The Experimental Study On Enhancing The Heat Transfer Of Natural Convection And Boiling Outside Of The Tube

In this paper, the heat transfer performance of the pin-fin tube, porous surface tube and smooth tube which are all made of B30 was first researched on the condition of convection. According to the experimental results, the capacity of heat transfer was compared and analyzed in order to find the optimal tube optimizing the heat exchanger. During the experiment, water is used as working medium.The form of heat transfer is steam condensation inside the tubes, while the water convection outside the tubes in this experiment. Under different experimental condition, the condensate inside the tubes, the temperature of outside wall and the cooling water were measured. The results indicate that, on the condition of boil with no cooling water flowing, the porous surface tube works best, while the pin-fin tube works poor but still better than the smooth tube; on the condition of cooling water flowing with low temperature and velocity, the pin-fin tube takes the optimal heat exchanging performance. And with the increase of system pressure and cooling water, the condensate and heat-transfer rate increase more and more. The precision of the temperature measurement of the outside wall influences the heat transfer coefficient of the outside the tube very much, so the way of the thermocouple's use and jointing should be well taken. The reasons of the heat-transfer performance differences between pin-fin tube, porous surface tube and smooth tube as well as the factor influencing the experiment are analyzed by adjusting the incline angle of the test tubes, changing tubes with different thickness of the wall and testing under different pressure. The results show that, the porous surface tube's heat transfer coefficient is 1.6-3.2 times the pin-fin tube's and 2.7-3.7 times the smooth tube's while the pin-fin tube's heat transfer coefficient is 1.03-1.15 times the smooth tube's when boiling, but the pin-fin tube's heat transfer coefficient is 1.2-1.4 times the porous surface tube, and 1.5-1.8 times the smooth tube's in other case .In this paper, the theoretical analysis of the heat transfer process was talked on, and the temperature model of the pin-fin was discussed either. And a simple introduction was made in this paper too.