ME 401 Suction Line Heat Exchangers

1. ME 401Suction Line Heat Exchangers

2. Rankine Refrigerator EnhancementSuction Line Heat Exchanger • Exchange heat between the suction gas line and the liquid line • The suction gas (exit from the evaporator) is cool…approximately evaporator temperature • The liquid line (exit from condenser) is warm…approximately ambient temperature • Warming (superheating) suction gas increases compressor work • Cooling liquid line refrigerant increases refrigeration capacity • If cooling capacity increases faster than compressor work, then performance is improved • Depends on specific refrigerant characteristics • R134a improves in performance (refrigerators) • R22 decreases in performance (house air conditioners)

3. Qcond Condenser 2 1 High P Expansion Device Compressor Low P 3 4 Wcomp Evaporator Qevap Rankine Refrigerator Enhancement • Basic System • No enhancement

4. Qcond Condenser 2 High P 4’ SLH 1 2’ Low P Compressor Expansion Device 3 4 Wcomp Evaporator Qevap Rankine Refrigerator Enhancement • Suction line heat exchanger • Find new points 2’ and 4’

5. Isentropes change • Increasing superheat increases work Liq x2=0 1 Thot 2’ P 2 Vapor Tcold 3 4’ 4 x4=1 h Suction Line Heat Exchange Note: changes in enthalpy across heat exchanger fluids are equal h2-h2’ = h4’-h4

6. Expansion Valves Thermostatic expansion valves: See description on: http://www.hvacmechanic.com/txv.htm