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shogun7
25-09-2004, 04:56 AM
In my estimation a technician not only needs to understand how the various components work together but he also needs to understand that commercially available components seldom will exactly match the design requirements of a given system, and since system design is normally based on estimated peak loads, the system may often have to operate at conditions other than design conditions. More than one combination of components may meet the performance requirements, the efficiency of the system normally being dependent on the point at which the system reaches stabilized conditions or balances under operating conditions. We know that the capacities of each of the three major system components, the compressor, the condenser, and the evaporator, are each variable but interrelated.
The compressor capacity varies with the evaporating and condensing temperatures and the factors involved in the variation in evaporator capacity are quite complex when both sensible heat transfer and condensation are involved. For component balancing purposes, the capacity of an evaporator where both latent and sensible heat transfer are involved (a wet coil) may be calculated as being proportional to the total heat content of the entering air, and this in turn is proportional to the wet bulb temperature. So because of the many variables involved, the calculation of system balance points is extremely complicated :confused:

Abe
25-09-2004, 10:50 PM
Marc..................helpppppp !!!!! :eek:

shogun7
26-09-2004, 03:13 AM
Site Moderator : and general nice guy...NOT!(Marc..................helpppppp !!!!! :eek:
I sorry Aiyub but that's as simple as I can make it however if its a strain on your pin head brain how about this " Balance" thats when the little bubble is centered :rolleyes:

Abe
26-09-2004, 01:33 PM
Hello Shogun,

Soreeee, I was just a bit in a crazy mood !!!!! :)
Hope youre having a nice Sunday !!!

Regards

Abe

Abe
26-09-2004, 01:39 PM
And just to " suck" up to you a bit more...............I think you are a very intelligent , knowleageable man, and I respect you !!

Now , am I still a nice guy ???

Lol

shogun7
27-09-2004, 12:28 AM
Aiyub: You are more then nice and you made me cry ;) If I misunderstood please accept my apologies :)

Gary
27-09-2004, 10:50 AM
You are too nice, Abe. He didn't say anything informative, and he certainly didn't answer the title question... LOL

Dan
29-09-2004, 01:50 AM
A nicely posed question, Gary. The variables and the implied invariables. But balance is easy. Systems always balance. Just as teeter totters (see-saws?) do. Levers and cranes and forklifts etc.

I enjoyed Aiyub's portended cry to Marc, because Marc loves to sneak up around unexpected corners for his explanations. Harmony and balance strike me as similar considerations. When is a system in harmony?

A very nice distinction is made between "component" and what I will call "load" considerations. If that distinction wasn't made and I read too much into it, I would suggest that we keep component (internals) and load (externals) as distinctions. I see it as a clear separation that a technician can retain.

Otherwise, it is all a blur for a technician, yet an easy piece of cake to a theoretician... because the theoretician doesn't really concern his or herself with the limitations of existing machinery... On the other hand, I have too often felt the effects of change in balance when my older brother would smile and me and step off of the bottom of the see-saw.

Perhaps "Change in Balance" addresses the question more properly.

Dan
29-09-2004, 03:07 AM
So because of the many variables involved, the calculation of system balance points is extremely complicated

I would start here and work backwards, as a teacher to find where I need to begin as a teacher who actually has a student.

If I were teaching a technician, I would avoid deductive (general to specific), and favor inductive (specific to general) logic as a starting point, and I would also simplify it. I would go all the way back to what happens within the refrigeration cycle when sensible temperatures change. That's a lesson scattered all over this wonderful discussion group, but that's the problem. It is scattered.

We could possibly condense a lot of our theoretical and training issues as tightly positioned answers to Gary's question.

Perhaps, we could develop the discussion as:

Here is what happens inside the pipe of a/c units and refrigerators with a constant load.
Here is what happens to the normal loads as a result.

Here is what happens to the inside of the pipe as the loads outside the pipe make those changes.

I am babbling. But I still think maintaining the distinctions between the change in balance that happens on the outside and inside of the piping is worthy.

Each thought is simple and should be taught as such. How, on earth, one does it in a discussion group is beyond me.

But if the focus remains on training the technician, I will share the only disagreement that I have ever had with Gary... that we should NOT begin by saying how complicated things are.

