Page 2 of 2 FirstFirst 12
Results 51 to 91 of 91
  1. #51
    Join Date
    Nov 2010
    Location
    London
    Posts
    625
    Rep Power
    15

    Re: Andy Schoen's Receiver Subcooling Article



    Quote Originally Posted by desA View Post
    Perhaps it's time to begin defining the problem a little more clearly?
    Patients - one thing at a time - things are made more clear by a slow process of eliminating those blury edges stunting our progress here.

    Quote Originally Posted by desA
    Marc, you will need to expound further on this. Please be advised that the Bernoulli equation is applied to flow along a streamline only, by definition & for a single-phase fluid.
    You'll have to wait a few days till I get back home to the comfort of my own desk.

    However - let me put it this way for starters. Are you sure you cannot see any similarility in the principles of physics between a pendulum and, say, an orifice plate - in either air or water?


    Only the dogmatist says he will never change his mind. We all know that some of our opinions are wrong but none of us know which they are for if we did then they just wouldn't be our opinions. - JS Mill.

  2. #52
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: Andy Schoen's Receiver Subcooling Article

    LOL... I tend to make my simulated theoretical pendulums display chaos - even though the gurus say it can't be done...
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  3. #53
    Join Date
    Nov 2010
    Location
    London
    Posts
    625
    Rep Power
    15

    Re: Andy Schoen's Receiver Subcooling Article

    Quote Originally Posted by desA View Post
    LOL... I tend to make my simulated theoretical pendulums display chaos - even though the gurus say it can't be done...
    Come on Des. Because the pendulum is a paradigmic icon - since back with even Galileo - but still especially central to the structure of our current scientific paradigm it is one of the first tools of description and analysis used in any field of physics including chaos theory. Did you read James Gleick?

    The pendulum is a prime tool used in the demonstrations of chaos theory.

    Watch this video to the end

    http://www.youtube.com/watch?v=Qe5Enm96MFQ

    Are you sure you are not just stalling on answering my last question
    Only the dogmatist says he will never change his mind. We all know that some of our opinions are wrong but none of us know which they are for if we did then they just wouldn't be our opinions. - JS Mill.

  4. #54
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: Andy Schoen's Receiver Subcooling Article

    Quote Originally Posted by DTLarca View Post
    Come on Des. Because the pendulum is a paradigmic icon - since back with even Galileo - but still especially central to the structure of our current scientific paradigm it is one of the first tools of description and analysis used in any field of physics including chaos theory. Did you read James Gleick?

    The pendulum is a prime tool used in the demonstrations of chaos theory.

    Watch this video to the end

    http://www.youtube.com/watch?v=Qe5Enm96MFQ

    Are you sure you are not just stalling on answering my last question
    You are confusing the classical 2D pendulum, with a 3D pendulum. Chaos theory requires an additional degree of freedom over that which a 2D pendulum can provide... however... it is a trivial matter to introduce chaos into the 2D classical nonlinear pendulum system.

    James Gleick's book is rather ancient, by now...

    You should attempt to further qualify your assertion of the link between the simple 2D pendulum & whatever you are attempting to prove. The proverbial ball is now in your court... Let your infinite wisdom proceed to shine...

    Personally, though, I would prefer you to set the process conditions for your receiver problem, so that detailed process modeling & simulation can proceed. I suspect that we'll be able to provide a few insights into your earlier dilemma.
    Last edited by desA; 29-12-2010 at 06:48 AM.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  5. #55
    Join Date
    Nov 2010
    Location
    London
    Posts
    625
    Rep Power
    15

    Re: Andy Schoen's Receiver Subcooling Article

    Quote Originally Posted by desA View Post
    You are confusing the classical 2D pendulum, with a 3D pendulum.
    It doesn't really matter - how many components the pendulum has - does it?

    The fact is there actually is no chaos in any of them - as the Gleick example illustrates - you will always find, from some perspective, a pattern in the chaos - chaos is only apparent. Put it this way - pendulums - all types - obey the laws we use to describe how nature goes - they cannot go any other way.

    Quote Originally Posted by desA View Post
    Chaos theory requires an additional degree of freedom over that which a 2D pendulum can provide... however... it is a trivial matter to introduce chaos into the 2D classical nonlinear pendulum system.
    Which was demonstrated in the video I linked to

    Quote Originally Posted by desA View Post
    James Gleick's book is rather ancient, by now...
    But not refuted

    Quote Originally Posted by desA View Post
    You should attempt to further qualify your assertion of the link between the simple 2D pendulum & whatever you are attempting to prove. The proverbial ball is now in your court... Let your infinite wisdom proceed to shine...
    Yes - I would like to discuss gas and liquid pendulums (Newton and Bernoulli) - especially liquid to eliminate a concern that Mad Fridgie has.

