Download Link: https://sites.google.com/view/varunpratapsingh/teaching-engagements (Copy URL) UNIT-2: Part-1 Zeroth law: Zeroth law, Different temperature scales and temperature measurement First law: First law of thermodynamics. Processes flow and non-flow, Control volume, Flow work and non-flow work, Steady flow energy equation, unsteady flow systems and their analysis. Second law: Limitations of first law of thermodynamics, Essence of second law, Thermal reservoir, Heat engines. COP of heat pump and refrigerator. Statements of second law and their equivalence, Carnot cycle, Carnot theorem, Thermodynamic temperature scale, Clausius inequality. Concept of entropy.

1. Basic Mechanical Engineering
UNIT-2
Thermodynamics' Laws
Part-One (Zeroth and First Law)
By
Mr. Varun Pratap Singh

7. NUMERICAL

15. In real practice it is found that an ideal gas while undergoing a non-flow process which may be any one or
combination of two of the heating / cooling and compression / expansion processes, follows the law.
PVn = Constant
Where n is known as index of compression or expansion.
It is a general form of any non-flow process and the value of n decides the particular type of process. For
example
If n = 0 ↔ then PV0 = constant Or P = constant
↔ constant pressure process.
If n = ∞ then PV∞ = constant
or P1/∞.V = constant or P0V = constant or V = constant
↔ constant volume process
If n = 1 then PV1 = PV = Constant.
Mixing it with ideal gas law
If PV = Constant, then T = constant
⟷ constant temperature process
If n = γ then PV γ = Constant
↔ adiabatic process
If n has any other value except 0, 1, γ and ∞
↔ polytrophic process
Depending on the value of n, all these processes can be represented on the PV- diagram as follows.

31. In an ideal nozzle,
1. The fluid pressure will be dropped and velocity
increases significantly.
2. Neither Work nor Heat crosses the system boundary.
3. No change in P.E. of the fluid takes place.
4. K.E. at the inlet is usually small and can be neglected.
So, the continuity equation will be,
And the energy equation will be,

32. Diffuser:
It is a device constructed to decelerate a high velocity fluid in a manner that results in a increase in pressure
of the fluid (opposite to Nozzle). So, its continuity equation and the energy equation will be same as of the
Nozzle.
In an ideal Diffuser,
1. The fluid pressure will be increase and velocity
decreases significantly.
2. Neither Work nor Heat crosses the system boundary.
3. No change in P.E. of the fluid takes place.
4. K.E. at the outlet is usually small and can be neglected.
So, the continuity equation will be,
And the energy equation will be,

35. 5. Steam Turbine / Water Turbine/ Gas Turbine:
It is a rotary SSSF Machine whose purpose is the production of shaft work in expense of pressure of the working
fluid.
In an ideal turbine
1. Change in P.E. and K.E. of the flow are negligible.
2. Heat rejection form the turbine is negligibly small and is undesirable
3. The turbine process is assumed to be adiabatic
Hence, the first law reduces to

36. 6. Compressor/ Centrifugal Pump/Compressor
Centrifugal Pump
It can be a reciprocating or a rotary device whose purpose it to increase the pressure of the
fluid by putting in some shaft work through external means. Devices fulfilling this purpose
for liquid are termed Pumps and those for gases are termed Compressors. Theoretically,
these devices work exactly in opposite to that of turbine. So,
1. Change in P.E. and K.E. of the flow are negligible.
2. Heat rejection form the turbine is negligibly small and is undesirable
3. The turbine process is assumed to be adiabatic
Hence, the first law reduces to

38. Perpetual Motion Machine of the First kind (PMM1)
A perpetual motion machine of the first kind produces work without the input of energy. It thus violates the first
law of thermodynamics: the law of conservation of energy. A perpetual motion machine of the second kind is a
machine which spontaneously converts thermal energy into mechanical work.

39. Limitation of the first law of thermodynamics
The limitation of the first law of thermodynamics is that it does not say anything about the direction of
flow of heat. It does not say anything whether the process is a spontaneous process or not with what
amount conversion will take place. The reverse process is not possible. In actual practice, the heat
doesn't convert completely into work