Pressure Drop in distributors

[MrReds]

Hallo to everybody,

please, could you suggest me if there is some literature concerning the pressure drop occurring in a distributor ?
Optimal solution cuold be having a software. Could you suggest me some good one ?

Thanks in advance

[Brian_UK]

Hi Mr Reds, try this document from Sporlan (1.14mb)

http://www.sporlan.com/20-10.pdf

[Peter_1]

You can't do anything with software, unless if it should be brand related.
And what do you want to calculate with it?

Software isn't the solution for most orf refrigeration related problem.
I seldom use software for my refrigeration work.
Coolpack solves almost anything for me.
Try to read AND...to understand what the Sporlan bulletin explains. Much better then trying a software package.

[US Iceman]

I agree with Peter. The software should only be used after you understand how the devices work. And more importantly, what the impact of any change can do to the performance of the device.

The overall question is not just, what is the pressure drop of the distributor. You need to know what the allowed pressure drop is for the distributor, distributor tubes, and their impact on the TXV selection for several different operating points; full load, part load, and summer & winter operation.

Software only performs calculations. Numbers IN = Numbers OUT. Any of these could be potentially wrong if a full understanding of the overall operation is not correct.

[MrReds]

Many thanks to everybody.
I'll take care of your advices.
Indeed we can say <<garbage in, garbage out>>.
Nevertheless I'd like to ask you if you could suggest me
some formulas or some models to simulate - and therefore to calculate - the pressure drop in the distributor first, and then in the capillars.
In the sporlan pdf I can get the description of how the distributor works, but not some models to simulate it.

hoping not to steal your patience, I thank you in advance

[US Iceman]

If I might ask a simple question...

Why are you modeling the distributor pressure drop?

[MrReds]

hallo !
I am trying to understand the phenomena, in order to know - since I work for a quality depth - if a distributor of a certain size can be acceptable.
My purchasing office is trying to get more suppliers, therefore I'd like to have some rules - different from them that I can get from catalogues - to valuate different proposals.
Moreover, I can be in the situation where I have to calculate both the pressure drop that I have in a distributor and in capillary in different conditions with respect of the one in the catalogue !

Thanks in advance for your help !

[Peter_1]

A student working in the purchase office :confused:
I don't think that the price of an evaporator will be determined by the price of a dsitributor.

I should stick with the common names and amongst those is Sporlan one of the better products.

If your purchase department (in school?) is looking for the cheapest solution without testing them in real life, then you will perhaps find a cheaper one but this will rarely be a better one.

Typically something for purchasers: pushing on the price and thinking that they finally saved money.

A distributor from A is not the same as a distributor from B and it's possible that the cheaper one works better with your product.

Kuba made his own distributor (Kuba Cal) which is a large piece of copper but it works very well.
http://www.grasso.pl/repository/images/dystrybucja/spc2_kuba_cal.jpg

[MrReds]

Dear Mr. Peter,

I am a student currently involved in a stage in quality depth of a company working in HVAC field.
Hope this clears your doubts.

I agree with you concerning the way of thinking of purchasing office, nevertheless they work according to imput, that is to try to save money.

I've been involved in some projects - one of this about distributors - and I was just trying to fix some rules to evaluate different distributors in different conditions.
Hope not to have offended anybody.
Should it be the case, please accept my excuses.

I was just looking for some advices, that's what the forums are, in my opinion.

Just a question: quotation of Lisa Simpson motto is for me ?

[US Iceman]

MrReds,

Are you evaluating distributors from different manufacturers, or, different distributors for different applications?

There is a difference between the two, if you will pardon the pun.:)

[Tycho]

excuse me for poking my head in here, but... I only work on large industrial plants and am not so strong on stuff like this.

When MrReds is talking about distributors, is he referring to the "octopus" on evaporators?

if so, shouldnt he be looking for a evaporator output/ performance/capacity instead of looking for the pressure drop in a distributor?

And if he is infact looking for a distributor, shouldn't he look for a distributor that correspond with the KW/W capacity of an evaporator?

also I would like to know, in laymans terms why he needs to know the pressuredrop since most of these items are sold (if it's an octopus) referring to the KW.

thanks :)

Dont want to hijack this thread, so if needed reply with a new post, but give me a tiny heads up :)

[Peter_1]

MrReds, sorry if I've offended you, this wasn't my meaning.

The only advice I can give is the following: if these distributors have to be used in a very large quantity, then personally I think you need to test in real life and compare the specs of an evaporator with distributor A with the same evaporator fitted with distributor B.
This will cost a lot of money.
But you're not sure that the best - A or B fitted on evaporator X - will also work the best on evaporator Y.

On the other hand, the only thing a distributor is doing is spreading the flashgas/low pressure liquid equal over all the circuits. In fact a very simple job. So if a cheap one is doing this very well, spread all equal with same SH, then I see no reason why you shouldn't fit the cheaper one.

