What does the T-S diagram look like for an ammonia heat pump?

In summary, an ammonia heat pump works by diverging the paths of the working fluid, and achieving a difference in entropy between the paths. This is done without using pressurization.
  • #1
swampwiz
571
83
I'm a bit confused as to what the Temperature-Entropy diagram looks like for an ammonia heat pump. I understand perfectly how a freon type of refrigerant heat pump works: starting with working fluid at a state of a low-Temperature & high-Entropy gas (which is at low pressure), do work on the working fluid by compressing it, thereby resulting in an increase in Pressure & Temperature (and ideally no change in Entropy, although in "real life", there is always some small increase) such that the Temperature is higher than the high-Temperature ambient environment; then allow that working fluid to lose heat to that ambient environment, thereby resulting in a loss of Entropy such that the working fluid loses pressure until it hits the gas-liquid saturation state, and then continuing on by condensing the working fluid into a liquid; then allow the working fluid to depressurize, typically via a throttling device that achieves depressurization back to (or nearly back to) the initial pressure by friction (i.e., of the working fluid itself, or the friction with the containing vessel), which achieves a drop in Temperature (albeit that the friction actually causes a small rise in Entropy, but nowhere near the initial state) that is lower than the low-Temperature ambient environment; then allow the working fluid to gain heat from that ambient environment, thereby increasing the entropy to get back the initial state. The net effect is that the state of the working fluid moves in a counter-clockwise path such that there are 2 functional paths in which one of the paths has a lower Entropy than the other, and with the heat that is lost to the high-Temperature ambient environment is the area under the high-Temperature path, the heat that is gained from the low-Temperature ambient environment is the area under the low-Temperature path, and thus the difference of the two is the amount of work that must be done in the compression, and which also is the area bounded by the 2 paths.

What I don't understand is how to achieve this divergence of these 2 paths in the ammonia system that doesn't seem to use any pressurization. Certainly, the only way that an ammonia system could work is to somehow have a pair of state paths with some difference in between, but how is this done without pressurization?
 
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  • #2
Is it simply by the evaporative cooling of the ammonia, and thus a decrease in pressure that is sufficient enough to cause a drop in Temperature? Is there some other mechanism at work here? Any insight would be greatly appreciated.
 

Related to What does the T-S diagram look like for an ammonia heat pump?

1. What is a T-S diagram?

A T-S diagram, also known as a Temperature-Entropy diagram, is a graphical representation of the thermodynamic properties of a substance. It shows the relationship between temperature and entropy, and is commonly used to analyze and visualize the thermodynamic cycles of systems.

2. How is a T-S diagram used in an ammonia heat pump?

A T-S diagram is used in an ammonia heat pump to show the changes in temperature and entropy during the refrigeration and heating cycles. It helps to determine the efficiency of the heat pump and identify any potential problems or areas for improvement.

3. What does the T-S diagram look like for an ammonia heat pump?

The T-S diagram for an ammonia heat pump typically consists of two main parts: the refrigeration cycle and the heating cycle. The refrigeration cycle is represented by a horizontal line at a constant temperature, while the heating cycle is represented by a vertical line at a constant entropy. The two cycles intersect at the condenser and evaporator, showing the transfer of heat between the two.

4. How does the T-S diagram change with different operating conditions?

The shape and position of the T-S diagram for an ammonia heat pump can change depending on the operating conditions, such as the pressure, temperature, and flow rate of the refrigerant. These changes can affect the efficiency and performance of the heat pump, and may require adjustments to optimize its operation.

5. What other factors can affect the T-S diagram for an ammonia heat pump?

In addition to operating conditions, the type and design of the heat pump, as well as the properties of the working fluid, can also affect the T-S diagram. For example, using a different refrigerant or changing the heat exchanger design can result in a different T-S diagram and performance of the heat pump.

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