent flow and transition flow equations. We note that in Toricelli flow the length of the pipe is reduced to zero and we go ahead to derive the governing equation. We go ahead to look at the head loss equations and derive the friction factors from them. we also go ahead to look at a spherical body falling under the influence of gravity alone and we derive the governing equations and terminal velocity equations. Other phenomena are explained too
THE COOLING CURVE SOLUTION IN NATURAL CONVECTION EXPLAINED.pdfWasswaderrick3
In this book we derive the generalized cooling law in natural convection for all temperature excesses from empirical results using the fact that Newton's law of cooling is obeyed for temperature excesses less than 30C. We derive an equation from empirical results that predicts the rate of cooling for a given temperature excess and then integrate and solve this equation to give us a straight line that predicts the temperature at a given time for a cooling body in natural convection for all temperature excesses
THE RATE OF COOLING IN NATURAL CONVECTION EXPLAINED AND SOLVED.pdfWasswaderrick3
In this book we derive the generalized cooling law in natural convection for all temperature excesses from empirical results using the fact that Newton's law of cooling is obeyed for temperature excesses less than 30C. We derive an equation from empirical results that predicts the rate of cooling for a given temperature excess and then integrate and solve this equation to give us a straight line that predicts the temperature at a given time for a cooling body in natural convection for all temperature excesses
TRANSIENT STATE HEAT CONDUCTION SOLVED.pdfWasswaderrick3
Here are the key claims, findings, and conclusions from the text:
Claims:
- Transient state heat transfer in a cylindrical metal rod with one end heated can be modeled mathematically. - The temperature profile along the rod depends on whether the rod is semi-infinite or finite.
- There is convection at the heated end of the rod as investigated experimentally in addition to conduction along the rod.
Findings: - For a semi-infinite rod, the temperature profile decays exponentially with distance from the heated end.
- For a finite rod with no flux at the far end, the temperature profile involves hyperbolic cosine functions.
- For a finite rod with convection at the far end, the temperature profile also depends on hyperbolic sine functions. - The models match experimental measurements of melting wax particles along aluminum rods. We deduce from experiment that there’s convection at the hot end and that the heat transfer coefficient at the far end varies with length of the metal rod.
Conclusions:
- The integral transform approach allows deriving temperature profiles satisfying boundary conditions.
- There is convection at the hot end, and the heat transfer coefficient at the far end varies with length L as investigated experimentally.
- The simple models provide good agreement with experimental temperature profiles in aluminum rods. In summary, the text presents mathematical models of heat transfer in metal rods that agree with experiments and provide insight into the temperature profiles by considering different boundary conditions. The key findings relate to the functional forms of the temperature profiles in semi-infinite versus finite rods.
DERIVATION OF THE MODIFIED BERNOULLI EQUATION WITH VISCOUS EFFECTS AND TERMIN...Wasswaderrick3
In this book, we use conservation of energy techniques on a fluid element to derive the Modified Bernoulli equation of flow with viscous or friction effects. We derive the general equation of flow/ velocity and then from this we derive the Pouiselle flow equation, the transition flow equation and the turbulent flow equation. In the situations where there are no viscous effects , the equation reduces to the Bernoulli equation. From experimental results, we are able to include other terms in the Bernoulli equation. We also look at cases where pressure gradients exist. We use the Modified Bernoulli equation to derive equations of flow rate for pipes of different cross sectional areas connected together. We also extend our techniques of energy conservation to a sphere falling in a viscous medium under the effect of gravity. We demonstrate Stokes equation of terminal velocity and turbulent flow equation. We look at a way of calculating the time taken for a body to fall in a viscous medium. We also look at the general equation of terminal velocity.
Integral methods for the analytic solutions to the heat equation.pdfWasswaderrick3
In this book, we solve the heat equation partial differential equation by first transforming it into an integral equation. We use exponential temperature profiles which satisfy the boundary conditions and also the initial condition. We also look at cases where ther is natural convection and go ahead and solve for both the transient and steady state solution. We also go ahead an solve the heat equation in cylindrical coordinates. We explain alot of phenomena observed experimentally for example the melting of wax on the sides of a metal rod when heat is applied on one end. For updated information about heat flow, follow the link below:
https://www.slideshare.net/Wasswaderrick3/analytic-solutions-to-the-heat-equation-using-integral-methods-with-experimental-resultspdf
DEEP LEARNING FOR SMART GRID INTRUSION DETECTION: A HYBRID CNN-LSTM-BASED MODELgerogepatton
As digital technology becomes more deeply embedded in power systems, protecting the communication
networks of Smart Grids (SG) has emerged as a critical concern. Distributed Network Protocol 3 (DNP3)
represents a multi-tiered application layer protocol extensively utilized in Supervisory Control and Data
Acquisition (SCADA)-based smart grids to facilitate real-time data gathering and control functionalities.
Robust Intrusion Detection Systems (IDS) are necessary for early threat detection and mitigation because
of the interconnection of these networks, which makes them vulnerable to a variety of cyberattacks. To
solve this issue, this paper develops a hybrid Deep Learning (DL) model specifically designed for intrusion
detection in smart grids. The proposed approach is a combination of the Convolutional Neural Network
(CNN) and the Long-Short-Term Memory algorithms (LSTM). We employed a recent intrusion detection
dataset (DNP3), which focuses on unauthorized commands and Denial of Service (DoS) cyberattacks, to
train and test our model. The results of our experiments show that our CNN-LSTM method is much better
at finding smart grid intrusions than other deep learning algorithms used for classification. In addition,
our proposed approach improves accuracy, precision, recall, and F1 score, achieving a high detection
accuracy rate of 99.50%.
Advanced control scheme of doubly fed induction generator for wind turbine us...IJECEIAES
This paper describes a speed control device for generating electrical energy on an electricity network based on the doubly fed induction generator (DFIG) used for wind power conversion systems. At first, a double-fed induction generator model was constructed. A control law is formulated to govern the flow of energy between the stator of a DFIG and the energy network using three types of controllers: proportional integral (PI), sliding mode controller (SMC) and second order sliding mode controller (SOSMC). Their different results in terms of power reference tracking, reaction to unexpected speed fluctuations, sensitivity to perturbations, and resilience against machine parameter alterations are compared. MATLAB/Simulink was used to conduct the simulations for the preceding study. Multiple simulations have shown very satisfying results, and the investigations demonstrate the efficacy and power-enhancing capabilities of the suggested control system.
Comparative analysis between traditional aquaponics and reconstructed aquapon...bijceesjournal
The aquaponic system of planting is a method that does not require soil usage. It is a method that only needs water, fish, lava rocks (a substitute for soil), and plants. Aquaponic systems are sustainable and environmentally friendly. Its use not only helps to plant in small spaces but also helps reduce artificial chemical use and minimizes excess water use, as aquaponics consumes 90% less water than soil-based gardening. The study applied a descriptive and experimental design to assess and compare conventional and reconstructed aquaponic methods for reproducing tomatoes. The researchers created an observation checklist to determine the significant factors of the study. The study aims to determine the significant difference between traditional aquaponics and reconstructed aquaponics systems propagating tomatoes in terms of height, weight, girth, and number of fruits. The reconstructed aquaponics system’s higher growth yield results in a much more nourished crop than the traditional aquaponics system. It is superior in its number of fruits, height, weight, and girth measurement. Moreover, the reconstructed aquaponics system is proven to eliminate all the hindrances present in the traditional aquaponics system, which are overcrowding of fish, algae growth, pest problems, contaminated water, and dead fish.
Using recycled concrete aggregates (RCA) for pavements is crucial to achieving sustainability. Implementing RCA for new pavement can minimize carbon footprint, conserve natural resources, reduce harmful emissions, and lower life cycle costs. Compared to natural aggregate (NA), RCA pavement has fewer comprehensive studies and sustainability assessments.
DERIVATION OF MODIFIED BERNOULLI EQUATION WITH VISCOUS EFFECTS AND TERMINAL V...Wasswaderrick3
In this book, we use conservation of energy techniques on a fluid element to derive the Modified Bernoulli equation of flow with viscous or friction effects. We derive the general equation of flow/ velocity and then from this we derive the Pouiselle flow equation, the transition flow equation and the turbulent flow equation. In the situations where there are no viscous effects , the equation reduces to the Bernoulli equation. From experimental results, we are able to include other terms in the Bernoulli equation. We also look at cases where pressure gradients exist. We use the Modified Bernoulli equation to derive equations of flow rate for pipes of different cross sectional areas connected together. We also extend our techniques of energy conservation to a sphere falling in a viscous medium under the effect of gravity. We demonstrate Stokes equation of terminal velocity and turbulent flow equation. We look at a way of calculating the time taken for a body to fall in a viscous medium. We also look at the general equation of terminal velocity.
