Cooling Coil Design

[Rayin]

Hi Friends..
I have to make an evaporator for a refrigerator having internal useful space 500mm Wide x 500 mm Deep x 1420 mm High.
Please see the attached sketch.(Condensing unit is mounted below this space).

The Refrigerator body and door are made out of 0.8 mm thick stainless steel (both inner and outer) and 50 mm thick PUF injected insulation. It has one no. hinged door with a clear opening space of 460x1300 mm.

The cooler is used to keep fresh meet (Lamb) approximately 15 to 20 Kg. There is 1 no. 32 W light inside. Room temperature 20 to 22 deg.C. Initial cooling time 3 hours.
Compressor to be used SC15G of danfoss made in Germany. Refrigerant 134a.

My questions are
1. What should be the total length of copper coil to make evaporator?

2. What is the equation to find out the total length?

3. What should be the space between fins?

4. Is it true that, if we use forced air evaporator for meat, color of meat changes?.

5. How do we estimate the number times of door opening?

Thank you very much indeed for all in advance.
Regards
RAYIN

[Peter_1]

You can't calculate this if you make this yourself.
How will you attach firmly the fins on the copper tubes?
What will be the thickness of the fins and the copper?
What will be the air flow rate over the coil?

You already gave us the type of compressor you want to use but is this compressor suitable for your purpose?
On what temperature do you want to evaporate?
Capillary or TEV?

The fact you already have your compressor determines already somehow the specs of your evaporator.

You must first do a heat load and then select your components. You 're doing it the opposite way.

I suggest you use a standard evaporator and try to evaporate with a DT of 7K and a compressor run time of 16 hours/day.
If it runs with a too big DT , then your meat will dry out, if it runs with a too small DT, then the skin it will not dry enough and you will notice bacteria growth on the skin. The meat will become slimy.
A static evaporator will not give satisfactory results for the preservation and cooling of fresh meat. You need air circulation.

One important factor you didn't gave us: outside conditions around the cooler.

So the answer to your questions
1. Impossible to calculate.
2. There's not such an equation
3. Between 2 and 10 mm.
4. Not only air circulation changes color: wrong humidity, wrong evaporating temperature, ... If the color changes, then there's something wrong with the selection and/or with the regulation of the total setup
5. Only you or your client can estimate this. Some open twice a day, some twice a minute.

[Rayin]

Dear Sir,
Thank you very much indeed for your reply.
(Foreword:- I am working in a factory manufacturing kitchen equipments including custom built refrigerators, in the Middle East. My duty is just to make drawings. But as I learned a little bit about refrigeration as part of my Mechanical Engineering Diploma course I also felt the way our techicians are working is not in the proper way. Designing or selecting refrigeration components are not my duty. Just to enhance my knowledge I posted the thread. Please read my thread as "In case if I need to make an evaporator...")
and now about your query...
We have Finn & tube evaporator making machine. Tube thickness 1 mm and finn (aluminium) thickness 0.7 mm. Tube dia is 1/2".
Capillary tube (0.54, 3.2 meter long) is used as expansion device. No air is forced over the evaporator coil, only static cooling. I already gave the ambient as 20 to 22 deg C but you take it as 24 to 27 Deg C (the cooler is in an Air conditioned room). Evaporator available in the market is not fitting well inside the cooler. (Our trefrigeration technician who never did a course in Refrigeration or Airconditioning, but has more than 15 years experience, fabricated the evaporator in the following way. No of raws 19, no. of columns 1, centre to centre distance of copper tube 35 mm, Finns per inch 4. Length of each pipe 450 mm. He never calculated any thing. He is sizing the evporator so as to cover half of the back wall of the cooler. That is it.
Inside temperature should be 0 to +2 Deg. C. Do not ask him about temperature difference, super heat, sub cooling etc.
SC15G is hermatic compreesor. Condensor is air cooled.
Finally the question again...How can we design a cooling coil? Even if I or my company can't make it, how others making? If we have the total heat to be removed from the product and space to be cooled, can't we calculate the total surface area of the tube required to transmit that heat to the refrigerant and thus the length of tube?
Thanks again
ragards
Rayin

[shinglai]

can anybody answer this guy's question? im kinda interested on what he wants to know too..

