Small Peltier element to detect real-time heat flux between apple and environment during postharvest storage

Abstract

Climate control mechanisms in the postharvest chain of fruit and vegetables are predominantly based on air temperature measurements. These, however, do not reflect the real heat exchange between the product and the environment in all situations. The direct recording of the incoming and outgoing heat flux should enable higher-quality statements to be made about the interaction between the food product and the environment since other influencing parameters are also taken into account (e.g. air velocity and radiation). Commercial heat flux sensors are readily available but expensive, and for a variety of reasons, are not suitable for use directly on horticultural products, or are suitable only to a limited extent (e.g. large products, such as melons). In this study, small and low-cost Peltier elements (PE) were primarily tested and successfully validated as an alternative for their use in measuring heat exchange. Cooling, fluctuating temperature, and re-warming tests were applied to evaluate and validate the use of PE during the heat absorption and release of individual apples. The results confirmed the reliable detection of minor heat fluxes, regardless of direction, with small temperature differences (<0.5 °C) between the fruit and the air. The new heat flux measurement methodology has potential applications in agricultural technology, including optimizing packaging, and designing storage equipment.