That's what they do in ASHRAE.: :)

Gary
30-09-2004, 04:27 PM
Actually, this is Shogun's question, not mine. And personally I think any discussion should start with a definition of "system balance". What does that term mean?

shogun7
01-10-2004, 12:14 AM
I suppose it would have been more appropriate to say “component balance” instead of system balance, but let’s discuss “system balance”…GARY. When we design a refrigeration system, one of the most important considerations is that of establishing the proper relationship or “BALANCE” between the vaporizing and condensing section of the system. So it is important to recognize that whenever an evaporator and a
Condensing unit is connected together in a common system; a condition of equilibrium or “BALANCE” is automatically established between the two such that the rate of vaporization is always equal to the rate of condensation. In other words, the rate at which the vapor is removed from the evaporator and condensed by the condensing unit is always equal to the rate at which the vapor is produced in the evaporator by the boiling action of the saturated liquid. So Gary, since all the components in a refrigeration system are connected together in series, the refrigerant flow rate through all the components is the same. So guess what? Doesn’t it follow that the capacity of all the components must be of necessity …the same? Obviously then, where the system components are selected to have equal capacities at the system design conditions, the point of system equilibrium or “BALANCE” will occur at where…”DESIGN CONDITIONS” OH on the other hand, when the components selected DO NOT have equal capacities at the design conditions, system equilibrium will be established at operating conditions OTHER then the system design conditions and the system will not perform at peak efficiency. In any event Gary, it is important to understand that, regardless of the equipment selected, the system will always establish equilibrium at SOME conditions such that all the system components will have equal capacity.
:confused:

Gary
01-10-2004, 11:47 AM
I agree. In a series closed loop system, under stabilized operation, mass flow of refrigerant is equal at all points (conservation of mass flow).

Where there are parallel paths, that same flow rate is divided between the paths, their combined flow rates equaling the flow rate through all other (series) paths in the system.

Whatsmore, the rate at which refrigerant is evaporated will be equal to the rate at which refrigerant is condensed.

Also, the rate at which heat is being absorbed will be equal to the rate at which heat is being rejected.

Would you then define "system balance" as 'stabilized operation, wherein refrigerant mass flow rate is equalized throughout the system, refrigerant evaporation/condensation is balanced, and heat absorption/rejection is balanced'?

I would call this "stabilized operation", but different people use different terms to describe the same thing. This is not a problem as long as we know what others mean when they use their terminology.

Or perhaps you are not talking about stabilized operation at all, but are referring to the proper matching of system components?

Please don't think I am picking on you. I am simply trying to clarify, so that we are all on the same page.

Gary
01-10-2004, 12:39 PM
I suppose it would have been more appropriate to say “component balance” instead of system balance, but let’s discuss “system balance”…GARY. When we design a refrigeration system, one of the most important considerations is that of establishing the proper relationship or “BALANCE” between the vaporizing and condensing section of the system. So it is important to recognize that whenever an evaporator and a Condensing unit is connected together in a common system; a condition of equilibrium or “BALANCE” is automatically established between the two such that the rate of vaporization is always equal to the rate of condensation. In other words, the rate at which the vapor is removed from the evaporator and condensed by the condensing unit is always equal to the rate at which the vapor is produced in the evaporator by the boiling action of the saturated liquid. So Gary, since all the components in a refrigeration system are connected together in series, the refrigerant flow rate through all the components is the same. So guess what? Doesn’t it follow that the capacity of all the components must be of necessity …the same? Obviously then, where the system components are selected to have equal capacities at the system design conditions, the point of system equilibrium or “BALANCE” will occur at where…”DESIGN CONDITIONS”

Assuming the system is not hunting, stabilized operation (equilibrium?) will occur shortly after startup, and will continue until cutout.


OH on the other hand, when the components selected DO NOT have equal capacities at the design conditions, system equilibrium will be established at operating conditions OTHER then the system design conditions and the system will not perform at peak efficiency. In any event Gary, it is important to understand that, regardless of the equipment selected, the system will always establish equilibrium at SOME conditions such that all the system components will have equal capacity.
:confused:

Yes. If all of the components are properly matched, then that equalized capacity will be design capacity/efficiency under design conditions.

If the components are not properly matched, then the equalized capacity will be other than design capacity/efficiency under design conditions.

I suspect we are saying the same thing. :)

Gary
01-10-2004, 12:52 PM
Each thought is simple and should be taught as such. How, on earth, one does it in a discussion group is beyond me.

