Home About us Contact
|
Home About us Contact | ||
|
|
||
Conduction Model (conduction + model)
Selected AbstractsEstimating baking temperatures in a Roman pottery kiln by rock magnetic properties: implications of thermochemical alteration on archaeointensity determinationsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2006Simo Spassov SUMMARY Absolute past geomagnetic field intensity determinations requiring laboratory heating are labourious and the success rate is rather low, mostly because of induced thermochemical magnetic mineral alterations. Archaeomagnetic intensity determinations are mainly limited to displaced ceramics produced in kilns. In this study, the suitability of an in situ baked structure is investigated. Different magnetic properties of baked material taken from the combustion chamber wall and floor of a Roman pottery kiln, with variable colouring, are examined in dependence on the distance to the combustion chamber. The temperature distribution is re-constructed based on rock magnetic experiments after stepwise heating. The rock magnetic temperature estimates agree fairly well with a mathematical heat conduction model demonstrating the penetration of heat into the combustion chamber wall. The rock magnetic results show that blackish- and greyish-coloured kiln parts, that had been in close contact with the fuel, during ancient kiln operation, are not suitable for intensity determinations. Although sufficiently baked, they strongly alter during laboratory heating and new remanence-carrying minerals are formed. The brownish-coloured material at a distance 65,80 mm away from the combustion chamber seems to be most suitable as its magnetic properties remain nearly unchanged during laboratory heating. Rock magnetic and modelled temperature estimates for this material consistently indicate ancient baking temperatures of about 600°C. The model demonstrates that cooling takes longer in the inner parts of the combustion chamber wall. Retarded cooling affects the blocking temperatures and hence the strength of the thermoremanent magnetization. The variability of cooling rates should be taken into account when investigating archaeointensities of specimens cut from large samples, or of samples taken from different parts of a kiln. [source] Investigation of the temperature oscillations in the cylinder walls of a diesel engine with special reference to the limited cooled caseINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2004C. D. Rakopoulos Abstract This work investigates the interesting phenomenon of the temperature (cyclic) oscillations in the combustion chamber walls of a diesel engine. For this purpose, a comprehensive simulation code of the thermodynamic cycle of the engine is developed taking into account both the closed and the open parts of it. The energy and state equations are applied, with appropriate combustion, gas heat transfer, and mass exchange with the atmosphere sub-models, to yield cylinder pressure, local temperatures and heat release histories as well as various performance parameters of the engine. The model is appropriately coupled to a wall periodic conduction model, which uses the gas temperature variation as boundary condition throughout the engine cycle after being treated by Fourier analysis techniques. It is calibrated against measurements, at various load and speed conditions, from an experimental work carried out on a direct injection (DI), naturally aspirated, four-stroke, diesel engine located at the authors' laboratory, which has been reported in detail previously. After gaining confidence into the predictive capabilities of the model, it is used to investigate the phenomenon further, thus providing insight into many interesting aspects of transient engine heat transfer, as far as the influence that engine wall material properties have on the values of cyclic temperature swings. These swings can take prohibitive values causing high wall thermal fatigue, when materials of specific technological interest such as thermal insulators (ceramics) are used, and may lead to deterioration in engine performance. Copyright © 2004 John Wiley & Sons, Ltd. [source] Factors affecting the formation of fingering in water-assisted injection-molded thermoplasticsADVANCES IN POLYMER TECHNOLOGY, Issue 2 2006Shih-Jung Liu Abstract Water-assisted injection-molding technology has received extensive attention in recent years, due to the lightweight of plastic parts, relatively low-resin cost per part, faster cycle time, and flexibility in the design and manufacture. However, there are still some unsolved problems that confound the overall success of this technology. One of these is the water "fingering" phenomenon, in which the water bubbles penetrate outside designed water channels and form finger-shape branches. This study has investigated the effects of various processing parameters on the formation of fingering in water-assisted injection-molded thermoplastic parts. Both amorphous and semicrystalline polymers were used to mold the parts. The influence of water channel geometry, including aspect ratio and fillet geometry, on the fingering was also investigated. It was found that water-assisted injection-molded amorphous materials gave less fingering, while molded semicrystalline parts gave more fingering when compared to those molded by gas-assisted injection molding. For the water channels used