Ice melting simulation with water flow handling

In this paper, we propose a new approach based on a particle-based model for ice melting simulation. Each particle has an attribute called virtual water. The amount of the virtual water of an ice particle indicates the amount of water surrounding the ice particle. The transfer of the virtual water is performed between the exterior ice particles so as to simulate the thin layer of water flow on the surface. Our approach also handles the transition between the virtual water and the water particles. We compute the isosurface of a density field defined by the ice particles and the virtual water. A simple ray tracing method is adopted for rendering the objects. We report the experimental results of several ice melting simulations with water flow and water drops.     

The determination of the effective ambient temperature for thermal flow sensors in a non-isothermal environment

Thermal flow sensor behaviour is investigated for the condition that the direct surrounding of the sensor, such as the plate on which the sensor is mounted, is at a temperature that is different from that of the flow. In that case the convective heat transfer depends on the difference between the (average) sensor temperature and the effective ambient temperature, where the latter is a weighed average of the plate and fluid temperatures. Knowledge of which temperature level represents the true effective ambient value is vital for a correct design and operation of a thermal flow sensor. In the present theoretical study this ambient-temperature weighing effect is examined by investigating the weighing function for the laminar heat transfer from a sensor mounted on a plate where (a part of) the upstream plate length is at a constant temperature which is different from that of the flow. The analysis reveals how the weighing effect, and hence the effective ambient temperature, depends on the non-isothermal upstream length, and that this dependence is significantly different for sensing methods that rely on either total or differential convective heat transfer.     

Response time of thermal flow sensors with air as fluid

Due to their fast response time miniaturized thermal flow sensors can be applied well for the measurement of instationary gas flow. For some applications, the response time of the sensor must be known with high accuracy. We investigated three methods for response time determination with air: a jump of temperature induced by electric heating, a gas velocity step made by a membrane burst and acoustic phase shifts between sound velocity and sound pressure (standing and traveling waves). The measurements have shown that the response time of thermal flow sensors is a function of flow velocity. For stagnant flow, the thermal response time is about 4.5 ms for our thermal flow sensors. With increasing flow from the heater to the thermopiles, the heat transfer rises. Thus, the response time is faster and decreases to about 1 ms.     

Local heat transfer process and pressure drop in a micro-channel integrated with arrays of temperature and pressure sensors

One of the most important components in micro-fluidic system is the micro-channel which involves complicated flow and transport process. This study presents micro-scale thermal fluid transport process inside a micro-channel with a height of 37 μm. The channel can be heated on the bottom wall and is integrated with arrays of pressure and temperature sensors which can be used to measure and determine the local heat transfer and pressure drop. A more simplified model with modification of Young’s Modulus from the experimental test is used to design and fabricate the arrays of pressure sensors. Both the pressure sensors and the channel wall use polymer materials which greatly simplify the fabrication process. In addition, the polymer materials have a very low thermal conductivity which significantly reduces the heat loss from the channel to the ambient that the local heat transfer can be accurately measured. The air flow in the micro-channel can readily become compressible even at a very low Reynolds number condition. Therefore, simultaneous measurement of both the local pressure drop and the temperature on the heated wall is required to determine the local heat transfer. Comparison of the local heat transfer for a compressible air flow in micro-channel is made with the theoretical prediction based on incompressible air flow in large-scale channel. The comparison has clarified many of the conflicting results among different works.     

Measurement technique for the thermal properties of thin-film diaphragms embedded in calorimetric flow sensors