    Quote Originally Posted by desA View Post
    Personally, though, I would prefer you to set the process conditions for your receiver problem, so that detailed process modeling & simulation can proceed. I suspect that we'll be able to provide a few insights into your earlier dilemma.
    We know we cannot achieve subcool in say a shell and tube condenser on, for instance, a water cooled centrif which has no liquid capturing tube at the bottom of the condenser still exposed to the condenser water - we have instead a low side float valve or even a high side fload valve.

    We are talking serpentine condenser coils per the article being examined here.

    Certainly 4K Subcool tends to be quite the normal thing on a serpentine condenser with receiver and site glass. 6K is achievable at full design load. Although with electronic expansion devices the subcool remains pretty constant through all load conditions because they do not have the capacity/superheat curve that TEV's do.
    Only the dogmatist says he will never change his mind. We all know that some of our opinions are wrong but none of us know which they are for if we did then they just wouldn't be our opinions. - JS Mill.

  6. #56
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: Andy Schoen's Receiver Subcooling Article

    Quote Originally Posted by DTLarca View Post
    It doesn't really matter - how many components the pendulum has - does it?

    The fact is there actually is no chaos in any of them - as the Gleick example illustrates - you will always find, from some perspective, a pattern in the chaos - chaos is only apparent. Put it this way - pendulums - all types - obey the laws we use to describe how nature goes - they cannot go any other way.
    Would your pendulum be of the linear, or non-linear variety?

    The observed effects of chaos are purely because the viewers have missed an important component in correctly visualising the complete description of the motion. The so-called chaos effects all suffer from the same fundamental mistake. In fact, the answers to chaos theory is incredibly trivial, if only the mathemagicians would bother to correctly review their knowledge of functions. I'll elaborate more on this aspect in a later paper.

    So now, would you like to proceed to draw the analogy between pendula & your refrigeration system?
    Last edited by desA; 29-12-2010 at 02:47 PM.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  7. #57
    Join Date
    Nov 2010
    Location
    London
    Posts
    625
    Rep Power
    15

    Re: Andy Schoen's Receiver Subcooling Article

    Quote Originally Posted by desA View Post
    Would your pendulum be of the linear, or non-linear variety?
    Both, Des, they both can only have apparent chaos - to be truly chaotic they would have to occur outside of the current natural descriptions of how our mechanical surroundings go - that is they would have to defy the universal laws of physics.

    If a computer can simulate a non-linear pendulum then it would be demonstrating predictive powers which could not be if there was chaos. Where something can be predicted - simulated - then there will also be patterns.

    Let me quote another source to back up my argument:

    Quote: "The observed effects of chaos are purely because the viewers have missed an important component in correctly visualising the complete description of the motion. The so-called chaos effects all suffer from the same fundamental mistake.

    Quote Originally Posted by desA View Post
    So now, would you like to proceed to draw the analogy between pendula & your refrigeration system?
    Indeed, I will, firstly, are you sure you do not see pendulum principles in an orifice plate?
    Last edited by DTLarca; 29-12-2010 at 03:29 PM.
    Only the dogmatist says he will never change his mind. We all know that some of our opinions are wrong but none of us know which they are for if we did then they just wouldn't be our opinions. - JS Mill.

  8. #58
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: Andy Schoen's Receiver Subcooling Article

    Quote Originally Posted by DTLarca View Post
    Indeed, I will, firstly, are you sure you do not see pendulum principles in an orifice plate?
    Please proceed to enlighten us...
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  9. #59
    Join Date
    Nov 2008
    Location
    Canada
    Posts
    24
    Rep Power
    0

    Re: Andy Schoen's Receiver Subcooling Article

    If one believes that you can put subcooled liquid into a receiver, and take subcooled liquid out of the receiver.
    This happens quite often. it happens when the receiver is liquid full.

    On a receiver that has gas /liquid mixture in it. If there is subcooled liquid entering the receiver, by definition the saturated liquid must be warmer... ( subcooled is colder than saturation. )
    Therefore for this to be true we would have to believe that it is possible to put cold refrigerant into the receiver, take cold refrigerant out, yet maintain the receiver at a higher temperature (saturated), but we add no heat. hmmmm...

    One interesting thing that I used to do when I taught refrigeration, was throttle a ball valve until I had bubbles in the sight glass. (saturated) I would cover the sight glass and have students fasten thermisters and gauges to the liquid line and measure the subcooling. Typical measured values would be 4 to 5 degrees subcooling.


    Yes I believe that you can measure subcooling coming out of a saturated receiver. I believe that this is a very common measurement.
    I dont however believe that this is true.

  10. #60
    Join Date
    Nov 2010
    Location
    London
    Posts
    625
    Rep Power
    15

    Re: Andy Schoen's Receiver Subcooling Article

    Quote Originally Posted by research View Post
    If one believes that you can put subcooled liquid into a receiver, and take subcooled liquid out of the receiver.
    This happens quite often. it happens when the receiver is liquid full.
    I like your Avatar - a PVT chart

    So you are saying that a sight glass - especially when located after a filter drier - that is located on a vertical rise up from the dip-tube from a receiver - must always flash?
    Only the dogmatist says he will never change his mind. We all know that some of our opinions are wrong but none of us know which they are for if we did then they just wouldn't be our opinions. - JS Mill.

