Experimental investigation into the integration of solid desiccant packed beds with oscillating heat pipes for energy efficient isothermal adsorption processes

Abstract

The heat of adsorption released during physical adsorption of water vapour on solid desiccants increases its surface vapour pressure consequently decreasing its adsorption capacity. In packed beds, this raises the bed temperature subsequently increasing the cooling load and energy required for the regeneration of the solid desiccants. In this study, we experimentally investigated helically coiled oscillating heat pipes (HCOHPs) using ethanol, methanol and deionized water respectively as working fluids integrated with packed beds of varying configurations towards isothermal adsorption. The results show average bed temperature reduction varied with heat output from the bed and the thermal performance of the HCOHPs. The fully packed bed (FPB) integrated with the ethanol HCOHP (EOHP) achieved maximum average bed temperature reduction of 14.0 °C. The annulus packed bed (APB) integrated with the water HCOHP (WOHP) achieved a temperature drop of 10.1 °C. Adsorption peak temperature reductions on the other hand were strongly dependent on HCOHP start-up. Maximum adsorption peak temperature reduction of 20.8 °C in Mass Transfer Zone (MTZ) 1 was attained by the FPB-EOHP integrated system. For the APB, maximum adsorption peak temperature reduction of 13.2 °C in MTZ 3 was recorded for Small APB (SAPB)-Methanol HCOHP (MOHP) integrated system. Adsorption rates in the FPB were influenced by the mal-distribution of flow within the bed and increased slightly on integration with the HCOHPs. Maximum adsorption rates of 1.47 × 10−06 kg/s was achieved by the FPB-EOHP. For the APB, the SAPB-WOHP achieved maximum adsorption rates of 1.21 × 10−05kg/s. The adsorption rates in the Medium APB (MAPB) on the other hand did not appear to be influenced on integration with the HCOHPs. Overall, performances of the integrated systems were found to be influenced partly by the packed bed configuration, the HCOHPs’ performance and the heat transfer resistance between the evaporators and the vessel walls. We recommend further optimization of the system parameters and investigation of its regeneration potential for future practical applications.