Explanation Write the energy balance equation for a closed system for which the plate is taken as the system. E in − E out = Δ E system Q in = Δ U Q in = m ( u 2 − u 1 ) = m c p ( T 2 − T 1 ) (I) Here, net energy transfer in to the control volume is E in , net energy transfer exit from the control volume is E out and change in internal energy of system is Δ E system , mass of the brass plate is m , specific heat capacity of the brass plate is c p , amount of heat transfer to the plates is Q in , internal energies of the brass plate at inlet and outlet conditions are u 1 and u 2 respectively and temperatures of the brass plate at inlet and outlet conditions are T 1 and T 2 respectively. Write the formula to calculate mass of the brass plate ( m ) . m = ρ V = ρ L A (II) Here, density of the brass is ρ , volume and area of the brass plate are V and A respectively and thickness of the brass plate is L . Write the formula to calculate rate of heat transfer to the plates in the furnace ( Q ˙ total ) . Q ˙ total = n ˙ plate Q in (III) Here, rate at which the plates are heated through the oven is n ˙ plate . Write the expression for the entropy balance on the closed extended system. S in − S out + S gen = Δ S system Q in T b,in + S gen = Δ S tank Q i n T b , i n + S gen = m ( s 2 − s 1 ) Q i n T b , i n + S gen = m c p ln T 2 T 1 S gen = m c p ln T 2 T 1 − Q in T b,in (IV) Here, entropy generation is S gen , change in entropy of the extended system is Δ S tank , net entropy at inlet condition is S in , net entropy at outlet condition is S out , entropies of the brass plate at inlet and outlet conditions are s 1 and s 2 respectively and base temperature is T b , i n Write the expression to calculate rate of entropy generation during the process ( S ˙ gen ) . S ˙ gen = n ˙ plate S gen (V) Write the expression to calculate rate of exergy destruction during the process ( X destroyed ) . X ˙ destroyed = T 0 S ˙ gen (VI) Here, dead state temperature is T 0 . Conclusion: The values of density and specific heat capacity of the brass are, ρ = 532.5 lbm / ft 3 c p = 0.091 Btu / lbm ⋅ ° F Substitute 532.5 lbm / ft 3 for ρ , 1.5 in . for L and ( 1 ft × 3 ft ) for A in Equation (II). m = ( 532.5 lbm / ft 3 ) ( 1.5 in . ) ( 1 ft × 3 ft ) = ( 532.5 lbm / ft 3 ) ( 1.5 in . × 1 ft 12 in . ) ( 1 ft × 3 ft ) = 199.7 lbm Substitute 199.7 lbm for m , 0

8th Edition

ISBN: 9780073398174

Author: Yunus A. Cengel Dr., Michael A. Boles

Publisher: McGraw-Hill Education

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Chapter 8.8, Problem 125RP

To determine

The rate of heat transfer to the plates in the furnace.

The rate of exergy destruction associated with the process.

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Chapter 8.8, Problem 124RP

Chapter 8.8, Problem 126RP

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The rate of heat transfer to the plates in the furnace. The rate of exergy destruction associated with the process.

Solution Summary: The author calculates the energy balance equation for a closed system for which the plate is taken as the system.

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The rate of heat transfer to the plates in the furnace. The rate of exergy destruction associated with the process.

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Chapter 8 Solutions

The rate of heat transfer to the plates in the furnace.

The rate of exergy destruction associated with the process.