In diaphragm-based micromachined calorimetric flow sensors, convective heat transfer through the test fluid competes with the spurious heat shunt induced by the thin-film diaphragm where heating and temperature sensing elements are embedded. Consequently, accurate knowledge of thermal conductivity, thermal diffusivity, and emissivity of the diaphragm is mandatory for design, simulation, optimization, and characterization of such devices. However, these parameters can differ considerably from those stated for bulk material and they typically depend on the production process. We developed a novel technique to extract the thermal thin-film properties directly from measurements carried out on calorimetric flow sensors. Here, the heat transfer frequency response from the heater to the spatially separated temperature sensors is measured and compared to a theoretically obtained relationship arising from an extensive two-dimensional analytical model. The model covers the heat generation by the resistive heater, the heat conduction within the diaphragm, the radiation loss at the diaphragm’s surface, and the heat sink caused by the supporting silicon frame. This contribution summarizes the analytical heat transfer analysis in the microstructure and its verification by a computer numerical model, the measurement setup, and the associated thermal parameter extraction procedure. Furthermore, we report on measurement results for the thermal conductivity, thermal diffusivity, and effective emissivity obtained from calorimetric flow sensor specimens featuring dielectric thin-film diaphragms made of plasma enhanced chemical vapor deposition silicon nitride.     

CFD assisted modeling for control system design: A case study

This paper presents a novel modeling approach of coupling transient computational fluid dynamics (CFD) simulation with system identification for control system involving fluid flow and heat transfer. In order to illuminate the feasibility of this method, a fluid flow and heat transfer related process, i.e. a three dimension (3-D) spatio-temporal air temperature distribution and input (inlet air temperature) dependent process in the desert climate chamber, is considered. The distributed parameter models of the chamber temperature are identified using transient CFD simulation results and are then validated against the results obtained from the CFD simulations with high RT² (more than 0.97) and negative Young’s information criterion (YIC, less than ?11.8). The PI controllers embedded in CFD simulation are then developed based on the models. The performance of the closed-loop systems is also evaluated within the full-scale CFD model. The results show that CFD-based system identification is feasible to model fluid flow and heat transfer related processes.     

Fast Particle‐based Visual Simulation of Ice Melting

The visual simulation of natural phenomena has been widely studied. Although several methods have been proposed to simulate melting, the flows of meltwater drops on the surfaces of objects are not taken into account. In this paper, we propose a particle‐based method for the simulation of the melting and freezing of ice objects and the interactions between ice and fluids. To simulate the flow of meltwater on ice and the formation of water droplets, a simple interfacial tension is proposed, which can be easily incorporated into common particle‐based simulation methods such as Smoothed Particle Hydrodynamics. The computations of heat transfer, the phase transition between ice and water, the interactions between ice and fluids, and the separation of ice due to melting are further accelerated by implementing our method using CUDA. We demonstrate our simulation and rendering method for depicting melting ice at interactive frame‐rates.     

Lattice Boltzmann computations of incompressible laminar flow and heat transfer in a constricted channel

A multi-population thermal lattice Boltzmann method (TLBM) is applied to simulate incompressible steady flow and heat transfer in a two-dimensional constricted channel. The method is validated for velocity and temperature profiles by comparing with a finite element method based commercial solver. The results indicate that, at various Reynolds numbers, the average flow resistance increases and the heat transfer rate decreases in a constricted channel in comparison to a straight channel. The effect of the constriction ratio is also investigated. The results show that the presented numerical model is a promising tool in analyzing simultaneous solution of fluid flow and heat transfer phenomena in complex geometries.     

An investigation of thermal comfort inside an automobile during the heating period

This paper describes a combined theoretical and experimental study of thermal comfort during the heating period inside an automobile. To investigate the effects of thermal conditions on the human physiology and thermal comfort during the heating period, temperature, humidity and air velocity were measured at a number of points inside the automobile, so thermal conditions were accurately determined. The human body was divided into 16 sedentary segments, and the change of temperature was observed both experimentally and theoretically. During transient conditions of the heating period, heat and mass transfer between the human body and the interior environment of an automobile were simulated by a computational model, and predictions were compared with the measured data. It is shown that there is a good agreement between the model predictions and experimental results. By means of the present model, the effects of the fast transient conditions of the heating period on the sensible and latent heat transfer from the body, body segments skin temperatures and thermal sensation were investigated in detail.     

