scholarly journals The effects of temperature and pressure on the thermal conductivities of solids. Part II.—The effect of low temperatures on the thermal conductivities of pure metals and alloys

1908 ◽  
Vol 80 (536) ◽  
pp. 143-145 ◽  
Keyword(s):  
Olive Oil ◽  
Thermal Contact ◽  
Metals And Alloys ◽  
Copper Tube ◽  
External Diameter ◽  
Electrical Conductivities ◽  
Effects Of Temperature ◽  
The Difference ◽  
A Current ◽  
Thermal Conductivities

The object of the work described in the present paper was to extend the measurements of Thermal Conductivities of Metals and Alloys made by Lorenz, Jäger and Diesselhorst, and others at temperatures between 0°C. and 100°C. down to the temperature of liquid air, and thus provide a means of comparing the Thermal and Electrical Conductivities of these substances over a much wider range of temperature than has hitherto been possible. The method adopted was a modification of that used originally by Wiedemann and Franz. A rod of the metal, 7 or 8 cm. long, 0∙6 cm. in diameter, was placed in the axis of a vertical copper tube of 2∙7 cm. internal 3∙3 cm. external diameter, 9∙5 cm. long, closed at the top. The lower end of the rod fitted into a copper disc, which in its turn fitted into the lower end of the copper tube. The joints were accurately made and were smeared with olive oil to exclude air and improve the thermal contact. The heat which flowed along the rod was supplied electrically by means of a current through a fine platinoid wire wound on a short thin brass sleeve, which was slipped on to the upper end of the rod. The difference of temperatures at two points of the rod, between the heating coil and the point where the rod entered the disc forming the lower end of the tube, was measured by means of two platinum thermometers, the wires of which were wound on two short thin brass sleeves, capable of sliding along the rod. The three sleeves fitted the rod closely, and thermal contact was improved by smearing rod and sleeves with a little olive oil.

scholarly journals XI. Bakerian lecture.―The effect of temperature and pressure on the thermal conductivities of solids.—Part II. The effects of low temperatures on the thermal and electrical conductivities of certain approximately pure metals and alloys

1908 ◽  
Vol 208 (427-440) ◽  
pp. 381-443 ◽  
Keyword(s):  
Low Temperatures ◽  
Metals And Alloys ◽  
Effect Of Temperature ◽  
The Third ◽  
Electrical Conductivities ◽  
Pure Metals ◽  
Temperature And Pressure ◽  
Thermal Part ◽  
Thermal Conductivities

During the last fifty years a considerable amount of attention has been bestowed on the question of the variations of the thermal and electrical conductivities of metals with the temperature, hut the results obtained by different observers, especially of thermal conductivities, differed so widely from each other that the answer to the thermal part of the question long remained doubtful. In recent years, however, there has been an accumulation of evidence in favour of a slight decrease of thermal con­ductivity with increase of temperature from 0°C. to 100°C. in the case of most of the metals. The experiments of Lorenz, and more especially the careful work of Jager and Diesselhorst have contributed greatly to this result. In both these cases the experiments were limited to the range of temperature between 0°C. and 100°C., and it seemed advisable, in view of the importance of both questions in the electronic theories of conduction of heat and electricity in metals, to extend the range over which the theories could be tested, particularly in the direction of low temperatures, where the experiments of Dewar and Fleming had already furnished information as to the electrical conductivities. The present paper contains an account of the measurements of the thermal and electrical conductivities carried out for this purpose, and the results obtained. The first section deals with measurements of the thermal, the second with measurements of the electrical, conductivities of certain metals and alloys, and the third section compares the results with the electronic theories.

scholarly journals Validation of a Method Based on Triglycerides for the Detection of Low Percentages of Hazelnut Oil in Olive Oil by Column Liquid Chromatography

