Subtopic: Preservation of food by cooling and freezing
Question Statement:
In a standard Vapor-Compression Refrigeration System (VCRS), the thermodynamic state change undergone by the refrigerant across the thermostatic expansion valve is an:
Options:
(A) Isenthalpic throttling expansion with constant enthalpy ($h_3 = h_4$)
(B) Isentropic reversible expansion ($s_3 = s_4$)
(C) Isothermal heat rejection
(D) Isobaric vaporization
Answer Key:
A
Step-by-Step Solution & Explanation
The expansion valve is an uninsulated throttling restriction with negligible work and heat exchange; flow through the restriction is an irreversible, constant-enthalpy (isenthalpic) process ($h_3 = h_4$).