Heat pump dehydrator is an energy efficient and environmentally friendly drying system which uses electricity to drive a compressor and evaporator. It can utilize thermal energy from the dry exhaust gas generated during vaporization of refrigerant, as well as electric energy supplied by the compressor to achieve a high efficiency (COP), lower SMER, and higher drying temperature.

Heat recovery is the most important aspect of heat pump drying. In a properly designed heat pump dryer, it recovers both latent and sensible energy that would otherwise be lost in conventional dryers during the venting process (Keeye 1978; Strumillo and Adamiec 1996).

The use of multiple modes of heat input, simultaneous or consecutive, as well as cyclical variations in velocity or operating pressure can further enhance drying kinetics of heat sensitive products, resulting in reduced product degradation, improved quality, low energy consumption, and high performance.

For example, Mujumdar (1991) used a heat pump dryer to accelerate the drying of oats at temperatures below the condensation point, resulting in improved color and aroma retention. In addition, the oats dried in a heat pump dryer had fewer oxidative changes in the lipids than those dried in cabinet or tunnel dryers.

Another example of a heat pump drying application is the drying of sapota pulp to produce sapota powder. A heat pump dryer produced sapota powder with less color change and ascorbic acid degradation than that obtained from cabinet or tunnel dryers. Furthermore, the sapota powder produced by the heat pump drying process was also superior to that from traditional cabinet and tunnel dryers in terms of lactone and terpenoid retention (Sunthonvit et al. 2007). heat pump dehydrator

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