Question

Thermodynamics

A two-stage vapour-compression refrigeration plant shown in Figure Q2 diagrammatically below is discharged with Refrigerant 12. Both compressors are single-acting, single-stage reciprocating machines with four cylinders and as isentropic efficiency of 80%. They each have a stroke/bore ratio of 1.2 and run at 600 rev/min with a volumetric efficiency of 90%. The condenser, flash chamber and evaporator pressures are 10 bar, 3 bar and 1 bar respectively. Saturation states exist at points 5 and 3 and the vapour at point l is superheated by 10 K a) Sketch the refrigeration cycles on T-s and P-h diagrams (8 marks) b) If the refrigeration capacity is 400 kW, determine the coefficient of performance (COP) of this plant, and the stroke and bore of HP compressor cylinder. Assuming that the flash chamber is adiabatic. (17 marks) Condenser HP compressor 6 Flash chamber LP compressor Evaporator Figure Q2 Table Q2 The given properties in the cycle Point 7 100 Point 4s* 271 Point 2s" 264 Point 5 Point 3 251 0.058 Point 1 244 0.17 Proper h (kJ/k V (m/kg) *h2, is for the state at 3 bar after an isentropic compression starting from state 1. #h4, is for the state at 10 bar after an isentropic compression starting from state 3.

Answer 1

L. 5 2. 3 9 .S m'n x ( h'_ h 8 )=q.oo 2.77 Kg/s 400/138.5 Cop RE/w 2. nw.

t5