The Study On Enhancement Heat Transfer Of Double Side Condensation On Vertical Tube Outside And Application In The Low Pressure Heater Of Power Station

At present, traditional low pressure heater in the power station is made up of U-shape copper tube, which makes the tube wall in the U-shape bend become thin and strength decrease .In the mean time, the thermal stress in the bend can not been destroyed thoroughly and makes the thermal stress concentrate and leads to the crack and leakage .On the other hand, the front end of copper tube is submerged is the water , which causes the temperature of top end of U-shape tube not to be stable , About all ,these may influence the regular function of power station, it is necessary to reform the traditional low pressure heater.Based on the design need of low pressure heater in Pan Zhihua Iron & Steel company, this paper has substituted the screw grooved tube for the original U-shape bent tube successfully and solved many problems which the U-shape bent tube has on the condition of not changing the original outside shape and tube connection.The enhanced heat transfer scheme of low pressure heater is put forward firstly and demonstrated secondly, the enhanced heat transfer ti-be is made finally.On the other hand, the heat transfer charateristic experiment of the enhance heat transfer tube has been done to provide the engineering design data, the relations between the convective heat transfer coefficient of condensation and cooling water side respectively and heat flux, pressure and flow rate have been discussed.In the meantime, the relations between the overall heat trarsfer coefficient of the enhanced heat transfer tube and heat flux, pressure and flow rate have also been discussed, the relative experimental curves are given and the heat transfer characteristic of enhanced heat transfer is compared with that of smooth tube. The experimental results show that the total heat transfer coefficient of the enhanced heat transfer tube is 1.5-1.6 tines than the smooth tube, but the heat transfer coefficient of coding water is 1.6-1.7 times than the smooth tube ,and the heat transfer coefficient of condensation is 2.2-2.3 times than the smooth tube.Finally,in accordance with the engineering practice of Pan Zhihua Iron & Steed Company, a new type low pressure heater is designed to used the enhanced heat transfer tube. The used results show that this new low pressure heater is not only safe and reliable, but also easy to maintain and has good heat transfer characteristic. It is proposed to use the new low pressure heater in the power station.This paper is of great value in engineering application.