Work & Heat Transfer | Mechanical Engineering SSC JE (Technical) PDF Download

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.

Work & Heat Transfer | Mechanical Engineering SSC JE (Technical)

  •  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

Work & Heat Transfer | Mechanical Engineering SSC JE (Technical)

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)

Work & Heat Transfer | Mechanical Engineering SSC JE (Technical)

(iv) Adiabatic (isentropic)

Work & Heat Transfer | Mechanical Engineering SSC JE (Technical)

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

  •  Mean effective pressure (Pm)

Work & Heat Transfer | Mechanical Engineering SSC JE (Technical)

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)

Work & Heat Transfer | Mechanical Engineering SSC JE (Technical)

  • Indicated power (for four stroke engine)

Work & Heat Transfer | Mechanical Engineering SSC JE (Technical)
Brake power (BP) =

Work & Heat Transfer | Mechanical Engineering SSC JE (Technical)

Mechanical efficiency

Work & Heat Transfer | Mechanical Engineering SSC JE (Technical)

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
    Work & Heat Transfer | Mechanical Engineering SSC JE (Technical)
    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.

Work & Heat Transfer | Mechanical Engineering SSC JE (Technical)

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

Specific heat c =Work & Heat Transfer | Mechanical Engineering SSC JE (Technical)
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.

The document Work & Heat Transfer | Mechanical Engineering SSC JE (Technical) is a part of the Mechanical Engineering Course Mechanical Engineering SSC JE (Technical).
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FAQs on Work & Heat Transfer - Mechanical Engineering SSC JE (Technical)

1. What is work transfer in the context of mechanical engineering?
Ans. Work transfer in mechanical engineering refers to the energy transfer that occurs as a result of a force acting through a distance. It is the process of converting mechanical energy into other forms, such as electrical or thermal energy. In simple terms, work transfer is the work done on or by a system.
2. How does heat transfer differ from work transfer?
Ans. Heat transfer and work transfer are both modes of energy transfer but differ in their mechanisms. Heat transfer occurs due to a temperature difference between two objects, resulting in the transfer of thermal energy. On the other hand, work transfer involves the application of a force on an object, causing it to move and transfer mechanical energy.
3. What are the different types of heat transfer?
Ans. There are three main types of heat transfer: conduction, convection, and radiation. - Conduction is the transfer of heat through direct contact between objects or substances. It occurs when heat energy travels through a solid material from a region of higher temperature to a region of lower temperature. - Convection is the transfer of heat through the movement of fluid, such as air or water. It involves the circulation of hot and cold fluids, which leads to the transfer of heat energy. - Radiation is the transfer of heat through electromagnetic waves. Unlike conduction and convection, radiation does not require a medium and can occur in vacuum or through transparent materials.
4. How is work calculated in mechanical engineering?
Ans. In mechanical engineering, work is calculated as the product of force and displacement. Mathematically, work (W) is given by the equation: W = F * d * cos(theta), where F is the applied force, d is the displacement, and theta is the angle between the force and displacement vectors. The unit of work is joules (J).
5. What are some examples of work and heat transfer in mechanical engineering?
Ans. Examples of work transfer in mechanical engineering include the work done by an engine to propel a vehicle, the work done by a motor to rotate machinery, and the work done by a human in lifting a heavy object. Examples of heat transfer in mechanical engineering include the dissipation of heat from a car engine through the radiator, the transfer of heat in a heat exchanger, and the cooling of electronic components using heat sinks.
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