A finnedtube heat exchanger is used as an airconditioning co

A finned-tube heat exchanger is used as an air-conditioning condenser. During a steady state operation, refrigerant in the tubes remains 2-phase state throughout the heat exchanger at the condensing temperature 75degreeC. Air enters the condenser at inlet temperature 24degree C and air mass flow rate is 0.7 kg/s. Refrigerant-side convection thermal resistance and tube wall conduction resistances are negligible. Airside total surface area is 8 m^2 and overall surface efficiency is 0.82. Airside average convection coefficient is 102 W/m^2. The specific heat of air is 1,003 J/(kgK). Determine the heat transfer rate in W.

Solution

Inlet tempearature = 24 C

Heat transfer rate = mass flow rate * Cp* ( 75 - Outlet temperature)   = 102 * 0.82 * 8 * ( Outlet Temperature - 24)

                           => 0.7 * 10003 * (75 - T) = 102*0.82 * 8 * (T - 24)

                           =>    75 - T = 0.9530266 *(T - 24)       => T = 50.1133 C

Heat transfer rate   = 0.7 * 1003 * (75 - 50.1133)    = 17472.952 W