Test: Refrigeration Cycles & Systems - 2 - Mechanical Engineering MCQ

In vapour-absorption cycle, the system formed by the generator-valve-absorber-pump may be considered to represent the heat engine part of the cycle. In this part, only the refrigerant- absorbent solution circulates. This part is known as solution circuit.

The compressor

Compression is the first step in the refrigeration cycle, and a compressor is the piece of equipment that increases the pressure of the working gas. Refrigerant enters the compressor as low-pressure, low-temperature gas, and leaves the compressor as a high-pressure, high-temperature gas.

Types of compressors

Compression can be achieved through a number of different mechanical processes, and because of that, several compressor designs are used in HVAC and refrigeration today. Other examples exist, but some popular choices are: 

1. Reciprocating compressors

2. Scroll compressors

3. Rotary compressors

The condenser

The condenser, or condenser coil, is one of two types of heat exchangers used in a basic refrigeration loop. This component is supplied with high-temperature high-pressure, vaporized refrigerant coming off the compressor. The condenser removes heat from the hot refrigerant vapor gas vapor until it condenses into a saturated liquid state, a.k.a. condensation.

After condensing, the refrigerant is a high-pressure, low-temperature liquid, at which point it’s routed to the loop’s expansion device.

The expansion device

These components come in a few different designs. Popular configurations include fixed orifices, thermostatic expansion valves (TXV) or thermal expansion valves (pictured above), and the more advanced electronic expansion valves (EEVs). But regardless of configuration, the job of a system’s expansion device is the same - create a drop in pressure after the refrigerant leaves the condenser. This pressure drop will cause some of that refrigerant to quickly boil, creating a two-phase mixture.  

This rapid phase change is called flashing, and it helps tee up the next piece of equipment in the circuit, the evaporator, to perform its intended function.

The evaporator

The evaporator is the second heat exchanger in a standard refrigeration circuit, and like the condenser, it’s named for its basic function. It serves as the “business end” of a refrigeration cycle, given that it does what we expect air conditioning to do – absorb heat.

This happens when refrigerant enters the evaporator as a low temperature liquid at low pressure, and a fan forces air across the evaporator’s fins, cooling the air by absorbing the heat from the space in question into the refrigerant.

After doing so, the refrigerant is sent back to the compressor, where the process restarts. And that, in a nutshell, is how a refrigeration loop works. If you have any questions about the refrigeration cycle or its components and how they work, give us a call. We've been helping customers get the most out of their HVAC and refrigeration equipment for nearly 100 years.

Boot-strap system: It has two heat exchanges ' instead of one and the expansion turbine drives a compressor rather than a fan. So, it cannot be used for ground cooling. The primary purpose of the Boot-strap system is to provide an additional cooling capacity when the primary source of air does not have a sufficiently high pressure to provide the amount of cooling required. The turbine drives the secondary compressor to raise the pressure of primary air before it enters the turbine.

Boot-strap air evaporative cooling system is similar to boot-strap air cycle system except that the addition of an evaporator between the second heat exchanger and the cooling turbine.

The regenerative air cooling system is a modification of simple air system with the addition of a secondary heat exchanger in which the air from the primary heat exchanger is further cooled with a portion of the refrigerated air bled after expansion in the turbine.

Dry ice when exposed to atmosphere sublimates by absorbing latent heat of sublimation.