air cooler equations

[ccorsi]

i'd like to know the thermal design equations for air coolers, are these similar to shell and tube h.e. equations?
how could i kown how many motors (and their power) should i use for cooling

 

[pmover]

i suggest that you refer to the following website for assistance:

http://www.wlv.com/products/databook/databook.pdf

good luck!
-pmover

 

[TD2K]

The GPSA data book also has a section on sizing air coolers.

 

[gunnarhole]

ccorsi,

Go to

http://www.hudsonproducts.com/download.html

They have free software that you can download that will size aerial/fin-fan coolers and fans. I have checked the results against HTRI and other proprietary packages and the results are surprisingly good. The U factor defaults are not always spot on but you can use your own if you have better ones available.

Regards,

Gunnar

 

[speco]

ccorsi,

You answer your question a little more directly, the equations used for air-cooler are the same as for shell and tube exchangers on the tubeside only. However, since they usually have fins on the outside of the tubes, you need a new set of formulae to calculate the extended surface area, fin efficiency, etc.

The Hudson program mentioned above works reasonably well, but uses fixed heat transfer coefficients (based on the bare tube area) as pointed out by gunnarhole. Remember that the tubeside coefficients are very much dependent on velocity, and therefore, available pressure drop. If your situation requires very low pressure drop, you would probably want to adjust the heat transfer coefficient downward.

The question of motors and fans is related to the overall face area, rate of air delivery, static pressure, etc. Most process coolers have two fans per bay, and approximately 40% fan coverage (fan area/face area).

 

[hiskore]

ccorsi

speco is right. tube side equations are same as for shell and tube exchangers. the fin side calculations require determination of finned tube area, projected perimeter, equivalent diameter, flow area (which is based on face area). the subsequent methodology is same like shell and tube exchangers - caln of mass velocity, reynolds no. jh factor and ho though the curves used are different.
We can vary various parameters like tube size, fin OD, fins/inch. fin material, fin thickness etc to arrive at the most optimum design. We can also play around with tube pitch and row pitch to adjust the shell side pr drop.

hi-skore