[US Iceman]

... can't we calculate the total surface area of the tube required to transmit that heat to the refrigerant and thus the length of tube?

Yes, but it is a topic that would require more time to explain than I have to spare. I am actually not too excited about talking about this because of the questions that will be asked. I can't promise anything, so don't expect a lot of replies. It's just too complicated and time intensive to do this.

Here is the basic problem...

You need the heat load and need to decide if you are designing for latent or sensible heat transfer or both on the fin side.

Now you have to know how to do the heat transfer calculations for the air side of the coil. These heat transfer coefficients are usually a lot less than the refrigerant side.

Then you have to be able to do the heat transfer calculations for the boiling refrigerant, which is usually two phase (boiling). This can get extremely complicated in a hurry.

Now you know the total heat transfer surface required and have to decide the ratio of primary surface (tubes) and secondary surface (fins) that will be used.

Now you have to find the coil circuiting which consists of the number of circuits and the circuit length to limit pressure drop through each circuit.

Then you have to re-check all of the calculations to see if it actually works on paper.

What I just described is a months worth of work that would have to be done to create the calculations for this.

He is sizing the evaporator so as to cover half of the back wall of the cooler.

That is one way of doing it, but it is trial and error to see if it works.

[nike123]

Maybe this software could help a litle:

EVAP-COND v2.2.1

This simulation package, developed by the National Institute of Standards and Technology (NIST), contains EVAP and COND, simulation models for predicting performance of air-to-refrigerant finned-tube evaporators and condensers. The models were prepared by:

Piotr A. Domanski
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899-8631

The modeling methods applied in EVAP and COND are in part reported in the following publications:

Domanski, P.A., 1999, "Finned-Tube Evaporator Model With a Visual Interface," Proceedings of 20th Int. Congress of Refrigeration, Sydney, Australia, September 19-24, 1999, International Institute of Refrigeration, Paris.

Domanski, P.A., 1991, Simulation of an Evaporator with Nonuniform One Dimensional Air Distribution, ASHRAE Transactions, Paper No. NY-91-13-1, Vol. 97, Part 1.

Domanski, P.A. and Didion, D.A., 1984, Mathematical Model of an Air-to-Air Heat Pumps Equipped with a Capillary Tube," International Journal of Refrigeration, Vol. 7, No. 4, pp. 249-255.

The visual interface was written by:

Janusz Wnek
ITEC Information Technology Consulting
6 Stonebridge Court
Germantown, MD 20874

Ryszard S. Michalski
INIS Inc.
9711 Maury Road
Fairfax, VA 22032


Development of this simulation package was supported by the National Institute of Standards and Technology, the U.S. Department of Energy, and the Air-Conditioning and Refrigeration Technology Institute.

Janusz Wnek provided the main upgrades to Version 2 with further modifications by Ben McIlwain of NIST.

http://www2.bfrl.nist.gov/software/evap-cond/

[mazbut]

Hi all

I have a 50TR airconditioning packaged unit for +20 deg C. I want to convert it for use in a coldstore at minus 20 deg C . What changes do I have to make to make it workable?

Ofcourse , I know that compressor capacity have to be increased;more evaporator coil and condenser added,
but how much?

thanks , please let me have your guidance

regards
mazbut

[nike123]

Hi all

I have a 50TR airconditioning packaged unit for +20 deg C. I want to convert it for use in a coldstore at minus 20 deg C . What changes do I have to make to make it workable?

Ofcourse , I know that compressor capacity have to be increased;more evaporator coil and condenser added,
but how much?

thanks , please let me have your guidance

regards
mazbut

Sell it, and then buy what you need.

[Peter_1]

Mazbut, you must start first from another question, what capacity do you need, not what have I and how can I use it?

Then next...an AC coil will never work in a freezer for several reasons. You could try it of course but all you efforts will finally end in the same conclusion: impossible to convert.

