When designing a plate heat exchanger for a process application, The factors such as design pressure, design temperature, media characteristics and economy should be considered.
(1) Selection of phe plate area
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 flow rate of the single-plate area can be considered to be about 6 m/s.
(2) Selection of flow velocity between plates
The flow rate of the fluid 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; otherwise, the opposite is true.Generally, the flow rate between the plates is 0.2-0.8 m/s, and the speed between the two fluid plates is as uniform as possible. When the flow rate is less than 0.2m/s, the fluid will not reach the turbulent state, and it will form a large dead zone. If the flow rate is too high, the resistance drop will increase sharply, and the flow velocity between the gas plates is generally not more than 10m/s.
(3) Determination of the passes
When the flow rates of the fluids on both sides are roughly equivalent, they should be arranged in an equal process as much as possible; when the flow rates of the fluids on both sides are relatively large, the side with the small flow rate is arranged in a multi-flow process or a plate heat exchanger with unequal cross-section passages.
(4) 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 pass, they are countercurrent; when the fluids on both sides are in unequal flow, the forward and reverse flows alternately, and the average temperature difference is smaller than that of pure countercurrent.