FUNDAMENTALS OF FLUID FLOW 3rd Edition .pdfWasswaderrick3
In this book we use energy conservation techniques on a differential element and derive the governing equation from which we get the Toricelli , Pouiselle , transition and turbulent flow equations all from one equation. The most important value in using the energy conservation techniques is to first get the Friction factor by solving the corresponding Navier Stoke's equation for a given geometry of pipe for laminar flow and then find the Friction factor whose value we use to derive the Toricelli governing equation, the laminar flow equation, turbulent flow and transition flow equations. We note that in Toricelli flow the length of the pipe is reduced to zero and we go ahead to derive the governing equation. We go ahead to look at the head loss equations and derive the friction factors from them. we also go ahead to look at a spherical body falling under the influence of gravity alone and we derive the governing equations and terminal velocity equations. Other phenomena are explained too
n this book we use energy conservation techniques on a differential element and derive the governing equation from which we get the Toricelli , Pouiselle , transition and turbulent flow equations all from one equation. The most important value in using the energy conservation techniques is to first get the Friction factor by solving the corresponding Navier Stoke's equation for a given geometry of pipe for laminar flow and then find the Friction factor whose value we use to derive the Toricelli governing equation, the laminar flow equation, turbulent flow and transition flow equations. We note that in Toricelli flow the length of the pipe is reduced to zero and we go ahead to derive the governing equation. We go ahead to look at the head loss equations and derive the friction factors from them. we also go ahead to look at a spherical body falling under the influence of gravity alone and we derive the governing equations and terminal velocity equations. Other phenomena are explained too
FUNDAMENTALS OF FLUID FLOW 3rd Edition.pdfWasswaderrick3
In this book we use energy conservation techniques on a differential element and derive the governing equation from which we get the Toricelli , Pouiselle , transition and turbulent flow equations all from one equation. The most important value in using the energy conservation techniques is to first get the Friction factor by solving the corresponding Navier Stoke's equation for a given geometry of pipe for laminar flow and then find the Friction factor whose value we use to derive the Toricelli governing equation, the laminar flow equation, turbulent flow and transition flow equations. We note that in Toricelli flow the length of the pipe is reduced to zero and we go ahead to derive the governing equation. We go ahead to look at the head loss equations and derive the friction factors from them. we also go ahead to look at a spherical body falling under the influence of gravity alone and we derive the governing equations and terminal velocity equations. Other phenomena are explained too
THE COOLING CURVE SOLUTION IN NATURAL CONVECTION EXPLAINED.pdfWasswaderrick3
In this book we derive the generalized cooling law in natural convection for all temperature excesses from empirical results using the fact that Newton's law of cooling is obeyed for temperature excesses less than 30C. We derive an equation from empirical results that predicts the rate of cooling for a given temperature excess and then integrate and solve this equation to give us a straight line that predicts the temperature at a given time for a cooling body in natural convection for all temperature excesses
THE RATE OF COOLING IN NATURAL CONVECTION EXPLAINED AND SOLVED.pdfWasswaderrick3
In this book we derive the generalized cooling law in natural convection for all temperature excesses from empirical results using the fact that Newton's law of cooling is obeyed for temperature excesses less than 30C. We derive an equation from empirical results that predicts the rate of cooling for a given temperature excess and then integrate and solve this equation to give us a straight line that predicts the temperature at a given time for a cooling body in natural convection for all temperature excesses
TRANSIENT STATE HEAT CONDUCTION SOLVED.pdfWasswaderrick3
Here are the key claims, findings, and conclusions from the text:
Claims:
- Transient state heat transfer in a cylindrical metal rod with one end heated can be modeled mathematically. - The temperature profile along the rod depends on whether the rod is semi-infinite or finite.
- There is convection at the heated end of the rod as investigated experimentally in addition to conduction along the rod.
Findings: - For a semi-infinite rod, the temperature profile decays exponentially with distance from the heated end.
- For a finite rod with no flux at the far end, the temperature profile involves hyperbolic cosine functions.
- For a finite rod with convection at the far end, the temperature profile also depends on hyperbolic sine functions. - The models match experimental measurements of melting wax particles along aluminum rods. We deduce from experiment that there’s convection at the hot end and that the heat transfer coefficient at the far end varies with length of the metal rod.
Conclusions:
- The integral transform approach allows deriving temperature profiles satisfying boundary conditions.
- There is convection at the hot end, and the heat transfer coefficient at the far end varies with length L as investigated experimentally.
- The simple models provide good agreement with experimental temperature profiles in aluminum rods. In summary, the text presents mathematical models of heat transfer in metal rods that agree with experiments and provide insight into the temperature profiles by considering different boundary conditions. The key findings relate to the functional forms of the temperature profiles in semi-infinite versus finite rods.
DERIVATION OF THE MODIFIED BERNOULLI EQUATION WITH VISCOUS EFFECTS AND TERMIN...Wasswaderrick3
In this book, we use conservation of energy techniques on a fluid element to derive the Modified Bernoulli equation of flow with viscous or friction effects. We derive the general equation of flow/ velocity and then from this we derive the Pouiselle flow equation, the transition flow equation and the turbulent flow equation. In the situations where there are no viscous effects , the equation reduces to the Bernoulli equation. From experimental results, we are able to include other terms in the Bernoulli equation. We also look at cases where pressure gradients exist. We use the Modified Bernoulli equation to derive equations of flow rate for pipes of different cross sectional areas connected together. We also extend our techniques of energy conservation to a sphere falling in a viscous medium under the effect of gravity. We demonstrate Stokes equation of terminal velocity and turbulent flow equation. We look at a way of calculating the time taken for a body to fall in a viscous medium. We also look at the general equation of terminal velocity.
Integral methods for the analytic solutions to the heat equation.pdfWasswaderrick3
In this book, we solve the heat equation partial differential equation by first transforming it into an integral equation. We use exponential temperature profiles which satisfy the boundary conditions and also the initial condition. We also look at cases where ther is natural convection and go ahead and solve for both the transient and steady state solution. We also go ahead an solve the heat equation in cylindrical coordinates. We explain alot of phenomena observed experimentally for example the melting of wax on the sides of a metal rod when heat is applied on one end. For updated information about heat flow, follow the link below:
https://www.slideshare.net/Wasswaderrick3/analytic-solutions-to-the-heat-equation-using-integral-methods-with-experimental-resultspdf
DEEP LEARNING FOR SMART GRID INTRUSION DETECTION: A HYBRID CNN-LSTM-BASED MODELgerogepatton
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networks of Smart Grids (SG) has emerged as a critical concern. Distributed Network Protocol 3 (DNP3)
represents a multi-tiered application layer protocol extensively utilized in Supervisory Control and Data
Acquisition (SCADA)-based smart grids to facilitate real-time data gathering and control functionalities.
Robust Intrusion Detection Systems (IDS) are necessary for early threat detection and mitigation because
of the interconnection of these networks, which makes them vulnerable to a variety of cyberattacks. To
solve this issue, this paper develops a hybrid Deep Learning (DL) model specifically designed for intrusion
detection in smart grids. The proposed approach is a combination of the Convolutional Neural Network
(CNN) and the Long-Short-Term Memory algorithms (LSTM). We employed a recent intrusion detection
dataset (DNP3), which focuses on unauthorized commands and Denial of Service (DoS) cyberattacks, to
train and test our model. The results of our experiments show that our CNN-LSTM method is much better
at finding smart grid intrusions than other deep learning algorithms used for classification. In addition,
our proposed approach improves accuracy, precision, recall, and F1 score, achieving a high detection
accuracy rate of 99.50%.
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Using recycled concrete aggregates (RCA) for pavements is crucial to achieving sustainability. Implementing RCA for new pavement can minimize carbon footprint, conserve natural resources, reduce harmful emissions, and lower life cycle costs. Compared to natural aggregate (NA), RCA pavement has fewer comprehensive studies and sustainability assessments.
