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• HFE-7100 boiling curves from the onset of boiling to dry-out, in a vertical and rectangular mini-channel. • Local heat transfer coefficient (HTC) calculated with an inverse heat conduction method. • Influence of subcooling and pressure on heat transfer, pressure drop and flow patterns. • Increasing pressure improves the critical heat flux (CHF) and HTC, delays the dry-out, and reduces pressure drops. • Increasing subcooling improves CHF and HTC, delays the dry-out, and modifies the flow pattern. The background of this study is the problem of thermal runaway in the battery cells of electric vehicles. Increasingly powerful and compact battery packs require highly efficient thermal management. One potential solution is the direct liquid cooling of lithium-ion battery cells using a dielectric liquid which boils over a safety limit temperature. This approach intends to prevent in a first step the cell thermal runaway and if it fails in a second step its propagation to its neighbors: the liquid boiling helps to mitigate the cell temperature rise and to transport and spread the heat. The arrangement of the cells in the pack and their close spacing induce a scientific problem of convective boiling in a mini-channel. To enhance designs using this solution, a comprehensive understanding of flow boiling and a precise local heat transfer quantification is essential. The HFE-7100 has been selected as a working fluid for its attractive thermophysical properties and a suitable saturation temperature. The present paper introduces new experimental results of flow boiling dielectric fluid, the HFE-7100, in a vertical rectangular mini-channel. Measurements are carried out from start of boiling to dry-out. Boiling curves are obtained for a mass flux of 391 kg/(m².s), at different pressures (0.7, 1, 1.5 bar) and at different subcoolings (Δ T s u b = 0 ; 15 ; 30 ; 45 ∘ C). The test section is an aluminum block instrumented with three lines of five K-type thermocouples located all along the flow. The visualization of the flow is achieved through a glass pane with a high-speed camera to identify different flow patterns. The local heat transfer coefficient is calculated by a resolution of a 2D inverse heat conduction method. The experiment mainly aims at determining the heat transfer coefficient, the critical heat flux (CHF) and the pressure drop and at characterizing both the flow regimes and the dry-out phenomenon. The influence of subcooling and pressure on flow boiling is analyzed. An increase in subcooling enhances the CHF and the heat transfer coefficient, and delays the dry-out. Subcooling has an impact on the flow pattern and modifies the type of CHF. In the operating conditions tested, a decrease in pressure enhances CHF and delays dry-out. On the other hand, the heat transfer coefficient increases with rising pressure. Similarly, pressure drops are lower with higher pressure. [ABSTRACT FROM AUTHOR]

This paper analyzes the influence of the anomalous diffusive effects caused by micro-scale heterogeneity and kinetic and inertial thermal relaxations on the optically induced thermoelastic bending component of the photoacoustic response. We calculated the temperature distribution for a one-dimensional heat transfer problem with planar and periodic excitation, neglecting the influence of thermoelastic strains on the temperature profile. Thermoelastic bending was evaluated using a theoretical approximation of a thin plate, while pressure fluctuations in the photoacoustic cell were obtained by assuming adiabatic changes in the closed air. The model analysis shows that the relaxation processes could significantly affect the mechanical piston component of the photoacoustic response at frequencies higher than the minima of the inverse of two thermal relaxation times, while the influence of micro-scale heterogeneity is observable in the whole frequency range. • The hyperbolic DPL model enhances accuracy of thermoelastic effect at higher frequencies. • Sensitivity to fractional order of DPL model emphasizes precision in TE control. • Anomalous DPL heat diffusion shifts and attenuates the peak of the hyperbolic result. • Maximum damping occurs to identical kinetic and thermal relaxation times. [ABSTRACT FROM AUTHOR]

