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Thread: Liquid receiver

  1. #1
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    Question Liquid receiver


    What i need to consider to size liquid receiver.

    Renato



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    Re: Liquid receiver

    How much liquid will you need at lowest capacity of system operation ? Full capacity minus lowest capacity liquid is needed to go into liquid receivermy understanding,only for ref

    rgds
    LC
    I hear...I forget;I see...I remember;I do...I understand

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    Re: Liquid receiver

    Hi,

    I think the size of liquid reciever can charge all of refrigerant in the system.

    Regards,
    Guapo

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    Re: Liquid receiver

    Or, in case you would like to recover all or most of the liquid into the receiver, calculate it for full charge.

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    Wink Re: Liquid receiver

    It is Copeland logic to recover all refrigerant in receive.Well can go wrong with this.

    Thanks all,
    Renato

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    Re: Liquid receiver

    What logic? Can you please elaborate? What can go wrong?

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    Thumbs up Re: Liquid receiver

    Nothing can go Wrong.In Copeland V volume write the same.But 300l receiver it is big mother ****er.And it isnt cheep.
    The trouble is that I can provide such big receiver in that short time so I need to make paralel conection of 2 receiver each of 90l.That is total 180l.

    I think thet will be enough.The manufacturer of chiller advice me 50l but I am not agree with his calculation.

    Renato

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    Re: Liquid receiver

    300 liters receiver? What a huge PV!
    Is that designed under PED certification?
    What compressor are you planning to use?

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    Cool Re: Liquid receiver

    Bitzer CSH8571-110Y R134A 400/3/50 X 2.

    Renato

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    Re: Liquid receiver

    If the system charge is 300 liters, the receiver needs to be about 125% larger so that you have some vapor space on top of the liquid.

    One question; how did you get from 180 liters to 300 liters for the receiver volume? That is quite an increase!
    Last edited by US Iceman; 11-04-2006 at 02:18 PM. Reason: spelling

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    Re: Liquid receiver

    That compressor would require a total charge (with a DX evaporator and condensing coil) of approx 80 to 110Kg.
    I would suggest a liquid receiver around the internal volume of the coil, for a flooded condensing coil control.
    Otherwise, for a fan speed controlled condensation, I would suggest a liquid reicever of the volume of the flooded circuits (if used for subcooling), let's say 15-30% of the volume of condensing coil.
    If EEV is required or used, reduce the volume further by 30%.

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    Smile Re: Liquid receiver

    1)I have 2 compressors in engine room.
    2)Discharge pipe first go to water condenser (sanitary water)
    3)Then pipe go 65m in lenght to the air condenser outside the building.(rise 4m)
    4)Pipes are from water condenser to air condenser "discharge"65 mm and back "liquid" 42 mm.
    5)density of R 134a is for liquid 1160kg/m3 and for wapor 300kg/m3.
    6)In situation when water condenser live refrigerant in liquid the 65mm would be full of 1160kg/m3,and when vapor leaves 300kg/m3.
    7)Ask for more?

    Renato

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    Smile Re: Liquid receiver

    It is water chiller.

    Renato

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    Re: Liquid receiver

    Well, thanks for pointing you were designing a split chiller. This is news. If you think there's anything else you would want to write in order to help us to help you, please feel free. Otherwise we could only be guessing.

    You can use the 65m pipe run as liquid receiver and reclaim it from the bottom in case of recovery need. Much better than filling the plant with unnecessary volumes.

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    Arrow Re: Liquid receiver

    We buy chiller from Italian suplier and we only mount it.But from the start i have bad filling with this.

    Soory if i give insufisent information.But I want to heard from you basic design prenciples and then start forvard.Also if I write the novell some of you will not read.

    Renato
    Last edited by Renato RR; 11-04-2006 at 02:47 PM.

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    Re: Liquid receiver

    Quote Originally Posted by Renato RR
    We buy chiller from Italian suplier and we only mount it.But from the start i have bad filling with this.

    Soory if i give insufisent information.But I want to heard from you basic design prenciples and then start forvard.Also if I write the novell some of you will not read.

    Renato
    Oh, then I'll stop helping , until you buy the chillers from us.