Oh BTW, welcome in this forum, i see you didn't pass via the introduction section.

[mazbut]

Hi all

I have a 50TR airconditioning packaged unit for +20 deg C. I want to convert it for use in a coldstore at minus 20 deg C . What changes do I have to make to make it workable?

Ofcourse , I know that compressor capacity have to be increased;more evaporator coil and condenser added,
but how much?

thanks , please let me have your guidance

regards
mazbut

What ought to be the size of the -20deg C coldstore 12 feet high??

[mazbut]

Peter-!,,,very funny of you! If you don't have an answer better not speak.
I have to use what I have,,,,fundamentals of refrigeration are the same--only you need to know how, when and where to apply them.

With some changes in the evaporator , condenser and compressor it is indeed possible to apply airconditioning stuff for cold storage purpose. I have been doing this with ammonia,,,,it should work with ***** 22 as well,,,and why not??

[mazbut]

Hi all

I have a 50TR airconditioning packaged unit for +20 deg C. I want to convert it for use in a coldstore at minus 20 deg C . What changes do I have to make to make it workable?

Ofcourse , I know that compressor capacity have to be increased;more evaporator coil and condenser added,
but how much?

thanks , please let me have your guidance

regards
mazbut

Sell it, and then buy what you need.

Sir, with due respect I have to tell you that I enjoy experiments with things that most people think impossible !
Man, you need lot of money to buy new equipment,,,I just want to restart from scratch !

[nike123]

Sir, with due respect I have to tell you that I enjoy experiments with things that most people think impossible !

Then, I am sure that you are going to enjoy a lot with this project!

Man, you need lot of money to buy new equipment,,,I just want to restart from scratch !

I nowhere said that you buy new equipment. Buy second hand equipment. That way, you maybe succeed with your goal.

[US Iceman]

Peter-!,,,very funny of you! If you don't have an answer better not speak.

I think you will find Peter always has some good comments and his post was just that. Unfortunately, I think since you did not get the answer you were looking for you decided to respond as you did.

It is indeed conceivable to take old AC equipment and force it to make colder temperatures. The question is; how reliable is it and how well does it work?

Obviously, from your post quoted below...

What changes do I have to make to make it workable?

You are forcing equipment to work beyond a reasonable design concept but do not understand what needs to be done. And, anyone buying this equipment is at risk of obtaining a reliable refrigeration system while risking their money in the process.

[lana]

Hi Friends..
I have to make an evaporator for a refrigerator having internal useful space 500mm Wide x 500 mm Deep x 1420 mm High.
Please see the attached sketch.(Condensing unit is mounted below this space).

The Refrigerator body and door are made out of 0.8 mm thick stainless steel (both inner and outer) and 50 mm thick PUF injected insulation. It has one no. hinged door with a clear opening space of 460x1300 mm.

The cooler is used to keep fresh meet (Lamb) approximately 15 to 20 Kg. There is 1 no. 32 W light inside. Room temperature 20 to 22 deg.C. Initial cooling time 3 hours.
Compressor to be used SC15G of danfoss made in Germany. Refrigerant 134a.

My questions are
1. What should be the total length of copper coil to make evaporator?

2. What is the equation to find out the total length?

3. What should be the space between fins?

4. Is it true that, if we use forced air evaporator for meat, color of meat changes?.

5. How do we estimate the number times of door opening?

Thank you very much indeed for all in advance.
Regards
RAYIN

Hi Rayin,

This is a late response sorry, but I write it anyway.

I am in coil manufacturing business which obviously involves calculations and design. There is no straight forward answer for designing cooling coils specially evaporators. What I do is use three different computer softwares + experience to design evaporators. Water cooling coils are much easier to design.
When using software, the designer must have proper knowledge about the parameters involved and the final decision is for the designer NOT the software.

I was involved with many "case" refrigeration as in your drawing before, but all of them needed initial calculations and then field test.

What I suggest is this: do not involve in heat exchanger design. Send your evaporator specifications to a coil manufacturer and buy what they suggest.

