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DIY Stirling engine heat pump/refrigerator cools to 36°F


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This little Stirling engine continues to surprise me! I thought it would be interesting to try it out as a heat pump (Stirling engines are reversible in function from engine to heat pump) by driving it with the motor/generator for a time and monitor the head temperature compared to the cooling water temp. I inserted the cylinder into an insulated box of 40 cu. in. volume and also monitored the temperature in the box. I taped a thermocouple probe to the bottom of the cylinder and the upper number on the thermometer shows this temperature. I used the non-contact thermometer, the lower number, to monitor the cooling water temp.

As you can see, it was able to generate a 57°F temperature drop and cooled the insulated space down to 36°F! That's refrigeration temperature! Actually, as the last photo shows, the temperature of the diaphragm at the top of the cylinder was 102°, a difference of almost 75° between top and bottom!

I really didn't expect it to reach such low temps since the engine has a very low compression ratio, so again I was pleasantly surprised by its performance. I'm sure there is a lot of room for improvement yet, too.

So now I'm wondering if one of these engines would drive another as a heat pump, or even using several inline? Stay tuned. Very fun stuff!

[Note: after I posted this video I tried reversing the wires and driving the engine the other direction - in about 10 minutes the head reached 162 deg. and the box was at 120 deg.]

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