The motivation of the research presented in this thesis was to investigate the potential of using a commercial 2.3 kW heat pump dehumidifier (HPD) simultaneously as a dryer for high-moisture agricultural products and for other domestic dehumidification/heating applications. A drying system incorporating the HPD was designed and constructed, along with instrumentation to gather data on the properties of process air as well as real-time weight of the material being dried. The HPD was equipped with an external water-cooled condenser that rejected excess heat out of the system. The design of the system allowed for conducting drying with recirculation of air as well as use of electrical heaters. In an open mode, the drying could be carried out simultaneously with room dehumidification and water heating in the secondary condenser. / The drying experiments were conducted with apple, tomato and agar gels. The system was found to be more effective in drying of material with higher amount of free moisture such as tomato. Comparisons were made between HPD assisted drying (partial and complete) and hot air drying (at 45°C and 65°C) in the same system using apple as the test material. Colour changes (L*a*b* values) in the samples were compared between treatments. It was observed that the degree of undesirable colour change was least in case of the HPD assisted system. The HPD dried fruit exhibited better rehydration properties than the hot air dried samples. Water activity of the HPD dried samples was noticeably lower than that of the hot air dried samples at the same water content, indicating that the residual moisture was probably held under higher tension. Histological observation indicated that there was a lesser degree of damage to the cellular structure of apple when dried with the HPD than when dried with hot air alone. / In terms of energy consumption, the process of HPD assisted drying is more expensive. Much of the energy input is rejected at the secondary condenser as excess heat. Unless this heat is recovered for another purpose, or the system is modified to reuse it for drying, the drying process must carry this loss entirely. The specific moisture extraction rate (SMER) for apple was as low as 0.1 kg per kWh with the HPD assisted system. The SMER values for drying at 45°C was 0.5 kg per kWh and was almost 0.8 kg per kWh at 65°C. / The HPD assisted drying system demonstrated the ability of heat pumps to link different energy related activities viz., drying, space dehumidification and water heating. The energy expenditure is expected to be impressive when considered for all the related applications. The concept of utilizing heat pumps on farms to link up different energy streams for better utilization of the low-grade heat sources is discussed. A possible drying efficiency assessment in the form of energy-based evaluation is proposed.

Ph. D.

No description available.

A deep-bed drying model simulating the drying of peanuts in a fixed bed is required for designing energy-efficient and automatically controlled dryers. A deep-bed drying model consists of a thin-layer drying model to calculate the moisture release from the material and a set of mass and energy balances. An experimental setup was constructed to determine drying rates of Virginia-type peanuts under 14 different drying air conditions. Selected empirical and semi-theoretical models available for modeling thin-layer drying rates were fitted to the collected data using nonlinear regression techniques. The modified Page's model and the two-term exponential model fitted the data better than other models considered. A deep-bed drying model PEATECH based on four coupled partial differential equations consisting of four variables, air temperature, peanut temperature, air humidity, and peanut moisture content was developed. Validation of the model was accomplished by using the data collected from 36 deep-bed drying experiments conducted using three laboratory dryers during 1987, 1988, and 1989. PEATECH predicted the variables within a peanut bed with an accuracy of less than ± 6%. The energy saving potential of exhaust-air recirculation was established by conducting simulated experiments using a modified version of PEATECH. / Ph. D.