Which of the following statements about refrigeration are TRUE and which are FALSE?

Here are the answers to the statements, indicating whether each is TRUE or FALSE:

• i. Cooling of a hot cup of coffee by leaving it on a table is refrigeration.

  • FALSE. Refrigeration typically refers to maintaining a temperature below the ambient temperature. Cooling to ambient is simply heat transfer.

• ii. One of the disadvantages of natural refrigeration methods is that they are uncertain.

  • TRUE. Natural methods are often dependent on environmental conditions, making their performance less predictable.

• iii. Throttling loss decreases as the evaporator temperature decreases.

  • FALSE. As evaporator temperature decreases, the pressure ratio across the throttling valve generally increases, leading to increased irreversibility and throttling loss.

• iv. In vapour compression refrigeration, isothermal heat rejection is replaced by isenthalpic throttling.

  • FALSE. Isenthalpic throttling replaces the isentropic expansion process of an ideal cycle, not the isothermal heat rejection.

• v. The COP of Carnot refrigeration is always lower than the COP of vapour compression refrigeration system.

  • FALSE. The Carnot COP is the maximum possible COP; actual vapor compression systems have a COP lower than or equal to the Carnot COP.

• vi. Superheating increases both the work input and refrigeration effect.

  • TRUE. Superheating increases the enthalpy at the compressor inlet ($h_1$), which increases both the refrigeration effect ($h_1 - h_4$) and the compressor work ($h_2 - h_1$).

• vii. The higher the volumetric flow rate, the lower the capacity of the compressor.

  • TRUE. If "volumetric flow rate" refers to the specific volume of the refrigerant at the compressor inlet, a higher specific volume means a lower mass flow rate for a given compressor displacement, thus reducing the refrigeration capacity.

• viii. At low evaporator temperature, effect of condensing temperature is very high.

  • TRUE. The COP is more sensitive to changes in condensing temperature when the evaporator temperature is low.

• ix. In actual system, the temperature of the heat sink will be several degrees higher than the condensing temperature for heat transfer to take place.

  • FALSE. For heat to be rejected, the condensing temperature must be higher than the heat sink temperature.

• x. A system with subcooling, the vapour fraction at the inlet evaporator is reduced.

  • TRUE. Subcooling reduces the enthalpy of the liquid entering the expansion valve, which in turn reduces the amount of flash gas (vapor fraction) at the evaporator inlet.

• xi. During sensible heating, the enthalpy increases.

  • TRUE. Sensible heating increases the temperature of a substance without phase change, which directly increases its enthalpy.

• xii. Useful superheating increase refrigeration effect and decrease work of compression.

  • FALSE. Useful superheating increases both the refrigeration effect and the work of compression.

• xiii. For the same system, degree of superheating is lower than degree of subcooling.

  • FALSE. There is no general rule; the degrees of superheating and subcooling depend on the specific system design and operating conditions.

• xiv. A SHF of 1.0 implies a pure sensible heat transfer.

  • TRUE. Sensible Heat Factor (SHF) of 1.0 means that the latent heat transfer is zero, indicating only sensible heat transfer.

• xv. During sensible cooling of air, both dry bulb and wet bulb temperatures decrease.

  • TRUE. Sensible cooling lowers the dry bulb temperature. If no dehumidification occurs, the wet bulb temperature will also decrease.

• xvi. In zone of vaso-motor regulation against cold, blood vessels adjacent to skin dilate.

  • FALSE. Against cold, vasoconstriction occurs to reduce blood flow to the skin and conserve heat. Vasodilation occurs in