LEVEL 3 ENGINEERING PRINCIPLES – THERMODYNAMIC SYSTEMS EQUATIONS Heat Transfer Equations Subject
Equation
Heat Transfer
Q = mCΔT
Q = ml Heat Required for Change of State
Q = ml
Variables and Units Q = heat energy in Joules (J) m = mass in kilograms (kg) C = specific heat capacity in Joules per kilogram Kelvin (J/KgK) ΔT = change in temperature in degrees Kelvin (K) Lv = latent heat of vaporisation in Joules per kilogram (J/kg) Lf = latent heat of fusion in Joules per kilogram (J/kg)
Thermal Power
P=
Q t
P = thermal power in Watts (W) t = time in seconds (s)
Thermal Expansion Equations Subject
Equation
Variables and Units ΔL = change in length (m)
Change in Length
ΔL = αL ΔT
α = thermal expansion coefficient (K-1) Lo = original length in meters (m)
New Length
L = L + ΔL
ΔT = change in temperature in degrees Kelvin (K) L = length (m)
Gas Laws Subject
General Gas Equation
Equation
Variables and Units
PV =C T
P = pressure in pascals (Pa) V = volume in cubic meters (M3) T = temperature in Kelvin (K)
PV PV = T T
C = arbitrary constant m = mass of gas in kilograms (kg) R = specific gas constant (J/Kg)
Ideal Gas Law
PV = mRT
Heat Transfer in Gases Subject Change in Internal Energy
Equation
Variables and Units ΔU = change in internal energy in Joules (J)
ΔU = mđ??ś ΔT
ΔH = change in enthalpy in Joules (J) m = mass in kilograms (kg) Cv = specific heat capacity at constant volume in Joules per kilogram Kelvin (J/KgK)
ΔH = mđ??ś ΔT Change in Enthalpy
Cp = specific heat capacity at constant pressure in Joules per kilogram Kelvin (J/KgK) ΔT = change in temperature in degrees Kelvin (K)
ΔH = ΔU + W
(where đ?‘Š = đ?‘ƒđ?›Ľđ?‘‰)
W = work done in Joules (J) P = pressure in pascals (Pa) ΔV = change in volume in cubic meters (m3)