Thermodynamics: Vapor-compression refrigeration

In summary, the refrigerator in a house is driven by a vapor-compression refrigeration cycle and is used to maintain the interior at -5oC while the kitchen's temperature is 32oC. The minimum electrical power to run the refrigerator is 8.3 kW and the rate of heat rejected to the kitchen is 21.7 kW assuming the same power consumption.
  • #1
Sara1
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The refrigerator at a house is driven by a vapor-compression refrigeration cycle shown in figure 6-19 in the textbook. Assume the refrigeration cycle is used to keep the interior of the refrigerator at -5oC at all times. When the kitchen’s temperature is 32oC, the refrigerator is estimated to be gaining heat at a rate of 30 MJ/h.

(a) The minimum electrical power to run this refrigerator in kW.
(b) The rate of heat rejected from the refrigerator to the kitchen in kW assuming the same power consumption in part (a).

I attempted solving it using the formula for a refrigeration cycle,
Wnet,in= QH-QL
However, i am not sure how to include the minimum electrical power. I don't understand that part.
 
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  • #2
(a) The minimum electrical power to run this refrigerator in kW is:Wnet,in = QH - QL = 30 MJ/hWnet,in = 8.3 kW(b) The rate of heat rejected from the refrigerator to the kitchen in kW assuming the same power consumption in part (a) is:QL = QH - Wnet,in = 30 MJ/h - 8.3 kW = 21.7 kW
 

1. What is vapor-compression refrigeration?

Vapor-compression refrigeration is a thermodynamic process used to extract heat from a low-temperature source (such as the inside of a refrigerator) and transfer it to a high-temperature sink (such as the outside air). This is achieved through the use of a refrigerant, which undergoes a cycle of compression, condensation, expansion, and evaporation.

2. How does a vapor-compression refrigeration system work?

A vapor-compression refrigeration system consists of four main components: a compressor, a condenser, an expansion valve, and an evaporator. The refrigerant is compressed by the compressor, which raises its temperature and pressure. The hot refrigerant then flows to the condenser, where it is cooled and condensed into a liquid. The liquid refrigerant then passes through the expansion valve, which reduces its pressure and temperature. Finally, the cool refrigerant enters the evaporator, where it absorbs heat from the surrounding environment and evaporates back into a gas, completing the cycle.

3. What are the advantages of vapor-compression refrigeration?

Vapor-compression refrigeration is the most widely used method of refrigeration because it is efficient, reliable, and relatively simple to operate. It also allows for precise control of temperature and can be used for both cooling and heating. Additionally, vapor-compression systems can be scaled up or down to suit a wide range of applications, from small refrigerators to large industrial cooling systems.

4. What are some common refrigerants used in vapor-compression systems?

Some common refrigerants used in vapor-compression refrigeration systems include hydrofluorocarbons (HFCs), such as R-134a, and hydrochlorofluorocarbons (HCFCs), such as R-22. However, due to their negative impact on the environment, these refrigerants are being phased out and replaced with more environmentally friendly options, such as hydrocarbons (HCs) and hydrofluoroolefins (HFOs).

5. What are some real-world applications of vapor-compression refrigeration?

Vapor-compression refrigeration is used in a wide range of applications, including residential and commercial refrigerators and freezers, air conditioning units, heat pumps, and industrial cooling systems. It is also used in transportation, such as in refrigerated trucks and trains, to transport perishable goods. Additionally, vapor-compression refrigeration is used in various industries, such as food and beverage production, pharmaceuticals, and chemical processing.

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