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Ablation of the thermal protection material of the reentry hypersonic flight vehicle is a complex physical and chemical process. To estimate the surface heat flux from internal temperature measurement is much more complex than the conventional inverse heat conduction problem case. In the paper, by utilizing a two-layer pyrogeneration-plane ablation model to model the ablation and charring of the material, modifying the finite control volume method to suit for the numerical simulation of the heat conduction equation with variable-geometry, the CGM along with the associated adjoint problem is developed to estimate the surface heat flux. This estimation method is verified with a numerical example at first, the results show that the estimation method is feasible and robust. The larger is the measurement noise, the greater is the deviation of the estimated result from the exact value, and the measurement noise of ablated surface position has a significant and more direct influence on the estimated result of surface heat flux. Furthermore, the estimation method is used to analyze the experimental data of ablation of blunt Carbon-phenolic material Narmco4028 in an arc-heater. It is shown that the estimated surface heat flux agrees with the heating power value of the arc-heater, and the estimation method is basically effective and potential to treat the engineering heat conduction problem with ablation. [ABSTRACT FROM AUTHOR]

Optimal design and performance of a combined infrared-convective drying system with respect to the energy issue is extremely put through the application of advanced engineering analyses. This article proposes a theoretical approach for exergy analysis of the combined infrared-convective drying process using a simple heat and mass transfer model. The applicability of the developed model to actual drying processes was proved using an illustrative example for a typical food. [ABSTRACT FROM AUTHOR]

Radiofrequency thermal ablation is the first therapeutic option for the minimally invasive treatment of liver tumors. This medical procedure employs the Joule heat produced by a RF electromagnetic field to kill tumor cells. The outcome of the procedure is strongly affected by the temperature distribution near the RF applicator, however the measurement of this distribution, even in ex vivo experiments, is not straightforward since most traditional local temperature measurement techniques are not well-suited, due to both electromagnetic interferences and the sensor heat sink effect. Given the importance of the temperature field knowledge, in this paper special care was devoted to its measurement employing both infrared thermal imaging and NTC thermistors. Several RF ablation tests on ex vivo porcine liver tissue were carried out measuring the space-time evolution of temperature during the procedure (with spatial resolution ≤1 mm) and producing useful data for the design and the calibration of a numerical model. Electro-thermal numerical simulations of the experimental tests were performed using a mathematical model suitable for the heating phase of the procedure (up to 95 °C). The simulations results allowed to check the physical consistency of the measured data and suggested that a constant thermal conductivity is satisfactory for modeling the temperature evolution during RF ablation. [ABSTRACT FROM AUTHOR]

In this paper a three-dimensional numerical model for cryosurgery is developed to study the effect of central probe on the cryosurgery process. The irregular boundary resulting due to the presence of cryoprobes is taken care by body-fitted multi-block non-orthogonal grids. The thermo-physical properties of biological tissue are considered as a function of temperature as phase change takes place over a wide temperature range for the biological tissue. It has been found that the cooling power requirement by the single offset cryoprobe is greater than that of the central cryoprobe. However, the presence of central cryoprobe markedly influenced the cryosurgery process, resulting in an increase in the ablation ratio by 57 % with an insignificant increase in cooling power by 4.5 %. This information can be utilised effectively in computerised planning of a cryosurgery protocol. [ABSTRACT FROM AUTHOR]

Validated by the correlated experiments, a nose-tip with forward-facing cavity/opposing jet/the combinatorial configuration of forward-facing cavity and opposing jet thermal protection system (TPS) are investigated numerically. The physical mechanism of these TPS is discussed, and the cooling efficiency of them is compared. The combinatorial system is more suitable to be the TPS for the high speed vehicles which need fly under various flow conditions with long-range and long time. [ABSTRACT FROM AUTHOR]

