Clément Vigneault

Effect of Container Openings and Airflow Rate on Energy Required for Forced-Air Cooling of Horticultural Produce

A research tool previously developed to investigate air distribution in horticultural produce containers during forced-air precooling was used to determine the effect of airflow rate and opening configuration on air pressure drop and rate and uniformity of cooling process. Further analysis performed on previously tested opening configurations determined their influence on energy efficiency. A system efficiency coefficient, consisting of the overall Energy Added Ratio (EAR) was demonstrated as a functional tool during the container design, since it considers peculiarities of the forced-air cooling system and produce physiology. The results obtained for containers with handling openings and 2, 4, 8, and 16% opening area were used to evaluate the additional energy required to remove the heat generated by the forced-air fan and produce respiration. These results were also compared to produce in bulk and to produce packed in containers having 4-0.5%-holes in the corners to analyze the influence of hole positioning. A four large 0.5% opening configuration results in poor energy performance and cooling uniformity when compared to uniformly distributed smaller holes. Furthermore, the airflow rate could be optimized based on the respiration rate of the produce and container opening area.

Effect of Different Accessories on Airflow Pattern Inside Refrigerated Semi-Trailers Transporting Fresh Produce

This study attempted to determine the effect of different accessories on air distribution in refrigerated semi-trailers transporting fresh horticulture produce. Air temperature data were gathered from mixed loads; including fruits, vegetables, cut flowers, and nuts, transported in 20 trailers equipped either with frame or solid bulkheads, and flat or duct floors. Some trailers were also equipped with an air-delivery duct to improve air circulation at the rear and sides of the load. However, the airflow patterns varied so greatly for trailers with similar conditions that no conclusive statement could be made about which set of accessories could better improve air distribution. Further research is necessary to determine the best accessories to be used to enhance air circulation during transport of fresh produce. However, one important conclusion could be drawn from this research project; the variability of air distribution is extremely high and there is not existing standard commercial procedure to correct this situation.

Method for Determining the Respiration Rate of Horticultural Produce Under Hyperbaric Treatment

A method was developed to determine the metabolic respiration rate (RRm) of fresh produce during the transient period at the beginning of a hyperbaric treatment. This method allowed for the correction in the apparent respiration rate (RRap) by considering the dilution effect of flushing the system and the error associated with gas solubilisation as the gas partial pressure varied. The dilution process was simulated by using the general equation for exhaust ventilation, thus allowing for the elimination of the dilution effect during the calculation of the net respiration rate (RRN). The error associated with the CO2 solubilisation in the flesh of the produce was solved by measuring the CO2 solubility in the tissues of tomato at various CO2 partial pressures and using this value to generate a mass balance of CO2 within the system. The RRm was estimated by incorporating the initial respiration rate (RRi) of untreated fruits with the respiration rate at equilibrium (RRe). The kinetic of the RRm was proposed to follow a negative exponential equation. The constant value (k) of the RRm model was found to decrease exponentially with the partial pressure of CO2 at equilibrium which affected the amount of gas solubilised and the time to reach equilibrium. The developed method should be validated for the RRm of other produce during the transient period at the beginning of a hyperbaric treatment.

Effect of the Presence of Openings as Container Handles on Cooling Efficiency of Horticultural Produce

The presence of large openings serving as handles in horticultural crop packages is problematic due to its effect on air flow distribution uniformity and processing time for precooling of produce. Measuring this effect will result in a better approach for designing package and optimizing openings. The aim of this research was to determine the influence of different handle configurations on forced air precooling efficiency of horticultural crops. Opening designs were evaluated based on the rate and uniformity of cooling process of produce simulators. A comparison was made between configurations resulting from total venting area percentages (2, 8 and 16%) and standard opening configurations (open and closed). The tests were conducted under airflow rates ranging from 0.25 to 2 L.s-1.kg-1. The results demonstrated the impact of using standard handles on the side of horticultural crop containers. Their influence on the enhancement of uniformity of air distribution through porous medium increased as the opening area was reduced and the airflow rate rose.

Effect of Peripheral Openings on Cooling Efficiency of Horticultural Produce

Due to the significant level of losses of horticultural produce during post-harvest operations, the reduction of the general process costs and the conservation of the produce quality are intensely searched. Among these processes, precooling plays an important role in the achievement of the latter two objectives. In turn, the precooling efficiency is decisively affected by the design of the container. The aim of this research was to quantify the effect of different container opening configurations for forced air precooling efficiency. The designs were evaluated based on the response of the rate and uniformity of cooling, and air pressure drop across the container and the produce. A comparison was made between eight configurations, which were formed by combining four total venting area percentages (0.67, 2, 4, and 8%) and two distributions on the package surface (peripheral and central). The tests were conducted under five airflow rates ranging from 0.125 to 3.9 L.s-1.kg-1. The results allowed the determination of the effect of the opening configuration on the cooling rate and uniformity through the entire horticultural produce package.

Indirect Airflow Distribution Measurements in Horticultural Crop Packages

The airflow distribution through a porous medium such as horticultural crops is a great challenge. The development of a method allowing the measurement of the air velocity or its distribution would be of large interest. The applicability of using instrumented balls as an indirect measurement of air velocity was evaluated. A group of 64 instrumented plastic balls were used as horticultural produce simulators and strategically distributed in an orthogonal matrix along with other 448 plastic spheres to simulate precooling of column stacked produce. The ball matrix was submitted to cooling process under controlled conditions. Correlations were determined by measuring the half-cooling time of 64 simulators positioned at fixed locations inside of the two-end-fully-open ball matrix. The surrounding air velocity was inferred as a function of the simulator locations in reference with the air entrance. This method was then evaluated by comparing the data obtained for three package opening areas (0.67%, 2%, and 6%), and six airflow rates (ranging from 0.125 to 3.9 L•s-1•kg-1), and performing a mass balance. This comparison showed the capacity of this method in predicting the variation of the cooling rate as a function of the airflow rate and its capacity in inferring the mean air velocity through the ball matrix.