This document discusses the design and analysis of cooling towers. It begins with a brief history of cooling tower design and the development of theories to analyze them. It then discusses key parameters that describe cooling tower performance such as range, approach, and water/air ratio. The document outlines methods for analyzing cooling tower performance, including the Merkel method and global conservation equations. It also discusses factors that affect heat transfer in cooling towers and how tower characteristics are determined. Finally, it covers other important design considerations like pressure drops, fan power requirements, and water losses through evaporation and drift.
The document discusses the history and scientific development of cooling tower design theory. It begins by explaining how Merkel developed the first scientific theory for evaluating cooling tower performance in 1925. It then provides definitions of key cooling tower concepts like approach, range, and heat transfer methods. The document goes on to describe parameters like tower characteristics, fan power requirements, and water loss factors. It also summarizes Merkel's assumptions and the development of generalized supply equations from manufacturer curves.
This document provides an overview of cooling towers. It begins with introductions and definitions, explaining that cooling towers reject heat from condenser water to the ambient air. It then discusses cooling tower fundamentals, components, performance factors like approach and effectiveness. It outlines the heat transfer process. It describes the two main types of cooling towers: natural draft and mechanical draft. Finally, it lists several parameters for assessing cooling tower performance, such as range, approach, effectiveness, cooling capacity, and cycles of concentration.
- Radiators are heat exchangers used to remove heat from engines and propulsion systems. Their design considers thermal performance, size constraints, and pressure drops.
- A radiator's thermal performance depends on parameters like mass flow rates, temperatures, heat transfer coefficients, and surface area. Its total surface area can be calculated using these parameters and equations from the first law of thermodynamics.
- An example calculation shows determining the surface area of a double pipe radiator given inlet/outlet temperatures, mass flow rates, heat capacities, and heat transfer coefficients. Assumptions like negligible wall resistance are made to simplify the early design stage calculations.
This document provides information about cooling towers, including:
1. Cooling towers reduce water temperature by bringing water and air into direct contact, with some water evaporating to cool the rest.
2. Key components include fill materials to maximize contact between water and air, nozzles to distribute water, and fans to pull air through.
3. Cooling tower performance is evaluated based on parameters like range, approach, and efficiency. Opportunities to improve energy efficiency include selecting an appropriately sized tower, optimizing fill materials and water distribution, and improving fans and pumps.
4. Materials used in cooling towers have evolved over time for factors like corrosion resistance and include galvanized steel, plastics, fiberglass,
This document discusses predicting the cold water temperature of a cooling tower under different conditions. It begins by explaining cooling tower theory and the accepted performance equation. It then shows how to calculate the tower characteristics (NTU) at design conditions using the Merkel equation. This involves calculating parameters like L/G ratio, enthalpy differences, and incremental NTU values. The example calculates the design tower characteristic (NTU) of 1.367 for a cooling tower in Mumbai with given design temperatures. It further demonstrates how to predict the new tower characteristic if the wet bulb temperature changes while other factors remain constant.
This document presents a rule-of-thumb design procedure for wet cooling towers that can be used for power plant cycle optimization. It begins with defining the design problem and specifying inlet/outlet water temperatures and ambient wet-bulb temperature. It then provides methods to calculate the outlet air temperature, tower characteristic, loading factor, and other key parameters. These include using the average of inlet/outlet water temperatures to approximate outlet air temperature, graphically integrating the Merkel equation to determine tower characteristic, and using graphs to determine the optimum loading factor based on design conditions. The goal is to provide simplified methods for estimating cooling tower dimensions, performance, costs and other details needed for power plant analysis without requiring detailed iterative design calculations.
The document discusses the history and scientific development of cooling tower design theory. It begins by explaining how Merkel developed the first scientific theory for evaluating cooling tower performance in 1925. It then provides definitions of key cooling tower concepts like approach, range, and heat transfer methods. The document goes on to describe parameters like tower characteristics, fan power requirements, and water loss factors. It also summarizes Merkel's assumptions and the development of generalized supply equations from manufacturer curves.
