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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]

This paper presents a numerical analysis of a horizontally oriented constant surface area isothermal helical coil under natural convection heat transfer and surface radiation. Numerical computations are carried out in the laminar regime of Rayleigh number (104 ≤ Ra ≤ 108), surface emissivity (0 ≤ ε ≤ 1), and geometrical parameters of the helical-coil, like diameter of the coil (8 ≤ D / d ≤ 24), pitch (3 ≤ p / d ≤ 7.5), and coil height (40 ≤ H / d ≤ 60) to study the heat transfer characteristics. This study is used for effectively designing the helical coils, which are typically manufactured at an extremely high temperature. The numerical computation has been validated by comparing the average Nusselt number (Nu) with the previous experimental results. Temperature-dependent fluid properties are incorporated to achieve precise results over a wide range of temperatures. The effect of the geometrical parameters on the heat transfer characteristics has been depicted graphically in terms of average Nu , relative convection and radiation heat transfer rate, and the temperature profile. It is found that the relative contribution of radiative heat transfer is 87.8% at an emissivity of 0.9 and Ra of 10(Ali, 1994 4), whereas, for an emissivity of 0.1 and Ra of 10(Moawed, 2005 8), the relative contribution of radiation heat transfer is only 6.4%. Lastly, a correlation has been developed for the average Nu based on all the pertinent parameters which can be beneficial to the engineers in the industry and also academic researchers. The developed correlation has been used to predict the cooling curve of the helical coil in certain situations. [ABSTRACT FROM AUTHOR]

A novel method of inserting a radiation enhancement plate in a turbine blade internal cooling channel is established in this paper. It can extend cold surfaces for radiation and thus enhance total heat transfer. Numerical investigations are carried out to explore the flow and coupled convection and surface radiation in the rotating channel for different channel models. The results indicate that the model inserting the radiation enhancement plate roughed with W-shaped ribs (model D) exhibits the highest cooling performance. Compared with the existing channel model (model A), the total Nusselt number ratio and the performance evaluation criterion increase by 90.53% and 21.67%, respectively, and the maximum and average temperature decrease by 339.80 K and 73.07 K, respectively. In addition, the heat transfer difference between the leading and trailing walls caused by the Coriolis force is remarkably reduced. Influences of pertinent parameters including the Reynolds number, the rotation number, the wall heat flux, and the wall emissivity are also investigated. It is demonstrated that the method has an excellent self-enhancement effect. • Heat transfer is enhanced in internal cooling channel of gas turbine blade. • A novel method by inserting radiation enhancement plate is established. • Coupled convective and radiative heat transfer in the channel is studied. • The maximum and averaged temperature decrease by 339.80 K and 73.07 K. • The method has an excellent self-enhancement effect. [ABSTRACT FROM AUTHOR]

In this paper, we examined the significance of nonlinear thermal radiation on 2-D magnetohydrodynamic flow of hybrid nanoliquid across two distinct geometries. The hybridized nanoliquid is encompassed with CuO and Al 2 O 3 nanomaterials suspended in the base liquid (water). The suitable similarity transmutations are utilized to convert the PDE's to the non-dimensional ODE's and solved them by employing Runge-Kutta method with shooting procedure. Further, simultaneous solutions are witnessed for flow over cone case and plate case respectively. The stimulus of dimensionless parameters on velocity and thermal fields are discussed thru plots, further, the wall friction and local Nusselt number are presented thru the tables. The results reveal that, the nonlinear thermal radiation has a propensity to boosts the thermal distributions and to decays the rate of heat transfer. The flow and thermal distributions are significant in flow over a plate as compared with flow over a cone case. Moreover, the thermal transport rate of the flow above a cone is considerably advanced than that of flow over a plate. [ABSTRACT FROM AUTHOR]