# How Can I Determine the Maximum Flow Rate for a Heat Exchanger Cooling Oil?

• cj8990
In summary, the goal is to find the range of coolant flows that can remove 200,000 Joules per minute from a heat exchanger cooling oil. The oil is initially at 133 C and is cooled to 120 C as it passes through the heat exchanger at a rate of 2.7 gallons per minute. The excess oil is rerouted to a sump with ~7 gallons of oil. To prevent the oil from heating up, the coolant cannot be hotter than 133 C. The minimum flow rate for the coolant is calculated to be 1.74 L / min, but there is difficulty in determining the maximum flow rate due to an assumed large pressure drop. The solution is to figure out the required coolant
cj8990
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.

I think what your work found was peak flow rate possible through the heat exchanger, not the flow rate you need..

I think the first thing you need to do is figure out how much flow of your coolant is needed in order to carry away the heat (200kJ/min), with an acceptable rise in coolant temp (IE, from 16C to 60C) an then size the pump for that.. Bear in mind that depending on the coolant, it may boil long before it gets to 133C.

So if you find you need 50L/min of coolant through your exchanger, find out how much pressure drop is required through it to get that flow, then size the pump to be able to deliver that flow at that pressure

## What is a heat exchanger and how does it work?

A heat exchanger is a device that is used to transfer thermal energy from one medium to another. It works by allowing a hot fluid to transfer heat to a cooler fluid through a barrier, without the two fluids coming into direct contact with each other.

## Why is it necessary to size heat exchanger flow?

Sizing heat exchanger flow is important because it ensures that the heat exchanger is able to effectively transfer heat between the two fluids. If the flow rate is too low, the heat transfer process will be slow and inefficient. If the flow rate is too high, it can cause pressure drops and damage to the heat exchanger.

## What factors affect the sizing of heat exchanger flow?

The main factors that affect the sizing of heat exchanger flow include the type of fluids being used, their flow rates and temperatures, the design and size of the heat exchanger, and the desired heat transfer rate.

## How do you calculate the required flow rate for a heat exchanger?

The required flow rate for a heat exchanger can be calculated using the formula Q = m x Cp x ΔT, where Q is the heat transfer rate, m is the mass flow rate of the fluids, Cp is the specific heat capacity of the fluids, and ΔT is the temperature difference between the hot and cold fluids.

## What are some common mistakes to avoid when sizing heat exchanger flow?

Some common mistakes to avoid when sizing heat exchanger flow include not considering the properties of the fluids, not taking into account the design and size of the heat exchanger, and not considering the desired heat transfer rate. It is important to carefully analyze all factors and use accurate calculations to ensure the proper sizing of heat exchanger flow.

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