Thermal Equilibrium Time Research Articles

Investigating the Effect of Curing and Thermal Equilibrium Time on Rutting Potential of Hot Mix Asphalt

Rutting is a common damage of flexible pavements, reducing the service life of asphalt pavement. Due to laboratory limitations, asphalt mixtures are subjected to different curing times (since construction until placement in the test chamber) and thermal equilibrium times (since placement in the test chamber until the beginning of the test) before rutting tests. Neglecting these factors can lead to errors in the laboratory results. Therefore, the present study attempted to investigate the effect of curing times of 1, 2, and 3 days at 25ºC and thermal equilibrium times of 2, 4, and 6 hours on the rutting potential of different hot-mix asphalt (HMA) mixtures. Results of rutting tests showed that the rutting potential of asphalt mixtures decreases by increasing the curing time, while the permanent deformation at the end of loading cycles and rutting potential increase by increasing the thermal equilibrium time. Additionally, the results of statistical analyses revealed that curing time and thermal equilibrium time change the rutting potential of asphalt mixtures.

Investigating the Effective Laboratory Parameters on the Stiffness Modulus and Fatigue Cracking of Warm Mix Asphalt

Lack of attention to the effect of laboratory conditions on the results of asphalt mixture tests, especially these of the warm mix asphalt (WMA), makes the analysis of results misleading. Thus herein, after examining the research on WMA and factors affecting test results in laboratory conditions, the effect of three parameters including short-term aging (asphalt binder storage in the oven), curing time (from construction to placement in the test chamber), and thermal equilibrium time (from placement in the test chamber to the test onset) were investigated on the characteristics of WMA at mid-temperature. To simultaneously examine these three factors, 36 modes were developed to evaluate their effect on the stiffness modulus and fatigue cracking, using the indirect tensile stiffness modulus test (ITSM) and indirect tensile fatigue test (ITFT), respectively. Results of the experiments showed that increasing the time of asphalt binder placement in the oven for 2–6 h significantly increased the stiffness modulus of the mixture, which reduced the fatigue life of the WMA. With increasing the curing time and improving the adhesion between asphalt binder and aggregates, the stiffness modulus and fatigue life of the specimens increased; however, by increasing the thermal equilibrium time, the stiffness modulus and fatigue life of the specimens decreased due to asphalt binder viscoelastic behavior and temperature sensitivity. Results of statistical analyses revealed that short-term aging, curing time, and thermal equilibrium time in laboratory conditions were effective on the stiffness modulus and fatigue life of WMA at a 95% confidence level.

The effect of moisture of cotton fabrics on steam sterilization

This paper is to study the effect of cotton fabric?s moisture on steam sterilization process. An experiment is designed to measure the thermal equilibrium time under different moisture concentrations. The results show that a higher moisture concentration leads to a longer thermal equilibrium time, and it does not affect the wet pack?s penetration efficiency when the moisture concentration is below the threshold value of 30%. The paper concludes that a higher humidity is unfavorable for the thermal conduction during the sterilization process.

Quartz Enhanced Conductance Spectroscopy for Polymer Nano-Mechanical Thermal Analysis

A fast and highly sensitive polymer nano-mechanical thermal analysis method for determining the melting temperature (Tm) of polymer microwires was proposed. In this method, a small-size, low-cost quartz tuning fork was used as a piezoelectric transducer to analyze the thermodynamics of polymer microwires at the nanogram level without changing its own properties. Due to the thin wire sample, which has a length of 1.2 mm and a diameter of ~5 µm, which is bridged across the prongs of the tuning fork, the nanogram-level sample greatly reduces the thermal equilibrium time for the measurement, resulting in a fast analysis for the melting temperature of the polymer sample. Compared with the traditional method, the analysis method based on the quartz enhanced conductivity spectrum (QECS) does not require annealing before measurement, which is an essential process for conventional thermal analysis to reduce the hardness, refine the grain, and eliminate the residual stress. In this work, the melting temperatures of three of the most commonly used polymers, namely polymers polymethyl methacrylate, high-density polyethylene, and disproportionated rosin, were obtained under the temperature from room temperature to >180 °C, proving the QECS method to be a useful tool for nano-mechanical thermal analysis.