  11. #61
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: Andy Schoen's Receiver Subcooling Article

    I like to use the example of a half full refrigerant container on a block of ice with a heating pad on top. There is superheated vapor on top, subcooled liquid on the bottom and saturation at the vapor/liquid interface. It is entirely possible to have superheat, subcooling and saturation all within the same container.

  12. #62
    Join Date
    Nov 2010
    Location
    London
    Posts
    625
    Rep Power
    15

    Re: Andy Schoen's Receiver Subcooling Article

    Quote Originally Posted by Gary View Post
    I like to use the example of a half full refrigerant container on a block of ice with a heating pad on top. There is superheated vapor on top, subcooled liquid on the bottom and saturation at the vapor/liquid interface. It is entirely possible to have superheat, subcooling and saturation all within the same container.
    Indeed, if the middle of the same container is at the triple point of the substance in question, which is located around the bottom left hand third of research's avatar, which is a PVT diagram of a substance that contracts on freezing (not water) then we could have a superheated vapour at the top, then going downward it could/would be saturated vapour, saturated liquid, subcooled liquid and finally "ice" or solid then finally a subcooled solid.
    Only the dogmatist says he will never change his mind. We all know that some of our opinions are wrong but none of us know which they are for if we did then they just wouldn't be our opinions. - JS Mill.

  13. #63
    Join Date
    Nov 2010
    Location
    London
    Posts
    625
    Rep Power
    15

    Re: Andy Schoen's Receiver Subcooling Article

    The PVT chart in research's avatar even depicts how ice has a vapour pressure - otherwise we could not have humidities of any degree whenever the atmosphere and ground were below freezing

    This is depicted along the bottom 3rd of the PVT diagram.
    Only the dogmatist says he will never change his mind. We all know that some of our opinions are wrong but none of us know which they are for if we did then they just wouldn't be our opinions. - JS Mill.

  14. #64
    Join Date
    Nov 2008
    Location
    Canada
    Posts
    24
    Rep Power
    0

    Re: Andy Schoen's Receiver Subcooling Article

    If the process was adiabatic with pressure drop.

    Yes the glass would bubble.


    However, The copper pipe rejects heat quickly.
    and it takes very little subcooling to overcome the small pressure drop of a drier, and a few feet of rise.

    With R134a, for a pressure loss of 2 psig, we would need less than 1 degree subcooling.
    For R410A a loss of 2 psig would need less than 1/2 °F subcooling.

    This is all that is required to keep the sight glass from bubbling.

    There can also be a 'small' amount of subcooling in the receiver as heat is lost through the bottom of the receiver to ambient and there is a small static head. This is small but can still overcome small pressure drops.


    There are countless applications with a drier sight glass located at the receiver that work just fine with clear glasses.

    However there are also some with receivers that must be almost liquid full before the glass will clear.

  15. #65
    Join Date
    Nov 2008
    Location
    Canada
    Posts
    24
    Rep Power
    0

    Re: Andy Schoen's Receiver Subcooling Article

    Even a simple ***** tank sitting in the sun can have superheated vapor on top, saturated in the middle, and subcooled on the bottom.
    Momma nature has no problems with that.

    However this system is static.
    Heat is added to the top. vapor is superheated.
    Liquid vapor iterface is saturated,
    liquid on the bottom can be cooler.. subcooled.
    no problems.

    If you were to pump the subcooled liquid out of the bottom of the tank and back into the top. and have the subcooled liquid travel through the superheated gas, then the liquid vapor interface and remove any sources of heat transfer, other than the liquid being pumped.
    I think that the temperature would end up the same everywhere. saturated.

    On a working system, I believe that there can be "small" amounts of subcooling in the bottom of a receiver, as there is a static increase in pressure, and the tank is warmer than ambient. However must emphasize small.

    I have been in this industry 40 years, and have changed my belief system on receivers several times.
    I guess that is why I love this industry so much.

    Isn't it amazing that the simplest piece of equipment on a refrigeration system, (it is basically just a pregnant pipe) can be such a difficult thing to understand. And that leaders in the industry can have such different opinions on the subject.

  16. #66
    Join Date
    Aug 2009
    Location
    New Zealand
    Age
    59
    Posts
    2,556
    Rep Power
    26

    Re: Andy Schoen's Receiver Subcooling Article

    Regardless if you have small or large amonts of sub cooling, it comes down to how you measure. My argument comes from those who measure discharge pressure and liquid temperature to give sub cooling. You must measure pressure and temp at the same point.

