Greater Temperature Difference Research Articles

Non-Fourier Heat Conduction in IC Chip

Instead of the classic Fourier equation based on diffusion, a hyperbolic equation based on a wave model has been used to predict the rapid transient heat conduction in IC chips. The peak temperature, spatial difference, and time variation of temperature, which are critical to thermal reliability of the chip, are given and compared with that obtained from the Fourier equation. Analytical and numerical results show that non-Fourier effects, including the higher peak temperature and thermal stress, greater temperature difference between components, and stronger thermal noise, are significant to IC chip reliability.

Modification of Texas Clear-cut Environments with Loblolly Pine Shelterwoods

The near-surface (within 0·30 m of the surface) environments of a clear-cut and a loblolly pine ( Pinus taeda L.) shelterwood in east Texas were instrumented to determine treatment effects on the radiation, thermal, humidity and wind components of microclimate. The shelterwood produced lower net radiation and photosynthetically-active radiation loads, lower daytime air temperatures, the same or slightly lower daytime vapor pressures and lower wind speeds than the clear cut. Although sunfleck incidence in the shelterwood allowed net radiation and photosynthetically-active radiation (PAR) to increase briefly to levels similar to those measured in the clear cut, seedlings within the shelterwood were subjected to sunflecks for only a short period of time before the sunfleck dissipated and shade returned. Air temperature differences between treatments were not great and soil temperature differences were negligible. The influence of the shelterwood on all environmental factors was primarily due to the partial overstory canopy, which dissipated incident radiation before it reached the near-surface environment where it could significantly alter the microclimate.

Mathematical modelling of heat transfer in Stockbarger-type units for ZnSe growth

Studies of heat transfer in units for ZnSe crystal growth were performed by means of mathematical modelling and experimental data. It was proved that if the pressure in the cell is over 1 atm and there are cavities with great temperature difference at their boundaries, the convective component of the heat transfer should be considered. A model substance was proposed to stimulate the heat transfer in translucent materials. The influence of various structural elements of the heat unit on the temperature distribution in the crucible was analyzed.

MODELLING OF LOCAL CLIMATE FOR PREDICTION OF ROAD SLIPPERINESS

Recent research concerning the Swedish Road Weather Information System (VVIS) is discussed along with a method for determining temperature variations attributable to topography during different weather situations. Topographical areas are classified according to factors determining temperature differences. The investigation concentrates on areas where great temperature differences occur during different weather situations, producing a risk of local road slipperiness. Geographical factors analyzed and discussed include valleys, height differences, shadow areas, bridges, and regional climate. Cold air pool intensities are shown to be influenced by weather but a variation between different valleys also occurs owing to valley width area of cold air production, wind shelter, and ratio between height and width of valley slopes. During neutral or unstable lapse rate conditions, the lowest road surface temperature is closely related to the air temperature and decreases with increasing altitude above sea level. Screened areas have a lower surface temperature than areas exposed to sun. Factors such as bridge size and type also affect road surface temperature on bridges. These different factors are integrated into a local climatological model. (Author/TRRL)

Effects of temperature on sister chromatid exchanges

The influence of temperature on sister chromatid exchanges was investigated, and the results are discussed in connection with factors possible involved in temperature-induced SCE-formation. Whereas the SCE frequency increased with increasing growth temperature in a cell line of Xenopus laevis (EAX), which permits the examination of great temperature differences, a Chinese hamster cell line (V-79) revealed a U-shaped temperature-response curve. In addition, it was found that cold treatment at 4 degrees C caused an induction of SCEs in the V-79 cell line. Different BrdU concentrations had no effect on the temperature-induced SCE frequencies and mitomycin C led to an induction of SCEs parallel to the base-line values at different temperatures.

Ignition of a gas in a boundary layer at a heated plate

The problem of the ignition of a moving homogeneous gaseous combustible mixture in a boundary layer along a heated flat semiinfinite plate is one of the main problems of the ignition of a combustible mixture in a flow (for example, [1]). The formulation of the problem includes the two-dimensional equations of motion and the equations of the transfer of heat and of the reacting substance, written taking a chemical reaction into consideration, as well as boundary conditions, and should lead to determination of the steady-state fields of the concentration and the temperature and, by the same token, of the position of the combustion zone. Different approximate numerical solutions of the problem were analyzed in [1–5]. One of the most important characteristics of the process is the length of the ignition, i.e., the distance from the edge of the plate to the point at which, thanks to the intrinsic chemical heat evolution in the gas, the heat flux from the plate to the gas becomes equal to zero. In the present work, for the case of large values of the activation energy of the chemical reaction and a sufficiently great temperature difference between the wall and the flow, an approximate expression is obtained for the length of the ignition.

