Study of heat transfer coefficients during refrigeration treatment of biological objects

Vollständiger Abstract

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Storing food products at low temperatures is one of the most effective and affordable preservation methods, extending their shelf life by slowing down the biochemical and microbiological processes occurring within the product. Optimizing refrigeration processes requires reliable data on the heat transfer coefficients of cooling media. The heat transfer coefficient depends on the thermophysical properties of the cooling medium and the product being cooled, the geometric shape and size of the object, the speed of the cooling medium, and other factors. The experiment involved measuring the steady-state electrical power of a heat source located within the sample, the surface temperature of the sample, and the ambient air temperature. Heat transfer coefficients were determined based on the measured heat transfer surface area of the samples, the magnitude of the heat flux, and the temperature difference between the surface temperature of the sample and the ambient air. Experimental studies were conducted using forced air convection with the specimen placed in a wind tunnel at surface heat fluxes of 20 and 35 W/m 2 and air velocities ranging from 1.0 to 5.0 m/s. The tunnel was installed in a refrigeration chamber maintained at minus 20 degrees Celsius. Under forced air convection conditions, with the Reynolds number varying from 2.7 x 10 4 to 5.1 x 10 4 for a spherical specimen, the total heat transfer coefficient varied from 33 to 52 W/(m 2 ·K), convective heat transfer from 30 to 49 W/(m 2 ·K), and radiant heat transfer from 2.8 to 3 W/(m 2 ·K). These studies allowed us to determine indicators characterising the intensity of heat transfer from meat specimens during refrigeration treatment, as applied to industrial meat production conditions, and can be used in heat engineering calculations.