Measurement Of Effective Thermal Conductivity Research Articles

Effective Thermal Conductivity Measurement and Analytical Heat Transfer Model on White Bread

The effective thermal conductivity of bread is an important physical property indispensable for an analysis of engineering phenomena in the process of baking and cooling of bread products. ln this study, bread was prepared with moisture contents in the range of 6 to 48%, and thermal conductivity was measured. The unsteady state hot wire method was mainly used for measuring thermal conductivity in the temperature range of 278 to 353K. The results of the study can be expressed by the empirical forrmula, using the volumetric fraction of water and temperature as parameters, ln addition, the bread was regarded as three-phase system consisting of solid, liquid and gas. The practical and simple thermal conductivity model was contrived by introducing the heat transition theory of Krischer et al. based on vapor enthalpy.

Thermal transport in chemically doped polyaniline materials

Simultaneous measurements of effective thermal conductivity ( λ e) and effective thermal diffusivity ( χ e) of four samples S1 (polyaniline mixed with 100% Ni), S2 (polyaniline mixed with 90% Ni and 10% Al), S3 (polyaniline mixed with 80% Ni and 20% Al) and S4 (polyaniline mixed with 70% Ni and 30% Al) of polyaniline mix with metal Ni and Al in different percentage have been made using transient plane source technique. In the temperature range from room temperature to 170 °C. Both λ e and χ e increase with increase in temperature. Addition of aluminium concentration at the cost of nickel in the composite increases the value of λ e and χ e over the entire range of temperature under investigation. It has been found that the values of λ e and χ e are maximum when 70% of Ni and 30% of Al are mixed in polyaniline matrix. This behaviour is also predicted by an empirical relation, which is obtained from polynomial fit of the experimental data and is explained on the basis of bond formation between metal (Ni and Al) and nitrogen of polyaniline matrix.

Experimental tests on Li-ceramic breeders for the helium cooled pebble bed (HCPB) blanket design

The Helium Cooled Pebble Bed (HCPB) Test Blanket Module (TBM) to be tested in ITER (International Thermonuclear Experimental Reactor) Reactor foresees the utilization of Lithiate ceramics as Tritium breeder in form of pebble beds. Since 1998, ENEA has launched many experimental activities for the evaluation of the breeder thermomechanics and the interaction between the pebble beds and the prismatic steel containment walls. Main objectives of these activities are the measurement of the pebble bed effective thermal conductivity, the wall heat transfer coefficient, the pressure loads and deformations on the lateral walls and their dependency from the mechanical constraints. The paper presents the progress of the second test campaign performed at ENEA Brasimone HE-FUS3 facility on Li 4SiO 4 pebbles.

Measurement and Prediction of Effective Thermal Conductivity for Woven Fabric Composites

The current paper deals with the measurement and prediction of thermal conductivities for plain weave fabric composites. An experimental apparatus was setup to measure the temperature gradients from which the thermal conductivities were obtained. The thermal conductivities were also calculated using finite element analyses for plain weave unit cell models and then compared with experimental results. In addition, the effect of a phase shift and the fiber volume fraction in the tow on the thermal conductivities was addressed.

Heat Transfer in High-Temperature Fibrous Insulation

The combined radiation/conduction heat transfer in high-porosity, high-temperature fibrous insulations was investigated experimentally and numerically. The effective thermal conductivity of fibrous insulation samples was measured over the temperature range of 300-1300 K and environmental pressure range of 1.33 x 10(exp -5)-101.32 kPa. The fibrous insulation samples tested had nominal densities of 24, 48, and 72 kilograms per cubic meter and thicknesses of 13.3, 26.6 and 39.9 millimeters. Seven samples were tested such that the applied heat flux vector was aligned with local gravity vector to eliminate natural convection as a mode of heat transfer. Two samples were tested with reverse orientation to investigate natural convection effects. It was determined that for the fibrous insulation densities and thicknesses investigated no heat transfer takes place through natural convection. A finite volume numerical model was developed to solve the governing combined radiation and conduction heat transfer equations. Various methods of modeling the gas/solid conduction interaction in fibrous insulations were investigated. The radiation heat transfer was modeled using the modified two-flux approximation assuming anisotropic scattering and gray medium. A genetic-algorithm based parameter estimation technique was utilized with this model to determine the relevant radiative properties of the fibrous insulation over the temperature range of 300-1300 K. The parameter estimation was performed by least square minimization of the difference between measured and predicted values of effective thermal conductivity at a density of 24 kilograms per cubic meters and at nominal pressures of 1.33 x 10(exp -4) and 99.98 kPa. The numerical model was validated by comparison with steady-state effective thermal conductivity measurements at other densities and pressures. The numerical model was also validated by comparison with a transient thermal test simulating reentry aerodynamic heating conditions.