Elimination of yield point phenomenon in mild steel by warm working

Wire and arc additive manufacturing (WAAM) is a promising technology for fabricating large-sized metal parts. However, to use this method efficiently, it is necessary to overcome the problem of severe heat accumulation that reduces manufacturing efficiency and deteriorates material properties. This paper proposes a new method using the in-situ gas cooling (ISGC) for reducing heat accumulation. Three parts were manufactured via the proposed method utilising CO2, N2, and air as cooling gases, respectively. A fourth part was fabricated with natural cooling (NC), without cooling gas. The temperature data measured by thermocouples and infrared pyrometers indicated that compared with NC, ISGC considerably reduced the temperature of the whole part and CO2 had the best cooling effect. ISGC efficiently mitigated heat accumulation, due to the large heat transfer coefficient and the great temperature difference between the high-temperature region behind the torch and the cooling gas. Numerical simulations verified by the experimental data further denoted that in ISGC, high-temperature areas near the molten pool shrank sharply and heat dissipation conditions in the molten pool were improved markedly. ISGC not only improved the surface quality of the parts, but also strengthened the mechanical properties of the parts by obtained fine grains. The maximum ultimate tensile strength (UTS) and yield strength (YS) increased to 483 MPa and 358 MPa, respectively, which represented an increase of 4.1 % and 4.7 % respectively. The average hardness was enhanced to 161.3 HV, representing an improvement of 3.7 %.

Oxygen Embolization During Deep Hypothermia

The recent application in man of deep hypothermia and circulatory arrest without an extracorporeal oxygenator15was followed by reports of brain damage in children undergoing this procedure.3The mechanism of this complication has not been elucidated. It has been suggested that gas solubility is perhaps the major practical consideration as far as temperature effects in the blood are concerned because during rapid cooling and rewarming, the great temperature difference could result in gas embolism (Fig. 1). These facts led to the experimental use in dogs of continuous extracorporeal oxygenation and circulation during deep hypothermia with arterial blood of high oxygen tension at relatively high flow rates. This experimental model was devised so that the animals would be subjected to extreme conditions which theoretically should result in gas embolization. Method Ten dogs weighing between 14.1 and 19.8 kg. were anesthetized with intravenous sodium pentobarbital (25 mg. per kilogram) and

I3. The reaction between a surface of solid carbon and oxygen

This research is divided into two parts: the first one investigates the case that at the surface the CO 2-pressure is extremely small (temperature higher than 1100 °C) and the second part the case that at the surface the CO 2-pressure is moderate and that oxygen can reach the surface (e.g. surface temperature about 800 °C). From experiments it is clear that in the first case a thin reaction zone exists inside the laminar boundary layer. In this zone CO burns at high temperature (2300 °C). As oxygen cannot reach the surface, this zone must deliver the heat for the endothermic gasification of the carbon with CO 2 at an accordingly much lower temperature of the surface (1500 °C). Formulae describing the phenomena in the different sections are given. For the reaction zone the 3 2 order reaction kinetics is treated completely; for the second and third order reactions only the results of the calculations are given. In the second case the reaction zone is bounded by the carbon surface. There is a negligible temperature maximum in the gas and the reaction zone is so thick that it can possibly fill the boundary layer. The calculations in this case are only informative, because we have neglected the temperature dependence of the different properties even though there are great temperature differences in this reaction zone, and because we have only treated the second order reaction. Experiments by G laudemans and S nelleman (University of Utrecht) and M ulder and de G raaf (T.N.O., Delft) confirm the results of the calculations.

