Hi,
Maybe for whole life like us ;)Quote:
Originally Posted by US Iceman
Best regards, Josip :)
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Hi,
Maybe for whole life like us ;)Quote:
Originally Posted by US Iceman
Best regards, Josip :)
Hi Josip,
I've been doing this for a long time and I still learn something new everyday. I bet you do too.;)
The next big project to figure out is process AC systems, something like your project you are working on now. I'm still going to school after all this time.:rolleyes:
hi josip and us iceman,
thnx
hi josip and us iceman,
thnx for the help... i hav seen the topics for the ice cream plant and im im currently
hi josip and us iceman,
thnx for the help... i hav seen the topics for the ice cream plant and im currently checking it out now... we hav a problem in finding the exit temperature of our refrigerant which is ammonia.. the temperature entering the evaporator is -30C and our only data is the temp of the ice cream which is the temp entering is 4degC and exits at -5degC... by the way this is the freezing of the ice cream which is a closed system... correct me if im wrong but we're doing the mass balance and energy balance.. is this correct? are we in the right track hope u reply because we're running out of time... thank you so much sir or sirs...
Hi corineramer,
If the liquid ammonia is being pumped into the evaporator at -30C, it also exits the evaporator at -30C on an overfed system.Quote:
the temperature entering the evaporator is -30C and our only data is the temp of the ice cream which is the temp entering is 4degC and exits at -5degC... by the way this is the freezing of the ice cream which is a closed system...
Therefore, if your ice cream is entering at 4C and leaving at -5C, that is your heat load for the mass flow you have.
To do the energy balance, the heat load divided by the latent heat of ammonia at -30C will provide the vapor mass flow out of the evaporator. You have to be careful, as the ammonia liquid mass flow will be even higher.
The whole purpose of an overfeed system is to pump in more liquid than will boil off.
hi us iceman,
i thought that there would be a temp change in the ammonia because of the heat transfer through the evaporator... so, there would be not temp change in the ammonia... thnx for the help.. just post here for my progress and questions.. tnx again
The refrigerant is boiling at -30C. As long as the refrigerant pump is supplying sufficient liquid into the evaporator, the refrigerant exits the evaporator at -30C.
If the pump is not selected properly, or the hand expansion valve is too far closed, you can get some superheating of the gas leaving the coil. With superheat, you would have a temperature change.
The boiling process is all latent heat, so the temperature does not change.
Good luck on the school project.
hi us iceman,
now its getting clear... our prof told us that there would be no temp change but the pressure will be higher so we need a back pressure valve before the vessel i think to minimize the pressure until it equals the temp of our vessel, right? then for the compressor, the suction pressure will be the pressure at the vessel and the discharge will be depending on the ambient condition in the condenser... pls correct me if im wrong... wow! it feels good now because im beginning to understand this system... the next will be the computations... im having fun in this design... hehehe
I'm not sure why he thinks you need a back-pressure regulating valve. These are used to keep the pressure higher in the evaporator. BY increasing the evaporator pressure with this valve, you increase the saturated evaporating temperature. This would reduce the evaporator capacity.Quote:
...but the pressure will be higher so we need a back pressure valve before the vessel i think to minimize the pressure until it equals the temp of our vessel,
Unless, there is something I don't know about in your system design.
Without this valve, the evaporating pressure would be equal to the compressor suction pressure plus the suction line pressure drop. If your ice cream freezer is the only evaporator on the system, the -30C evaporating temperature will require a slightly lower compressor suction temperature.
The suction line pressure loss is equal to a specific value for the equivalent temperature loss.
Adding a back-pressure valve at -30C increases the suction line pressure loss and also decreases the compressor capacity.
hi us iceman,
now im getting confused... this is his explanation, when the ammonia leaves the evaporator there will be a slight or big increase in the ammonia pressure I think...then he said that the pressure of the refrigerant should be equal to the vessel thats why we nid this valve... he said that the compressor suction pressure should be equal to the saturation pressure at -30C... By the way he said that this valve decreases the pressure of the ammonia so that it will be equal to the pressuer of the vessel... what does a back-pressure valve do? is this correct? i have another question he added that we can use 1 condenser in our freezing, hardening and storage... he said that when the ammonia has been compressed by the 3 compressors we can join them in 1 line to the condenser... is this possible? then im thinking on how to distribute the ammonia that exits from the condenser... im really confused... can I send u the details of our design to your email? if its ok with you.. and have your comment on it.. thank you for the time..