This document provides an overview of cooling towers. It begins with introductions and definitions, explaining that cooling towers reject heat from condenser water to the ambient air. It then discusses cooling tower fundamentals, components, performance factors like approach and effectiveness. It outlines the heat transfer process. It describes the two main types of cooling towers: natural draft and mechanical draft. Finally, it lists several parameters for assessing cooling tower performance, such as range, approach, effectiveness, cooling capacity, and cycles of concentration.
- Radiators are heat exchangers used to remove heat from engines and propulsion systems. Their design considers thermal performance, size constraints, and pressure drops.
- A radiator's thermal performance depends on parameters like mass flow rates, temperatures, heat transfer coefficients, and surface area. Its total surface area can be calculated using these parameters and equations from the first law of thermodynamics.
- An example calculation shows determining the surface area of a double pipe radiator given inlet/outlet temperatures, mass flow rates, heat capacities, and heat transfer coefficients. Assumptions like negligible wall resistance are made to simplify the early design stage calculations.
This document provides information about cooling towers, including:
1. Cooling towers reduce water temperature by bringing water and air into direct contact, with some water evaporating to cool the rest.
2. Key components include fill materials to maximize contact between water and air, nozzles to distribute water, and fans to pull air through.
3. Cooling tower performance is evaluated based on parameters like range, approach, and efficiency. Opportunities to improve energy efficiency include selecting an appropriately sized tower, optimizing fill materials and water distribution, and improving fans and pumps.
4. Materials used in cooling towers have evolved over time for factors like corrosion resistance and include galvanized steel, plastics, fiberglass,
This document discusses predicting the cold water temperature of a cooling tower under different conditions. It begins by explaining cooling tower theory and the accepted performance equation. It then shows how to calculate the tower characteristics (NTU) at design conditions using the Merkel equation. This involves calculating parameters like L/G ratio, enthalpy differences, and incremental NTU values. The example calculates the design tower characteristic (NTU) of 1.367 for a cooling tower in Mumbai with given design temperatures. It further demonstrates how to predict the new tower characteristic if the wet bulb temperature changes while other factors remain constant.
This document presents a rule-of-thumb design procedure for wet cooling towers that can be used for power plant cycle optimization. It begins with defining the design problem and specifying inlet/outlet water temperatures and ambient wet-bulb temperature. It then provides methods to calculate the outlet air temperature, tower characteristic, loading factor, and other key parameters. These include using the average of inlet/outlet water temperatures to approximate outlet air temperature, graphically integrating the Merkel equation to determine tower characteristic, and using graphs to determine the optimum loading factor based on design conditions. The goal is to provide simplified methods for estimating cooling tower dimensions, performance, costs and other details needed for power plant analysis without requiring detailed iterative design calculations.
As run energy efficiency of cooling towersD.Pawan Kumar
This document discusses factors that affect the energy efficiency of cooling towers, including entering wet bulb temperature, cooling range, effectiveness, and approach temperature. It notes that simultaneous achievement of maximum range, capacity, and effectiveness with lowest input energy is desirable. The performance of cooling towers in actual operation should be assessed against design conditions and performance curves. Key factors to examine include heat load, water flow, fan power, range, and effectiveness. Optimizing factors like fan operation, cycles of concentration, drift eliminators, and load segregation can improve efficiency.
The document describes a numerical simulation of the transient thermal behavior of a flat plate solar collector. The simulation applies finite differences to a two-dimensional grid representing the absorber plate and calculates temperatures and heat transfer. It examines the effects of irradiance, mass flow rate, and other parameters on temperatures, heat loss coefficient, and collector efficiency over time. Results are compared to previous studies and conclusions discuss future research opportunities.
This document provides guidelines for cooling tower design, including key parameters to consider. It discusses heat load calculation, circulating water rate, wet bulb temperatures, optimizing costs, makeup water, blowdown rates, and cycles of concentration. Electrical installations for cooling towers must use corrosion-resistant materials and hazardous area classifications due to possible flammable gas releases. Environmental and safety concerns like effluent quality and fire protection are also addressed.
