Reply to Thread

I didn't like calculus.

Math isn't supposed to do that.

Originally Posted by Andy Schoen

Icemeister, the software is released: http://boxload.tecumseh.com/

Thanks, Andy.
Didn't want to let your cat out of the bag without knowing for sure.

Originally Posted by Andy Schoen

Calculating quality of refrigerant as it flows thru the evaporator or condenser can be done with NIST RefProp http://www.nist.gov/srd/nist23.cfm

Not for the faint hearted, however. One should have an understanding of the various two-phase flow models. I find the Dukler model useful in this regard.

It would be helpful to understand calculus to do the necessary math.

Calculus, I remember studying that. I was never any good at foreign languages or cards either.

newbieeng I think plotting a Pressure Enthalpy chart will help you. with the required data and some basic math you will gain much of the information you are looking for.

Originally Posted by icemeister

I would like to point out a new predictive program recently written by Andy Schoen of Tecumseh Products which is based on the Wolf-Pate Correlation as published in ASHRAE and is unquestionably the best one to date. I would post a link to it, but since it's in Beta at this point, I'm not sure if Andy want's it released in this general forum area. Perhaps he will chime in on this soon.

Icemeister, the software is released: http://boxload.tecumseh.com/

Calculating quality of refrigerant as it flows thru the evaporator or condenser can be done with NIST RefProp http://www.nist.gov/srd/nist23.cfm

Not for the faint hearted, however. One should have an understanding of the various two-phase flow models. I find the Dukler model useful in this regard.

It would be helpful to understand calculus to do the necessary math.

I'm not intimately familiar with how domestic a refrigerator's system components are matched, but if the premise here is that it is done primarily by trial and error then so be it.

I am somewhat familiar with how commercial and industrial systems' components are matched up however. Most commonly, such system components have their performance characteristics pretty well defined and as such that performance may be easily predicted over a wide range of conditions using computer modeling programs which have been readily available to design engineers for over 30 years or so. Prior to that, their performance was calculated using slide rules...a rather tedious method, but quite effective regardless.

All predictive models use varying degrees of estimation, assumption and slop...the latter being better defined as a safety factor to account for possible error. Today's programs will produce far more accurate results than those of the old days and in doing so, the resulting performance of the total system will reflect a much more accurate picture of real-world operation.

So with all that said, is your goal one of "reinventing the wheel" or simply refining it further?

Adding a thought here...I know that nearly every domestic refrigeration system is designed utilizing a capillary tube as its refrigerant metering device. Cap tubes a the essence of simplicity, very effective and inexpensive to produce but they have historically been quite elusive when it comes to predicting performance. It is one component which is still very much selected on the basis of trial and error.

I would like to point out a new predictive program recently written by Andy Schoen of Tecumseh Products which is based on the Wolf-Pate Correlation as published in ASHRAE and is unquestionably the best one to date. I would post a link to it, but since it's in Beta at this point, I'm not sure if Andy want's it released in this general forum area. Perhaps he will chime in on this soon.

Originally Posted by newbieeng

I do not claim that evaporators and condensers are being designed by trial and error. I meant that the combination of these equipment are beign designed by trial and error. In refrigeration cycles these equipment combinations are beign tested as couples to find the best matching and efficient systems. I demand to get a scientific, methodologic method to obtain most efficient combinations and refrigeration systems rather than by using this traditional trial and error method. Is it clear??

You think you are the first person to recognize this and to attempt to do something about it?

Gotta be a newbie.

If there were a better, smarter method than trial and error, I'm confident that method would be used in favor of trial and error.

With all due respect things could be done better. It always comes down to first costs compared to lifetime costs. If we follow the "KISS" school we have something that is adequate and understandable. As long as energy costs are cheap enough there is no reason to spend a thousand bucks to save a hundred.

Flooded evaporator or not I still suggest looking at what has been done with chillers. More meaningful advances have taken place there. A household refrigerator just doesn't consume enough energy dollars for the same advances to be worthwhile.

Originally Posted by stonewallred

The phase change in the condenser and evaporator is never the same, unless every aspect of it is the same, including the ambient temp crossing the coils, the swirls picked up by the liquid refrigerant as it goes through the tubing, the humidity of the air crossing the coils and even the amount of surface oxidation present on the coils. Any variation will alter the composition of the refrigerant.

I think you are failing to grasp that the condenser and evaporator are the results of years of research and design, not trial and error as you claim. That is why "x" coil must be matched to "y" OD unit, and why each matching is engineered to provide "z" cooling and heating at stated design conditions. Research and design, not some group of engineers trying different matches.

I do not claim that evaporators and condensers are being designed by trial and error. I meant that the combination of these equipment are beign designed by trial and error. In refrigeration cycles these equipment combinations are beign tested as couples to find the best matching and efficient systems. I demand to get a scientific, methodologic method to obtain most efficient combinations and refrigeration systems rather than by using this traditional trial and error method. Is it clear??

The phase change in the condenser and evaporator is never the same, unless every aspect of it is the same, including the ambient temp crossing the coils, the swirls picked up by the liquid refrigerant as it goes through the tubing, the humidity of the air crossing the coils and even the amount of surface oxidation present on the coils. Any variation will alter the composition of the refrigerant.

I think you are failing to grasp that the condenser and evaporator are the results of years of research and design, not trial and error as you claim. That is why "x" coil must be matched to "y" OD unit, and why each matching is engineered to provide "z" cooling and heating at stated design conditions. Research and design, not some group of engineers trying different matches.

