Time Variation Of Temperature Research Articles

Boundary conditions in theory of photothermal processes in solids

In this work general boundary conditions are obtained for the linear nonstationary heat diffusion equation. It is shown that both surface heat conduction and surface heat accumulation must be taken into account for the validity of energy balance at the surface. The latter process is important at fast temperature variation in time.

繊維媒体を用いた蓄冷式熱交換器の低温性能評価

In this study, the cryogenic performance of a regenerator that utilizes fibrous media is estimated. The decrease in the specific heat of the matrix causes a loss of thermal efficiency in cryogenic regenerators. Water vapor condenses in regenerators as frost, which is one of the serious problems in cryogenic air separation plants. A single-blow experiment and numerical analysis considering the effect of temperature dependence on thermal properties as well as the effect of phase change of water vapor were performed. Good agreement of the temperature time variation in the regenerator was obtained for experimental and numerical results. The decrease in specific heat of the matrix causes a loss in efficiency, especially when the switching period is long. Furthermore, the evaporation and condensation of water vapor in a regenerator is simulated under the condition of continuous operation. It was calculated that frost deposition occurs where the temperature gradient is large, and the amount of frost increases linearly with operating time. The drying process is needed once a day for the present condition. The interval increases for lower inlet temperature and higher gas pressure.

On the study of deformation and failure of solids

The behavior of an elastoplastic material under loading (in particular, at the supercritical stage) is rather intricate. The material passes through different deformation stages from the development of different kinds of damage to gross failure. In this case, the complete description of changes in the physicomechanical properties of material is complicated by the fact that, due to rearrangement of the structure, the initially uniform stressed state (because of the development of significant plastic deformations) becomes nonuniform. Moreover, deformation is accompanied by the formation and development of defects in the form of pores and microcracks at the supercritical stage and the intensity of the processes changes. Hence, determination of the material properties at the different stages of deformation is complicated. The occurrence of limiting states (the loss of stability of one or another process) is accompanied by changes in the mechanisms of deformation, structural modifications (attainment of the critical values), development of discontinuities, and changes in the dynamics of the processes occurring in a material. It is of interest to investigate the development of deformation and damage accompanying deformation in an integrated approach uniting the method for constructing the true deformation curve and the methods for recording the variations of different physical parameters. A study of the development of elastoplastic deformations and damage will provide physically justified estimates for the mechanical properties of a material. In this paper, the deformation and failure of a strengthening elastoplastic material are studied by analyzing the true deformation curve and variation in temperature of a deformed sample. It is known that the transition to the plastic stage of deformation is accompanied by the appearance of irreversible plastic deformations and dissipation of energy into heat [1‐11]. The engineering of advanced measuring systems with quite high IR sensitivity makes it possible to analyze IR images in real time and to determine the time variation in temperature of the sample under investigation. We investigated plane samples that were made of the low-alloyed 18G2S steel and had operative parts of 65 〈 15 〈 2.4 mm dimensions. The mechanical characteristics determined from testing by the standard technique are as follows: yield point σ t = 406.5 MPa, breaking point σ v = 563 MPa, residual elongation δ k = 25.85%, and narrowing ψ k = 55%. The samples were subjected to uniaxial tension on an Instron-1195 testing machine with a rate of 8.3 〈 10 ‐5 m/s. The kinetics of development, localization of deformation, and variation in temperature of the samples were investigated by the IR radiation method. The technique simultaneously records a deformation curve and the pattern of IR radiation and variation in temperature of a sample right up to its failure. The kinetics of the IRfield development and variation in temperature of a sample were investigated with the aid of a Thermovision 550 (Agema) IR imager with an IR sensitivity of ∠ 0.1 K [10]. The sample temperature in the process of deformation was also measured by using copper‐constantan thermocouples and a Hewlett-Packard 3497A Data Acquisition/Control Unit with an accuracy of ∠ 0.05 K.