Redefining brain tumor segmentation: a cutting-edge convolutional neural netw...IJECEIAES
Medical image analysis has witnessed significant advancements with deep learning techniques. In the domain of brain tumor segmentation, the ability to
precisely delineate tumor boundaries from magnetic resonance imaging (MRI)
scans holds profound implications for diagnosis. This study presents an ensemble convolutional neural network (CNN) with transfer learning, integrating
the state-of-the-art Deeplabv3+ architecture with the ResNet18 backbone. The
model is rigorously trained and evaluated, exhibiting remarkable performance
metrics, including an impressive global accuracy of 99.286%, a high-class accuracy of 82.191%, a mean intersection over union (IoU) of 79.900%, a weighted
IoU of 98.620%, and a Boundary F1 (BF) score of 83.303%. Notably, a detailed comparative analysis with existing methods showcases the superiority of
our proposed model. These findings underscore the model’s competence in precise brain tumor localization, underscoring its potential to revolutionize medical
image analysis and enhance healthcare outcomes. This research paves the way
for future exploration and optimization of advanced CNN models in medical
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Optimizing Gradle Builds - Gradle DPE Tour Berlin 2024Sinan KOZAK
Sinan from the Delivery Hero mobile infrastructure engineering team shares a deep dive into performance acceleration with Gradle build cache optimizations. Sinan shares their journey into solving complex build-cache problems that affect Gradle builds. By understanding the challenges and solutions found in our journey, we aim to demonstrate the possibilities for faster builds. The case study reveals how overlapping outputs and cache misconfigurations led to significant increases in build times, especially as the project scaled up with numerous modules using Paparazzi tests. The journey from diagnosing to defeating cache issues offers invaluable lessons on maintaining cache integrity without sacrificing functionality.
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3. TABLE OF CONTENTS
SEMI INFINITE WALL ANALYTICAL SOLUTION TO THE HEAT EQUATION................3
ALTERNATIVE SOLUTION TO THE SEMI-INFINITE WALL PROBLEM ...........................5
HOW DO WE EXPLAIN THE EXISTENCE OF THE FOURIER LAW IN STEADY
STATE?......................................................................................................................................................8
HOW DO WE DEAL WITH CONVECTION AT THE SURFACE AREA OF THE METAL
ROD...........................................................................................................................................................11
EQUAL FIXED TEMPERATURES AT THE END OF AN INSULATED METAL ROD....14
UNEQUAL FIXED TEMPERATURES AT THE END OF AN INSULATED METAL ROD.
....................................................................................................................................................................17
HOW DO WE DEAL WITH OTHER TYPES OF BOUNDARY CONDITIONS?..................20
HOW DO WE DEAL WITH CONVECTION AT THE SURFACE AREA OF THE METAL
ROD FOR FIXED END TEMPERATURE......................................................................................22
WHAT HAPPENS WHEN THE INITIAL TEMPERATURE IS A FUNCTION OF X? .......31
HOW DO WE DEAL WITH CYLINDRICAL CO-ORDINATES?..............................................34
4. SEMI INFINITE WALL ANALYTICAL SOLUTION TO THE
HEAT EQUATION.
The differential equation to be solved is
𝜕𝑇
𝜕𝑡
= 𝛼
𝜕2
𝑇
𝜕𝑥2
Where the initial and boundary conditions are
𝑻 = 𝑻𝒔 𝒂𝒕 𝒙 = 𝟎 𝒇𝒐𝒓 𝒂𝒍𝒍 𝒕
𝑻 = 𝑻∞ 𝒂𝒕 𝒙 = ∞ 𝒇𝒐𝒓 𝒂𝒍𝒍 𝒕
𝑻 = 𝑻∞ 𝒂𝒕 𝒕 = 𝟎 𝒇𝒐𝒓 𝒂𝒍𝒍 𝒙
We postulate:
𝑌 =
𝑇 − 𝑇∞
𝑇𝑠 − 𝑇∞
And
𝜂 =
𝑥
2√𝛼𝑡
We get
𝑑2
𝑌
𝑑𝜂2
+ 2𝜂
𝑑𝑌
𝑑𝜂
= 0 (1)
With the transformed boundary and initial conditions
𝑌 → 0 𝑎𝑠 𝜂 → ∞
And
𝑌 = 1 𝑎𝑡 𝜂 = 0
The first condition is the same as the initial condition 𝑇 = 𝑇∞ 𝑎𝑡 𝑡 = 0 and the
boundary condition
𝑇 → 𝑇∞ 𝑎𝑠 𝑥 → ∞
Equation 1 may be integrated once to get
𝑙𝑛
𝑑𝑌
𝑑𝜂
= 𝑐1 − 𝜂2
𝑑𝑌
𝑑𝜂
= 𝑐2𝑒−𝜂2
5. And integrated once more to get
𝑌 = 𝑐3 + 𝑐2 ∫ 𝑒−𝜂2
𝑑 𝜂
Applying the boundary conditions to the equation, we get
𝑌 = 1 − erf (
𝑥
2√𝛼𝑡
)
𝑻 − 𝑻∞
𝑻𝒔 − 𝑻∞
= 𝟏 − 𝐞𝐫𝐟 (
𝒙
𝟐√𝜶𝒕
)
Or
𝑻𝒔 − 𝑻
𝑻𝒔 − 𝑻∞
= 𝐞𝐫𝐟 (
𝒙
𝟐√𝜶𝒕
)
6. ALTERNATIVE SOLUTION TO THE SEMI-INFINITE WALL PROBLEM
The problem of the semi-infinite wall could also be solved as below:
Given the boundary and initial conditions
𝑻 = 𝑻𝒔 𝒂𝒕 𝒙 = 𝟎 𝒇𝒐𝒓 𝒂𝒍𝒍 𝒕
𝑻 = 𝑻∞ 𝒂𝒕 𝒙 = ∞
𝑻 = 𝑻∞ 𝒂𝒕 𝒕 = 𝟎
And the governing equation
𝜕𝑇
𝜕𝑡
= 𝛼
𝜕2
𝑇
𝜕𝑥2
We assume an exponential temperature profile that satisfies the boundary
conditions:
𝑇 − 𝑇∞
𝑇𝑠 − 𝑇∞
= 𝑒
−𝑥
𝛿
We can satisfy the initial condition if we assume that 𝛿 will have a solution as
𝛿 = 𝑐𝑡𝑛
Where c and n are constants so that at 𝑡 = 0, 𝛿 = 0 and the initial condition is
satisfied as shown below.
𝑇 − 𝑇∞
𝑇𝑠 − 𝑇∞
= 𝑒
−𝑥
0 = 𝑒−∞
= 0
𝑇 = 𝑇∞ 𝑎𝑡 𝑡 = 0
We then transform the heat governing equation into an integral equation as:
𝛼 ∫ (
𝜕2
𝑇
𝜕𝑥2
) 𝑑𝑥
𝑙
0
= ∫
𝜕𝑇
𝜕𝑡
𝑑𝑥
𝑙
0
𝛼 ∫ (
𝜕2
𝑇
𝜕𝑥2
) 𝑑𝑥
𝑙
0
=
𝜕
𝜕𝑡
∫ 𝑇𝑑𝑥
𝑙
0
You notice that the integral
𝜕
𝜕𝑡
∫ 𝑇𝑑𝑥
𝑙
0
=
𝜕
𝜕𝑡
∫ (𝑇 − 𝑇∞)𝑑𝑥 =
𝜕
𝜕𝑡
∫ 𝑇𝑑𝑥
𝑙
0
−
𝜕(𝑙𝑇∞)
𝜕𝑡
𝑙
0
Since 𝑙 and 𝑇∞ are constants independent of time
𝜕(𝑙𝑇∞)
𝜕𝑡
= 0
7. So
𝜕
𝜕𝑡
∫ 𝑇𝑑𝑥
𝑙
0
=
𝜕
𝜕𝑡
∫ (𝑇 − 𝑇∞)𝑑𝑥
𝑙
0
We go ahead and find
𝜕2
𝑇
𝜕𝑥2
=
(𝑇𝑠 − 𝑇∞)
𝛿2
∫ (
𝜕2
𝑇
𝜕𝑥2
) 𝑑𝑥
𝛿
0
= −
(𝑇𝑠 − 𝑇∞)
𝛿
(𝑒
−𝑙
𝛿 − 1) =
(𝑇𝑠 − 𝑇∞)
𝛿
(1 − 𝑒
−𝑙
𝛿 )
𝜕
𝜕𝑡
∫ (𝑇 − 𝑇∞)𝑑𝑥
𝛿
0
=
𝑑𝛿
𝑑𝑡
[(𝑇𝑠 − 𝑇∞) (1 − 𝑒
−𝑙
𝛿 )]
Substituting into the integral equation, we get
𝛼
(𝑇𝑠 − 𝑇∞)
𝛿
(1 − 𝑒
−𝑙
𝛿 ) =
𝑑𝛿
𝑑𝑡
(1 − 𝑒
−𝑙
𝛿 )
