Design Process of a heat exchanger(evaporator) and fan

[droc22]

Hello,

I need help with my fourth-year design project. The part that I need particular help with is how to design an evaporator and how to size the fan that will create the forced convection over the fins.

What are the main things to consider in terms of design steps?

What are some good resources that will point me in the right direction?

What calculations are involved?

Any help you can provide would be great.

Thanks,

 

[Mech_Engineer]

Well, basically you will have to take into account the following things-

- The maximum amount of power (W) you need to dissipate through the heat exchanger
- The worst-case (highest) ambient air temperature your heat exchanger will be exposed to
- Air density (sea level, 30,000ft asl, wherever)

Subjects most pertinent to this design would be thermodynamics, heat transfer, and fluid dynamics. With a basic grasp of these subjects, you should have everything you need.

You will probably need to start with a guess at how many fins your heat exchanger will likely have (and how the fluid might travel through the fins), and their approximate surface area, and the flow area of the exchanger (rough estimates are fine, since you will probably end up iterating towards a final solution). Alternatively you could guess at a size fan you want based on the ambient air temperature and the projected air temperature using the power being dissipated. Then, you could work out how many fins you would need and how big they would need to be.

With the above quantities, you can calculate how much heat you can dissipate from the exchanger based on an amount of air flow, and iterate to find a properly sized fan. It is also possible to do an optimization study to minimize the number fins or the volume of the heat exchanger by looking at relationships of the design parameters with respect to each other. Things like how changing the number of fins changes their required surface area,of the size of the fan versus the amount of air it can push.