2007 ◽  
Vol 90 (5) ◽  
pp. 1346-1353 ◽  
Author(s):  
Diego L García-González ◽  
María Viera-Macías ◽  
Ramón Aparicio-Ruiz ◽  
Maria T Morales ◽  
Ramón Aparicio
Keyword(s):  
Liquid Chromatography ◽  
Olive Oil ◽  
Carbon Number ◽  
Hazelnut Oil ◽  
Equivalent Carbon Number ◽  
Experimental Conditions ◽  
Mathematical Algorithm ◽  
Relative Standard ◽  
Triglyceride Content ◽  
The Difference

Abstract The difference between theoretical and empirical triglyceride content is a powerful tool to detect the presence of any vegetable oil in olive oil. The current drawback of the method is the separation between equivalent carbon number ECN42 compounds, which affects the reliability of the method and, hence, its cutoff limit. The determination of the triglyceride profile by liquid chromatography using propionitrile as the mobile phase has recently been proposed to improve their quantification, together with a mathematical algorithm whose binary response determines the presence or absence of hazelnut oil. Twenty-one laboratories from 9 countries participated in an interlaboratory study to evaluate the performance characteristics of the whole analytical method. Participants analyzed 12 samples in duplicate, split into 3 intercomparison studies. Statistically significant differences due to the experimental conditions were found in some laboratories, which were detected as outliers by use of Cochran's and Grubbs' tests. The relative standard deviations (RSD) for repeatability and reproducibility were determined following the AOAC Guidelines for Collaborative Studies. The analytical properties of the method were determined by means of the sensitivity (0.86), selectivity (0.94), and reliability (72) for a cutoff limit of 8 (probability 94).

Through-Plane Thermal Conductivity of PEMFC Porous Transport Layers

2010 ◽  
Vol 8 (2) ◽  
Author(s):  
Odne S. Burheim ◽  
Jon G. Pharoah ◽  
Hannah Lampert ◽  
Preben J. S. Vie ◽  
Signe Kjelstrup
Keyword(s):  
Thermal Conductivity ◽  
Contact Resistance ◽  
Thermal Contact Resistance ◽  
Thermal Contact ◽  
Residual Water ◽  
Order Of Magnitude ◽  
Thermal Conductivities

We report the through-plane thermal conductivities of the several widely used carbon porous transport layers (PTLs) and their thermal contact resistance to an aluminum polarization plate. We report these values both for wet and dry samples and at different compaction pressures. We show that depending on the type of PTL and the existence of residual water, the thermal conductivity of the materials varies from 0.15 W K−1 m−1 to 1.6 W K−1 m−1, one order of magnitude. This behavior is the same for the contact resistance varying from 0.8 m2 K W−1 to 11×10−4 m2 K W−1. For dry PTLs, the thermal conductivity decreases with increasing polytetrafluorethylene (PTFE) content and increases with residual water. These effects are explained by the behavior of air, water, and PTFE in between the PTL fibers. It is also found that Toray papers of differing thickness exhibit different thermal conductivities.

Production of quicklime from Ashaka limestone through calcination process

2021 ◽  
Vol 1 (2) ◽  
pp. 041-048
Author(s):  
Benson Chinweuba Udeh
Keyword(s):  
Particle Size ◽  
Critical Value ◽  
Operating Conditions ◽  
Quadratic Model ◽  
Particle Sizes ◽  
Calcination Process ◽  
Process Effects ◽  
Effects Of Temperature ◽  
The Difference ◽  
The Relationship

This study is on the production of quicklime from Ashaka limestone through calcination process. Effects of temperature, particle size and time on quicklime yield were determined. The experiment was carried out at temperatures of 800, 900, 1000, 1100 and 1200 0C, particle sizes of 80mm, 90mm, 100mm, 300mm and 425mm and times of 0.5hr, 1hr, 2hrs, 3hrs and 4hrs. Analyses of the results showed that quicklime was successfully produced from Ashaka limestone through the calcination process. Quadratic model adequately described the relationship between quicklime yield and calcination factors of temperature, particle size and time. Recorded model F-value of 134.35 implies that the model is significant. The predicted R² of 0.9597 is in reasonable agreement with the adjusted R² of 0.9844; the difference is less than the critical value of 0.2. Optimum yield of 73.48% was obtained at optima operating conditions; temperature of 1000 0C, particle size of 90 µm and time of 3 hrs.

scholarly journals Investigation of changes in the characteristics of LED matrices of the on-board luminaire during tests in the electrocycling mode.

