4. Heat Exchanger are one of the
most common pieces of
equipment found in all plant.
In a heat exchanger there is no
direct contact between the
fluids, they are separated with
the help of some metallic pipes.
5. WHY WE USE HEAT
EXCHANGERS?
To get fluid streams to the right
temperature for the next
process.
6. TYPES OF HEAT
EXCHANGERS:
Heat exchangers can be
characterized according to the flow
arrangement and type of
construction.
Some important types we discuss
here.
8. SHELL ANDTUBE HEAT
EXCHANGER
This is a schematic diagram of a shell-and-tube
heat exchanger with one shell pass and one tube
pass. The cross-counterflow mode of operation is
indicated.
11. HEATEXCHANGERWITH
FINS
Here heat is
transferred by
increasing their
surface contact area.
By which the rate of
Heat transferred is
increased.
12. COOLING
TOWERS
A COOLING TOWER IS A SPECIALIZED HEAT
EXCHANGER IN WHICH AIR AND WATER ARE BROUGHT
INTO DIRECT CONTACT WITH EACH OTHER IN ORDER
TO REDUCE THE WATER'S TEMPERATURE. AS THIS
OCCURS, A SMALL VOLUME OF WATER IS
EVAPORATED, REDUCING THE TEMPERATURE OF THE
WATER BEING CIRCULATED THROUGH THE TOWER.
13.
14. CLASSIFICATION ACCORDING TO TYPE OF
FLOW……
•1.PARALLEL FLOW
•2.COUNTER FLOW
•3.CROSS FLOW
• IN PARALLEL FLOW HEAT EXCHANGERS, THE
TWO FLUIDS ENTER THE EXCHANGER AT THE
SAME END,AND TRAVEL IN PARALLEL TO ONE
ANOTHER TO THE OTHER SIDE.
• IN COUNTER FLOW HEAT EXCHANGERS THE
FLUIDS ENTER THE EXCHANGER FROM
OPPOSITE ENDS. THE COUNTER CURRENT
15. IN A CROSS FLOW HEAT EXCHANGER,
THE FLUIDS TRAVEL ROUGHLY
PERPENDICULAR TO ONE ANOTHER
THROUGH THE EXCHANGER
18. LOGARITHMIC MEAN
TEMPERATURE
DIFFERENCE
THE LOGARITHMIC MEAN TEMPERATURE
DIFFERENCE (ALSO KNOWN AS LOG MEAN
TEMPERATURE DIFFERENCE OR SIMPLY BY
ITS INITIALISM LMTD) IS USED TO DETERMINE THE
TEMPERATURE DRIVING FORCE FOR HEAT
TRANSFER IN FLOW SYSTEMS, MOST NOTABLY
IN HEAT EXCHANGERS. THE LMTD IS
A LOGARITHMIC AVERAGE OF THE TEMPERATURE
DIFFERENCE BETWEEN THE HOT AND COLD
FEEDS AT EACH END OF THE DOUBLE PIPE
EXCHANGER. THE LARGER THE LMTD, THE MORE
HEAT IS TRANSFERRED.
19. FOR COUNTER CURRENT FLOW
(I.E.WHERE THE HOT STREAM, LIQUID OR
GAS, GOES FROM SAY LEFT TO RIGHT ,
AND THE COLD STREAM, AGAIN LIQUID OR
GAS GOES FROM RIGHT TO LEFT) ,IS
GIVEN BY THE FOLLOWING EQUATION
20. AND FOR PARALLEL FLOW
(I.E.WHERE THE HOT STREAM,
LIQUID OR GAS, GOES FROM SAY
LEFT TO RIGHT, AND SO DOES THE
COLD STREAM), IS GIVEN BY THE
FOLLOWING G EQUATION:
21. T1=HOT STREAM INLET TEMP.
T2=HOT STREAM OUTLET
TEMP.
SMALL T1=COLD STREAM
INLET TEMP.
SMALL T2=COLD STREAM
OUTLET TEMP
22. APPLICATIONS:
Some common applications are
found in:
Electronic equipment.
Ventilation & air conditioning systems.
Radiator & internal combustion Engine.
Condenser.
Pre heaters & pre coolers in fluid
systems.
