Question

Thermodynamics

Ammonia enters the expansion valve of a refrigeration system at a pressure of 10 bar and a temperature of 18oC and exits at 5.0 bar. The refrigerant undergoes a throttling process. Determine the temperature, in oC, and the quality of the refrigerant at the exit of the expansion valve.

Step 1 Determine the temperature of the refrigerant at the exit, in oC. T2 =   oC

Answer 1

Given data :

Ammonia at P1 = 10 bar ; T1 = 18 degree celcius And P2 = 5.0 bar

Ammonia enters the expansion valve as compressed liquid.

From saturated liquid tables for Ammonia, we get for T(sat) = 18 degree celcius , we get P(sat) = 8.035 bar

Since we have 10 bar at inlet, we have 10 bar < P(sat). So state of ammonia at intet is compressed liquid.

From the tables we get, h(f) = h(1) = 265.5 kJ/ kg (In the absence of compressed liquid data, we can consider the ammonia as saturated liquid at the given temperature)

Now at exit we have P2 = 5.0 bar and h2 = h1 = 265.5 kJ/kg

From the same saturated tables, we get h(f2) = 199.18 kJ/kg ; h(g2) = 1446.19 kJ.kg

Since  h(f2) < h2 < h(g2) , we have saturated liquid-vapor mixture at the exit.

265.5 = 199.18 + x2 (1446.19 - 199.18)

x2 = 0.053

x2 = 5.3%

And T2 = 4.13 degree celcius (from the saturated tables for ammonia)

Students can refer to the saturated tables for ammonia externally.

An upvote will be highly appreciated.