Modification of air flows within an industrial carcass chiller using delta wing vortex generators

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Massey University
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The chilling of carcasses after slaughter has a considerable bearing on process costs and quality of the meat. Uniform air distribution is essential for the optimal operation of carcass chillers, yet many existing chillers have highly variable and ineffective air flow. This directly affects the uniformity of evaporative weight loss and carcass cooling rates within the chiller. Delta plan aerofoils are known to convert a unidirectional air stream, progressively into a rotational and then turbulent multidirectional fragments of moving air. The aim of this research was to evaluate the use of delta wings to improve air flows inside a venison carcass chiller of typical design used in the New Zealand meat industry. Air flow patterns within the chiller were characterised by measuring mean air speeds with a hot-wire anemometer over 61 grid points at 4 levels in height. Air speeds were found to be highly time-variable so the mean, standard deviation and range of 60 one second air speed measurements were used to represent the air flow at each point on the grid. The measurement of air velocity (speed and direction) using three othoganally mounted propeller anemometers had limited success, as air speeds within the chiller were often below the threshold of the anemometer. Measurements before the installation of the delta wings indicated that a poor air flow distribution existed within the chiller as the majority of air was found to circulate around the walls and floor, producing near stagnant conditions between the carcasses. Delta wings were constructed in two sizes from thin aluminium sheets. Wings were installed into the chiller by suspending them from the ceiling within the evaporator fan delivery air stream. Two wing configurations were trialed: The first wing configuration utilised 3 large delta wings mounted in front of the evaporator fans followed by a row of 6 small wings then a row of 7 small wings (3,6,7). The second delta wing configuration utilised a row of 6 large wings closest to the evaporator fans followed by a row of 9 small wings then a row of 13 small wings (6,9,13). The second delta wing configuration showed superior performance over the first. In comparison to the unmodified chiller without wings, the mean air speeds in the critical region amongst the carcasses increased from 0.4 m/s to 0.6 m/s; the standard deviation of mean air speeds decreased from 0.33 m/s to 0.22 m/s and the percentage of mean air speeds between half and twice the mean increased from 84% to 95%. The second configuration of delta wings also produced a 14% increase in the mean air turbulence intensity (measure of the time-variability in air speed) and reduced the variability of evaporative weight loss within the chiller. Overall, the delta wings were found to be an economic way to improve the performance of a chiller by providing a more uniform and effective air distribution without increasing fan power. This can result in a reduction in chilling times and less potential for weight loss. Their use in both new and existing chillers is recommended.
New Zealand Refrigeration refrigerating machinery, Meat Preservation, Aerofoils