Question

11.26 The compartment heater of an automobile exchanges heat between warm radiator fluid and cooler outside air. The flow rate of water is large compared to the air, and the effectiveness, ε, of the heater is known to depend on the flow rate of air according to the rela- tion, e 25 (a) If the fan is switched from low to high and irs doubled, determine the percentage increase in the heat added to the car, if fluid inlet temperatures remain the same. b) For the low-speed fan condition, the heater warms outdoor air from-10 to 30°C. When the fan is turned to medium, the airflow rate increases 50%. Find the new outlet temperature.

Answer 1

Calculate the effective ness ratio -0.25 ε mar -025 -0.25 -0.25 E27-025 0.841 Calculate the percentage increase in the heat added to the car 0.841 0.841 22-0.841 41 G-93x100%-(1-0.841) x100% 41 = 15.9%

Calculate the effective ness ratio -0.25 ε = mar 1.25 2, L1.5mm e,a(1.5)". 0.9036 1.5 Calculate the percentage increase in the heat added to the car

30.9036 g, 0.9036 9 22-0.9036 (1.5m)c,(4-263) =0.9036 (m)c,(303-263)0,9036 (6-263) (0.9036) (303-263) (1.5 7-263) = T = (0.9036) (303-263) +263 1.5 287.096 K = 14.096 °C