Challenge

FINAL INDEPENDENT PROJECT

RRamachal Pandey29 May 2020

TOPIC: COUNTER FLOW HEAT EXCHANGER

AIM: - Write a program in matlab to find the length of the heat exchanger.

A counter flow, concentric tube heat exchanger is designed to heat water from 20⁰C to 80⁹C using hot oil, which is supplied to the annulus at 160⁰C and discharged at 140⁰C.

The thin-walled inner tube has diameter of D₁ = 20 mm

Overall heat transfer co-efficient is 500 W/m²K.

The design condition calls a toul heat transfer rate of 3000 W.

What is the length of the heat exchanger?

Assume the 10 to 11-point temperature and find the total length and compare with previous temperature and newest temperature.

Plot the graph temperature vs length.

HEAT EXCHANGER

Heat exchanger are the devices that facilitate the exchange of heat between two fluids that are at different temperature while keeping them from mixing with each other.

Or it is a rate of heat transfer between two fluids.

Classification of Heat Exchangers by Flow Configuration

There are four basic flow configurations:

Counter Flow
Cocurrent Flow
Crossflow
Hybrids such as Cross Counterflow and Multi Pass Flow

Counter Flow: -

The two fluids enter at opposite ends of the heat exchanger and flow counter to one another. In this design, the temperature differences are less but more constant over the length of the exchanger. It is possible that the fluid being heated may leave the exchanger at a higher temperature than the exit temperature of the heating fluid. This is the most efficient design because of higher temperature differential over length of the exchanger.

Countercurrent flow.: -

Illustrates an idealized counterflow exchanger in which the two fluids flow parallel to each other but in opposite directions. This type of flow arrangement allows the largest change in temperature of both fluids and is therefore most efficient (where efficiency is the amount of actual heat transferred compared with the theoretical maximum amount of heat that can be transferred).

Crossflow

The two fluids flow perpendicular to one another.

There can be more than one method of heat transfer in a heat exchanger. Heat transfer will occur using one or more modes of transfer, conduction, convection, or radiation.

Cocurrent Flow:

In cocurrent flow heat exchangers, the streams flow parallel to each other and in the same direction as shown in. This is less efficient than countercurrent flow but does provide more uniform wall temperatures.

Formula:

The tube length needed to achieve the prescribed condition

Where

(Delta)T₁ = T_h,I – T_c,o

(Delta)T₂ = T_h,o – T_c,i

(delta)T₁are the temperature difference between hot temperature in and cold temperature out.

(delta)T₂ are the temperature difference between hot temperature out and cold temperature in.

(delta)T_1m = mean temperature = [(delta)T₂ - (delta)T₁] / ln[(delta)T₂ / (delta)T₁]

L = q / {pi * D * U* (delta)T_1m}

Where,

L = length of heat exchanger

q = toul heat exchanger rate

D = inner tube diameter

(delta)T_1m = mean temperature

Example of counter flow heat exchanger graph

In counter flow, on the other hand, the hot and cold fluid enter the heat exchanger at opposite end and in opposite direction.

MATLAB PROGRAMMING

clc;

clear all;

close all;

%INPUT DATA

% Toul heat tansfer rate in W

q = 3000;

% inner tube diameter in m

D = 0.02;

% Overall heat tansfer co-efficient in W/m^2k

U = 500;

% Hot oil and cold water heat temperature in degree celsius

temp1 = [160:-2:140];

temp2 = [80:-6:20];

% temperature Diffrence between hot oil and cold water

temp3 = temp1 - temp2;

% plot the graph and arrow text and arrow direction

figure(1);

plot(temp1);

x = [0.32 0.55];

y = [0.85 0.85];

annotation('textarrow',x,y,'String','Oil flow down')

hold on

plot(temp2);

x = [0.55 0.32];

y = [0.2 0.2];

annotation('textarrow',x,y,'String','Water flow up ')

hold on;

legend('temp1 (temp diff hot oil in and cold water out)','temp2 (temp diff hot oil out and cold water in)');

temp4 = temp3(11)-temp3(1);

temp5 = log(temp3(11)/temp3(1));

% mean temperature

deltatm = temp4/temp5;

% length of heat exchanger

L = q/(pi*D*U*deltatm)

% compare the L value and L_newest value

for i =1:10

temp6(i) = temp3(i+1)- temp3(i);

temp7(i) = log(temp3(i+1)/temp3(i));

deltatmnew(i) = temp6(i)/temp7(i);

L_new(i) = q/(pi*D*U*deltatmnew(i));

end;

L_newest = mean(L_new)

xlabel('length direction');

ylabel('temperature');

grid on

EXPLAINATION OF PROGRAMMING

Start the program with 'clear all','close all', and 'clc' commands
To provide the input data toul heat transfer rate, inner tube diameter and over all heat transfer co-efficient.
In a hot oil and cold water heat temperature in degree Celsius, generating the matrix temp1 and temp2, specified the start, end point and matrix variation point that is [160:-2:140] and [80:-6:20].
To provide the other temp3 command that is, temp3 = temp1 - temp2 it is a temperature Difference between hot oil and cold water.
then to plot the graph and arrow text and arrow direction using a command are

annotation('textarrow',x,y,'String','enter the text name')

In a annotation command use to create arrow,

x,y are coordinate and textarrow first show text then arrow and string command use to writing the text.

Use the formula find out the length value.
Plot the graph using a plot command and using legend command to specified the curve line name.
After that using a for loop and find the L_new (i) value.
L_newest = mean(L_new), in this case using the mean command find the L_new mean value and compare the L_newest and L value (mean command is a default command of matlab to easy to find the mean value)
Using a xlabel and ylabel command to specified the x and y direction name
After that using a grid on command use to on the grid in graph

OUTPUT (PLOT GRAPH)

the hot and cold fluid enter the heat exchanger at opposite end and in opposite direction to find the length.

COMMAND WINDOW RESULT VALUE AND COMPARE THE LENGTH

L =

0.9680

L_newest =

0.9680

Both the length is same.

WORK SPACE RESULT SCREENSHORT

CONCLUSION: -

We are successfully find the length of heat transfer and compare length is also same.

REFFERENCE

FINAL INDEPENDENT PROJECT

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in your own course.

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Ship work like thisin your own course.

Talk to a career counsellor

Ship work like this
in your own course.