Answer to Question #303422 in Thermal Power Engineering for nisha

Question #303422

The radiator of a steam heating system has a volume of 20 L and is filled with superheated vapor at 200 kPa and 150°C. At this moment both the inlet and exit valves to the radiator are closed. After a while the temperature of the steam drops 40C as a result of heat transfer to the room air. Determine the entropy change of the steam during this process.


1
Expert's answer
2022-02-28T11:10:18-0500

Solution;

Given;

"V=20L =0.02m^3"

At "P_1=200kPa,T_1=150\u00b0c;"

"v_1=0.93m^3\/kg"

"s_1=7.2kJ\/kgK"

At "T_2=40\u00b0c"

"v_1=v_2"

"v_f=0.001m^3\/kg"

"v_g=19.51m^3\/kg"

Therefore;

"v_2=v_f+x(v_g-v_f)"

"0.93=19.51+x(19.51-0.001)"

"x=0.047"

"s_2=s_f+xs_{fg}"

"s_2=0.57+0.047(7.638)"

"s_2=0.93kJ\/kgK"

Hence;

"\\Delta s=s_1-s_2=7.2-0.93"

"\\Delta s=6.27kgK"

"m=\\frac{V}{v_1}=\\frac{0.02}{0.93}=0.022kg"

"\\Delta s=6.27\u00d70.022"

"\\Delta s=0.138kJ\/K"


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