ASHRAE LO-09-043-2009 A Comparative Study of the Effect of Initial Turbulence on the Performance of an Open Vertical Refrigerated Multi-Deck—A Numerical Study and its Experimental Validation
ASHRAE - American Society of Heating@ Refrigerating and Air-Conditioning Engineers@ Inc.
Scope
INTRODUCTION Open refrigerated display cases (ORDC) are common used in supermarkets to maintain the food products at setting temperatures. In typical design of ORDC@ having a correct temperature setting and an appropriate controlling entrainment or infiltration rate are the most crucial deign parameters as far as energy saving is concerned. The suitable design parameters can be obtained either numerically or experimentally. As far as cost is concerned@ CFD is regarded as the best design tool because it is generally fast and reliable. Hence@ there were many researchers adopt CFD tools to optimize the design parameters and to improve the performance of open display cases [1@ 3-6@ 8-14]. Amid the CFD examinations of relevant design parameters under vertical design situation@ most of them were performed in two-dimensional conditions [1@ 3-5@ 9-14]@ and only very few literatures (D'Agaro et al. 2006; Foster et al. 2005) were using three-dimensional simulation. The simulations [1@ 5-6@ 8-14] were generally compared with experimental tests but its agreement with the experimental data was usually qualitative rather than quantitative. For the horizontal refrigerated display cases@ the simulation by Cui and Wang (2004) is the only one that is in line with measured temperature profile at the outlet of the air curtain. For the vertical refrigerated display cases@ unfortunately@ none of the existing literatures can provide a quantitative agreement with the experimental data. Notice that in vertical refrigerated display case the momentum force of air jetting from DAG and buoyancy force counteracts with each other@ resulting in imbalance during simulations. Yet the importance of buoyancy force can be made clear from the numerical simulation carried out by Bhattacharjee and Loth (2004) and was confirmed experimentally by Field and Loth (2006). Without considering the influence of buoyancy force@ it was not surprised that the simulation results [9-14] were not consistent with the measurements. There were some studies associated with the influence of buoyancy force. Cortella et al. (2001@ 2002) included the buoyancy force in the simulation but the simulation was unable to extend to 3D situation for the model was based on streamvorticity formulation. D'Agaro et al. (2006) considered both buoyancy force and 3D effects@ and showed that the cabinet performance was highly dependent on 3D flow structures. However@ they mentioned that it was quite difficult to achieve full agreement with experimental data due to the uncertainty in the experimental boundary conditions@ especially in the velocity distribution at the curtain outlets@ small imperfection in the actual cabinet geometry@ or modeling issues in radiative heat transfer. The forgoing survey suggests that a 3D simulation model taking into account the effect of buoyancy force accompanied with and the exact boundary conditions would resolve the present inaccurate agreements between simulations and experiments. Hence it is the purpose of this study to include these effects for simulation. The simulation is made in a typical ORDC having six decks (Fig. 1). In addition@ the experimental verification is also carried out to compare with the simulation result.