Measurements of effective thermal conductivity of ceramic breeder pebble beds

The use of lithium ceramic pebble beds in the design of blankets for fusion reactors makes the mechanical and thermal properties of ceramic pebble beds key issues to be investigated. In the last years measurements of the effective thermal conductivity of lithium oxide, lithium orthosilicate, lithium metatitanate and lithium metazirconate pebble beds were performed at the Research Centre of Karlsruhe (Germany), at University of California (USA) and at JAERI (Japan). The measurements performed at FZK and at UCLA were based on steady-state methods, at JAERI a transient method (Hot wire method) was used instead. In the present paper, the results from these experiments are compared and discussed.

Effective Thermal Conductivity Measurement of the Candidate Ceramic Breeder Pebble Beds by the Hot Wire Method

The effective thermal conductivity of the pebble beds is one the most important design parameters for pebble bed solid breeder blanket. In the framework of IEA Implementing Agreement on Solid Breeder Subtask Group, measurement of pebble bed thermal conductivity by the hot wire method were defined as one of tasks to provide comparative information on the effective thermal conductivity of candidate ceramic pebble beds for DEMO blanket designs and ITER breeding blanket design. The authors previously reported the preliminary result of the pebble bed thermal conductivity for Li2O, Be and Al2O3. This paper presents the result of Li2TiO3, Li2ZrO3 (1 mm diameter) from CEA, and Li4SiO4 (0.25 - 0.63 mm diameter) from FZK.Observation was compared to the correlations, SZB model and HM model. Contact area fraction was obtained by correlation fitting, of which the value is 4.9×10−3 for Li2TiO3, Li2ZrO3 (the same value as Li2O) and 1×10−6 for and Li4SiO4.

Thermal Diffusivity and Adsorption Kinetics of Silica-Gel/Water

There have been performed experimental measurements of effective thermal conductivity of silica-gel for a stagnant cylindrical fixed bed under transient and steady state conditions in the presence of dry air at different pressures and for different amounts of adsorbed water. The Bauer-Schlunder and Kunii-Smith models have been used to identify the thermal solid conductivity of silica gel pellets from measurements of the conductivity in an adsorbent bed. Sorption rates of water vapor in silica gel were measured using a single-step thermal method by monitoring the sample surface temperature by infrared detection. In order to obtain the mass diffusivity it is necessary to match the numerical solution of the mathematical model to the experimental data.

An estimate of ground heat flux for a seasonal snow cover

An estimation of ground heat flux for two locations has been done using temperature gradient method. Effective media approach has been adopted for predicting the effective thermal conductivity of ground. For comparison, in situ measurement of effective thermal conductivity of ground has also been done by thermal probe method. The measured values of thermal conductivity are in agreement with the calculated values. The estimated values of ground heat flux have been used to evaluate the melt rate at ground-snow interface.

Effective Thermal Conductivity Measurements of the Binary Pebble Beds by Hot Wire Method for the Breeding Blanket

This work presents the results of measurements of the effective thermal conductivity of Li2O and Be pebble beds using a hot wire method1. Also, preliminary results for a binary bed using Al2O3 pebbles are presented. The measured value for an Al2O3 single packing bed showed good agreement with Schulunder's correlation2 and Hall-Martin's correlation3 with a contact area fraction of 5 × 10−5. The value of the contact area fraction in this study showed consistency with that reported by Dalle Donne et al.4. Results for the binary bed of Al2O3 (0.3 mm and 3 mm) pebbles showed good agreement with the same correlation using the same value of contact area fraction. The measured value of the effective thermal conductivity for an Li2O bed using 1 mm pebbles agreed with the correlation using a value of 4.9 × 10−3 for the contact area fraction. The measured values of the effective thermal conductivity for 0.6 mm and 1mm Be pebble beds showed consistency with the correlation using 1 × 10−4 for the contact area fraction.

Measurement of effective thermal conductivity of wheat as a function of moisture content

The effective thermal conductivity of two varieties of Triticum durum wheat and a wheat product, bulgur, is determined at different moisture contents and at ambient temperature by the transient line heat source method. The moisture contents of the samples ranged from 9.17 to 38.65 percent wet basis and the bulk densities ranged from 675 to 827 kg/m 3. Under those conditions, the measured effective thermal conductivities ranged from 0.159 to 0.201 W/m.K. The effective thermal conductivity is found to be linearly increasing with moisture content. The results are also in good agreement with literature values.

