Figure P737 provides steadystate data for a composite of a h

Figure P7.37 provides steady-state data for a composite of a hot plate and two solid layers. Perform a full exergy accounting, in kW, of the electrical power provided to the composite, including the exergy transfer accompanying heat transfer from the composite and the destruction of exergy in the hot plate and each of the two layers. Let T0=300K.

Solution

BY FORMULA HEAT ENERGY SUPPLIED Q = m x c x T

FROM TOPMOST SOLID LAYER TO AIR, ASSUMING HEAT TRANSFER AT PER UNIT OF TIME, WE GET FROM ABOVE EQUATION Q(1kW) = mc (400-300) AND SO mc = 1000 / 100 = 10

(NOTE- WE ASSUME THAT THIS PRODUCT mc IS CONSTANT FOR ALL LAYERS.)

FROM MIDDLE SOLID LAYER TO TOPMOST SOLID LAYER Q = 10 (600-400) = 2000 WATTS

FROM HOT LAYER TO MIDDLE SOLID LAYER Q = 10 (1000 - 600) = 4000 WATTS

FROM AIR TO HOT LAYER Q = 10 (300 - 1000) = 7000 WATTS

ANSWERS ----