2021 ◽  
Author(s):  
I.V. Frolov ◽  
◽  
V.A. Sergeev ◽  
A.M. Hodakov ◽  
S.A. Zaytsev ◽  
...  
Keyword(s):  
Leakage Current ◽  
Direct Current ◽  
Coefficient Of Variation ◽  
Convection Heat Transfer ◽  
Voltage Range ◽  
The Matrix ◽  
Operating Current ◽  
In Series ◽  
The Difference ◽  
A Current

The paper presents the results of studies of changes in the characteristics of LED COB matrices of the GW P9LR31.EM - DURIS S 8 type as part of a LED luminaire when tested under the direct current in a continuous mode and in an electrocycling mode. The arrays consist of eight InGaN/GaN LED dies connected in series, coated with a phosphor. Calculation in the Comsol Multiphtsics environment of the temperature field of the luminaire at the rated operating current and free convection heat transfer showed that the maximum overheating of the matrices does not exceed 46 K, and the difference in their temperatures is 2 K. At the same time, the experimental values of the thermal resistances of the matrices of a real lamp vary from 42 to 58 K/W. Before testing, the I-V characteristics of the matrices differ markedly in the level of leakage current in the voltage range from 14 V to 19 V, and the LEDs in the luminaire matrices have a significant spread in the brightness of emission in the microcurrent mode. The degree of this scatter within each matrix was estimated by measuring the luminescence brightness of each die of the matrix and calculating the coefficient of variation γ. It was found that the coefficient of variation of the emission brightness of the COB matrix dies measured at a current of 100 nA strongly correlates with the leakage current. When testing a luminaire under the direct current, the most significant changes in the electrophysical and optical characteristics of COB matrices are observed in the range of microcurrents: the distribution of the emission brightness of the matrix dies at a current of 100 nA becomes more uniform. The greatest changes in matrix characteristics were observed after the first 700 hours of testing, that is, at the running-in stage. At the same time, no correlation was found between the degree of change in the characteristics of the matrices during tests and their thermal resistances.

scholarly journals A Comparative Study between the Effects of Magnetic and Nonmagnetic Dopants on the Properties of ZnO Varistors

2010 ◽  
Vol 2010 ◽  
pp. 1-9 ◽  
Author(s):  
A. Sedky ◽  
E. El-Suheel
Keyword(s):  
Comparative Study ◽  
Nonlinear Coefficient ◽  
Xrd Analysis ◽  
Breakdown Field ◽  
Doping Content ◽  
Leakage Currents ◽  
Electrical Conductivities ◽  
Zno Varistors ◽  
The Difference ◽  
Zno Ceramics

A comparative study between effects of Mn and Al on the properties of ZnO varistor sintered at 1200 is investigated by XRD, SEM hardness, and I-V measurements. Although both Mn and Al do not influence the well-known peaks related to wurtzite structure of ZnO ceramics, some other unknown peaks could be formed at higher doping content (). Also, the shape and size of grains are clearly different for both dopants. Average crystalline diameters, deduced from XRD analysis, are between 42 nm and 62 nm, which are 50 times lower than those obtained from SEM micrographs, while the oxygen vacancies deduced from EDAX analysis, are gradually decreased by doping content for both dopants. Interestingly, the values of breakdown field, nonlinear coefficient and barrier height are found to be higher in Mn samples as compared to Al samples, while the opposite is reported for leakage currents, hardness, and electrical conductivities. The values of are changed from 2.67 V/cm to 41.67 V/cm for Al, and from 1928 V/cm to 6571 V/cm for Mn. The conductivity of Al samples is higher than that of ZnO, and it is nearly (103–105) times the conductivity of Mn samples. These results are discussed in terms of the difference of magnetic moment and valence state between these two additives.