Energy Conservation Opportunities in Cooling Tower.pdfNITIN ASNANI
A cooling tower works by evaporating a portion of circulating water to reject process heat into the atmosphere. It has components like fill media, drift eliminators, nozzles, and fans. Key performance parameters include range, approach, effectiveness, cooling capacity, and cycles of concentration. Cooling tower performance depends on factors like heat load, flow rate, wet bulb temperature, and approach. Proper sizing considers these factors and energy efficiency can be improved through control strategies and opportunities like optimized fan operation.
1) The revised report analyzes the performance of a cooling tower under varying operating conditions, focusing on efficiencies and characteristics at different water flow rates.
2) Improvements were made to the report, including formatting, removing unnecessary explanations, focusing on theory over derivation, explaining the significance of cooling towers, and providing more detailed conclusions.
3) The results show that increasing the water flow rate decreases the cooling tower characteristic and efficiency, in agreement with previous literature and Merkel theory.
This document provides information on cooling towers, including types, components, performance parameters for assessment, and opportunities for improved energy efficiency. It discusses the main types of cooling towers as natural draft, mechanical draft (forced draft, induced draft cross flow, induced draft counter flow). Key performance parameters reviewed are range, approach, effectiveness, cooling capacity, evaporation loss, cycles of concentration, blow down losses, and liquid to gas ratio. Energy efficiency opportunities discussed include selecting an appropriately sized tower, using efficient fill media and fans, optimizing water distribution and treatment, and increasing cycles of concentration.
The document discusses the vapor compression refrigeration cycle. It contains sections on refrigeration, refrigerants, the four main components of the vapor compression cycle (compressor, condenser, expansion valve, evaporator), coefficient of performance calculations, effects of varying operating parameters, advantages/disadvantages, and applications. The vapor compression cycle uses a refrigerant that is compressed to a high pressure and temperature gas, condensed to a high pressure liquid, expanded to a low pressure liquid, and evaporated to absorb heat before repeating the cycle.
This document discusses air conditioning processes and psychrometrics. It defines key terms like dry bulb temperature, wet bulb temperature, dew point temperature, relative humidity, specific volume, and specific enthalpy as they relate to moist air. It also describes the adiabatic saturation process, where unsaturated air is blown over a water spray, causing it to become saturated at a constant wet bulb temperature. Key psychrometric concepts like humidity ratio and degree of saturation are also introduced.
An Investigation in Performance Enhancement of Induced Draft Counter Flow Wet...IRJET Journal
This document discusses an investigation into enhancing the performance of an induced draft counterflow wet cooling tower. It begins with an overview of cooling towers and their operation. The authors then describe their methodology, which includes designing a cooling tower using calculations and Creo software, modeling air and water flow using CFX analysis in ANSYS, and performing a Taguchi analysis in Minitab to determine which design parameters minimize outlet water temperature. The exercise was conducted at a plastics manufacturing facility to provide cool water for their processes.
1. The document discusses vapor compression refrigeration systems (VCRS), which are the most commonly used refrigeration systems. In VCRS, the refrigerant undergoes phase change and the refrigeration effect occurs during evaporation.
2. VCRS have higher efficiency and smaller size than air refrigeration systems for a given capacity, but have higher initial costs and issues with refrigerant leakage.
3. The standard VCRS cycle introduces irreversibilities from isenthalpic expansion and non-isothermal heat rejection, lowering its COP compared to the ideal Carnot cycle. Subcooling and superheating can improve the cycle efficiency.
Cooling of mine air by chilled water system (final)Safdar Ali
This document discusses methods for cooling mine air, specifically using a chilled water system. It describes the vapor compression refrigeration process used to produce chilled water, involving an evaporator, compressor, condenser, and expansion valve. Cooling towers and coils are then used to transfer heat from the mine air to the chilled water, with cooling towers using evaporative cooling and coils using direct contact between the air and water circuits. Spray systems can also be used underground as a direct contact heat exchanger method.
