Refrigerators and Heat Pumps

Refrigerators and heat pumps depend upon Carnot’s cycle. Carnot’s cycle was proposed by Sadi Carnot in 1824, based on the second law of thermodynamics. The second law of thermodynamics states that “the complete conversion of heat energy into work energy without any compensation or loss of energy (in other forms such as heat and light energy) in-between.”

A conceptual and mathematical model, thermodynamics refrigeration cycles, and heat pump cycles utilise heat transfer from cold to hot. On one side, the heat pump cycle is a mechanical method that consists of transmitting a location or course from a low temperature to another source at a higher temperature.

On the other hand, the mechanism of the refrigerator cycle allows the source at a higher temperature to transfer to a source or location at a lower temperature. 

History of Refrigeration

Earlier, the cooling of food involved ice. The refrigeration process began somewhat in the mid-1750s. However, it developed in the early 1800s. The first-ever vapour-compression refrigeration started in 1834, and the first commercial ice-making machine was produced in 1854. 

The refrigerators for household purposes were invented in 1913, while the first self-contained unit was made in 1923. 

The Component of Refrigerators

The refrigerator has four components. The components of refrigerators are as follows:

1. The Compressor
2. The Condenser
3. The Expansion Device
4. The Evaporator

Working of the Refrigerator

The working of refrigerators with respect to the components of refrigerators is as follows:

The Compressor- It is the first step in refrigeration that is responsible for increasing the pressure of the working gas. In compressors, the refrigerant gas enters at low pressure with low temperature. However, it leaves the compressor as both high-pressure and high-temperature gas. 

There can be three different types of compressors:

• Reciprocating Compressor
• Scroll Compressor
• Rotatory Compressor

The Condenser- It is one of the basic refrigeration loops. The high-temperature and high-pressure refrigerant gas from the compressor enters the condenser. The condenser is responsible for removing heat from the refrigerant and making the vapour gas until it condenses into a saturated liquid. Now, the refrigerant gets high-pressure but low-temperature.

The Expansion Device- The expansion devices come in different designs. Some of these are fixed orifices, thermostatic expansion valves (TXV) or thermal expansion valves, and the more advanced electronic expansion valves (EEVs).

The primary job of the expansion device is to create a drop in pressure as the refrigerant leaves the condenser. This refrigerant drop causes a quick boil and creates a two-phase mixture. This phase change is called the flashing, which helps prepare for refrigerant entry into the evaporator. 

The Evaporator- The evaporator absorbs heat energy when the refrigerant enters it. The refrigerant, after leaving the expansion device, is of low temperature and low pressure. A fan-force present in the evaporator cools the air and absorbs the heat. Now, the refrigerant is again sent back to the compressors and the cycle restarts. 

HEAT ENGINES

Heat engines consist of a thermodynamic process where the heat supply is converted into mechanical work. 

TYPES OF HEAT ENGINES 

1. Internal combustion engine
2. Gas turbine

Major parts of an engine 

The major parts of a heat engine are as follows:

• Working Substance: A substance through which heat is absorbed or rejected into the sink is termed a working substance
• Source: For the mechanism to occur, a heat source of infinite thermal capacity is required that must be at a constant high temperature
• Sink: At a constant low temperature, there should be a body called a sink of finite thermal capacity for withdrawing or giving heat

HEAT PUMPS

A device used to pump heat into a system is termed a heat pump. The main agenda is to transfer energy to a high-temperature environment such as a home. It runs on electricity and is much better than burning fuel for keeping your house nice and warm. One of the biggest cons of heat pumps is that they can be more expensive than burning fuel if the work used is provided by electrical energy. 

In colder temperatures, heat pumps extract energy from the outside and transfer it to higher temperatures on the inside. However, when it’s warmer outside, the process is reserved, and the system then performs like an air conditioner, cooling your home down. 

TYPES OF HEAT PUMPS 

• Geothermal (ground-source) Heat Pump
• Water Source Heat Pump
• Air Source Heat Pump
• Exhaust Air Heat Pump
• Solar-assisted Heat Pump
• Absorption Heat Pumps

Difference between Refrigerator and Heat Pumps

• The refrigerant cools down the substance and maintains a lower temperature level in the freezer, it absorbs heat through the above-mentioned process
• In contrast, the main objective of a heat pump is to provide heat to the room or other place
• In the refrigerator, the evaporator is present inside the freezer, whereas in the heat pump, it is present outside the room, which needs heating

We can say that, even though both refrigerators and heat pumps are based on the principle of Carnot’s cycle, they are different in several aspects. 

Conclusion

Now, we know that refrigerators and heat pumps work on the principle of reversed Carnot’s cycle. The second law of thermodynamics is the principle for the Carnot’s cycle. A refrigerator lowers the temperature, whereas the heat pump does the opposite. It warms up the room in which it is present.