Flat plate oscillating heat pipe (FP-OHP) is a unique heat transfer device and considered as a promising candidate for effective heat transfer device in electronics industries. A number of theoretical studies and experimental investigations have been carried out on FP-OHP in the past decades after its invention. However, due to the operational characteristics of FP-OHP, the effect of various parameters on the thermal performance of FP-OHP has not been completely revealed so far. This paper attempts to discuss the effect of operational parameters on the thermal performance of FP-OHP. In this study, the FP-OHP was investigated with different charge ratios, orientations, working fluids, and heat loads from 10 W to 150 W. In order to investigate the effect, 18 parallel square channels of 2 × 2 mm2 are machined onto pure copper plate (93 × 70 × 8 mm3) to form FP-OHP. DI water, ethanol, methanol, acetone, and FC-72 are investigated. The measured thermal resistance was strongly dependent on operational parameters. The optimum performance was observed with acetone with a charge ratio of 70% in the vertical orientation. The lowest thermal resistance of 0.39 °C/W is achieved using acetone as a working fluid at 100 W. A Kutateladze number (Ku) was used to compare the experimental data and found to be suitable for prediction of the thermal performance of FP-OHP with standard deviation of 15%.

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The closed-loop flat-plate oscillating heat pipe (CL-FPOHP) is a new two-phase heat transfer device for an effective thermal management in different systems. A number of theoretical and experimental investigations have been carried out on the CL-FPOHP in the past decades after its invention. However, due to the operational mechanism of the CL-FPOHP, the effects of channel profile on the thermal resistance have not been completely revealed so far. This paper aims at discussing the thermal resistance and thermal conductivity by changing the shape and size of the CL-FPOHPs channel. The thermal resistances of the CL-FPOHPs were investigated by varying the channel shape from square to circular, channel sizes from 2 × 2 mm 2 to 5 × 5 mm 2 , and heat load from 10 to 120 W. The pure copper was used to develop the CL-FPOHP and charged with the acetone with a charge ratio of 70%. The most suitable channel shape for the CL-FPOHP was found to be a square channel, and the most suitable channel size was observed to be 2 × 2 mm 2. The highest thermal conductivity of the CL-FPOHP reached to 2137 W/m °C. Keywords Flat-plate oscillating heat pipe • Two-phase heat transfer • Thermal resistance • Channel profile List of symbols Bo Bond number, g(l − v) r h 2 g Gravitational force (m/s 2) l Liquid density (kg/m 3) Subscripts CL-FPOHP Closed-loop flat-plate oscillating heat pipe FPOHP Flat-plate oscillating heat pipe TOHP Tubular oscillating heat pipe e Evaporator c Condenser l Liquid v Vapor W Watt L Distance of the two centers of the evaporator and condenser A Total cross-sectional area of CL-FPOHP

Heat transfer management is present issue which is progressively increasing importance in line with technology. Effective thermal management is needed to serve to the present trends of power & flux level of upcoming micro devices. This article describes the development of flat plate oscillating heat pipe (FP-OHP) as new entry in the family of two phase heat transfer system. As a unique heat transfer device, flat plate oscillating heat pipe has been considered have a smart prospect due to its advantages: simple fabrication methods & structure, low cost & outstanding heat transfer capability. The development of FP-OHP application is founded on the basis of experimental and theoretical research on two phase heat transfer in FP-OHP. With substantial expectation of FP-OHP application in the coming years, this article attempts to review the development of FP-OHP products. Simultaneously, some favorable and innovative applications of FP-OHP are also studied. This article is predicted to provide fundamental reference for future researcher.