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    Evaporation Temparature Control: Is it possible?



    Dear Colleagues;
    I am not much experienced in refrigeration, so my following question may seem little naive.

    I know that the pressure difference between an evaporator and a condenser is maintained by the compressors volumetric compression rate and the size of the TEV orifice (at least thats what I think so far). So, for a given compressor and TEV, theorically we have a fixed evap. pressure, am I right? (considering that everything else is kept constant)

    Question is that, is there a way to adjust evap. pressure (and therefore its temperature) so that we could adjust the temparature of the cooled medium? For example, I like to obtain cooled water at a precisely defined temperature. And this temperature may be any thing between 5 to 20C. Cooling load and condenser temperature are assumed to be constant .

    I know that water temperature can be adjusted by on-off control of the compressor, but I think that this may not be a precise way of temperature control.

    I like to thank all of the suggestions or comments ahead of time. Looking forward hearing from you.



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    Re: Evaporation Temparature Control: Is it possible?

    You could utilise an electronic expansion valve to control the evaporator temperature but you must also consider maintaining the cooling of the compressor so some modifications to the basic circuit may be required.

    Valve details here...
    http://www.sporlanonline.com/100-20_092008.pdf
    Brian - Newton Abbot, Devon, UK
    Retired March 2015

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    Re: Evaporation Temparature Control: Is it possible?

    It would be a task to find the correct eva. temperature. If you want to hold water at 5c you have to let the eva. temperature be lower so it could end up icing up the eva. or otherwise wait a day to cool down the water and still have to use an eva. temperature lower than the bath temperature you need.The system should have a good cirkulator to move the water over the eva. to get some decent temperature all over. If not the lower part would be cold and the upper much warmer.
    We trade some waterbaths which use a very exact driven heater and the control by heat is for sure the best way. Those systems can be adjusted inside 0,001c and is controlling inside 0,005c. Your idea is not to reach such a level? Anyway, a controlhead with a pump and heater would give you a pretty good temperature and a good circulation could make a 5c without any freezing up if water is the medium.

    Norseman

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    Re: Evaporation Temparature Control: Is it possible?

    Use of an evaporator pressure regulator to maintain suction pressure above freezing point and compressor thermostat control would give desired control effect.

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    Re: Evaporation Temparature Control: Is it possible?

    Use evaporator pressure regulator( Back pressure regulator valve )to maintain suction pressure
    and to adjust it in (different temperature - delta T) it is better you put one gage on suction line before this valve
    Last edited by mbc; 04-03-2010 at 09:50 AM.

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    Re: Evaporation Temparature Control: Is it possible?

    I like to thank All the colleagues that reply my question.

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    Re: Evaporation Temparature Control: Is it possible?

    Thanks to univer...
    you also several doubts of mine too.. thanks to all above..

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    Re: Evaporation Temparature Control: Is it possible?

    sorry thats UNVER....*

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    Re: Evaporation Temparature Control: Is it possible?

    Unver , we have some systems running at +/-0.2°C in a closed and relative stable circuit.
    Let's say you need 10°C supply, we cool an isolated drum at 5°C with a DT of +/- 2°C.
    A 3-way watervalve (STAEFFA Control) in the return is bypassing some preheated process water to the supply water of 5°C, sensed by a PT100 in the supply

    Or you can use an pressure evaporator regulator and regulate very precise the evaporating temperature, they even exist electrically controlled (Danfoss) http://www.danfoss.com/BusinessAreas...f63b74b82.html
    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: Evaporation Temparature Control: Is it possible?

    Dear Peter;
    Thanks for the mixing valve suggestion. But we were trying to find an alternative solution to that. That was where my original question was originated from.

    But let me ask then, is there an electronically controlled mixing valve in small sizes (about 10cmx10cmx10cm). Motor controlled mixing valves i have seen are usually very big for our 1kW cooling system.

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    Re: Evaporation Temparature Control: Is it possible?

    1 kW is new for us, do it with a controlled hot gas injection, very precise. Keep suction temperatures no too high so that Sh stays within margins
    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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