Drying Characteristic of Agricultural Products under Dehumidified Air and Estimation of Its Quality (Part I) : A Fundamental Drying Experiment for a Method to combine Solid Moisture Adsorbent and Dehumidifier

In order to develop a high efficient drying system for agricultural products, some fundamental experiments for generating air at normal temperature and under lower humidity were performed. Considerations were paid about a practical combination of solid absorbent and heat pump dehumidifying methods. The efficiency of absorption and the moisture absorption for each method were investigated under practical applications. The results obtained can be summarized as follows : 1. In case of air ventilation with high humidity, the efficiency of absorption of desiccant silica gel decreased rapidly at more than 35% (d.b.) moisture content. 2. Judging from the analysis of absorption water of desiccant silica gel, relationship between limit absorption time T (h) and thickness of sedimentary layer Xn (n : tray number) was shown as follows. T=0.75+0.725Xn 3. Change of absorption water of desiccant silica gel was obserbed at various sorts of the thickness of sedimentary layer (Fig.7). The efficiency of absorption was investigated under practical applications. 4. A break point was estimated from air condition through desiccant silica gel. Average moisture content of desiccant silica gel was about 27.5% (d.b.) at the break point. Relationship between the break point time T (h) and ratio of silica gel weight M (kg) to air flow G (kg/h) was shown as follows. T=0.558+115.87(M/G) 5. Calorific value of absorbent of desiccant silica gel was measured at absorption process. The value of dried silica gel 1 kg was estimated at 450 kcal within the break point time. 6. In order to investigate the drying efficiency fitness for refreshement of desiccant silica gel, heat ventilation drying was carried out by using high moisture content silica gel. Relationship between refreshment time T (h) and M/G was shown as follows. T=0.475(M/G)^<0.726> 7. The performance of heat pump dehumidifying was investigated. In case of using air with high temperature and humidity under practical applications, removal moisture in the air could be estimated 1.6～2.0 kg/h by 1 kw compressor power in heat pump dehumidifier. 8. As heat pump dehumidifying efficiency changed with absolute and/or relative humidity, it was considered to be suitable for heat pump dehumidifier to have moisture removed from the high temperature and humidity air