Transient Temperature Response Research Articles

Heat transfer from warm water to a moving foot in a footbath

A model is proposed in this work to investigate the impact of a moving foot on the transfer of heat from a constantly heated warm water into the foot immersed within a footbath. The model is simply based on the well-known Pennes bioheat equation that governs the thermal process of the fat part of the foot in action. Both the steady and transient temperature responses of the foot are analytically evaluated. The visible physical effects of the up and down movement of the foot on the skin layer heat and also on the scaled heat flux in the fat layer are later explored and discussed. It is found that the upward motion heats up the foot whereas the downward motion cools down the foot leading to a better thermal sensation and comfort during the thermal process of the foot in the footbath which is highly desirable during a physiotherapy.

Numerical Analysis of Transient Temperature Response of Soap Film

Measurements of thermophysical properties of thin liquid films are important to understand interfacial phenomena due to film structures composed of amphiphilic molecules in soap film, phospholipid bilayer of biological cell and emulsion. A transient hot-wire technique for liquid films less than 1 $$\upmu $$ m thick such as soap film has been proposed to measure the thermal conductivity and diffusivity simultaneously. Two-dimensional heat conduction equations for a solid cylinder with a liquid film have been solved numerically. The temperature of a thin wire with liquid film increases steeply with its own heat generation. The feasibility of this technique is verified through numerical experiments for various thermal conductivities, diffusivities, and film thicknesses. Calculated results indicate that the increase in the volumetric average temperature of the thin wire sufficiently varies with the change of thermal conductivity and diffusivity of the soap film. Therefore, the temperature characteristics could be utilized to evaluate both the thermal conductivity and diffusivity using the Gauss–Newton method.

Transient Heat Transfer of a Hollow Cylinder Subjected to Periodic Boundary Conditions

The purpose of this paper is to study the transient temperature responses of a hollow cylinder subjected to periodic boundary conditions, which comprises with a short heating period (a few milliseconds) and a relative long cooling period (a few seconds). During the heating process, the inner surface is under complex convection heat transfer condition, which is not so easy to approximate. This paper first calculated the gas temperature history and the convective heat transfer coefficient history between the gas flow and the inner surface and then they were applied to the inner surface as boundary conditions. Finite element analysis was used to solve the transient heat transfer equations of the hollow cylinder. Results show that the inner surface is under strong thermal impact and large temperature gradient occurs in the region adjacent to the inner surface. Sometimes chromium plating and water cooling are used to relief the thermal shock of a tube under such thermal conditions. The effects of these methods are analyzed, and it indicates that the chromium plating can reduce the maximum temperature of the inner surface for the first cycle during periodic heating and the water cooling method can reduce the growth trend of the maximum temperature for sustained conditions. We also investigate the effects of different parameters on the maximum temperature of the inner surface, like chromium thickness, water velocity, channel diameter, and number of cooling channels.

Thermal behavior of a microdevice under transient heat loads

An experimental study was carried out to investigate the transient response of a thermal microsystem to both a step change and a square wave pulse change in heat flux. The microsystem consisted of a single microchannel etched on a silicon microdevice that was bonded to a Pyrex wafer. A thin-film titanium heater was deposited on the Pyrex substrate. The heater acted as the power source as well as the resistance temperature device. The influence of flow convection on the transient response was studied for two fluids: air and HFE-7000. The effects of heat flux, Reynolds number, fluid properties, and pulse parameters (amplitude, width, duty cycle) on the transient temperature response were identified. The temperature response consisted of an initial rapid temperature rise followed by slower convection dynamics. For longer pulse widths, the temperature of the microdevice reached steady state. Higher order dynamics were identified at the beginning of the temperature response. Convection dynamics were approximated as a first-order response, and the effects of Reynolds number and fluid properties on the time constant of the first order response were identified.

Numerical analysis on the transient measurement of gas temperature in porous material using thermocouples at high temperatures

Heat transfer in porous materials is significantly important in various engineering fields. The temperature distributions are essential for comprehensive understanding of the process. The current study aims to investigate the uncertainties associated with the gas temperature measurement in porous material using thermocouples at high temperatures by means of two hierarchical models. The transient coupled radiative and convective heat transfer within porous material is firstly simulated using the local thermal non-equilibrium model with Monte Carlo method. The flow is transient, incompressible and laminar. The porous material is considered as a homogeneous, absorbing, emitting and isotropic scattering medium. Based on the velocity and temperature fields, a numerical heat transfer model for thermocouple junction is developed with the lumped energy balance. Monte Carlo method is also adopted for the radiation simulation between the junction and porous material. The transient temperature response of thermocouple is computed and compared with the local gas temperature. The effects of wall temperature and the emissivity and diameter of thermocouple junction are analyzed. The results show that thermal inertia of thermocouple and thermal radiation have a significant effect on the gas temperature measurement inside porous material. The measurement error varies obviously during the transient measurement process. The junction diameter has a higher influence on the measurement error than junction emissivity. In addition, compared with low emissivity, the error is larger for high junction emissivity when the steady state is reached.