Cheers

[The MG Pony]

Maz< I will repeat what one of my refrigeration teachers told me: "Using R-22 in a low temp application you will enjoy such misserable failure"

There is your answer, take it as you will.

[Rayin]

Hi Lana,
Thank you for you response,
As I put in the reply to Peter_1, our Refrigeration Technician is fabricating the cooling coil so as to cover half of the back wall, and it works in many cases. But what I wanted to know is what is the correct procedure of designing the cooling coil, provided we have the heat load, temperature required inside the cooler, ambient temeprtaure, refrigerant to be used etc. US Iceman gave a broad outline of designing the cooling coil. Can you explain it in a little more detail?.Or can you guide me, how to calculate the coil size, if it was used to wind around a tank of size 500x500x500 mm for cooling water. (Ofcourse the tank is insulated)
My thanks to Peter_1, US Iceman, Nike123 and others as well
Regards
Rayin

[US Iceman]

Each type of evaporator has some very different types of calculations involved. An air-cooling evaporating (forced convection or natural) operates in a fundamentally different manner than an evaporator wrapped around a tank cooling water (agitated or non-agitated).

I'm in agreement with lana. Purchase your evaporator from someone who has the experience. Refrigerant evaporators of any type are just about the worse design problem to have with all of the variables. And... the heat transfer equations are not very precise in their answers. I suspect that is why lana uses three different programs to verify the calculated results.

[mazbut]

Hmmmm...there are so many views by the experts!

Okay, let us see the quetion this way: How much cu ft of closed insulated space can a 2TR airconditioning unit cool down to minus 20 C , for example??--

[Peter_1]

Sir, with due respect I have to tell you that I enjoy experiments with things that most people think impossible !
Man, you need lot of money to buy new equipment,,,I just want to restart from scratch !

Me too likes to experiment but I don't try to re-invent the hot water.
Nike 123 just wants a good working installation that's all and this will cost indeed some money.

Although your answer wasn't in such a way to help you any further - BTW , what did I say that made you laugh, I don't see it and it wasn't anyhow even the purpose I will try.
What will happen to you AC with very narrow fin spacing in a freezer?
What will happen with your unheated drainpan?
How will you defrost your coil which will freeze in minutes?
You can't use HG defrost in a coil that wasn't made for this.
How will you handle the high discharge temperatures when using R33 with a freezer?
Is you fans suited to run at -20°C?

To answer your last question: how many feet can an AC handle at -20°C?
Answer is very straight forward and this isn't a joke in case you should think this once again but it's based on 25 years experience in this business: 0 ft³.

But try it if you're so convinced, we perhaps all can learn from your experiments.

[nike123]

But try it if you're so convinced, we perhaps all can learn from your experiments.

And if I may add to this: PLEASE mazbut, inform us about your result!

[monkey spanners]

Hi all

I have a 50TR airconditioning packaged unit for +20 deg C. I want to convert it for use in a coldstore at minus 20 deg C . What changes do I have to make to make it workable?

Ofcourse , I know that compressor capacity have to be increased;more evaporator coil and condenser added,
but how much?

thanks , please let me have your guidance

regards
mazbut

If i wanted an aircon system to give a temperature reading of minus 20 deg C i'd do what some dairy farmers do in this country and that is to remove the needle on the temperature gauge and put it back on at the required temperature, job done

[US Iceman]

For an experiment to see what happens when you try this.... then that's fine.

For the concept of selling this to unsuspecting owners I am wholey against the idea of using air conditioning equipment for low temperature use. It will never work properly and the owner will continue to throw good money after bad in an attempt to keep it operating.

[lana]

Hi Rayin,

What others said is about the air conditioning system working as a refrigerator is completely correct DO NOT DO IT. What I am trying to explain is the evaporator calculation.
US Iceman is correct, every software gives you different answers but this is you who have to make the correct decision. When bare tube is wrap around a tank then this is completely different problem. In this case there are more experiments and experiences are involved.

Calculation procedure is like US Iceman explained but nobody does that by hand calculation nowadays (thanks GOD).
Reliable software is more expensive, at least in my experience. I tell you something, if the evaporator is calculated for a specific application which the designer has no previous experience then field test will be a MUST.

