Group Assignment in Industrial Engineering
Submitted To: Dr. K.V.S.S. Narayana Rao, NTIE
Submitted By: Sachin Jaynt, Roll No.: 80,
PGDIE-42, NITIE
Vaishali Gurjer,
Roll No.: 100, PGDIE-42, NITIE
Engineering Principles applied in Designing of Heat Exchanger
Ma nufacture
The basic princip les of plate fin heat exchanger manufacture are the same for all sizes and all materials. The corrugations, side-bars, parting sheets and cap sheets are held together in a jig under a predefined load, placed in a furnace and brazed to form the plate fin heat exchanger b lock. The header tanks and nozzles are then welded to the block, taking care that the brazed joints remain intact during the welding process. Differences arise in the manner in which the brazing process is carried out. The methods in common use are salt bath brazing and vacuum brazing. In the salt bath process, the stacked assembly is preheated in a furnace to about 550 C, and then d ipped into a bath of fused salt composed mainly of fluorides or chlorides of alkali metals. The mo lten salt works as both flux and heating agent, maintaining the furnace at a uniform temperature. In case of heat exchangers made of aluminium, the molten salt removes
grease
and the tenacious
layer
of aluminium oxide, which would otherwise
weaken the joints.
Brazing takes place in
the
bath when
the temperature is raised above the melting point of the brazing alloy. The brazed block is cleansed of the residual solid ified salt by dissolving in water, and then thoroughly dried.
In the vacuum brazing process, no flux or separate pre-heating furnace
is required. The assembled block is heated to brazing temperature by rad iation from electric
heaters
and by conduction from the exposed surfaces into the interior of the block. The absence of oxygen in the brazing environment ensured by application of high vacuum (Pressure ≈ 10mbar). The composition of the residual gas is
further
improved
(lower oxygen content) by alternate evacuation and filling with an inert gas as many times as experience dictates. No washing or drying of the brazed block is required. Many metals, such as aluminium, stainless steel, copper and nickel alloys can be brazed satisfactorily in a vacuum furnace.
Full control over the entire production process from material roll
to finished
packages creates the best conditions for efficiently producing
high-quality heat
exchanger plates. Here is the AP&T way of making your
manufacturing process
more efficient.
Feed-in
The material is fed in on a coil or as cut blanks. We have the
necessary
experience to adapt the equipment to create the best functionality
– from
stainless steel coil and copper foil coil or with blank feeding.
Cutting
On brazed heat exchanger plates, some of the channel holes and
contour are
cut prior to embossing. In some cases, it is better to cut after
embossing the
plate pattern. AP&T has experience and processes for both
variants.
Embossing
Embossing with the right surface within narrow tolerances across
the entire
heat exchanger plate is a vital property of the end product. The
tolerances are
critical for brazability in brazed heat exchangers. In addition,
the tolerances
affect the power exchange in heat exchangers with gaskets between
the plates.
AP&T knows how to work with both of these types and has
presses with the
right stability for the job – something that is verified with FEM
analyses.
Automation
An effective and reliable automated process is a necessity for
enduring
high production capacity and high end product quality. Over the
years, we
have developed and adapted our range of feeders and conveyor
systems
to standard products for handling small heat exchanger plates
through
hole punching and embossing operations. Large plates are handled
by
AP&T press robots and conventional conveyor systems.
Stacking – handling after pressing
In order to ensure product quality while retaining flexibility,
AP&T offers a
number of methods after the press operation. For small plates,
construction
of the heat exchanger is integrated by the desired number of
plates being
stacked at the end of the press line. In conjunction with
stacking, components
such as connecting plates are mounted to make the exchanger ready
for
subsequent brazing. Large plates are picked with transfer or
feeder. They are
then stacked or placed on a conveyor or fixture for subsequent
assembly.
Service
AP&T’s service organization and experienced service
technicians are
at your service around the world – both for installation and for
support
during the service life of the machines. Within the framework of
our One
Responsible Partner® concept, we take full responsibility for
ensuring that
all component equipment works well together as a single unit. We
are
happy to share our production
experience
and can train both operators
and
maintenance personnel.
plate construction
Depending upon type, some plates employ diagonal flow while others
are designed for vertical flow (Figure 8). Plates are pressed in thicknesses
between 0.020 and 0.036 inches (0.5 to 0.9 mm), and the degree of mechanical
loading is important. The most severe case occurs when one process liquid is operating
at the highest working
tube
Tube No. of passes No. of passes Side side No. of tubes/pass No.
of passages/pass one Shell No. of cross passes No. of passes Side side (No. of
baffles +1) two
Shell diameter No. of passages/pass B pressure, and the other is
at zero pressure.
The maximum pressure differential is appliedacross the plate and
results in a considerableunbalanced load that tends to close the typical 0.1 to
0.2 inch gap.
It’s essential, therefore, that some form of interplate support is
provided to maintain the gap and two different plate forms do this.
One method is to press pipes into a plate with deep washboard
corrugations to
provide contact points for about every 1 to 3 square inch of heat
transfer surface Another is the chevron plate of relatively shallow
corrugations with support maintained by peak/peak contact (Figure 10).
Alternate plates are arranged so that corrugations cross to provide a contact
point for every 0.2 to 1 square inch of area. The plate then can handle a large
differential pressure and the cross pattern forms a tortuous path that promotes
substantial liquid turbulence, and thus, a very high heat transfer coefficient.
Mixing and variable length
To obtain optimum thermal and pressure drop performance while
using a minimum
number of heat exchanger plates, mixing and variable length plates
are available for several APV paraflow plate heat exchanger models. These
plates are manufactured to the standard widths specified for the particular heat
exchanger involved but are offered in different corrugation patterns and
plate lengths. Since each type of plate has its own predictable
performance characteristics, it is possible to calculate heat transfer surface,
which more precisely matches the required thermal duty without
oversizing the exchanger. This results in the use of fewer plates and a smaller,
less expensive, exchanger frame.
To achieve mixing, plates–which have been pressed with different
corrugation angles–are combined within a single heat exchanger frame. This
results in flow passages that differ significantly in their flow
characteristics, and thus, heat transfer capability from passages created by
using plates that have the same corrugation pattern.
