2 replies to this topic

[Barry675]

Hello,

I'm trying to size an 18 kW air cooled heat exchanger (HX) that needs to be mounted on a truck. The HX obviously has very tight space requirements and mass requirements (1 x 1m face area, 0.2m depth and max 60-70kg). In addition to the physical requirements, I also have a very tough power budget in terms of parasitics (max 0.6 kW for blower fans).

Blower fan power is the most powerful factor driving the design optimization. I obviously want to keep size and mass to a minimum but I must have a sufficiently large face area to keep the pressure drop/fan power down. I am trying to find a good correlation for the air side pressure drop as I want to double check the values that I've already calculated.

I have found several different friction factor correlations online and in books for my configuration but they can differ by a factor of 10 depending on which one I used and so the overall fan power requirement is extremely wide depending on what I use. This is the key factor driving the overall design so I have to be sure that I am within say 30% of a believable value.

You can find more details below in my spreadsheet: https://www.dropbox....qi5/Radiator...

I would appreciate any help that people can offer or if you could take a quick glance at the spreadsheet to see if the values are believable. One note, I have not properly dealt with the fin efficiency yet as I'm struggling to understand the calculation method (dividing the finned area up into virtual hexagonal areas?).
My background is in physics and I am now doing a mechanical engineering PhD so I lack a lot of "gut feeling" for heat exchanger type problems. I don't know whether my blower power is reasonable or 10 times what it could/should be.

Kind regards,

Barry

[srfish]

I have the following questions:

       What fluid is flowing inside the tubes? Is that water?

       Is "characteristic length" under tube-side properties the tube ID?

 

The Reynolds number on both sides is unusually low.

[Barry675]

I have the following questions:

       What fluid is flowing inside the tubes? Is that water?

       Is "characteristic length" under tube-side properties the tube ID?

 

The Reynolds number on both sides is unusually low.

 

It's 40% ethylene-glycol water mixture (engine coolant) running inside of the tubes. 

 

The characteristic length is the tube inside diameter. You can see it referenced to the HX Sizing sheet and is 0.009525m 

 

Regards,

 

Barry