The plate heat exchanger is a kind of high-efficiency heat exchanger made of a series of metal sheets with a certain corrugated shape. Thin rectangular channels are formed between various plates, and heat is exchanged through the plates.Increasing the average flow velocity of the medium in the plate channel can increase the heat transfer coefficient and reduce the area of the plate heat exchanger.However, increasing the flow rate will increase the resistance of the plate heat exchanger and increase the power consumption and equipment cost of the circulating pump.The power consumption of the circulating pump is proportional to the third power of the medium flow rate. It is not economical to obtain a slightly higher heat transfer coefficient by increasing the flow rate.When the flow of hot and cold media is relatively large, the following methods can be used to reduce the resistance of the plate heat exchanger and ensure a high heat transfer coefficient.
1. Set the bypass tube of plate heat exchanger
When the flow of hot and cold media is relatively large, a bypass pipe can be installed at the inlet and outlet of the plate heat exchanger on the side with a large flow to reduce the flow into the plate heat exchanger and reduce the resistance.To facilitate adjustment, a regulating valve should be installed on the bypass pipe.This method should adopt a counter-current arrangement to make the temperature of the cold medium exiting the plate heat exchanger higher, and ensure that the temperature of the cold medium after the outlet of the plate heat exchanger meets the design requirements.The plate heat exchanger bypass pipe can ensure that the plate heat exchanger has a high heat transfer coefficient and reduce the resistance of the plate heat exchanger, but the adjustment is slightly complicated.
2. Use multiple process combinations
When the flow of hot and cold media is large, a multi-process combination arrangement can be adopted. More processes are used on the small flow side to increase the flow rate and obtain a higher heat transfer coefficient.Less flow is used on the high flow side to reduce the resistance of the plate heat exchanger.Multi-flow combination appears mixed flow pattern, the average heat transfer temperature difference is slightly lower.The fixed plate and movable plate of the multi-process combined plate heat exchanger are taken over, and the workload is large during maintenance.
3. Adopt asymmetrical plate heat exchanger
Symmetric plate heat exchangers are composed of plates with the same corrugated geometry on both sides of the plates, forming plate heat exchangers with equal cross-sectional areas for hot and cold flow channels.Asymmetrical (unequal cross-sectional area) plate heat exchangers change the wave geometry of both sides of the plate according to the heat transfer characteristics and pressure drop requirements of hot and cold fluids to form plate heat exchangers with different cross-sectional areas for hot and cold flow channels The diameter of the corner hole on the side of the wide runner is larger.The heat transfer coefficient of the asymmetric plate heat exchanger decreases slightly, and the pressure drop is greatly reduced.When the flow of hot and cold media is relatively large, using an asymmetric single-flow process can reduce the plate area by 15% to 30% compared to a symmetric single-flow plate heat exchanger.