5.2.2 Heat exergyPotential work of heatT=(1-)8QSEroM=Q-T·△S=Q-TJExoWoAno =Q- Exo =T·△S中To
T T0 0 (1 ) x Q T E Q T = − xQ 0 0 Q E Q T Q T S T = − = − 5.2.2 Heat exergy Potential work of heat A Q E T S nQ xQ = − = 0 W0
TErQTo3......AnQ65sFor constant temperature heat resourceExo = Q(1 - 0)=Q-TAS=0=T.AS
0 0 (1 ) xQ T E Q Q T S T = − = − 0 nQ 0 T A Q T S T = = For constant temperature heat resource T0
TI园ErQT.3AnQ56For finite heat resourceEx0o=J(1-)Q=J(1-)mcpT=Z-TT= mcp[(T, -T)- TIn0=Q(1-1
For finite heat resource 2 1 0 0 2 1 2 2 1 0 2 1 1 0 (1 ) (1 ) [( ) ln ] (1 ) T XQ P T P T T E Q mc dT T T T T T mc T T T T T T T Q T = − = − − = − − − = − 1 2 2 1 ln T T T T T − = T0 T T0
Influential factors:Heat quantityHeat resource temperatureT个Ex ↑, △S ↓二T， Ex, △S个Environmental temperature T。T=T.Ex = 0If the system absorbs heat, it absorbs exergy;If the system discharges heat, it discharges exergy;
Influential factors: ⚫Heat quantity ⚫Heat resource temperature , , , xQ xQ T E S T E S ⚫Environmental temperature T0 0 0 T T E = = xQ If the system absorbs heat, it absorbs exergy; If the system discharges heat, it discharges exergy;
Example1kg air withtemperature of200Cwascooled to 4oC.Please calculate the heatTheisofairspecificheatexergy.theenvironmentalCp=1.004kJ/(kg.K)temperatureisT.=25C
Example 1kg air with temperature of 200℃ was cooled to 40℃. Please calculate the heat exergy. The specific heat of air is cp =1.004kJ/(kg.K). the environmental temperature is T0=25℃