Study On Flow And Enhanced Heat Transfer Of Hydrocarbon Fuel In Samall-scale Rectangular Channels

The small-scale rectangular cooling channel has great varieties of applications in the areas of industrial heat transfer equipment, nuclear power station and thermal protection system of aerospace power. Recently, lots of researchers pay more and more attention on the process of heat transfer in this field. Specifically, the process of flow and heat transfer based on supercritical hydrocarbon fuel in the asymmetric heating channel exhibits prodigious differences when comparing with the uniform heating channel because there are some special phenomena in this process, such as transcritical flow and nonuniform distribution of temperature. In this paper, we focus on the millimeter-scale cooling channels to carry out this relative work through building up fluid- solid- heat coupling simulation model in the view of fully three-dimension and building experimental measurement table.In this paper, the relevant treatme nt methods of thermophysical property of n-decane at supercritical pressure are used to capture the sharp variations of properties near the critical point, during which some of correctional methods are considered. Results show that the average error is les s than 10% compared with NIST database. After that, in order to analyze the formed mechanism of nonuniform distribution of temperature, and the effects on heat transfer, four different geometries based on different channel aspect ratios, AR=1,2,4,8, are built. In this way, specific formed mechanis m of thermal stratification is obtained through defining temperature nonuniform coefficient and effective turbulent thermal diffus ivity coefficient. Results show that increasing the channel aspect ratio can enhance the heat transfer performance before reaching AR=4. Finally, the comparison of two simulation model, with solid domain and without solid domain is conducted to illustrate the importance of coupling model when dealing with the heat transfer development in asymmetric heating rectangular channel.Based on the study of aspect ratio, with an aim to discuss the strategies of enhanced heat transfer in small-scale cooling channel, three common heat transfer methods used in heat exchanger are chose to compare the heat transfer performance and the princ iple of enhancing heat transfer process, including rib roughness, delta winglet vortex generator and dimple. It is shown that delta winglet vortex generator can bring the obvious enhanced heat transfer performance, and there is the lowest flow resistance in dimple. In other words, considering the pressure loss effect, dimple has great potential application in small-scale rectangular cooling channel.Also, considering the effect of lateral wall in single channel, anothe r main content is about discussing the influence of dimple arrangement pattern and streamwise pitch on flow and heat transfer in the given configuration channel. It is shown that better thermal performance benefits from small streamwise pitch, however, with lager pressure loss. Under the same arrangement density of dimples, compared with single row dimp les, double-cross row dimples can obtain better heat transfer performance with low flow resistance. In addition, there are remarkable differences about the distribution of velocity field and thermal field between these two arrangement patterns of dimples. Furthermore, in the range of subcrit ical temperature, double- cross row dimples are beneficial to enhance heat transfer. However, when reaching the supercritical state, the enhanced effect will disappear.Finally, several parameters on thermal performance are measured both in the multi-dimple and smooth cooling channels through building an heat transfer measurement table based on narrow rectangular cooling cha nnel. During this process, different outlet temperatures of pre- heating section and mass flow rate of coolant act as the basic varietes. Experimental results show that multi-dimple channel can gain better heat transfer performance and this trend will be strengthened with the increase of fluid temperature under sub-critical temperature.