Experimental Investigation on Multi-Turn Oscillating Heat Pipes

Thermal management is the challenge of the day in electronic product development. Presently, the chip heat flux level ranges between 40 to 120 W/cm2. It is expected to increase to 200 W/cm2 in the next few decades. Several cooling methods are employed to cool the electronic devices. Heat Pipe is being explored for electronic cooling devices with promising results. Even though the conventional heat pipes are excellent heat transfer devices their application is mainly confined to transferring small amount of heat over relatively short distances. Oscillating Heat Pipes (OHPS) has proved to transport heat for longer distances, helping in placing the condenser away from compact cabinets. OHPS is simple in structure with a small diameter pipe filled with certain working fluid in it and extended from the heat source to sink. OHPS uses the technique of transporting the working fluid by means of differential pressure across liquid slugs and vapor plugs from evaporator to condenser and back. The fluid from the evaporator is pushed towards the condenser in the form of discrete liquid slugs and vapor bubbles. The vapor gets partially condensed at the condenser and looses the heat and returns to evaporator to complete the cycle. The heat transfer in a OHPS is due to the sensible heat and latent heat combination. In the present work experimental studies are carried out on a five-turn OHP. Copper is used as a material in the evaporator and condenser sections. Glass tube is used as a material in the adiabatic section. Copper and glass tubes are connected with the help of silicon rubber tubes. Acetone, Methanol& Ethanol are used as the working fluids and their suitability in the operation of OHPS is tested. At first stage of the present work experiments are conducted for different heat input and fill ratio. The effect of working fluids on the performance of OHPS is studied by comparing parameters like thermal resistance and heat transfer coefficient. From the results it is found that Acetone is the most suitable working fluid among all the individual fluids used for OHPS operation in the present work. It is also found that the heat transfer and fluid flow performance of OHP is better at a fill ratio of 80 %.