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The Radiant Zone Dryer was developed to directly address the issue of flashing off initial moisture quickly without thermal damage to heat sensitive fruit, vegetable and extract products in order to increase the drying rate and thereby lower production and energy costs. The liquid product is applied to a clear polyester belt. The radiant heaters, below the belt, and the infrared temperature sensors, above the belt, are divided into multiple zones down the length of the drying chamber. The product temperature in each zone is set by the operator, typically between 45ºC and 90ºC. An infrared sensor reads the temperature of the drying product and the controller and relay regulate the heat to achieve the product set point. The zones compensate for changes in latent heat of vaporization and product temperature sensitivity.
The zones allow for more initial heat input during the constant rate drying period to allow for maximum evaporation to occur without raising product temperature, preventing thermal damage and a high production rate. In this early drying phase, the large amount of moisture in the product has a high latent heat of vaporization, so more heat is put into the product without significantly raising the product temperature. The water vapor is prone to flash off while the product viscosity is still fluid enough to allow for rapid vapor diffusion. By changing heat profiles, the throughput is dramatically increased and nutrient content is preserved.
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