But if the focus remains on training the technician, I will share the only disagreement that I have ever had with Gary... that we should NOT begin by saying how complicated things are.

That's what they do in ASHRAE.: :)

Perhaps we can clarify a little here:

When we are attempting to teach, we must of necessity assume our audience possesses some minimum level of knowledge.

On the other hand, if we tell someone something they already know, then we teach them nothing.

Therefore, in order for a discussion to be informative, it must progress, in a step by step manner, from a lesser level of knowledge to a greater level of knowledge. It is then informative to those in the audience who are at or above that lesser level of knowledge, but below that greater level of knowledge.

Too many discussions start and end at the same level. Their intent is to impress, rather than enlighten.

ASHRAE publications are impressive. My books are enlightening. Unfortunately, impressive sells better. :)

shogun7
01-10-2004, 10:18 PM
ASHRAE publications are impressive. My books are enlightening. Unfortunately, impressive sells better. :)

"That's because ASHRAE actually does research and publishes working papers for technical review...not just one mans opinion". :rolleyes: :D

shogun7
01-10-2004, 11:05 PM
[QUOTE=Gary]Assuming the system is not hunting, stabilized operation (equilibrium?) will occur shortly after startup, and will continue until cutout.

That's not necessarily true because heat loads and OSA conditions etc.can change.
I also have to take issue with you concerning the term "Stable"

Gary the word “stable” is a poor choice for “balance” because stable means resistant to sudden change of position or condition, maintaining equilibrium and as we know the changes in a refrigeration system equilibrium can change often during a 24 hour period where as balance refers: to be in OR come to equilibrium, which to me is a better description of what the refrigeration process does :)

Gary
02-10-2004, 02:26 PM
"That's because ASHRAE actually does research and publishes working papers for technical review...not just one mans opinion". :rolleyes: :D


Considering that you have no idea how much research I have or have not done, and you have never seen nor read my books, you haven't done enough research to form an opinion about them. Seems this statement was pulled straight out of your posterior regions... as usual. :)

Gary
02-10-2004, 02:31 PM
[QUOTE=Gary]Assuming the system is not hunting, stabilized operation (equilibrium?) will occur shortly after startup, and will continue until cutout.

That's not necessarily true because heat loads and OSA conditions etc.can change.
I also have to take issue with you concerning the term "Stable"

Gary the word “stable” is a poor choice for “balance” because stable means resistant to sudden change of position or condition, maintaining equilibrium and as we know the changes in a refrigeration system equilibrium can change often during a 24 hour period where as balance refers: to be in OR come to equilibrium, which to me is a better description of what the refrigeration process does :)

In which case the system would be temporarily hunting, adjusting itself to the new conditions. The point is that stabilized operation, equilibrium, balance, or whatever we call it, is not something that occurs only at design conditions.

In any case, I have no objections to using different terminology, so long as we define our terms and are thus able to communicate the concepts.

shogun7
04-10-2004, 06:19 AM
In which case the system would be temporarily hunting, adjusting itself to the new conditions. The point is that stabilized operation, equilibrium, balance, or whatever we call it, is not something that occurs only at design conditions.( you don't say!!!!) :confused:

In any case, I have no objections to using different terminology, so long as we define our terms and are thus able to communicate the concepts.Gee,thanks%

What nonsense, sounds your parroting what I’m saying :confused:

Gary
04-10-2004, 01:09 PM
What nonsense, sounds your parroting what I’m saying :confused:

Actually, as I stated earlier, I am clarifying what you are saying, in hopes that this thread may become useful. Now that we all have the equalibrium picture (stable throughout the cycle, aside from momentary adjustments for changing conditions), shall we move on to component balance? That is what you really wanted to discuss, right?

Dan
07-10-2004, 04:29 AM
A nicely posed question, Gary.

My apology, Shogun7. A nicely posed question, Shogun7. Beyond that, I have to catch up on the discussion. Not that me restating the nicely posed part has any meaning anymore.

Good question Shogun7. Let me read some of this stuff.

Dan
07-10-2004, 04:56 AM
Okay, I have read the discussion. I hope my comments were not distracting from the original question. Gary, it would not hurt my feelings if you summed up the question for myself and other lackards. Have we defined system balance and are we now defining component balance? Did we skip anything?