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    Cool Re: Liquid receiver

    There is time for ewriting.Now is time for helping.

    Renato

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    Re: Liquid receiver

    OK Guys, let's start over.

    Quote Originally Posted by Renato RR
    What i need to consider to size liquid receiver?
    First you need to know the total volume of refrigerant in the system if you want to do a pump down for 100% of the system charge.

    You need to know the condenser charge: this depends on the head pressure control method. A flooded condenser coil will hold a lot of liquid during the winter.

    Next you need to calculate the volume of the refrigerant piping, evaporators and accessories (driers, etc).

    Use the liquid and vapor density at each component's operating condition to find the mass.

    Total all of the mass calculations and you have the total refrigerant charge.

    The receiver is normally sized to provide a volume equal to approximately 125% of the total system charge.

    If you have some components that can trap liquid (maybe the water-cooled condenser), the amount of refrigerant calculated maybe too small.

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    Cool Re: Liquid receiver

    Thanks Ice.

    Renato

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    Re: Liquid receiver

    Croatia is not a EU member yet, do they need to complie then with PED?
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: Liquid receiver

    Quote Originally Posted by NoNickName
    Oh, then I'll stop helping , until you buy the chillers from us.
    NoNickName, he wants a chiller which gives no problems
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: Liquid receiver

    Ok all

    What internal volume is the evaporator and will it need to be pumped out to service.
    I work all out in litres, say the coil has an internal volume of 300litres and it is DX, which would mean a liquid content of 200 litres, then calculate the liquid line volume, won't be much in a chiller add it together and you have the net litres required. The gross volume will be
    300 divided by 6 and multiplied by 7 350 litres gross.

    Hope this helps.

    Generally chiller receivers are sized at 50% of the above, due to the fact that they usually don't pumpdown, if they do the first figure is the one to go for.

    Kind Regards. Andy

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    Re: Liquid receiver

    Quote Originally Posted by Peter_1
    NoNickName, he wants a chiller which gives no problems
    Well, charging 300Kg + of refrigerant is not the way to go for "no problems".

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    Re: Liquid receiver

    Quote Originally Posted by NoNickName
    Well, charging 300Kg + of refrigerant is not the way to go for "no problems".
    300litres would not be 300kg with the given density it would be 360kg aproximately.

    This would not necessarily be a large charge, I have just sized the receiver for what I would call a small 404a blast freezer the net volume is about 700 litres.

    Receiver volume is based on 2/3 of the evaporator volume + the liquid line, NOT the condenser volume, the volume in the condenser is just that, pumping down the system will not change the volume in the condenser or the condensate line.


    Better an oversized receiver with less charge in it rather than a small receiver over charged.

    Kind Regards. Andy

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    Re: Liquid receiver

    Quote Originally Posted by Andy
    Receiver volume is based on 2/3 of the evaporator volume + the liquid line, NOT the condenser volume, the volume in the condenser is just that, pumping down the system will not change the volume in the condenser or the condensate line.
    If you are using head pressure controls to flood an air-cooled condenser, the volume of the condenser does matter.

    You could use the entire volume of the condenser (to calculate the mass of course) if the condenser is operating in very cold weather.

    The liquid has to go somewhere in the summer.

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    Re: Liquid receiver

    Quote Originally Posted by US Iceman
    If you are using head pressure controls to flood an air-cooled condenser, the volume of the condenser does matter.

    You could use the entire volume of the condenser (to calculate the mass of course) if the condenser is operating in very cold weather.

    The liquid has to go somewhere in the summer.
    Never thought of that one

    Again a very good reason for not undersizing the receiver. Generally I would use inverters on the condenser fan rather than back large amounts of liquid into the condenser, reduces the refrigerant charge.

    Kind Regards. Andy

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    Re: Liquid receiver

    Flooding the condenser in winter results in high subcooling, which in turn results in low evaporating temperatures and subsequent low compressor performance. Much better Andy's solution: a chopper or frequency converter on fans.