Hi corineramer,
Let's see if we can clear this up.
No. When the liquid is pumped into the hand expansion valve, the pressure is reduced to the evaporating pressure (the saturation pressure of the ammonia at -30C). The pressure does not rise. In fact, the pressure decreases some due to the pressure loss of the refrigerant flowing through the evaporator circuits.Quote:
when the ammonia leaves the evaporator there will be a slight or big increase in the ammonia pressure I think
If we neglect all pressure losses, the evaporator pressure is the same as the vessel pressure is the same as the compressor suction pressure.Quote:
then he said that the pressure of the refrigerant should be equal to the vessel thats why we need this valve... he said that the compressor suction pressure should be equal to the saturation pressure at -30C
My guess is, he is making a common mistake on liquid overfeed systems. The refrigerant pump provides the pressure to move the liquid out to the evaporators. When the liquid flows through the hand expansion valves, the liquid pressure is reduced down to the evaporating pressure on the outlet of the hand expansion valve.Quote:
By the way he said that this valve decreases the pressure of the ammonia so that it will be equal to the pressure of the vessel...
Once the liquid is in the evaporator, it is also at the evaporating pressure equal to -30C. The pump pressure is all gone. All of the gas and liquid exist at the evaporating/suction pressure (Again, I'm assuming we have neglected the pressure losses due to flow.).
The refrigerant flashes in the evaporator, not after the back-pressure valve.
[/quote]
what does a back-pressure valve do?
[/quote]
A back-pressure regulating (BPR) valve controls the pressure of the refrigerant upstream of the valve. If the BPR valve is set for a pressure higher than the evaporator pressure, the liquid will not boil at -30C. Adding BPR's to a liquid overfeed system creates a lot of additional problems that must be solved.
If you only have one evaporating temperature on your system (-30C) you do not need a BPR to make the system work.
That's OK. This is done all of the time. You must make sure the piping on the condenser is absolutely correct to allow gravity drainage. Condenser piping is probably one of the most mis-understood areas of indutrial refrigeration systems.Quote:
he said that when the ammonia has been compressed by the 3 compressors we can join them in 1 line to the condenser
The outlets of each condenser coil (most larger condensers have at least two outlet connections) must be trapped at the bottom. The equalizing line from the receiver to the condenser inlets must also be large enough to allow the liquid to drain properly.
Hi,
seems to me that the teacher is more confused then students:)
Best regards, Josip :)
HI Josip,
That teacher would not be the first either.:D
I have not been on in a while. Seems Summer breakdowns have had us running. North Star Icemakers (My favorite). Compressor seals, etc.
So lets open a can of worms on Hand Expansion Valves used with Liquid Recirculation.
Just once I have installed a AFR3 Flow Control from Refrigeration Specialties. In all other cases we have used H.E. Valves.
I believe you can calculate the orifice size of any H.E. Valve from the Manufacturer's literature and from then calculate the approximate opening turns to start with, although I have never done it.
The proper method of adjusting after startup is to open the H.E. Valves until Evap performance starts ti fall off. (Using Air Temp measurements across a coil for instance). Once the coil is overfed ("Brining") the performance starts to fall off.
Of course if the Liquid pump loses pressure as the valves are opened you need to start over.
Last Summer I started up a Medium Temp warehouse with a dozen or so NH3 Evaps. It would have taken several days to go through the procedure, especially as product was being moved in as we were starting up.
So we make an educated guess as to the settings. That is made easier by the fact that this customer does not insulate the control valves, and that they are installed on the roof. You can see the effects of the liquid return and adjust accordingly.
Liquid recirculation is certainly more tolerant of underfeed and overfeed than other methods but I suspect many of the systems I work on are underfeeding.
Does anyone have a better adjustment system, or is this way most of you do it?
