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04-12-2002, 01:31 PM #1
TEV capacity related to pressure drop
How is the capacity of a thermostatic expansion valve (Danfoss TEN2, orifice 0X in my case) affected when the pressure drop over the valve decreases?
In my small liquid chiller, measurements showed that with a pressure drop of about 9 bars (temp measured in the center of the condenser: 48 degrees C -> 12.5 bar pressure, evaporating at 3.2 bar measured) , the full open capacity of the valve is about 400W. This fits the datasheet, which says 0.5 kW capacity at 8 bar difference.
But, when the pressure drop over the valve is only approximately 4 bars (temp measured in the center of the condenser: 22 degrees C -> 6.1 bar pressure, evap pressure 1.78 bar measured), full open valve capacity drops below 150W. This does not match the datasheet, which says 0.43kW capacity at a pressure drop of 4 bars.
The full open capacity is measured by adding a known amount of heat to the system using a variable voltage source and a resistive heater element, and adding that to the amount of heat leakage determined earlier. The TEV was set to full open by heating the bulb a bit with a hair dryer.
I have about 15K subcooling at the TEV inlet, so flash gas seems not to be a problem. Is the datasheet wrong? (only 0.07kW less capacity when halving the pressure drop seems a bit odd to me). Do I have another problem somewhere?
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