The boundary conditions are
𝛿 = 0 𝑎𝑡 𝑡 = 0
We find
𝛿 = √2𝛼𝑡
We substitute in the temperature profile and get
𝑻 − 𝑻∞
𝑻𝒔 − 𝑻∞
= 𝒆
−𝒙
√𝟐𝜶𝒕
You notice that the initial condition is satisfied by the temperature profile
above i.e.,
At 𝑡 = 0
𝑻 − 𝑻∞
𝑻𝒔 − 𝑻∞
= 𝒆
−𝒙
√𝟐𝜶𝒕
Becomes
𝑻 − 𝑻∞
𝑻𝒔 − 𝑻∞
= 𝒆
−𝒙
𝟎 = 𝒆−∞
= 𝟎
Hence 𝑻 = 𝑻∞ throughout the rod at 𝑡 = 0
8. Observation.
The two equations
𝑻 − 𝑻∞
𝑻𝒔 − 𝑻∞
= 𝒆
−𝒙
√𝟐𝜶𝒕
And
𝑻 − 𝑻∞
𝑻𝒔 − 𝑻∞
= 𝟏 − 𝐞𝐫𝐟 (
𝒙
𝟐√𝜶𝒕
)
Should give the same answer. Indeed, they give answers that are the same with
a small error since the error function is got from tables after rounding off yet in
the exponential temperature profile there is no rounding off.
9. HOW DO WE EXPLAIN THE EXISTENCE OF THE
FOURIER LAW IN STEADY STATE?
The Fourier law states:
𝑄 = −𝑘𝐴
𝜕𝑇
𝜕𝑥
Under steady state.
It can be stated as:
𝜕𝑇
𝜕𝑥
= −
𝑄
𝑘𝐴
Under steady state.
To satisfy the Fourier law under steady state, we postulate the temperature
profile to be:
𝑻 − 𝑻∞ =
𝑸
𝒌𝑨
𝜹𝒆
−𝒙
𝜹
𝛿 is a function of time 𝑡 and not distance 𝑥
We believe that after solving for 𝛿, 𝛿 will be directly proportional to time t so
that 𝛿 = 𝑘𝑡𝑛
sothat at 𝑡 = ∞ , 𝛿 = ∞
And taking the first derivative of temperature with distance x at 𝑡 = ∞ , we get
𝜕𝑇
𝜕𝑥
|𝑡=∞ = −
𝑄
𝑘𝐴
𝑒
−𝑥
𝛿 = −
𝑄
𝑘𝐴
𝑒
−𝑥
∞ = −
𝑄
𝑘𝐴
𝑒0
𝝏𝑻
𝝏𝒙
= −
𝑸
𝒌𝑨
Hence the Fourier law is satisfied.
Now let us go ahead and solve for 𝛿.
Recall
PDE
𝜕𝑇
𝜕𝑡
= 𝛼
𝜕2
𝑇
𝜕𝑥2
The initial condition is
𝑇 = 𝑇∞ 𝑎𝑡 𝑡 = 0
The boundary conditions are
10. 𝑇 = 𝑇∞ 𝑎𝑡 𝑥 = ∞
𝜕𝑇
𝜕𝑥
|𝑥=0 = −
𝑄
𝑘𝐴
The PDE is
The temperature profile that satisfies the conditions above is
𝑇 − 𝑇∞ =
𝑄
𝑘𝐴
𝛿𝑒
−𝑥
𝛿
We transform the PDE into an integral equation
𝜕
𝜕𝑡
∫ (𝑇 − 𝑇∞)𝑑𝑥
𝛿
0
= 𝛼 ∫ (
𝜕2
𝑇
𝜕𝑥2
) 𝑑𝑥
𝛿
0
And using the temperature profile, we get
∫ (
𝜕2
𝑇
𝜕𝑥2
) 𝑑𝑥
𝛿
0
=
𝑄
𝑘𝐴
(1 − 𝑒
−𝑙
𝛿 )
𝜕
𝜕𝑡
∫ (𝑇 − 𝑇∞)𝑑𝑥
𝛿
0
=
𝑄
𝑘𝐴
𝛿2
(1 − 𝑒
−𝑙
𝛿 )
We then substitute into the integral equation
𝛼
𝑄
𝑘𝐴
(1 − 𝑒
−𝑙
𝛿 ) = 2𝛿
𝑑𝛿
𝑑𝑡
(
𝑄
𝑘𝐴
(1 − 𝑒
−𝑙
𝛿 ))
The boundary conditions are
𝛿 = 0 𝑎𝑡 𝑡 = 0
𝛿 = √𝛼𝑡
Substituting into the temperature profile, we get
𝑇 − 𝑇∞ =
𝑄
𝑘𝐴
𝛿𝑒
−𝑥
𝛿
𝑻 − 𝑻∞ =
𝑸
𝒌𝑨
× √𝜶𝒕 × 𝒆
−𝒙
√𝜶𝒕
You notice that the initial condition is satisfied
12. HOW DO WE DEAL WITH CONVECTION AT THE
SURFACE AREA OF THE METAL ROD
Recall that the temperature profile that satisfies the Fourier law was
𝑇 − 𝑇∞ =
𝑄
𝑘𝐴
𝛿𝑒
−𝑥
𝛿
Recall
PDE
𝛼
𝜕2
𝑇
𝜕𝑥2
−
ℎ𝑃
𝐴𝜌𝐶
(𝑇 − 𝑇∞) =
𝜕𝑇
𝜕𝑡
The initial condition is
𝑇 = 𝑇∞ 𝑎𝑡 𝑡 = 0
The boundary conditions are
𝑇 = 𝑇∞ 𝑎𝑡 𝑥 = ∞
𝜕𝑇
𝜕𝑥
|𝑥=0 = −
𝑄
𝑘𝐴
We transform the PDE into an integral equation
𝛼 ∫ (
𝜕2
𝑇
𝜕𝑥2
) 𝑑𝑥
𝑙
0
−
ℎ𝑃
𝐴𝜌𝐶
∫ (𝑇 − 𝑇∞)𝑑𝑥
𝑙
0
=
𝜕
𝜕𝑡
∫ (𝑇 − 𝑇∞)𝑑𝑥
𝑙
0
Where:
We are dealing with a cylindrical metal rod.
𝑃 = 2𝜋𝑟 𝑎𝑛𝑑 𝜌 = 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑚𝑒𝑡𝑎𝑙 𝑟𝑜𝑑
And using the temperature profile, we get
∫ (
𝜕2
𝑇
𝜕𝑥2
) 𝑑𝑥
𝑙
0
=
𝑄
𝑘𝐴
(1 − 𝑒
−𝑙
𝛿 )
∫ (𝑇 − 𝑇∞)𝑑𝑥
𝑙
0
=
𝑄
𝑘𝐴
𝛿2
(1 − 𝑒
−𝑙
𝛿 )
Substituting in the integral equation above, we get
𝛼 −
ℎ𝑃
𝐴𝜌𝐶
𝛿2
= 2𝛿
𝑑𝛿
𝑑𝑡
The boundary condition is
13. 𝛿 = 0 𝑎𝑡 𝑡 = 0
We solve and get
𝛿 = √
𝐴𝜌𝐶𝛼
ℎ𝑃
(1 − 𝑒
−ℎ𝑃𝑡
𝐴𝜌𝐶 )
Substituting in the temperature profile, we get
𝑇 − 𝑇∞ =
𝑄
𝑘𝐴
𝛿𝑒
−𝑥
𝛿
𝑻 − 𝑻∞ =
𝑸
𝒌𝑨
× √
𝑨𝝆𝑪𝜶
𝒉𝑷
(𝟏 − 𝒆
−𝒉𝑷𝒕
𝑨𝝆𝑪 ) × 𝒆
−𝒙
√𝑨𝝆𝑪
𝒉𝑷
(𝟏−𝒆
−𝒉𝑷𝒕
𝑨𝝆𝑪 )
We notice that the initial condition and boundary conditions are satisfied.
