Thin-layer modeling in heat pump drying of green peas
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The current drying of heat sensitive materials is mostly done by conventional vacuum freeze drying. The major challenges are a long residence time, a low drying capacity and high energy use. An innovative drying process has been developed at NTNU. This process is based on non-freeze and freeze drying at atmospheric pressure by application of heat pump technology. The advantages are energy efficiency, process sustainability and high product quality.However, there are still possibilities to improve the process by modeling kinetics and there is a need to study potential procedures to further reduce drying time and increase energy efficiency. This thesis work objectives includes a literature review and experimental tests in a laboratory heat pump dryer. The literature on the current and past research in this field will provide the status of the engineering in heat pump drying and will indicate further needs in the present research. Experiments will be performed at different heat pump drying conditions and using multi thin-layer of green peas. The experimental results of the drying tests will be acquired and analyzed concerning to kinetics, drying rates, moisture content as function of time, energy use and color of the dried green peas. The results will indicate how the heat pump drying temperatures, air psychrometric properties and position of the green pea layers will reflect upon the residence drying time, efficiency and quality of the product. Additionally, suggestions will be made for further experiments and studies on heat pump drying of green peas and other sensitive vegetables.