Thermodynamics issue with absorption heat pumps

In summary, the conversation discusses the differences between standard heat pumps and absorption heat pumps. It is noted that absorption heat pumps use heat energy to operate, but some argue that it is not the same as using high quality energy. The concept of a Carnot heat pump is introduced, which creates a heat gradient efficient enough for a Carnot heat engine to utilize and extract the exact amount of energy required. However, using a Carnot heat pump to operate an absorption heat pump may result in a violation of the second law of thermodynamics. After further consideration, it is realized that an absorption heat pump is not purely a heat pump, but also a heat engine. The conversation concludes with the mention of another heat pump concept that the speaker is still struggling
  • #1
striphe
125
1
I have been recently trying to advance my understanding of thermodynamics, but i have encountered a problem when it comes to absorption heat pumps and similar systems.

The standard heat pump requires an energy input, to move heat energy from one location to another. Most would consider absorption heat pumps no different as they use heat, a form of energy to operate. My consideration would say otherwise, as a standard heat pump uses, high quality energy to operate. Using high quality energy one can yield much more heat energy, using a heat pump.

From my understanding, a Carnot heat pump creates a heat gradient efficient enough for a Carnot heat heat engine to utilise and extract the exact amount of energy that was required to create the heat gradient. There is no reduction of entropy in this perfect system and so there is no second law violation.

If i decided to use a Carnot heat pump to operate an absorption heat pump, the heat added by the Carnot heat pump, is less than the heat expelled by the absorption heat pump. Using a Carnot heat engine to make use of the gradient, I would expect that the engine would produce surplus high quality energy, in violation of the second law.

So where have a gone wrong in my understanding in this case?
 
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  • #2
After more consideration I understand where my mistake has come from.

An absorption heat pump is not purely a heat pump, it is a heat engine and a heat pump. The heat used is converted to a higher quality energy which is utilised by the heat pump.

however I still have problems with another heat pump concept, but i will do another post for that one.
 
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1. What is a thermodynamic issue with absorption heat pumps?

The main thermodynamic issue with absorption heat pumps is the low coefficient of performance (COP), which is a measure of the energy efficiency of the pump. This means that for every unit of energy input, the pump is only able to produce a small amount of usable heat output.

2. How does the absorption process work in heat pumps?

In absorption heat pumps, a refrigerant is absorbed into a liquid solution, which is then heated to evaporate the refrigerant. The resulting vapor is compressed and condensed to release heat, which is then used to heat a space or water. The refrigerant is then reabsorbed into the solution to repeat the cycle.

3. What is the difference between absorption heat pumps and traditional vapor compression heat pumps?

The main difference is the type of refrigerant used. Traditional vapor compression heat pumps use a refrigerant that can easily change between liquid and vapor states, while absorption heat pumps use a refrigerant that is absorbed into a liquid solution. This allows for a lower energy input requirement, but also results in a lower COP.

4. Can absorption heat pumps be used for both heating and cooling?

Yes, absorption heat pumps can be used for both heating and cooling by reversing the direction of the refrigerant flow. This allows for the pump to act as both a heater and an air conditioner, providing year-round climate control.

5. What are some potential solutions to improve the efficiency of absorption heat pumps?

There are several potential solutions being researched, including using alternative refrigerants with higher heat absorption capacities, improving the design of the heat exchangers, and utilizing waste heat from other sources to power the pump. Additionally, proper maintenance and regular cleaning can also help improve the efficiency of absorption heat pumps.

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