Dynamic Temperature Distribution Research Articles

Dynamic Temperature Distribution in Photo‐induced Alignment of Azobenzene Liquid Crystalline Polymer

AbstractA theoretical model has been established to describe the dynamic temperature distribution during the alignment of an azobenzene liquid crystalline polymer irradiated by a linearly polarized laser beam. The dynamic heat diffusion equations are used, and the relationship between heat source item and time is introduced, based on experimental results. With the model, the contours of the temperature distribution at different time have been worked out. It can be found from the theoretical model that there is a maximum temperature rise during the photo‐induced alignment, which is coincident with the analysis of experimental observations. The existence of a minimum laser power and an offset photo‐alignment temperature Toff required to carry on photo‐induce alignment are explained based on the theoretical model.Temperature distribution after two minutes.imageTemperature distribution after two minutes.

Computer simulation of a workpiece temperature field during the grinding process

The study focus about the status of the grinding temperature has been changed from static to transient. A model has been built of the grinding temperature field based on the finite element method (FEM). The dynamic temperature distribution of a workpiece during the whole grinding process can be displayed using Media Player. In this way the variational temperature distribution of the process can be known exactly. There is little difference between this simulation result and the previous analytical solution for dry grinding and accordingly it is credible to apply FEM to a wet grinding field. The FEM results possess higher precision, less calculation and wider scope than analytical results when applying and considering more influencing factors. Finally, the experimental data are compared with the simulated data to test the reliability of the latter. The results show that the method is suitable for obtaining temperature distribution using FEM.

Analysis of temperature and pressure fields in molten carbonate fuel cell stacks

AbstractA mathematical model based on fluid dynamics and heat‐transfer theories was applied to predict gas dynamic pressure and temperature distribution in a coflow molten carbonate fuel cell (MCFC) stack. The mass balance was simplified to obtain exact solutions with an assumption of uniform current density in the cell. The simulations were compared with data from a pilot‐scale MCFC stack. The effect of internal geometry of gas channels was simulated to accurately predict the gas‐pressure drop. A close prediction of pressure drop was possible from a partially blocked gas channel model that approximates the significant flow resistance. The effect of external boundary conditions on stack temperature profile was also analyzed. Temperatures were accurately predicted from a boundary heat conduction model with a reasonable assumption of wet seal temperatures. The 2‐D boundary conditions could be extended to 3‐D simulations to predict temperature distribution with the same accuracy. The model was applied to see the effect of scale‐up on the maximum temperature rise and average cell potential. The result verified a significant effect of cell size on the maximum stack temperature.

Freezing and Melting With Multiple Phase Fronts Along the Outside of a Tube

This paper addresses the modeling and analysis of thermal storage systems involving phase change with multiple phase fronts. The problem involves a fluid flowing inside a long tube surrounded by a phase-change material (PCM). The fluid temperature at the tube inlet cycles above and below the freezing temperature of the PCM, causing alternating liquid and solid layers to form and propagate from the tube outside surface. The objective of this paper is to predict the dynamic performance, temperature distribution, and phase front distribution along the tube. The problem is modeled as axisymmetric and two dimensional. Axial conduction is neglected and the problem is discretized into axial segments. Each of these axial sections is modeled as a transient, one-dimensional problem involving phase change with the possibility of multiple phase boundaries. The boundary element method (BEM) is used to obtain the transient solution in each axial section. Each axial segment communicates with downstream segments through the fluid flowing inside the tube. In order to ensure numerically stable results, a fully implicit discretization is used in both the axial and time variables. Results are presented for the time and axial evolution of the phase fronts and temperatures in response to a fluid inlet temperature that periodically alternates between values above and below the freezing temperature. This BEM is tested against the thermal network method (TNM) and the negligible sensible heat approximation (NSH) by comparing the outlet temperature and the latent state of charge. Results are found to be consistent and accurate.

