Three techniques for heat transfer enhancement of plate heat exchanger

1, heat transfer coefficient

The heat transfer coefficient of the heat exchanger can be improved only by increasing the surface heat transfer coefficient of the hot and cold sides of the plate, reducing the thermal resistance of the fouling layer, selecting the plate with high thermal conductivity and reducing the thickness of the plate.

(1) to improve the surface heat transfer coefficient of plate with corrugated plate heat exchanger can make the fluid turbulence in small flow rate (Reynolds number 150), so it can obtain higher surface heat transfer coefficient, surface heat transfer coefficient and plate corrugation geometry and flow condition of the medium. The waveform of the plate comprises a herringbone shape, a straight line shape, a spherical shape, etc.. After many years of research and experiments, it is found that the shape of the corrugated section is triangular (sinusoidal surface heat transfer coefficient is the largest, the pressure drop is small, the stress distribution is uniform, but the processing is difficult.) The herringbone plate has a higher surface heat transfer coefficient, and the greater the angle of the corrugation, the higher the flow rate of the medium in the inter channel, the larger the surface heat transfer coefficient.

(2) the plate material with high thermal conductivity can be used to select austenitic stainless steel, titanium alloy, copper alloy and so on. Thermal properties of stainless steel, thermal conductivity of about 14.4 W/ (m.K), high strength, stamping performance is good, not easy to be oxidized, the price ratio of titanium alloy and copper alloy is low, most used in heating engineering, but its ability to resist chloride ion corrosion difference.

(3) the key to reduce the fouling resistance of the heat exchanger is to prevent the fouling of the plate. When the thickness of the plate is 1 mm, the heat transfer coefficient is reduced by about 10%.. Therefore, it is necessary to pay attention to monitoring the water quality of the cold and hot sides of the heat exchanger to prevent the fouling of the plate, and to prevent the impurities in the water. Some heating units in order to prevent the theft of water and steel corrosion, heating medium in the addition of chemicals, it is necessary to pay attention to water quality and viscosity caused by debris contamination heat exchanger plate. If there are sticky impurities in the water, should use special filters for processing. When selecting a medicament, it is advisable to choose a non adhesive agent.

(4) the design thickness of the sheet thickness plate is not related to the corrosion resistance, and is related to the bearing capacity of the heat exchanger. The thickness of the plate can improve the bearing capacity of the heat exchanger. The herringbone plate combination, adjacent plates mutually inverted, corrugated contact with each other, forming a high density and uniform distribution of the fulcrum, the plate angle and edge seal alone L structure has been gradually improved, the heat exchanger has good bearing capacity. The maximum bearing capacity of domestic detachable heat exchanger has reached 2.5 MPa., the thickness of the plate has great influence on the heat transfer coefficient, thickness of 0.1mm, the total heat transfer coefficient of symmetric plate type heat exchanger is increased by about 600W/ (m.K), asymmetrical type increased by about 500 W/ (m.K) ". In order to meet the pressure bearing capacity of heat exchanger next, the thickness of the plate should be chosen smaller.

2, improve the logarithmic mean temperature difference

Plate heat exchanger flow pattern has the reverse current, the concurrent flow and the mixed flow pattern (both counter current and concurrent flow). Under the same operating conditions, the average logarithmic temperature difference is the largest, and the minimum is the minimum, 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 near current as far as possible.

3, import and export pipe position determination

For the single flow arrangement of plate heat exchanger, for easy maintenance, fluid inlet and outlet pipe should be arranged on the side of the fixed plate heat exchanger. The medium temperature increases, the natural convection flow is stronger, the formation of the retention effect is more obvious, so the medium inlet and outlet position shall be hot fluid progress under the cold fluid inlet on the arrangement, in order to reduce the retention zone effect, improve the heat transfer efficiency.