When designing plate heat exchanger for a certain process, the design pressure, design temperature, dielectric characteristics and economy should be taken into account. (1) The selection of a single board area is too small, then the number of plates is large, the area is large, and the resistance drop is reduced; On the contrary, if the single plate area is too large, the number of plates will be small, the area will be small, and the resistance will decrease, but it will be difficult to ensure an appropriate inter-plate flow rate. Therefore, the general single plate area can be considered for the angular hole flow rate of about 6m/s. (2) The flow rate of the selected fluid between the plates affects the heat transfer performance and pressure drop. The flow rate is high, the heat transfer coefficient is high, and the resistance drop also increases; On the contrary, it is the opposite.
In general, the flow rate between the plates is 0.2-0 .8 m/s, and the velocity between the two fluid plates is as consistent as possible. When the flow rate is less than 0.2 m/s, the fluid does not reach the turbulent state and will form a larger dead zone; Excessive flow rate will lead to a sharp increase in resistance, and the flow rate between gas plates is generally not greater than 10 m/s. (3) The flow of fluids on both sides of the process is roughly the same, and should be arranged according to the same schedule as far as possible; When the flow of fluid on both sides is quite different, the side with small flow is arranged according to multiple processes or plate heat exchangers with unequal cross-sectional channels. In addition, when the temperature rise or temperature drop of a medium is large, multiple processes can also be used. The side where the phase transition occurs is generally a single process, and the interface mode is the next step. In multi-flow heat exchangers, the same number of channels should be used for each flow in the same fluid. Heat exchanger pressure drop correction coefficient, single process take 1.2 ~ 1.4, 2 ~ 3 process take 1.