Transient Heat Transfer of Automobile A/C System Prepared by: Jason Hixson, Don Scott, and Michael Hickey August 29, 2005

A/C Schematic Recycled AirCooled Air R-134a M 2,T 2 M 1, T 1 M 3,T 3 M 4,T 4 R-134a

Objectives Measure temperatures & velocities of cooled air. Perform material and energy balance. Measure temperature of recycled air. Make estimates of coolant temperatures. Make estimates of air volume in car. Observe pseudo steady-state transient behavior.

The Energy Balance: Air Side: ∆H=m 2 *C p (T 2 -T 1 ) ∆H=UA ∆T lm Refrigerant Side: ∆H=m 3 (H 4 -H 3 )

Variables & Assumptions Entrance temperature Exit temperature Fan speed Velocity Engine RPM Time C p =1.004 kJ/kg*K H 3 =17.14 kJ/kg H 4 = kJ/kg T 3 =T 4 =40 °C

Quick Facts Fan setting 4 was unable to lower car temperature. R-134a mass flow rate is dependant on engine rpm. Air mass flow rate is not affected by engine rpm. Cab volume=2.3 m 3 Traveling at 2000 rpm, maximum heat transfer will occur at fan setting 3 where: UA=0.3 kJ/°C m 1 =0.13 kg/s