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- Study of the aerodynamic sealing of a cold store – Experimental and numerical approachesPublication . Goncalves, J.C.; Costa, J.J.; Figueiredo, A.R.; Lopes, A.M.G.An experimental study was conducted in a laboratory scale model in order to characterize the airflow generated by an air curtain device (ACD) on the aerodynamic sealing of refrigerated spaces. The laboratory scale model consists of two similar adjacent rooms connected by a door over which the ACD device was installed. The tracer gas technique was used to calculate the sealing effect achieved with the air curtain at different jet velocities. A three-dimensional numerical model was also developed to simulate the heat and mass transfer phenomena, as well as the aerodynamic sealing performance of an ACD. The numerical study was carried out using a commercial CFD code (ANSYS-CFX®) and the turbulence effects were approached by two different turbulence models (k–ε and k–ω SST). The experimental and numerical results show a good agreement for validation purposes. No significant differences were found in the results obtained with the two turbulence models, although the k–ω SST model seems to be more appropriate for the simulations. The existence of an optimum discharge air jet velocity was confirmed. The results also indicate that the air curtain is more efficient in reducing the mass transfer than the energy flow rate across the doorway.
- CFD modelling of aerodynamic sealing by vertical and horizontal air curtainsPublication . Goncalves, J.C.; Costa, J.J.; Figueiredo, A.R.; Lopes, A.M.G.This work presents a comparative study of the aerodynamic sealing of doorways of refrigerated rooms, obtained by vertical and horizontal air curtain devices (ACD). The sealing efficiency is estimated for different situations, with the ACD installed inside, outside or on both sides of the door. For this purpose, a numerical model was developed for the simulation of the turbulent non-isothermal 3D airflow generated by the air curtain in the transient period after the door is opened. The buoyancyinduced airflow field when the ACD is turned off and the door is open was taken as a reference to assess the sealing efficiency. Numerical results are plausible and comply with the physical interpretation of the convective phenomena. In line with previous investigations, the optimum velocity of the air jet was found, corresponding to the highest sealing effect. The advantage of installing the ACD outside the refrigerated room was shown by the present simulations. According to the present study, downward blowing air curtains present better sealing efficiency (over 70%) compared to horizontal jet air curtains (about 55%). Although the direct air recirculation provides a better sealing efficiency (over 80%), the system complexity and the installation and maintenance costs inhibit its common use.
- A Study on the Sealing Efficiency of Air Curtains: 2D and 3D ApproachesPublication . Goncalves, J. C.; Costa, J.; Figueiredo, R.; Lopes, A.In industrial refrigerated spaces, such as retail stores, where sometimes doors must be open for long periods, the infiltration loads can represent more than half of the total refrigeration load. The use of air curtains can significantly reduce the air infiltration through doorways and, at the same time, it allows the free access by persons and equipment [1]. Besides the experimental research, computational fluid dynamics (CFD) has been commonly used, either adopting a two dimensional (2D) approach [1] or, more recently, through a three-dimensional (3D) perspective [2,3]. This work presents a numerical and experimental study on the performance of air curtain devices in the aerodynamic sealing of access doors of refrigerated spaces. For this propose, a 3D numerical model was developed aiming at the simulation of the turbulent non-isothermal airflow generated by the air curtain since the moment the door is opened. The calculation domain represents a laboratory scale model consisting of two similar adjacent rooms connected by a doorway over which the air curtain device is installed. One of these rooms represents a refrigerated chamber and the other, the outdoor environment. The numerical study was carried out using a commercial CFD code (ANSYS-CFX) and the turbulence effects were approached by k-_SST turbulent model. In the experimental study, the tracer gas technique was used to estimate the air exchange rate through the doorway in the initial period of the transient process and consequently assess the sealing effect obtained with the air curtain device operating at different jet velocities. The numerical results show that the air curtain simulated is appropriate to protect the doorway in its whole width, and a good agreement is verified with the experimental measurements. Results of a simplified 2D approach are also shown and compared with the 3D simulation