Fluid Flow And Heat Transfer Performance Research On Heat Exchanger With Vibration And Reciprocating Screw Inserted

The turbine condenser whose operating efficiency and the vacuum degree willdirectly affect the power generation efficiency of the turbine is the most crucialequipment of the thermal power station. The statistic results show that due to thegeneration of fouling the vacuum degree of the condenser decreases by an average of3%, the turbine power decreases by an average of2.5%, and the total economic lossvalue reaches more than￥3.6billion each year in the whole country. So the studyon the cleaning technology in the heat transfer tube of the turbine condenser hasimportant practical significance to improve the power generation efficiency andreduce economic losses.To solve the fouling problem in the heat transfer tube of the condenser the onlinefouling removal mechanism with the reciprocating and vibrating spiral-insert is putforward on the basis of a brief analysis of the technical characteristics of the existingonline cleaning technology. The vibration performance and resistance performance ofthe cleaning spiral-insert were researched through theoretical analysis, and theinfluence of the mechanism baffle opening that caused the flow velocity fluctuationswas also researched. Through the research it was found that the smaller outer diameterof the spiral-insert and the bigger screw pitch will arouse the lower start-up vibrationvelocity and the stronger vibration ability. In addition, only the outer diameter of thespiral-insert maintain at least5mm with the tube inner diameter can the spiral-insertvibrate steady. The bigger outer diameter of the spiral and the wire diameter and thesmaller screw pitch will arouse the bigger axial force, which can be adjudged by thecomprehensive evaluation factor of axial force. As the outer diameter of thespiral-insert becomes bigger and the screw pitch and the wire diameter becomesmaller, the value of will become bigger. In the condition of the low velocity, thequick fouling formation and the strict demand of resistance along the line, thespiral-insert with a lower value of should be chose; Otherwise, the one with ahigher value of should be chose. The frictional resistance coefficient and theprecision of the accuracy of the resistance coefficient of the spiral-insert arerespectively calculated of78.6%and92.5%by using the formula that fitted by theexperimental data, and the helix angle (or the screw pitch) has a significant effecton both of the above two coefficients.The influence on the internal velocity fluctuations by the baffle opening isresearched by the numerical simulate while the quantitative analysis is researched by the experiment, then the calculation method of the velocity fluctuation mechanismopening is obtained. The result shows that the flow characteristic of the baffle isconsistent with the parabolic law. When the baffle opening h is less than d/4, it willshow a strong role in the regulation of the flow rate, and the smaller of h thestronger of the throttling capability will be. But while h is more than d/4, itsfunction of adjusting the flow velocity will vanish; the error of the formula used tocompute the velocity in the tube is limited to less than20%. Under the similarexperimental conditions, the fouling removal effect of the reciprocating and vibratingspiral-insert is the best, which is proved through simulating the heat transferexperiment of fouling: the time that the heat transfer coefficient began decreasingseverely was prolonged by14times and1time respectively，and the heat transfercoefficient than the empty tube and the mere vibration spiral increased by60%and20%respectively after the heat transfer becomes stable.The reciprocating and vibrating spiral-insert cleaning mechanism has the simplestructure and low cost, which is very suitable for the new equipment manufacturingand the old equipment modification, so it can be promoted widely in the heat transferequipment of the tube for single-phase flow.