Predicting heat conduction during solidification of a food inside a freezer due to natural convection

A new mathematical model for numerical simulation of two dimensional food freezing due to natural convection is presented. Fluid mechanics and heat transfer by natural convection between air and a solid food in a freezer are predicted along with the heat conduction inside a plate shaped food. The mathematical model used includes continuity, linear momentum and energy partial differential equations for air and the non-linear heat diffusion equation for the solidification of the water content in the food. Unsteady two dimensional results of the velocity and temperatures distributions in the air around the food obtained by using the finite volume method are presented. Experimental data of temperature variation in time for a slab shaped food inside a freezer are used to assess the accuracy of the mathematical model and the solution procedure. It is found that the use of this model, that does not require heat transfer coefficients, allows to simulate two dimensional freezing experiments in a slab shaped food by natural convection with maximum and mean deviations of 5.2% and 1.2%, respectively.

Studies on a probable correlation between thermal conductivity, kinetics of devitrification and changes in fiber radius of an aluminosilicate ceramic vitreous fiber on heat treatment

Degradation in heat insulation properties of vitrified ceramic fiber blankets has commonly been observed during prolonged use in heat treatment furnaces The associated physico-chemical property changes during such a heat treatment process has been studied under laboratory conditions with systematic time–temperature variations. Alumino-silicate ceramic fiber blanket .samples were subjected to temperature variations from 1100 to 1350 °C and soaking time variations from 1 to 4 h. Additionally, scanning electron microscopic studies of the fibers were undertaken to study progressive shrinkage of the fibers with rise in time and temperature. Quantitative estimation of mullite formation from devitrified fiber was made through an X-ray diffraction (XRD) study. Association of these two concurrent phenomenon made kinetics of devitrification process study difficult and established mathematical kinetics relationship valid for cylindrical (fiber) samples namely (1− α) 0.5=(1− kt/ r) [H.S. Roy, J. Thermal Analysis 36 (1990) 743–764] (where, α, fraction reacted in time t, r, fiber radius and k, reaction rate constant, yielded wide variation in k values. A modification in fiber radius was thus made taking its n th relationship (where n is an empirical constant), such that the factor n took care of the concurrent phenomenon of mullitization associated shrinkage behavior. Plots were made between ln (1−(1−α) 0.5) vs. ln kt. The slope gave the value of n ln r. A value of n=1.7–1.8 was consistent for all the data points with fiber diameter varying between 1.0 and 3.5 μ. The modified equation for this type of reaction can thus be established as (1−(1− kt/ r 1.7–1.8). The radiant energy heat transfer at higher temperature which characterizes different varieties of ceramic blankets is disclosed in a relationship k T = a T b (where k=thermal conductivity, T=temperature and a, b are constants). Log–log plot of k T vs. T yields values of b=1.3–1.5 and the equation connecting quantity of heat transfer, Q, temperature, T, and fiber blanket thickness Z, can be correlated as Q ∝ ( a ( T1 b − T2 b )/ Z b . This indicates that the use of a common temperature ( T1+ T 2)/2 and an average k at that temperature leads to misleading results unless a correction in Z as Z b is brought into the equation. The value of Z modified as Z b finds favor on our observation of b=1.3–1.5≈ n=1.3–1.5 as mentioned earlier and appears to have given rise to a correlation between thermal conductivity and kinetic parameters involving kinetics of mullitization reaction, reaction rate constant and shrinkage in fiber radius with heat treatment.

Prediction of temperature evolution by FEM during multi-pass hot flatrolling of aluminium alloys

In rolling, deformation is applied by a series of passes, which arenecessarily separated by holding periods between passes. The formation of thetemperature profile therefore has a complex history. Accurate information onthe time variation of temperature is essential for predicting microstructuraldevelopment during hot working conditions and for the design of anacceptable rolling pass schedule. In the present paper, the finite-elementmethod is employed to compute temperature changes under both laboratoryand industrial breakdown rolling conditions. The calculated results are thencompared with temperature records extracted from the literature. Thedifference between laboratory and industrial rolling is discussed. By usinginverse analysis methods, appropriate heat transfer coefficients can beascertained.