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    Re: Liquid receiver

    Quote Originally Posted by NoNickName
    ...high subcooling, which in turn results in low evaporating temperatures and subsequent low compressor performance
    I'm not sure how you equate high subcooling values with loss of compressor performance. The lower pressure ratio due to the decreased discharge pressure and the higher net refrigerating effect provide a substantial boost in compressor performance.

    I can see the evaporating temperature dropping a bit, since there is not as much flash gas. But then again, if the compressors have capacity control, this would not be an issue. The compressor would unload and the evaporating pressure would be constant.

    I'm not promoting flooded condensers and discharge pressures, but if you are operating an air cooled refrigeration system in the winter with TXV's you have to do something besides VFD's.

    No argument about the need to reduce the system charge.

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    Re: Liquid receiver

    No, it is not a matter of flash gas... suppose the liquid refrigerant is 40°C in summer, and it is 20°C in winter.
    What would you think the temperature after evaporation would be in the two cases?

    It would be lower in the second case, that would results in lower evaporation pressure and lower suction pressure, and lower compressor performance.

    I personally do not like to flooded condensers, though at standstill liquid migrates from receiver back to condenser. Air cooled chillers here are operated with just VFD, and we have installations in Russia and Finland.

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    Re: Liquid receiver

    Doctors differ patients die

    As far as I can see you are both correct

    The problem is actually TXV's not the head pressure, this do not operate correctly at low pressure drop.

    Flooded condensers are not much used in the circles I travel in, perhaps it's just not cold enough in Ireland in the winter, it just about freezes.

    Large amounts of subcooling increase system cycle efficiency, but cause liquid distribution problems.

    We use EEV's (Danfoss) and float the heat normally.

    where we are employing heat recovery we use the original condenser for subcooling, controlling the heat recovery condenser at 45 deg an dthe subcooled one at 30 deg c, increases the standard comercial type system C.O.P from 2.74 in the summer to 3.38 and only slightly reducing the C.O.P from 3.48 compared to floating head in the winter.

    Kind Regards. Andy

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    Re: Liquid receiver

    Quote Originally Posted by NoNickName
    suppose the liquid refrigerant is 40C in summer, and it is 20C in winter.
    What would you think the temperature after evaporation would be in the two cases?
    OK, let's take a look at this.

    If the mass flow at the evaporating temperature using40C liquid refrigerant is 1 kg/min (just an example number), the 1 kg coming out of the evaporator (at the evaporating pressure) is comprised of the flash gas from 40C to the evaporating pressure. The flash gas will be some percentage of the vapor volume leaving the evaporator. Let's say 15%.

    The remainder of the mass flow (say 0.85 kg ; what's left after the flash gas) is the refrigerant that provides the refrigerating effect in the evaporator. This portion of the mass flow also provides some portion of the total vapor volume leaving the evaporator.

    The total of the two above constitute the entire mass flow out of the evaporator. (0.85 kg + 0.15 kg/minute). The volume flow would then be 1 kg/minute X the vapor specific volume at the evaporating pressure.

    When the liquid temperature is decreased, the amount of flash gas formed decreases. (let's say we are now down to 0.1 kg) We are assuming the evaporating pressure remains constant. (more on this later)

    Since we now have 0.1 kg of flash gas per minute, the mass balance available is 0.9 kg/minute available for cooling.

    The refrigeration effect is increased due to the increased enthalpy difference so we have more capacity available from the remaining 0.9 kg.

    With this we now have 0.9 kg/minute (higher mass flow available that is useful) and the greater enthalpy difference. Therefore the compressor has greater capacity.

    Since the volume of flash gas formed is reduced, and the compressor is a constant volume device (assuming it has no capacity control), you would have a decrease in suction pressure.

    So I agree with you the suction pressure will decrease if the liquid temperature is lowered, if the compressor does not have capacity control.

    If the compressor has capacity control, it should be controlling the suction pressure at a constant pressure.

    The lower volume flow coming from the evaporator will balance with the decreased compressor swept volume that is active at approximately the same pressure.


    Quote Originally Posted by Andy
    The problem is actually TXV's not the head pressure, this do not operate correctly at low pressure drop.
    I agree Andy. The TXV's are the reason for head pressure control in the first place.