Cheers

[The MG Pony]

Hmmmm...there are so many views by the experts!

Okay, let us see the quetion this way: How much cu ft of closed insulated space can a 2TR airconditioning unit cool down to minus 20 C , for example??--

You do not grasp the core problem, at this temp the machine will eat its self due tot he extreamly high discharge temp of R-22 at low temp aplications, add this tot he heat of the compressor, Now our condencer is under sized, our displacment too small.

In mind you could make a could store of 2 - 4C but certainly not a freezer, I asked this verry same question once.

"To use R-22 in low temp applications you'll enjoy such misserable failure" was my answer, and the why of the answer is above: Discharge temp, Compressor displacement, Condensor undersized.

IE easier to trade or buy proper used or new equipment

[mazbut]

You do not grasp the core problem, at this temp the machine will eat its self due tot he extreamly high discharge temp of R-22 at low temp aplications, add this tot he heat of the compressor, Now our condencer is under sized, our displacment too small.

In mind you could make a could store of 2 - 4C but certainly not a freezer, I asked this verry same question once.

"To use R-22 in low temp applications you'll enjoy such misserable failure" was my answer, and the why of the answer is above: Discharge temp, Compressor displacement, Condensor undersized.

IE easier to trade or buy proper used or new equipment

sorry, I still fail to understand why are you against R22 when as a matter of fact some foreign suppliers/manufacturers are offering me plate freezers running on R22 and guaranteed for temp as low as minus 35 deg C for fish freezing?

BTW what refrigerant does a reefer container normally use for frozen fish transport??

As regards a 2 TR airconditioner , myquestion was to devise a cubicle corresponding to the AC's capacity without affectng factors mentioned by you,,,,presuming that the ambient temp and other conditions remain constant.

please substantiate your statements with scientific reasons rather than conveying hearsay,,,

rgds

[mazbut]

Me too likes to experiment but I don't try to re-invent the hot water.
Nike 123 just wants a good working installation that's all and this will cost indeed some money.

Although your answer wasn't in such a way to help you any further - BTW , what did I say that made you laugh, I don't see it and it wasn't anyhow even the purpose I will try.
What will happen to you AC with very narrow fin spacing in a freezer?
What will happen with your unheated drainpan?
How will you defrost your coil which will freeze in minutes?
You can't use HG defrost in a coil that wasn't made for this.
How will you handle the high discharge temperatures when using R33 with a freezer?
Is you fans suited to run at -20°C?

To answer your last question: how many feet can an AC handle at -20°C?
Answer is very straight forward and this isn't a joke in case you should think this once again but it's based on 25 years experience in this business: 0 ft³.

But try it if you're so convinced, we perhaps all can learn from your experiments.

sorry i took your footnote as part of your previous reply hence my reply,,,pls ignore it ,,,i didnt mean to offend you pls!

I appreciate your questions,,,,you are very correct.


too close fin spacing =will surely be troublesome,,,so will remove some fins making them 8 to an inch (currently they are 12 to an inch)

Will add more coil to existing air cooled condenser to curb down higher discharge pressures

Have plenty of all sizes of fans available,,if air velocity is not enough or fans weak for the job will change them !

I think there is no reason now for the unit not to work on freezing or cooling down to -20 C

Will further check out a reefer container for evaporator , condenser and compressor size,,,,and try stay close to its dimensions/parameters for positive results

pls note we have hot weather in Karachi ,,,almost round the year except mild winter in Dec/Jan

best regards
maz

[US Iceman]

There is nothing wrong with using R-22 for a freezer application as long as you provide some means of desuperheating the suction gas to provide a low enough discharge temperature. Otherwise the compressor will run so hot it might glow in the dark.

This is why R-502 was so popular for low temperature applications. You could operate very cold evaporating temperatures and use air cooled condensers and the compressors would not get too hot.

It is a function of the refrigerants specific heat ratio.

