Abstract
This study examines the performance of three heat pump dryers: the original reference design, a modified drying chamber, and an external desiccant wheel design. Unlike most existing studies that normally adopt organic products as the drying materials, in this study we used moist sodium polyacrylate (Orbeez) as the drying material for consistent characterization of the heat pump performance. R-134a was adopted as the refrigerant for the heat pump system. The experiments were performed subject to different weights of Orbeez (drying material) at a constant volumetric flow rate of 100 m3/h. During experimentation, different parameters like the coefficient of performance (COPHP), drying rate, heat transfer rate by the condenser, moisture extraction rate, and specific moisture extraction rate were calculated. The average COPHP, mass transfer rate, heat transfer rate, MER, and SMER of the system were calculated as 3.9, 0.30 kg/s, 0.56 kW, 0.495 kg/h, and 1.614 kg/kWh, respectively. The maximum COP for the refrigeration system was achieved at lower test loads with the desiccant wheel. The moisture extraction rate for a lower test loading was higher than that for a higher test load due to the higher penetration of drying air at the lower test load, although the maximum test load showed the maximum relative humidity at the dryer outlet. The desiccant wheel showed good performance in terms of moisture extraction rate and COPHP, but it showed poor performance in terms of the specific moisture extraction rate due to the high power consumption (around 2.6 kW) of the desiccant dehumidifier. The moisture extraction rate (MER) for all designs increased to a maximum value, followed by consistent decline. However, the maximum MER for the desiccant design exceeded those for the other designs.
Highlights
Drying is widely used in polymer, food, pharmaceutical, mineral, and other industrial processes
In order to increase the drying efficiency of the traditional heat pump dryer and pre-condition the humid air before it enters the dryer, in this study, we developed an adsorption dehumidification device at the entrance of the traditional heat pump dryer, namely, a desiccant rotary wheel, to reduce the inlet humidity and use the energy released by the adsorption process to increase the inlet temperature
We developed a heat pump dryer (HPD) to assess the performance closed-loop heat dryera system, and dryer a modified chamber was
Summary
Drying is widely used in polymer, food, pharmaceutical, mineral, and other industrial processes. The drying process is strongly associated with ambient conditions in terms of humidity This is an especially essential consideration in tropical or subtropical countries where the humidity is comparatively high. An alternative drying process is via heat pump, which transports heat energy from a low temperature source to a high temperature source with supplied work. It can offer much larger thermal energy at the expense of much lower input work. Many efforts have been made in the literature to resolve these limitations of conventional drying methods These efforts include improving the product quality and overcoming the operational problems. Most of the conventional drying methods (either by convection or direct heating) employ fossil fuels as the power source and are thereby accompanied by greenhouse gas emissions and pollution, which are a prime concern
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