Thermodynamics: Vapor Compression Refrigeration that is Adiabatic?

In summary, a heat pump is using the vapor-compression refrigeration cycle with 0.2 kg/s of refrigerant-134a to maintain a house at 26oC while absorbing heat from the outdoors at 3oC. The refrigerant enters the compressor at 200 kPa as a saturated vapor and leaves at 900 kPa, 50oC. The refrigerant then leaves the condenser as a saturated liquid. However, in order to find the COP, QH is needed but cannot be obtained since all devices are well-insulated. To proceed, the COP can be calculated using the equation COP(heating) = Q-hot/W-net,in. The enthalpy values at various points
  • #1
Sara1
12
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Consider a heat pump works on the vapor-compression refrigeration cycle with 0.2 kg/s of refrigerant-134a as the working fluid. The cycle is used to maintain a house at 26oC while absorbing heat from the outdoors at 3oC. R-134a enters the compressor at 200 kPa as a saturated vapor and leaves at 900 kPa, 50oC. The refrigerant leaves the condenser as a saturated liquid. Assuming the four devices to be well-insulated:

I need to find COP, but in order for that i need QH, which i can't have because all the devices are insulated. How do i proceed?
 
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  • #2
COP (heating)=Q-hot/W-net,in

COP (heating)=M-dot * (h2-h4)/m-dot * (h2-h1)

Pt 1: 200 kPa,3 C
Pt 2: 900 KPa,50 C
Pt 4: 900 KPa, 26 C

See if that works
 
  • #3
Correction

Pt 1:200 kPa, sat. Vapor, -9 C

Pt 2: 900 kPa, 50 C

Pt 4: 900 kPa, sat. liquid, 35.4 C

Find enthalpy' s for various points, use equation for COP-heat
 
  • #4
Thank you
 
  • #5


I would first clarify the question by asking for more information about the specific devices being referenced in the scenario. Are they well-insulated in a theoretical sense, or are they actually insulated in practice? If they are actually insulated, I would ask for more details about the insulation properties and whether any heat transfer occurs between the devices and their surroundings. This information would be necessary in order to accurately calculate the COP of the heat pump.

If the devices are truly well-insulated and no heat transfer occurs, then it is not possible to calculate the COP of the heat pump. This is because the COP is a measure of the heat transferred from the cold reservoir (outdoors) to the hot reservoir (inside the house) divided by the work done by the compressor. Without knowing the heat transfer, the COP cannot be determined.

In this case, I would suggest considering other factors such as the energy efficiency of the compressor and the environmental impact of using R-134a as the working fluid. Additionally, it may be helpful to explore alternative refrigeration cycles or technologies that could potentially improve the efficiency of the heat pump.
 

Related to Thermodynamics: Vapor Compression Refrigeration that is Adiabatic?

1. What is the purpose of a vapor compression refrigeration system and how does it work?

A vapor compression refrigeration system is used to remove heat from a space or substance by circulating a refrigerant through a series of components. The refrigerant absorbs heat from the space or substance and then releases it outside, resulting in cooling. The refrigerant is compressed, condensed, and expanded in a continuous cycle to maintain the cooling process.

2. What is the role of adiabatic processes in a vapor compression refrigeration system?

Adiabatic processes refer to processes that occur without the transfer of heat. In a vapor compression refrigeration system, the compression and expansion of the refrigerant are adiabatic processes. This means that no heat is added or removed from the refrigerant during these stages, ensuring that the system remains energy efficient.

3. How does the efficiency of a vapor compression refrigeration system compare to other refrigeration methods?

Vapor compression refrigeration systems are known for their high efficiency and are commonly used in household and commercial refrigerators. They are more efficient than other refrigeration methods such as absorption refrigeration, which relies on heat rather than mechanical work to circulate the refrigerant.

4. What are the main components of a vapor compression refrigeration system?

The main components of a vapor compression refrigeration system include a compressor, condenser, expansion valve, and evaporator. The compressor is responsible for compressing the refrigerant and raising its temperature, the condenser removes heat from the refrigerant, the expansion valve reduces the pressure of the refrigerant, and the evaporator absorbs heat from the surrounding environment.

5. How can the performance of a vapor compression refrigeration system be improved?

There are several ways to improve the performance of a vapor compression refrigeration system, including using a more efficient compressor, ensuring proper insulation, and regular maintenance. Additionally, using a refrigerant with a higher efficiency and lower environmental impact, such as hydrofluorocarbon (HFC) or hydrochlorofluorocarbon (HCFC) can also improve the overall performance of the system.

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