For small time the term
ℎ𝑃𝑡
𝐴𝜌𝐶
≪ 1
And using binomial approximation of the exponential, we get
𝑒
−ℎ𝑃𝑡
𝐴𝜌𝐶 = 1 −
ℎ𝑃𝑡
𝐴𝜌𝐶
Then
(1 − 𝑒
−ℎ𝑃𝑡
𝐴𝜌𝐶 ) =
ℎ𝑃𝑡
𝐴𝜌𝐶
Upon substitution in the temperature profile, we get
𝑇 − 𝑇∞ =
𝑄
𝑘𝐴
× √𝛼𝑡 × 𝑒
−𝑥
√𝛼𝑡
Upon rearranging, we get
𝑥
√𝛼𝑡
= ln (
𝑄
𝑘𝐴
√𝛼𝑡) − ln (𝑇 − 𝑇∞)
𝑥
√𝑡
= √𝛼ln(√𝑡) + √𝛼 [ln (
𝑄
𝑘𝐴
√𝛼) − ln(𝑇 − 𝑇∞)]
What we observe is
14. 𝒙
√𝒕
= √𝜶𝐥𝐧(√𝒕) + √𝜶 [𝐥𝐧 (
𝑸
𝒌𝑨√𝜶
(𝑻 − 𝑻∞)
)]
That is what we observe for short times.
When the times become big, we observe
𝑻 − 𝑻∞ =
𝑸
𝒌𝑨
× √
𝑨𝝆𝑪𝜶
𝒉𝑷
(𝟏 − 𝒆
−𝒉𝑷𝒕
𝑨𝝆𝑪 ) × 𝒆
−𝒙
√𝑨𝝆𝑪
𝒉𝑷
(𝟏−𝒆
−𝒉𝑷𝒕
𝑨𝝆𝑪 )
And in steady state (𝑡 = ∞), we observe
𝑻 − 𝑻∞ =
𝑸
𝒌𝑨
× √
𝑨𝝆𝑪𝜶
𝒉𝑷
× 𝒆
−𝒙
√𝑨𝝆𝑪𝜶
𝒉𝑷
𝛼 =
𝑘
𝜌𝐶
We finally get
𝑻 − 𝑻∞ =
𝑸
𝒌𝑨
× √
𝒌𝑨
𝒉𝑷
× 𝒆
−𝒙
√𝒌𝑨
𝒉𝑷
the heat flow in steady state is given by:
𝜕𝑇
𝜕𝑥
= −
𝑄
𝑘𝐴
𝑒
−𝑥
√𝑘𝐴
ℎ𝑃
−𝒌𝑨
𝝏𝑻
𝝏𝒙
= 𝑸𝒆
−𝒙
√𝒌𝑨
𝒉𝑷
15. EQUAL FIXED TEMPERATURES AT THE END OF AN
INSULATED METAL ROD.
PDE
𝜕𝑇
𝜕𝑡
= 𝛼
𝜕2
𝑇
𝜕𝑥2
BCs
𝑻 = 𝑻𝒔 𝒂𝒕 𝒙 = 𝟎 𝟎 < 𝒕 < ∞
𝑻 = 𝑻𝒔 𝒂𝒕 𝒙 = 𝒍 𝟎 < 𝒕 < ∞
IC
𝑻 = 𝑻∞ 𝒂𝒕 𝒕 = 𝟎 𝟎 ≤ 𝒙 ≤ 𝒍
we know a Fourier series solution exists given by
𝑻 − 𝑻𝒔
𝑻∞ − 𝑻𝒔
=
𝟒
𝝅
∑
𝟏
𝒏
∞
𝒏=𝟏
𝒔𝒊𝒏 (
𝒏𝝅𝒙
𝒍
) 𝒆
−(
𝒏𝝅
𝟐 )
𝜶𝒕
(
𝒍
𝟐
)𝟐
𝒏 = 𝟏, 𝟑, 𝟓, …
You notice that this solution is not entirely deterministic since it involves
summing terms up to infinity.
There is an alternative solution as shown below:
𝜕𝑇
𝜕𝑡
= 𝛼
𝜕2
𝑇
𝜕𝑥2
BCs
𝑻 = 𝑻𝒔 𝒂𝒕 𝒙 = 𝟎 𝟎 < 𝒕 < ∞
𝑻 = 𝑻𝒔 𝒂𝒕 𝒙 = 𝒍 𝟎 < 𝒕 < ∞
IC
𝑻 = 𝑻∞ 𝒂𝒕 𝒕 = 𝟎 𝟎 ≤ 𝒙 ≤ 𝒍
We assume an exponential temperature profile that satisfies the boundary
conditions:
𝑇 − 𝑇∞
𝑇𝑠 − 𝑇∞
= 𝑒
−𝑥
𝛿
(1−
𝑥
𝑙
)
16. You notice that the temperature profile above satisfies the boundary
conditions. We can satisfy the initial condition if we assume that 𝛿 will assume
a solution as
𝛿 = 𝑐𝑡𝑛
Where c and n are constants so that at 𝑡 = 0, 𝛿 = 0 and the initial condition is
satisfied as shown below.
𝑇 − 𝑇∞
𝑇𝑠 − 𝑇∞
= 𝑒
−𝑥
0 = 𝑒−∞
= 0
𝑇 = 𝑇∞ 𝑎𝑡 𝑡 = 0
We transform the PDE into an integral equation
𝜕
𝜕𝑡
∫ (𝑇 − 𝑇∞)𝑑𝑥
𝑙
0
= 𝛼 ∫ (
𝜕2
𝑇
𝜕𝑥2
) 𝑑𝑥
𝑙
0
∫ (
𝜕2
𝑇
𝜕𝑥2
) 𝑑𝑥
𝑙
0
= [
(−𝑙 + 2𝑥)
𝛿𝑙
× 𝑒
−𝑥
𝛿
(1−
𝑥
𝑙
)
] 𝑙
0
=
2
𝛿
∫ (𝑇 − 𝑇∞)𝑑𝑥
𝑙
0
= [
𝛿𝑙
(−𝑙 + 2𝑥)
× 𝑒
−𝑥
𝛿
(1−
𝑥
𝑙
)
] 𝑙
0
= 2𝛿
Substituting in the integral equation above, we get:
𝛼 (
2
𝛿
) = 2
𝑑𝛿
𝑑𝑡
𝛿 = √2𝛼𝑡
Substituting back 𝛿 into the temperature profile, we get
𝑻 − 𝑻∞
𝑻𝒔 − 𝑻∞
= 𝒆
−𝒙
√𝟐𝜶𝒕
(𝟏−
𝒙
𝒍
)
Or
𝑻 − 𝑻𝒔
𝑻∞ − 𝑻𝒔
= 𝟏 − 𝒆
−𝒙
√𝟐𝜶𝒕
(𝟏−
𝒙
𝒍
)
You notice that the initial condition is satisfied.
You notice that when 𝑙 = ∞ , we reduce to the temperature profile we derived
before
17. 𝑻 − 𝑻∞
𝑻𝒔 − 𝑻∞
= 𝒆
−𝒙
√𝟐𝜶𝒕
you notice that in the temperature profile developed, we get an exact solution
to the problem not an approximate as the Fourier series.
18. UNEQUAL FIXED TEMPERATURES AT THE END OF AN
INSULATED METAL ROD.
𝜕𝑇
𝜕𝑡
= 𝛼
𝜕2
𝑇
𝜕𝑥2
The boundary conditions are:
𝑇 = 𝑇𝑠 𝑎𝑡 𝑥 = 0 𝑓𝑜𝑟 𝑎𝑙𝑙 𝑡
𝑇 = 𝑇1 𝑎𝑡 𝑥 = 𝑙 𝑓𝑜𝑟 𝑎𝑙𝑙 𝑡
The initial condition is
𝑇 = 𝑇∞ 𝑎𝑡 𝑡 = 0 0 ≤ 𝑥 ≤ 𝑙
The temperature profile that satisfies the boundary conditions is:
𝑻 − 𝑻∞
[
𝒙
𝒍
(𝑻𝟏 − 𝑻∞) + (𝑻𝒔 − 𝑻∞) (𝟏 −
𝒙
𝒍)]
= 𝒆−
𝒙
𝜹
(𝟏−
𝒙
𝒍
)
For now, we shall have a solution where 𝛿 is proportional to time t so that at
𝑡 = 0, 𝛿 = 0 and the initial condition will be satisfied.