We had in the past 2 independent evaporators of KU BA on R22, each connected to a Copeland Discus Demand Cooling with the so praised CAL distributor.
They were mounted in a freezer room.

We had calculated these evaporators for a DT of 7K because the freezer had to run during the night at -30°C (-22°C), so evaporating very close to atmospheric pressure. With the DT of 7 K, we had a little margin in case the evaporators frosted u a little bit.
TEV's were the TE5's from Danfoss, so the bigger ones.

We started everything and we had a DT of 14K on both! The first you think is a wrong calculation, wrong selection of evaporator/compressor.
Then, the orifice is not the right one. It was.

We finally measured the distribution over the coil (+/- 8 to 10 injections) and what we found was that only the upper and the lower circuit in the evaporator were fed with a relative wide hunting and a DT of +/- 6K.

What was the reason for this: a faulty concept of the underpressure casing of the fan (between fan and coil) So that the upper and the lower side of the coil had an aiflow of almost nothing.
I remember when we put a small piece of paper on the front side, upper side (suction side) of the coil that it was blown of the coil +/-2 inches lower where it then was sucked.

Finally, after long discussion, the R&D engineer from Kuba Germany came on site and a lot of blablabla and using difficult terms, but he couldn't solve the problem. The evaporators are still in place after more then 10 years.

So, this evaporator was fitted with the patented, so praised CAL distributor but an evaporator is only as good as its whole design of coil - especially the coil - the distributor, the casing (also important) and the fan.

So, what I'm trying to say, if your purchasing department will compose an evaporator with the cheapest parts they can find, it will be a problem evaporator. It will blown and it will give cold but then we have said it all.

[US Iceman]

When MrReds is talking about distributors, is he referring to the "octopus" on evaporators?


YEs that is the item, although it can sometimes have less than 8 tentacles.:)



if so, shouldnt he be looking for a evaporator output/ performance/capacity instead of looking for the pressure drop in a distributor?


It's a combination of the both. You need to know the pressure drop of the distributor and tubes since they impact the available differential pressure for the TXV capacity.

If we work backwards from the evaporator, you would find this; Evaporator pressure + distributor tube pressure loss + distributor pressure loss = the outlet pressure of the TXV.



...so if needed reply with a new post, but give me a tiny heads up


You are doing just fine Tycho.

[Dan]

A bit off topic, and something I should probably know, but the orifice numbers that indicate the size of the orifice of Sporlan distributors - how do they translate into diameter sizes in inches or millimeters?

[US Iceman]

Hi Dan,

I want to say they are based on the drill sizes, but I've been know to be wrong before. At least that's the first thing that popped into my find.

[Lc_shi]

From my test ,if there's pressure drop of distributor +evap coil is below 1bar. System capacity change little.

[Abby Normal]

the pressure drop of the distributers, the tubes etc, should all be accounted for in the selection of the expansion device

I think someone is trying to get their homework done for them all over the internet

[cygbob]

dear all,
i have the same question. In our DX evaporator, we design a orifice plate as a distributor to create pressure drop and cause the refrigerant to flash or boil. but we don't know how to calculate the prussure drop and how big the pressure drop of the refrigerant orifices and distributors is proper?
For example, DX evap, R404a; tube outer diameter:16mm; duty:606kw; tube count:1480; 4 tubeside passes; Te= - 40 C.

could someone help me? I will be very appreciate for your help! Thanks a lot!
Best regards!

[mickandlee]

Blow through coils i.e. the fan blowing through the coil (unit coolers -> ahus) nearly always have very uneven airflow distribution and therefor problems with refrigerant distribution. This normally shows up in manufacturers rating tables where both blow through and draw through types are offered. Draw through units normally have higher duties.

In the field check each circuit for even refrigerant flow. (I have see an even 'older timer than me' use a pair of pliers to good effect in a realy bad case)

Problm in air handling units can be overcome by perforated plates between fan and coil.

So dont always blame the poor distributor.

Final thought
I remember a large Diakin commercial split unit (15 TR or thereabouts) making use of two 1/2 in distributor tubes as expansin device !!!!. Good head pressure control required I should think.

Mick

[Peter_1]

I remember a large Diakin commercial split unit (15 TR or thereabouts) making use of two 1/2 in distributor tubes as expansin device !!!!. Good head pressure control required I should think.

Mick
But in the liquid line just before the distributor or even in the distributor was an inline restrictor, like those used in car AC, acting also as an NRV in opposite direction.
We used some time those of Aeroquip.
If interested, I can take some pictures of it.

[mickandlee]

Its a long time ago

Picture would stir the old grey atter
Mick

[Samarjit Sen]

Wether it is a small plant or an industrial plant, a distributor plays a very important role in the operation of an Evaporator. Wherever there is a multiple cicuits, a distributor has to be put. The selection of a distributor and its orifice is also important.

Parker and Sporlan have a very good selection system. They also have necessary software. But then it is very important that one is aware of the various datas and the applications before being able to operate the Softwares.