  17. #67
    Join Date
    Nov 2008
    Location
    Canada
    Posts
    24
    Rep Power
    0

    Re: Andy Schoen's Receiver Subcooling Article

    Quote Originally Posted by mad fridgie View Post
    Regardless if you have small or large amonts of sub cooling, it comes down to how you measure. My argument comes from those who measure discharge pressure and liquid temperature to give sub cooling. You must measure pressure and temp at the same point.
    Absolutely....

    100% agreement...

  18. #68
    Join Date
    Nov 2010
    Location
    London
    Posts
    625
    Rep Power
    15

    Re: Andy Schoen's Receiver Subcooling Article

    Quote Originally Posted by research View Post
    If the process was adiabatic with pressure drop.

    Yes the glass would bubble.


    However, The copper pipe rejects heat quickly.
    and it takes very little subcooling to overcome the small pressure drop of a drier, and a few feet of rise.
    What are the numbers?

    Do you agree or disagree that even with between 2 and 3K measured subcool we can see vapour carry-over in a sight glass - especially with receiver-less systems and especially with liquid line velocities above 0.5m/s?
    Only the dogmatist says he will never change his mind. We all know that some of our opinions are wrong but none of us know which they are for if we did then they just wouldn't be our opinions. - JS Mill.

  19. #69
    Join Date
    Nov 2008
    Location
    Canada
    Posts
    24
    Rep Power
    0

    Re: Andy Schoen's Receiver Subcooling Article

    Quote Originally Posted by DTLarca View Post
    What are the numbers?

    Do you agree or disagree that even with between 2 and 3K measured subcool we can see vapour carry-over in a sight glass - especially with receiver-less systems and especially with liquid line velocities above 0.5m/s?
    I agree that there can be flashing vapor is subcooled liquid. However this is a function of time. Vapor bubbles transfer heat poorly, and once created take time to collapse.
    The proof is simple. Cavitating propellers are simply creating flash gas by the reduction of pressure.
    This link clearly shows flash gas in subcooled liquid.
    wikipedea under cavitation
    it wont let me post a url. so i have removed the link

    Submarines can cavitate propellers at great depths. often subcooled more than 150°F .


    The dynamics of receivers is very complex, and is rarely static.

    I do not agree with the theory presented in Andy Shoens article.

  20. #70
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: Andy Schoen's Receiver Subcooling Article

    Quote Originally Posted by research View Post
    On a receiver that has gas /liquid mixture in it. If there is subcooled liquid entering the receiver, by definition the saturated liquid must be warmer... ( subcooled is colder than saturation. )
    Therefore for this to be true we would have to believe that it is possible to put cold refrigerant into the receiver, take cold refrigerant out, yet maintain the receiver at a higher temperature (saturated), but we add no heat. hmmmm...
    That is the essence of it. For some part of the system to be at higher temp than the surroundings, heat-transfer will take place. Practically, the heat-transfer between atmosphere & vessel should be understood.

    The way in which the system boundary is selected, will be important i.e. the macro-picture is important. These decisions are pretty much forced on you, if a process simulator is used. Here we install in/out conditions onto a receiver vessel - can include a pre-valve as well - then study how the system reacts. The flash processes in the receiver are also included.

    This is why I suggested that the exercise be reduced to a simulation & the results be interrogated. All of the many possible scenarios can be shown.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  21. #71
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: Andy Schoen's Receiver Subcooling Article



    I have extended the model of the sub-cooled liquid feeding through a restriction, then into the receiver (flash vessel) - with vapour & liquid take-offs.

    If someone would like to firm up the simulation scenarious, I'd be happy to proceed with a range of simulations, which could prove very informative & put a number of myths to bed.

    Propose :
    R-134a ; Tc,sat = 65'C ; SC=3K ; T,liq,in = 62'C @ 1.89 MPa; adiabatic (insulated) receiver.

    We will then gradually increase the valve restriction & observe what occurs in streams 2, 3, & 4.
    Last edited by desA; 23-01-2011 at 08:51 AM.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  22. #72
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: Andy Schoen's Receiver Subcooling Article



    Varying dP across valve. Temp & vapour fraction at valve exit.

    At present simulated as unhindered vapour feed off top of receiver - doesn't affect action across the valve/restriction. We can discuss further cases after this e.g. high-pressure balance pre-condenser.

    So, depending on where the system is measured, the receiver exit could show deep sub-cooling.
    Last edited by desA; 23-01-2011 at 11:43 AM.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  23. #73
    Join Date
    Nov 2008
    Location
    Canada
    Posts
    24
    Rep Power
    0

    Re: Andy Schoen's Receiver Subcooling Article

    So, depending on where the system is measured, the receiver exit could show deep sub-cooling.[/QUOTE]

  24. #74
    Join Date
    Nov 2008
    Location
    Canada
    Posts
    24
    Rep Power
    0

    Re: Andy Schoen's Receiver Subcooling Article

    Quote Originally Posted by desA View Post



    So, depending on where the system is measured, the receiver exit could show deep sub-cooling.
    This is a very interesting statement. As mad fridgie has said earlier, it depends on where you measure your values.
    The graph presented clearly shows a vapor mass fraction (shown in pink) if there is vapor and liquid present at the same temperature and pressure. If there is liquid and gas together, by definition the mixture is saturated.

