The effect of alternating ventilation on forced air pre-cooling of cherries

Large temperature gradients caused by the traditional forced air pre-cooling method leads to the decrease of the shelf life of horticultural products. An alternating ventilation of air pre-cooling is one of the key methods to reduce the temperature inhomogeneity of cherries. The research results on the alternating ventilation change showed that the operating time of fan was not neglected in the forced air pre-cooling. It reached up to 7.70% of total pre-cooling time when the number of ventilation changes no more than five. In general, the total pre-cooling time was proportional to the number of ventilation increase. The final inhomogeneity of cherries first quickly decreased from 0.237 to 0.097 with air direction changing once and then fluctuated from 0.09 to 0.120 with the number of ventilation changing from 1 to 5. Through the comprehensive analysis of temperature inhomogeneity and pre-cooling time, the optimal alternating ventilation on forced air pre-cooling of cherries was ventilation changing once.

Thermal physical properties of the golden pomfret at low temperatures

Food thermal properties are essential for calculating freezing time and analyzing energy cost during food freezing or thawing. However, there are currently few data or models of physical properties for foods below −40 °C (e.g., thermal conductivity of food at lower temperatures are lacked due to limitations of device testing below −40 °C). In this paper, the thermophysical parameters of golden pomfret were tested in the temperature range from −100 °C to room temperature. The freezing point was determined. The specific heat and enthalpy of golden pomfret were measured by using a DSC, and the thermal conductivity was measured by a novel self-designed device cooled by a pulse tube cryocooler that can give low temperatures to −253 °C. Finally, the temperature profile obtained by numerical calculation was consistent with experimental results, which proves that predicted models of thermal physical properties in this work will provide reliable data support for the cryogenic freezing of food.

Evaluation and optimization of air-based precooling for higher postharvest quality: literature review and interdisciplinary perspective

Precooling is of significant importance for postharvest fruits and vegetables to control the quality degradation and prolong the shelf-life. Current precooling methods include room cooling, forced-air cooling, hydrocooling, vacuum cooling, contact or package icing, and cryogenic cooling, all of which have their advantages and disadvantages. The first two methods with the cooling medium of air are extensively used because of the wide applicable range of fruits and vegetables. Numerous studies have been devoted to cope with the drawbacks of these two air-based precooling methods with various evaluation criteria and optimization methods. A systematic literature review on these studies is firstly conducted with respect to experimental and numerical investigations respectively for the two methods. The main contributions from the previous studies are also summarized respectively with the research objectives and performance metrics. The literature review indicates that the current performance evaluation is limited to apparent parameters and the optimal design is only proposed based on the performance evaluation and comparison. Furthermore, with inspiration from the research in other domains, a scheme of advanced evaluation and optimization for air-based precooling methods is proposed with thermodynamic evaluation metrics and constructal optimization methods from the interdisciplinary perspective.

Impact of ventilation design on the precooling effectiveness of horticultural produce—a review

Optimizing the ventilation design of packaging system is of crucial importance for improving the efficiency of the forced-air precooling process to maintain the quality of horticultural produce and extend the shelf life in food cold chain. Many efforts had been devoted to the study about the impact of ventilation design on airflow and temperature distribution inside ventilated packages. This paper reviews relevant research methods, commonly used quantities for the measurement of precooling effectiveness, attractive design parameters, and their impact on precooling effectiveness. These allow us to know exactly the characteristic and deficiency of each research method, identify dominant design parameters, and seek a promising way for the future improvement of the ventilated packaging system.