Abstract
This paper provides the practical implementation of the single blow technique as an effective approach of average convective heat transfer coefficient measurement for a packed bed of horticultural products. The measurement approach was positively validated for the case of a packed bed of balls. The presented results cover heat transfer coefficient results for carrots stored in packed beds for two various arrangements (regular and irregular) and bed of apples under conditions of various turbulent intensity at the inlet to the bed. The turbulent intensity (defined as the ratio of the root mean square of the turbulent fluctuation of the air velocity to the mean air velocity) varied from 0.02 to 0.14. The applied velocity ranges for the tests refers to the conventional storage conditions. The heat transfer correlations were proposed based on the obtained results for each arrangement. It was demonstrated that due to flow laminarization inside the bed, the turbulence intensity has no significant effect on heat transfer inside the bed. Heat transfer enhancement of up to 25% was demonstrated for the case of the irregular carrot arrangement in the tested bed. The flow resistance correlations were additionally proposed for the tested beds. It was demonstrated that the product arrangement does not produce an important effect on the pressure drop.
Highlights
Knowledge of the mean surface heat transfer coefficient during cold storage of vegetables and fruits is important for the appropriate design of refrigerated storage chambers
The convective heat transfer coefficient is determined by means of comparison of the actual air temperature profile measured at the outlet of the tested bed with the predicted temperature profile determined based on the theoretical model
The above range of the Prandtl number corresponds to humid air as heat transfer fluid, which is the most common case for practical implementation of proposed heat transfer correlations
Summary
Knowledge of the mean surface heat transfer coefficient during cold storage of vegetables and fruits is important for the appropriate design of refrigerated storage chambers. Measurement of the surface heat transfer coefficient in a packed bed of horticultural products may be thought of as a complicated task. An additional complexity is caused by difficulties of the temperature distribution measurement at the products’ surface. This is related to the selection of possible fast and non-invasive approaches that should be applied in order to obtain accurate and reliable results. For this reason, it is difficult to directly apply the simplest methods based on direct measurement of the average surface temperature of horticulture products, temperature distribution of the air flowing between the products, and/or heat flux density
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