I suppose the way I go about it would be. Check my selection on the Dircal software, it gives valve openings.Quote:
Originally Posted by NH3LVR
Setthe valves up something less than that. Observe the frosting on the evaporator, should be less than fully fed. Keep opening the valves until the evaps are all frosted, all just fully flooded and all the same. Then give the valves another 1/2 turn or so open. I would then check the air on and offs on the central monitoring system, they should be all similar, the poor ones I would then look at more closely and adjust to get the best performance. To my mind you should have no big drop off when overfeeding, if you do you are just wasting pump power at the expense of evaporator and system performance.
Kind Regards Andy:)
HI NH3LVR,
Welcome back.
Yes, that is correct. A little number crunching will get you there.Quote:
Originally Posted by NH3LVR
I'm not saying this is better, it's just the way I would go about it.Quote:
Does anyone have a better adjustment system,...
The first thing to do is to check the refrigerant pump pressures and operation to make sure it is dialed in properly. If a small compressor has been started to pull down the suction pressure in the vessel, the pump will start to cool off. As the suction pressure approaches the normal operating condition, the pump should be very close to it's operating temperature.
It is a lot easier to do a cold start-up on a liquid overfeed system than a hot start-up.
The evaporators that are the farthest away from the pumps, or the ones that are at the highest elevation are the coils that need the most liquid pressure to HE valves.
I would start at one of these coils with the adjustment of the HE valves. Shut off the fans on the coil and begin to crack open the HE valve. As the frost pattern begins to approach the suction outlet header, you are getting fairly close. Turn the fans on and move to the next coil.
Continue to work your way back to the pumps.
Once you get this far, you can go back and check the air temperature drops across the coil. You can determine the exact number (TD) you should be trying to get. By the time you get ready to start measuring air TD's, the system is starting to stabilize.
I certainly don't think this question is, or will be a can of worms, but it is a very good question. I think the biggest problem is the HE valves are normally adjusted too far open, causing the coils to overfeed and nuisance problems with the pumps.
BTW, we have another thread going under English Language... . You should post this saying " a can or worms" in there.
hi us iceman,
our equips are not complete do you know a site where i can have brochures of liquid receivers?? tnx.. BTW, the hand expansion valve is located after the pump before the evaporator, right?
If you go back to the Evapco web site, they will have a complete brochure for various pressure vessels. You should be able to find something in there.
The liquid feed valve train for the coil usually consists of these items:
Having a service valve on the beginning and the end of the valve train allows you to service any of the valves in that valve group, without pumping down the evaporator coil.
- Service valve
- solenoid valve with close-coupled strainer
- Hand expansion valve
- Check valve (required only if hot gas defrost is being used)
- Service valve
Here is a link for some information about one type of refrigerant pump. It shows some of the typical installation details. These details vary somewhat if you use a hermetic pump.
hi us iceman,
wat link are you referring to? the evapco site or other sites? we're really confused.. we're not that familiar with this system because the cycle that we have studied is the vapor compression cycle... im sorry if our progress is slow... i thought we understand this cycle but not there's a lot of things we need to learn.. also we have 3 evaporators that has 3 different temp we're trying to figure out if we will use one condenser in this 3 evaps or provide them with their own condensers... tnx
Hi corineramer,
Use this link to review vessel information.
http://www.evapco.com/media/pdf/asme-pressure.pdf
Nothing has changed. This is still a vapor compression cycle. It's just not a direct expansion system.Quote:
...the cycle that we have studied is the vapor compression cycle
If you try to add other coils which are operating at higher evaporting temperatures, you would need back-pressure valves on those coils operating at the higher temperatures (greater than -30C).
This really complicates a liquid overfeed system and the explanation of how it operates.
If this is supposed to be a school project your professor has actually given you one of the hardest problems to work on.:(
Hi US Iceman,
I'm a groupmate of corineramer. We are really confused about the liquid overfeed refrigeration system. This is what we understand about it.
You will supply more liquid refrigerant flowrate in the evaporator than required to enchance heat transfer by providing a higher velocity in the coils.
In our subject, we need to design a refrigeration system(liquid overfeed) for ice cream manufacturing plant.
We have used a separate refrigeration system for each process, freezing, hardening, storage.
Our professor said that we can tap the discharge line in the compressor because it has the same discharge pressure.