This document discusses heat exchangers and provides details on shell-and-tube heat exchangers. It describes the basic components and design of shell-and-tube heat exchangers, including tubes, tube sheets, baffles, and shells. Equations for heat transfer and thermal analysis of shell-and-tube exchangers are presented. An example problem demonstrates the design calculations to determine the required heat exchanger area and fluid flow rates.
- What are the heating and cooling energy demand and loads for buildings?
- What is the effect of the thermal mass on the energy performance of buildings?
- What is the effect of freezing/thawing cycles and energy balance on the energy performance of buildings?
- What is the thermo-hydro-mechanical behavior of thermal piles?
- What is the result of excessive heat extraction from the geothermal piles?
This document provides an overview of cooling towers, including:
- The main components and types of cooling towers such as natural draft, mechanical draft, forced draft, induced draft, cross flow, and counter flow towers.
- Parameters for assessing cooling tower performance including range, approach, effectiveness, cooling capacity, and cycles of concentration.
- Energy efficiency opportunities for cooling towers related to selecting tower size and type, fill media, pumps, fans and motors.
This document provides an overview of cooling towers, including:
- The main components and types of cooling towers, such as natural draft, mechanical draft, forced draft, induced draft, cross flow, and counter flow towers.
- Parameters for assessing cooling tower performance like range, approach, effectiveness, cooling capacity, and cycles of concentration.
- Opportunities for improving energy efficiency, such as selecting towers based on heat load and wet bulb temperature, using efficient fill media and fans, and optimizing water treatment.
This document provides information on cooling towers, including types, components, performance parameters for assessment, and opportunities for improved energy efficiency. It discusses the main types of cooling towers as natural draft, mechanical draft (including forced draft, induced draft counter flow and cross flow), and compares fill media options. Key performance parameters covered include range, approach, effectiveness, cooling capacity, and cycles of concentration. Energy efficiency opportunities discussed include selecting an appropriately sized tower, optimizing fill media, improving water distribution and treatment, upgrading fans and motors, and reducing drift losses.
This document describes a study on improving the performance of a parabolic solar concentrator by using Al2O3-water nanofluid. The objectives were to design and fabricate a parabolic solar collector, conduct experiments using water and nanofluids of different concentrations as working fluids, and compare the results. Experimental results showed that nanofluids increased collector efficiency compared to water, with higher concentrations performing better. Numerical analysis using ANSYS software also showed higher temperature distributions in the absorber tube when using nanofluids. The use of nanofluids enhanced heat transfer and improved solar collector efficiency.
This document is a research project submitted in partial fulfillment of the requirements for a degree in Mechanical and Mechatronics Engineering. It contains an abstract, introduction, and 4 chapters that discuss cooling towers, their components, thermal performance testing, and electrical components. The introduction provides background on cooling towers and how they work to lower water temperature through evaporation and heat transfer to the atmosphere. It also discusses prior research on improving cooling tower performance. The abstract indicates the research examines different types of cooling towers, their application, efficiency, and working principles, and includes a simulation of flow fields around a cooling tower.
Discovering the Best Indian Architects A Spotlight on Design Forum Internatio...Designforuminternational
India’s architectural landscape is a vibrant tapestry that weaves together the country's rich cultural heritage and its modern aspirations. From majestic historical structures to cutting-edge contemporary designs, the work of Indian architects is celebrated worldwide. Among the many firms shaping this dynamic field, Design Forum International stands out as a leader in innovative and sustainable architecture. This blog explores some of the best Indian architects, highlighting their contributions and showcasing the most famous architects in India.
As run energy efficiency of cooling towersD.Pawan Kumar
This document discusses factors that affect the energy efficiency of cooling towers, including entering wet bulb temperature, cooling range, effectiveness, and approach temperature. It notes that simultaneous achievement of maximum range, capacity, and effectiveness with lowest input energy is desirable. The performance of cooling towers in actual operation should be assessed against design conditions and performance curves. Key factors to examine include heat load, water flow, fan power, range, and effectiveness. Optimizing factors like fan operation, cycles of concentration, drift eliminators, and load segregation can improve efficiency.
