1. Improve heat transfer efficiency
FS-EIIiott cooler is a kind of heat exchanger with inter wall heat transfer. The hot and cold fluid transfers heat through the heat exchanger plates, and the fluid contacts the plates directly. The heat transfer mode is heat conduction and convection heat transfer. The key to improve the heat transfer efficiency of plate heat exchanger is to improve the heat transfer coefficient and logarithmic average temperature difference.
① to improve the heat transfer coefficient of the heat exchanger, it is necessary to increase the surface heat transfer coefficient of both sides of the plate, reduce the thermal resistance of the fouling layer, select the plate with high thermal conductivity and reduce the thickness of the plate, so as to effectively improve the heat transfer coefficient of the heat exchanger.
A. improve the surface heat transfer coefficient of plates
Because the ripple of the FS-EIIiott cooler can make the fluid produce turbulence at a small flow rate (Reynolds number 150), it can obtain a higher surface heat transfer coefficient, which is related to the geometry of the plate ripple and the flow state of the medium. The waveforms of the plates include herringbone, straight, spherical, etc. After years of research and experiments, it is found that the shape of corrugated cross-section is triangle (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 which is difficult to process has a higher surface heat transfer coefficient, and the larger the included angle of corrugated, the higher the flow velocity of medium in the channel between plates, the greater the surface heat transfer coefficient.
B. reduce the thermal resistance of dirt layer
The key to reduce the thermal resistance of fouling layer of heat exchanger is to prevent the plate from scaling. When the scale thickness of the plate is 1 mm, the heat transfer coefficient decreases about 10%. Therefore, it is necessary to monitor the water quality on both sides of the heat exchanger to prevent the plate from scaling and the water debris from adhering to the plate. In order to prevent water theft and steel corrosion, some heating units add chemicals to the heating medium. Therefore, it is necessary topay attention to the contamination of heat exchanger plates caused by water quality and adhesive chemicals. If there are sticky impurities in the water, special filter shall be used for treatment. When choosing the medicament, it is better to choose the medicament without viscosity.
C. select plates with high thermal conductivity
The plate material can be austenitic stainless steel, titanium alloy, copper alloy, etc. Stainless steel has good thermal conductivity, thermal conductivity of about 14.4w / (M? K), high strength, good stamping performance, and is not easy to be oxidized. The price of stainless steel is lower than that of titanium alloy and copper alloy. It is used most in heating engineering, but its ability to resist chloride ion corrosion is poor.
D. reduce plate thickness
The design thickness of the plate is not related to its corrosion resistance, but to the pressure bearing capacity of the heat exchanger. Plate thickening can improve the pressure bearing capacity of heat exchanger. When herringbone plates are combined, the adjacent plates are inverted and the corrugations touch each other, forming a fulcrum with high density and uniform distribution. The plate angle L and edge sealing structure have been gradually improved, which makes the heat exchanger have a good pressure bearing capacity. The maximum pressure bearing capacity of domestic removable plate heat exchanger has reached 2.5 MPa. The thickness of the plate has a great influence on the heat transfer coefficient. The thickness decreases by 0.1M m. The total heat transfer coefficient of the symmetrical plate heat exchanger increases by about 600W / (M? K), and the asymmetrical plate heat exchanger increases by about 500W / (M? K). On the premise of meeting the pressure bearing capacity of the heat exchanger, a smaller plate thickness should be selected as far as possible.
② increase the logarithmic average temperature difference
The flow pattern of Fusheng cooler includes counter flow, forward flow and mixed flow (both counter flow and forward flow). Under the same condition, the logarithmic mean temperature difference is the largest in the upstream and the smallest in the downstream, and the mixed flow pattern is between them. The method to increase the logarithmic mean temperature difference of heat exchanger is to adopt the mixed flow pattern of countercurrent or close to countercurrent as far as possible, to increase the temperature of hot side fluid as far as possible, and to reduce the temperature of cold side fluid.
③ determination of the position of the inlet and outlet pipes
For the Fusheng cooler with single process arrangement, for the convenience of maintenance, the fluid inlet and outlet pipes shall be arranged on the fixed end plate side of the heat exchanger as far 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 formed retention zone. Therefore, the location of the medium inlet and outlet should be arranged according to the up in and down out of the hot fluid and the down in and up out of the cold fluid, so as to reduce the influence of the retention zone and improve the heat transfer efficiency.