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The electronics in logging tools are susceptible to thermal failure due to the extreme thermal environment. Passive thermal management system (PTMS) has been proven to protect the electronics for several hours. In this paper, a numerical model based on the equivalent thermal conductivity method was developed to determine the transient temperature of downhole electronics. Compared with the traditional analytical model or numerical model considering only one single heat transfer process, the complex heat transfer in the logging tool were comprehensively considered through the proposed model. Briefly, the heat transfer processes in the vacuum bottle were theoretically calculated rather than empirically acquired, and the convective and radiative heat transfer inside the vacuum bottle was equated to the temperature-dependent thermal conductivity of air. In addition, the proposed numerical model was compared with experiments and previous numerical models to verify the accuracy of the model, and the temperature deviation of the electronics was within 5 °C. Moreover, the computational time was greatly reduced compared with the traditional three-dimensional numerical simulation process while ensuring the accuracy of calculation. Therefore, the proposed numerical model achieved both computational accuracy and efficiency, which was expected to be widely used in the development of PTMS for logging tools. • A numerical model based on equivalent thermal conductivity method was proposed. • The complex heat transfer processes in PTMS were comprehensively considered. • The proposed model possessed high computational accuracy and efficiency. [ABSTRACT FROM AUTHOR]

Nowadays, a bio-inspired heat exchanger incorporating a triply periodic minimal surface (TPMS) structure has demonstrated great potential in the fields of new energy research and aerospace, which necessitates achieving a balance between low volume and high heat transfer efficiency while maintaining low pressure drop. In this paper, the adjustable heat efficiency of the heat exchanger with TPMS in gradient thicknesses is specially designed. A steady-state conjugate heat transfer (CHT) model is coupled with computational fluid dynamics (CFD) analysis. In addition, the temperature profile and velocity streamline are also checked to analyze the fluid flow behavior of the radiator. The results show that the convective heat transfer coefficient of the Gyroid with gradient level set values is 26.02–60.10% higher than that of the uniform Gyroid model, and the pressure drop is decreased by 9.66–18.05%. Both high heat transfer efficiency and low pressure drop can be achieved when the thickness is 0.2–0.3 mm and Re is 100–125. The heat exchangers with a TPMS thickness gradient in the ratio of 2:4:6 demonstrate a remarkable enhancement in overall heat transfer efficiency, achieving a 30.22% improvement compared to those with a TPMS thickness gradient in 6:4:2. [ABSTRACT FROM AUTHOR]

Optimizing and increasing the efficiency of heat transfer systems was one of the main challenges for engineers and designers in recent years. Therefore, the use of nanoparticles in base fluids is known as a passive method to improve heat transfer and shrink heating and cooling systems. In this research, the heat transfer of copper nanoparticles with ammonia refrigerant in a nanochannel was investigated by molecular dynamics simulation. The results show that, with increasing the electric field frequency from 0.1 1/ps to 0.5 1/ps, the phase change time increases from 2 ns to 3 ns and the thermal conductivity decreases from 0.76 W/m.K to 0.72 W/m.K. Also, the effect of the different cavities (hermetic, spherical, and cube shape) in the nanochannel on the atomic and thermal behavior of the simulated atomic samples is investigated. The results show that the maximum thermal conductivity of the sample with a cubic cavity is 0.80 W/m.K. The particle phase change value and the phase change time of samples with hermitic, spherical, and cube atomic cavities are obtained 65, 66, and 68%, and 2.88, 2.87, and 2.85 ns, respectively. [ABSTRACT FROM AUTHOR]