Is it possible if we only have 1 to 2 condenser? is it possible if we only have one condenser and 3 expansion valve?
Back to liquid overfeed. for example, in our freezing process, we have a -10 degree C ammonia. The ammonia pump will pump the refrigerant to the evaporator and increase the pressure of the refrigerant thus increaseing the boiling point. So we need the hand expansion valve to bring back the saturation pressure at -10 degree C? In liquid overfeed, the refrigerant that comes out from the evaporator is a mixture of liquid refrigerant and vapor right? then it will go to the separator to separate liquid and vapor. Then the compressor will suck the vapor at saturation pressure of the -10 degree C. The discharge pressure will depend on the ambient temperature in the condenser. We have a 35 degree C. Then after passing in the condenser, it will pass to the expansion valve to bring down the pressure to the saturation pressure at -10 degree C then stored in the liquid receiver for use when the level of refrigerant in the separator is low. is this correct?
Sorry if we ask so many question, we are really confused and thank you so much for spending time and helping us. Thanks :)
For a brief description of liquid ampliciation go here-Quote:
Originally Posted by ipelatak
http://www.hysave.com/
and click on 'live demo'
which is a small vid of the process..however each case needs careful examination and application which I understand is where they badly went wrong in the early days..
cheers
richard
hi us iceman,
BTW ipelatak is my groupmate... his message is the one after your latest post pls read his message, tnx... actually our professor told us to pick an industrial plant and design one of its utilities so that it would be easier for us because if he would choose what we're gonna design then it will be very difficult but unfortunately we picked a hard one not the easy ones... we have problems in selecting the compressor because our reference is the suction pressure, is this correct? for example our suction is 42.3psig and discharge press is 190psig... our prof told us to base our compressor to this given data but when im looking for the compressor they are giving the refrigeration capacity not the pressure... is this correct? or convert the TOR to refrigerating capcity and use it in selecting the compressor.. we're really confused... sorry if we'er disturbing you..
Hi kurimaw & latek,
Expansion valve before liquid reciever is WRONG!:eek:
I think you should go back from the very basic of refrigeration before jumping out for the design. You shoul know the function of every components of refrigeration.;)
Are you a first year college student? what school?:(
Don't rely too much in your prof. you should do your own researh & study.
Regards,
Guapo:)
Hi ipelatak,
You are supplying more liquid into the evaporator than the amount that boils off. The purpose of using a liquid overfeed system is that the excess liquid provides a complete wetting of the heat transfer surface of the evaporator coil.Quote:
Originally Posted by ipelatak
In a DX system, you loose some of the capacity of the evaporator due to the need to provide superheat. If you look at the evaporator ratings you will see a DX coil has about 15% less capacity than the same coil for liquid overfeed.
OK, that makes the design process much easier then.Quote:
Originally Posted by ipelatak
You can have one condenser or multiple condensers. All of your compressors can be connected to a common discharge line, which is piped to a single large condenser, or smaller multiple condensers. The condenser(s) would drain down to a common high pressure receiver. From this receiver, you can feed liquid to your separator (the one with the refrigerant pumps).Quote:
Originally Posted by ipelatak
The pump provides the pressure to transport the liquid to the hand expansion valves. The pressure supplied by the pump overcomes the friction and other losses to ensure the liquid is getting to the hand expansion valves.Quote:
Originally Posted by ipelatak
You are correct about the increase in boiling temperature. The added pressure generated by the pump actually seems similar to subcooling of the liquid. Therefore, the liquid will not boil until the pressure is reduced. The hand expansion valve is really a balancing valve. You are using it to adjust the flow rate into all of the evaporators.
OK, so far.Quote:
Originally Posted by ipelatak
The discharge pressure will depend on the ambient conditions and the capacity of the condenser. If you are using an evaporative condenser, you are concerned with the condensing temperature and entering wet bulb temperature of the air.
In a typical system, the liquid will flow into a high-pressure receiver after it drains out of the condenser. When the level in the separator begins to decrease, a control system will allow liquid from the high-pressure receiver to flow into the separator to maintain the liquid level. The liquid in the high-pressure receiver would be at 35C.Quote:
Originally Posted by ipelatak
I'm not sure whay you have an expansion valve after the condenser as you described. (Note: I have done something like this before, but quite different than what you are describing.
