Here is all information about heat transfer & heat exchanger

1. HEAT TRANSFER
RANVEER CHAUHAN
M.Sc(IC)FINAL YEAR
ROLL-16311115
[2018]

2. REFERENCE:-
1.http://www.chegg.com/homework-
help/definitions/heat-transfer-5
2. https://en.wikipedia.org/wiki/heat transfer
3.Coulson & Richardson,Chemical Engineering –vol
(6), Edn.4th , Chp.12
4.Coulson & richardson ,chemical engineering -vol.
(1),End.6,Chp.9
5. http://mahans.com/water-cooled-heat-exchangers-
vs-air-cooled-heat-exchangers/

3. CONTENTS:
1.WHAT IS HEAT TRANSFER
2.MODE OF HEAT TRANSFER
3.HEAT EXCHANGER

4. What is heat transfer ?
Heat transfer ,also referred to simply as
heat ,is the movement of thermal energy
from one thing to another thing of different
temperature .these objects could be two
solids ,a soild and a liquid or gas .[1]
or
Heat transfer (or heat) is thermal energy in
transit due to a spatial temperature
difference[2]

5. Mode of heat transfer
Heat can travel from one place to
another in three ways:
 Conduction
 Convection
 Radiation [2]

6. Conduction:
Thermal conduction is the transfer of heat(internal
energy) by microscopic collisions of particles and
movement of electrones within a body.
Conduction take place in all phases of matter
,including solids,liquids,gases and waves
 A/c to fourier law ,the heat flux is proportional to the
temperature gradient and opposite to it in sign. For
one dimensional heat flow , fourrier law:
Where qx = rate of heat transfer
k= proportionality constant
A=surface area And T = temp.[2]

7. Convection:
Convection is the heat transfer due to bulk of molecules
within fluids such as gases and liquids
Convection takes place through advection , diffusion or
both.
Two kind of convection A.forced convection
B.natural convection
In forced convection,flow currents are set in motion by an
external agents like pupm&stirrer
Natural convection occur when temperature gradients in
the system generate localized density differences which
result in flow currents.[2]

8. Radiation:
Heat transfer by radiation is the transfer of
energy through electromagnetic waves.
All bodies absorb and emit radiation
No medium is required between two bodies
for heat transfer to take place.
Heat transfer through vacuum is called
thermal radiation.[2]

9. HEAT EXCHANGER:-
The process of heat exchange between two
fluids that are at different temperatures and
separated by a solid wall occurs in many
engineering applications. The device used to
implement this exchange is termed a heat
exchanger.
They are widely used in space heating ,
refrigeration,airconditioning, power station
,chemical plants etc.[3]page634

10. Type of heat exchangers:
1.Plate-type exchanger
2.Spiral heat exchanger
3.Scraped heat exchanger
4.Air cooled heat exchanger

11. 1.Plate-type exchanger:
Its a type of heat exchanger which consist of many
corrugated stainless sheet separated by polymer gasket and
clamped into a steel frame .
PHE transfer heat by placing thin ,corrugated metal sheets
side by side and connecting them by gaskets
Flow of the substance to be heated and cooled takes place
between alternating sheets allowing heat to transfer through
metal sheets.[3] page756

12. Working principle:
Channels are formed between the plates and the
corner ports are arranged so that the two media flow
through alternate channels.
 The heat is transferred through the plate between the
channels, and complete counter-current flow is
created for highest possible efficiency.[3]page 756

13. PARTS OF PHE:
Frame:-
The frame is made up of thick steel pressure retainning
part,the fixed cover and movable cover ,that when pulled
together with the tightening bolts from the pressure
retainning structure for plates or plate pack.
Plates & Its patterns:-
PHE consists of a stack of closely spaced thin plates
clamped together in a frame. A thin gasket seals the plates
round their edges.
The heat exchanger construction allow a plate heat
exchanger to be easily opended for inspection and
cleaning.[3]

14. .
Plates are designated as hard or soft,
depending on whether they generate a high
or low intensity of turbulence.