[mazbut]

There is nothing wrong with using R-22 for a freezer application as long as you provide some means of desuperheating the suction gas to provide a low enough discharge temperature. Otherwise the compressor will run so hot it might glow in the dark.

This is why R-502 was so popular for low temperature applications. You could operate very cold evaporating temperatures and use air cooled condensers and the compressors would not get too hot.

It is a function of the refrigerants specific heat ratio.

Many thanks ,,,,I will consider your advice and that's indeed helpful.

Before commissioning the unit I will test coils with air pressure ----suction 150 psi and discharge 300 psi in case of R22 or 502 to ensure hot gas defrost could be done.
Would be adding more coils and fixing a stronger fan to condenser to function properly (or perhaps opt for an evaporative air+water cooled condenser-- Surely I will have to reduce the fin spacing in that case to avoid clogging) Evaporator coils would also need removal of some fins --will try to increase fin gap to 1/8 inch or so inorder that they dont choke soon.
thnks again,,
cheers
maz

[monkey spanners]

Before commissioning the unit I will test coils with air pressure ----suction 150 psi and discharge 300 psi ........

cheers
maz

Hi Mazbut, please don't pressure test with air, it might be the last thing you do. The oxygen from the air can combine with any residual oil in the pipework to form an explosive mixture, basically you will have made a diesel engine out of your pipework. Best to pressure test with nitrogen (ofn).

Jon

[nike123]

Surely I will have to reduce the fin spacing in that case to avoid clogging) Evaporator coils would also need removal of some fins --will try to increase fin gap to 1/8 inch or so inorder that they dont choke soon.
thnks again,,
cheers
maz

How do you planing to do this? I ask this, because I don't have a clue how you are going to remove fins between pipes in evaporator.
Second, what is your plan for defrosting evaporator, and how are you going to control this. You could not use electric defrost.
Third, how you planing to match existing evaporator converted to new role, to new compressor capacity for different compression ratio. Condenser could be too big.
Also, how you are going to ensure proper cooling of existing compressor wit new reduced mas flow of refrigerant who actually, in present configuration, do the job of cooling of compressor (i mean that higher mas flow of refrigerant in air conditioning do most of the compressor cooling, witch is not the case when we have significantly smaller mas flow in low temperature applications)?
And last. What if capacity you got from all this modification is not enough for your need?

[The MG Pony]

sorry, I still fail to understand why are you against R22 when as a matter of fact some foreign suppliers/manufacturers are offering me plate freezers running on R22 and guaranteed for temp as low as minus 35 deg C for fish freezing?

BTW what refrigerant does a reefer container normally use for frozen fish transport??

As regards a 2 TR airconditioner , myquestion was to devise a cubicle corresponding to the AC's capacity without affectng factors mentioned by you,,,,presuming that the ambient temp and other conditions remain constant.

please substantiate your statements with scientific reasons rather than conveying hearsay,,,

rgds

We use R-507 or 404a here. R-22 is excellent at mid to high temp, but seriously drops off as you get lower and the discharge temp steadily rises as you go lower. In Other words it is a poor choice of gase for the given aplication.

[US Iceman]

...but seriously drops off as you get lower ...

What seriously drops off?

I agree there may be better choices (R-507 comes to mind), but there are a lot of R-22 systems running single stage with air-cooled condensers out there in supermarkets, etc.

[nike123]

I worked on automation on fast freezing tunnel, for one meat industry, with one screw Copeland compressor who has worked on R22 with evaporation temperature of -42°C. After 9 years of operation, it still work without major difficulties.
Just to add, it is cooled with oil!

[mazbut]

How do you planing to do this? I ask this, because I don't have a clue how you are going to remove fins between pipes in evaporator.
Second, what is your plan for defrosting evaporator, and how are you going to control this. You could not use electric defrost.
Third, how you planing to match existing evaporator converted to new role, to new compressor capacity for different compression ratio. Condenser could be too big.
Also, how you are going to ensure proper cooling of existing compressor wit new reduced mas flow of refrigerant who actually, in present configuration, do the job of cooling of compressor (i mean that higher mas flow of refrigerant in air conditioning do most of the compressor cooling, witch is not the case when we have significantly smaller mas flow in low temperature applications)?
And last. What if capacity you got from all this modification is not enough for your need?