My pleasure. I hope I have not added to the confusion.:DQuote:
Originally Posted by ipelatak
Hi US iceman,
Uhm we thought we should need to use a expansion valve after the condenser to reduce the pressure back to the refrigerants saturation pressure at -10 degree C.Quote:
Originally Posted by US Iceman
So after condenser, we should put a high pressure liquid reciever. The temp of the refrigerant is 35 degree C = to the ambient temperature of the condenser. When the level in the separator begins to decrease, a control system will allow liquid from the high-pressure receiver to flow into the separator to maintain the liquid level. The temp in the separator is -10 degree C and the temp in the high pressure reciever is 35 degree C. We thought we need a expansion valve to bring back the pressure and temperature of the refrigerant in high pressure reciever equal to the refrigerant's temp and pressure in the separator.
Do we still need a pump after the high pressure reciever or the pressure will transport the refrigerant back to the separator and bring back the temperature and pressure because of the pressure drop in the pipe?
thanks a lot masters, were really thankfull that you guys are helping us. thanks a lot :)
Hi corineramer,
I had a long explanation of the compressor rating procedures written out and when I tried to post it, something happened and I lost the whole thing.
The short version is:
You have to include the suction and discharge pressure losses to correct for the actual compressor performance.
Discharge pressure = condensing pressure + piping pressure lossses
Suction pressure = evaporating pressure - piping pressure losses
Convert the suction and discharge pressure to their equivalent saturation temperatures. These are the temperatures you want to use for selecting the compressors.
No. The condensing temperature is not the ambient temperature. If you want to condense at 35C, then you have to select the condenser for a condensing temperature of 35C with whatever your local wet bulb temperature is for. In the Phillipines it is probably quite high.Quote:
Originally Posted by ipelatak
You need an expansion device to feed the liquid into the separator to maintain the liquid level. The liquid comes from the reciever at 35C, goes through the expansion valve, into the separator.Quote:
We thought we need a expansion valve to bring back the pressure and temperature of the refrigerant in high pressure reciever equal to the refrigerant's temp and pressure in the separator.
Ahh, crap... Know I see. You guys are designing a Hysave system. That is not a liquid overfeed system, it's a DX system.:mad:Quote:
Do we still need a pump after the high pressure reciever...
The refrigerant pump in an overfeed system is under the separator and operates at suction pressure.
Hi :)
No, from receiver to surge drum (-10C) you have only a pipe with liquid ammonia under condensing pressure and little subcooled. On this pipe you can have (because there are some other solutions) installed stop valve, solenoid valve, expansion valve and again stop valve just before entering into separator (surge drum -10C). At this expansion valve our high pressure and high temp ammonia expand giving us a mixture of liquid and vaporized ammonia with temperature what we have in our surge drum (-10C), liquid remain in separator and vapour we remove from surge drum with compressor. This liquid with temperature of -10C we can transport (pump) to our cooling units (homogenizers).Quote:
Originally Posted by ipelatak
Coming to compressor sizing first you have to calculate your heat load=compressor capacity (not exactly, but good for example) for defined evaporating temperature/pressure (-10C, -15C, -35C or -40C) and defined condensing temperature/pressure i.e. one compressor can run at each suction temperature/pressure from -15C to + 5C with the same (or different) condensing temperature/pressure but allways with different capacity.Quote:
Originally Posted by corineramer
To obtain needed capacity, compressor capacity is very important but power of motor also.
Hope this will help a little;)
Best regards, Josip :)
Are you sure, Iceman? Seemed to me they are trying to sort out an overfeed system. I was actually puzzled why Richard assumed they were looking at using a pump to increase liquid pressure. The mention of hand expansion valves had me puzzled until you sorted them out as balancing valves. But the original premise is returning liquid and vapor to a separation drum. This is not DX to my thinking.Quote:
Ahh, crap... Know I see. You guys are designing a Hysave system. That is not a liquid overfeed system, it's a DX system.
Hi,
I based my condenser designed to 45C, you will have a very huge condenser if you based on 35C.