And Marc, what's so bad about stating the obvious? We Americans have an attention span that requires peridodic repetition. The Brits merely have a penchant for feigning boredom.:)

By the way, friends. Got fired today. Hussmann has accepted my resignation.

Peter_1
07-10-2004, 12:35 PM
Considering that .....you have never seen nor read my books, you haven't done enough research to form an opinion about them. Seems this statement was pulled straight out of your posterior regions... as usual. :)

Here we go again.
BTW, I saw some time ago your book (HVACR troubleshooting) Gary and it wasn't realy usefull at all for me. Sorry, but that's my opinion.
I even think it's dangerous to let people work on systems the way you describe it, assuming no previous theoretical HVACR knowledge at all.
It looked more like a 'copy and paste' through all the sections.
I'm happy I never bought it.
Dossat's book reamins still the best book I ever read.

Gary
07-10-2004, 01:19 PM
Here we go again.
BTW, I saw some time ago your book (HVACR troubleshooting) Gary and it wasn't realy usefull at all for me. Sorry, but that's my opinion.
I even think it's dangerous to let people work on systems the way you describe it, assuming no previous theoretical HVACR knowledge at all.
It looked more like a 'copy and paste' through all the sections.
I'm happy I never bought it.
Dossat's book reamins still the best book I ever read.

Copy and paste? On the contrary, most HVACR books are copied, and there is a list of acknowledgements confessing where they copied from. There is no such list in my book, because it is based entirely on original research.

Or perhaps you are referring to repetition in the book. The infomation is weighted, with the most important bits repeated most. This drills the reader in the TECH sequence. When read from beginning to end, the basic sequence is thoroughly understood by the time he gets to the last page.

The book is not intended to teach HVACR theory, hence the word "Troubleshooting" in the title. It is about troubleshooting and nothing else. And yes, it is very easy to read and understand. I consider this a plus.

The book is not for everyone, and I accept that some will not find it useful, but then that is true of any book. How useful it is depends on the prior knowledge of the reader.

The TECH Method is about troubleshooting sequence, first checking "T" (Temperature controls), then "E" (Evaporating unit), then "C" (condensing unit), then "H" (Heat measurements), this being the most efficient and accurate sequence, and how to adapt this same basic sequence to virtually any system. Most will need to follow the exact sequence, in the real world, troubleshooting actual systems, before they get it.

Most people in our industry believe that it doesn't matter which part of the system they check first. This is probably true for the most common and obvious problems, but sequence matters very much when searching for the more elusive problem, and/or multiple problems.

A recipe is more than a list of ingredients. Sequence matters.

shogun7
08-10-2004, 03:48 AM
Gary's books are perhaps much more about philosophy and a reductive procedure of elimination. You can't compare it to Dossat, you might as well compare it to an English language dictionary if you're going to do that.
Well then Gary should say that he's teaching philosophy in order to solve and trouble shoot Refrigration problems. He may even sell more books!:D LOL

shogun7
08-10-2004, 04:29 AM
Gary
Traditional theories of learning that focus on knowledge reproduction (your method) rather than knowledge use, are inadequate when learning approaches advanced knowledge domains where tasks become more complex, dynamic, and ill-structured. There are three stages of knowledge acquisition: introductory,
advanced and expertise. Skills in the introductory stage are limited to
reproductive tasks and elemental applications of knowledge based upon rigid
Examples from a limited number of oversimplified cases as in the “TECH METHOD” As the learner approaches the advanced knowledge acquisition stage, learning theories dominating introductory acquisition domains are inadequate because skills obtained in this stage of learning are limited in their transferability. It is the stage of advanced knowledge acquisition that we discuss books like DOSSET. This intermediate stage of knowledge is characterized by the need to acquire knowledge to solve COMPLEX problems that are unique and unpredictable. Therefore, learners must develop flexible representations of the domain that reflect the dynamics of the real world in which they will use the knowledge. Transfer skills are paramount to successful learning in this stage of knowledge acquisition. The learner must obtain knowledge that illustrates the interrelationships within the domain as well as having the ability to apply knowledge in different perspectives throughout the domain. For example, as Marc stated you couldn’t compare it to Dossat, you might as well compare it to an English language dictionary if you're going to do that :confused:

shogun7
08-10-2004, 04:40 AM
Peter, Professor Roy J Dosset is my hero! I bought his book in 1962 when I was a freshman in a community college taking classes in HVACR. At this very minute I have his book on my desk and it is open to something I was researching. I have 100's of books, still his is my favorate and so easy to read. :D

shogun7
08-10-2004, 04:49 AM
My apology, Shogun7. A nicely posed question, Shogun7. Beyond that, I have to catch up on the discussion. Not that me restating the nicely posed part has any meaning anymore.