    Let me back up a minute and state the older systems I have worked on were before the balanced port TXV's were available for refrigeration. With the older TXV's you had to have good head pressure control to feed liquid on very cold days (say below 0C). Down to this point fan cycling or fan speed control worked just fine.

    However, when the air temperature got down to about -28C, it was a different problem. In this case with the old valves you needed the flooded condenser controls to keep the system running.

    With the new balanced port valves I suspect fan speed control may work just fine.

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    Re: Liquid receiver

    Quote Originally Posted by US Iceman

    So I agree with you the suction pressure will decrease if the liquid temperature is lowered, if the compressor does not have capacity control.
    Good, we came at an agreement.
    Now, suppose the compressor has capacity control. In this case the COP will be increased by the lower mass flow, but it will be decreased by the disproportion of the motor size to the actual mass flow.
    This will also negatively affect the power factor of the plant because

    Quote Originally Posted by BC Hydro hxxp://www.bchydro.com/rx_files/psbusiness/psbusiness1531.pdf
    Factors affecting the power factor of an induction motor are size, speed and load. The larger the
    motor and faster its speed, the higher the full-load
    power factor. The power factor of a motor varies
    according to its load. The higher the percentage of
    the rated load, the higher the power factor.

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    Re: Liquid receiver

    So you agree the flash gas does have something to do with it then???

    Since we are in agreement?

    Quote Originally Posted by NoNickName
    In this case the COP will be increased by the lower mass flow
    Only if you consider the use of all of the heat transfer surfaces and the re-balance that occurs. Since less mass flow is circulating at part load, the suction pressure can be increased slightly and the condensing temperature reduced a little.

    The refrigeration system itself can become more efficient, but when you consider the motor load and power factor with this, the amount of energy used per kg circulated can increase.

    This final effect of this is also determined by the compressor type and if a VFD is used to provide speed regulation. (plus the drive losses too)
    Last edited by US Iceman; 12-04-2006 at 09:01 PM. Reason: editing text

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    Re: Liquid receiver

    I agree on the conclusions, and on the fact that higher subcooling does not equates in better overall performance

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    Re: Liquid receiver

    Quote Originally Posted by NoNickName
    No, it is not a matter of flash gas... suppose the liquid refrigerant is 40C in summer, and it is 20C in winter.
    What would you think the temperature after evaporation would be in the two cases?

    It would be lower in the second case, that would results in lower evaporation pressure and lower suction pressure, and lower compressor performance.
    Haven't read thoroughly the whole thread:
    Liquid 40C in summer and 20C in winter will give a lower evaporationg temperature in winter conditions at the same condensing pressure??
    It will increase the net effect on the evaporator a lot because teh enthaply of the liquid has increased seriously.
    The COP of the compressor will increase with +/-25 to 30% and you're talking about a lower performance?

    The power factor of a motor varies
    according to its load. The higher the percentage of
    the rated load, the higher the power factor
    This is true but it may not be exagerated to much.
    What is then the advantage of the digital scroll?
    And form the unloader valves on larger machines and so many small semi-hermetic machines?

    The net effect you gain by increasing the suction pressure by unloading is by far much higher then the negative effects of increase of the power factor.

    We measured this some 15 years ago on a open 8CC compressor of DWM/Copeland and there was as far as I can remember almost no measurable difference.

    And you pay - at least in Belgium - only the power you consume for smalelr applications, not the apparent power.
    Line current will be a little bit higher but that's all. So if power factor rises, you could say, who cares!?

    I agree on the conclusions, and on the fact that higher subcooling does not equates in better overall performance
    I'm almost sure this is a wrong statement. Will try to simulate this the next days.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: Liquid receiver

    Guys, I'm not talking about a theoretical refrigeration circuit. I'm talking about reality. Suppose you've got a 100kW evaporator (you choose the design temperature, I don't care, it's just for example).
    Now, the liquid in the TEV will decrease its temperature, with the net result of a lower evaporating temperature. Yes, you've got a higher performance for that amount of liquid, and the evaporator will benefit, but it will give still 100kW at the design temperature... or more but at a lower Te.
    Now, suppose you've got more kW to evaporate as a net result of a higher subcooling. The evaporator will react by lowering its average Te. The TEV is a slave of the evaporator and will react accordingly to keep the set SH.
    You see there's no gain whatsoever from a high subcooling IN A REAL CASE.
    If by chance the evaporator was selected with a safety margin, than you'll probably have a benefit, but who really installs evaporators that generous?
    Who cares what the enthalpy gain is, when one cannot take advantage of it. Worst of all: too much enthalpy gain will cause a relative undersizing of the evaporator.