We then transform the heat governing equation into an integral equation as:
𝛼 ∫ (
𝜕2
𝑇
𝜕𝑥2
) 𝑑𝑥
𝑙
0
= ∫
𝜕𝑇
𝜕𝑡
𝑑𝑥
𝑙
0
Where:
𝑙 = 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑚𝑒𝑡𝑎𝑙 𝑟𝑜𝑑
You notice that the integral
∫
𝜕𝑇
𝜕𝑡
𝑑𝑥
𝑙
0
=
𝜕
𝜕𝑡
∫ 𝑇𝑑𝑥
𝑙
0
=
𝜕
𝜕𝑡
∫ (𝑇 − 𝑇∞)𝑑𝑥
𝑙
0
Since 𝑙 and 𝑇∞ are constants independent of time
So, the integral equation becomes:
𝛼 ∫ (
𝜕2
𝑇
𝜕𝑥2
) 𝑑𝑥
𝑙
0
=
𝜕
𝜕𝑡
∫ (𝑇 − 𝑇∞)𝑑𝑥
𝑙
0
We go ahead and find
21. HOW DO WE DEAL WITH OTHER TYPES OF BOUNDARY
CONDITIONS?
Consider the following types of boundary conditions and initial condition:
A)
𝑻 = 𝑻𝒔 𝒂𝒕 𝒙 = 𝟎
𝒅𝑻
𝒅𝒙
= 𝟎 𝒂𝒕 𝒙 = 𝒍
𝑻 = 𝑻∞ 𝒂𝒕 𝒕 = 𝟎
B)
𝑻 = 𝑻𝒔 𝒂𝒕 𝒙 = 𝟎
−𝒌
𝒅𝑻
𝒅𝒙
= 𝒉(𝑻 − 𝑻∞) 𝒂𝒕 𝒙 = 𝒍
𝑻 = 𝑻∞ 𝒂𝒕 𝒕 = 𝟎
Let us go about solving for the above boundary conditions but let us deal with set A
boundary conditions and then we can deal with set B later.
We start with a temperature profile below:
𝑇 − 𝑇∞ = (𝑇𝑠 − 𝑇∞)𝑒−
𝑥
𝛿
(1−
𝑥
𝑙
)
[
𝑥
𝑙
(𝑇1 − 𝑇∞)
(𝑇𝑠 − 𝑇∞)
+ (1 −
𝑥
𝑙
)]
we take the derivative
𝒅𝑻
𝒅𝒙
𝒂𝒕 𝒙 = 𝒍 and equate it to 0 and get:
𝑑𝑇
𝑑𝑥
|𝑥=𝑙 = (
(𝑇1 − 𝑇∞)
𝑙
−
(𝑇𝑠 − 𝑇∞)
𝑙
+
(𝑇1 − 𝑇∞)
𝛿
)
𝑑𝑇
𝑑𝑥
|𝑥=𝑙 = (
(𝑇1 − 𝑇∞)
𝑙
−
(𝑇𝑠 − 𝑇∞)
𝑙
+
(𝑇1 − 𝑇∞)
𝛿
) = 0
We finally get
(𝑇1 − 𝑇∞) = (𝑇𝑠 − 𝑇∞)(
𝛿
𝑙 + 𝛿
)
We substitute 𝑇1 − 𝑇∞ into the temperature profile and get
(𝑻 − 𝑻∞) = (𝑻𝒔 − 𝑻∞)𝒆−
𝒙
𝜹
(𝟏 −
𝒙
𝒍
)
[
𝒙
𝒍
(
𝜹
𝜹 + 𝒍
) + (𝟏 −
𝒙
𝒍
)]
22. So, the temperature profile above satisfies the set A) boundary and initial
conditions and we can go ahead and solve the governing equation using the
temperature profile above.
For set B) boundary conditions, we again start with the temperature profile
below:
𝑇 − 𝑇∞ = (𝑇𝑠 − 𝑇∞)𝑒−
𝑥
𝛿
(1 −
𝑥
𝑙
)
[
𝑥
𝑙
(𝑇1 − 𝑇∞)
(𝑇𝑠 − 𝑇∞)
+ (1 −
𝑥
𝑙
)]
we take the derivative
𝒅𝑻
𝒅𝒙
𝒂𝒕 𝒙 = 𝒍 and equate it to:
𝑑𝑇
𝑑𝑥
|𝑥=𝑙 = (
(𝑇1 − 𝑇∞)
𝑙
−
(𝑇𝑠 − 𝑇∞)
𝑙
+
(𝑇1 − 𝑇∞)
𝛿
)
𝒅𝑻
𝒅𝒙
|𝒙=𝒍 = −
𝒉
𝒌
(𝑻𝟏 − 𝑻∞)
We then find the required temperature profile which we can use to solve the
governing equation.
23. HOW DO WE DEAL WITH CONVECTION AT THE
SURFACE AREA OF THE METAL ROD FOR FIXED END
TEMPERATURE
𝛼
𝜕2
𝑇
𝜕𝑥2
−
ℎ𝑃
𝐴𝜌𝐶
(𝑇 − 𝑇∞) =
𝜕𝑇
𝜕𝑡
We shall use the integral approach.
The boundary and initial conditions are
𝑻 = 𝑻𝒔 𝒂𝒕 𝒙 = 𝟎 𝒇𝒐𝒓 𝒂𝒍𝒍 𝒕
𝑻 = 𝑻∞ 𝒂𝒕 𝒙 = ∞
𝑻 = 𝑻∞ 𝒂𝒕 𝒕 = 𝟎
Where: 𝑻∞ = 𝒓𝒐𝒐𝒎 𝒕𝒆𝒎𝒑𝒆𝒓𝒂𝒕𝒖𝒓𝒆
First, we assume a temperature profile that satisfies the boundary conditions
as:
𝑇 − 𝑇∞
𝑇𝑠 − 𝑇∞
= 𝑒
−𝑥
𝛿
where 𝛿 is to be determined and is a function of time t.
The governing equation is
𝛼
𝜕2
𝑇
𝜕𝑥2
−
ℎ𝑃
𝐴𝜌𝐶
(𝑇 − 𝑇∞) =
𝜕𝑇
𝜕𝑡
Let us change this equation into an integral as below:
𝛼 ∫ (
𝜕2
𝑇
𝜕𝑥2
) 𝑑𝑥
𝑙
0
−
ℎ𝑃
𝐴𝜌𝐶
∫ (𝑇 − 𝑇∞)𝑑𝑥
𝑙
0
=
𝜕
𝜕𝑡
∫ (𝑇 − 𝑇∞)𝑑𝑥
𝑙
0
… … . . 𝑏)
𝜕2
𝑇
𝜕𝑥2
=
(𝑇𝑠 − 𝑇∞)
𝛿2
𝑒
−𝑥
𝛿
∫ (
𝜕2
𝑇
𝜕𝑥2
) 𝑑𝑥
𝑙
0
=
−(𝑇𝑠 − 𝑇∞)
𝛿
(𝑒
−𝑥
𝑙 − 1)
∫ (𝑇 − 𝑇∞)𝑑𝑥
𝑙
0
= −𝛿(𝑇𝑠 − 𝑇∞)(𝑒
−𝑥
𝑙 − 1)
24. Substituting the above expressions in equation b) above, we get
𝛼 −
ℎ𝑃
𝐴𝜌𝐶
𝛿2
= 𝛿
𝑑𝛿
𝑑𝑡
We solve the equation above assuming that
𝛿 = 0 𝑎𝑡 𝑡 = 0
And get
𝛿 = √
𝛼𝐴𝜌𝐶
ℎ𝑃
(1 − 𝑒
−2ℎ𝑃
𝐴𝜌𝐶
𝑡
)
𝛿 = √
𝐾𝐴
ℎ𝑃
(1 − 𝑒
−2ℎ𝑃
𝐴𝜌𝐶
𝑡
)
Substituting for 𝛿 in the temperature profile, we get
𝑻 − 𝑻∞
𝑻𝒔 − 𝑻∞
= 𝒆
−𝒙
√𝑲𝑨
𝒉𝑷
(𝟏−𝒆
−𝟐𝒉𝑷
𝑨𝝆𝑪
𝒕
)
From the equation above, we notice that the initial condition is satisfied i.e.,
𝑻 = 𝑻∞ 𝒂𝒕 𝒕 = 𝟎
The equation above predicts the transient state and in steady state (𝑡 = ∞) it
reduces to
𝑻 − 𝑻∞
𝑻𝒔 − 𝑻∞
= 𝒆
−√(
𝒉𝑷
𝑲𝑨
)𝒙
What are the predictions of the transient state?
