On the Inconsistencies Related to Prediction of Flow into an Enclosing Hood Obstructed by a Worker

Abstract

The recirculating flow structures formed in the wake of a worker standing in front of an enclosing fume hood were numerically investigated. Two- and three-dimensional, unsteady, laminar/turbulent computations were performed for a Reynolds number (Re) range of 1.0 x 10(3)-1.0 x 10(5). The standard k-epsilon, Renormalization group (RNG) k-epsilon, and Shear Stress Transport (SST) k-omega models were used in Unsteady Reynolds Averaged Navier-Stokes (URANS) computations, and the results were compared with each other and also with the previous predictions reported in the literature. Numerical issues regarding the grid convergence and the inadequacies of turbulence models that may come into play at low Reynolds numbers were addressed. On the whole, SST k-omega model was found to be promising for qualitatively accurate prediction of both steady and unsteady recirculatory flow patterns in the wake of the worker. On the other hand, the standard and RNG k-epsilon models failed in prediction of anticipated unsteadiness at low Reynolds numbers. In a more realistic three-dimensional simulation with SST k-omega model, the anticipated unsteady and recirculating flow field in the wake of the worker was captured. Present results seem to qualitatively agree with the deductions made from experimental analyses in the literature while conflicting with some aspects of the previously reported numerical results. The apparent inconsistencies observed between the current results and those published in the literature were elucidated.

Flow Characteristics of a Servco Fume Cupboard

“…CFD enable the comprehensive visualization of airflow structure in the fume cupboard such as recirculation region downstream of the sash (in the working chamber). The size of this recirculation region has been stated to contribute to the poor performance of a fume cupboard [2][3][4][5][6][7][8]. CFD simulations has been used to investigate the effect of design elements in 2-dimensional such as louvered bypass and baffles and in 3-dimensional such as outlet and obstruction in front of a fume cupboard [8,9].…”

Tracer Gas Exposure of Human Subjects Doing Simulated Work at a Benchtop Enclosing Hood in a Wind Tunnel

“…The performance of different RANS models, such as the standard k-ε, the RNG k-ε, and the SST k-ω at high, moderate, and low Reynolds numbers were tested by Karaismail and Celik, (2010). They performed two-and threedimensional, unsteady, laminar and turbulent computations for Reynolds numbers of 1.0x10 3 , 1.0x10 4 , and 1.0x10 5 .…”

“…Limited studies about the factors affecting the performance of benchtop enclosing hoods have been done (Guffey and Barnea, 1994;He, 2010;Karaismail and Celik, 2010). Face velocity is the most important factor that affects worker exposure (Guffey and Barnea, 1994;He, 2010).…”

“…He (2010) found that the simultaneous effects of V face and V cross had a significant effect in the performance of enclosing hoods using a heated and breathing anthropometric manikin. In addition, the wake region formation was predicted downstream of a simple manikin using numerical simulation (Karaismail and Celik, 2010).…”

“…Despite a diligent search, two experimental studies, Guffey and Barnea (1994) and He (2010), and two numerical studies, Dunnett (1994) and Karaismail and Celik (2010) are the only published studies about plain enclosing hood performance. They studied the effects of V face , V cross , worker orientation, flanges (He, 2010;Guffey and Barnea;1994), recirculating flow and airflow patterns on the performance of plain hoods (Dunnett, 1994;and Karaismail and Celik, 2010). However, although the effects of these factors on the performance of benchtop enclosing hoods were demonstrated with these studies, these results have not been validated with human subjects.…”