    Suppose we measure the pressure before the throttling valve and the temperature after. Could we theoretically determine that the mixture is subcooled? Yes we could, however, this would be incorrect.
    The properties of a substance must be measured at a single point to determine the state of the substance.


    The true conditions in a receiver are very complex. Most simulations attempt to model the receiver as a STATIC entity. This is seldom true.
    The flow through a operating receiver is very seldom static.
    Example. The TX valve or metering device on a system typically will open and close according to conditions it sees at the evaporator outlet. It does not communicate to the receiver when it will open or close. Therefore the flow at the outlet of a receiver will change in response to the opening and closing of the metering device. (tx valve).

    The flow INTO a receiver is a function of how fast the gas pumped by the compressor is being condensed and drained into the receiver. Therefore at any given time, the flow rate into and out of the receiver are not the same.
    This has many implications on the dynamics in the receiver.

    If the discharge pressure in a system is not stable (ie windy day) The pressure can slowly rise and than fall. Interesting things happen.
    (I have seen many systems where the discharge temperature will hunt 25psig (250 to 275) and then back again over 5 minute intervals.)

    When the discharge pressure drops, the receiver pressure drops and the liquid line pressure drops. With a drop in pressure all saturated liquid must boil. (again definition)

    It is not uncommon to see flashes of bubbles in the liquid line at this time. What causes the bubbles is that the temperature of the liquid must also drop. (cannot have liquid at a temperature above its boiling temperature)
    The bubbles are cause by the liquid self cooling because of the pressure drop.

    When the pressure in the system starts to rise, it rises in the receiver, liquid line etc. We are changing the conditions.

    The TEMPERATURE of the liquid in the receiver will not change without the addition of heat. So as the pressure increases the saturation temperature increases, the actual temperature stays the same, and the liquid is subcooled.

    The explanation by andy shoen is of a static system. One where a cold liquid enters a warmer tank. The cold liquid leaves, but the surface of the liquid in the tank stays warm. AND, there is no external energy added to the system.

    My current position is that andys explanation is incorrect.

  25. #75
    Join Date
    Nov 2010
    Location
    London
    Posts
    625
    Rep Power
    15

    Re: Andy Schoen's Receiver Subcooling Article

    If you are not measuring the pressure at the same frictional and elevational point as you are measuring your temperature then you are NOT measuring subcool. If you measured your pressure somewhere frictionally and statically different from where you measure your temperature then to derive subcool you will have do some compensatory calculation (liquid pendulum).
    Only the dogmatist says he will never change his mind. We all know that some of our opinions are wrong but none of us know which they are for if we did then they just wouldn't be our opinions. - JS Mill.

  26. #76
    Join Date
    Nov 2008
    Location
    Canada
    Posts
    24
    Rep Power
    0

    Re: Andy Schoen's Receiver Subcooling Article

    In my lab, I have set up a test jig to test this principal.
    i took an air conditioner i was testing and installed a sporlan ORI (open on rise of inlet) head pressure control, a Sporlan ORD4 (open on rise of differential) discharge bypass valve. and a receiver. I put multiple sightglasses on the system to see the refrigerant at various points of interest

    R407C air conditioning system with a flooded head pressure control.


    The system is a Ten ton roof top air conditioning system. I tapped into the liquid line after the condenser, and piped the liquid line to a receiver mounted external to the unit. The piping from the condenser to the receiver is through a Sporlan ORI 10, I installed a sight glass immediately at the outlet of the ORI . To control saturated conditions entering the receiver, i installed an ORD4-30 with a ball valve to shut it off, between the discharge line and the condensate line after the ORI sight glass.
    After the ORD connection, into the condensate line I installed another sight glass so I could see the refigerant entering the receiver.
    At the outlet of the receiver there is another sight glass installed.
    Flow
    Compressor....discharge line....TEE1.....into condenser.. turn to liquid... into subcooler circuit..... out of condenser..... into liquid line...into ORI 10....into sightglass1....TEE2.....into sightglass2....into receiver......receiver outlet.....sightglass 3. liquid line... TX valve ...Distributor.... evaporator.... suction line...compressor.

    Bypass gas ... Discharge line TEE1.... Ball valve ...ORD4-30... into TEE2.

    This is set up exactly like a low ambient air conditioning system, except that I left the subcooling circuit in the condenser (the condenser has subcooling circuits integral to the coil), to demonstrate the issues with subcooling before receivers.

    The receiver is a Westermyer receiver 6" diameter, and 60 inches long.

    The system was evacuated and charged with refrigerant to a clear sight glass leaving the receiver. At this point the receiver was "torched" and an operating level was determined and marked on the side. This is done to ensure that the system was not overcharged and operating with a liquid full receiver.