Rewetting of Vertical Pipes by Bottom Flooding Using Nanofluid as a Coolant

The present investigation reports the rewetting phenomenon by bottom flooding in vertical pipes using both water and nanofluid as coolant. The transient temperature response of rewetted surface indicates that rewetting takes place faster in nanofluids than in water. The effect of several parameters, including the coolant flow rate, distance from the inlet of fluid, concentration of nanoparticle loading on the rewetting characteristics, has been investigated. The rewetting velocity, for both water and nanofluid, is observed to depend strongly on the inlet coolant flow rate and initial wall temperature of the tube. The rewetting velocity is observed to follow the correlation for water proposed in an earlier work. Starting from the logic proposed in that previous report, the authors propose a correlation for predicting the rewetting velocity in nanofluids.

Modeling and Simulation of Temperature Field in High Speed Milling based on Weighted Residual Method

In the process of high speed milling of titanium alloy, the milling temperature change had an adverse effect on machining accuracy, machining surface integrity and machining efficiency. To deal with this problem, heat conduction mode, the heat convection between cutting tools and air medium, and heat flux intensity boundary conditions in actual milling process are fully considered. And according to general heat equation, the heat conduction model of transient temperature field is built. The differential form of temperature field model are converted into corresponding form of the integral functional equation by the weighted residual method. A certain accuracy method for calculating the approximate solution is presented. And the transient temperature response of space element in milling system is obtained under equal time intervals. Finally it is proved that the model is correct by experiment result, which laid a solid foundation for accurately analyzing milling temperature.

Relationship between Thermal Conduction Process and Transient Temperature Response of Printing Papers in DTP Process

Relationship between Thermal Conduction Process and Transient Temperature Response of Printing Papers in DTP Process

Application of the hybrid particle swarm optimization algorithms for simultaneous estimation of multi-parameters in a transient conduction–radiation problem

A Simplex Bare-bones Particle Swarm Optimization (KSM-BBPSO) algorithm based on the K-means clustering was introduced, and on this basis, an improved hybrid Simplex-Particle Swarm Optimization algorithm based on K-means clustering (KSM-PSO) was developed to retrieve the multi-parameters of the semi-transparent media simultaneously in a transient conduction–radiation problem. The conduction–radiation parameter, scattering albedo, and boundary emissivity in a one-dimensional (1-D) homogenous semitransparent slab were estimated simultaneously to illustrate the performances of the KSM-BBPSO and KSM-PSO algorithms. The transient temperature responses on both sides of the medium boundaries exposed to the pulse laser irradiation, which was simulated directly by Finite Volume Method (FVM), were served as input for the inverse analysis. By the KSM-BBPSO algorithm introduced and KSM-PSO algorithm developed, all the thermophysical parameters could be estimated with reasonable accuracy, even with noisy temperature measurements. The KSM-PSO algorithm was proved to be fast, accurate, and robust, while the KSM-BBPSO algorithm has better versatility.

Transverse heat transfer coefficient in the dual channel ITER TF CICCs Part II. Analysis of transient temperature responses observed during a heat slug propagation experiment

A heat slug propagation experiment in the final design dual channel ITER TF CICC was performed in the SULTAN test facility at EPFL-CRPP in Villigen PSI. We analyzed the data resulting from this experiment to determine the equivalent transverse heat transfer coefficient hBC between the bundle and the central channel of this cable. In the data analysis we used methods based on the analytical solutions of a problem of transient heat transfer in a dual-channel cable, similar to Renard et al. (2006) and Bottura et al. (2006). The observed experimental and other limits related to these methods are identified and possible modifications proposed. One result from our analysis is that the hBC values obtained with different methods differ by up to a factor of 2. We have also observed that the uncertainties of hBC in both methods considered are much larger than those reported earlier.