Model for cooling and phase transformation behaviour of transformation induced plasticity steel on runout table in hot strip mill

A mathematical model has been developed considering non-symmetric cooling in the thickness direction of strip on a runout table (ROT). In order to solve a one-dimensional transient heat transfer equation including the heat evolved from phase transformation, a finite element method was applied, coupled with thermodynamic and kinetic analyses. The heat capacities of each phase and heat evolution owing to phase transformation were obtained from thermodynamic analysis of the Fe–C–Mn–Si system using Thermo-Calc. The phase transformation kinetics of a transformation induced plasticity (TRIP) steel were derived by using continuous cooling experiments and thermodynamic analysis. Heat transfer coefficients of strips on the ROT were, by applying an inverse method, determined from actual mill data under various cooling conditions. Using the developed model, temperature–time variations of plain carbon and TRIP steels on the ROT were calculated. The calculated results were in good agreement with the actual mill data. In addition, quantitative phase evolution during cooling could also be predicted by the model. From this analysis, the optimum cooling pattern on a ROT for the production of TRIP steel could be determined.

Electron-beam initiated polymerization of acrylate compositions, 2. Simulation of thermal effects in thin films

The thermal effects taking place during the electron beam-induced polymerization of acrylate type formulations were numerically simulated on the basis of the general heat equation applied to a one-dimensional system, The nature, the dimensions and the environment of the polymerizing medium were defined for representing the actual conditions of kinetic experiments performed with a 175 kV laboratory accelerator and FTIR monitoring. The modeled system was constituted of a polymerizable composition coated onto a NaCl plate, initially at 20°C in gaseous nitrogen at the same constant temperature, with or without a PET film covering the reactive layer, Polymerization profiles describing the progress of the reaction as a function of dose were modeled on a phenomenological basis from actual data obtained by discontinuous FTIR monitoring of typical epoxy acrylate or polyurethane acrylate compositions. The influence of the reactive layer thickness (10/100 μm), dose rate (10-110 kGy.s -1 ), maximum polymerization heat (200-400 J.g -1 ) on the temperature-time variations was examined for continuous irradiation. In spite of the relatively small thickness of the reactive layer, significant temperature rise is simulated when heat production is large and fast compared to energy dissipation at the reactive layer boundaries. The obtained data substantiate the fact that upon fractionated EB-treatment with small dose increments (down to 0.6 kGy per pass) at low dose rate (down to 10 kGy.s -1 ) the heat release can be considered weak and without noticeable influence on the conversion data processed for a detailed kinetic analysis. For example, a maximal temperature rise of 6°C was calculated for a fractionated irradiation of 2 kGy increments at 19 kGy.s -1 applied to a polymerizable formulation releasing a maximum enthalpy of 300 J.g -1 .

A model for high carbon steel phase transformation and cooling behavior on run-out table of hot strip mill

A model was developed considering non-symmetric cooling in the thickness direction of strip on a run-out table of hot strip mill. In order to solve the one-dimensional transient heat transfer equation, including the heat evolved from phase transformation, a finite element method coupled with thermodynamic and kinetic analyses were employed. The heal capacity of each phase and the heat evolution due to phase transformation were obtained by thermodynamic analysis of the Fe-C-Mn system using a sublattice model. The phase transformation kinetics of high carbon steels was derived using continuous cooling experimente and mermodynamic analysis. By applying an inverse method, the heat transfer coefficients of the strips on the run-out table were determined from actual mill data under various cooling conditions. Using the developed model, the temperature-time variations of high carbon steels on the run-out table were calculated. The results calculated were in good agreement with the actual mill data. In addition, the quantitative phase evolution during cooling on the run-out table could also be predicted by the model. From this analysis, it was possible to design an optimum cooling pattern on the run-out table ensuring a desirable microstructure of high carbon steel and a stable cooling operation.

Temperature changes during hot plane strain compression testing

Detailed understanding of the flow stress and microstructural development during plane strain compression testing requires accurate knowledge of the time variation of temperature. A finite difference model of the temperature variations has been developed and implemented in a computer program on a PC, which can rapidly produce results for multideformation schedules. An outline and validation of the model is presented here; the validation exercise compares temperature records taken during a variety of plane strain compression tests with those generated by the model.