    On another basis: why few to no manufacturers are using subcooling circuits in condensing coils?

    It sounds strange to me that in Belgium you pay for active power. I think the utility company let you pay for kWh+kvarh and not just kWh, like in most parts of the world. And kvarh are more expensive than kWh.

    EDIT: oh, BTW, I wanted to buy digital scrolls from Copeland. They told me they are not on sell.

    EDIT2: as you see, I didn't mention flash gas, because I never ever want to see flash gas in any working conditions. And, my experience teach me that the smaller liquid receiver, the better, eventually no liquid receiver is best, when combined with a good fan speed regulator.
    Last edited by NoNickName; 12-04-2006 at 11:15 PM.

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    Re: Liquid receiver

    On another basis: why few to no manufacturers are using subcooling circuits in condensing coils?
    They cost extra money and no one will buy then!

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    Re: Liquid receiver

    Worst of all: too much enthalpy gain will cause a relative undersizing of the evaporator.
    This might be true if the liquid temperature is lower than the evaporator temperature. Then the liquid entering the evaporator must first be warmed up before it will boil.

    You loose evaporator capacity because the evaporator must warm up the liquid, which takes the place of the phase change surface area and delays the superheating of the vapor.

    There is such a thing as too much subcooling. One I mentioned above. The other is if the TXV capacity is not adjusted for the increase in capacity due to the lower enthalpy.

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    Re: Liquid receiver

    Quote Originally Posted by US Iceman
    This might be true if the liquid temperature is lower than the evaporator temperature. Then the liquid entering the evaporator must first be warmed up before it will boil.
    I'm not expert of flooded evaporators, on the other hand liquid cannot enter the evaporator at all in a DX operation.

    Quote Originally Posted by US Iceman
    There is such a thing as too much subcooling. One I mentioned above. The other is if the TXV capacity is not adjusted for the increase in capacity due to the lower enthalpy.
    How can TXV capacity be adjusted on the fly between summer and winter?

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    Re: Liquid receiver

    Quote Originally Posted by NoNickName
    ...on the other hand liquid cannot enter the evaporator at all in a DX operation
    Sure it does. There is about 85% of the entering liquid which is atomized into droplets after the TXV which enters the evaporator coil. This is where the evaporator capacity comes from in the first place. The balance (+/-15%) is the flash gas created during the expansion process, if the liquid temperature is warmer than the evaporating temperature.

    If the liquid temperature entering the evaporator is lower than the evaporating temperature, the liquid will not boil.

    Quote Originally Posted by NoNickName
    How can TXV capacity be adjusted on the fly between summer and winter?
    You don't. And I'm not suggesting you adjust the TXV's from summer to winter.

    The valves have to be selected for the amount of subcooling that may be found. A selection that meets both operating criteria.

    In a DX system designed for subcooling (which is a good thing to prevent or reduce the flash gas in the liquid lines) the valve capacity must be corrected for the amount amount of subcooling that will be seen.

    The subcooling increases the valve capacity.

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    Re: Liquid receiver

    Quote Originally Posted by US Iceman

    The subcooling increases the valve capacity.
    by a negligible fraction of the TEV design capacity.
    I'm afraid that we have to agree to disagree on this matter.
    But I'm proud to read opinions from such competent forumists.

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    Re: Liquid receiver

    Thank you
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: Liquid receiver

    It's very good discussion
    Many basic concepts are coming out from fuzzy pictures.
    Enough subcooling can prevent flashgas and then affect the valve capacity.
    It should be said that: subcooling prevent valve normal capacity not decrease

    really appreciate master's opinions!
    Wish there's some day to come together to have face to face talk and argument

    rgds
    LC
    I hear...I forget;I see...I remember;I do...I understand

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    Re: Liquid receiver

    Yes,subcooling increase valve capacity.But how can eneywone predict the amount of subcooling for all year condition.During summer subcoling can be 5 K but in the winter 25 K.
    I have to reed some Sporlan bulletin to continue, scuse me.Untill then keep this discusion live.

