1 answer

(100 points) Figure below shows the schematic diagram of a two-stage cascade refrigeration system (also called...

Question:

(100 points) Figure below shows the schematic diagram of a two-stage cascade refrigeration system (also called the Economizer
State P (bar) T(°C) h (kJ/kg) s (kJ/kg-K) .X Phase description - 32 1.0 (2) 2 4 3 1.0 (4) 4 5 0 6 7 0 8
(100 points) Figure below shows the schematic diagram of a two-stage cascade refrigeration system (also called the Economizer 2-Stage Refrigeration Cycle). Comparing to the cascade two-stage refrigeration system discussed in In-class Activity #10a, in this case, the flash chamber (now called Flash Intercooler) is still used but the mixing chamber is removed. The superheated vapor (2) out of the low-pressure compressor (1) is routed into the flash chamber, and the saturated vapor (3) out of the flash chamber enters directly the high-pressure compressor (II). Saturated liquid (5) out of condenser is throttled through Valve A into the Flash Intercooler; while saturated refrigerant liquid (7) exits the bottom of the flash chamber and is further throttled through expansion valve (B) into the evaporator. Let Refrigerant R134a be used as the working fluid and the mass flow rate through the evaporator be m = 0.12 kg/s. Assume that the refrigerant leaves the evaporator as a saturated vapor and both compressors operates with an isentropic efficiency of 87%. With the given operating temperature (T1) of the evaporator and the operating pressures (P and Ps) of the Flash Intercooler and Condenser as indicated in the table, you are asked to do the following: 1. Find out the corresponding properties in the table below for a thermodynamic analysis. 2. Plot schematically the cycle on a T-s diagram, clearly show all principle states. 3. Determine the mass flow rate of refrigerant, ,, entering the high-pressure compressor (II) by performing the analysis of mass and energy balance over the Flash Intercooler. 4. Determine the total power consumed by the two compressors, W. 5. Calculate the cooling load of the cycle, Oly, in tons. 6. Calculate the coefficient of the performance of the system, COPR Condenser Valve A Compressor € 6 3 Flash Intercooler 2 Compressor Valve B Evaporator 8 w
State P (bar) T(°C) h (kJ/kg) s (kJ/kg-K) .X Phase description - 32 1.0 (2) 2 4 3 1.0 (4) 4 5 0 6 7 0 8

Answers

state P(bar) T(celsius) h(KJ/Kg) s(KJ/Kg.k) x Phase Description
1 0.7704 -32 227.9 0.9456 1 saturated vapour
2s 4 NA 260 0.9456 NA superheated vapour
2 4 NA 264.79 NA NA superheated vapour
3 4 8.93 252.32 0.9145 1 saturated vapour
4s 14 NA 278 0.9145 NA superheated vapour
4 14 NA 281.837 NA NA superheated vapour
5 14 52.43 125.26 0.4453 0 saturated liquid
6 4 8.93 125.26 0.464 0.3323 liquid+ vapour mixed region
7 4 8.93 62 0.2399 0 saturated liquid
8 0.7704 -32 62 0.25769 0.2403 liq+vap mixed region

5 Py 14 bar & 45 Р so Tina 6 P2=4 bar 2s 2 3 Ti = - 320 8 m=0.12 h At i- R134 a table at T = -32°c from P = 0.7704 bar. he =At 2 0.87 Given, isentropic efficiency of compressor I has-hy hathi Moon comp 0.87 - 260 - 227.9 h2-227.9 h2=264.79 KJ kg AT=> hy=281.837 AL 5: At iybar & saturated conditions Tsat - 52.43°c S5 = 0.9453 hs - 125.26 Atsi Isenthapic process 7 hs - (25AL 7 62 hf shy st S 0.2399 At 89 Isenthapic process) hy - h8 - 62 - 32°ck 0.7704 bar wf = 9.52 / Lag = 218.37 - 0.9456 -0.90545 is m 3 T j २ y niz 1 6 ingringen 8 im S32 balance : im at a t im at t - im at 3+ in at 7 mi at 2 - m ant 6 ini =m3 m 3 3 - 7 = าท 1 > m, & inz-ingting Energy balancmichah) compressor za power consumed by compressor 1 WI 0.12( 264.79.-22 7.9) inputh I 4.4268 kW Pomeransumes by ing (hy-hy)

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