Parametric Analysis of the In-bed gas flowing calorimetry of metal hydride bed employed in CFETR SDS

Gas flowing calorimetry is considered to be one of the most promising tritium measurements method in fusion fuel cycles, yet the parametric study of the structure design is still insufficient. In this study, three-dimensional models, combining with commercial computational fluid software, has been used to evaluate the calorimetric performance of tritium storage beds. The effects of structural geometry and cooling method on the heat transfer behavior have been systematically studied. The results show that the proposed model can effectively characterizes the evolution of the temperature difference of the cooling gas with time during the calorimetric process. Typically, increasing number of the U-shaped cooling tubes, thickness of the metal hydride layer and flow rate of the cooling liquid are beneficial for reducing the thermal equilibrium time. When the number of calorimeter bed cooling tubes is 12, the thickness of the metal hydride layer is 23, and the cooling gas is 20 SLMP of CO2, the thermal equilibrium time is only 4.5h. Furthermore, through optimizing the structural parameters, which can have an important influence on calorimetric performance, highly efficient and accurate gas flow calorimeter can be developed in the future.

Heat Transfer and Temperature Characteristics of a Working Digital Camera.

Digital cameras represented by industrial cameras are widely used as image acquisition sensors in the field of image-based mechanics measurement, and their thermal effect inevitably induces thermal-induced errors of the mechanics measurement. To deeply understand the errors, the research for digital camera’s thermal effect is necessary. This study systematically investigated the heat transfer processes and temperature characteristics of a working digital camera. Concretely, based on the temperature distribution of a typical working digital camera, the heat transfer of the working digital camera was investigated, and a model describing the temperature variation and distribution was presented and verified experimentally. With this model, the thermal equilibrium time and thermal equilibrium temperature of the camera system were calculated. Then, the influences of thermal parameters of digital camera and environmental temperature on the temperature characteristics of working digital camera were simulated and experimentally investigated. The theory analysis and experimental results demonstrate that the presented model can accurately describe the temperature characteristics and further calculate the thermal equilibrium state of working digital camera, all of which contribute to guiding mechanics measurement and thermal design based on such camera sensors.

Numerical Simulation of the Influence of Flow Velocity on Granite Temperature Field Under Thermal Shock

Under thermal shock, the heat conduction between granite and fluid will lead to the redistribution of rock temperature field, while indoor thermal shock test cannot determine the distribution rule of temperature field inside granite accurately. In order to explore the influence of fluid velocity on the thermal shock process of granite, the temperature field and flow field is numerically simulated by COMSOL. The results show that heat transfer between granite and fluid is in the form of waves. In the process of heat conduction, the internal temperature and heat balance time of granite are greater than those of rock surface. The time of heat balance in rock provides reference for the design of indoor thermal shock test. After thermal shock, the temperature of granite is lower than the initial temperature. With the increase of fluid velocity, the thermal equilibrium time of granite decreases, and the final rock stable temperature decreases. According to the relationship between velocity and granite temperature, a linear correlation model between velocity and maximum instantaneous thermal shock velocity is proposed. It is also verified that the thermal fluid–solid coupling model of granite under thermal shock is feasible to simulate the heat conduction and temperature distribution in granite.

Thermal error controlling for the spindle in a precision boring machine with external cooling across coated joints

Spindles in precision boring machines usually operate without internal cooling, and thermal error in such spindles is nonnegligible and can severely affect the end-processing quality of the machines. This study aims to investigate the effects that external cooling exerts on the thermal behavior of such spindles. A helical tube cooler is taken for external cooling. An analytical thermal resistance model for the grease-coated cooler-housing joint surface, which considers the pressured cambered-flat contact pair and rough metal surface-grease contact, is presented and validated, and a numerical thermal–fluid–solid coupling model for the cooler-spindle system is then established. An evaluation method is put forward to obtain the stability of the thermal error, which determines the boring processing accuracy and thermal equilibrium time, from experimental data. Then, the external cooling was optimally designed based on the simulation results from the numerical model. Experiments show that the designed cooler reduced the thermal equilibrium time by 47.13% and the maximum thermal error by 81.7%, and the proposed model can accurately predict the cooling effect on the spindle thermal behavior. This study not only provides a thermal error control method for the spindle but is expected to advance the theoretical basis of cooling design for complex electromechanical systems.