Let us make 𝑥 the subject of the equation of transient state and get:
𝑥2
= [ln (
𝑇𝑠 − 𝑇∞
𝑇 − 𝑇∞
)]2
×
𝐾𝐴
ℎ𝑃
(1 − 𝑒
−2ℎ𝑃
𝐴𝜌𝐶
𝑡
)
When the time duration is small and
2ℎ𝑃
𝐴𝜌𝐶
𝑡 ≪ 1
25. We use the binomial expansion approximation
𝑒
−2ℎ𝑃
𝐴𝜌𝐶
𝑡
= 1 −
2ℎ𝑃
𝐴𝜌𝐶
𝑡
Substituting in the equation of 𝑥2
as the subject, we get
𝑥2
= 2𝛼[ln (
𝑇𝑠 − 𝑇∞
𝑇 − 𝑇∞
)]2
× 𝑡
Where:
𝛼 =
𝐾
𝜌𝐶
What that equation says is that when you stick wax particles on a long metal
rod (𝑙 = ∞) at distances x from the hot end of the rod and note the time t it
takes the wax particles to melt, then a graph of 𝑥2
against 𝑡 is a straight-line
graph through the origin as stated by the equation above when the times are
small. The equation is true because that is what is observed experimentally.
How do we measure the heat transfer coefficient?
From,
𝑥2
= [ln (
𝑇𝑠 − 𝑇∞
𝑇 − 𝑇∞
)]2
×
𝐾𝐴
ℎ𝑃
(1 − 𝑒
−2ℎ𝑃
𝐴𝜌𝐶
𝑡
)
When the times concerned are big, we shall observe the above equation.
Let us call
𝐵 = [ln (
𝑇𝑠 − 𝑇∞
𝑇 − 𝑇∞
)]2
×
𝐾𝐴
ℎ𝑃
So, the equation above becomes
𝑥2
= 𝐵 (1 − 𝑒
−2ℎ𝑃
𝐴𝜌𝐶
𝑡
)
Let’s take the derivative of x against time t and get
𝑥
𝑑𝑥
𝑑𝑡
= 𝐵
2ℎ
𝑟𝜌𝐶
𝑒
−2ℎ𝑃
𝐴𝜌𝐶
𝑡
26. 𝑒
−2ℎ𝑃
𝐴𝜌𝐶
𝑡
=
(𝐵 − 𝑥2
)
𝐵
Substitute and get
𝑥
𝑑𝑥
𝑑𝑡
=
2ℎ
𝑟𝜌𝐶
(𝐵 − 𝑥2
)
𝒙
𝒅𝒙
𝒅𝒕
=
𝟐𝒉
𝒓𝝆𝑪
𝑩 −
𝟐𝒉
𝒓𝝆𝑪
𝒙𝟐
A graph of 𝑥
𝑑𝑥
𝑑𝑡
against 𝑥2
when the time is big has a negative gradient of
ℎ
𝑟𝜌𝐶
from which h can be measured experimentally.
From experiments using aluminium rod, h was found to be
ℎ = 5.7712𝑊𝑚−2
𝐾−1
h can also be got from Stefan’s law of cooling that reduces to the Newton’s law
of cooling.
Stefan’s law of cooling in natural convection states
𝒅𝑸
𝒅𝒕
= (𝟏 + 𝜷)𝑨𝝈𝜺[𝑻𝟒
− 𝑻∞
𝟒
]
From tables
𝜺 = 𝟎. 𝟑 𝒇𝒐𝒓 𝒂𝒍𝒖𝒎𝒊𝒏𝒊𝒖𝒎
Where:
𝜷 = 𝟒. 𝟓𝟕𝟗𝟕 = 𝒌𝑷𝒓𝒏
Considering
𝑇 = 𝑇∞ + ∆𝑇
𝑑𝑄
𝑑𝑡
= (1 + 𝛽)𝐴𝜎𝜀[(𝑇∞ + ∆𝑇)4
− 𝑇∞
4
]
Factorizing out 𝑇1, we get
𝑑𝑄
𝑑𝑡
= (1 + 𝛽)𝐴𝜎𝜀[𝑇∞
4
(1 +
(𝑇 − 𝑇∞)
𝑇∞
)4
− 𝑇∞
4
]
It is known from Binomial expansion that:
(1 + 𝑥)𝑛
≈ 1 + 𝑛𝑥 𝑓𝑜𝑟 𝑥 ≪ 1
So:
27. (1 +
(𝑇 − 𝑇∞)
𝑇∞
)4
≈ 1 + 4
(𝑇 − 𝑇∞)
𝑇∞
= 1 + 4
∆𝑇
𝑇∞
= 𝑓𝑜𝑟
∆𝑇
𝑇∞
≪ 1
Simplifying, we get Newton’s law of cooling i.e.
𝒅𝑸
𝒅𝒕
= 𝟒(𝟏 + 𝜷)𝑨𝝈𝜺𝑻∞
𝟑 (𝑻 − 𝑻∞)
𝒅𝑸
𝒅𝒕
= 𝒉𝑨(𝑻 − 𝑻∞)
Where:
𝒉 = 𝟒(𝟏 + 𝜷)𝝈𝜺𝑻∞
𝟑
Substitute for the above parameters of aluminium and get h theoretically and
compare as got experimentally.
How do we deal with metal rods of finite length 𝒍 ?
The boundary and initial conditions are
𝑻 = 𝑻𝒔 𝒂𝒕 𝒙 = 𝟎
28. −𝒌
𝒅𝑻
𝒅𝒙
= 𝒉(𝑻 − 𝑻∞) 𝒂𝒕 𝒙 = 𝒍
𝑻 = 𝑻∞ 𝒂𝒕 𝒕 = 𝟎
Let us go about solving for the above boundary conditions
We start with a temperature profile below:
𝑇 − 𝑇∞ = (𝑇𝑠 − 𝑇∞)𝑒−
𝑥
𝛿
(1−
𝑥
𝑙
)
[
𝑥
𝑙
(𝑇1 − 𝑇∞)
(𝑇𝑠 − 𝑇∞)
+ (1 −
𝑥
𝑙
)]
Which says
𝑇 = 𝑇𝑠 𝑎𝑡 𝑥 = 0
𝑇 = 𝑇1 𝑎𝑡 𝑥 = 𝑙
𝑇 = 𝑇∞ 𝑎𝑡 𝑡 = 0
Provided 𝛿 = 0 𝑎𝑡 𝑡 = 0 , then the initial condition above is satisfied
we take the derivative
𝒅𝑻
𝒅𝒙
𝒂𝒕 𝒙 = 𝒍 and equate it to −
ℎ
𝑘
(𝑇1 − 𝑇∞) and get:
𝑑𝑇
𝑑𝑥
|𝑥=𝑙 = (
(𝑇1 − 𝑇∞)
𝑙
−
(𝑇𝑠 − 𝑇∞)
𝑙
+
(𝑇1 − 𝑇∞)
𝛿
)
𝑑𝑇
𝑑𝑥
|𝑥=𝑙 = −
ℎ
𝑘
(𝑇1 − 𝑇∞)
We equate the two and get
(
(𝑇1 − 𝑇∞)
𝑙
−
(𝑇𝑠 − 𝑇∞)
𝑙
+
(𝑇1 − 𝑇∞)
𝛿
) = −
ℎ
𝑘
(𝑇1 − 𝑇∞)
We finally get
(𝑇1 − 𝑇∞) = (𝑇𝑠 − 𝑇∞)(
𝛿𝑘
𝛿𝑘 + 𝑙𝑘 + ℎ𝑙𝛿
)
We substitute 𝑇1 − 𝑇∞ into the temperature profile and get
(𝑻 − 𝑻∞) = (𝑻𝒔 − 𝑻∞)𝒆−
𝒙
𝜹
(𝟏 −
𝒙
𝒍
)
[
𝒙
𝒍
(
𝜹𝒌
𝜹𝒌 + 𝒍𝒌 + 𝒉𝒍𝜹
) + (𝟏 −
𝒙
𝒍
)]
This the temperature profile that satisfies the boundary and initial conditions
below
31. 𝛿 = √
𝐾𝐴
ℎ𝑃
(1 − 𝑒
−2ℎ𝑃
𝐴𝜌𝐶
𝑡
)
We go ahead and substitute for 𝛿 in the temperature profile below
(𝑻 − 𝑻∞) = (𝑻𝒔 − 𝑻∞)𝒆−
𝒙
𝜹
(𝟏 −
𝒙
𝒍
)
[
𝒙
𝒍
(
𝜹𝒌
𝜹𝒌 + 𝒍𝒌 + 𝒉𝒍𝜹
) + (𝟏 −
𝒙
𝒍
)]
When the time is small, 𝛿 using binomial approximation becomes
𝛿 = √
𝐾𝐴
ℎ𝑃
(1 − 𝑒
−2ℎ𝑃
𝐴𝜌𝐶
𝑡
)
2ℎ𝑃
𝐴𝜌𝐶
𝑡 ≪ 1
𝑒
−ℎ𝑃
𝐴𝜌𝐶
𝑡
= 1 −
2ℎ𝑃
𝐴𝜌𝐶
𝑡
1 − 𝑒
−2ℎ𝑃
𝐴𝜌𝐶
𝑡
=
2ℎ𝑃
𝐴𝜌𝐶
𝑡
𝛿 = √2𝛼𝑡
We substitute for 𝛿 in the temperature profile.
