# Parallel Flow Heat Exchanger || Its 3 important FAQ’S ||

## Parallel flow heat exchanger theory

##### The Enthalpy loss of hot fluid is equal to the Enthalpy gain by cold liquid. The variation of temperature between hot fluid and cold fluid in the direction of the flow always decreases.

Where,

Th,in: Temperature of inlet hot fluid

Th,out: Temperature of outlet cooled fluid

Tc,in: Temperature of inlet cold fluid

Tc,out: Temperature of outlet warm fluid

## Parallel flow and counter flow heat exchanger experiment

##### The experiment setup consists of the following component,
• Heater
• Pump
• Hot water inlet and outlet
• Cold water inlet and outlet
• Temperature sensor
• Flow regulator

Procedure:

First, we have to switch ON the testing apparatus, Then switch ON the heater and set the temperature of the water heater. We have to Wait for the temperature of the water to raised upto the set point. Switch ON the pump for both hot and cold water. Set the mass flow rate of both hot and cold water using a flow regulator knob. All the temperature at inlet and exit are recorded. First, set the heat exchanger in a parallel configuration and note the readings.

Specific capacity of hot fluid: _________

Specific capacity of cold fluid: _________

1. Adjusted mass flow rate of hot fluid (mh) are recorded
2. Adjusted mass flow rate of cold fluid (mc) are recorded
3. Set Inlet temp. of hot fluid are recorded (Th1)
4. The Outlet temp. of hot fluid  are recorded (Th2)
5. Inlet temp. Of cold fluid are recorded (Tc1)
6. Outlet temp. of cold fluid are recorded (Tc2)

## Numerical question:

Que: Hot water at 46℃ enters the heat exchanger to increase the enthalpy of water that enters at 10℃ and comes out of the heat exchager at 38℃. The mass flow rate of hot fluid is 25 l/s, and the mass flow rate of cold fluid is 19 l/s. If no heat losses take place during heat transfer, What is the temperature of the hot fluid at the exit?

Sol: Given inlet temperature of hot fluid (T1) = 46℃

Given inlet temperature of cold fluid (T3) = 10℃

Given exit temperature of cold fluid (T4) = 38℃

To find exit temperature of hot fluid (T2) = X

Density of water () = 1000 kg/m3

Mass flow rate of hot fluid (mh)= 25 l/s

Mass flow rate of cold fluid (mc) = 19 l/s

Heat capacity of water (c) = 4186 J/kg-K

Heat lost by hot water is the same as the heat gained by the cold fluid.

mh*c*(T1-T2) = mc*c*(T3 – T4)

25 (46 – T2) = 19 (38 – 10)

T2 = 24.72℃

The exit temperature of the hot water is 24.72℃

## Where does parallel flow heat exchanger used

The parallel flow heat exchanger is mainly used where limited transfer of heat is recommended.The limit of the exit temperature of cold fluid is exit temperature of hot fluid in case of parallel flow heat exchanger.

## When water is heated and oil is cooled in a heat exchanger.  will it follow a counterflow path or parallel flow path?

Both type of heat exchanger can be used, but counter flow type heat exchanger will occupy less space as compared to parallel flow type heat exchanger.

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