Molecular dynamics–continuum hybrid simulation for condensation of gas flow in a microchannel

A molecular dynamics-continuum coupling method combining fluid flow and heat transfer is developed to study the condensation process of gas flow in a microchannel. The computational domain is decomposed into particle (P), continuum (C) and overlap (O) regions with solving approaches of molecular dynamics simulation, finite volume method and the developed coupling method, respectively. Continuities of momentum and energy in O region are ensured by constraint dynamics and the Langevin method. The validity of the developed method is confirmed by a good agreement between hybrid results and analytical solutions from two cases including the unsteady dynamical and thermal problems. For the condensation process of gas flow, the hybrid transient velocity and temperature fields indicate that the process does not progress smoothly but wavily with noticeable fluctuation, leading to oscillation in temperature field and recirculation flow in velocity field. Analysis based on heat and mass transfer is carried out in P region, and the Kapitza resistance and the thermal conductivity in liquid are obtained with the satisfying agreement with experimental data, which shows the availability of the developed model for the investigation on the thermal boundary resistance. The good performance had demonstrated that the developed coupling method and computational model are available to provide a multiscale overview in dynamical and thermal problems including phase-transition from nanoscale to microscale, which will show significantly potential in micro fluidics and thermal engineering.     

Lattice Boltzmann equation for axisymmetric thermal flows

A simple lattice Boltzmann equation (LBE) model for axisymmetric thermal flow is proposed in this paper. The flow field is solved by a quasi-two-dimensional nine-speed (D2Q9) LBE, while the temperature field is solved by another four-speed (D2Q4) LBE. The model is validated by a thermal flow in a pipe and some nontrivial thermal buoyancy-driven flows in vertical cylinders, including Rayleigh-Bénard convection, natural convection, and heat transfer of swirling flows. It is found that the numerical results agree excellently with analytical solution or other numerical results.     

混合记录气膜温度场仿真

混合记录是实现超高密度存储的重要途径之一,是当前国际超高密度存储研究的热点。该技术利用高矫顽力的磁记录材料进行热辅助写入,并在常温下读出和保存,可克服超顺磁极限实现超高密度存储。基于对流换热理论建立了混合记录介质与浮动气膜间的对流换热模型。磁头在不同的飞行姿态下分别可以用层流换热模型和紊流换热模型来求解气膜温度场。注意到磁记录磁头飞高在纳米量级的特点,运用边界层理论求解了浮动气膜的温度场,得到了近场光、磁混合记录中由近场馈热导致气膜温升的影响规律及相关的数据,     

热式气体流量计温度补偿研究

恒温型热式流量计加热探头与被测介质之间交换的热量不仅与质量流量有关还与被测介质的温度有关。通过对流量计热交换模型的分析,导出了热式气体流量计温度补偿的模型。同时对传感器的结构和常用的驱动电路进行了分析,指出了现有补偿电路的不足,提出了一种新的温度补偿电路。通过电路分析和试验证明,新补偿电路能改善温度补偿效果。     

降膜蒸发过程的数值模拟和传热传质分析

利用CFD软件对逆流降膜蒸发过程进行了实验模拟研究,研究了速度边界层、热边界层和浓度边界层的变化对降膜蒸发传热传质特性的影响规律;通过建立一维逆流降膜蒸发的数学方程编程求解出了对流传热传质的Nu数和Sh数,利用Fluent软件模拟出的实验结果采用回归分析得出了气液流量比Raw、流道的长宽比αL、空气进口无量纲温度θai以及空气进口Re数与Nu数、Sh数之间的无量纲关系式,可为降膜蒸发换热器的设计提供参考。     

Thermal interactions in nanoscale fluid flow: molecular dynamics simulations with solid–liquid interfaces

Molecular dynamics (MD) simulations of nano-scale flows typically utilize fixed lattice crystal interactions between the fluid and stationary wall molecules. This approach cannot properly model interactions and thermal exchange at the wall–fluid interface. We present a new interactive thermal wall model that can properly simulate the flow and heat transfer in nano-scale channels. The new model utilizes fluid molecules freely interacting with the thermally oscillating wall molecules, which are connected to the lattice positions with “bonds”. Thermostats are applied separately to each layer of the walls to keep the wall temperature constant, while temperature of the fluid is sustained without the application of a thermostat. Two-dimensional MD simulation results for shear driven nano-channel flow shows parabolic temperature distribution within the domain, induced by viscous heating due to a constant shear rate. As a result of the Kapitza resistance, temperature profiles exhibit jumps at the fluid–wall interface. Time dependent simulation results for freezing of liquid argon in a nano-channel are also presented.     