Thermal analysis for the large precision EDM machine tool considering the spark energy during long-time processing

Thermal error is a major factor influencing the accuracy of large precision electrical discharge machining (EDM) machine tools, especially when processing continuously for a long time. In this paper, a novel thermal analysis model was set up to identify the static and dynamic thermal behaviour of the large EDM machine tool. The thermal effect of multiple spark discharges is considered. An equivalent heat flux method was proposed to model the intermittent heat flux for the first time. Both the steady and transient analyses were applied to investigate the thermal equilibrium time of critical points. It is found that when the study point is far away from the heat source, the longer thermal equilibrium time is needed. And the thermal equilibrium time of the machine tool was also estimated. Verification experiment has been performed, indicating the simulation accuracy of 87 % on the temperature rise of the electrode. Moreover, on the displacement of the spindle, the simulated result matched with the experimental result in Z direction error of 7 %. Finally, suggestions for reducing the thermal deformation were proposed to further improve the machining accuracy of large EDM machine tools.

STAGNATION POINT FLOW OF DUSTY CASSON FLUID WITH THERMAL RADIATION AND BUOYANCY EFFECTS

The aim of the study is to examine the stagnation point flow of a dusty Casson fluid over a stretching sheet with thermal radiation and buoyancy effects. The governing boundary layer equations are represented by a system of partial differential equation. After applying suitable similarity transformations, the resulting boundary layer equations are solved numerically using the Runge Kutta Fehlberg fourth-fifth order method (RKF-45 method). The behaviors of velocity, temperature and concentration profiles of fluid and dusty particles with respect to change in fluid particle interaction parameter, Casson paramter, Grashof number, radiation parameter, Prandtl number, number density, thermal equilibrium time, relaxation time, specific heat of fluid and dusty particles, ratio of diffusion coefficients, Schmidt number and Eckert number are analysed graphically and discussed. Our computed results interpret that velocity distribution decays for higher estimation of Casson parameter while temperature distribution shows increasing behavior for larger radiation parameter.

Heat transfer during pasteurization of fruit pulps stored in containers with arbitrary geometries obtained through revolution of flat areas

Thermal diffusivity of papaya pulp, stored in metal container with arbitrary geometry obtained through revolution of flat areas, was determined through optimization using experimental data. To describe heat conduction during pulp pasteurization, the diffusion equation in generalized coordinates was discretized and numerically solved, through the finite volume method, with a fully implicit formulation. Temperature over time during heating was measured by placing a thermocouple at the point of the container where the equilibrium temperature occurs with greatest delay. Once the expression for thermal diffusivity as a function of local temperature was known by optimization, it was possible to determine, through simulation, the minimum time necessary for the pulp stored in a new container, also with arbitrary geometry obtained through revolution of flat areas, to come into thermal equilibrium with the pasteurization temperature. Microbiological analysis performed before and after the second pasteurization showed that there was a strong reduction of the total microorganisms. Since the thermal equilibrium time was determined through simulation for the new container, the use of a thermocouple for its experimental determination became unnecessary.

Development of an improved wearable device for core body temperature monitoring based on the dual heat flux principle

Objective: In this paper, a miniaturized wearable core body temperature (CBT) monitoring system based on the dual heat flux (DHF) principle was developed. Approach: By interspersing calcium carbonate powder in PolyDimethylsiloxane (PDMS), a reformative heat transfer medium was produced to reduce the thermal equilibrium time. Besides, a least mean square (LMS) algorithm based active noise cancellation (ANC) method was adopted to diminish the impact of ambient temperature fluctuations. Theoretical analyses, finite element simulation, experiments on a hot plate and human volunteers were performed. Main results: The results showed that the proposed system had the advantages of small size, reduced initial time (~23.5 min), and good immunity to fluctuations of the air temperature. For the range of 37–41 °C on the hot plate, the error compared with a Fluke high accuracy thermometer was 0.08 ± 0.20 °C. In the human experiments, the measured temperature in the rest trial (34 subjects) had a difference of 0.13 ± 0.22 °C compared with sublingual temperature, while a significant increase of 1.36 ± 0.44 °C from rest to jogging was found in the exercise trial (30 subjects). Significance: This system has the potential for reliable continuous CBT measurement in rest and can reflect CBT variations during exercise.

