I've been looking for a numeral answers but I've only found explanations of which one is the best out of (cross-flow, counter-flow and parallel-flow) the designs. So if anyone knows like a rounded number or something like that I'd be really grateful. It's for a presentation, and I was told that I had to look for numerical answers without doing calculations. I know for a fact that counter-flow is the most efficient, but by what percentage over the other two heat exchangers. Also it's for an HVAC application.
It only makes sense to talk about efficiency if it is a regenerative or non-regenerative HE. Non-regenerative HE have zero efficiency, because the waste heat is rejected and none of it is recovered. It may be more or less efficient, if it is clean or not, but that is not efficiency, it is a fouling factor, which would start at zero and increase from there. Regenerative HE work at 100% efficiency, if they are fully insulated. IOW, the sum of heat that goes in is the same that comes out. Rotary HE, on the other hand may have efficiencies lower than one, because of their design, which allows some heat to escape. I have no idea how much this could be, but figure 5%. The fouling factor is also applicable to regenerative heat exchangers and varies according to the product. For example, steam is a clean fluid and does not foul, while for other products they have a fouling curve. IOW, heat exchanger efficiency should be called fouling factor, instead. Questions? .
