Value Proposition canvas- Customer needs and pains
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1. BIET
NAME – SAMIR UDDIN
UNIVERSITY ROLL -11800722069
REGISTRATION NO- 221180120383
DEPARTMENT – MECHANICAL
SEMESTER – 5TH
SUBJECT – HEAT TRANSFER
SUBJECT CODE- PC-ME501
2. VARIOUS MODES OF
HEAT TRANSFER
,STATEMENT OF
FOURIERS LAW OF
HEAT CONDUCTION
AND IT’S
ASSUMPTIONS
~Samir uddin
3. HEAT
HEAT : It is denoted by symbol Q and is defined as follows “heat
is something which appears at the boundary when a system
changes its state due to adifference in temperature between the
system and surroundings .” Heat appears
only at the boundary while the change takes place inside the
system.
SIGN CONVENTION : if heat flows from system to surroundings
,the quantity is sad to be negative .
In other words ,
Heat received by system =+Q
Heat rejected by system=-Q
4. 4
Difference between heat transfer and thermodynamics :
Let us take an example of a hot steel bar kept in a water bath.
Thermodynamics predicts only the equilibrium temperature and state of the system but it
doesn’t predicts the time taken by the system to reach the equilibrium and the temperature
of the hot steel bar .
Heat transfer on the other hand helps in predicting the temperature of both the bar and the
water as a function of time
MODES OF HEAT TRANSFER :
There are three modes of heat transfer:
CONDUCTION CONVENTION
RADIATION
Heat transfer occurs as a result of these modes modes of heat transfer . Heat always flows
in the direction of lower temperature .
5. CONDUCTION
The transfer of heat from one part of a substance to another part of the same substance, or from
one substance to another in physical contact with it , without any displacement of molecules
forming the substance .
In solids , the heat is conducted by the following two mechanics :
1. Lattice vibrations (the faster moving molecules or atoms in the hottest part of a body
transfer heat impact some of their energy to adjacent molecules )
2. by transport of free electrons ( free electrons provide an energy flux in the direction of
decreasing temperature.)
In liquids, the process is similar but as they are more closely placed than gases , the
intermolecular forces comes into play .
In gases , the kinetic energy of molecules is a function of temperature . The molecules are in
constant random motion with energy and momentum. When a molecule from high T region
coincides with a molecule of low T region, it loses energy by collisions .
FOURIERS LAW OF HEAT
6. 6
CONDUCTION :
IT STATES THAT ,” FOR A HOMOGENOUS SOLID THE RATE OF HEAT FLOW IS DIRECTLY
PROPORTIONAL TO AREA OF SELECTION AT RIGHT ANGLES TO THE DIRECTION OF HEAT
FLOW AND TO CHANGE OF TEMPERATURE WITH RESPECT TO LENGTH OF THE PATH OF HEAT FLOW
.”
Assumptions of fourier law :
Conduction of heat takes place under steady state conditions .
The heat flow is unidirectional .
The temperature gradient is constant and the temperature flow is linear .
There is no heat generation .
7. Presentation title
ESSENTIAL FEATURES OF FOURIER LAW :
It is applicable to all matter .( solid ,liquid , gas ) It
is based on experimental evidence .
It is vector expression indicating the heat flow rate is in the direction of decreasing temperature .
The material is homogenous and isotropic.
7
8. 8
It helps to define thethermal conductivity of medium through which heat
is conducted .
CONVECTION
It is the mode of energy transfer between a solid and
the adjacent liquid or gas in motion and it involves the
combined effect of conduction and fluid motion . The
faster the fluid motion , the greater is the convection.
The rate equation for the convective heat transfer
between a surface and an adjacent fluid is described by
Newton’s Law of Cooling .
9. 9
Statement of Newton’s Law of Cooling :
The coefficient of convective heat transfer (h) is defined as “the amount of heat transmitted for a
unit temperature difference between the fluid and unit area of surface in unit time .”
The value of ( h) depends on :
1. Thermodynmic and transport properties .
2. Nature of fluid flow.
3. Geometry of surface .
4. Prevailing thermal conditions.
10. 10
RADIATION
It is the transfer of heat through space or matter by means other than conduction or convection .
Radiant energy (being electromagnetic radiation ) requires no medium for propagation and will pass
through vaccum.
LAWS OF RADIATION
Wien’s Law : it states that the wavelength corresponding to the maximum energy is inversely
proportional to absolute temperature T of hot body .
11. Stefan-Boltzmann Law: The emissive power of black body is directly proportional to fourth power
of absolute temperature.
