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Heat Transfer Equi

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by

Syaza Rahizad

on 19 September 2013

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Transcript of Heat Transfer Equi

Heat Transfer Equipments
Chapter 7
Principles of Heat Transfer
a) Heat is transferred one material to
another when each has a different
temperature.

heat flows

b) Warmer material colder one

c) temperature, heat transfer


CONDUCTION
Process of heat transfer from


to another
without any movement
HOT COOLER
CONVECTION
Transfer heat from one portion of or gas
NATURAL

FORCE
naturally happen due to the difference of density
happened due to force that is given to the fluid
RADIATION
Heat energy transferred by electromagnetic waves
Radiation energy
absorbed
reflected
Types of Processing
Batch Processing
and semi liquid product ( )

undergo and
problem
caramelized flavour
poor colour retention
a lack of a reproducible product
Continuous Processing
pumped through a system, and while continuously flowing down the processing line
Indirect Heating
product and the medium,
not in direct contact
Direct Heating
product and medium are in
direct contact
Process That Suitable For
Continuous Processing

Aseptic Process
(for high and low acid products)

Pasteurised/UHT
(reduce loss of volatiles)
filled (under sterile condition)
Hot Filled Process
(for high acid products)

Pasteurised
filled directly using
heat of the product
Pasteurisation Process
(for low acid products)

Pasteurised
hold
chilled
1) Plate Heat Exchanger (PHE)
Disadvantage
- consist of series of plates connected on a frame
- Plates are sealed by gaskets at its edges and ports to prevent intermixing of liquids.
- Suitable for low viscosity
homogenous products
Advantage
Heat re-generation (transfer) over 90% with required differences of temperature
Cross contamination by unsterile product due to pinholes on plates
2. Tubular Heat Exchanger (THE)
Product is pumped through a tube or multiple tubes, which are fixed inside a larger tube. In the space between, heating or cooling media is pumped in counter flow to the product.
Types of tubular heat exchanger:
i) Double Pipe
Exchanger
Tube held within a tube.
The product flows through the central tube and is surrounded by outer tube, which contains the heating or cooling medium.
Applied for particulate products
as there are less blocking problems.
ii. Triple Tube
Exchanger
- surrounded by a second jacketed tube containing heating or cooling medium
-through the center of the product tube is a further tube which also has the heating or cooling media flowing through
Applied for : viscous products
fruit purees, concentrates and sauces such as
mustard and mayonnaise
iii. Shell and Tube
one of the fluid streams flows inside
the tube while the other fluid
stream is pumped over the tubes
through the shell
Applied for low viscous products
such as fruit juices
iv. Scraped Surface
Heat Exchanger
- similar to double pipe. Central tube contains product with the heating or cooling media on the outer shell
- central tube contains a shaft which has blades attached for a scrapping action.
Applications:

* Processes - heating, pasteurizing, sterilizing,
whipping, gelling, emulsifying

* Products - yogurt, margarine, orange juice
Advantages:
very viscous product, reduced burn on and
lower pressure drop
Disadvantages:
High cost, more floor space and
damage to fragile particles
Advantages:
Available to produce wide product range
Able to process particulate product
Very simple design - cuts down maintenance cost
Disadvantages:
Thermal crack
High pressure drops
Fouling and burn on
Indirect Heating Equipments
Direct heating equipments
Principles of direct heating
1)steam injection-injecting pressurized steam into product
2)steam infusion-injecting product into steam
Both systems work as the steam comes into contact with product it will condense and give up latent heat cause the product heat up quickly
Steam injection and steam infusion
Preheating -product preheated by outgoing product then by steam to a constant temperature in the range 75 c to 85 c in PHE
Steam injection-steam injected to the product flow in high pressure heating chamber to achieve sterilization temperature 144 c
Holding-sterilized product then held at 144 c for a holding time of 2-6 secin a holding tube
Cooling-product immediately boiled in vacuum chamber ,cooled and collect at the base.the product temperature is kept at 1 to 3 c higher than of the product at the pre-heater
vacuum chamber
Homogenization-product homogenized before cooling to ambient or chilled temperature by tube or PHE
Applications:
1)steam injection-low viscosity,homogenous product suck as milk and juices
2)Steam infusion-can handle small particles e.g. cells in juices
Disadvantages
1)Dilution-water as condensed steam will remain in product.allowance for the dilution must be made in the product formulation
2)Contamination-steam must be of culinary standard
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