Good question Shogun7. Let me read some of this stuff.
Dan, Anytime someone complements me it's always quite meaningful :D Sorry to hear about your delema, hope all works out for you...I have found it always turns out for the better :)

shogun7
08-10-2004, 05:12 AM
The book is not for everyone, and I accept that some will not find it useful, but then that is true of any book. How useful it is depends on the prior knowledge of the reader.

Gary: As I'm retired and on a limited income I dare not spend 1 sheckel for your most "enlightening methds of troublesooting systemic problems in rerigeraton", Heck all I have to do is go to the source....Marc, don't you know? ;)

RogGoetsch
08-10-2004, 06:20 AM
Gary
Traditional theories of learning that focus on knowledge reproduction (your method) rather than knowledge use, are inadequate when learning approaches advanced knowledge domains where tasks become more complex, dynamic, and ill-structured. . . . It is the stage of advanced knowledge acquisition that we discuss books like DOSSET.

When I began to manage technicians it came as a shock to me to discover just how rare good analytical skills are. Now I tend to separate techs into "how it works" types and "why it works that way" types. (I also encountered many "haven't a clue" types, but we kept them busy with installations.)

Dossat is great for the "why" guys if you can ever find one, but the "how" types need to be helped along in the beginning, and many will always need to be reminded to get the data and analyze the results before starting to change parts.

I think most posters to this forum are far beyond the basic skill levels addressed in cook-book approaches. That doesn't mean there is no place for such. Personally, I am grateful to anyone fighting to improve the skill level of our trade. God knows it needs it!

Actually, it takes great skill to reduce system analysis to an easily understood set of procedures. Just consider how difficult it is to extract the meaning of some of the more erudite posters to this forum! Understanding does not guarantee communication skills any more than intelligence is a reliable measure of emotional maturity.

Rog

FreezerGeezer
08-10-2004, 09:21 AM
I agree. Gary's TECH Method isn't meant to teach you refrigeration, it's meant to instill in you (especially if you're new to the game - an apprentice or some such) a methodology for fault finding.
Many's the time in my younger days I would have found TECH method useful, instead of barging in like the proverbial bull in a china shop! ;-)

Gary
08-10-2004, 03:48 PM
Gary
Traditional theories of learning that focus on knowledge reproduction (your method) rather than knowledge use, are inadequate when learning approaches advanced knowledge domains where tasks become more complex, dynamic, and ill-structured. There are three stages of knowledge acquisition: introductory, advanced and expertise.

In truth, you have no idea what my method is, much less which category it fits into. Why do you insist on pretending otherwise? You are assuming, and we all know what assuming does.



Skills in the introductory stage are limited to
reproductive tasks and elemental applications of knowledge based upon rigid Examples from a limited number of oversimplified cases as in the “TECH METHOD” As the learner approaches the advanced knowledge acquisition stage, learning theories dominating introductory acquisition domains are inadequate because skills obtained in this stage of learning are limited in their transferability. It is the stage of advanced knowledge acquisition that we discuss books like DOSSET. This intermediate stage of knowledge is characterized by the need to acquire knowledge to solve COMPLEX problems that are unique and unpredictable. Therefore, learners must develop flexible representations of the domain that reflect the dynamics of the real world in which they will use the knowledge. Transfer skills are paramount to successful learning in this stage of knowledge acquisition. The learner must obtain knowledge that illustrates the interrelationships within the domain as well as having the ability to apply knowledge in different perspectives throughout the domain.

In point of fact, a very large portion of my book is devoted to developing transfer skills. But you didn't know that, did you?



For example, as Marc stated you couldn’t compare it to Dossat, you might as well compare it to an English language dictionary if you're going to do that :confused:

Marc, who has actually read the book, is entirely correct. Comparing it to Dossat is a comparison of apples to oranges. The focus, intent, and content of the two books are entirely different. Comparing them makes no sense whatsoever, and serves no purpose.