Measurements of Effective Thermal Conductivity of CaCl2 Reactor Beds Used for Driving Chemical Heat Pumps.

An experimental method has been developed to measure the effective thermal conductivity of a bed consisting of CaCl 2 reactive particles accompanying the variations of thermophysical properties with the progress of gas-solid reactions. Using this method, measurements have been performed for the beds in CaCl 2 /CH 3 NH 2 , CaCl 2 /CH 3 OH and CaCl 2 /NH 3 reaction systems. The effective thermal conductivity of the reactive bed, which was reduced to less than one half of that of the initial anhydrous CaCl 2 bed, increased with the absorption and decreased with the desorption of the reactive gas. Corresponding to the variations of effective thermal conductivity, the void fraction varied during the reaction cycles. The relation between the effective thermal conductivity and the void fraction inside the particle indicates that the main cause of the reduction in the effective thermal conductivity is attributed to a decrease in the thermal conductivity of the solid product.

Study of thermophysical and mechanical properties of particulate composite polyethylene-CaCO3

Starting from the formulae for effective parameters of the particulate composite derived within the average field approximation, the formula for the percolation threshold is derived. The maximum value of the percolation threshold is 1/3 in the case of the isotropic granules of globular shape. Further, the experimental data obtained from the measurement of effective thermal conductivity and elastic shear modulus of the particulate composite polyethylene-CaCO 3 cannot be interpreted in the framework of the average field approximation. For this reason it was necessary to modify the formulae for effective parameters, and they were able to describe the experiment.

Effective thermal conductivity measurements by the transient hot-wire method: investigation of the interpretation procedure of experimental data

The evaluation and control of self-ignition hazards in stored granular materials require accurate values of their thermal properties, and the transient hot-wire method can be used for the determination of the thermal conductivity. Starting from the usual model of Carslaw and Jaeger, improvements in the interpretation model for the experimental data produced in the conventional hot-wire device are presented, taking into account the contact resistance between the wire and the powder, as well as the finite dimensions of the cylindrical medium, and enabling the time domain for the interpretation of experimental data to be estimated. In addition, the deviation from the linear plot of temperature against logarithmic time was shown to be due to the temperature dependence of the heat power. The interpretation method was successfully applied to the determination of the thermal conductivity of four powders depending on the temperature; in particular, the results obtained with glass particle packed bed were compared with published data.

Effective thermal conductivity of granular porous materials

In this study, various conduction models for two-phase materials are considered and the range of applicability of these models is discussed. Experimental work is carried out on construction sand of various grain size and different porosity in air at atmospheric pressure, and the results are compared with theoretical models. A modified hot-wire method is used in the measurement of effective thermal conductivities.

製造および保存過程における食パンの有効熱伝導度の測定

製造および保存過程における食パンの有効熱伝導度の測定

非定常法による小豆の有効熱伝導率の測定

非定常法による小豆の有効熱伝導率の測定

Mathematical Analysis of the Effective Thermal Conductivity of Food Materials in the Frozen State

The effective thermal conductivity of binary aqueous solutions or gel systems of glucose, sucrose, potato starch, gelatin, and egg albumin in the frozen state were theoretically investigated. Structural models were used for evaluating heat conduction combined with the ice fraction measured for the same sample as that used in the measurement of effective thermal conductivity. The temperature-dependency of the ice fraction was determined by the phase diagram or DSC method. The structural models employed, with no fitting parameters involved, were the series, parallel, and Maxwell-Eucken models with ice as the dispersed phase (ME1 model) and as the continuous phase (ME2 model). The intrinsic thermal condictivity for each component was determined from measurements taken on unfrozen sample. Although all of the four models were applicable to the unfrozen sample with no substantial difference in prediction, the ME1 model, which was composed of the dispersed ice phase and continuous thick solution phase, was the o...

Measurement of the effective thermal conductivity of a metal hydride bed with chemical reaction

Measurement of the effective thermal conductivity of a metal hydride bed with chemical reaction

Measurement of Effective Thermal Conductivity of Coke.

Effective thermal conductivity of metallurgical coke was measured in the temperature range from 100 to 1 400°C by using the laser flash method. Effective thermal conductivity k of coke increased with a rise of temperature, and decreased with an increase of porosity of coke. The effect of radiation in the pore of coke on the value of effective thermal conductivity of coke was very small. The following empirical equation was obtained for the determination of effective thermal conductivity k (W/m K) as a function of temperature T(K) and porosity e(–) of coke.k={0.973+6.34×10–3(T–273)}(1–e2/3)