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Thermodynamics HW Solutions 64

Thermodynamics HW Solutions 64 - Chapter 1 Basics of Heat...

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Chapter 1 Basics of Heat Transfer 1-124 Water is heated from 16°C to 43°C by an electric resistance heater placed in the water pipe as it flows through a showerhead steadily at a rate of 10 L/min. The electric power input to the heater, and the money that will be saved during a 10-min shower by installing a heat exchanger with an effectiveness of 0.50 are to be determined. Assumptions 1 This is a steady-flow process since there is no change with time at any point within the system and thus Δ Δ m E CV CV and = = 0 0 ,. 2 Water is an incompressible substance with constant specific heats. 3 The kinetic and potential energy changes are negligible, Δ Δ ke pe 0 . 4 Heat losses from the pipe are negligible. Properties The density and specific heat of water at room temperature are ρ = 1 kg/L and C = 4.18 kJ/kg·°C (Table A-9). Analysis We take the pipe as the system. This is a control volume since mass crosses the system boundary during the process. We observe that there is only one inlet and one exit and thus m m . Then the energy balance for this steady-flow system can be expressed in the rate form as &
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