Research On Heat Exchange Enhancement And Anti-fouling Characteristics Of Heat Exchanger Tube With Helical Spring Inserts

Heat exchanger tube with helical spring inserts was a typical passive heat transferenhancement technology. It can greatly improve the heat transfer coefficient of the heatexchanger, while leading to small fluid resistance loss and achieving online cleaningfouling. The characteristics of heat transfer enhancement and anti-fouling wassystematically researched in heat exchanger tube with helical spring inserts in this paper.The main researchs are as follows:First, the heat transfer enhancement comprehensive test-bed was build.Experimental study of the characteristics of heat transfer and flow were carried out insmooth pipe and tube with different geometric parameters helical spring inserts bycomparative experimental research methods. Experimental results show that the heattransfer tubes with helical spring inserts has a good heat transfer enhancementperformance. Under the same conditions, the maximum heat transfer coefficient of tubeswith helical spring inserts is1.3times of the smooth pipe, while the drag coefficient is2.1-4.2times of the smooth pipe.Second, the flow and heat transfer characteristics in tube with helical spring insertswere simulated using Fluent software. The effects of spring application on flow field，pressure drop and heat transfer performance were investigated. And the main factorsaffecting on flow and heat transfer were studied. Simulation results show that, on thesame Reynolds number, the Nu number of heat exchange tubes with helical spring insertswere higher than smooth tubes, while pressure drop and drag coefficient has increasedsignificantly. And when tubes were inserted helical spring with small pitch, large wirediameter and big outer diameter exhibited a better heat transfer effect.Finally, the fouling experimental system was established. The experiment of foulingthermal resistances of smooth tubes and tube with helical spring inserts were carried out,which using CaCO3as the main fouling of industrial heat transfer equipment. Then, therelationship of fouling resistance and induction period with temporal variationrelationship will be got. And the effects of water hardness, heat transfer temperature, flow rate, as well as heat transfer tube’s geometrical parameters on the fouling processwere studied. The experimental results show that tubes with helical spring inserts havinga slow scale velocity, long induction period and small fouling asymptotic value. And asthe water hardness increasing, the heat transfer temperature rising, airflow velocityincreasing, fouling rate will accelerate and thermal resistance tend to increase. For tubeswith helical spring inserts, when the spring with smaller pitch, larger wire diameter, bigouter diameter,the tubes exhibit good anti-fouling performance.