Study On Flow And Heat Transfer Process Of Working Fluid In Cooling Channel

A common thermal protection scheme for scramjet engines is to use cooling fluid to absorb heat from the wall,and the cooling passages are often designed to be rectangular.Inside the rectangular channel,there is a complex flow structure named as the second flow of Prandtl's second kind,which is worth exploring the heat transfer process in the rectangular channel.In this thesis,from the perspective of thermoelectric conversion,helium is selected as the cooling medium.The isolator is taken as an example to simulate the flow and heat transfer process of helium in the rectangular cooling channel.The effects of heat flux density distribution and the rectangular channel aspect ratio on the flow and heat transfer process of the working fluid are mainly studied.Firstly,according to the relevant experimental data in the existing publications,the applicability of the numerical calculation method used in this thesis to the flow field calculation in the rectangular cooling channel is verified.And the model of the rectangular cooling channel is introduced.Meanwhile,the grid independence is testified.Secondly,according to the verified numerical calculation method,the effects of physical parameter changes,buoyancy and radiation on the flow and heat transfer process of the working fluid were studied.The results show that the secondary flow structure enhances the heat transfer in the cooling channel;the flow and heat transfer process of the working fluid in the cooling channel is greatly affected by the changes of the physical properties of the working fluid,and is less affected by buoyancy and radiation.Then,the effects of different heat flux distributions on the flow and heat transfer process of the working fluid in the rectangular channel were studied.Under the example of this thesis,the results show that the non-uniform distribution of heat flux on the wall of the isolator will have a significant impact on the flow velocity of the helium and the temperature distribution of the cooling channel wall.For helium flow rates,the results between non-uniform and uniform heat flux distributions can differ by up to 13%.For wall temperature,the difference between these two heat flux distributions is above 10% before x=0.2m,accounting for 28% of the total length of the cooling channels.Under different working conditions,the fluctuation of heat flux will have a significant effect on the wall temperature of the outlet of the cooling channel,and the highest temperature difference is about 100 K.Finally,the influence of the aspect ratio on the flow and heat transfer process of the working fluid is studied.The results show that under different aspect ratios,the vortex distributed along the long side wall always dominates the flow field,and the secondary flow near the long side wall has a significant influence on the mainstream constant velocity line,and bends to the inside of the flow field.The vortex distributed along the short side wall is always suppressed,which makes the secondary flow structure near the short side wall have no obvious influence on the mainstream isotach.At the same time,when the long side wall is long enough,the secondary flow of the wall symmetry position is weakened,so that the maximum deformation position of the mainstream isotach is offset from the center of the wall surface to both sides.Changes in the mainstream isotach can have an effect on the heat transfer at the coupled wall.Due to the vortex distributed along the long side wall dominates the flow field,so that the mainstream velocity distribution curve near the wall surface shows a concave tendency,so that the heat flux density distribution curve at the corresponding position is also suppressed.Along the short side,the vortex distributed in the wall is suppressed in the flow field,and does not have a significant influence on the mainstream velocity distribution curve.Therefore,the heat flux distribution curve at the short side wall surface is not significantly deformed.In general,where the main stream is suppressed by the secondary flow structure,the heat transfer is also correspondingly suppressed.For the cooling performance of different aspect ratio channels,the results show that the aspect ratio has a significant effect on the heat transfer of the single-direction wall.The heat transfer of the sidewall increases with the increase of the aspect ratio,and the heat transfer of the inferior wall increases with decrease of the aspect ratio.The maximum wall temperature decreases as the aspect ratio increases,and the uniformity of wall temperature distribution is also improved.In general,the cooling performance of the high aspect ratio channel is better under the calculation conditions of this thesis.