Gary
08-10-2004, 03:59 PM
Gary: As I'm retired and on a limited income I dare not spend 1 sheckel for your most "enlightening methds of troublesooting systemic problems in rerigeraton", Heck all I have to do is go to the source....Marc, don't you know? ;)

Being that I am also retired on a limited income, I completely understand this. What I don't understand is why you pretend to know what is contained in a book that you haven't read.

Gary
08-10-2004, 04:14 PM
I agree. Gary's TECH Method isn't meant to teach you refrigeration, it's meant to instill in you (especially if you're new to the game - an apprentice or some such) a methodology for fault finding.
Many's the time in my younger days I would have found TECH method useful, instead of barging in like the proverbial bull in a china shop! ;-)

Actually, many old timers have found my methods useful. It is however more difficult for them as it requires un-learning and re-learning basic skills. It might be analogous to lifting your house and installing a stronger foundation, when the old foundation was strong enough to get by. The more experienced techs are often unwilling to go through the transition. Old habits die hard. Most techs throughout the industry are getting by, and have little interest in remedial training.

Gary
08-10-2004, 04:24 PM
Actually, it takes great skill to reduce system analysis to an easily understood set of procedures. Just consider how difficult it is to extract the meaning of some of the more erudite posters to this forum! Understanding does not guarantee communication skills any more than intelligence is a reliable measure of emotional maturity.

It took me 4 years to do the research and write the books. That's 4 years, full time, without a paycheck. I know for a fact that there is no more efficient, more thorough, more accurate, more flexible trouble shooting sequence, having thoroughly tested every conceivable approach.

Peter Croxall
09-10-2004, 12:47 PM
Hi Gary,
As an “Old timer” myself, :) I agree with you. After studying your books, it makes sense to think in terms of refrigerant temperature as apposed to pressure, (especially with the myriad of refrigerants we have to contend with now).

In my day one usually only had to contend with R22 and R12, although I did come across a few fridges running on Methyl chloride and SO2. Not very nice for the nasal passages. :eek: :eek: :eek:

Brian
09-10-2004, 03:23 PM
Firstly I would like to pointout that there is no such conservation law that states "mass is conserved" and also the book is by the professor Dossat not Dosset. Cheers!!!! :eek: :mad:

shogun7
09-10-2004, 10:06 PM
Sorry Brian, I didn't mean to confuse you. :cool:

Gary
10-10-2004, 03:06 PM
Hi Gary,
As an “Old timer” myself, :) I agree with you. After studying your books, it makes sense to think in terms of refrigerant temperature as apposed to pressure, (especially with the myriad of refrigerants we have to contend with now).

Hi Peter,
The TECH Method was initially written before the new refrigerants were introduced. Even then it made more sense to think in terms of temps instead of pressures. With the new refrigerants, it was not necessary to revise the book. All my readers needed was a new P/T chart. The transition was relatively easy for them.



In my day one usually only had to contend with R22 and R12, although I did come across a few fridges running on Methyl chloride and SO2. Not very nice for the nasal passages. :eek: :eek: :eek:

Now there's an understatement. Anyone who thinks the introduction of *****s was a bad thing needs a snootful of the nasty stuff they replaced.

Gary
10-10-2004, 04:39 PM
Pressures? Useless, I wish, like Gary says, they were never included on service guages.


Before the new refrigerants were introduced, I used to recommend that people paint over the pressure scales on their gauges, so they would be forced to look at the temperature scales. From a troubleshooting viewpoint, temps are what matters. It made their job MUCH easier.

RogGoetsch
10-10-2004, 07:01 PM
I think I was lucky in that, from the beginning, evaporators and condensers were of course heat exchangers all abiding by the formula kW = AxUxdT or AxUxLMTD.

The heat exchange suface is the exposed surface of a material that has a coefficient of heat flow W/m˛.K meaning that U amount of Watts will pass per m˛ with a 1K (1°C) temperature difference.

Just a reminder that "U" is the overall coefficient of heat transfer, so the thermal conductivity of a given material is usually only a small factor in heat exchanger design. In my experience, surface film factor coefficients rule.

In one biomedical heat exchanger using stainless steel instead of copper for example, the thermal conductivity of copper was something like seven times that of stainless, but when U was calculated with film factors, the difference in U values between the two heat exchangers was too small a decimal to survive rounding.

