Converting a TEV into a heat motor operated EEV

[DaBit]

I am still looking for some form of affordable electronic expansion for my overclocking related systems. This will use R410A and later R170 in the CPU evaporator stage.

A stepper motor controlled EEV would be the first on my list, but it's cost is prohibitive.

Now another weird idea: I have an externally equalised R134a TEV which I don't use anymore. I also have a few TEC's which I don't use anymore. So, to convert a TEV into a heat motor, I could put the bulb on one side of the TEC, and another space filled with R134a which is connected to the external equaliser input on the other side of the TEC.

Now, by varying the current and polarity of the TEC supply, I could control the TEV.

The only problem is the sealing of the external equaliser chamber from the main refrigerant space. The R134a will probably leak away into the main refrigerant system, or R410A/R170 will leak into the external equaliser chamber, making this idea useless.

Has anyone else a good idea on how to electronically control a TEV?

[Prof Sporlan]

DaBit, controlling TEV operation by using a resistance heater on the sensing bulb has been done in the past. Using thermo-electrics instead of a resistance heater would be an elaboration of this idea.

Ideally, you would want the equalizer connected to the system. Using some fixed pressure source on the equalizer invites leakage to or from the system thru the TEV pushrod(s) to whatever source you are using.

You would be better off reading evaporator temperature via a temperature sensor, and using that reading to adjust your sensing bulb thermo-electric control, unless you want to consider a pressure transducer to read evaporator pressure and covert to temperature. But accurate pressure transducers aren’t particularly cheap.

[DaBit]

I see a problem: with low evaporator pressures, I also need low temperatures on the bulb to control the TEV. I can adjust somewhat by turning the superheat setting way up, but not enough to get controlling temperature up to room temperature range.

What would happen if I chop off the bulb, replace it with my own 'bulb', and use a gas such as butane (R600) as the thermostatic charge?

To control the 'EEV', I would indeed use temperature sensors to sense superheat. A thermocouple seems a good candidate for this since it basically senses temperature difference between the cold and hot junction.

[shooter]

sporlan is correct it is done by heating the bulb.
Use a normal tex valve and set it just normal way.
Put a heating resistor next to the bulb it should give about 50 watts on 24 volt.
and you will have to use electronics to check superheat.
So you will need a pressure sensor and a tempsensor on the gasoutletline. and some device to calculate the curve.
you can use two tempsensors one on this gas line and one on the inlet of the cooler.
thenn you would only need an amplifier.
Very old danfoss controller did it this way, not available anymore.