Effects of environmental temperature and humidity on thermal flying height adjustment

Thermal actuated sliders are being widely used in today’s hard disk drive industry for its advantages of easier control of flying height (FH) and less risk of contacts with the disk. This article uses a coupled-field analysis method, which includes an air bearing model, a heat transfer model and a thermal-structural finite element model to investigate the FH changes of thermal actuated sliders at various environmental conditions. The mechanism of water vapour’s contribution to air bearing pressure loss is explained and a new humidity model is proposed to calculate this pressure loss. The temperature effects are also considered in the simulation models. It is observed that the environmental temperature and humidity have significant effects on slider’s FH changes, but their effects on the thermal protrusion height are limited. A humidity sensitivity study is also made and the results are discussed. It is found that the slider with thermal protrusion on its trailing pad will be more sensitive to the humidity. Besides air bearing stiffness, some other factors such as peak pressure, protrusion shape and air bearing surface (ABS) design will also contribute to the slider’s humidity sensitivity.     

Precomputed Radiance Transfer Field for Rendering Interreflections in Dynamic Scenes

In this paper, we introduce a new representation – radiance transfer fields (RTF) – for rendering interreflections in dynamic scenes under low frequency illumination. The RTF describes the radiance transferred by an individual object to its surrounding space as a function of the incident radiance. An important property of RTF is its independence of the scene configuration, enabling interreflection computation in dynamic scenes. Secondly, RTFs naturally fit in with the rendering framework of precomputed shadow fields, incurring negligible cost to add interreflection effects. In addition, RTFs can be used to compute interreflections for both diffuse and glossy objects. We also show that RTF data can be highly compressed by clustered principal component analysis (CPCA), which not only reduces the memory cost but also accelerates rendering. Finally, we present some experimental results demonstrating our techniques.     

Heat transfer in cylindrical shrouded cavities

The flow field, temperature field and the heat transfer rates in cylindrical shrouded cavities with rotation, recirculation and coolant through-flow have been analyzed numerically. Two cavity configurations are considered. In the first configuration, a heated cylindrical shroud is enclosed by a stationary insulated stator disc and a rotating insulated rotor disc. The coolant air enters the cavity by a central opening in the rotor and exits through an annular gap at the rim of the rotor. The second configuration studies the heat transfer from an air cooled gas turbine disc using the model of a plane disc rotating close to an insulated shrouded stator. The coolant enters centrally through the stator disc and exits radially through a gap between the shroud and the rotor. The flow field and heat transfer rates are computed for several values of coolant flow rate, the rotor swirl speed, the cavity aspect ratio and the exit gap width in the two cavity configurations. The swirl of the rotor changes immensely the flow pattern, recirculating zones and isotherms inside such cavities. In general, increasing coolant flow rate, decreasing swirl and decreasing aspect ratio enhances the heat transfer from the shroud in the first cavity configuration. For the second cavity configuration, the heat transfer rates increase with increasing coolant flow rate, increasing swirl of the rotor, increasing size of the cavity and decreasing exit gap width between the stator and the rotor.     

Iteration method for analysis of write-current-induced thermal protrusion

This article presents a detailed iteration method for coupled air bearing and thermal-structure analysis, and introduces a node-to-node schematic for mapping the heat transfer coefficient into the thermal-structure analysis as boundary conditions. A three-dimensional finite element model is developed. The heat transfer coefficient on the air bearing surface of slider is calculated by a quasi-steady heat transfer model and applied to the thermal-structure analysis through the proposed node-to-node mapping schematic. The results show that the iteration process is indispensable for the air-bearing-thermal-structure analysis under high write power, but changeable under low write power. Among iterations, the values and distribution of the heat transfer coefficient vary significantly, especially around the protruding regions. The corresponding thermal protrusion induced by write current and its effects on flying attitude are different and the difference is increased with the heating power. For the application of high heating power and large thermal protrusion, at least a three-time iteration of the heat transfer coefficient is needed.