Non-condensable Gas For Dropwise Condensation Tube Condensation Heat Transfer In A Pilot Study,

In this paper, we expound firstly the history and actuality of the influence of non-condensable gas on condensation heat-exchange and dropwise condensation research, then analyze and summarize the two facts research work. In this base, an experiment apparatus is designed and set up. The contrastive influence of non-condensable gas on the performance between dropwise condensation and film condensation, and numerical simulation and analysis on the steam flow field and heat transfer performance are studied by experiment and theory.There are two kinds of condensation: dropwise condensation and film condensation. Nowadays, film condensation widely used in heat-exchange equipments in industry. Compared to film condensation, dropwise condensation is a more efficient one, which heat-exchange coefficient is once to twice high of the film condensation. If dropwise condensation can be used in industry, the heat-exchange area will cut down to a great extent so that energy can be saved and the cost of apparatus will be decreased, which will enhance economic benefit. In addition, there are many factors to influence condensation heat-exchange, while non-condensable gas is the most important one. Therefore, the study on the influence of non-condensable gas on condensation heat-exchange is one of the most significant tasks in the study of energy saving.So an emulational condenser as an experiment apparatus is designed and set up, in which ion implanted copper tubes and brass tubes are separately set up in the two containers of the condenser in order to realize the dropwise condensation and film condensation. In this experiment, the turbine exhaust steam is simulated by the steam which is generated by electrical boiler and cooled by the cooling pipes in the testing tubes. The air is inhaled through air flowmeter during the experiment process because of the subatmospheric pressure in the experiment containers in order to study the influence of excessive air in-leakage upon the twokinds of condensation performance. The circulating water flows through the cooling pipes and takes away the heat of steam. The air tightness tests of the whole system are strictly done in order to ensure the reliability of the experiment.The experiment results show that the flux of excessive air in-leakage makes different impact on thermodynamic characters of the emuiational condenser to realize dropwise condensation and film condensation, such as the influence to condenser pressure, temperature, TTD (terminal temperature difference), temperature of tube wall and coefficient of heat transfer, etc. The coefficient of heat transfer decreases appreciably with the augment of the flux while the other parameters almost remain constant when the flux of excessive air in-leakage is no more than the critical flux. However, when the flux exceeds the critical value, the heat transfer coefficient will decrease rapidly while the other parameters rise quickly with the augment of the flux.Otherwise, the experiment results also show that the outcome of heat exchanging in ion implanted copper tubes is higher obviously than that of brass tubes because the surface energy of ion implanted copper tubes is lower than that of brass tubes. Otherwise compared to the brass tubes, the condensation heat-exchange coefficient of the ion implanted copper tubes can be enhanced 2~10 factors and the full heat-exchange coefficient can increase more than 50 percent. Based on the experiment data and the observation result from the front-transparent-wall of the condenser, A kind of condensation between dropwise condensation and film condensation has basically formed. Besides, the influence of excessive air in-leakage upon the performance of ion implanted copper tubes is less than that of brass tubes. With the increase of flux of excessive air in-leakage, the extent to decrease of full heat-exchange coefficient of the ion implanted copper tubes is 50 tO 150 percent more to that of the brass tubes, and the extent to decrease of condensation heat-exchange coefficient of the ion implanted copper tubes is 70 tO 120 percent more to that of the brass tubes.In addition, with the development of computer and the emergence of great CFDsoftware, not only experiment but also more perfect computer numerical simulation which method can save a lot of money. In this paper, used the three-dimensional continuum model based on the PHOENICS software, the complicated behaviors of the steam flow field and heat transfer in the emulational condenser are simulated and analyzed. The results are almost consistent with the facts.