CONVECTIVE DRYING OF BANANA, GUAVA AND POTATO PIECES : EFFECT OF CYCLICAL VARIATIONS OF AIR TEMPERATURE ON DRYING KINETICS AND COLOR CHANGE

ABSTRACT Pieces of banana, guava and potato were dried in a two-stage heat pump dryer capable of precise control of air humidity with predetermined cyclic variations of air temperature entering the drying chamber. The air temperature variations tested were : a cosine, a reversed cosine and three different square wave profiles with peak-to-valley variations from 20°C to 40°C. The cycle time was about 60 minutes with drying time of approximately 300 minutes. The drying samples were placed on trays in a thin layer. With appropriate choice of temperature-time variation, it is possible to reduce the overall color change while maintaining high drying rates.

DIRECT NUMERICAL SIMULATION OF LAYER MERGING IN A SALT-STRATIFIED SYSTEM

Time-dependent double-diffusive convection was studied numerically to clarify the mechanism of layer merging in a salt-stratified system. Using the Chebyshev collocation method, a typical example of stably stratified salt fluid subject to a lateral temperature difference in a rectangular enclosure (Ar = 1.25) is considered for realistic values of parameters (RaT = 2.7 X 107, Ni = 0.882, Pr = 7.15, and Sc = 685). Two cases that differ by the initial salt concentration profile, i.e., linear and steplike profiles, are examined. Although globally, in both cases, the layer merging process is characterized by the mass transfer across the interface separating two convection layers, the two instances are quite different with respect to the interface structure. For the linear profile, vertical motion due to salt fingers is dominant, whereas for the steplike profile horizontal motion due to strong shear flows prevails. In particular, in the latter case, unlike for the linear profile case, traveling plumes perpendicular to shear flows that lead to the time variations in temperature and concentration are periodically generated within the interface. Predictions obtained with the simulations are in good agreement with experimental data.

Two-dimensional quench simulation of composite CuNb/Nb 3Sn conductors

In order to clarify effect of utilizing a Nb rich CuNb reinforment on superconducting stability, r– z two-dimensional time-dependent numerical simulations on composite CuNb/Nb 3Sn wires are conducted. The time variations of temperature and current density distributions, minimum quench energy (MQE), and normal zone propagation velocity ( v p) of a Cu–17vol%Nb/Nb 3Sn wire, a Cu–63vol%Nb/Nb 3Sn wire, and a conventional Cu/Nb 3Sn wire are investigated. The increase of the volume fraction of an outermost Cu stabilizer provides high MQE but decreases the total current density. Although the v p is not significantly influenced by the Nb fraction, the Nb rich CuNb reinforcement sacrifices the MQE for its high tensile strength. It is important for magnet design to control the volume fraction of the Cu stabilizer and Nb fraction in the CuNb reinforcement to balance the desired current density, tensile strength, and superconducting stability.

Conjugate forced convection and heat conduction with freezing of water content in a plate shaped food

The finite volume method is used to describe unsteady forced convection and heat conduction in a meat plate during freezing. External fluid mechanics and internal solidification of water content in the meat are predicted from a mathematical model that includes continuity, Navier–Stokes and energy equations for air around the food and the heat diffusion equation inside the meat. Unsteady results are presented for both velocity vectors and temperature distributions in air, temperature variations in the food and for heat transfer coefficients. Experimental data for the temperature variation in time are used to assess the accuracy of the predicted values.

Modeling biogas production at landfill site

Abstract Biogas production is characteristic of municipal solid waste landfills. A knowledge of the trend of this production allows an exploitation of this energy source. The here presented model is more accurate than those that already exist as it takes the temperature variation in time and depth and the landfill settlement into account. The obtained model fits experimental data well.

Simultaneously estimating the initial and boundary conditions in a two-dimensional hollow cylinder

This study is intended to provide a different perspective for solving two-dimensional inverse heat conduction problems. At the beginning of the study, finite-difference methods are employed to discretize the problem domain and then a linear inverse model is constructed to identify the initial and boundary conditions. The present approach is to rearrange the matrix forms of differential governing equation and estimate coefficients of unknown condition. Then, the linear least-squares method is adopted to find the solution. The results show that if the measurement errors are considered, more measuring points are needed in order to increase the congruence of the estimated results to exact solutions. In this paper, temperature-time variations are measured at internal and outside points. A little effect of the measurement time interval on the estimates are shown with the method proposed.

