Amateurish Refrigeration Research

I have a High School Diploma, and that is about the extent of my formal education.  My real education comes from years of mechanic jobs, fiddling with and fixing things around the house, building things I need rather than buying them, and of course books – lots of antique books.

Knowledge or interest in refrigeration does not require a college degree nor a position at General Electric.  I am a tinkerer.  I am not required to play by anyone’s rules regarding what is conventional or profitable.  My incessant ramblings do not have to be based in fact, nor does my analytical approach need to adhere to any “international standard”.  At times I may blather on about something I don’t really understand, and other times I may gloss over my methods simply because I am “fudging it”.

I do not care.  I am enjoying myself.

I have no specific goal, I am wandering for the simple entertainment of what lies beyond the next iteration of my machine.  Not an engineer by trade, I am an amateur, practicing for the sheer enjoyment of it all.

When this refrigeration research started back up a few months ago, I had decided the goal was to see how much ice a human powered machine could make in one hour.  I won’t outline every reason for this, but the main one was just because I thought it would be funny.  That’s really the crux of it.  It would also be difficult, and teach the need to squeeze out every possible increase in efficiency, due to the vicious feedback brought on by an hour of hard peddling for a small quantity of water ice.  The work I shared in Refrigeration Test Bench Part I shows the process of acquiring a belt driven compressor and building a simple refrigeration circuit driven by a treadmill motor.  The intention was to develop the system under electric motor driven conditions until I felt I could take over the work myself, and continue from there.  Unfortunately, I found limits to what I could accomplish with The York compressor running at a very low RPM.  I decided to switch over to a hermetic compressor for now, and focus on developing a better evaporator unit, as well as collecting data on the system so I can model the whole thing analytically.

Part III is where the system stands now, more or less.  Currently, inline thermocouples are being developed, where the sensors are sealed directly in the refrigerant stream, in order to provide more accurate, and more responsive readings. – temperature and pressure logging will be following in time.

There are so many ideas I want to explore, however I must develop a strategy for how I wish to proceed.  For my benefit, I’m going to outline that here:

1. Finish developing thermocouple temperature sensors, and observe their performance in the current system.
2. Design and build an evaporative cooler for the the condenser cooling water, in order to increase run times and maintain system pressures.
3. Utilizing fluid temperatures, pressures, and refrigerant tables, crunch out some COP values based on specific enthalpies in the refrigeration circuit.  This will have little to do with compressor current draw, but will instead be based on “effective compression”.  Perform these calculations under various system conditions.
4. Implement some manner of temperature logging.  Pressure logging would be a plus!
5. Acquires and/or construct an easier to control expansion valve.  This may be a modified TXV or a computer controlled EXV.
6. Design and build the second generation ebullator which will be made to create flat plate ice in a metallic can.  Special considerations will be made for appropriate sight glasses, and the possibility of an ejector type throttling valve.
7. Install the ebullator inside of a small refrigerator cabinet for better control over air movement and insulation.
8. Formulate some manner of “standard conditions”, and observe changes in COP, gaining a better understanding as to the performance.  A simple version of this COP will be the relative energy usage of the compressor for a given quantity of ice production. – essentially, “tonnage”.
9. Design and build an ejector type “expressor”, which will conserve some of the kinetic energy of the high pressure liquid refrigerant exiting the expansion device, imparting it to the suction gas through a venturi device, thereby raising the suction pressure, lower the compression ratio, increase the refrigerating effect, and improve overall COP.  As of this date, I intend to utilize a manually controlled expansion device in the ejector, and perhaps a gravity float device to admit medium pressure liquid from a separator after the ejector, and pass it through to the plate ice ebullator.  This ejector expressor is a rather recent revelation of mine, which I thought for a short time was my own idea, but quickly found out it already exists, which is where I discovered some of the terminology.  Nonetheless, it is reassuring to find that the principle is sound, so I would like to investigate and test it myself.
10. Compare the expressor device to a conventional expansion valve through the aforementioned methods.
11. Investigate methods of subcooling high pressure liquid refrigerant through means of sky radiative cooling.
12. Break out the York 210 compressor and re-adapt it to the system as it exists at that date.
13. Determine the performance of the York 210 in terms of volumetric efficiency and investigate any means by which to improve upon it.  This will likely include a determination of the degree by which the refrigerant is miscible in the compressor oil, and the changes to the viscosity of the oil therein.
14. If it appears possible to make the machine pedal powered, adapt a bicycle drive-train to the apparatus, at which point I will be the prime mover myself.  Study COP and the ice productive capabilities of human power.  Improve and repeat.
15. Investigate the possibility of instituting other forms of compressors including turbines, liquid based U-shaped compressors, rotary liquid compressors, and of course variable speed hermetics.
16. Build and investigate the performance of a grey water heater recovery – domestic water heater, a dehumidifier, a domestic heat pump, and a better refrigerator.
17. Explore other methods of exergy conservation including petroleum powered compressors, wood gas, and solar thermal organic rankine.
18. Have a beer or two.  Or three…

This is just a rough outline of some of my interests within the field of vapor compression technology.  These will change greatly in the coming months and years, but I’m sure the reader can appreciate the scope of what I believe I can accomplish if I keep up the level of obsession, I possess.

-M.C. Pletcher