# Electrical power out of R134a phase changes

• jonks
In summary, J is trying to figure out the required turbine size for a Rankine cycle using R134a as the working fluid to extract 5kW of electrical energy from a system with an available heat source of 70C and cooling source of 20C. J has already determined that a 2.54cm coiled copper tube will be suitable for the evaporator, but is unsure about the other design details such as turbine size and amount of R134a needed. J is looking for guidance on how to determine these parameters and is not interested in idealizing the cycle. Possible solutions could involve calculating the amount of R134a and frequency of the cycle based on the specified temperatures and power output, and making allowances for the non
jonks
Hi

My 2'nd year of engineering doesn't quite let me to find an answer to the following problem:

In a nutshell:
I want to use rankine cycle to extract 5kW worth of electrical energy from a system utilizing R134a as working fluid.

The properies of R134a are as follows:
Tag R134a
Compound CH2FCF3
MolMass 102.03
Critical T 101.08
Critical P 4060.3
Critical D 515.3
Critical V 0.00194
Gas Cosnt 0.0815

http://www.pandikas.ee/kool/r134a/propertiesR134a.jpg

Available heat source is 70C and cooling 20C
The evaporator needs to be of X size, the Condenser needs to be of X size and I am sorry to say the turbine size isn't preset either - they just have to be big enough. No real idea on how to go a bout it.
Now, working with handy materials I figured the standard 2.54cm coiled copper tube will do nicely as evaporator emerged in the 70C water.
This assumption gives me the force value of 1072.91 kg*m/s - the other values I dare not to put down in here as they seem way too unrealistic...

Could someone just guide me to right direction on how to go about those multiple problems I've encountered here?

Br,
J

My previous work can be found in attachment area.

#### Attachments

• Arvutused (Autosaved).pdf
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What exactly are you trying to determine? No. of kg of required R134A? Speed (frequency) of the cycle? Amounts of heat extracted from the 70C reservoir and dumped into the 20C reservoir per cycle?

Yea it's not really clear what exactly you are looking for...

You already know the operating temperatures and specified power output but beyond knowing what you are looking for we don't know if you are idealizing the cycle either or if you are counting in isentropic efficiencies

Thank you for your answer and a happy new year to you all.

I am not trying to idealize at all.

To put it simply, I am trying to figure out the turbine size needed to extract the 5kW.

Br,
J

jonks said:
Thank you for your answer and a happy new year to you all.

I am not trying to idealize at all.

To put it simply, I am trying to figure out the turbine size needed to extract the 5kW.

Br,
J

Question is, what you mean by "size".

The important parameters to be deduced are the amount of R134 and the frequency of the Rankine cycle. If you were to specify one, the other could be computed based on your inlet and exhaust temperatures, and electrical power requirements. We could compute an answer based on a reversible (ideal) cycle and also take a shot at a realistic efficiency for your power plant.

The size of the turbine: I would like to calculate the approximate height, depth and width of the blades. To visualize, here is the turbine project.
http://www.pandikas.ee/kool/r134a/turbine191212.jpg

This is what I have so far - but aside from the general idea - for the moment at least, I don't have much else to work with.

As for the amount of R134a - this is interesting: This is something that should be possible to calculate from the evaporator outlet diameter and pressure. However, this would again lead me to the point of where I'd need to know the rate of flow - which I don't. =/

rude man said:
Question is, what you mean by "size".

The important parameters to be deduced are the amount of R134 and the frequency of the Rankine cycle. If you were to specify one, the other could be computed based on your inlet and exhaust temperatures, and electrical power requirements. We could compute an answer based on a reversible (ideal) cycle and also take a shot at a realistic efficiency for your power plant.

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Jonks, I finally looked at your work and I think you're looking for some pretty advanced and detailed info which I doubt you'll get on this forum, but maybe you will.

I looked at this from a pretty basic, theoretical viewpoint. In this view the salient features of the Rankine cycle are the two temperatures and the type of working fluid (specifically its 'steam tables' from which enthalpies and entropies are either looked up or calculated. A p-v diagram for R134 would be a big help also.) This enables one to compute the efficiency of the cycle (assuming reversibility) = work output/heat input at the higher temperature. The latter two are computed from the aforesaid steam table entries on a per-unit-weight of working fluid basis ("specific" entropies and enthalpies). Then, you'd have to make allowances for the fact that no part of the cycle is really reversible. That drops the efficiency by at least half.

So to get output power you'd need to know the amount of fluid which would give you the work output per cycle. Then the work output per unit time, which is your power, is just that work times the frequency of running the cycle (set by the pump adiabatically pushing the pressure up from p2 to p1 and corresponding temperature up from T2 to T1.

You'd need this info in any case, on top of your other design details you're looking for, seems to me. Anyway, I hope you find what you're looking for, here or elsewhere.

## 1. How does R134a produce electrical power through phase changes?

R134a is a refrigerant that undergoes phase changes between liquid and gas when exposed to different temperatures. This change in state can be harnessed to produce electrical power through the use of a turbine and generator system.

## 2. What is the efficiency of electrical power generation using R134a phase changes?

The efficiency of electricity production using R134a phase changes depends on various factors such as the temperature difference between the hot and cold reservoirs, the design of the turbine and generator, and the type of refrigerant cycle used. Generally, the efficiency can range from 10-15% for small-scale systems and up to 40% for large-scale systems.

## 3. What are the advantages of using R134a for electrical power generation?

R134a has several advantages as a refrigerant for electrical power generation. It is non-toxic, non-flammable, and has a low environmental impact. It also has a high energy density, making it a suitable choice for compact power generation systems.

## 4. Can R134a be used in all types of power generation systems?

R134a can be used in a variety of power generation systems, including steam, organic Rankine, and Kalina cycles. However, it may not be suitable for all applications, and the specific design and operating conditions must be carefully considered for optimal performance.

## 5. Are there any limitations or challenges associated with using R134a for electrical power generation?

One limitation of using R134a for electrical power generation is its low critical temperature, which limits the maximum temperature difference that can be achieved in a power cycle. Additionally, the cost of R134a and its availability may also pose challenges for large-scale power generation projects.