Can someone expand of this?
intuition tells me that a regenerative design can be no better than 50% efficient, and would be worse at recovering latent heat
a counter flow heat exchanger can get the temperature higher than the average because 30c exhaust is meeting partially warmed intake, and 0c intake is meeting partially cooled exhaust.
Unless theres a phase change???
I was trying to reason it out, you have the thermal mass of the heat exchanger material, that you aren't going to be able to tune to every temp differential.
at the start of the cycle, it may be very efficient, but at the end of the cycle where the heat exchanger temperature is going to approximate the temperature of the air, efficiency is going to drop, and that would be happening along the length of the heat exchanger, so by the end of the cycle the inlet would be basically doing nothing, and the exhaust quickly getting to that point (in the best case).
I was starting to confuse myself at this point, so the constant temp model seemed easier to reason about.
Although, having written all this the model would basically be a constantly shortening counter flow heat exchanger? with a thermal mass not necessarily tuned to the temp diff.
So its still going to be worse than a counterflow heat exchanger, at least theoretically.
I'm not proposing this as a practical design, but it convinces me that 50% efficiency is not the limit.
This assumes that the heat exchanger has just enough thermal capacity so that raising/lowering its temperature by 5 degrees would get the air to the same temperature. In fact, it might be easier to imagine if the air doesn't blow continuously. Each chamber could fill up with air and wait for the heat exchanger and the air to get to the same temperature, before moving the air to the next chamber.