The document describes a numerical simulation of the transient thermal behavior of a flat plate solar collector. The simulation applies finite differences to a two-dimensional grid representing the absorber plate and calculates temperatures and heat transfer. It examines the effects of irradiance, mass flow rate, and other parameters on temperatures, heat loss coefficient, and collector efficiency over time. Results are compared to previous studies and conclusions discuss future research opportunities.
This document provides guidelines for cooling tower design, including key parameters to consider. It discusses heat load calculation, circulating water rate, wet bulb temperatures, optimizing costs, makeup water, blowdown rates, and cycles of concentration. Electrical installations for cooling towers must use corrosion-resistant materials and hazardous area classifications due to possible flammable gas releases. Environmental and safety concerns like effluent quality and fire protection are also addressed.
Energy Conservation Opportunities in Cooling Tower.pdfNITIN ASNANI
A cooling tower works by evaporating a portion of circulating water to reject process heat into the atmosphere. It has components like fill media, drift eliminators, nozzles, and fans. Key performance parameters include range, approach, effectiveness, cooling capacity, and cycles of concentration. Cooling tower performance depends on factors like heat load, flow rate, wet bulb temperature, and approach. Proper sizing considers these factors and energy efficiency can be improved through control strategies and opportunities like optimized fan operation.
1) The revised report analyzes the performance of a cooling tower under varying operating conditions, focusing on efficiencies and characteristics at different water flow rates.
2) Improvements were made to the report, including formatting, removing unnecessary explanations, focusing on theory over derivation, explaining the significance of cooling towers, and providing more detailed conclusions.
3) The results show that increasing the water flow rate decreases the cooling tower characteristic and efficiency, in agreement with previous literature and Merkel theory.
This document provides information on cooling towers, including types, components, performance parameters for assessment, and opportunities for improved energy efficiency. It discusses the main types of cooling towers as natural draft, mechanical draft (forced draft, induced draft cross flow, induced draft counter flow). Key performance parameters reviewed are range, approach, effectiveness, cooling capacity, evaporation loss, cycles of concentration, blow down losses, and liquid to gas ratio. Energy efficiency opportunities discussed include selecting an appropriately sized tower, using efficient fill media and fans, optimizing water distribution and treatment, and increasing cycles of concentration.
The document discusses the vapor compression refrigeration cycle. It contains sections on refrigeration, refrigerants, the four main components of the vapor compression cycle (compressor, condenser, expansion valve, evaporator), coefficient of performance calculations, effects of varying operating parameters, advantages/disadvantages, and applications. The vapor compression cycle uses a refrigerant that is compressed to a high pressure and temperature gas, condensed to a high pressure liquid, expanded to a low pressure liquid, and evaporated to absorb heat before repeating the cycle.
This document discusses air conditioning processes and psychrometrics. It defines key terms like dry bulb temperature, wet bulb temperature, dew point temperature, relative humidity, specific volume, and specific enthalpy as they relate to moist air. It also describes the adiabatic saturation process, where unsaturated air is blown over a water spray, causing it to become saturated at a constant wet bulb temperature. Key psychrometric concepts like humidity ratio and degree of saturation are also introduced.
An Investigation in Performance Enhancement of Induced Draft Counter Flow Wet...IRJET Journal
This document discusses an investigation into enhancing the performance of an induced draft counterflow wet cooling tower. It begins with an overview of cooling towers and their operation. The authors then describe their methodology, which includes designing a cooling tower using calculations and Creo software, modeling air and water flow using CFX analysis in ANSYS, and performing a Taguchi analysis in Minitab to determine which design parameters minimize outlet water temperature. The exercise was conducted at a plastics manufacturing facility to provide cool water for their processes.
