Thermal performance of a novel helically coiled oscillating heat pipe (HCOHP) for isothermal adsorption. An experimental study

Abstract

Helically Coiled Oscillating Heat Pipes (HCOHPs) have been designed and tested under laboratory conditions to investigate their potential to achieve isothermal adsorption when integrated with a cylindrical solid desiccant packed bed system. The HCOHPs fabricated out of copper, are essentially single turn closed loop oscillating heat pipes with their evaporator and condenser sections helically coiled. They were charged with ethanol, methanol and deionised water respectively at approximately 60% volume fill ratio and tested by slotting through their helically coiled evaporators an empty cylindrical copper vessel which allowed hot air to be blown through at various heat loads to ascertain their thermal performances.The results showed there were critical heat fluxes which varied with heat input amount at the evaporator, beyond which dry-out commenced and thermal resistance increased. These heat fluxes were ≤ 70 for the ethanol HCOHP and ≤ 105 for both the methanol and deionised water HCOHPs. Performance instabilities owing to liquid phase of the working fluid transitioning in the drying-out stage was observed for the methanol HCOHP beyond 234W. The variation of the effective thermal conductivities at the evaporators were found to influence the thermal contact resistance experienced at the contact interface of integration and the maximum heat input amount at the evaporators. Optimum performance between the HCOHPs was observed with the deionised water type. Overall, the HCOHPs were capable of managing relatively large amounts of heat input due to their helically coiled sections creating comparatively larger evaporator sections holding relatively more working fluid than the conventional serpentine single turn closed loop OHP system of the same volume and fill ratio. Investigations involving the visualization of the internal flow dynamics is recommended for future studies.

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

“…as MOHP and the deionised water (𝐻 2 𝑂) as WOHP [32] . The HCOHPs were made of copper tubes of internal diameter, 2mm and thickness, 1mm.…”

“…In our previous work [32] , we developed helically coiled oscillating heat pipes (HCOHPs) charged with ethanol, methanol and deionized water respectively at approximately 60% volume fill ratio and tested them under laboratory conditions to evaluate their capacity to cool adsorption packed beds. In subsequent studies [33] , we experimentally investigated the influence of the Heggs et al [34] Z-annulus configuration on the enhancement of the physical adsorption process.…”

“…The study also builds up on work done by Yeboah [35] . In this present investigation, we have integrated the HCOHPs that we developed [32] with the investigated [33] solid desiccant packed bed adsorbers in order to evaluate their thermal effectiveness for isothermal adsorption processes. As passive two-phase heat transfer devices [24][25] , the Helically Coiled Oscillating Heat Pipes (HCOHPs) do not require external energy for the cooling of the solid desiccant packed bed adsorbers and the whole process is envisaged to help achieve an isothermal adsorption process.…”

Experimental data on Helically Coiled Oscillating Heat Pipe (HCOHP) design and thermal performance

“…The data presented here are for ethanol, methanol and deionized water charged Helically Coiled Oscillating Heat Pipes (HCOHPs) tested under laboratory conditions at three different heat inputs [1] . The tests were designated Run 1 or (R1), Run 2 or (R2) and Run 3 or (R3) representing maximum heat input element temperatures of 100 °C, 125 °C and 192 °C, respectively.…”

Numerical Simulation of Helically Coiled Closed Loop Pulsating Heat Pipe

“…This is the Neumann boundary condition because it involves the value obtained from the derivate of thermal energy per unit area with respect to time. In some of the experiments performed by researchers (Yeboaha et. al (2018)), the walls of evaporator is heated by a hollow cylindrical pipe in which a hot liquid flows.…”