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The Way To Improve The Heat Transfer Efficiency Of Plate Heat Exchanger
Jun 15, 2017

First, the plate heat exchanger optimization design direction

In recent years, the plate heat exchanger technology is increasingly mature, its high heat transfer efficiency, small size, light weight, low dirt coefficient, easy disassembly, plate varieties, wide range of applications, in the heating industry has been widely used. Plate heat exchanger according to the assembly method can be divided into removable, welded, brazed, plate and so on. As the detachable plate heat exchanger to facilitate the demolition of cleaning, increase or decrease the heat exchanger area is flexible, in the heating project to use more. Detachable plate heat exchanger by the rubber gasket heat-resistant temperature limit for water and water heat transfer. In this paper, the optimal design of the performance of the removable plate heat exchanger is studied.

Improve the efficiency of plate heat exchanger is a comprehensive economic benefits, should be determined through the technical and economic comparison. Improve the heat transfer efficiency of the heat exchanger and reduce the resistance of the heat exchanger should be considered at the same time, and should be a reasonable choice of sheet material and rubber gasket material and installation methods to ensure the safe operation of equipment to extend equipment life.

Second, plate heat exchanger optimization design method

2.1 improve heat transfer efficiency

Plate heat exchanger is a wall heat transfer heat exchanger, hot and cold fluid through the heat exchanger plate heat transfer, fluid and plate in direct contact, heat transfer for the heat conduction and convection heat transfer. The key to improve the heat transfer efficiency of the plate heat exchanger is to improve the heat transfer coefficient and logarithmic mean temperature difference.

① improve the heat transfer coefficient of heat exchanger only at the same time improve the heat and heat on both sides of the plate surface heat transfer coefficient, reduce the thermal resistance of the dirt layer, the choice of high thermal conductivity of the plate, reduce the thickness of the plate in order to effectively improve the change Heat transfer coefficient of heaters.

A. Improve the surface heat transfer coefficient of the plate

Because the ripple of the plate heat exchanger can cause the turbulence of the fluid at a small flow rate (Reynolds number 150), a higher surface heat transfer coefficient, surface heat transfer coefficient and plate corrugation geometry and medium Of the flow state. Plate of the waveform, including herringbone, straight, spherical and so on. After many years of research and experiments found that the shape of the corrugated cross-section of the triangle (sinusoidal surface heat transfer coefficient is the largest, the pressure drop is small, uniform pressure distribution under pressure, but the processing difficulties?) Of the chevron plate has a high surface Thermal coefficient, and the greater the corners of the corners, the higher the medium flow rate between the plate, the greater the surface heat transfer coefficient.

B. Reduce the thermal resistance of the dirt layer

The key to reducing the thermal resistance of the heat transfer layer is to prevent plate scaling. When the plate fouling thickness is 1 mm, the heat transfer coefficient is reduced by about 10%. Therefore, we must pay attention to monitoring the hot and cold heat exchanger on both sides of the water quality, to prevent plate scaling, and to prevent the debris in the water attached to the board. Some heating units to prevent the theft of water and steel corrosion, in the heating medium to add pharmaceutical, it must pay attention to water quality and stickers * debris caused by debris heat exchanger plate. If there is a sticky debris in the water, it should be treated with a special filter. When choosing a medicament, it is advisable to choose a non-sticking agent.

C. Selection of high thermal conductivity of the plate

Plate material can choose austenitic stainless steel, titanium alloy, copper alloy and so on. Stainless steel has good thermal conductivity, thermal conductivity of about 14.4 W / (m • K), high strength, stamping performance is good, easy to be oxidized, the price is lower than the titanium alloy and copper alloy, heating the most used, but its Resistance to chloride ion corrosion is poor.

D. Reduce plate thickness

The design thickness of the plate is independent of its corrosion resistance and is related to the pressure capacity of the heat exchanger. Plate thickening, can improve the heat capacity of the heat exchanger. In the case of the combination of the chevron plate, the adjacent plates are inverted to each other and the corrugations are in contact with each other to form a fulcrum with uniform density and uniform distribution. The corners of the corners and the edge seal structure have been gradually improved to make the heat exchangers very well Pressure capacity. Domestic detachable plate heat exchanger maximum pressure capacity has reached 2.5 MPa. The thickness of the plate has a great influence on the heat transfer coefficient and the thickness is reduced by 0.1mm. The total heat transfer coefficient of the symmetrical plate heat exchanger is about 600W / (m • K), and the asymmetric type increases by about 500 W / (m • K ). To meet the heat capacity of the premise of the heat exchanger, should try to use a smaller plate thickness.

② increase the logarithmic mean temperature difference

Plate heat exchanger flow patterns are countercurrent, downstream and mixed flow (both upstream and downstream). Under the same conditions, the logarithmic mean temperature difference is the largest in the countercurrent flow, the minimum is the downstream flow, and the mixed flow pattern is between the two. The method of increasing the logarithmic mean temperature difference of the heat exchanger is to use the mixed flow pattern of countercurrent or countercurrent as far as possible, to increase the temperature of the hot side fluid as much as possible and to reduce the temperature of the cold side fluid.

③ the location of the import and export pipe to determine

For single-process layout of the plate heat exchanger, for easy maintenance, fluid inlet and outlet pipes should be arranged as far as possible in the heat exchanger fixed side of the board. 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, cold fluid into the layout, to reduce the impact of the belt , To improve heat transfer efficiency.

2.2 ways to reduce the resistance of heat exchangers

Raise the average flow rate of the medium in the runner to improve the heat transfer coefficient and reduce the area of the heat exchanger. But to improve the flow rate, will increase the resistance of the heat exchanger to improve the circulating pump power consumption and equipment costs. The power consumption of the circulating pump is proportional to the third power of the medium flow rate, and it is not economical to obtain a slightly higher heat transfer coefficient by increasing the flow rate. When the hot and cold medium flow is relatively large, the following methods can be used to reduce the resistance of the heat exchanger, and to ensure a higher heat transfer coefficient.

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