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Air compresors employ water jacketed cylinders to keep them cool while hot air discharged from first stage cylinder is cooled in intercooler to reduce power consumption in second stage. High temperature air finally discharged from second stage cylinder is cooled in aftercooler.
While efforts have always
been focused on recovering heat from cylinder cooling water, intercooler & after cooler water, it would carry more sense to approach isothermal compression. Although in real life situation, achieving isothermal compression has been accepted as highly uneconomical due to extremely slow working machine with enormous area for heat dissipation, probably no one has considered heat pipe. the excessively high heat dissipation rate possible with heat pipe would make it possible to reach close to isothermal compression but installing them around air compressor cylinders.
Heat pipe info
http://www.cheresources.com/htpipes.shtml
some info on heat pipes for the coming debate. [ConsulFlaminicus, Oct 04 2004, last modified Oct 05 2004]
[link]
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I don't understand the bit about the heat pipes. The conduction of air through the compressor wall would be too slow.
Why not consider a water spray at the inlet, and then drain the hot water off at the outlet? |
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compressed air required for instrumentation must be dry; for that purpose, air discharged from compressor passes through dryer before going to storage vessel. water spray would in no way serve the purpose. if you mean to say cooling jacket for the compressor cylinder, i have already mentioned it. it is a standard feature for water cooled compressors which helps keep cylinder temperature within limits but cannot cool air enough to approach isothermal compression. heat pipe may probably do it. |
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What is the magic heat pipe made of that makes it so fast? And anyway, these seem to be two unrealated ideas--energy recovery and energy savings due to isothermal compression. |
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energy conservation and energy savings are synonyms. |
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You're dumping heat during compression, requiring less energy for compression (energy savings), and you're dumping even more heat with your magic heat pipe, but you never said where it goes (energy recovery). |
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heat pipe is a fully baked idea consisting of fluid stored under vacuum in a pipe which evaporates on heating and condenses at other end of pipe by releasing heat to heat capturing fluid. condensate recirculates by returning to evaporator end of pipe. as far as i know, this has not been applied for air cooling during compression. the lower air temperature you have during compression, lower will be power consumed by motor (revisit gas equation p1v1/t1=p2v2/t2). |
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You still have to cool the other end of your heat pipe, and are effectively just moving the location of your water cooling. So, all things being equal, this will be less effective than water cooling. |
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[worldgineer] the system may be imagined as follows - large number of heat pipes on the periphery of air compressor cylinder acting as pin fins, condenser of each heat pipe connected to separate channel for coolant flow. depending on heat pipe fluid evaporation temperature and regulation of coolant flow rate, air compressor cylinder temperature (and hence compressed air temperature) may be achieved much lower compared to water jacketed system which involves counterflow principle. a little extension of idea-design the piston of reciprocating air compressor as heat pipe and imagine the benefit. |
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The only way this would provide any benefit is if you were limited by available volume of water. Otherwise, surface area is your limitation, and sufficient coolant flow will be available whether that coolant is water or a refrigerant. Any configuration you can run your refrigerant in you can just as easily (or, more easily) run water. |
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but you can vary the size (capacity) of heat pipes along the length of compressor cylinder (i am not sure but it may give sort of parabolic profile) because air temperature during compression increases along with piston movement and it is maximum at the top dead centre. also, individual channel of coolant for each heat pipe would ensure equal & minimum temperature of coolant at heat pipe condenser inlet unlike counterflow jacketed cooling system with which there is gradual rise in coolant temperature along the length of air compressor cylinder. |
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Then use individual channels of water. Or if the temperature rise is significant, increase the flow until it's not. |
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[worldgineer] thanks. individual insulated channels is really a good idea. can we further refine the concept ? |
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Increasing the surface area using individual channels sounds good to me as well, but there would be no need for them to be insulated. |
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[worldgineer]if insulation between channels is not chosen then starting from piston bottom dead centre end to top dead centre of the cylinder, the coolant flow must be progressively increased in each channel to dissipate progressively increasing heat (temperature)in compressed air. |
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Are you talking about optimizing the design for minimum water waste? Because I don't see why too much cooling would be bad anywhere in the cylinder. And I still see no reason for insulation. |
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i think i have not been able to explain my point clearly. too much cooling to achieve isothermal compression is the basic objective. insulation between adjacent channels would facilitate in achieving the objective by preventing heat transfer across the channels as there would be progressive temperature differential along piston stroke. if option of progressive flow increase for various channels starting from bottom dead centre is selected, there would be no need for insulation. |
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