The same is not true of insulating materials where surface convection coefficients are not very significant.

Rog

shogun7
11-10-2004, 02:36 AM
[QUOTE=RogGoetsch]Just a reminder that "U" is the overall coefficient of heat transfer, so the thermal conductivity of a given material is usually only a small factor in heat exchanger design. In my experience, surface film factor coefficients rule.

Rog,
With regards to surface film factor coefficients ruling we know how oil logging has a significant impact on the operation of a remote, low-temperature refrigeration unit in addition, a similar situation exists when we have laminar oil flow which results in poor oil return to the compressor and poor heat transfer so a concept to remedy this situation is called Altered Bi-phase Flow (ABF) regime; an annular (ring-like) film maximizes heat transfer throughout the evaporator, increasing the useable evaporator tube surface area. The result is a cooler tube wall with a higher evaporator pressure. The technology’s primary benefits are the elimination of laminar refrigerant flow and the resulting poor heat transfer coefficients.
The present method has been focused on having liquid at the entry to the evaporator to ensure that the maximum heat transfer capacity was available. This new approach focuses more on the rate of heat transfer. The method has been described as “distributed enthalpy,” because the slow-moving refrigerant at the evaporator entry is more evenly distributed throughout the length of the evaporator. It develops a multistage pressure drop in that it separates the liquid from the vapor and entrains the liquid into the higher vapor velocity. The resulting temperature and pressure uniformity within the evaporator improves frost formation, refrigerant feed stability, compressor ratios, and net cooling rate. That directly impacts product temperature recovery and the annular flow that is derived from distributed enthalpy encourages oil to return to the crankcase and provides proper lubrication — even after extended periods of operation. :cool:

shogun7
12-10-2004, 01:05 AM
Lol, so what about it, Shogun?
What about what? :confused: Merk :D
Is that supposed to be cute or do you have a question?

RogGoetsch
14-10-2004, 05:20 AM
With regards to surface film factor coefficients ruling we know how oil logging has a significant impact on the operation of a remote, low-temperature refrigeration unit in addition, a similar situation exists when we have laminar oil flow which results in poor oil return to the compressor and poor heat transfer so a concept to remedy this situation is called Altered Bi-phase Flow (ABF) regime; an annular (ring-like) film maximizes heat transfer throughout the evaporator, increasing the useable evaporator tube surface area. The result is a cooler tube wall with a higher evaporator pressure. The technology’s primary benefits are the elimination of laminar refrigerant flow and the resulting poor heat transfer coefficients.
The present method has been focused on having liquid at the entry to the evaporator to ensure that the maximum heat transfer capacity was available. This new approach focuses more on the rate of heat transfer. The method has been described as “distributed enthalpy,” because the slow-moving refrigerant at the evaporator entry is more evenly distributed throughout the length of the evaporator. It develops a multistage pressure drop in that it separates the liquid from the vapor and entrains the liquid into the higher vapor velocity. The resulting temperature and pressure uniformity within the evaporator improves frost formation, refrigerant feed stability, compressor ratios, and net cooling rate. That directly impacts product temperature recovery and the annular flow that is derived from distributed enthalpy encourages oil to return to the crankcase and provides proper lubrication — even after extended periods of operation. :cool:

I think what Marc means, and with good reason, is that this is just a teaser. What about "ABF"? How is it achieved? What is the design difference? Any examples with data? What is your experience with it?

Your remarks serve as an introduction but seem to stop there without contributing anything of substance. At least please refer us to your sources.

Thanks,

Rog

shogun7
30-10-2004, 03:10 AM
[QUOTE=RogGoetsch]I think what Marc means, and with good reason, is that this is just a teaser. What about "ABF"? How is it achieved? What is the design difference? Any examples with data? What is your experience with it?

