# Exit flow rate in a Plate Heat Exchanger

• harishree90
In summary, a project involving plate heat exchangers connected in a cascade system is being worked on to heat water in a large system. The problem statement involves a boiler producing hot water at 65 degC and circulating it to a heat exchanger, which then exits at 50 degC. Another fluid, also water, needs to be heated from 45 degC to 60 degC by this hot water. The volume flow rate is 5.0 m3/hr and the diameter of the pipe is DN50. Using energy equilibrium, the heat transfer rate in the first heat exchanger is calculated to be 85KW. The hot water at 50
harishree90
TL;DR Summary
Calculation of Exit Mass flow rate in a Plate Heat Exchanger to design a Cascade Heating Network
Hello All,

I am working on a project with plate heat exchangers connected in a cascade system to heat up water connections in a huge system

The Problem Statement :

A boiler produces and circulates hot water at 65 degC to a Heat Exchanger and come out at 50 degC, where as the other fluid is also water which needs to be heated to 60 degC from 45 degC , The volume flow rate of hot water is at 5.0 m3/hr and the dia meter of the pipe is DN50

Using energy Equilibrium , Heat transfer rate in the first heat exchanger

Q = m X Cp X ΔT which come around 85KW

now from the outlet of the Heat Exchange in the hot Side which is at 50 degC, I am connecting it as an Input to another heat Exchanger, which is also used to heat water from 10 degC to 45 degC and the hot water connected back to the Boiler which is at 15 degC

My question is, how can I calcuate the volume flow rate or mass flow rate or velocity of water at the outlet in the first heat exchanger which acts as an Input to second HX, so that I can calculate the heat transfer rate of the second HX to determine if need to have a pump in the circuit.

If my question is not clear please let me know

Hello harishree,

Your question is indeed unclear to me: if the volume flow is not 5 m3/h, where would the difference go ?

And the 5 m3/h, where does that come from, if not from a pump ?

Or:
With 'outlet' you mean the 60 C outlet ? Your heat exchange rate of 87 kW more or less dictates 5 m3/h too (with the given ##\Delta##T)

harishree90
BvU said:
Hello harishree,

Your question is indeed unclear to me: if the volume flow is not 5 m3/h, where would the difference go ?

And the 5 m3/h, where does that come from, if not from a pump ?

Or:
With 'outlet' you mean the 60 C outlet ? Your heat exchange rate of 87 kW more or less dictates 5 m3/h too (with the given ##\Delta##T)

The 5 m3/h volume flow at the inlet of the heat exchanger comes from a hot water boiler.

And by Outlet I mean the output with 50 C which acts as a input to the second heat exchanger.

My question is ...due to pressure loss in the heat exchanger (Considering 0,1 bar), will there be a change in velocity of the fluid at the exit (at 50 C) ?

harishree90 said:

The 5 m3/h volume flow at the inlet of the heat exchanger comes from a hot water boiler.

And by Outlet I mean the output with 50 C which acts as a input to the second heat exchanger.

My question is ...due to pressure loss in the heat exchanger (Considering 0,1 bar), will there be a change in velocity of the fluid at the exit (at 50 C) ?
No significant change. And, of course, the mass flow rate won't change at all.

harishree90
Chestermiller said:
No significant change. And, of course, the mass flow rate won't change at all.

Thank you for the explanation Chestermiller and BvU

I was under the wrong idea that since there will be a pressure loss in the heat exchanger, it would affect the velocity and the flow rate also.
Now I understand

## What is exit flow rate in a Plate Heat Exchanger?

The exit flow rate in a Plate Heat Exchanger refers to the rate at which the heated or cooled fluid exits the heat exchanger. This is an important parameter in determining the efficiency of the heat exchanger and the overall heat transfer process.

## How is exit flow rate calculated in a Plate Heat Exchanger?

The exit flow rate in a Plate Heat Exchanger is calculated by dividing the total volume flow rate of the fluid by the number of channels in the heat exchanger. This can also be calculated by measuring the flow rate at the exit of the heat exchanger using a flow meter.

## What factors affect the exit flow rate in a Plate Heat Exchanger?

The exit flow rate in a Plate Heat Exchanger can be affected by several factors such as the inlet flow rate, the heat transfer coefficient, the temperature difference between the hot and cold fluids, and the design and size of the heat exchanger.

## Why is it important to maintain a consistent exit flow rate in a Plate Heat Exchanger?

Maintaining a consistent exit flow rate in a Plate Heat Exchanger is important because it ensures that the heat transfer process is efficient and that the heated or cooled fluid is being circulated at a constant rate. This helps to maintain a stable temperature and prevent any potential damage to the heat exchanger.

## How can the exit flow rate be controlled in a Plate Heat Exchanger?

The exit flow rate in a Plate Heat Exchanger can be controlled by adjusting the inlet flow rate, changing the design or size of the heat exchanger, or by using flow control valves. It is important to regularly monitor and adjust the exit flow rate to ensure optimal performance of the heat exchanger.

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