Chapter 1 Basics of Heat Transfer 1-129 A room is to be heated by 1 ton of hot water contained in a tank placed in the room. The minimum initial temperature of the water is to be determined if it to meet the heating requirements of this room for a 24-h period. Assumptions 1 Water is an incompressible substance with constant specific heats. 2 Air is an ideal gas with constant specific heats. 3 The energy stored in the container itself is negligible relative to the energy stored in water. 4 The room is maintained at 20°C at all times. 5 The hot water is to meet the heating requirements of this room for a 24-h period. Properties The specific heat of water at room temperature is C = 4.18 kJ/kg·°C (Table A-9). Analysis Heat loss from the room during a 24-h period is Q loss = (10,000 kJ/h)(24 h) = 240,000 kJ Taking the contents of the room, including the water, as our system, the energy balance can be written as ( ) ( )0 air water out energies etc. potential, kinetic, internal, in Change system
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