Outdoor air (cp = 1.005 kJ/kg·°C) is to be preheated by hot exhaust gases in a crossflow heat exchanger before it enters the furnace. Air enters the heat exchanger at 101 kPa and 30°C at a rate of 0.5 m3 /s. The combustion gases (cp = 1.10 kJ/kg·°C) enter at 350°C at a rate of 0.85 kg/s and leave at 260°C. Determine the rate of heat transfer to the air and the rate of exergy destruction in the heat exchanger.

5-84 Air (Cp=1.005 kJ/kg°C) is to be preheated by hot exhaust gases in a cross-flow heat exchanger before it enters the furnace. Air enters the heat exchanger at 95 kPa and 20°Ct at rate of 0.6 m³/s. The combustion gases (Cp=1.10 kJ/kg°C) that enter at 160°C at a rate of 0.95 kg/s and leave at 95°C. Determine the rate of heat transfer to the air and its outlet temperature. Air 95 kPa 20°C 0.6 m³/s Exhaust gases 0.95 kg/s 95°C

A vessel initially contains 5.0 kg of liquid water and 2.0 kg of ice at 0°C. Energy is added until the ice has just melted. The temperature at the boundary where heat transfer occurs is taken to be the system temperature during the process. The enthalpy of melting is 333.5 kJ/kg. Consider the following processes used to melt the ice. a. Heat is added from the environment at 20°C. Determine the entropy flux and the total entropy generation, both in kJ/K. b. Heat is added from a reservoir at 727°C. Determine the same quantities as in part (a). c. Paddle-wheel work is used to change the state. Determine the total entropy production for the process, in kJ/K. d. Comment on the relative degree of irreversibility for the three processes.

A heat exchanger is to heat water (cp = 4.18 kJ/kg·oC) from 25oC to 60oC at a rate of 0.2 kg/s. The heating is to be accomplished by geothermal water (cp = 4.31 kJ/kg·oC) available at 159oC at a mass flow rate of 0.3 kg/s. Find the exit temperature of geothermal water.

Air (cp = 1.005 kJ/kg·°C) is to be preheated by hot exhaust gases in a cross-flow heat exchanger before it enters the furnace. Air enters the heat exchanger at 95 kPa and 20°C at a rate of 0.75 m3/s. The combustion gases (cp = 1.10 kJ/kg·°C) enter at 160°C at a rate of 0.95 kg/s and leave at 95°C. Determine the rate of heat transfer to the air and its outlet temperature. The rate of heat transfer to the air is ___ kW. The outlet temperature is ___°C.