The Physical Behavior of Basaltic Lava Flows

With reference to the course taken over pre-existing topography by a liquid flood, the behavior of lava flows differs greatly from that of streams of water. Because of great temperature differences in space and time and low conductivity of solid or molten rock, lava only remotely approaches the physical concept of a perfect liquid. Various forms of solidified lava masses which suggest former liquidity are the result of sequential emplacement of small liquid additions and cannot be interpreted as if the whole mass had been capable of acting as a liquid at one time. The rapid congealing of successive parts of the lava flow and increase in the quantity of floating and grounded crust blocks give a lava flow the character of an overloaded and aggrading stream. Like such streams, the lava flow builds up its bed, often breaks out from newly built levees, and may, by repetition of such changes, assume a downslope course that is very difficult to predict and that differs greatly from that which a stream or flood of water might take. In the maintenance of a given channel flow, the lava stream not only must have adequate mechanical energy to overcome friction on the existing slope but must, by its* own flow, convey enough thermal energy to maintain temperatures permitting continued flow. This requirement for dual conservancy of energy has an important bearing on the shapes of channels built by lava flows and on the survival of movement in a given channel. These factors are discussed in relation to the problem of man-made barriers protective against lava-flow damage in critical areas on Hawaii. It is evident that the great volume of lava flows from Mauna Loa vents and the form of the terrane preclude building barriers sufficient to impound prospective lava flows completely. Rather, the placing of barriers at points most promising for unit diversion and the multiplication of such barriers in a calculated and detached en echelon arrangement seem to offer the best prospect of an effective delaying action. This plan is considered superior for any given amount of barrier volume to the alternative of trying at one point to develop a continuous diversion barrier which could so easily fail by being at the wrong place or inadequate to accomplish the desired total diversion.

The problem of respiratory acclimatization

1. In 1916 August Krogh called attention to the fact that related species, or animals belonging to the same species, sometimes inhabit localities with extremely different temperatures. In such cases it would appear unlikely from a teleological point of view that the respiratory exchange should differ as much as the temperature difference would ordinarily imply. According to K rogh one would expect that animals living at a very low temperature should show a relatively high metabolism compared with others living normally at a high temperature. 2. The hypothesis advanced by Krogh with special reference to great temperature differences has been treated in this paper with reference to a fairly small and seasonal temperature difference: The temperature difference in summer between a lake, Rorbaek So, having a temperature of 18°, and a brook, Funder Aa, with a temperature of 11° C. In both localities there was a large population of Ancylus fluviatilis and this species was used as the experimental animal. 3. The comparative experiments were carried out at 11° C and 18° C for both the cold-water form of Ancylus fluviatilis from the brook and the warm-water form from the lake. 4. The experiments have shown no such acclimatization with regard to the oxygen consumption of the two Ancylus fluviatilus populations that live in different temperature environments, as was expected according to the above-mentioned hypothesis. But there exists an acclimatization of the opposite nature (a “reversed acclimatization”): The animals from the summer-warm environment (18° C) had acquired a greater oxygen consumption than those from the summer-cold environment (11° C). 5. Aug. Krogh (1914, p. 504) established a curve showing the quantitative relation between the temperature and the standard metabolism in animals. The increase in the oxygen consumption of Ancylus fluviatilis with increasing temperature — as found in the experiments at 11° and at 18° C — agrees well with Krogh's curve. 6. The oxygen consumption increases 1.9 times when the temperature of the experimental animals increases from 11° C to 18° C. The “reversed acclimatization” found for Ancylus fluviatilis is about 1.4. It means that the observed respiration of the warmwater animals in relation to that of the cold-water animals is about 1.4 times greater than would be implied from the temperature difference between their habitats. 7. The oxygen determinations made in this study were carried out by means of the polarometric method.

Heat Transfer by Great Temperature Difference in the Case of Turbulent Boundary Layer of Gas (1st Report)

Heat Transfer by Great Temperature Difference in the Case of Turbulent Boundary Layer of Gas (1st Report)

Heat Transfer by Great Temperature Difference in the Case of Turbulent Boundary Layer of Gas (2nd Report)

Heat Transfer by Great Temperature Difference in the Case of Turbulent Boundary Layer of Gas (2nd Report)

Heat Transfer by Great Temperature Difference in the Gas of Lamina Boundary Layer of Gas

Heat Transfer by Great Temperature Difference in the Gas of Lamina Boundary Layer of Gas