1. The document discusses vapor compression refrigeration systems (VCRS), which are the most commonly used refrigeration systems. In VCRS, the refrigerant undergoes phase change and the refrigeration effect occurs during evaporation.
2. VCRS have higher efficiency and smaller size than air refrigeration systems for a given capacity, but have higher initial costs and issues with refrigerant leakage.
3. The standard VCRS cycle introduces irreversibilities from isenthalpic expansion and non-isothermal heat rejection, lowering its COP compared to the ideal Carnot cycle. Subcooling and superheating can improve the cycle efficiency.
Cooling of mine air by chilled water system (final)Safdar Ali
This document discusses methods for cooling mine air, specifically using a chilled water system. It describes the vapor compression refrigeration process used to produce chilled water, involving an evaporator, compressor, condenser, and expansion valve. Cooling towers and coils are then used to transfer heat from the mine air to the chilled water, with cooling towers using evaporative cooling and coils using direct contact between the air and water circuits. Spray systems can also be used underground as a direct contact heat exchanger method.
This document discusses heat exchangers and provides details on shell-and-tube heat exchangers. It describes the basic components and design of shell-and-tube heat exchangers, including tubes, tube sheets, baffles, and shells. Equations for heat transfer and thermal analysis of shell-and-tube exchangers are presented. An example problem demonstrates the design calculations to determine the required heat exchanger area and fluid flow rates.
- What are the heating and cooling energy demand and loads for buildings?
- What is the effect of the thermal mass on the energy performance of buildings?
- What is the effect of freezing/thawing cycles and energy balance on the energy performance of buildings?
- What is the thermo-hydro-mechanical behavior of thermal piles?
- What is the result of excessive heat extraction from the geothermal piles?
This document provides an overview of cooling towers, including:
- The main components and types of cooling towers such as natural draft, mechanical draft, forced draft, induced draft, cross flow, and counter flow towers.
- Parameters for assessing cooling tower performance including range, approach, effectiveness, cooling capacity, and cycles of concentration.
- Energy efficiency opportunities for cooling towers related to selecting tower size and type, fill media, pumps, fans and motors.
This document provides an overview of cooling towers, including:
- The main components and types of cooling towers, such as natural draft, mechanical draft, forced draft, induced draft, cross flow, and counter flow towers.
- Parameters for assessing cooling tower performance like range, approach, effectiveness, cooling capacity, and cycles of concentration.
- Opportunities for improving energy efficiency, such as selecting towers based on heat load and wet bulb temperature, using efficient fill media and fans, and optimizing water treatment.
This document provides information on cooling towers, including types, components, performance parameters for assessment, and opportunities for improved energy efficiency. It discusses the main types of cooling towers as natural draft, mechanical draft (including forced draft, induced draft counter flow and cross flow), and compares fill media options. Key performance parameters covered include range, approach, effectiveness, cooling capacity, and cycles of concentration. Energy efficiency opportunities discussed include selecting an appropriately sized tower, optimizing fill media, improving water distribution and treatment, upgrading fans and motors, and reducing drift losses.
This document describes a study on improving the performance of a parabolic solar concentrator by using Al2O3-water nanofluid. The objectives were to design and fabricate a parabolic solar collector, conduct experiments using water and nanofluids of different concentrations as working fluids, and compare the results. Experimental results showed that nanofluids increased collector efficiency compared to water, with higher concentrations performing better. Numerical analysis using ANSYS software also showed higher temperature distributions in the absorber tube when using nanofluids. The use of nanofluids enhanced heat transfer and improved solar collector efficiency.
This document is a research project submitted in partial fulfillment of the requirements for a degree in Mechanical and Mechatronics Engineering. It contains an abstract, introduction, and 4 chapters that discuss cooling towers, their components, thermal performance testing, and electrical components. The introduction provides background on cooling towers and how they work to lower water temperature through evaporation and heat transfer to the atmosphere. It also discusses prior research on improving cooling tower performance. The abstract indicates the research examines different types of cooling towers, their application, efficiency, and working principles, and includes a simulation of flow fields around a cooling tower.
