Chapter 3 Work And Heat Transfer - Thermodynamics, Mechanical Engineering Mechanical Engineering Notes | EduRev

Mechanical Engineering SSC JE (Technical)

Mechanical Engineering : Chapter 3 Work And Heat Transfer - Thermodynamics, Mechanical Engineering Mechanical Engineering Notes | EduRev

The document Chapter 3 Work And Heat Transfer - Thermodynamics, Mechanical Engineering Mechanical Engineering Notes | EduRev is a part of the Mechanical Engineering Course Mechanical Engineering SSC JE (Technical).
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WORK AND HEAT TRANSFER

  • Work done by the system is positive and when the work is done on a system, it is taken to be negative.
  •  Work is a path function and inexact or imperfect differential.

Chapter 3 Work And Heat Transfer - Thermodynamics, Mechanical Engineering Mechanical Engineering Notes | EduRev

  •  For closed system and reversible process work done is calculated by ∫pdV.
  •  In Cyclic Process:
  •  For point function total change in property, in the cycle is zero.

ΔV=0, ΔP=0, ΔT=0, ΔU=0, Δh=0

  • For path function net change in the cycle can may or may not be zero.

Work done in various reversible processes

Chapter 3 Work And Heat Transfer - Thermodynamics, Mechanical Engineering Mechanical Engineering Notes | EduRev

Process Work done
(i) Constant pressure (isobaric) w1-2 = p(v2 – v1) = mR (T2 – T1)
(ii) Constant volume (isochoric) w1–2 = 0
(iii) Constant Temperature (isothermal)

Chapter 3 Work And Heat Transfer - Thermodynamics, Mechanical Engineering Mechanical Engineering Notes | EduRev

(iv) Adiabatic (isentropic)

Chapter 3 Work And Heat Transfer - Thermodynamics, Mechanical Engineering Mechanical Engineering Notes | EduRev

n = polytropic const.
m = no. of moles
g = Adiabatic constant

  •  Mean effective pressure (Pm)

Chapter 3 Work And Heat Transfer - Thermodynamics, Mechanical Engineering Mechanical Engineering Notes | EduRev

Id — length of the p–v diagram along v–axis
ad — area of the p–v diagram
k — Spring constant

  •  Indicated power (for two stroke engine)

Chapter 3 Work And Heat Transfer - Thermodynamics, Mechanical Engineering Mechanical Engineering Notes | EduRev

  • Indicated power (for four stroke engine)

Chapter 3 Work And Heat Transfer - Thermodynamics, Mechanical Engineering Mechanical Engineering Notes | EduRev
Brake power (BP) =

Chapter 3 Work And Heat Transfer - Thermodynamics, Mechanical Engineering Mechanical Engineering Notes | EduRev

Mechanical efficiency

Chapter 3 Work And Heat Transfer - Thermodynamics, Mechanical Engineering Mechanical Engineering Notes | EduRev

L — stroke of the piston
A — cross sectional area of the cylinder(πD2/4)

N — r.p.m of the crank shaft
n — number of cylinders
T — Torque on the crank shaft

  • Mass Flow rate
    Chapter 3 Work And Heat Transfer - Thermodynamics, Mechanical Engineering Mechanical Engineering Notes | EduRev
    V — Velocity of flow
    v — Specific volume
    A — Cross sectional area

Flow work : The flow work in an open system represents the energy transfered across the system boundary as a result of the energy imparted to the fluid by a pump, blower or compressor to make the fluid across the control volume. It is analogous to
displacement work. Flow work per unit mass Wflow = PV
P — pressure
v — specific volume

  •  Expansion of a gas against vacuum is called free expansion.
  •  There is no work transfer involved in free expansion.
  •  Heat flow out of a system is taken as negative while heat flow into a system is taken as positive.

Chapter 3 Work And Heat Transfer - Thermodynamics, Mechanical Engineering Mechanical Engineering Notes | EduRev

  • Heat like work is also a path function so is inexact or imperfect differential.

Specific heat c =Chapter 3 Work And Heat Transfer - Thermodynamics, Mechanical Engineering Mechanical Engineering Notes | EduRev
Heat capacity C = m.c

  • For solids, specific heat does not depend on the process.
  • The latent heat of fusion is the amount of heat transferred to melt unit mass of solid into liquid or to freeze unit mass of liquid to solid at a constant pressure and temperature.

FQ = mlF
lF = Latent heat of fusion
• The latent heat of vaporisation is the amount of heat transferred to vaporize unit mass of liquid into vapour or condense unit mass of vapour into liquid at a constant pressure and temperature.

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