Investigations into the thermal performance of a helically coiled closed loop oscillating heat pipe

A numerical and experimental investigation has been carried out to evaluate the thermal performance of a helically coiled closed loop oscillating heat pipe (OHP). The OHP was designed to have its condenser and evaporator sections helically coiled to fit around a cylindrical packed bed vessel to offer a wider surface area of contact for enhanced heat transfer via the walls. The numerical investigation was carried out using an explicit Eulerian Volume of Fluid (VOF) model in ANSYS Fluent R15.0. Three working fluids within the required operating temperature range having suitable properties and compatible with copper were used to fill the OHPs to a volume fraction of 0.6. User defined functions (UDFs) were developed for realistic boundary conditions. The numerical results show that the OHPs at different heat inputs were still able to maintain a good temperature difference between the evaporator and condenser sections. The numerical model overall was able to give indication of the internal working conditions of the OHPs. For the experimental study, prototypes of the numerical models were developed and tested under laboratory conditions. Here OMEGA k-type thermocouples were used to obtain temperature data from the evaporator and condenser sections. The experimental results showed that the OHPs had the ability to maintain evaporator-condenser temperature difference at varied heat inputs. Thermal performance was found to be significantly different at start-up for the three working fluids, however overtime only a slight variation in thermal performance was observed at the varied heat inputs. Overall, there was reasonable agreement between experimental and the numerical study.