scholarly journals Substitution Versus Full-Heusler Segregation in TiCoSb

Metals ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 935 ◽  
Author(s):  
Maryana Asaad ◽  
Jim Buckman ◽  
Jan-Willem Bos
Keyword(s):  
Powder Metallurgy ◽  
Power Factor ◽  
Thermoelectric Materials ◽  
Room Temperature ◽  
The Difference ◽  
P Type ◽  
Full Heusler ◽  
Thermal Conductivities

Half-Heuslers (HHs) are promising thermoelectric materials with great compositional flexibility. Here, we extend work on the p-type doping of TiCoSb using abundant elements. Ti0.7V0.3Co0.85Fe0.15Sb0.7Sn0.3 samples with nominal 17.85 p-type electron count were investigated. Samples prepared using powder metallurgy have negative Seebeck values, S ≤ −120 µV K−1, while arc-melted compositions are compensated semiconductors with S = −45 to +30 µV K−1. The difference in thermoelectric response is caused by variations in the degree of segregation of V(Co0.6Fe0.4)2Sn full-Heusler and Sn phases, which selectively absorb V, Fe, and Sn. The segregated microstructure leads to reduced lattice thermal conductivities, κlat = 4.5−7 W m−1 K−1 near room temperature. The largest power factor, S2/ρ = 0.4 mW m−1 K−2 and ZT = 0.06, is observed for the n-type samples at 800 K. This works extends knowledge regarding suitable p-type dopants for TiCoSb.

scholarly journals Identity or Prestige: The Chameleon Effect on EFL Pronunciation

2018 ◽  
Vol 8 (2) ◽  
pp. 82
Author(s):  
Hanan Taqi ◽  
Nada Algharabali ◽  
Dalal Almubayei
Keyword(s):  
Kuwait University ◽  
Actual Performance ◽  
Male And Female ◽  
Short Questionnaire ◽  
International Language ◽  
Chameleon Effect ◽  
Language Knowledge ◽  
The Difference ◽  
A Current

Although there is a current tendency to deal with English as an international language, EFL pronunciation seems to be motivated by conceptions on identity and prestige. In this respect, the following study investigates the effect of identity and/or prestige on EFL speakers' English speech (or usage) in two different settings. Male and female participants from Kuwait University (63 in total), were given debate topics to engage in. Both their meetings and actual debates were recorded. The participants also filled a short questionnaire. The recordings were analyzed using Praat, while the questionnaire results were obtained using SPSS. The results show that the EFL speakers use different accents and various realizations of English consonants as a reflection of what is known as the Chameleon Effect. This study aims at helping teachers understand the difference between the speakers’ language knowledge and their actual performance.

scholarly journals The thermal conductivities of certain approximately pure metals and alloys at high temperatures

1931 ◽  
Vol 134 (823) ◽  
pp. 57-76 ◽  
Keyword(s):  
Heat Flow ◽  
High Temperatures ◽  
Heat Losses ◽  
Metals And Alloys ◽  
Maximum Temperature ◽  
Internal Heating ◽  
Heating Coil ◽  
Pure Metals ◽  
Guard Tube ◽  
Thermal Conductivities

Measurements have been made by several observers on the thermal conductivities of metals and alloys up to high temperatures. Heat losses to the surroundings become large at high temperatures, hence the guard tube method, which to a great extent eliminates these losses, has been popular for work at these temperatures. This method was described and used by Berget in 1888, and later by Wilkes. These observers measured the rate of heat flow by a calorimetric method, which is not suitable for work at high temperatures. Honda and Simidu, using an internal heating coil, determined the heat flow from the energy input and were able to obtain results for nickel and steel to over 800°C. More recently, Schofield, using the guard tube method with an internal heating coil, has obtained results up to a maximum temperature of 700°C. with five metals. The present work was undertaken with a view to continuing the work of Professor C. H. Lees on the effect of temperatures between —160°C. and 15°C. on the thermal conductivities of nine metals and six alloys.

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