Design and Analysis of an Energy Efficient Dehumidification System for Drying Applications
The motivation of this research project was in response to problems of re-condensation in drying, reduced drying rate encountered by the food and beverage packaging industry which led to the aim of developing a better performing drying system as well as achieving high energy efficiency. A hybrid dryer suited for rapid drying applications is designed, constructed and experimentally tested and considered in atmospheric environment only. The system employs a heat pump in conjunction with a heat reactivated desiccant wheel to provide an efficient drying capability and supply low dew point temperature (DPT) conditions. The combined system utilises the heat dissipated by the condenser in regenerating the desiccant wheel, to increase the economic feasibility of such a hybrid system. Up to 60% heat energy can be saved by using the hybrid system in the rapid surface drying applications. Mathematical models are developed to obtain the correlations among the design operating and performance parameters of the dehumidification systems. The mathematical models can be used to estimate the performance of the hybrid system as well as the performance of the individual components of the system. A prototype model was designed, fabricated and tested. The experimental facility consisted of a heat pump desiccant dehumidifier with the new ecological R134a as a refrigerant which used the heat dissipated by the condenser. An analysis of the experimental data was conducted to determine the practical relationship between the operational parameters (COP, ma and TR) and performance parameters (SMER, DPT and ε) of the system. The observed behaviours of the test cases are suggested to be governed by a specific combination of the operation parameters. The analysis shows that the proposed hybrid system can deliver supply air at a much lower DPT compared with the single refrigerant circuit and a desiccant wheel. It is shown that the specific moisture extraction rate (SMER) for conventional dryers is 0.5 - 1 kg/kWh and SMER for heat pump based system is 3 - 4 kg/kWh whereas the hybrid system achieves SMER >5 kg/kWh. By operating the combined system in tandem, a greater amount of dehumidification could be realised due to the improved ratio of latent to the total load. The present research also confirms the importance of improving heat recovery to improve the performance of a heat-pump-assisted drying system.
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