Erratum to: Femtosecond pulse laser ablation of chromium: experimental results and two-temperature model simulations

In this work, the results of experimental and computational single- and multi-shot ablation threshold and the incubation effect of chromium metal sample, irradiated by ultrashort laser pulses, are presented. The experimental value of the ablation threshold is determined based on $$D^{2}$$ method by measuring the outer ablation crater diameters as a function of incident laser pulse energy using $$800 \, \mathrm{nm}, 30 \, \mathrm{fs},$$ laser pulses. The value of $$0.19 \pm 0.04 \, (\mathrm{J/cm}^{2} )$$ , is obtained for the single-shot ablation threshold fluence. The experimental results are compared with time-dependent heat flow calculations based on the two-temperature model and the effect of number and separation time of two consecutive laser pulses with the same total fluence is studied for the Cr target. Moreover, the role of pulse width and absorbed fluence in thermal equilibrium time between electrons and lattice is investigated in two-temperature model. The thermal equilibrium between electron and lattice is established after a few picoseconds for low fluences and after a few tens of picoseconds at higher fluences.

Determination of thermal equilibrium in a sealed cell based on optical depth

An effective method based on optical depth (OD) is presented to measure thermal equilibrium in a cell. First, the principle of determining the temperature distribution in the cell by using the OD is demonstrated. Subsequently, relevant experiments are carried out. Original experimental results showed that some gradients of OD distributions in the cell at different wavelengths and variations of the OD increased slowly along the direction of motion of the beam at a fixed wavelength. At a wavelength of 766.6839 nm, which is about 7 GHz blue shifted with respect to the potassium resonance, the average value of the OD was about 0.764 and the maximal and the minimum inhomogeneity biases among all location points were about 6.07% and 0.56%, respectively. As for the corresponding wavelengths of 766.67785 nm and 766.73004 nm, some deviations from previous results, which were caused by different absorptions of the alkali-metal atoms at different frequencies of the laser beam, were observed. The nonuniform OD values along the direction of motion of the beam reflected an inhomogeneous distribution of the temperature in the cell, which may have been caused by layout of the oven. When the layout of the oven was modified, comparative experiments comparable to these with the previous layout of the oven demonstrated that the uniformity of the temperature distribution in the cell was improved and that thermal equilibrium time was shorter by about 10 minutes. This method played an important role in determining the thermal equilibrium time in the cell.

Comparisons of thermal conductive behaviors of epoxy resin in unidirectional composite materials

This paper reports thermal conductive behaviors of three kinds of materials, i.e., epoxy resin bar, carbon fiber bundles/epoxy system, and unidirectional carbon fiber/epoxy lamina along 0° and 90° directions. The apparatus for thermal conduction measurement was manufactured and calibrated with an aluminum bar with known thermal conductivity. The thermal conductive behaviors, including the thermal conductive rate and thermal equilibrium time, were tested and numerically simulated with finite element method. It is found that these materials have similar thermal conductive characteristics with same trends of temperature–time curves and thermal gradient–time curves. In addition, with the increase in fiber volume content or decrease in fiber orientation angle, the thermal conductive rate will be speeded up and thermal equilibrium time will be reduced. The temperature of epoxy resin in composite will increase with the increment of fiber volume content. Due to the existence of interface between fiber and resin, the overall thermal conductive ability of composite will be weakened. Owing to the epoxy resin, carbon fiber bundles/epoxy system and unidirectional carbon fiber/epoxy lamina are the basic materials for the laminates or complex preform reinforced composites, and the thermal conductive behaviors of these basic materials could be extended to design the thermal conductive behaviors of laminates and complex reinforcement composite materials.

