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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.
- Numerical study of the optimal nozzle width and jet orientation in a downward blowing air curtainPublication . C. Goncalves, J.; Costa, José Joaquim Da; Gameiro Lopes, Antonio; Figueiredo, A. RuiThis paper presents a numerical study of the performance of an air curtain device (ACD) installed on top of the access door of a refrigerated room, aiming to quantify the influence of some parameters (nozzle width, initial orientation and discharge velocity of the jet) towards the maximization of the sealing effect. For this purpose, a numerical model was developed to simulate the turbulent non-isothermal 3D airflow generated by the ACD jet, focusing on the period after the door is opened. The situation when the ACD is switched off is taken as the reference for the performance evaluation. The results allow identifying an optimum jet nozzle width corresponding to maximum sealing efficiency and lower jet airflow rate (lower energy consumption in the air curtain operation). For the present conditions (ACD installed outside the refrigerated room), the sealing efficiency is highest with the ACD oriented vertically and is practically unaffected if the jet discharge is directed towards the warmer space. On the contrary, a jet discharged towards the cooler space is very detrimental to the ACD sealing effect
- Analysis of the air infiltration through the doorway of a refrigerated room using different approachesPublication . Gonçalves, J. C.; Costa, J.J.; Lopes, A.M.G.This paper presents the study of the air movement through the doorway of a refrigerated room, using both numerical and experimental approaches. Firstly, a comparison is made between the experimentally observed infiltration rates and the predictions by seven empirical models. For different test conditions of the specific laboratory configuration under analysis (a refrigerated room at laboratory scale), the infiltration rate was measured using the tracer gas technique. A three-dimensional numerical model was developed to simulate the heat and mass transfer phenomena, using a commercial CFD code (ANSYS-CFX®). For the simulations, turbulence effects were taken into account using the k- SST turbulence model. CFD results showed a good agreement with experimental data, confirming that the numerical model is appropriate to evaluate this physical phenomenon. The experimental and numerical results showed that the neutral flow level is located above the doorway mid-height and that the maximum airflow velocity occurs near the doorposts. Results also evidenced that, although most of the empirical models tend to overestimate the infiltration rate, some of them present a quite good prediction ability. Measurements in a real scale refrigerated room confirmed the trend obtained in the laboratory installation.
- Parametric study on the performance of an air curtain based on CFD simulations - New proposal for automatic operationPublication . Goncalves, J. C.; Costa, J.J.; Lopes, A.M.G.This paper presents a parametric study on the performance of an air curtain installed over an access door of a refrigerated room. The aim of this work is to quantify, in an integrated way, the influence of the following geometrical and dynamic parameters: door height; temperature difference between rooms, nozzle thickness; initial orientation angle; jet discharge velocity. A numerical model was used to simulate the turbulent non-isothermal 3D airflow generated in the transient period after the door is opened, with the air curtain device turned on or off. Turbulence effects were taken into account with the k-SST model. Results show that the optimum discharge velocity of the air curtain increases with the door height, as well as with the temperature difference between both sides of the air curtain. It was also possible to find an optimum jet nozzle width corresponding to maximum sealing efficiency and lower jet airflow rate. A proposal is made for an empirical correlation to predict the optimum jet discharge velocity as function of the variables used in the parametric study. Additionally, to ensure that the air curtain operates near the optimum conditions, the appropriate air curtain settings are discussed and a new strategy is suggested.
- Computational Fluid Dynamics Modeling of Ammonia Concentration in a Commercial Broiler BuildingPublication . Goncalves, J. C.; Lopes, António M. G.; Pereira, José L.S.In the present study, a numerical model was developed to predict the flow pattern inside a broiler building. The model intends to predict the velocities fields inside the domain and am-monia (NH3) emitted or released by litter from poultry housing. The numerical model developed in Computational Fluid Dynamics (CFD) commercial code, intends to represent a commercial broiler building, and intends to simulate the 3D and heat transfer, in steady state flow. The evaporative cooling pads were also included in the model. The validation of the model was based in experimental measurements obtained in previous studies. The simulations were fo-cused on Summer, Winter and also Mid-Season situation. The numerical results of NH3 concen-tration were compared with the experimental measurements, and a quite good agreement was verified. The numerical results allowed the characterization of: the inside flow pattern devel-oped for the summer and winter situation; the inside NH3 distribution, and the velocity field distribution inside the broiler building. It was found that NH3 concentration increases along the tunnel, especially in low flow rate imposed from the exhaust fan. Also, it was verified that the low velocities inside domain are no sufficient to remove the gaseous pollutants.
- 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
- Empirical correlation to estimate the optimum jet velocity of an air curtainPublication . Goncalves, J. C.; Costa, José; Figueiredo, A. Rui; Lopes, AntónioThis paper presents the results of a parametric study to quantify the influence of some thermal and geometrical parameters (door height) on the performance of an Air Curtain Device (ACD). The experimental facility 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. Using a commercial CFD software, a numerical study was also performed to simulate the heat and mass transfer phenomena, as well as the aerodynamic sealing efficiency. A good agreement was observed between experimental and numerical results, showing that the optimum discharge velocity of the ACD air jet increases almost linearly with the door height, as well as with the temperature difference between both sides of the air curtain. It was possible to establish an empirical correlation that predicts reasonably well the optimum discharge jet velocity of a vertical air curtain device, depending on the temperature difference and the doorway height. An electronic device can be included in the ACD enabling the automatic adjustment of the air curtain jet velocity based this correlation, in order to continuously operate close to maximum sealing efficiency.