Kenta Hashimoto¹, Guohui Sun¹, Yasushi Koito^2,*

Frontiers in Heat and Mass Transfer, Vol.22, No.3, pp. 687-702, 2024, DOI:10.32604/fhmt.2024.052928

Abstract Centered or striped wick structures have been used to develop ultrathin heat pipes. Differing from traditional heat pipes, the centered or striped wick structures leave noncontact container surfaces with the wick structure. In this study, experiments and numerical analyses were conducted to investigate the influence of these noncontact surfaces. In the experiments, a strip-shaped wick structure was placed vertically, the top was sandwiched between wider rods and the bottom was immersed in a working fluid. The rod width was greater than the wick width; thus, noncontact surfaces were left between the rod and the wick… More >

Yasushi Koito^1,*, Akira Fukushima²

Frontiers in Heat and Mass Transfer, Vol.22, No.3, pp. 869-887, 2024, DOI:10.32604/fhmt.2024.050910

Abstract Thermal and fluid-flow characteristics were numerically analyzed for ultra-thin heat pipes. Many studies have been conducted for ultra-thin heat pipes with a centered wick structure, but this study focused on separated wick structures to increase the evaporation/condensation surface areas within the heat pipe and to reduce the concentration of heat flux within the wick structure. A mathematical heat-pipe model was made in the three-dimensional coordinate system, and the model consisted of three regions: a vapor channel, liquid-wick, and container wall regions. The conservation equations for mass, momentum, and energy were solved numerically with boundary conditions… More >

Nobuhito Nagasato¹, Zhengyuan Pei¹, Yasushi Koito^2,*

Frontiers in Heat and Mass Transfer, Vol.22, No.1, pp. 49-63, 2024, DOI:10.32604/fhmt.2024.047502

Abstract Visualization experiments were conducted to clarify the operational characteristics of a polymer pulsating heat pipe (PHP). Hydrofluoroether (HFE)-7100 was used as a working fluid, and its filling ratio was 50% of the entire PHP channel. A semi-transparent PHP was fabricated using a transparent polycarbonate sheet and a plastic 3D printer, and the movements of liquid slugs and vapor plugs of the working fluid were captured with a high-speed camera. The video images were then analyzed to obtain the flow patterns in the PHP. The heat transfer characteristics of the PHP were discussed based on the… More >

Tomoki Hirokawa^a,*, Masahiko Murozono^a, Oleg Kabov^b,c, Haruhiko Ohta^a

Frontiers in Heat and Mass Transfer, Vol.5, pp. 1-8, 2014, DOI:10.5098/hmt.5.17

Abstract Experiments are performed to study the liquid film behavior and corresponding local heat transfer to shear-driven liquid film flow of water in the cocurrent nitrogen gas flow. The heated channel has a cross section of 30mm in width and 5mm in height, where the bottom is operated as a heating surface of 30mm in width and 100mm in length. The heated section is divided into segments to evaluate the local heat transfer coefficients. Under most gas Reynolds numbers, the local heat transfer coefficients are increased with increasing heat flux, where three mechanisms are important; (i) More >

Asmaa Habib Alanzi, N. Ameer Ahammad^*

Frontiers in Heat and Mass Transfer, Vol.21, pp. 179-197, 2023, DOI:10.32604/fhmt.2023.042009

Abstract The conversion of solar radiation to thermal energy has recently attracted a lot of interest as the requirement for renewable heat and power grows. Due to their enhanced ability to promote heat transmission, nanofluids can significantly contribute to enhancing the efficiency of solar-thermal systems. This article focus solar energy aspect on the effects of the thermal radiation in the flow of a hyperbolic tangent nanofluid containing magnesium oxide (MgO) and silver (Ag) are the nanoparticle with the base fluid as kerosene through a wedge and stagnation. The system of hybrid nanofluid transport equations are transformed into… More >

Yasushi Koito^1,*, Shoma Hitotsuya², Takamitsu Takayama², Kenta Hashimoto²

Frontiers in Heat and Mass Transfer, Vol.21, pp. 33-46, 2023, DOI:10.32604/fhmt.2023.041829

Abstract An ultra-thin flattened heat pipe has been developed with a centered wick structure. This structure is essential to make the heat pipe thinner. However, the centered wick structure reduces the evaporation and condensation surface areas of the wick structure because it is sandwiched between heat pipe walls. In this study, because detailed discussion has not been made, heat transfer experiments were conducted for the wick structure sandwiched between two solid walls. This study focused on the evaporation heat transfer characteristics from the sandwiched wick structure. The experiments were conducted with three wick structures, that is,… More >

Zhuohuan Hu¹, Sixian Sun¹, Chengwei Yuan¹, Yan Cao², Jiayin Xu^1,*

Frontiers in Heat and Mass Transfer, Vol.21, pp. 107-123, 2023, DOI:10.32604/fhmt.2023.041837

Abstract Loop Heat Pipe (LHP) is an efficient two-phase heat transfer device, which can be used in waste heat recovery, electronics cooling, aerospace and other fields. The wick, the core component of LHP, plays an important role in its start-up and operation. In this paper, the wick fabricated by 3D printing technology had uniform and interconnected pores. In the experiment, the position of the parallel vapor removal grooves was always fixed towards the vapor outlet. When the cylindrical wick was placed in the evaporator, the rotation angle relative to its central axis could be changed, thus… More > Graphic Abstract

Amnart Boonloi¹, Withada Jedsadaratanachai^2,*

Frontiers in Heat and Mass Transfer, Vol.21, pp. 317-336, 2023, DOI:10.32604/fhmt.2023.044929

Abstract Thermal performance enhancement in a square channel heat exchanger (HX) using a passive technique is presented. Vortex turbulator insertion in a square channel HX as a passive technique is selected for thermal improvement. The vortex turbulator of interest is discrete X-V baffles (XVB). The discrete XVBs are inserted in the square channel with the main aim of generating vortex flow. The vortex flow generated can support the enhanced convective heat transfer coefficient and also enhance HX performance. Effects of baffle configuration (type A and B), baffle size (w/H = 0.05, 0.10, 0.15 and 0.20), baffle… More > Graphic Abstract

Amnart Boonloi^a, Withada Jedsadaratanachai^b,*

Frontiers in Heat and Mass Transfer, Vol.13, pp. 1-18, 2019, DOI:10.5098/hmt.13.23

Abstract The purpose of the present work is to study flow configuration and heat transfer behavior in a square channel heat exchanger equipped with C-shaped baffle. The influences of flow attack angle and baffle size on flow and heat transfer characteristics are considered for the laminar flow regime with the Reynolds number around 100 – 2000. The numerical study with finite volume method is selected for the present investigation. The SIMPLE algorithms is opted to solve the numerical problem. The numerical results are concluded in terms of flow and heat transfer mechanisms in the tested section.… More >

Xiaoyong Gu^*, Guohe Jiang, Yang Wo, Biwen Chen

Frontiers in Heat and Mass Transfer, Vol.15, pp. 1-8, 2020, DOI:10.5098/hmt.15.3

Abstract The heat transfer characteristics of propylene glycol-water (PG-W) mixture with different concentrations in shell side of spiral wound heat exchanger (SWHE) with different geometric parameters were studied numerically. Experiment was carried out and the average difference between the simulated results and the experimental results was 5.3%. The simulation results show that heat transfer coefficient increases with the increase of center core diameter and longitudinal spacing of tubes, but decreases with the increase of tube outer diameter. The center core diameter and tube outer diameter have greater effects on heat transfer performances at higher concentration. Economic More >