Ambient is already 28-34C.
Hi Dan,
Here is why I thought the discussion took a different turn of events:
That to me says a Hysave system or something very similar. The only reason to have a pump after the high-pressure receiver is to boost the liquid pressure.Quote:
Originally Posted by ipelatak
The post that Mr. Bartlett made did not really have anything to do with a liquid overfeed system, other than it uses a refrigerant pump. Different system, different reason.
I agree Dan. They did state they had a separator, and it certainly sounded like an overfeed system, but when they mentioned the pump after the high-pressure receiver, that is something completely different.Quote:
Originally Posted by Dan
I guess I made some assumptions too. I should have asked what type of condenser they are using. I assumed they were evaporative condensers, since it was an ammonia system.
I just hope the students are beginning to understand this type of system. An overfeed system is not hard to understand, but it sounds like their professor has told them some conflicting information.
I think we can get them to understand this, but I'm not sure if they have enough time before their school project is due.
Hi to all,
Sorry if we make some confusion in what we said in the previous posts.
This is what we understand so far, pls correct us if we're wrong.
New example:
Ambient temp = 34C
Condensing temp = 45C
Evaporating temp = -10C
The liquid refrigerant in the separator is at -10C. The refrigerant will be pumped by a ammonia centrifugal pump. The pump will supply more liquid refrigerant into the evaporator than the amount that boils off.
The pump provides the pressure to transport the liquid refrigerant. The pump will increase the pressure of the refrigerant thus increasing the boiling point so
we need a hand expansion valve to bring back the saturation pressure of the refrigerant.
The liquid refrigerant will pass through the evaporator and leaves at the same temperature of -10C but a mixture of liquid and vapor. The mixture of the refrigerant will go to the Separator to separate the liquid refrigerant and the vapor refrigerant.
The vapor refrigerant at -10C will be sucked by the ammonia compressor. The discharge pressure of the ammonia compressor will be the pressure of ammonia at the ambient temperature in the condenser.
The refrigerant will be condensed at 45C by a water-cooled condenser. The refrigerant still under high pressure leaves the condenser and passes to a high-pressure receiver where it is stored for later use for supply in the separator.
We expansion device after the high-pressure receiver to feed the liquid into the separator to maintain the liquid level. The liquid comes from the reciever at 45C, goes through the expansion valve, into the separator.
what are the valves we need and where to place them? sorry out professor didnt taught us how
to do this.
Uhm.. if you have some free time, can you pls tell us how liquid overfeed works?
In getting the mass flowrate in the system
mass flowrate of refrigerant (latent heat of vaporization ammonia) = Heat added by the
evaporator
Sizing of compressor
Suction pressure = Psat at -10C, ammonia
Discharge pressure = Psat at 34C(ambient temp), ammonia
work of compressor = m(delta h), mass flowrate (enthalpy at 34C - enthalpy at -10C)
Sizing of condenser
Condensing temp = 45C
Heat rejected = work of compressor + heat added by the evaporator
Cooling tower
Air temp in = 32 C
temp of water in reservoir = 34C
temp of water entering condenser = 34C
temp of water leaving condenser = 50C
water flowrate
water flowrate (sp. heat water) (50C - 34C) = Heat rejected by condenser
Sorry if we ask so many, thanks for all your help and thanks for spending time with us. thanks masters. :)
It's not one of my strong points (ammonia) but some of this needs explaining to be able to understand.
This equates to 34C?Quote:
The discharge pressure of the ammonia compressor will be the pressure of ammonia at the ambient temperature in the condenser.
Quote:
The refrigerant will be condensed at 45C by a water-cooled condenser.
How does the ammonia vapour condensing at 34C get up to 45C?Quote:
The liquid comes from the reciever at 45C, goes through the expansion valve, into the separator.
OK, so far... Except, the ambient temperature does not matter if you are using water-cooled condensers. I want you to clarify the condenser type. Is it a shell & tube condenser, or a plate heat exchanger?Quote:
Originally Posted by ipelatak
No. The discharge pressure of the compressor is the condensing pressure (pressure at 45C) plus the discharge line pressure loss. Ambient dry bulb temperature only matters if the condenser is air-cooled.Quote:
The discharge pressure of the ammonia compressor will be the pressure of ammonia at the ambient temperature in the condenser.