in this study, the channels with a rib on the top produced parts with the least water fingering. Water fingering in molded parts decreases with the height-to-thickness ratio of the channels. The water pressure, water injection delay time and short-shot size were found to be the principal parameters affecting the formation of water fingering. In addition, a numerical simulation based on the transient heat conduction model was also carried out to help better explain the mechanism for the formation of fingering in water-assisted injection-molded thermoplastics. © 2006 Wiley Periodicals, Inc. Adv Polym Techn 25: 98,108, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20062 [source] The thermal conductivity of Nylon 6/clay nanocompositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Hu Zhou Abstract Nylon 6/clay nanocomposites (NCNs) of different clay loadings are prepared by melt compounding. The effects of clay loading and dispersion on the thermal conductivity of NCNs are investigated using XRD, TEM, DSC, and POM. The results show that the thermal conductivity of the exfoliated NCNs decreases with an increase of clay content; but the thermal conductivity of the intercalated NCNs does not decrease, indeed, it increase markedly at high clay content. Such results observed in the exfoliated NCNs are opposite to the expectation of the classic Maxwell thermal conduction model. The further investigations indicate that such decrease observed in the exfoliated NCNs is due mainly to the exfoliation of clay layers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Dipole moments of polyenic oligomeric systems.JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2005Part II, allenes, molecular organic wire resistivities: polyacetylenes, polyynes Abstract Polyacetylenic, allenic and polyynic molecular wire series, containing electron-donor (D) and electron-acceptor (A) groups as two terminal units of the oligomeric bridge (D,wire,A), can be well described by means of a one-dimensional conduction model, which considers a scattering process of electrons through the charge-transfer conduction bridge. The conduction constants (,i) of the oligomeric structures of the three molecular series under study were determined from the functional dependence between the dipole moment of the oligomers (,n) and the ,-molecular orbital bridge length (L). According to our one-dimensional molecular organic wire model: where ,o is the dipolar moment of the first compound of the oligomeric series without a bridge unit (n,=,0) and ,, is a limit value for L,,,,. By means of the Landauer theoretical expression for the conductance of a metallic one-dimensional conductor and our molecular wire conduction constants (,i), we determined the intrinsic resistivities associated with the molecular resistances of these oligomeric wires. Using this approach we determined, for the first time, the linear and non-linear contributions to the net molecular resistivity. The order of magnitudes of the linear resistivities determined in these oligomeric systems agrees very well with the expected results of experimental measurements for macroscopic wires. Copyright © 2005 John Wiley & Sons, Ltd. [source] Cryogen spray cooling: Effects of droplet size and spray density on heat removalLASERS IN SURGERY AND MEDICINE, Issue 2 2001Brian M. Pikkula BS Abstract Background and Objective Cryogen spray cooling (CSC) is an effective method to reduce or eliminate non-specific injury to the epidermis during laser treatment of various dermatological disorders. In previous CSC investigations, fuel injectors have been used to deliver the cryogen onto the skin surface. The objective of this study was to examine cryogen atomization and heat removal characteristics of various cryogen delivery devices. Study Design/Materials and Methods Various cryogen delivery device types including fuel injectors, atomizers, and a device currently used in clinical settings were investigated. Cryogen mass was measured at the delivery device output orifice. Cryogen droplet size profiling for various cryogen delivery devices was estimated by optically imaging the droplets in flight. Heat removal for various cryogen delivery devices was estimated over a range of spraying distances by temperature measurements in an skin phantom used in conjunction with an inverse heat conduction model. Results A substantial range of mass outputs were measured for the cryogen delivery devices while heat removal varied by less than a factor of two. Droplet profiling demonstrated differences in droplet size and spray density. Conclusions Results of this study show that variation in heat removal by different cryogen delivery devices is modest despite the relatively large difference in cryogen mass output and droplet size. A non-linear relationship between heat removal by various devices and droplet size and spray density was observed. Lasers Surg. Med. 28:103,112, 2001. © 2001 Wiley-Liss, Inc. [source] Delayed quasilinear evolution equations with application to heat flowMATHEMATISCHE NACHRICHTEN, Issue 5 2010BártaArticle first published online: 15 MAR 2010 Abstract In this paper we show local and global existence for a class of (hyperbolic) quasilinear equations perturbed by bounded delay operators. In the last section, the abstract results are applied to a heat conduction model (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||