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This study is investigated the thermal performance of seven turns of the oscillating heat pipe (OHP) by an experimental investigation and CFD simulation. The OHP is designed and made from a copper tube with an inner diameter 3.5 mm and thickness 0.6 mm and the condenser, evaporator, and adiabatic lengths are 300, 300, and 210 mm respectively.  Water is used as a working fluid with a filling ratio of 50% of the total volume. The evaporator part is heated by hot air (35, 40, 45, and 50) oC with various face velocity (0.5, 1, and 1.5) m/s. The condenser section is cold by air at temperature 15 oC. The CFD simulation is done by using the volume of fluid (VOF) method to model two-phase flow by conjugating a user-defined function code (UDF) to the FLUENT code. Results showed that the maximum heat input is 107.75 W while the minimum heat is 13.75 W at air inlet temperature 35 oC with air velocity 0.5m/s. The thermal resistance decreased with increasing of heat input. The results were recorded minimum thermal resistance 0.2312 oC/W at 107.75 W and maximum thermal resistance 1.036 oC/W at 13.75W. In addition, the effective thermal conductivity increased due to increasing heat input.  The numerical results showed a good agreement with experimental results with a maximum deviation of 15%.

A pulsation heat pipe is an efficient heat pipe used in many engineering applications. This study aims to test the effect of working fluids on the thermal performance of pulsation heat pipe. Seven turned pulsation heat pipes were designed and manufactured from a copper pipe with a 3.5 mm inner diameter. The lengths of an evaporation part, an adiabatic passage, and a condenser part were 300 mm, 210 mm, and 300 mm, respectively. In this study, three different fluids were used as the working fluid: distilled water, methanol, and binary fluid (a mixture of water and methanol) with a 50% filling ratio. Compared to water, the experimental results suggested that methanol had a better thermal performance when used as a working fluid in the PHP. On the other hand, a binary fluid enhanced the lower thermal performance of water (29% reduction in the thermal resistance and a 20% increase in the effective thermal conductivity of the PHP).

In this study, an oscillating heat pipe heat exchanger has been used as a heat recovery device in air ductwork, and the characteristics of the thermal performance of the energy-saving were investigated by using a circular and elliptical cross-sectional tubes. An experimental study was conducted by oscillating heat pipe made from copper with an inner diameter of 3.5 mm for the conventional tube, and the major and minor axis of 4.2 and 2.2 mm for the elliptical tube. The working fluid was water with filling ratio of 50% of the total volume. The experimental data implied that the thermal effectiveness and the energy-saving highly affected by the inlet air temperature and velocity. The proposed model of the oscillating heat pipe heat exchanger possessed the effectiveness of 19.5% at 50 ºC and 0.5 m/s, and the potential energy-saving of 1117 W at 50 ºC and 2 m/s. The comparison results between the elliptical and conventional cross-sectional area of oscillating heat pipe heat exchanger indicated that the energy-saving and effectiveness enhanced by the ratio of 18%, and 14%.