(1) Selection of heat transfer area per plate
If the area of the veneer is too small, the number of plates is large, the floor space is large, and the resistance drop is reduced. Conversely, if the area of the veneer is too large, the number of plates is small, the floor space is small, and the resistance drop is increased, but it is difficult to ensure proper flow rate between plates. Therefore, the general single-plate area can be considered at a corner hole flow rate of about 6 m/s.
(2) Selection of flow velocity between plates
The flow rate between the plates affects heat transfer performance and pressure drop. The flow rate is high, the heat transfer coefficient is high, and the resistance drop is also increased; the opposite is true. Generally, the flow rate between the plates is 0.2-0.8 m/s, and the plate heat exchanger is used to make the speed between the two fluid plates uniform. When the flow rate is less than 0.2m/s, the fluid will not reach the turbulent state, and a large dead zone will be formed; if the flow rate is too high, the resistance drop will increase sharply, and the gas plate will increase.
(3) Selection of flow direction
In single-phase heat exchange, the countercurrent has the largest average temperature difference, and the fluid is generally arranged to be countercurrent as much as possible in the design of the plate heat exchanger. When the fluids on both sides are in the same process, it is countercurrent.when the fluids in the liquid nitriding furnaces on both sides are in unequal flow, the forward and reverse flows alternately, and the average temperature difference is smaller than that of the pure countercurrent. The flow rate is generally not more than 10m / s.
(4) Determination of the plate arrangement
When the flow rates of the fluids on both sides are approximately the same, they should be arranged in an equal process as much as possible. When the flow rates of the fluids on both sides are different, the side with the small flow rate is arranged according to multiple processes or a plate heat exchanger with unequal cross-section channels. In addition, when the temperature rise or temperature drop of a certain medium is large, the salt bath nitriding furnace can also adopt multiple processes. The side where the phase change occurs is generally a single process, and the interface mode is up and down. In a multi-pass heat exchanger, the number of flow paths that should normally be used for the same fluid in each process. The pressure drop correction coefficient of the heat exchanger is 1.2~1.4 for a single process, 1.8~2.0 for a 2~3 process, and 2.6~2.8 for a 4~5 flow path.