Evaluation of the effects of water agitation by air injection and water recirculation on the heat transfer coefficients in immersion cooling

Most industrial food cooling is performed by air blast, water spraying and immersion cooling. Immersion cooling is simple, with low operational cost and leads to food quick cooling. The objective of this work was to investigate the influence of water agitation method (water injection, air injection and water injection coupled to a Venturi ejector) on the average heat transfer coefficient (h¯) between food and cooling water. Time–temperature evolutions of a sphere immersed in the cooling media were used to determine the heat transfer coefficients at different positions in a cooling tank. Air injection and water injection coupled with a Venturi ejector significantly increased the heat transfer coefficient between food and cooling water. For the investigated conditions, h¯ was increased up to eight times, when air injection was used. However, the complex flow of bubbles and water inside the tank created heterogeneous water agitation, creating zones with different heat transfer coefficients. Furthermore, the use of water recirculation coupled with a Venturi ejector can be very convenient for cases where pressurized air is not available, but the best agitation solution depends on each case.