15. 3.Gaskets.
Each plate has a gasket that produces a
sealing and channel system through the entire
plate pack in which the two heat exchanging
media flow in a counter–current direction.
The circular potion of gasket stops the fluid
from going across the heat transfer plate and
send it to the next open channel.
The remaining potion or field gasket directs
the opposing fluid across the heat transfer
surface.[3]

16. Advantage:-
Plate heat exchangers are easier to maintain.
Low approach temps can be used, as low as 1 degree
celcius.
Plate heat exchangers are more suitable for highly viscous
materials.
Disadvantages:-
A plate is not a good shape to resist pressure and plate heat
exchangers are not suitable for pressures greater than about
30 bar.
The maximum operating temperature is limited to about 250
degree celcius, due to the performance of the available
gasket materials.Might cause clogging as pathways are very
narrow.[3]page757

17. 2.SPIRAL HEAT EXCHANGER:-
The spiral plate heat exachanger is made by rolling
two long metal plate around a center core to form
two concentric spiral flow passage ,one for each
fluid.
The plate edges are welded shut so that each fluid
stays within its own passage and there is no flow
bypassing or intermixing.The gap between the sheets
varies between 4 to 20 mm;depending on the size of
the exchanger and the application.
The maximum operating pressure is limited to 20
bar and the temperature to 400 degree celcius
.[3]p765

18. Working principle:-
Fluids can flow through a spiral heat exchanger in a
few different patterns. Countercurrent flow entails
one of the fluids entering at the center of spiral and
exiting at the circumference , while the other fluids
does exactly the opposite, entering at the
circumference and exiting at the center.

19. Advantages:-
They are easily cleaned and the turbulence in the
channels is high, spiral heat exchangers can be used
for very dirty process fluids and slurries.
 mechanical cleaning is also possible with removal
of end covers .thus ,maintenance is less than with a
plate heat exchanger
No insulation is used outside the exchanger .
Disadvantage:-
The maximum operating pressure is limited to 20
bar and the temperature to 400 degree celcius.
Field repair is difficult due to construction features

20. 3.SCRAPED HEAT EXCHANGER:-
 Scraped surface heat exchanger are commonly
used for high fouling and viscous fluid application.
In which a rotating element has spring-loaded
scraper blades which wipe the inside surface of tube
which may typically be 0.15mm in diameter.
Inside every votators , a motor shaft rotates within a
tube . the product is pumped through the cylinder
while the heating or cooling medium is circulated
b/w the cylinder and the jacket and the unit is
insulated to minimize energy loss.[4]p 553

21. General view of scraped
surface heat exchangers:-

22. Working principle:-
 The rotating shaft has blades which continuously
scrape produt film from the heat transfer tube wall,
thereby enhancing heat transfer , and agitating the
product to produce a homogenous mixture.

23. Advantage:-
Efficient heat transfer by continuous scraping
entire surface.
No damage to product
Easy maintenance and inspection
No dead zones or difficult places where
product can accumulate
Disadvantage:-
No major disadvantage found except cost of
equipment.[5]

24. 4. Air cooled exchanger
Air-cooled exchangers should be
considered when cooling water is in short
supply or expensive. They can also be
competitive with water-cooled units even
when water is plentiful.
Air-cooled exchangers consist of banks of
finned tubes over which air is blown or
drawn by fans mounted below or above
the tubes (forced or induced draft).[3] page
769

25. Forced draft & induced draft[ACHE]

26. Advantages:-
heat exchanger capacity is very less in small flow area
It lead less labour & power consumption is less
Installation and operational and maintances are cost is
low
Disadvantage:-
Disadvantages of these oil coolers include higher
horsepower requirements, less accessible fans when
it’s time for maintenance, and the need to remove
plenums to replace bundles.[5]