Discovering the Best Indian Architects A Spotlight on Design Forum Internatio...Designforuminternational
India’s architectural landscape is a vibrant tapestry that weaves together the country's rich cultural heritage and its modern aspirations. From majestic historical structures to cutting-edge contemporary designs, the work of Indian architects is celebrated worldwide. Among the many firms shaping this dynamic field, Design Forum International stands out as a leader in innovative and sustainable architecture. This blog explores some of the best Indian architects, highlighting their contributions and showcasing the most famous architects in India.
Practical eLearning Makeovers for EveryoneBianca Woods
Welcome to Practical eLearning Makeovers for Everyone. In this presentation, we’ll take a look at a bunch of easy-to-use visual design tips and tricks. And we’ll do this by using them to spruce up some eLearning screens that are in dire need of a new look.
Explore the essential graphic design tools and software that can elevate your creative projects. Discover industry favorites and innovative solutions for stunning design results.
Architectural and constructions management experience since 2003 including 18 years located in UAE.
Coordinate and oversee all technical activities relating to architectural and construction projects,
including directing the design team, reviewing drafts and computer models, and approving design
changes.
Organize and typically develop, and review building plans, ensuring that a project meets all safety and
environmental standards.
Prepare feasibility studies, construction contracts, and tender documents with specifications and
tender analyses.
Consulting with clients, work on formulating equipment and labor cost estimates, ensuring a project
meets environmental, safety, structural, zoning, and aesthetic standards.
Monitoring the progress of a project to assess whether or not it is in compliance with building plans
and project deadlines.
Attention to detail, exceptional time management, and strong problem-solving and communication
skills are required for this role.
1. Thermal Analysis and Design of Cooling Towers
P M V Subbarao
Professor
Mechanical Engineering Department
I I T Delhi
Pay material for Electric Power….
3. Artistic to Scientific Design of Cooling Towers
• The art of evaporative cooling is quite ancient, although it
is only relatively recently that it has been studied
scientifically.
• Merkel developed the theory for the thermal evaluation of
cooling towers in 1925.
• This work was largely neglected until 1941 when the paper
was translated into English.
• Since then, the model has been widely applied.
• The Merkel theory relies on several critical assumptions to
reduce the solution to a simple hand calculation.
• Because of these assumptions, the Merkel method does
not accurately represent the physics of heat and mass
transfer process in the cooling tower fill.
4. Parameters of Cooling Towers
• A number of parameters describe the performance of a
cooling tower.
• Range is the temperature difference between the hot water
entering the cooling tower and the cold water leaving.
• The range is virtually identical with the condenser rise.
• Note that the range is not determined by performance of
the tower, but is determined by the heat loading.
5. • Approach is the difference between the temperature of the
water leaving the tower and the wet bulb temperature of the
entering air.
• The approach is affected by the cooling tower capability.
• For a given heat loading, water flow rate, and entering air
conditions, a larger tower will produce a smaller approach; i.e.,
the water leaving the tower will be colder.
• Water/Air Ratio (mw/ma) is the mass ratio of water (Liquid)
flowing through the tower to the air (Gas) flow.
• Each tower will have a design water/air ratio.
• An increase in this ratio will result in an increase of the
approach, that is, warmer water will be leaving the tower.
• A test ratio is calculated when the cooling tower performance
is evaluated.
9. SSSF Model for Cooling Tower
Conservation of Mass for dry air:
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10. Enthalpy of Wet air
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11. Local Heat and Mass Transfer in water air system
dz
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12. Local Air-side control volume of fill
dA
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13. Mechanism of Heat Transfer in Cooling Towers
• Heat transfer in cooling towers occurs by two major
mechanisms:
• Sensible heat from water to air (convection) and
• transfer of latent heat by the evaporation of water (diffusion).
• Both of these mechanisms operate at air-water boundary
layer.
• The total heat transfer is the sum of these two boundary layer
mechanisms.
• The total heat transfer can also be expressed in terms of the
change in enthalpy of each bulk phase.
