查看更多>>摘要：? 2022 Elsevier LtdIn this paper, using analytical methods of the theory of thermal conductivity, the issue of accumulative 3D heating under multipulse laser irradiation of inorganic materials and biological tissues is studied. For a number of practically important cases, comparatively simple analytical dependences of the residual temperature on the number of laser pulses and their repetition rate have been obtained. The limits of their applicability are discussed. Examples of the application of the developed theory for specific cases of pulse-periodic laser irradiation of various materials, in particular, titanium, monocrystalline silicon, and bone tissue, are demonstrated.
查看更多>>摘要：? 2022 Elsevier LtdAt present, thermal-fluid–structure coupling problems always need to be considered for the design of hypersonic flight vehicle. This work proposes numerical analysis of thermal-aero-elastic characteristic of a typical all-moving control surface for hypersonic flight vehicle. Basic aerodynamic and aero-thermal analysis of the model were gotten through finite volume simulations. By adopted transient temperature distribution of the control surface, thermal effects were interpolated to structural stiffness which could change modes of the control surface. Material nonlinearity of it due to thermal effect was included. Aeroelasticity analysis of the control surface was presented to find the difference of divergence speed between the usage of ‘thermal mode’ and ‘normal mode’. Flutter boundary was investigated to present the influence due to thermal effects. Different Mach numbers were used in flutter computations. It was seen from the results that thermal effects could obviously influence aeroelastic characteristic of the all-moving control surface. The proposed numerical process can provide a useful engineering method for aeroelastic studies on hypersonic flight vehicles.
查看更多>>摘要：? 2022 Elsevier LtdWith the development of science and technology, how to recycle the waste heat of high-temperature exhaust gas discharged from daily life and industry has become the focus of attention of the scientific community. Using thermoelectric generation technology to recover and utilize the waste heat of high-temperature gas of this part can effectively improve the efficiency of energy utilization. The thermoelectric generator (TEG) is modified by inserting the foamed metal copper (FMC) at the core flow field of the heat exchanger tube to enhance the heat transfer, and the heat exchange capacity of the heat exchanger can be effectively improved, so that the power generation efficiency of the TEG can also be effectively improved. At the same time, the core flow filling method can also reduce the increased amplitude of the back pressure of the TEG. Therefore, in this article, experiments have been conducted to investigate the effect of improved heat transfer of FMC at the core flow field on the performance of TEG with different power generation characteristics. We first evaluate the effect of different enhanced heat transfer conditions on the heat transfer capacity of TEG hot end heat exchanger with the Performance Evaluation Comprehensive (PEC) evaluation method. The results showed that the enhanced heat transfer by the FMC at the core flow field can significantly improve the heat transfer capacity of the heat exchanger. Then we use the Overall Performance (OP) evaluation method to evaluate the effect of TEG on its performance under different enhanced heat transfer conditions. The results showed that the power generation of the TEG filled with FMC at the core flow field is higher than that of the unfilled TEG, and the filling of FMC with a high filling rate and high pore density can significantly improve the power output and power generation efficiency of the TEG. However, by evaluating the TEG filled with FMC at the core flow field through the OP evaluation method, it was found that the use of FMC with a low filling rate and low pore density can better improve the overall performance of TEG.
查看更多>>摘要：? 2022 Elsevier LtdThis study aims to reveal the thermo-aerodynamic characteristics of gas foil thrust bearings in the presence or absence of viscosity dissipation. The lubrication models in the cross-section of the gas film have been described, and the term of viscosity dissipation in energy equations is decoupled. The influence of different factors on gas film temperature distribution is discussed and compared. The results show when considering viscosity dissipation, the peak temperature is located near the circumferential outlet and the side of the outer diameter where has more shear stress. However, with the absence of viscosity dissipation, the peak value takes place near the end of the convergence channel where the gas compression is the most severe. Contrary to the case that without viscosity dissipation, gas film temperature decreases with the increase of wedge factor in the presence of viscosity dissipation. As wedge height increases, backflow will occur at the bearing entrance, reducing inlet temperature. When rotational speed increases, the gas film temperature caused by viscous dissipation increases much faster. The increase of film thickness reduces film temperature and bearing performance rapidly, but has no effect on the temperature distribution. This study confirmed that viscosity dissipation plays a significant role in the temperature rise and flow field of gas foil thrust bearings. More specially, temperature rise in the presence of viscosity dissipation accounts for more than 90% of the aerodynamic heat. The results obtained in this study are significant because they provide basic design guidelines for a temperature rise of the gas film.
查看更多>>摘要：? 2022 Elsevier LtdSolar cooling systems are part of energy-saving technologies aiming to reduce energy consumption and achieving the goals of combating climate change. A mathematical model of a double-acting solar collector (DASC) for daytime solar heating and nocturnal radiative cooling for its application to a single-effect absorption chiller (SEAC) H2O-LiBr was developed in this study. The performances of the DASC were studied for all day, and optimization study of the operating parameters for all components of a SEAC applied to the DASC was examined in Bamako weather conditions. Thermal efficiency of the DASC with at zero reduced temperature reached 0.734 with a heat loss of 4.51 W/ (m2K) in daytime, and an average net radiative cooling power of 58.74 W/m2 in nighttime. A COP of a SEAC H2O-LiBr reached 0.87, and a performance of the whole system was 0.64.
查看更多>>摘要：? 2022 Elsevier LtdExact quasi-steady solution of temperature distribution for one-dimensional non-charring ablation in a semi-infinite material with temperature-dependent thermo-physical properties is obtained analytically, in which the surface temperature and the surface recession velocity are assumed to be constant. The analytical solutions for the cases in which thermo-physical properties are expressed by low degree polynomial functions of temperature are also obtained. Two kinds of non-charring ablation models are considered. One is a single phase model composed of a single phase (the crystalline phase), in which the surface recedes due to ablation. The other is a two-phase model composed of two phases (the crystalline and the amorphous phases) such as Teflon, in which the surface of the amorphous region recedes. The calculated results of the analytical solution agreed well with those of the numerical solution by the finite difference method. The basic behavior of Teflon ablation is calculated by using the analytical solution. The simple and exact analytical solution obtained in this paper is easy to calculate and is helpful in understanding the ablation behavior easily. It allows for rapid estimation of the ablation behavior for engineering purposes. The solution also provides a means to verify computer solutions obtained by numerical methods.
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