Development Of New Plate Heat Exchanger And Visualization Of Its Gas-liquid Two-phase Flow

As an efficient heat exchange equipment,the plate heat exchangers have important value in energy saving and emission reduction.With the continuous development of heat exchange technology,energy shortage and environmental degradation,the design and development of new plate heat exchangers are imperative in the face of more efficient,more energy-saving and more environmentally friendly requirements.Based on the pit structure plate,a new plate heat exchangers —continuous circular concave-convex point plate heat exchanger was developed,and its performance and visualization of gas-liquid two-phase flow were studied and analyzed.(1)Through the numerical simulation,the influence of geometric structure on the performance of the new plate heat exchanger was analyzed.It is found that when the new plate has a wave point diameter of 3.5mm,a wave point depth of 1.5mm and a wave point inclination of 50°,the new plate heat exchanger has relatively good flow and heat transfer properties.At the same time,through the simulation comparison of the new and herringbone plate heat exchangers,it is proved that the new plate heat exchanger has better flow and heat transfer performance.(2)A new plate heat exchanger was developed based on the simulation results.The thermal performance and flow resistance characteristics of the new and herringbone plate heat exchangers were compared experimentally.Under the same conditions,the total heat transfer coefficient K of the new plate heat exchanger is 20% higher than the herringbone.Furthermore,its average pressure is lower than that of the herringbone plate heat exchanger.(3)For the optimization of the plate,the flow mechanism in the new plate heat exchanger was studied.In this paper,the flow mechanism of the plate heat exchanger was researched through the visualization of the flow between the plates.First,a fullsize transparent plate was processed on a high-permeability acrylic plate according to the developed new plate structure.Then,the clamping tool of the transparent plate was designed,and the visual experimental system of the new plate heat exchanger was built.Finally,the flow between the transparent plates was photographed by a high-speed camera,and flow analysis was performed.(4)By observing the flow distribution characteristics of the gas-liquid two phases in the entire flow channel,it is found that the bubbles will float above the flow channel due to the influence of gravity and the position of the inlet and outlet.And the number of bubbles increases with the increase of the flow rate and the gas content.By observing the local area of the flow channel,it is discovered that the bubble with its largest diameter smaller than the diameter of the wave point occupies the majority,and Its movement was basically unimpeded,which contributes to the improvement of the heat transfer performance of the plate heat exchanger.The bubble with its largest diameter greater than or equal to the diameter of the wave point occupies the minority,and the flow channel was blocked during its movement,thereby causing an increase in the flow resistance between the plates and affecting the heat exchange efficiency.In addition,the relationship between Reynolds number Re and the average diameter of the bubble was fitted,and it is found that the average diameter of the bubble gradually decreased as Re increased.Finally,the fusion of bubbles and vortex were discovered.The fusion of bubbles mainly occurs between unequal bubbles and affects the heat transfer and mass transfer characteristics of the entire system.The vortex phenomenon hinders the normal flow of the fluid and was detrimental to heat transfer.