• A fundamental equation o f heat transfer in cooling towers
(the Merkel equation) is obtained.
air
air
a
sa
W
W
CW dh
m
dV
h
h
KA
dT
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m
14. The Merkel Method
• The Merkel method, developed in the 1920s, relies on
several critical assumptions to reduce the solution to a
simple manual iteration.
• These assumptions are:
• The resistance for heat transfer in the water film is
negligible,
• The effect of water loss by evaporation on energy balance
or air process state is neglected,
• The specific heat of air-stream mixture at constant pressure
is same as that of the dry air, and
• The ratio of hconv/hdiff (Lewis factor) for humid air is unity.
• Merkel combined equations for heat and water vapor
transfer into a single equation similar as
15. where:
kAV/mw = tower characteristic
k= mass transfer coefficient
A = contact area/tower volume
V = active cooling volume/plan area
mw = water flow rate
T1 = hot water temperature
T2 = cold water temperature
T = bulk water temperature
hsa = enthalpy of saturated air-water vapor mixture at bulk water temperature
(J/kg dry air)
ha = enthalpy of air-water vapor mixture (J/kg dry air )
1
2
T
T a
sa
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M
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Me
17. Tower Characteristics
• Tower Characteristic (MeM or NTU) is a characteristic of
the tower that relates tower design and operating
characteristics to the amount of heat that can be
transferred.
• For a given set of operating conditions, the design
constants that depend on the tower fill.
• For a tower that is to be evaluated using the characteristic
curve method, the manufacturer will provide a tower
characteristic curve.
n
a
w
m
m
C
NTU
21. SUPPLY TOWER CHARACTERISTIC
• The supply tower characteristic of the cooling tower can be
evaluated with the help of cooling tower fill characteristics
curves provided by manufacturer which takes into account
the effect of rain and spray zones as well as fill fouling.
• These curves are certified by the cooling tower institute.
24. Generalized Equation for Cooling Tower Supply
• A generalized equation for cooling tower supply can be
developed from the manufacturer curves (known as the
supply equation) and is of the form:
m
a
w
n
air
m
m
u
C
L
KAV
25. Air Side Pressure Drop
• Manufacturer pressure drop curves are available
for pressure drops at the inlet louvers, drift
eliminators and the fill packing.
• These curves are shown in the following slides.
• Using curve fitting software, generalized pressure
drop equations are found developed so as to
calculate the pressure drops.
29. BHP OF THE FAN
• The total pressure drop (PD) across the cooling
tower which is the summation of the pressure
drops across the drift eliminators, inlet louvers and
the fill packing (constituting the static pressure
drop) and also the velocity pressure drop is
calculated.
• Now, the total fan power required is calculated as
BHP = (CFM * PD)/ (n * 6356)
where n is the efficiency of the fan.
30. ANOTHER METHOD
• We can also map the demand curve foe
varying KAV/L values with varying L/G on
the manufacturers curves for tower
characteristics in order to find the L/G ratio
of the cooling tower.
• After obtaining the L/G ratio all the steps to
be followed are same as the previous
method.
31. Loss of Water
• Evaporation Rate is the fraction of the circulating water
that is evaporated in the cooling process.
• A typical design evaporation rate is about 1% for every
12.5C range at typical design conditions.
• It will vary with the season, since in colder weather there is
more sensible heat transfer from the water to the air, and
therefore less evaporation.
• The evaporation rate has a direct impact on the cooling
tower makeup water requirements.
32. • Drift is water that is carried away from the tower in the form
of droplets with the air discharged from the tower.
• Most towers are equipped with drift eliminators to minimize
the amount of drift to a small fraction of a percent of the water
circulation rate.
• Drift has a direct impact on the cooling tower makeup water
requirements.
• Recirculation is warm, moist air discharged from the tower
that mixes with the incoming air and re-enters the tower.
• This increases the wet bulb temperature of the entering air and
reduces the cooling capability of the tower.
• During cold weather operation, recirculation may also lead to
icing of the air intake areas.