Rog, The heat transfer process through use of “ABF” from "XDX Innovative Refrigeration" differs from the ordinary inefficient direct-expansion feed of a *****-type refrigerant system in several ways. The process uses a special valve to allow a thin coating of refrigerant to line the entire inside of the evaporator tubing, resulting in rapid removal of heat from the product or conditioned space. Temperatures improve, the system runs less, and equipment performs better in this controlled manner of refrigerant feed. I have no dirct experence with this technology, it was introduced for purposes of information only. If you want to read more about the process go to
http://www.pressreleasenetwork.com/newsroom/news_view.phtml?news_id=1004 ;)

coolman
02-01-2005, 10:04 PM
A System is in balance when is does not fall over

Happy Newyear

Victor

shogun7
02-01-2005, 11:34 PM
A System is in balance when is does not fall over

Happy Newyear

Victor
Not fall over ...WHAT? :confused:

shogun7
03-01-2005, 01:03 AM
Itself, where "itself" coincides with its centre of gravity.
And what does that have to do with the original subject? :confused:

Victorman
10-01-2005, 07:21 PM
Actually, this is Shogun's question, not mine. And personally I think any discussion should start with a definition of "system balance". What does that term mean?

It is the selection of the components , including the compressor, condenser, evaporator, refrigerant flow control device, fan, motor, and controls.

The characteristics of each of the components are related to the other components, and the system formed by them must perform properly at design conditions and every other condition that may be expected during operation.

It is true the systems always balance, however we want them to be efficient at any point of balance.


Victorman

Lc_shi
18-01-2006, 05:44 AM
this long thread is a very worthy topic-:)I wouldn't like it stop here.
Any system can only work properly within the designed scope.Usually we design the system at 2 or 3 condition point,we can't afford to review all the states.the system "balance automaticlly" according to No1\No2 thermodynamics law. The simulation tool is developed rapidly ,may be it can predict the system performance precisely during design stage some day-:)

rgds
LC

lana
18-01-2006, 08:02 AM
The compressor capacity varies with the evaporating and condensing temperatures and the factors involved in the variation in evaporator capacity are quite complex when both sensible heat transfer and condensation are involved. For component balancing purposes, the capacity of an evaporator where both latent and sensible heat transfer are involved (a wet coil) may be calculated as being proportional to the total heat content of the entering air, and this in turn is proportional to the wet bulb temperature. So because of the many variables involved, the calculation of system balance points is extremely complicated :confused:

Hi there,
It is complicated.
My brother and I did our M.Sc. thesis on System balancing at University College London both for reciprocating and screw systems and I know it is complicated. We also developed two computer programmes ( which we sell it now:D ) .
System balancing is the behaviour of 3 selected components as a whole unit. Three components because TEV does not come into the balancing equations because balancing means energy balance and as you know in TEV (h3=h4).
For a required design conditions you select proper equipment from their manufacturer. In this selection, you choose a component with the nearest capacity. After connecting the components they will work somehow differently as designed. System balancing will show you how the whole system will work before you buy the equipment.
It is very helpful also for part load estimation. Our recip. programme also does the capacity control with sylinder unloading which is also very helpful in practice.
Cheers:)

Peter_1
18-01-2006, 12:56 PM
Link seems not working

wambat
18-01-2006, 10:08 PM
Just copy and paste any part of Shogun's post into google and you find the right link.
The fact of the matter was that I do a lot of reading in various sources because I am a professor at a community college in HVACR and when I found interesting material I would copy and paste sometimes, maybe copy something out of a book or wherever. The point is it seemed to me was to stimulate discussion. Now I don't know whats wrong with copy and paste any thing I may read of extract from a public forum like the internet as long as I don't claim it's my original work. If anyone has a problem with that it isn't my concern. I only care about getting as much out there thats useful as possible. I have been low key because I lost interest in this web site when all I was doing was arguing and loosing the main purpose of what I was trying to contribute so now I mostly read and observe until I will probably get kicked off again :) :cool: ;)

US Iceman
19-01-2006, 03:41 AM
...was arguing and loosing the main purpose of what I was trying to contribute...

Bravo... I could not have said it better.

wesmax
19-01-2006, 04:52 AM
system balance is simple if you just take one condition at a time, and this is what a tec will do is take on conition at a time and one componant at a time and work it out.

wesmax

Peter_1
19-01-2006, 06:30 AM
Some never doubt in the capacities and abilities of some for me very valuable posters ;)

Other posts copies of superheat tables but that doesn't botter me, not at all, as long as it is informative for this forum.

Not everybody has the time and the money to sit the whole day....and night... behind the computer.
Some have to work and also a family life with wife and kids and besides that a social life. So there's sometimes no that much spare time for this forum.
BTW, where's Chemi?

frank
19-01-2006, 09:47 AM
Chemi told me at Christmas that he was back at college studying after work so he doesn't get much time at the moment to visit the forum. :)