Optimization design method of plate heat exchangers
The plate heat exchanger is a heat transfer type heat exchanger. The hot and cold fluid transfers heat through the heat exchanger plate, and the fluid is in direct contact with the plate. The heat transfer mode is heat conduction and convection heat transfer. The key to improving the heat transfer efficiency of plate heat exchangers is to increase the heat transfer coefficient and the logarithmic mean temperature difference.
(1)Improve heat transfer efficiency
Increasing the heat transfer coefficient of the heat exchanger can only improve the surface heat transfer coefficient on both sides of the plate , reduce the thermal resistance of the fouling layer, and select the plate with high thermal conductivity and reduce the thickness of the plate to effectively improve the heat transfercoefficient of the device.
(2)Improve the logarithmic mean temperature difference
Plate heat exchangers have countercurrent, downstream and mixed flow patterns (both countercurrent and downstream). Under the same working conditions, the logarithmic mean temperature difference is the largest in the countercurrent and the smallest in the downstream flow, and the mixed flow pattern is in between. The method of increasing the logarithmic mean temperature difference of the heat exchanger is to adopt a mixed flow pattern of countercurrent or near countercurrent as much as possible, to increase the hot fluid temperature and reduce the cold side fluid temperature.
(3) Determination of the location of the inlet and outlet pipes
For the plate heat exchangers arranged in a single process, for the convenience of maintenance, the fluid inlet and outlet pipes should be arranged as far as possible on the side of the fixed end plate of the heat exchanger. 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 hot fluid is placed inlet uppter and outlet bottom, and the cold fluid is opposite to reduce the influence of the retention zone. , improve heat transfer efficiency.