# Sizing Heat Exchanger Flow

## Main Question or Discussion Point

I'm trying to figure a range of flows of coolant that will pull 200,000 Joules per minute from a heat exchanger cooling oil. The oil is passing through a head that adds 200,000 Joules per minute to 0.5 L / min. The 0.5 L is dumped into a sump with ~7 gallons of oil. The oil then passes through the heat exchanger at 2.7 Gallons / min and is cooled to 120 C. It enters the head from here... any excess is rerouted to the sump.

So far I know 200,000 Joules / min will need to be removed by the heat exchanger (assuming perfectly insulated and incompressable fluid) or else a perpetual increase in temp will occur.

So with P = (Mass Flow) * (Specific Heat of Oil) * (Delta T)... T_initial (temp of oil in sump) = ~133 C

So the entering temp of oil is 133 C so the coolant cannot be hotter than 133 C or else it will heat the oil instead of cooling it.

For the coolant Tf = 133 C and Ti = 16 C (another assumption.. entering coolant temp is a random cool temperature). Again using P = (Mass Flow) * (Specific Heat of Coolant) * (Delta T) this gives a min value for the flow at 1.74 L / min.

The problem I'm having arises when trying to find a max flow..

The heat exchanger is rated at a max pressure of 300 psi. Using bernoulli..

P1 + 0.5 * density * V1^2 = P2 + 0.5 * density * V2^2

with P1 = 300, V1 = 0, P2 = atmospheric (assumption since I cannot determine a pressure drop) and solving for V2.

With V2 I calculate the flow and get ~262 L / min.

This is obviously unrealistic and it is because I'm assuming such a huge pressure drop. Any idea how I can rectify this to get a more accurate idea of the max flow?

In case you're wondering.. I am an intern at a company and this is a project given to me to get an idea of the pump sizing that will be needed. I'm hitting a wall on this and would prefer to not look like a fool. Appreciate any help that can be offered.