    Normal operation
    Sight glass 1

  27. #77
    Join Date
    Nov 2008
    Location
    Canada
    Posts
    24
    Rep Power
    0

    Re: Andy Schoen's Receiver Subcooling Article

    Normal operation With low ambient...Ord operating
    Sight glass 1 (ORI) Sight glass 2 (into receiver) Sight glass 3 (Out of receiver)
    Clear bubbly clear
    If I shut off the ORD valve
    CLEAR CLEAR Bubbly

    If I adjusted increased the ambient in the test chamber. ORI open.... ORD closed

    CLEAR CLEAR Bubbles... clear
    OSCILLATING in 1 to 3 minute hunts.

    These tests were repeatable and consistent. The affect on the system when the liquid bubbles were oscillating was that the TXvalve was also hunting as it tried to accommodate the changing head pressure and the affects of the bubbles.

    When subcooled liquid entered into the receiver, the outlet sightglass would bubble and then clear and then bubble and then clear and then bubble and then ..... etc.....etc.....etc....

    The ONLY way to stop this, was to add refrigerant until the liquid receiver was full.. (90%+)
    Then Sightglass 1 was clear, sight glass 2 was clear, sightglass 3 was clear.

  28. #78
    Join Date
    Mar 2009
    Location
    U.S.A.
    Posts
    320
    Rep Power
    20

    Re: Andy Schoen's Receiver Subcooling Article

    That was some Christmas Eve you boys had!

    And you can preserve subcooling coming from a condenser, all the way to the point of expansion....Tube in Tube arrangement at Through Type receiver will come close, but not for more than about 10-deg K of SC and even then not with a free draining arrangement. Surge Type receiver will let cold liquid go right by it and still maintain liquid pressures....It is one way to utilize condensers on a big circuit during the winter months. Flood the smallest condenser in reverse flow (or even one section of a split) and your liquid delivery temp at the expansion device will be withing 5-deg of the ambient. Maybe not good for a TXV but frequently works very well with motor driven expansion valves, etc.

  29. #79
    Join Date
    Nov 2008
    Location
    Canada
    Posts
    24
    Rep Power
    0

    Re: Andy Schoen's Receiver Subcooling Article

    Yep..
    If you want subcooling and you want a receiver, then you either need a receiver then a subcooler.... OR
    you need a subcooler and a surge receiver.
    Surge receivers work great when properly applied.

  30. #80
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: Andy Schoen's Receiver Subcooling Article

    Thanks very much 'research' for a fascinating experiment.

    I'm most interested in the thermal oscillations in the system dynamics. Could you please elaborate a little further on the TXV control strategy used? Standard, MOP, cross charge etc.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  31. #81
    Join Date
    Nov 2008
    Location
    Canada
    Posts
    24
    Rep Power
    0

    Re: Andy Schoen's Receiver Subcooling Article

    The test unit is located in our environmental test chamber. The ambient temperature is controlled to a very stable 95°F. The evaporator air is ducted from another environmental room controlled to a temperature of 80°F/67WB. as per ARI standard 340/360. The static across the unit is controlled and the supply air temperature is ducted through parabolic nozzles to measure air flow. As per the standard. We are typically measuring capacity and EER of our systems.
    All conditions through the air conditioning system are controlled and are stable.

    When running a test, we monitor pressure and temperatures with a data logging system. there are 40 temperature channels and twenty analog channels for pressure, power, and process monitoring. All channels are fed into a computer with using LABVIEW to analyze the data.

    Without the receiver, the saturated pressures and subcool/superheat temperatures are extremely stable. Flat line on the graphs. We are using a standard TXV with a 100psi MOP. Typical settings superheat= 12°F. Subcooling = 10°F.
    (these can be changed depending on the tests we are doing) but stable once adjusted.

    When our company uses a flow-through receiver, we always size the condensate line for sewer flow and free drain down to the receiver as per recommendations in ASHRAE REFRIGERATION HANDBOOK. All subcooling circuits are piped after the receiver. These systems are extremely stable and reliable.


    To test the affects of subcooling BEFORE the receiver, we put a receiver on a 10 ton rooftop unit with integral subcooling circuits in the condenser. The receiver was mounted on the back wall of the environment chamber. The line entering the receiver was liquid line size, and the receiver was not vented.

    When the receiver was added we were just interested in the affects of subcooled liquid entering a flow through receiver.

    The environmental room conditions were stable but unfortunately, as this was not a specific test, the data acquisition system was not connected. (it takes a couple of days to set up)

    When the ORI/ORD were active, the system was stable. Constant Head pressure, constant suction pressure.

    The ORI was adjusted to a low pressure (IE OPEN) and the ORD bypass was shut off.

    This allowed subcooled liquid to enter the receiver. This causes a periodic change in the head pressure.

    Approximately 10-15psi change in head pressure (275sig=>265psig=>275) The pressure would drop fairly quickly then rise slowly over a 2 to 3 minute period. The TX valve would get bubbles, then would correct by opening, then would get clear liquid, overfeed then close. The suction pressure fluctuated 2 to 5 psig with the head pressure. Although not in sync. The conditions in the environment room were stable, and airflows were constant.

