Study Of Buoyancy In Mixed Convection In Vertical Passages

Many researches have been carried out about explaining and making use of the phenomenon astonishing researchers a lot, which comes out of buoyancy in mixed convection. Presently Launder Sharma low Reynolds number k-εturbulent model has been reported to describe the features of tube flow involving buoyancy perfectly well. Therefore it is available to do a further research about the heat transfer and flow in vertical annular passage that frequently seen as one surface is heated while the other adiabatic in various thermal systems.In this paper, research was mainly done through numerical computation. In the beginning, problems like choosing the exact computation method and turbulent model, determining the calculation procedures, were solved. Later, we started from a generalized FORTRAN program pointing to circular tube flow, then reserved the right sentences, and made a program which applied to our model. Through months of continuous modification and debugging time, converged solution can be obtained. Then, some of the referential experiment data were chosen to compare with those obtained from computation. And the simulated model was also determined from the referential experiment -- the vertical annular passage is 5 m long, including a test section 3 m long. The outer surface is considered adiabatic with a diameter of 140 mm while inner uniformly heated of 76 mm. In addition, calculation parameters were within the Reynolds number from 1300 to 4000 and a heating power 7.5 kw.Data analysis can be categorized into three types. One is direct referential experiment data analysis. Second is comparisons among data without those from experiment. The last is the comparison between computational data and some of the referential experiment data under the same conditions. Through comparisons, it can be concluded that the program currently is not still suitable to describe the features in a wide range, especially in upward flow, though it can reflect some features in downward flow in low Reynolds number quite well.