Numerical Simulation and Experimental Study on Defouling Performance of Solid-Liquid Two Phase Flow on Heat Transfer Surface

Heat exchangers are extensively used but fouling problems may cause heat transfer tube clogging and energy consumption increase. Therefore, a solid-liquid two phase flow defouling technique was applied to prevent and remove fouling on heat exchanger wall. Effects of sand particles on shear stress, erosion and promotion of heat transfer coefficient were studied through simulation. The results show that the maximum erosion decreases first and then increases with the increase of flow rate. The highest erosion rate appears at 90° corners. The maximum erosion increases quickly with the increase of sand concentration and diameter. The simulation results also show that the shear stress at pipe wall without sand is 16.8 Pa. However, the area-weighted average shear stress on the pipe wall is 158.4 Pa after adding sand into heat exchanger pipes, which is enough to remove fouling. When the flow rate increases from 0.6 to 2 m·s^-1 at the same working velocity, the heat transfer coefficient increases from 2.6% to 23% after adding sands to the heat exchanger. A sewage heat exchanger was used as an experimental platform, and the solid-liquid fluidized defouling technology was studied. The experimental results show that sands with diameter of 2 mm can be fluidized if the sewage water flow rate is over 0.87 m·s^-1. The sand recycling efficiency is 95%. 4% volume fraction of sand is enough to guarantee high removal efficiency and also reduce wall abrasion.