Abstract  Pool boiling heat transfer characteristics on treated surfaces were investigated experimentally. Surface treatments were performed with sandpapers, building micro structures by etching, and micro-porous coating. Copper blocks of 20 mm × 20 mm were used as test sections and PF5060 was used as a working fluid. The effect of wall superheat (0–35 K), surface orientation (0°, 45°, 90°), and subcooling (0, 5, 10 K) on treated surfaces were also investigated. Heat transfer performance on inclined surface was better than that of horizontal surface in all test sections. Because bubble generation was suppressed by subcooling, higher wall superheat was needed to initiate boiling in all surfaces. Micro-porous coated surface showed the highest heat transfer enhancement among tested surfaces. [ABSTRACT FROM AUTHOR]

Abstract  Forced convective heat transfer coefficients and friction factors for flow of water in microchannels with a rectangular cross section were measured. An integrated microsystem consisting of five microchannels on one side and a localized heater and seven polysilicon temperature sensors along the selected channels on the other side was fabricated using a double-polished-prime silicon wafer. For the microchannels tested, the friction factor constant $$ \user2{C} = \user2{f}Re_{{D_{h} }} $$ obtained are values between 53.7 and 60.4, which are close to the theoretical value from a correlation for macroscopic dimension, 56.9 for D h  = 100 μm. The heat transfer coefficients obtained by measuring the wall temperature along the micro channels were linearly dependent on the wall temperature, in turn, the heat transfer mechanism is strongly dependent on the fluid properties such as viscosity. The measured Nusselt number in the laminar flow regime tested could be correlated by $$ Nu = 0.00058{\text{ }}Re_{{D_{h} }} ^{{1.15}} {\text{ }}Pr^{{1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-\nulldelimiterspace} 3}} {\left( {{{\mu} {\left( \user2{T} \right)}} \mathord{\left/ {\vphantom {{{\mu} {\left(\user2{T} \right)}} {{\mu} {\left( {\user2{T}_{\infty } } \right)}}}} \right. \kern-\nulldelimiterspace} {{\mu} {\left( {\user2{T}_{\infty } } \right)}}} \right)}^{{2.76}} {\left( {\user2{W} \mathord{\left/ {\vphantom { \user2{{W H}}}} \right. \kern-\nulldelimiterspace} \user2{H}} \right)}^{{0.3}} , $$ which is quite different from the constant value obtained in macrochannels. [ABSTRACT FROM AUTHOR]

Abstract  Fluid flow and heat transfer characteristics around a semi-circular tube in cross flow were experimentally and numerically investigated. Three different tube-flow arrangements were considered. Firstly, the flat surface of the tube was placed parallel to the freestream flow; secondly, the flat surface of the tube was facing the upstream flow and thirdly, the curved surface of the tube was facing the upstream flow. For the second and the third arrangements, different angles of attack were studied. Flow visualization was carried out to illustrate streamlines around the tube and to verify flow patterns obtained from the numerical calculations. It was found that: (1) for any angle of attack, the arrangement of the curved surface facing the flow gave higher average Nusselt number than the arrangement of the flat surface facing the flow and (2) for all tube-flow arrangements, increasing the angle of attack slightly increases the average Nusselt number. Correlations of Nusselt numbers in terms of Reynolds number and angle of attack were deduced from the experimental results for the three arrangements. The comparisons between the experimental data, correlations’ predictions and numerical results showed reasonable agreements. [ABSTRACT FROM AUTHOR]

AbstractTo predict the integral performance of transpiration and ablation cooling during the reentry of hypersonic vehicles, an unsteady numerical model based on the assumption of thermal equilibrium is presented. The non-thermal equilibrium model and the thermal equilibrium model are coupled by the effective thermal properties of the porous matrix and the coolant. The calculation using the thermal equilibrium model shows the influence of the variation of the effective thermal properties on the numerical results by a comparison between constant and variable thermal properties. The comparison indicates that near the melting temperature of the porous matrix, the position of the moving boundary due to ablation is sensitive to the temperature, therefore, the variation of the thermal properties are considered in this paper. The process of ablation and transpiration cooling is simulated under different numerical conditions. The simulations demonstrate that the injection rate of coolant mass flow and initial temperature of cooling are important parameters for the control of the ablation process. [ABSTRACT FROM AUTHOR]