I appreciate your concerns,,,

Labor is very cheap in Pakistan and I can depute some guy to pinch off undesired fins to leave a gap of 1/8 or more.

Ofcourse, as the condenser capacity will be increased by fixing a secondary or baby coil so will be the evaporator...

Inorder to match the condenser and evaporator capacity it may be that I check out a walk in freezer for their sizes and capacities and devise my unit accordingly plus 10 percent above its capacity.

By adopting the above means I dont think there would be problem with the compressor ,,,whose displacement can be calculated easily by taking the evaporating and condensing temps , dew point or wet bulb temp and cooling load , etc

Since R22 (and R12) is easily available here and relatively much economical I would be obliged to use it as some manufacturers of such equipment have advised me to do so in the equipment offered by them.
R502 or 507 are very expensive here and not easily available so I have to live with what is available here ...

BTW am trying to replace evaporator coils with freezing coils of 5/8 OD with Al fins placed abt 1/4 inch apart and to employ the narrow finned evaporators coils for air cooled condensers ....

Testing with air may be risky but Nitrogen is again expensive and not readily available here ,,,,,so will clean off the tubes first by pumping oil into them and then pumping air into them at around 150 psi. I dont know whether I would then be doing the right thing ,,,but i have no other choice! Nay, one more idea ! why not test the coils with vacuum ??

Observations and comments of all friends here have been very useful and helpful,,,,please note am a practical hobbyist not much familiar with advanced theoretical ''secrets'' of refrigeration. My expertise has been in ammonia , this is the first time I would be handling ***** system as skilled workers are getting scarce here and as you may know large ammonia system is usually manual operated!( I only saw one automatically controlled and operated in Tampa in 1986 but you dont get controls here,,,,,so all I can do is DIY!

cheers!
maz

[nike123]

I wish you luck with your project!

[mazbut]

I wish you luck with your project!

thanks lot, friend !

[avdheshastri]

i will be thankful to the one who let me knows how to design AHU, ie blower, chw coil etc etc

[mazbut]

Hello hayin

By the rule of thumb an evaporator pipe fitted with fins 1/4 inch apart is enough to provide cooling equal to about 10 feet of bare or prime evaporator pipe,,,,,from this simple observation you can calculate the cu ft of cold room it will cool down to your desired temp depending on the components and your requirement.

2. My question is ''How can I make a single contact Plate coil freezing plate 10 feet long by 2 ft wide ? The freezing plate tht would serve as a shelf for freezing fish has to be fixed underside with round tubing (flat square one not available) and will run on R22+R12,,,,

any suggestions on the way to snugly fix copper tubes to the aluminum sheet to ensure max heat transfer??
thanks

[mazbut]

here again,,,,,,,

please read one foot of finned pipe ,,,,,,,,equals 10 ft of prime pipe without fins....

[mazbut]

here again,,,,,,,

please read one foot of finned pipe ,,,,,,,,equals 10 ft of prime pipe without fins....

but this is only applicable on forced air cooling units which pls note

[Peter_1]

MAzbut, this is how we do it.
This is the machine we're using for it. (some sort sort of stud welder) http://www.lasstiften.nl/apparatuur/apparatuur.htm

Teh second picture was another technique

[Rayin]

Hello hayin

By the rule of thumb an evaporator pipe fitted with fins 1/4 inch apart is enough to provide cooling equal to about 10 feet of bare or prime evaporator pipe,,,,,

I didn't get you Mazbut. What length of evaporator pipe with fins are equal to 10 ft bare pipe? Is it same diameter?
Regards
Rayin

[mazbut]

I didn't get you Mazbut. What length of evaporator pipe with fins are equal to 10 ft bare pipe? Is it same diameter?
Regards
Rayin

Yes, the pipe is same OD,,,,
thus 1 linear foot of 1 inch OD finned pipe will be equal in cooling capacity to 10 linear feet of 1 inch OD bare/prime pipe subject to use of forced air ,,,,,I practically tried this with ammonia 1 and 1.25 inch pipe and wasn;t disappointed !

rgds

[mazbut]

MAzbut, this is how we do it.
This is the machine we're using for it. (some sort sort of stud welder) http://www.lasstiften.nl/apparatuur/apparatuur.htm

Teh second picture was another technique

it looks more or less like the plasma welding machine or the CO2 welder??

