Experimental Investigation On Condensation Heat Transfer For Mechanically Fabricated Porous Surface Tube

With the development of our country's industry and improvement of people's living standard, the consumptions for the energy resource increase day by day. Enhanced heat transfer in vapor condensation has important significance in saving energy, raw material and construction, for both the reasonable utilization of available energy and the exploitation of new energy.The energy expense in thermal-chemical units accounts for about sixty percent of its overall operating cost, so it has great significance to design high efficient and compact heat exchangers for optimizing energy application and enhancing heat transfer. There are two reasons making enhancement of condensing heat transfer as a key technique for the improvement of thermal-chemical equipment's performance. Firstly, there are still many condensing heat transfer devices where smooth tubes with low heat transfer effects are still used. Secondly, condensing resistance accounts for the major part of the whole thermal resistance in shell and tube heat exchangers.The direction of condensation heat transfer enhancement is to improve membranous condensation coefficient, as it is used widely in the present industrial application. We can know from the mechanism that, the key to the heat transfer enhancement is to promote the discharge fluid so as the liquid is getting thinner. Mechanical method is one of many methods to improve condensation coefficient, which is a simple, economical one. The principle is that the condensation liquid is pulled down by surface tension and flows away quickly, while the fluid left on top is very thin.In this paper, two different surfaces of porous tube, which were obtained by means of mechanical process, were studied experimentally at 1 bar. Water and alcohol were used as working fluids in the experiments. The experimental results showed that the heat transfer coefficients of those porous surfaces were 3.5—5.6 and 1.75—3.5 times larger than that of smooth tubes. The performance of condensing heat transfer of water is better than that of alcohol when the condition is the same, while in different condition performance of part condensation is better than that of all condensation as the vapor flow makes condensation fluid urged more quickly from the wall. Based on the arrangement of experimental data, the porous surface's condensing heat transfer mechanism was analyzed, and various influence factors on heat transfer enhancement were discussed. Finally, according to the condensing heat transfer mechanism and experimental results, a reasonable form of correlation for condensing heat transfer was selected, and the condensing heat transfer performance as a function of the key parameter of porous tubes and the working fluids'properties.