That part is OK.Quote:
The refrigerant will be condensed at 45C by a water-cooled condenser. The refrigerant still under high pressure leaves the condenser and passes to a high-pressure receiver where it is stored for later use for supply in the separator.
We expansion device after the high-pressure receiver to feed the liquid into the separator to maintain the liquid level. The liquid comes from the reciever at 45C, goes through the expansion valve, into the separator.
He should have. If he did not teach this, then what is he doing?:confused:Quote:
sorry our professor didnt taught us how to do this.
The mass flow calculations are a little complicated for an overfeed system. It is different in various parts of the system.
In general terms, the liquid supply to the separator provides sufficient liquid to maintain the level. The refrigerant that boils off in the evaporator is this amount.
The refrigerant pump circulates about 300-400% this amount to the evaporator. The 300-400% mass flow is flowing through the liquid line from the pumps, to the evaporator, and back to the separator.
I think you are getting the idea.:)
Hi, :)
I think the best for you is to visit those links:Quote:
Originally Posted by ipelatak
http://www.danfoss.com/Asean/Products/Categories/
http://www.danfoss.com/Pacific/Busin...+Conditioning/
here you can find all products you need for refrigeration or AC plant. There you can find also some brochures and so on...;)
Here you can find almost all you need:) valves, systems&vessels, accessories
http://haphillips.com/
http://haphillips.com/products.html?pc=67#77
Pls, don't show that to your professor:D
Hope this will help to finalize your project on time:)
Best regards, Josip :)
shell and tube condenser.Quote:
Originally Posted by us iceman
thanksQuote:
Originally Posted by us iceman
for mass flowrate, pls correct us if we're wrongQuote:
Originally Posted by us iceman
the flow will be the same at the separator to pump, pump to hand ex to evaporator to separator.
In separator (vapor) to compressor to condenser to high-pressure liquid reciever.
High-pressure receiver to ex valve to separator.
aahh so this is the flowrate in the high-pres receiver to separator? thanksQuote:
Originally Posted by us iceman
thanks for the link:)Quote:
Originally Posted by josip
haha dont worry, we wont:D
Thanks alot masters, ur our savior. thanks for spending time with us and for helping us. can we ask again if we have a problem somewhere again in our project? thanks master us iceman, master josip and to all:)
Here is how the mass flow rate works.Quote:
Originally Posted by ipelatak
From the refrigerant pump to the hand expansion valve, to the evaporator, and back to the separator the mass flow is higher. This is where the mass flow will be about 3 or 4 times higher than the other part of the system.
The mass flow from the separator (gas) to the compressor, to the condenser, to the receiver and out to the hand expansion valve on the separator (maintaining the liquid level) is based on the mass flow that boils off in the evaporator, PLUS...
The flash gas that is generated when the 45C liquid flashes off down to 10C, which is being fed into the separator to maintain the liquid level.
So, what you have coming out of the separator as gas (back to the compressor) is the flash gas + the gas boiled off in the evaporator coils.
The excess liquid that is not boiled off in the evaporator, just simply recirculates. Someone may say you need to recirculate more liquid than 3-4 times what boils off.
I say you can design the system for less, so you do not have to pump as much liquid. We will save that discussion for another time.
It sounds like you guys are getting close to being finished. I hope you get a big A++ on your project.:D
Best Regards,
US Iceman
how can we calculate the gas that flashed in the expansion valve??? we're computing it for our compressor capacity...:confused:Quote:
The flash gas that is generated when the 45C liquid flashes off down to 10C, which is being fed into the separator to maintain the liquid level.
So, what you have coming out of the separator as gas (back to the compressor) is the flash gas + the gas boiled off in the evaporator coils.
we're still confused in getting the compressor capacity because we have computed it using the enthalpy differencence between the discharge and suction times the mass flowrate(we assumed that the refrigerant that will vaporize in the evaporator is 25% of the overfeed massflowrate of the refrigerant that enters the evap. we havnt included the mass of the flash gas) is this correct??
BTW our overfeed is 400%