Finite Element Simulation Analysis of Micro Thermoelectric Switch Structure

Considering of the thermal resistant of metal Ni-Cr, as well as the insulating characteristic of SiO2 membrane, aluminium electric line, energetic material, solder and other materials, we designed three MEMS thermo-electric switches, which can realize On-Off (or Off-On) transition to control the initiation of weapon system. We also simulated and analyzed the static and the transient thermal processes and the stress analysis of switches using finite element simulation analysis (FEA) tool ANSYS. The results of temperature distributing, transient response and stress distributing have been obtained.

Cross Flow Heat Exchanger Modeling of Transient Temperature Input Conditions

The effectiveness of heat exchangers strongly influences the thermal performance of data center cooling systems. Rear door heat exchangers, in-row and overhead coolers, and fully contained water cooled cabinets are some examples of liquid and hybrid cooling systems used in data centers. Modeling the dynamic behavior of heat exchangers is important for the design of control strategies to improve energy efficiency. In this paper, an existing 2-D model of the transient temperature response of an unmixed-unmixed cross flow heat exchanger, of the type that is widely used in data center cooling equipment, is solved numerically. A detailed analysis of the transient response to a step, ramp, or exponential change in the hot fluid inlet temperature is conducted. The heat capacity rate ratio (E), thermal resistance (R), capacitance ratio (V), and number of transfer units are varied over a wide range to determine their influence on the heat exchanger dynamic thermal performance under different transient input conditions. In addition, the thermal response to the magnitude and time period of the transient input functions are evaluated. The modeling results are used to analyze specific data center cooling scenarios, and provide a means for predicting the transient behavior of heat exchangers used in data center cooling equipment.

Erratum: “Transient Temperature Response of Variable Flow Heat Exchangers in a Marnoch Heat Engine” [Journal of Heat Transfer, 2014, 136(11), p. 111801

Erratum: “Transient Temperature Response of Variable Flow Heat Exchangers in a Marnoch Heat Engine” [Journal of Heat Transfer, 2014, 136(11), p. 111801

Part II: Numerical study on the flow and thermal characteristics of an integrated deflector under the periodic impingement of a supersonic high temperature jet

A three-dimensional numerical simulation of an integrated deflector under periodical impingement of a supersonic high-temperature air jet was conducted on the basis of the Renormalized Group (RNG) k–ɛ model. The heat capacity and thermal conductivity of the deflector materials as functions of temperature were measured to establish the model. The predicted transient temperature response of the impinged and back surfaces of the deflector agreed well with experimental data. The flow and thermal performance of jet impinging on the deflector were investigated, and the effects of separation distance, horizontal angle, and vertical angle were analyzed. The predicted results of the experimental case revealed that the impingement jet generated a shock wave at the plate center and an expansion wave at 0.5D<y<1.5D. The maximum pressure, Nusselt number, and temperature on the impinged surface displaced from the geometric impingement center at y=−0.3D, y=−0.1D, and y=0.3D, respectively. Parameter analysis revealed that larger separation distance resulted in lower maximum pressure. The peak of maximum Nusselt number occurred near the end of the potential core of the free jet with the same parameters, whereas the maximum temperature appeared prior to the end of the potential core. When the horizontal or vertical angle decreased from the perpendicular case at 90°, the asymmetry of wall jet distribution in the corresponding direction was augmented. This condition decreased maximum pressure, Nusselt number, and temperature, but increased the displacement of maximum points from the geometrical impingement point.

Study on ESD Effects of GaAs HBT Power Amplifiers for DCS/GSM Dual Band Handsets

Study on electrostatic discharge (ESD) impact on the GaAs HBT power amplifier (PA) in DCS/GSM dual band handsets is performed in this paper, which has been regarded as its main reliability issue accounting for most failures of radio frequency integrated circuits. In order to suppress the positive ESD impact on the PA in an effective but very economic way, a set of forward ESD diodes at its input port is replaced by the PN junction of GaAs HBT transistor in its first-stage. Alternatively, to introduce a set of thin film resistors (TFRs) at the front of a HBT transistor is necessary for improving the S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> -parameter and stability of PA; however, their electrothermal breakdown possibilities do exist. Therefore, both performance degradation and breakdown events of several PA dies are measured for different ESD voltages described by the human body model, with different TFRs chosen for both DCS and GSM bands, respectively. Their transient temperature responses are also captured and compared for different ESD waveforms, which are predicted using the in-house developed algorithm based on the hybrid time-domain finite-element method.