A System Identification Approach for Modelling the Response of Heat Production of Broiler Chickens to Variations in Physical Environmental Variables

Abstract The objective of the research reported in this paper is to model the dynamic response of the heat production of broiler chickens to time variations in temperature and light-dark alterations. This biosystem is modelled using a state space black box model structure. It is demonstrated that the complex process of the dynamic response of heat production of broiler chickens to changes in air temperature and light-dark alterations can be simulated with a r2 between measured and simulted heat production ranging from 0.61 to 0.92. Such models can be used in a next step to develop a model based climate controller for poultry production houses.

Heat Transfer and Film Cooling Effectiveness in a Linear Airfoil Cascade

A warm (315°C) wind tunnel test facility equipped with a linear cascade of film cooled vane airfoils was used in the simultaneous determination of the local gas side heat transfer coefficients and the adiabatic film cooling effectiveness. The test rig can be operated in either a steady-state or a transient mode. The steady-state operation provides adiabatic film cooling effectiveness values while the transient mode generates data for the determination of the local heat transfer coefficients from the temperature–time variations and of the film effectiveness from the steady wall temperatures within the same aerothermal environment. The linear cascade consists of five airfoils. The 14 percent cascade inlet free-stream turbulence intensity is generated by a perforated plate, positioned upstream of the airfoil leading edge. For the first transient tests, five cylinders having roughly the same blockage as the initial 20 percent axial chord of the airfoils were used. The cylinder stagnation point heat transfer coefficients compare well with values calculated from correlations. Static pressure distributions measured over an instrumented airfoil agree with inviscid predictions. Heat transfer coefficients and adiabatic film cooling effectiveness results were obtained with a smooth airfoil having three separate film injection locations, two along the suction side, and the third one covering the leading edge showerhead region. Near the film injection locations, the heat transfer coefficients increase with the blowing film. At the termination of the film cooled airfoil tests, the film holes were plugged and heat transfer tests were conducted with non-film cooled airfoils. These results agree with boundary layer code predictions.

Modelling The Dynamic Response of Chicken's Heat Production for Control Purposes

Present climate controllers in animal production units do not take into account any physiological or behavioural responses measured on the animal. itself, although these bioresponses are most interesting for process information. An important step in the development of more optimal climate control Uers, could be to measure and feed back relevant responses of the animal to its varying environment and to apply modem control theory to this process. To achieve so the dynamic relations between the process variables are modelled as a basis for a more optimal model based climate controlThe objective of the research reported in this paper is to measure and model bioresponses of chickens to a varying physical environment as a basis for a more optimal climate control. More specific, laboratory experiments are carried out to measure the dynamic response of the heat production of broiler chickens to time variations in temperature and light-dark alterations. This biosystem is modelled using mathematical identification techniquesIt is demonstrated that the complex process of the response of heat production of broiler chickens to changes in air temperature and light-dark alterations can be predicted based on the developed dynamic models, with a relative prediction error ranging from 3.6% to 11.6% depending on the prediction horizon and the response variable considered. Such models can be used in a next step to develop a model based controller

通電した太陽電池アレイ上の雪滑落時における表面温度変化

When a photovoltaic (PV) array is installed at a roof, the snow on the array and the roof needs to be removed not only to reduce the snow load but also to effectively utilize the solar system. If dc current is flowed through each PV module from a power supply, the surface of it was surely heated, to assist snow sliding on the array. In the electrically heating system, snow sliding at the array needs to be detected to turn the system off and to generate the electric power by the solar system. In the preliminary tests for snow sliding, the instance of snow sliding on the PV array which consists of ten PV panels was identified by the VTR pictures taken every one minute during the tests. To find out the event of snow sliding over the PV panel, the time variation of temperature at the under surface of the PV panel measured at intervals of ten minutes was investigated in detail. It was revealed that the temperature at the under surface of the array always rose above 3°C at least whenever snow slid at the PV panel.