Abstract
Although numerous studies have been made in the numerical method for predicting room air distribution, there appear very few reports which aim to investigate its computational accuracy and performance of predicting ability by comparing the calculated predictions with the experimental ones. In our previous report, trying to supplement those deficiency of research, it was made to compare the experimental results with numerical ones especially as for room air temperature distribution and discussed the predicting ability of our numerical method including wall functions and two-equation models of turbulence which used turbulence energy and its viscous dissipation rate as two dependent variables. Following this investigation, it was tried again to compare the calculation by almost the same method as in the previous report with measurements of room air velocity and gas concentration distribution which was conducted in detail in the two-dimensional room models. Here, in this report, we summarized the methods of computation and experiment and described the results of comparison in one typical case of model configurations which had various positions of supply-exhaust opening in our experiments. As was mentioned above, the method of calculation was the same as previous one except that in this report, the concentration was used in place of temperature as a dependent variable of conserved property, but it was necessary to develop newly how to treat the boundary conditions of pollutant gas injection, then we constructed the appropriate numerical models of these situations after many preliminary numerical experiments. Experiments were made in the model room of dimensions of 32cm×32cm cross section, 64cm breadth in which the air velocity and concentration distribution were sufficiently secured of two-dimensionality by giving our careful consideration to regulate the air flow upstream of the model room. Ethylene gas was used for pollutant gas because its molcular weight was nearly the same as air's, then we could neglect the effect of density difference on the room air flow and distribution. Hot wire anemometer (KANOMAX, Model-21) and hydrocarbon analyzer (Toshiba-Beckman, Model 400-J) were used for measurements of velocity and concentration, and time averaged value of these were taken by recording the output and averaging on the charts. Following aspects resulted in this investigation: 1) As for velocity, experimental flow pattern by visualization and velocity distribution at various sections in model room agreed well with the theoretical results except that experimental curvature of jet flowing from supply to exhaust opening and maximum axial velocity of jet were showed a little difference with computations. 2) Theoretical concentration distributions gave somewhat low values compared to experiment, and difference was rather great especially in regions of high concentration distribution. This difference could be attributed to the fact that model room had a little poorer two-dimensionality of concentration in region of high value than other, and indicated the necessity of improved treatment of gas injection.