Thermal Equilibration in the Cavity Volume of a Farmer Ion Chamber for Routine Dosimetry

A Farmer ion chamber with an air cavity volume is the most widely used dosimeter for accurate dose determinations in radiotherapy. The quantity of ionization in the cavity volume occurred a given radiation dose has to be corrected to the cavity air temperature according to a dosimetry protocol because the mass of air in the cavity volume is subject to atmospheric variations. In the present study, we aim to measure the thermal equilibration time in the cavity volume of a Farmer ion chamber for the routine dosimetry. The Farmer ion chamber’s electrode was replaced by a thin thermocouple and coated by the PMMA for a waterproofing so that the measurement of the temperature in the cavity performed in water. As a result of the measurement, A Farmer ion chamber in thermal equilibrium with waterproofing equilibrates rapidly, followed by an exponential fall-off. In water, equilibration to less than 10% of the initial temperature difference required only a few minutes. Thermal equilibrium time is hardly affected by the room temperature change.

Theoretical modeling and experimental investigations of the effective thermal equilibrium time for Yb:YAG crystal

Theoretical modeling and experimental investigations of the effective thermal equilibrium time for Yb:YAG crystal

Thermal error simulation and compensation in a jig-boring machine equipped with a dual-drive servo feed system

A jig-boring machine equipped with a dual-drive servo system can operate with high speed and accuracy. However, different friction behaviours and asymmetrical preloads of the double drive structures as well as asynchronous control over the master-slave motors can make the machine produce tremendous heat, causing uneven temperature distributions in the feed system and eventually leading to thermal deformation that reduces the positional accuracy of machines. To investigate the effects of thermal behaviours on machining accuracy, the thermal–structure finite element method was employed to analyse the transient thermal deformation and temperature field of the machine at different feed rates, considering boundary conditions such as the convective heat transfer coefficient and heat generation by motors, bearings, and screws. Additionally, a synchronous acquisition system was developed to measure the thermal behaviours, and the transient changes in temperature and deformation were compared with simulated values. Consequently, a synthetic thermal model was established to make accurate predictions based on the analysis of relationships between thermal error and equilibrium time, coordinate position and screw temperature. Finally, thermal error compensation was performed using a feedback integration method. The experimental data indicate that the finite element method model can accurately predict temperature distributions and thermal errors. Moreover, thermal errors were compensated at 24.1 °C and 22.6 °C with a feed rate of 18 m/min, and machining accuracy was increased by 73% and 62%, respectively.

Temperature Field Analysis and Thermal Error Testing for CNC Machine Tool's Headstock

The dynamic and thermal characteristics of spindle assembly will affect the final machining performance of a machine tool seriously. It is of great significance to study the dynamic and thermal characteristics of the spindle assembly for improving the level of machine tool's design and manufacturing. The paper takes a high precision computer numerical control lathe as the research object. First the thermal characteristics were obtained by using finite element method. Then the laser triangle measuring instrument and the infrared thermal imager were used to measure the temperature field and thermal deformation of the spindle assembly. Finally in order to get the thermal equilibrium time and the thermal deformation data of spindle system, the wavelet toolbox was used to deal with thermal testing data. The paper's work laid a foundation for the further research on the thermal characteristics analysis and thermal error's compensation of machine tools.

Thermal-structure characteristics coupling analysis and optimisation for horizontal CNC machining centre spindle

In this paper, the thermal-structural coupling field analysis model of spindle system is established, and the numerical simulation which accounts for the spindle component system’s structure, the actual working condition, the influence of heat source and lubrication system condition factors, etc. which are from a machine tool factory, such as ambient temperature, flow velocity of coolant, and the rotating speed of spindle motor, etc., is conducted. It is found that the maximum temperature up to about 38.8°C appears in the spindle where the double row cylinder roller bearing is installed, while the maximum comprehensive deformation of the spindle’s front-end reaches 0.93 × 10 –5 m. And the spindle system needs nearly 1 hour to reach thermal equilibrium state when the system uses the L-HM32 lubricant. However, temperature rise, heat deformation and the thermal equilibrium time are reduced by 11.1%, 22.6% and 12%, respectively, when the lubricant of the lubrication system is replaced by Shell-tellus22, and the maximum Von-Mises stress value is 125.6 MPa. The results are beneficial for providing a basis for the requirements of practical manufacture, especially the optimisation of structure, cooling system and compensation system design.