[mazbut]

MAzbut, this is how we do it.
This is the machine we're using for it. (some sort sort of stud welder) http://www.lasstiften.nl/apparatuur/apparatuur.htm

Teh second picture was another technique

Hi

Don't you think the way you are fixing round tubes to the plate allow lesser contact area with the plate?
Am also planning to build a single contact (top side only) plate freezer and for that I think having the copper or aluminum alloy tubes first roll pressed to half round and then fixing them flat surface down to the plate would very considerably increase the tube-plate contact area.
Ofcourse the half round tubes could then be welded with the stud welder you are using and clamped as shown in the pic.

please let me have your comments
thanks

[Peter_1]

Mazbut, we install between the copper and the stainless steel plate an aluminum plate to increase heat transfer.
Stainless steel has a very bad heat transfer.
We also increase contact with a special heat transfer paste.
If you want to see some pictures of this, then let me know.
You idea of pushing the tubes to an oval tube is +/- the same as we did in the second picture. The tubes are coming +/- 1mm out of the white Forex plate.
They then go under a hydraulic press like they use in the furniture industry to flatten the round tube a little bit.
like this one where most bigger kitchen or furniture manufacturers has one of these.
Finding the right clamps for a round tube is easy but I don't know where you can find those for a flattened pipe.

[mazbut]

Sell it, and then buy what you need.

You are right on the path to ''enlightenment'' ! When you don't have an answer, confuse !!

Man, money us very dear in our area ,,,,we have to live with what we have,,,,do or die ! I mean live within our means otherwise we would be killed !

As an ex-member ASHRAE i will try to get an answer from them directly as some of the know-alls here don't seem to take my problem seriously !

[mazbut]

Mazbut, we install between the copper and the stainless steel plate an aluminum plate to increase heat transfer.
Stainless steel has a very bad heat transfer.
We also increase contact with a special heat transfer paste.
If you want to see some pictures of this, then let me know.
You idea of pushing the tubes to an oval tube is +/- the same as we did in the second picture. The tubes are coming +/- 1mm out of the white Forex plate.
They then go under a hydraulic press like they use in the furniture industry to flatten the round tube a little bit.
like this one where most bigger kitchen or furniture manufacturers has one of these.
Finding the right clamps for a round tube is easy but I don't know where you can find those for a flattened pipe.

Hi
this is really excellent post from you and solves the dilemma ! May I know the brand names or identity of the conductor pate that you use and which is available in your country? I will try to find it out here in Karachi but am not very hopeful of getting it here,,,

for square tubles i may suggest that you have small cubes of aluminium casted similar to the lego blocks or a small oblong chocolate bar with a hole in the middle the size of the tube, ,,,,,fasten the block on the plate and insert pipe in the block's central hole throughtout the entire length of the plate, ,,you can fix several such blocks either by bolting or riveting or perhaps welding or by the use of paste. For more tight bond between the tube and the plate you can try using a split block ie a block split horizontally and parallel to the run of the hole and then tighten it like we tighten a clamp.

I would highly appreciate and be thankful to you if you will kindly mail me more fotos representing plate forming and fixing of tubes,,,,also pic of the tools and the paste and other stuff used ( this is requested because we usually do not get many stuff here which is normally avalible in developed countries ,,,I hope you will realize my limitations)

[Peter_1]

Mazbut, we use this product http://vaber.fogliato.it/prod_bianco_eng.php?id=15
We can buy it at several wholesalers in Belgium.

Mazbut, do you have broadband connection?
I otherwise can zip some high resolution pictures in one file and post those on an external server like Megaupload.