Measurement and prediction of dynamic temperatures in unsymmetrically cooled glass windows

Semitransparent materials such as glass have many applications in high-temperature environments such as supersonic aircraft canopies and spacecraft windows. At elevated temperatures, the energy transfer within semitransparent materials is dominated by radiation, making both the prediction and measurement of internal temperatures substantially more difficult than for opaque substances. Experimental measurement of the dynamic internal temperature distribution in soda-lime glass plates cooling from an initial temperature of about 550 C was carried out. The boundary conditions on the plates were established using the laboratory ambient for the front surface and employing a radiant heater at the rear surface. The surface and internal plate temperatures were measured using thermocouples fused in the glass. The temperature data are compared to predictions obtained from the solution of the transient energy equation where the internal radiative transfer has been accounted for using rigorous radiative transfer theory. The predicted and measured temperatures, the experimental method, the process used to fuse the thermocouples in the test plates, and the formulation of the energy equation for semitransparent materials are discussed. 18 refs.

Measurement and Prediction of the Dynamic Temperature Distributions in Soda‐Lime Glass Plates

Experimental measurement of the dynamic internal temperature distribution in soda‐lime glass plates using thermocouples fused in the glass has been carried out. Experimentally measured temperatures are compared to predictions obtained from the solution of the transient energy equation where the internal radiative transfer has been accounted for using rigorous radiative transfer theory. A discussion of the experimental method, the process used to fuse the thermocouples in the test plates and the rigorous formulation of the energy equation, for semitransparent materials is given. Predicted and measured instantaneous surface temperatures are compared and very good agreement is obtained. It is also concluded that the empriical equation for the phonon conductivity used in the analysis underpredicts the conductivity. A 20% increase in phonon conductivity is shown to significantly improve the agreement between measured and predicted centerline to surface temperature differences.

The dynamic temperature distribution in stripe geometry lasers

The two dimensional analysis of the stripe geometry semiconductor laser dynamic temperature distributions is given using a numerical solution technique.

Thermoanalytical investigation of composite lamination

AbstractGlass cloth reinforced epoxy resins are commonly used to make composites. The performance of these laminates depends strongly on optimizing cure kinetics and rheology for a given chemical composition and temperature/pressure profile. Aborted flow tests (weight percent resin squeezed out during a given temperature/pressure cycle) is frequently used to emulate lamination processes and/or to evaluate new formulations. The cure reaction was monitored using differential scanning calorimetry, rheology, and dielectrometry. These techniques show that the cure kinetics are controlled by the temperature profile. The viscosity and the macroscopic flow, however, are affected by the temperature profile, i.e. decrease in viscosity with rising temperature, as well as the cross‐linking kinetics which lead to an increase in viscosity. Gravimetric and thickness measurement indicated a non‐uniform resin distribution across the laminate, with a lower resin content found at the edges. Macroscopic flow is controlled by three dimensional heat transfer, which leads to a dynamic temperature distribution and, concomitantly, to a cure/rheology profile. This was demonstrated graphically by marking layers of reinforced resin and monitoring the movement of the markers.

The dynamic wall and gas temperature distributions in a graphite furnace atomiser

A model is presented for calculation of the dynamic wall and gas temperature distribution of a heated graphite furnace used for analytical atomic absorption measurements. Numerical iterative procedures were used to obtain data for a furnace of specific dimensions (28 × 6 mm), as well as “shaped” variants of this bask design. Instrumental parameters such as the voltage applied and the resistivity of the graphite were measured accurately and the values used in the model so that the real situation on a commercial instrument was resembled well Results of absorbance-time measurements enabled the temperature distribution to be known at all stages of the evolution of the analyte absorbance pulse. It is shown that for shaped furnaces, the gas temperature at the centre of the furnace can be lower than that at some intermediate positions, as well as higher than the furnace wall temperature at the centre. Results for the gas temperature at tube centre agree reasonably well with that of another model put forward recently. Due to problems associated with experimental measurement of gas temperatures, such values do not compare well with the theoretically calculated ones.

Comparison of thermal time lag in the response of thermocouple neutron detectors in the normal and intrinsic configuration

The thermal time lag in the response of a normal thermocouple neutron detector, which employs a thermocouple junction surrounded by neutron sensitive material, is compared with that of an intrinsic fission-couple, in which the neutron sensitive material forms an integral part of the thermocouple circuit. After working out the dynamic temperature distribution in their thermoelements, it is shown how the time response of a fission-couple becomes about a million times faster than that of a normal thermocouple neutron detector.