A plate-fin heat exchanger is used to condense a saturated refrigerant vapor in an air-conditioning system. The vapor has a saturation temperature of 45?C and a condensation rate of 0.015 kg/s is dictated by system performance requirements. The frontal area of the condenser is fixed at A_fr = 0.25 m² by installation requirements, and a value of h_fg = 135 kJ/kg may be assumed for the refrigerant.

(a) The condenser design is to be based on a nominal air inlet temperature of T_c,i = 30?C and nominal air inlet velocity of V = 2 m/s for which the manufacturer of the heat exchanger core indicates an overall coefficient of U = 50 W/m² ? K. What is the corresponding value of the heat transfer surface area required to achieve the prescribed condensation rate? What is the air outlet temperature?

(b) From the manufacturer of the heat exchanger core. it is also known that U ? V^0.7 . During daily operation the air inlet temperature is not controllable and may vary from 27 to 38?C. If the heat exchanger area is fixed by the result of part (a), what is the range of air velocities needed to maintain the prescribed condensation rate? Plot the velocity as a function of the air inlet temperature.

Transcribed Image Text:

Tco Refrigerant m, Tsat Vapor Frontal area, A Atmospheric air V, Ti