    Renato

  45. #45
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    Re: Liquid receiver

    Quote Originally Posted by US Iceman
    This might be true if the liquid temperature is lower than the evaporator temperature. Then the liquid entering the evaporator must first be warmed up before it will boil.

    You loose evaporator capacity because the evaporator must warm up the liquid, which takes the place of the phase change surface area and delays the superheating of the vapor.

    There is such a thing as too much subcooling. One I mentioned above. The other is if the TXV capacity is not adjusted for the increase in capacity due to the lower enthalpy.
    Mike,

    What about pump systems where the coil/evaporator is fed with pure liquid. Liquid arives at -10C for a cooling room, so it is injected or fed in the coil at a temperature +/-10 K lower then the room temperature.
    It must be warmed up first before it starts to boil.

    What is the difference?

    The liquid has also a better thermal contact with the copper tubes then a gas/liquid mixture.
    The more surface you can cover with low temperature liquid, the larger the capacity will be.

    And with a TEV, the portion of the liquid that is transformed to flashgas while decreasing the pressure is +/- 30%. The energy to transform this change is taken from the liquid itself.
    The more we feed liquid at evaporating temperature, the less flashgas will form behind the TEV, the more nergy remains in the liquid for a given mass flow, the more surface there will be covered with liquid.

    So, I still remain sceptic with the statement that subcooling not allways increases evaporator capacity.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  46. #46
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    Re: Liquid receiver

    Dossat/Horan say, When liquid refrigerant is subcooled before entering the metering device, the refrigeration effect per unit mass is increased. The example given is the heat removed (6.96btu/lbm). for the saturated cycle, in the example, the refrigeration effect per unit mass is 60.38btu/lbmas shown in a proof11.11 in section 11.6. the proof states for the sub cooled cycle, the refrigeration effect per unit mass, is 67.34btu/lb, a difference of 11.53% This is for actual refrigeration cycle
    This in turn reduces mass flow rate by 10.27% and since the mass flow rate is less for the sub cooled cycle, it follows that the volume of vaporthat the compressor must handle per unit of capacity will also be less. Going on, the compressor displacement required for the sub cooled cycle is smaller then that required for the saturated cycle because the volume of vapor per unit of capacity is less. so the COP will increase by 11.5% in the example.

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    Re: Liquid receiver

    Quote Originally Posted by wambat
    ... so the COP will increase by 11.5% in the example.

    This is the example of how books should not be read.
    In real life we already have a compressor, a TEV and an evaporator, the three chosen for a given SC.
    In case SC is increased, there will be no COP increase and no different mass flow, because the components are still the same.
    The net enthalpy gain will become lower evap. pressure, which in turn becomes as a lower compressor suction pressure, and a lower COP.

    If the manufacturer declares data with 3K SC, please stay with that. Any increase in SC will result in poorer performance for a given chiller.

  48. #48
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    Re: Liquid receiver

    Gee when you write your book ...please let us know, I can always use a good laugh

  49. #49
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    Re: Liquid receiver

    Ok, Let's publish some producers data. I attach the image below. sorry, the catalogue is in Italian, so I will translate for you.

    The capacity of the evaporator must be corrected if the subcooling is different than 4K. the corrected capacity is obtained by DIVIDING the evaporator capacity by the correction factor.

    Eg. 15K 40kW R22, the new evaporator capacity is 40:1.11 = 36kW

    So the evaporator capacity DECREASES as subcooling increases.
    Last edited by NoNickName; 21-03-2008 at 04:22 PM.

  50. #50
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    Re: Liquid receiver

    My intuition told me there's some misunderstanding. I'll think it over and come back.

    thanks for every one endeavour to make it clear.

    rgds
    LC
    I hear...I forget;I see...I remember;I do...I understand

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