What happens when the length is big or tends to infinity?
(𝑻 − 𝑻∞) = (𝑻𝒔 − 𝑻∞)𝒆−
𝒙
𝜹
(𝟏 −
𝒙
𝒍
)
[
𝒙
𝒍
(
𝜹𝒌
𝜹𝒌 + 𝒍𝒌 + 𝒉𝑳𝒍𝜹
) + (𝟏 −
𝒙
𝒍
)]
Becomes
(𝑻 − 𝑻∞) = (𝑻𝒔 − 𝑻∞)𝒆−
𝒙
𝜹
(𝑻 − 𝑻∞) = (𝑻𝒔 − 𝑻∞)𝒆
−
𝒙
√𝑲𝑨
𝒉𝑷
(𝟏−𝒆
−𝟐𝒉𝑷
𝑨𝝆𝑪
𝒕
)
Which is what we got before.
32. WHAT HAPPENS WHEN THE INITIAL TEMPERATURE IS
A FUNCTION OF X?
The governing equation is
𝛼
𝜕2
𝑇
𝜕𝑥2
=
𝜕𝑇
𝜕𝑡
BCs
𝑻 = 𝑻𝒔 𝒂𝒕 𝒙 = 𝟎 𝟎 < 𝒕 < ∞
𝑻 = 𝑻𝒔 𝒂𝒕 𝒙 = 𝒍 𝟎 < 𝒕 < ∞
IC
𝑻 = ∅(𝒙) 𝒂𝒕 𝒕 = 𝟎 𝟎 ≤ 𝒙 ≤ 𝒍
We assume an exponential temperature profile that satisfies the boundary
conditions:
𝑇 − ∅
𝑇𝑠 − ∅
= 𝑒
−𝑥
𝛿
𝑇 = ∅ + 𝑇𝑠𝑒
−𝑥
𝛿 − ∅𝑒
−𝑥
𝛿
The PDE becomes an integral equation given by:
𝛼 ∫ (
𝜕2
𝑇
𝜕𝑥2
) 𝑑𝑥
𝛿
0
=
𝜕
𝜕𝑡
∫ 𝑇𝑑𝑥
𝛿
0
You notice the limits of the integral become from 0 𝑡𝑜 𝛿 as this eliminate
exponentials which are functions of 𝛿 and this will make the integration
simpler.
Let us give an example say
∅ = 𝑥
We make T the subject of the formula and get
𝑇 = ∅ + 𝑇𝑠𝑒
−𝑥
𝛿 − ∅𝑒
−𝑥
𝛿
∅ = 𝑥
𝑇 = 𝑥 + 𝑇𝑠𝑒
−𝑥
𝛿 − 𝑥𝑒
−𝑥
𝛿
34. There are three roots of 𝛿 but we choose those which reduce to zero when time
is zero.
The two roots that satisfy the above condition are
𝛿1 = −
𝑏
3𝑎
+
1 + 𝑖√3
6𝑎
√(
1
2
) [2𝑏3 + 27𝑎2𝑑 + √(2𝑏3 + 27𝑎2𝑑)2 − 4𝑏6)]
3
+
1 − 𝑖√3
6𝑎
√(
1
2
) [2𝑏3 + 27𝑎2𝑑 − √(2𝑏3 + 27𝑎2𝑑)2 − 4𝑏6)]
3
Or
𝛿2 = −
𝑏
3𝑎
+
1 − 𝑖√3
6𝑎
√(
1
2
) [2𝑏3 + 27𝑎2𝑑 + √(2𝑏3 + 27𝑎2𝑑)2 − 4𝑏6)]
3
+
1 + 𝑖√3
6𝑎
√(
1
2
) [2𝑏3 + 27𝑎2𝑑 − √(2𝑏3 + 27𝑎2𝑑)2 − 4𝑏6)]
3
After getting the solution of 𝛿 ,we go ahead and substitute it into the
exponential temperature profile.
We shall be faced with more scenarios where 𝛿 is a cubic equation with time
but the root or solution of 𝛿 to choose is the one for which 𝛿 = 0 𝑎𝑡 𝑡 = 0.
Using this analytical method, we can also go ahead and solve PDES like
𝜕𝑇
𝜕𝑡
= 𝛼
𝜕2
𝑇
𝜕𝑥2
+ 𝑓(𝑥)
Again, we take limits from 0 𝑡𝑜 𝛿 when solving the integral equation to eliminate
exponentials with a function of 𝛿 in order to make solving for the solution easy.
35. HOW DO WE DEAL WITH CYLINDRICAL CO-
ORDINATES?
We know that for an insulated cylinder where there is no heat loss by
convection from the sides, the governing PDE equation is
𝛼 [
𝜕2
𝑇
𝜕𝑟2
+
1
𝑟
𝜕𝑇
𝜕𝑟
] =
𝜕𝑇
𝜕𝑡
The boundary conditions are
𝑇 = 𝑇𝑠 𝑎𝑡 𝑟 = 0
𝑇 = 𝑇∞ 𝑎𝑡 𝑟 = ∞
The initial condition is:
𝑇 = 𝑇∞ 𝑎𝑡 𝑡 = 0
The temperature profile that satisfies the conditions above is
𝑇 − 𝑇∞
𝑇𝑠 − 𝑇∞
= 𝑒
−(𝑟−𝑟1)
𝛿
We transform the PDE into an integral equation
𝛼 [
𝜕2
𝑇
𝜕𝑟2
+
1
𝑟
𝜕𝑇
𝜕𝑟
] =
𝜕𝑇
𝜕𝑡
𝛼 ∫ (
𝜕2
𝑇
𝜕𝑟2
) 𝑑𝑟
𝛿+𝑟1
𝑟1
+ 𝛼 ∫ [
1
𝑟
(
𝜕𝑇
𝜕𝑟
)]𝑑𝑟
𝛿+𝑟1
𝑟1
=
𝜕
𝜕𝑡
∫ 𝑇𝑑𝑟
𝛿+𝑟1
𝑟1
We then go ahead to solve and find 𝛿 as before.
∫ (
𝜕2
𝑇
𝜕𝑟2
) 𝑑𝑟
𝛿+𝑟1
𝑟1
= [
𝜕𝑇
𝜕𝑟
]
𝛿 + 𝑟1
𝑟1
= −
𝑇𝑠 − 𝑇∞
𝛿
[𝑒
−(𝑟−𝑟1)
𝛿 ]
𝛿 + 𝑟1
𝑟1
=
𝑇𝑠 − 𝑇∞
𝛿
(1 − 𝑒−1
)
𝜕𝑇
𝜕𝑟
= −
𝑇𝑠 − 𝑇∞
𝛿
𝑒
−(𝑟−𝑟1)
𝛿
∫ [
1
𝑟
(
𝜕𝑇
𝜕𝑟
)] 𝑑𝑟
𝛿+𝑟1
𝑟1
= −
(𝑇𝑠 − 𝑇∞)
𝛿
∫
1
𝑟
𝑒
−(𝑟−𝑟1)
𝛿 𝑑𝑟
𝛿+𝑟1
𝑟1
∫
1
𝑟
𝑒
−(𝑟−𝑟1)
𝛿 𝑑𝑟
𝛿+𝑟1
𝑟1
= 𝑢𝑣 − ∫ 𝑣
𝑑𝑢
𝑑𝑟
𝑑𝑟
37. 𝛼
(𝑇𝑠 − 𝑇∞)
𝛿
(1 − 𝑒−1
) + 𝛼(𝑇𝑠 − 𝑇∞)(
𝑒−1
2𝛿 + 𝑟1
−
1
𝛿 + 𝑟1
) =
𝑑𝛿
𝑑𝑡
((𝑇𝑠 − 𝑇∞)(1 − 𝑒−1) + 𝑇∞)
We go ahead and solve for 𝛿
We can also go ahead and look at situations where there is natural convection
and other situations where the radius r is finite and not infinite.