Recent content by GreenWombat

My error: I meant "the pressure-volume diagram showing constant pressure"

Tom, That scroll compressor moving diagram is fantastic. Your hose was helpful. Thanks.

Hi Russ. In your contribution (Saturday, 24 August), you wrote that the pressure drop across the evaporator was “too small to be visible on the P-V diagram and can be ignored.” For me, that was brilliant because it resolved the contradiction of (1) the pressure-volume diagram showing constant...

I’ve been thinking about worst case situations, like an uncommonly cold night in Australia with the air at minus 1C. Russ wrote: [My heat pump scenario] is pretty much all fine. Only a couple of minor comments. Your approach temperatures (minimum difference between the working fluid and the...

Thanks again Russ, You say, “There are no pools, only tubes. … the refrigerant is forced to flow through by the pump.” No pools, I’m not understanding something here. In my propane heat pump scenario, the propane is at 16 atm and between 74C and superheated 78C. After it has passed through...

Many hot water heat pumps have (1) a fan and evaporation at the top and (2) a condenser/heat exchanger embracing the water tank nearly to the base. I wondered how the refrigerant gets from the bottom of the condenser near the bottom of the water tank to the evaporator and fan at the top. Here is...

Once again, you've got me thinking. I'm working out my next post.

I am trying to show how a heat pump works by roughly identifying one set of temperatures and pressures for each stage of the heat pump cycle. I want to understand how propane can be useful as a refrigerant when it boils at minus 43°C at one-atmosphere pressure. I am considering: . an...

Thanks for your help. After a radical re-think, this is how I see it. Does it make sense now? The heat pump process is a steady-state, continuous cycle. It is not a sequence of stop-and-start processes. The compressor does not stop and start, and the expansion valve does not alternate between...

Wow. You fellows are fantastic. I'm experiencing a little revolution as I digest the concept of a " Steady state continuous process cycle." I'll check my conclusions with you in a bit. I need to do some shopping now. Thanks.

Hello Russ, After re-reading what you wrote, I am back to my original uncertainty. Apologies; sometimes, it's complicated to sort out my misunderstandings. ******* Possibility A: You wrote, “The gas moves into the cylinder [piston chamber] from the evaporator through one check valve, then...

Thanks for confirming that. I’ve focused on heat pumps for about a month now and going nutty. I’ve asked three clever and experienced science/engineering friends and was surprised when they said they couldn’t tackle my questions. A kind person inserted the pressure-volume diagram in my initial...

Thanks for including those diagrams. I get the four stages of heat pump operation. I've been wrestling with the concept of how a heat pump compressor can compress a gas that it holds in a fixed volume. At first, I thought of the compression stage as like a bicycle pump, heating the air in the...

I completed 4 years of science, including a thermodynamics unit, but that was way back. I am refamiliarising myself with things like latent heat and specific heat capacity. I’ve found Wikipedia helpful and have questions about the Wikipedia pressure-volume diagram. The temperature-entropy...

A heat pump is a sealed unit that contains the refrigerant within a constant volume. How does the compressor increase the pressure within the high-pressure compressor and condensation spaces? Does it do this by pumping refrigerant gas from the evaporator and into the high-pressure space? Is this...