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How to improve the heat exchange efficiency of heat exchanger

  How to improve the heat exchange efficiency in the application process of heat exchanger? Let's take a look at what factors have an impact on it.

  1. Increase the logarithmic mean temperature difference

  Plate heat exchanger flow patterns include counter-current, co-current and mixed flow (both counter-current and co-current). Under the same working conditions, the logarithmic mean temperature difference is the largest in the countercurrent flow and the smallest in the downstream flow, and the mixed flow pattern is somewhere between the two. The method to increase the logarithmic mean temperature difference of the heat exchanger is to use countercurrent or close to countercurrent mixed flow as much as possible, increase the temperature of the fluid on the hot side as much as possible, and reduce the temperature of the fluid on the cold side.

  2. Determination of the position of inlet and outlet pipes

  For the plate heat exchanger arranged in a single process, for the convenience of maintenance, the fluid inlet and outlet pipes should be arranged on the side of the fixed end plate of the heat exchanger as much as possible. The greater the temperature difference of the medium, the stronger the natural convection of the fluid, and the more obvious the influence of the stagnation zone. Therefore, the inlet and outlet positions of the medium should be arranged in accordance with the hot fluid up and down, and the cold fluid in and out to reduce the influence of the stagnant zone. , Improve heat transfer efficiency.

  3. Improve heat transfer efficiency

  Plate heat exchanger is a partition heat exchanger. The hot and cold fluid transfers heat through the heat exchanger plates, and the fluid directly contacts the plates. The heat transfer method is heat conduction and convection heat transfer. The key to improving the heat transfer efficiency of the plate heat exchanger is to increase the heat transfer coefficient and the logarithmic average temperature difference.

4. Improve the heat transfer coefficient of the heat exchanger. Only by simultaneously increasing the surface heat transfer coefficient of the hot and cold sides of the plate, reducing the thermal resistance of the dirt layer, choosing a plate with high thermal conductivity and reducing the thickness of the plate can it be effectively improved The heat transfer coefficient of the heat exchanger.

  A. Improve the surface heat transfer coefficient of the plate

Because the corrugation of the plate heat exchanger can cause the fluid to produce turbulence at a small flow rate (Reynolds number-150), it can obtain a higher surface heat transfer coefficient, the surface heat transfer coefficient and the geometric structure of the plate corrugation and the medium The flow status is related. The waveform of the plate includes herringbone, straight, spherical and so on. After years of research and experiments, it has been found that the corrugated cross-section shape is triangular (the sinusoidal surface has the largest heat transfer coefficient, the pressure drop is small, and the stress distribution is uniform under pressure, but the herringbone plate that is difficult to process has a higher surface heat transfer coefficient. , And the greater the angle of the corrugation, the higher the velocity of the medium in the flow channel between the plates, and 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 fouling layer of the heat exchanger is to prevent the plate from fouling. When the plate fouling thickness is 1mm, the heat transfer coefficient is reduced by about 10%. Therefore, care must be taken to monitor the water quality on both sides of the heat exchanger to prevent fouling of the plates and prevent debris in the water from adhering to the plates. In order to prevent water theft and corrosion of steel parts, some heating units add chemicals to the heating medium. Therefore, attention must be paid to water quality and viscous chemicals that cause debris to contaminate heat exchanger plates. If there are viscous debris in the water, special filters should be used for treatment. When choosing medicaments, it is advisable to choose non-sticky medicaments.

  C. Use plates with high thermal conductivity

  The plate material can choose austenitic stainless steel, titanium alloy, copper alloy, etc. Stainless steel has good thermal conductivity, with a thermal conductivity of about 14.4W/(m?K), high strength, good stamping performance, and is not easy to be oxidized. The price is lower than that of titanium alloy and copper alloy. It is most used in heating engineering, but it is resistant The ability of chloride ion to corrode is poor.

  D. Reduce plate thickness

  The design thickness of the plate has nothing to do with its corrosion resistance, but is related to the pressure-bearing capacity of the heat exchanger. Thicker plates can improve the pressure-bearing capacity of the heat exchanger. When the herringbone plate combination is adopted, the adjacent plates are turned upside down, and the corrugations are in contact with each other, forming a fulcrum with high density and uniform distribution. The corners of the plates and the edge sealing structure have been gradually improved, so that the heat exchanger has a good performance. Pressure endurance. The maximum pressure-bearing capacity of the domestic detachable plate heat exchanger has reached 2.5MPa. The thickness of the plate has a great influence on the heat transfer coefficient, the thickness is reduced by 0.1mm, the total heat transfer coefficient of the symmetrical plate heat exchanger is increased by about 600W/(m?K), and the asymmetrical type is increased by about 500W/(m?K) . On the premise of meeting the pressure-bearing capacity of the heat exchanger, the thickness of the plate should be as small as possible.