    The fluctuations in head pressure were thought to be a function of the dynamics of the subcooled liquid entering the receiver only.

    A change in the receiver saturation temperature of 2°F will cause a change in the receiver pressure of (115°=274.9psig 113°=267.5psig delta2°=7.4psig.)

    The system was watched and the following is our belief of what was happening.
    It was felt that when the liquid line bubbled, the txv would open, thus increasing flow in the liquid line, reducing pressure slightly, thus making more bubbles. When the valve finally opened enough to stabilize the evaporator superheat, the valve would close. This reduced liquid line flow, reduced bubbles, sightglass would clear. Flow from the receiver would be reduced. As the receiver was not vented, flow INTO the receiver would then be reduced as well. This increases subcooling in condenser. Subcooled liquid then enters the receiver. Receiver temperature drops several degrees. High side pressure drops everywhere by 7 -10 psig. Saturated liquid in the liquid line drops pressure therefore flashes. TX valve opens to compensate. Cycle repeats over and over.

    This is what I believe is happening. This phenomenon was repeated over and over again. We demonstrated this affect to several of our designers and service people. The unit was then removed to make room for real testing.

  32. #82
    Join Date
    Aug 2009
    Location
    New Zealand
    Age
    59
    Posts
    2,556
    Rep Power
    26

    Re: Andy Schoen's Receiver Subcooling Article

    "research" very good info. It would have been interesting to compare the R407 with say R22, and how glide (or lack of it) would have influence your TEV control, would your hunting swings be as large (diff in presuure) and would the time of each cycle be quicker (my thought) or slower. What is also interesting is how do you size your expansion device. Many suppliers are now suggesting over sizing TEVs for the R4*** based refrigerants, this suggests that they seem to expect some level of vapour entrapment in the liquid feed to the TEV. (normally oversized TEVs cause hunting) One evap manufacturer says he is seeing systems that are correctly sized,(good theoretical balance of equipment) actually running lower SST and higher superheats, indicating that the evaps are actually being starved. (he had been called in as the systems did not seem to perform as indicated, and the evap design had been called into question)

  33. #83
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: Andy Schoen's Receiver Subcooling Article

    Excellent review. Thank you.

    Flash dynamics versus TXV response characteristic. Would be interesting to see how a 'tuned' EEV would perform.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  34. #84
    Join Date
    Nov 2008
    Location
    Canada
    Posts
    24
    Rep Power
    0

    Re: Andy Schoen's Receiver Subcooling Article

    On our units, the TX valve are selected using manufacturers extended capacity tables. we've had good luck so far.


    We evaluated Electronic expansion valves (EEV) last year. We found that they can be dialed in when conditions are stable and give extremely good performance. However we were using them on the Danfoss VSH 088 variable speed scroll compressor and could not find a suitable PID setting to stablilize the EEV over the wide capacity range of the compressor. (4 to 12 tons) We tried two valves, one valve, and then we tried an off the shelf, old fashioned dual ported TX valve.
    We found that overall the old fashioned standard TX valve gave better overall performance.
    At a specific capacity we could tune the EEV to give better performance. But found that it would hunt when the capacity changed. This was felt to be not the fault of the TX valve but of the PID control loop not adapting to the variable loading.

    The standard old TX valve gave equivalent or better performance over the entire range of capacity.
    We now uses standard dual ported TX valves on all our variable compressor applications and have had very good success with them. They are also easier to understand for the average mechanic and therefor we have less service issues.

    note, this was for variable speed compressors, when we use the Digital scroll, the electronic expansion valve is required.

  35. #85
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: Andy Schoen's Receiver Subcooling Article

    We found that overall the old fashioned standard TX valve gave better overall performance.
    At a specific capacity we could tune the EEV to give better performance. But found that it would hunt when the capacity changed. This was felt to be not the fault of the TX valve but of the PID control loop not adapting to the variable loading.
    Agreed. PID loops have definite limits, unless they are well understood - especially in tracking control problems.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  36. #86
    Join Date
    Nov 2010
    Location
    London
    Posts
    625
    Rep Power
    15

    Re: Andy Schoen's Receiver Subcooling Article

    Here's an example of the sort of flow through receiver Calvin uses. The subcool cyclic pattern occurs here too unless you have both stable condenser capacity control (inverters with clever PID algorithms) and stable TEV/EEV operation. Of course the larger the receiver volume in relation to the system capacity the better.

    exhibition 049.jpg
    Only the dogmatist says he will never change his mind. We all know that some of our opinions are wrong but none of us know which they are for if we did then they just wouldn't be our opinions. - JS Mill.

  37. #87
    Join Date
    Nov 2008
    Location
    Canada
    Posts
    24
    Rep Power
    0

    Re: Andy Schoen's Receiver Subcooling Article

    DTLarca

    That receiver looks like a pumped refrigerant assembly... It also look like a quality job.
    Who sells that??

