radiator calculation

[harini]

hi..
i was wondering how to measure the speed of air entering and leaving the radiator.Also what formulas do you use to calculate the number of fins per square inch and the number of tubes required in the radiator.this is my first year so dont know much on how to go about this.any help will be great. thanks.

[harini]

hi..
i was wondering how to measure the speed of air entering and leaving the radiator.Also what formulas do you use to calculate the number of fins per square inch and the number of tubes required in the radiator.this is my first year so dont know much on how to go about this.any help will be great. thanks.

[BeaverGuy]

Here are my suggestions regarding design, go read the section in your heat transfer text about heat exchanger design then grab a copy of Compact Heat exchangers by Kays and London. Then go write a program like thisRadiator Evaluator (http://home.comcast.net/%7Ejoshuagillett/Radiator_Evaluator.htm) The reason for the program is two-fold. First, the detail design of a heat exchanger generally requires information you don't have and several iterations until your initial "guesstimate" is sufficiently close to the calculated value. With an automtive "radiator" type heat exchanger there are at least 2 values where this is the case and depending on your idea of "sufficiently close" and your iteration method it can take a lot of iterations to solve. Lastly, is why would you ever want to solve the same problem twice when you can solve it once(writing a fomula or program) and be done with it?

[TPS]

Remember it is not only about the size of the Heat Exchanger there are many other factors involved in the design of an efficient cooling system.

[harini]

thanks for all the help....i was also wondering if anyone has a soft copy of the compact heat exchangers book....i have tried everywhere but cant seem to get hold of it...thanks.

[Mike Claffey]

Harini I'm suprised you didn't try this link

http://www.amazon.com/exec/obidos/tg/detail/-/1575240602?v=glance

Regards,

Mike C
UWA

[simonsuarez]

On the same topic of compact heat exchangers, i have been trying to calculate the convection coefficient the outer fluid (air but it's for a charge air intercooler). Anyways there are a few ways to approach this from what i have read:

1. Calculate the Nu number assuming that the frontal area of the IC is a vertical plate under forced convection. With an air velocity of roughly 53 km/h throughout endurance from there calculate the h for the outside air.

2. Another option would be calculating Nu from the relations for forced convection through an arrange of tubes and correcting the h coeff if the number of tubes columns is > 10.

3.Also i read on a paper about and fsae radiator that the considered the flow against this face to be laminar and use yet another corrolation for Nu.

Obviously there are many ways since these coefficients cant be calculated to an exact value because of the nature of the air flow. But maybe someone could share his/her thoughts about this and what kind of approach they used.

Also what effectiveness have you actually noticed on these devices?

Thanks

[BeaverGuy]

What you use to determine the Nusselt number really depends on what you have at your disposal. If you have a collection of tables and charts for various tube and fin geometries and those geometries match what you can make then I would use those. Compact Heat Exchangers has a fairly good collection of tube and fin geometries but it is far from exhaustive. There is another text the Kays and London worked on that is pretty much just a list of exchanger correlations and geometry that is supposed to have data on nearly every concievable duct and tube/fin arrangement but I haven't been able to locate it and don't remember its name off hand.

When I initially wrote my heat exchanger program I treated the air side as a series of ducts. I did this because I felt that the finned area between the tubes were essentially small ducts. I later came across SAE paper 2000-01-0579, The Effect of Changes in Ambient and Coolant Radiator Inlet Temperatures and Coolant Flowrate on Specific Dissipation, in their calculations they treated the louvered fin areas as flat plates with laminar flow following a method that was layed out in SAE paper 710208, A Method of Calculating the Heat Dissipation from Radiators to Cool Vehicle Engines.

I continued to do my calculations as a ducts because I didn't see how an enclosed area would act as a flat plate. Then about 9 months ago I acquired some data that I was able to check my program against. Using the correlations for duct flow, my calculations were about 20-30% low on the amount of heat rejected for a given configuration. So, I went and revisited the paper the specific dissipation paper and used the correlation that they used. When I did this my calculated values for heat rejected were now at most 10% lower and frequently less.

In doing this again, I would try and get data earlier and a lot more of it. The data that I used was data that was published in another paper and had a very limited arrangement of configurations. I would still write my program using the correlations that I had available and thought appropriate. I would then adjust my correlation selection to those that fit the data best.

The Effect of Changes in Ambient and Coolant Radiator Inlet Temperatures and Coolant Flowrate on Specific Dissipation (http://www.delphi.com/pdf/techpapers/2000-01-0579.pdf)