Thermal Engineering

Specific Heat of a Substance

Q = m . C . Δt

Q = heat transfer in kJ,

m = mass in kg

C = specific heat

Δt = $t_2 – t_1$ = temperature change in Kelvin (final temperature – initial temperature)

Unit: kJ/kg K

Enthalpy

H = U + p . V

H = specific enthalpy

U = specific internal energy of gas

First Law of Thermodynamics (Joule’s Experiment)

First law as applied to closed system

∮d’ Q = ∮d’ w

First law as applied to closed system processes

Q = W + ΔU

Coefficient of Performance (C.O.P)

$W = Q_1 – Q_2$

$\table(C.O.P.)_{refrigerator}, = ,{\text"Desired effect"}/{\text"Energy input"};,=,{Q_2}/W = {Q_2}/{Q_1 – Q_2};(C.O.P.)_{heat-pump},=,{\text"Desired effect"}/{\text"Energy input"},=,{Q_1}/W = {Q_1}/{Q_1 – Q_2}$

$(C.O.P.)_{heat-pump} – (C.O.P.)_{refrigerator} = 1$

Efficiency of heat engine

η = 1 – ${Q_2}/{Q_1}$