Originally Posted by icemeister

I understand the concept of "quality" with respect to two-phase refrigerant flow, but what puzzles me here is "why" one would have a need to physically measure this value in an operating system?

Normally, we measure the refrigerant state at the beginning and at the end of the evaporator or the condenser. Those points can easily be measured with pressures and temperatures. The varying quality of the refrigerant in between those points becomes much more problematic to get a reading for, since quality doesn't follow the P/T rules directly.

Perhaps if you divulge the reason one might need to physically take snapshots of a refrigerant's active phase change, we may get a better idea of how we may help.

Are you looking to further cost-reduce a system's heat exchangers...or something to that effect?

My aim is to light the refrigeration system clearly. Up to now design of refrigerators are being made up of by trial and error. My main aim is to change this and obtain a scientific method to design them rather than trial and error. First target is to characterize the flow in the system and in the light of this characterization to design evaporator and condenser respectively.

I understand the concept of "quality" with respect to two-phase refrigerant flow, but what puzzles me here is "why" one would have a need to physically measure this value in an operating system?

Normally, we measure the refrigerant state at the beginning and at the end of the evaporator or the condenser. Those points can easily be measured with pressures and temperatures. The varying quality of the refrigerant in between those points becomes much more problematic to get a reading for, since quality doesn't follow the P/T rules directly.

Perhaps if you divulge the reason one might need to physically take snapshots of a refrigerant's active phase change, we may get a better idea of how we may help.

Are you looking to further cost-reduce a system's heat exchangers...or something to that effect?

Originally Posted by Paul Bee

"Troubleshooting and servicing modern air conditioning and refrigeration systems" by John Tomczyk. Mr Tomczyk has a degree in mechanical engineering and his books reflect that. www.powells.com/technicalbooks might be a good place to start.

Thank you

"Troubleshooting and servicing modern air conditioning and refrigeration systems" by John Tomczyk. Mr Tomczyk has a degree in mechanical engineering and his books reflect that. www.powells.com/technicalbooks might be a good place to start.

Originally Posted by Russ57

I'm with JP. Weight and density along with temperatures and pressures can provide answers. However in any real system things will be changing all the time. Something like a chiller would be closer to steady state. Thermodynamics, basically being four dimensional, is never easy.

Maybe if we knew what the goals were it would help. Are you an engineer, inventor, student, or scientist?

I am a mechanical engineer. I have expressed my aim numerous time under this topic. You can learn it from the 1st thread.

I'm with JP. Weight and density along with temperatures and pressures can provide answers. However in any real system things will be changing all the time. Something like a chiller would be closer to steady state. Thermodynamics, basically being four dimensional, is never easy.

Maybe if we knew what the goals were it would help. Are you an engineer, inventor, student, or scientist?

I might be able to hang with you here....

Problem is, I don't think you are going to like my answers.

Determining the mass of liquid refrigerant in the system at any one given time during operation is going to be tricky because it will change as operating conditions change.

I supposed that, if you can measure the ID of the tubing, the length of the tubing, then calculate the density of the refrigerant contained in it, you could come close, but you still have a varying amount contained in the condenser and evaporator as well as variable temperatures.

I don't know of any way to account for these variables, but then again, I'm not the engineer.

Originally Posted by newbieeng

with the data provided by tranducers we can obtain its phase, quality, in shortly its thermophysical properties but in reality, it does not fit the actual one. That right there is Greek to me (I don't understand)

In the system there are a lot of losses. I can agree with this statement.

Flow characterization during the system on seems impossible using that kind of implementations (using transducers of temperature & pressure). My aim is to explain its characterisation simultaneously, without cut-off the system. Some methods for measurement of mass does not fit in that way.
More Greek. Thanks.

I'm sorry, but I don't think I can be of any assistance in this matter.

Originally Posted by Fabrk8r

newbieeng, define "quality" as you used it in your original post.

I am getting the impression that what you are asking is "how do i know what state the refrigerant is in (such as gas or liquid) in each component of the unit I am working on?"

Am I correct? If that is what you want to know, then you don't have to physically see the refrigerant to know it's state. As was said by mspanky, a temperature/pressure chart will tell you whether the refrigerant is in a gaseous or liquid state by using the correct refrigeration gauges.

If you are concerned with the actual quality of the refrigerant, then you would have to take a sample and have it analyzed. Seeing the refrigerant won't tell you if it's contaminated, although sometimes you can tell by the odor if there has been a problem within the system.

Thanks for your interest Fabrk8r. That I wanted to mean with "Quality" is that mass of liquid phase of refrigerant divided by the total mass of it (mixture). I am not interested in the refrigerant's state, I want its real properties, qualitatively. You are right about charts, with the data provided by tranducers we can obtain its phase, quality, in shortly its thermophysical properties but in reality, it does not fit the actual one. In the system there are a lot of losses. Flow characterization during the system on seems impossible using that kind of implementations (using transducers of temperature & pressure). My aim is to explain its characterisation simultaneously, without cut-off the system. Some methods for measurement of mass does not fit in that way. Thanks.

newbieeng, define "quality" as you used it in your original post.

I am getting the impression that what you are asking is "how do i know what state the refrigerant is in (such as gas or liquid) in each component of the unit I am working on?"

Am I correct? If that is what you want to know, then you don't have to physically see the refrigerant to know it's state. As was said by mspanky, a temperature/pressure chart will tell you whether the refrigerant is in a gaseous or liquid state by using the correct refrigeration gauges.

If you are concerned with the actual quality of the refrigerant, then you would have to take a sample and have it analyzed. Seeing the refrigerant won't tell you if it's contaminated, although sometimes you can tell by the odor if there has been a problem within the system.