Transient Temperature Response of Variable Flow Heat Exchangers in a Marnoch Heat Engine

Within a Marnoch heat engine (MHE), a water/glycol mixture transfers heat from the heat source into a set of variable flow heat exchangers and removes heat from adjoining cold heat exchangers. The compressed dry air is used as the working medium in this heat engine. The MHE has four shell and tube heat exchangers, which operate transient and variable flow conditions. A new transient heat transfer model is developed to predict this transient behavior of the heat exchangers for different flow regimes and temperatures. The results from the model are validated against experimental results from an MHE prototype. The heat transfer model shows 85% agreement with measured data from the MHE prototype for the individual heat exchangers. This model can be used for similar shell and tube heat exchangers with straight or U-shaped tubes. The heat transfer model predicts the gas temperature on the shell side, when a step change is imposed on the liquid entering the tubes.

Advanced phase change composite by thermally annealed defect-free graphene for thermal energy storage.

Organic phase change materials (PCMs) have been utilized as latent heat energy storage and release media for effective thermal management. A major challenge exists for organic PCMs in which their low thermal conductivity leads to a slow transient temperature response and reduced heat transfer efficiency. In this work, 2D thermally annealed defect-free graphene sheets (GSs) can be obtained upon high temperature annealing in removing defects and oxygen functional groups. As a result of greatly reduced phonon scattering centers for thermal transport, the incorporation of ultralight weight and defect free graphene applied as nanoscale additives into a phase change composite (PCC) drastically improve thermal conductivity and meanwhile minimize the reduction of heat of fusion. A high thermal conductivity of the defect-free graphene-PCC can be achieved up to 3.55 W/(m K) at a 10 wt % graphene loading. This represents an enhancement of over 600% as compared to pristine graphene-PCC without annealing at a comparable loading, and a 16-fold enhancement than the pure PCM (1-octadecanol). The defect-free graphene-PCC displays rapid temperature response and superior heat transfer capability as compared to the pristine graphene-PCC or pure PCM, enabling transformational thermal energy storage and management.

The on-chip temperature compensation and temperature control research for the silicon micro-gyroscope

In this paper, the on-chip temperature compensation and temperature control research for the silicon micro-gyroscope are presented. The proposed micro-gyroscope architecture which integrates an on-chip temperature sensor and a serpentine micro-heater achieves the on-chip temperature compensation and the on-chip temperature control of the micro-gyroscope. We first analyze the thermodynamic steady-state temperature distribution and transient temperature response of micro-gyroscope structure. Then we simulate the temperature response of the micro-gyroscope structure by Ansys software. The Deep Dry Silicon on Glass process and wet etching process are combined for fabrication of the integrated micro-gyroscope structure. The signal measurement and control circuit based on the FPGA platform are implemented. The temperature coefficients of zero bias and scale factor are compensated with the integrated temperature sensor. Taking advantage of the drive mode resonant frequency as the temperature sensor, a high precision on-chip temperature control of micro-gyroscope is realized simultaneously. The on-chip temperature compensation and temperature control experiment of micro-gyroscope prototype is tested. Experimental results indicate that the temperature coefficients of the scale factor and zero bias decrease by 3.95 times and 3.49 times separately by on-chip temperature compensation, which optimizes significantly the temperature characteristics of the micro-gyroscope prototype. The control accuracy of drive-mode frequency reaches to 3.57 × 10?4 Hz (that is 0.123 ppm and the calculated temperature accuracy of 0.0067 °C) from 0 to 40 °C by the on-chip temperature control, which demonstrates an achievement of the precision on-chip temperature control for the micro-gyroscope.

Performance Testing of Fast Read Digital Thermometers1

Performance Testing of Fast Read Digital Thermometers1

Transient temperature response of near field scanning optical microscope probes under pulsed illumination

Time resolved thermoreflectance imaging with a nanosecond laser is applied to study the transient thermal response of near field scanning optical microscope (NSOM) probes driven by either microsecond (μs) or nanosecond (ns) laser pulses. It is found that when the laser energies are the same, μs and ns laser pulses show similar trend of close to adiabatic heating during the laser pulse and close to conductive cooling after the laser pulse. The peak temperature is almost linear with respect to input laser energy for the energy selected. The peak temperature of the NSOM probe is increased when the aperture size of the probe is smaller and when the incident laser wavelength is shorter. However, compared with μs laser pulses, small physical damages appear around the NSOM aperture, which gradually decreases the optical-thermal energy conversion efficiency in the NSOM probe when ns laser pulses are applied.