  38. #88
    Join Date
    Jan 2008
    Location
    Somerset
    Posts
    77
    Rep Power
    17

    Re: Andy Schoen's Receiver Subcooling Article

    Yeah. That looks like a Liquid Pressure Amplification (LPA) set up.


    lpa R1[1].pdf

    I believe in recent years, it's starting to be used a lot more on bigger systems in the UK. It allows the head pressure to be reduced considerably to improve the energy efficiency of the system, but uses the pump to maintain the liquid pressure to the expansion device.

    Rule of thumb - For every 1k we lower SCT = 3% decrease in energy consumption.

    Apparently, by reducing the condensing temperatures by 15-20'c can see energy savings of 30-40%.

    http://www.acr-news.com/news/news.asp?id=1507

  39. #89
    Join Date
    Nov 2010
    Location
    London
    Posts
    625
    Rep Power
    15

    Re: Andy Schoen's Receiver Subcooling Article

    Research, Calvin Bekker, originally from Durban South Africa but now here in the UK, owns the patents. His website is...

    http://www.hysave.com/

    Even with head pressures floated lower - EEV's tend not to need the pressure boost given by the pump so the pump is generally not needed for close coupled systems so long as the drainage from condenser to EEV is cleverly thought-out. But for remote evaporators either at the same level as the receiver or higher than the receiver you need a liquid delivery system to ensure a solid bore of liquid is delivered to the expansion device inlet at all times. None the less stable EEV and Condenser capacity is still required though less so than without the delivery system. The Assembly in the image is simply called a Liquid Delivery System or LDS.
    Only the dogmatist says he will never change his mind. We all know that some of our opinions are wrong but none of us know which they are for if we did then they just wouldn't be our opinions. - JS Mill.

  40. #90
    Join Date
    Nov 2008
    Location
    Canada
    Posts
    24
    Rep Power
    0

    Re: Andy Schoen's Receiver Subcooling Article

    Thanks

    looks good.

  41. #91
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    62
    Posts
    5,645
    Rep Power
    34

    Re: Andy Schoen's Receiver Subcooling Article

    Quote Originally Posted by mad fridgie View Post
    Regardless if you have small or large amonts of sub cooling, it comes down to how you measure. My argument comes from those who measure discharge pressure and liquid temperature to give sub cooling. You must measure pressure and temp at the same point.
    Was searching for something on RE and stumbled on this post of MF within this thread some posts back.
    Sorry to re-open it a little bit but I think my experiences an/or visions can throw (perhaps) some light on this issue.
    Or make it even more confusing.

    You're right MF when you say that you must measure pressure and temperature at the same point but you have also to take in account the measuring fault of your thermometer.

    Same remark for DTLArca when measuring SC with - sorry - the rubbish Refco digital manifold (we have 3 of those and rarely use those any longer)
    The temperature measured on the outside of a pipe - even a copper pipe - is never on the same actual temperature of the liquid flowing in that pipe.

    When we take F-gas exams, we even monitor if the candidates are aware of this measuring error.

    If you measure right after the TEV or on the first bend of an evaporator, then you should measure exactly Te (given no Dp on the evaporator)
    Then, if you measure the bends on a condenser (not the beginning an not the end of course and neglect Dp) - like in the video of Monkey Spanners - then you should measure exactly your condensing temperature.

    You will find out you never will measure the correct Te and Tc and you will notice differences of 2 to 4K.
    Let this now be the amount of measured SC on the outside of a copper tube.

    This is for me the measuring error, partly due to thermal resistance of the copper and partly due to a measuring error of the instrument and partly due to the temperature probe.

    Therefore, processes which needs very accurate temperature measurements always have immersed probes and many times in a bend where there's a good contact with the flowing liquid.

    PS: the small digital meter from Monkey Spanners is a cheap infrared meter which works very well on black surfaces. When you need to measure Stainless steel , color it first with a black marker. I have the opportunity in evening classes to buy all these things/gadgets and test them while been paid for it. And find solutions for it.
    We also found out something where you can optimize pressure testing with nitrogen and where I never saw this method in books. Will make a separate post for this.
    Last edited by Peter_1; 10-07-2011 at 02:19 PM.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

Page 2 of 2 FirstFirst 12

Similar Threads

  1. Superheat and Subcooling
    By Chunk in forum Fundamentals
    Replies: 42
    Last Post: 15-01-2011, 02:24 AM
  2. Auxilary receiver to increase subcooling?
    By liptow in forum Fundamentals
    Replies: 21
    Last Post: 27-11-2009, 05:30 AM
  3. Replies: 9
    Last Post: 21-05-2006, 06:24 PM
  4. Subcooling & Refrigerants
    By US Iceman in forum Fundamentals
    Replies: 40
    Last Post: 29-04-2006, 02:59 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •