Question

In a mechanical refrigeration system, the highest temperature of refrigerant occurs

• A. Between condenser and evaporator
• B. In evaporator
• C. Before expansion valve
• D. Between compressor and condenser

Hint:

In any vapor-compression cycle (refrigeration or heat pump), the compressor's discharge line always carries the hottest fluid, while the expansion valve's exit carries the coldest.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to identify the location of the highest refrigerant temperature within a standard vapor-compression refrigeration cycle.


Step 3: Detailed Explanation:
Let's analyze the state of the refrigerant across the standard components of a refrigeration cycle:
• Compressor: The refrigerant enters as a low-pressure, low-temperature vapor. The compressor does mechanical work on the fluid, compressing it. This process is ideally isentropic, leading to a significant increase in both pressure and temperature. The refrigerant exits the compressor as a highly superheated vapor.
• Condenser: The hot, high-pressure vapor enters the condenser where it rejects heat to the environment. It cools down to its saturation temperature and condenses into a liquid. Thus, temperature decreases here.
• Expansion Valve: The high-pressure liquid undergoes an isenthalpic expansion, causing a sharp drop in both pressure and temperature.
• Evaporator: The cold, low-pressure mixture enters the evaporator, absorbs heat from the refrigerated space, and evaporates back into a vapor before returning to the compressor. The temperature is lowest here. Therefore, the highest temperature in the entire cycle is reached immediately after the compression process, right before any heat is rejected. This physical location is exactly between the compressor and the condenser.


Step 4: Final Answer:
The highest temperature occurs between the compressor and condenser.

Answer 2

The vapor-compression refrigeration cycle has four key locations, and to find where the refrigerant is hottest, we can check the physical process happening at each of the four listed locations directly.

1. Between condenser and evaporator (through the expansion valve): Here the refrigerant undergoes a throttling expansion, which causes a sharp pressure drop and, with it, a sharp temperature drop. This is one of the coldest points in the cycle, not the hottest.
2. In evaporator: Here the refrigerant absorbs heat from the space being cooled while staying at a low, near-constant temperature as it evaporates. This is the coldest region of the entire cycle.
3. Before expansion valve: This location is right after the condenser, where the refrigerant has already released its heat and cooled down to a saturated liquid at moderate temperature, well below its post-compression peak.
4. Between compressor and condenser: The compressor performs mechanical work on the refrigerant vapor, compressing it and raising both its pressure and temperature substantially. Immediately after leaving the compressor, before any of that heat has been rejected in the condenser, the refrigerant is at its highest temperature in the whole cycle.

Since compression is the only process in the entire cycle that adds energy and raises temperature significantly, and no heat has yet been removed at that point, the discharge line right after the compressor is where the refrigerant is hottest.

Therefore, the correct answer is Between compressor and condenser.