Optimization Design Method of Plate Heat Exchanger
2.1
Improve heat transfer efficiency
Plate heat exchanger is a wall-type heat
transfer heat exchanger, hot and cold fluid are transferred through the heat
exchanger plate, fluid and plates are directly in contact with each other, and
the heat transfer mode is conduction and convective heat transfer. The key to
improve the heat transfer efficiency is to improve the heat transfer
coefficient and logarithmic mean temperature difference。
1).
Improving the heat transfer coefficient of the heat exchanger is at the same time to improve the heat
and heat on both sides of the plate surface heat transfer coefficient, reduce the
thermal resistance of the dirt layer, choose high thermal conductivity of the
plate, reduce the thickness of the plate in order to effectively improve the
heat transfer.
a.
Improve the surface heat transfer coefficient of the plate
Since the ripple of the plate heat
exchanger can make turbulence of the fluid at a small flow rate, a higher
surface heat transfer coefficient can be obtained. The surface heat transfer
coefficient is related to the geometrical structure of the plate ripple and the
flow state of the medium。
b.
Reduce the thermal resistance of the sludge layer
The key to reduce the thermal resistance of
the sludge layer is to prevent the plate from scaling, and when the sheet
fouling thickness is 1 mm, the heat transfer coefficient is reduced about 10%. Therefore,
we must pay attention to monitor the heat exchanger on both sides of the hot
and cold water quality, to prevent the film scaling, and to prevent the debris
attached to the plate.
c.
Select plates with high thermal conductivity
Plate materials can use austenitic
stainless steel, titanium alloy, copper alloy and so on. Stainless steel
thermal conductivity is good, and thermal conductivity is of about 14.4W / (m.k),
with high strength, good stamping performance, which is not easy to be oxidized.
The price of it is lower than the titanium alloy and copper alloy, most used in
heating, but its resistance ability to chloride ion corrosion is poor.
d.
Reduce plate thickness
The design thickness of the plate is not
related to its corrosion resistance, but related to the pressure bearing
capacity of the heat exchanger. Plat thickening can improve the heat pressure capacity.
2).
Increase logarithmic mean temperature difference
The plate heat exchanger process has
countercurrent, downstream and mixed type. Under the same conditions, the
logarithmic mean temperature difference is the largest in the countercurrent,
the minimum is the downstream, and the mixed flow is between the two. The
method of increasing the logarithmic mean temperature difference is to use
countercurrent or near countercurrent a mixed flow,as much as possible to increase the
temperature of the hot side fluid and to reduce the temperature of the cold
side fluid.
3).
Identification of inlet and outlet pipes
The greater the temperature difference of
the medium, the stronger the natural convection of the fluid, the more obvious
the impact of the formation of the retention zone, so the media inlet and
outlet position should be carried out by the hot fluid and the cold fluid in
different way, in order to reduce the impact of the belt, Improve heat transfer
efficiency.
2.2
Reduce the resistance of the heat exchanger
Improving the average flow velocity of the
medium in the inter-plate flow channel, can improve the heat transfer
coefficient and reduce the heat exchanger area. But improving the flow rate,
will increase the heat exchanger resistance, increase the circulating pump
power consumption and equipment costs. When the hot and cold medium flow is relatively
large, you can use the following ways to reduce the resistance of the heat
exchanger, and to ensure a higher heat transfer coefficient.
1).
Use hot mixing plate
On both sides of hot mixing plate are the
same corrugated geometric structure, according to the corners of the corrugated
angle the plate is divided into hardboard H and soft board L, the angle is
generally greater than 90, for the hard board; less than 90 for the soft board.
Combine soft and hard board can form HH, HL, LL three flow channels to meet the
needs for different conditions.
2).
Use asymmetric plate heat exchanger
Asymmetric plate heat exchanger according
to the cold and heat fluid heat transfer characteristics and pressure
requirements, change the two sides of the board waveform geometry, to form different
cross-sectional area of the plate heat exchanger. The heat transfer coefficient
of this is small and the pressure drop is greatly reduced.
3).
Use multi-process combination
When the hot and cold medium flow is large,
you can use multi-process combination of arrangements. In small flow side, using
of more processes to improve the flow rate, accesses to get higher heat
transfer coefficient. The large flow side uses less flow to reduce the heat
exchanger resistance.
4).
The heat exchanger bypass pipe
When the hot and cold medium flow is large,
you can install the bypass pipe in the large flow side between the heat
exchanger inlet and outlet, to reduce the flow into the heat exchanger to get
low resistance. For ease to adjust, a regulating valve should be installed on
the bypass pipe.
2.3
Rubber gasket material and installation
1).
Material selection
Water to water heat exchanger, hot and cold
media on the rubber gasket is non-corrosive. The key to select rubber gasket
materials is temperature and sealing performance, rubber gasket material can be
selected according to the literature.
2).
Installation options
The installation of Rubber gasket is commonly
adhesive type and buckle type.
2.4
Reasonable selection of plate material
Stainless steel sheet may produce corrosion
failure phenomenon such as pitting, crevice corrosion, stress corrosion,
intergranular corrosion, uniform corrosion, etc. Stress corrosion rate is
higher.
评论
发表评论