• Application of MCrAlY coating to increase heat transfer during water spray cooling. • The use of the coating intensifies heat transfer compared to the uncoated surface. • The thickness of the coating affects the intensity of the heat removal. The main purpose of the paper was to determine the influence of NiCoCrAlY coating application and its thickness on the heat transfer during water spray cooling under surface boiling conditions. The scope of the research included: sensor preparation, measurements of the sensor temperature during cooling, and numerical calculations to determine the intensity of sensor cooling. The intensity of heat removal was determined by the average values of the heat flux on the cooled surfaces. The inverse method for the heat conduction equation was used to determine the heat transfer boundary conditions. Temperature measurements during cooling were carried out for an initial sensor temperature of 500°C, 700°C and 900°C and a liquid pressure 0.1 MPa, 0.2 MPa. Due to this, it was possible to select a coating thickness that contributed to the greatest extent to the increase in the intensity of heat dissipation from the hot surface. The highest values of the heat flux were obtained during the cooling of the sensor with a 134.5 μm coating. [ABSTRACT FROM AUTHOR]

• The chemical source term is the main control factor of thermal runaway. • The higher the temperature intensity, the shorter the explosion delay time. • The critical temperature of thermal runaway for AP/HTPB propellant is 458 K. • If the propellant is thick enough, the temperature distribution remains constant. For the safe use of solid rocket motors, it is crucial to investigate the thermal effect of AP/HTPB propellants. Transient high temperature may cause AP/HTPB propellants to burn or explode, resulting in serious damage. The fundamental equations that describe the thermal effect of AP/HTPB propellants are the heat conduction differential equation and Arrhenius law. In this paper, the thermal safety of AP/HTPB at transient high temperature is obtained by solving the heat conduction differential equation. The results show that the chemical source term S (T) is the main control factor of thermal runaway. When the action duration of the external high-temperature is short (ms-s magnitude), the first explosion occurs closest to the high-temperature source. When the action duration of the external high-temperature action is long (min-h magnitude), the first explosion occurs inside the propellant. The higher the high-temperature intensity of external action, the shorter the explosion delay time, but the explosion temperature does not change accordingly. The critical temperature of thermal runaway is 458 K under the condition of no shell and a high-temperature action duration of 2 h. At high-temperature intensities of 458 K, 459 K, and 500 K, the propellant explosion temperatures are 533 K, 539 K, and 540 K, and the explosion delay time is 1592s, 1102s, and 160 s, respectively. The critical duration of thermal runaway is 430 ms, 650 ms, 1350 ms, and 9820 ms, and the stable explosion delay time is 450 ms, 680 ms, 1400 ms, and 9920 ms, respectively, under the conditions of 2000 K, 1500 K, 1000 K, and 600 K without the shell. The propellant explosion temperature remains constant as the shell thickness grows while the explosion delay time gradually increases. When the propellant is thick enough, the temperature distribution of the system remains constant. The results of this study may be useful as a guide for assessing the thermal safety of AP/HTPB propellant. [ABSTRACT FROM AUTHOR]

• Semi-analytic methods are used to solve 3D DPL problems. • Compared with FEM, the semi-analytic method has higher computational efficiency. • The phase lag of heat flow and the phase lag of temperature gradient have influence on the temperature response speed and the formation of temperature field. With the development of picosecond laser technology, the dual-phase-lagging (DPL) model is more suitable to describe the heat transfer problem with micro-scale effect and micro-time effect. In this paper, a three-dimensional dual-phase-lagging heat transfer model for picosecond laser processing is established. Then Fourier transform (FT) and Laplace transform (LT) are used to derive the frequency response functions (FRFs) of the problem in the frequency domain, and the inverse Laplace transform (ILT) and discrete-convolution fast Fourier transform (DC-FFT) algorithm are used to solve the temperature field. The calculation accuracy of this method is verified and the effect of phase lag constants on temperature field is studied. The results show that the semi-analytical method has a high accuracy for solving the dual-phase-lagging heat conduction model, and the phase lag of heat flux will affect the heating rate in the heating stage, and the phase lag of temperature gradient will delay the formation of temperature field. The effect of phase lag constants on temperature-time history is investigated and the related phenomena are explained by using the two-step heat transfer theory. This semi-analytical method provides a new approach to solve the problem of three-dimensional dual-phase-lagging heat transfer. [ABSTRACT FROM AUTHOR]