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The transient temperature profiles in continuous-wave (cw) end-pumped Q-switched lasers are investigated by solving a numerical model coupling the transient heat conduction equation and the rate equations, in which the influences of the thermal time constant, the fluorescence lifetime and the repetition rate on the temperature variation are considered. Furthermore, the buildup dynamics of thermal equilibrium in several laser crystals are presented and compared with each other. The numerical simulation results reveal that the buildup time of thermal equilibrium mainly depends on the thermal time constant, however, the temperature rise is primarily influenced by the absorption cross section. Compared with the influences of the other parameters, fluorescence lifetime principally determines the thermal oscillation contrast. In addition, it is also found that the repetition rate and the pump power have significant effects on the thermal characteristics in Q-switched lasers.

Fast scanning calorimetry becomes more and more important because an increasing number of materials are created or used far from thermodynamic equilibrium. Fast scanning, especially on cooling, allows for the in situ investigation of structure formation, which is of particular interest in a wide range of materials like polymers, metals, and pharmaceuticals to name a few. Freestanding silicon nitride membranes are commonly used as low addenda heat capacity fast scanning calorimetric sensors. A differential setup based on commercially available sensors is described. To enhance performance of the device a new asymmetric power compensation scheme was developed. The hardware realization of the scheme and calculation of differential power are presented in the first part of this paper. The fast analog amplifiers allow calorimetric measurements up to 100,000 K/s. The lower limit is defined by the sensitivity of the device and is 1 K/s for sharp melting or crystallization events in metals and ca. 100 K/s for broad transitions in polymers. Another limiting factor is accuracy of sample temperature measurement. A strong dependency of temperature on sample placement on the sensor is observed; even reproducibility is within ±1 K. For finite sample thicknesses the commonly observed thermal lag must be considered too. Uncertainty of the temperature measurement based on previous thermopile calibration is in the order of ±10 K. A significant improvement is possible by adding a small particle of a temperature calibration standard, e.g. indium or tin, on top of the sample under investigation. Then uncertainty is about ±3 K. The second part of the paper describes sample heat capacity determination and an example to demonstrate the performance of the device.

In this second part of a two-part study, full nonlinear simulations of miscible thermo-viscous fingering are carried out using Hartley transform-based Pseudo-spectral method. Vorticity-streamfunction formulation is applied to the model equations developed in Part 1. Time evolutions of nonlinear fingers are examined qualitatively by plotting concentration and temperature iso-surfaces. The effect of increase in the thermal mobility ratio as well as decrease in the thermal lag coefficient is examined first for a hypothetical value of the Lewis number, Le = 1. For fixed solutal mobility ratio, an enhancement in instability is observed with the increase in the thermal mobility ratio for all values of the thermal lag coefficient. However, at large values of the Lewis number, the instability is seen to be strictly dominated by the solutal mobility ratio. At unity thermal lag coefficient, for the tested values of the other parameters, less complex finger structures are observed than in a reference isothermal case with the same solutal mobility ratio but zero thermal mobility ratio. As the thermal lag coefficient is decreased, a highly diffuse thermal front lags farther behind the fluid front, and the stabilizing effect of strong thermal diffusion gets alleviated. Consequently, the fluid front becomes as unstable as the reference isothermal case. The qualitative observations are further substantiated quantitatively using relative contact area (R.C.A.) and Sweep Efficiency as well as through identifying the relative contributions of solutal and thermal vorticity components in the development of the instability. The conclusions drawn from this study are in complete qualitative agreement with the ones obtained from Part 1, particularly using the initial value calculations (IVC) approach. Such agreement infers the superiority of (IVC) approach over the quasi-steady-state approximation (QSSA) approach in linear stability analysis of the problem under investigation.

Current design weather data recommended by ASHRAE and CIBSE may result in overestimated peak cooling loads. This is because solar radiation, and outdoor dry-bulb and wet-bulb temperatures selected for design conditions do not occur coincidently. Hence, the data cannot reflect the joint statistical distribution of these three weather parameters. Moreover, the peak cooling load largely depends on the characteristics of both weather and buildings. A statistical method has been developed for the rational selection of sequences of coincident design weather parameters in order to properly determine peak cooling loads. Overall periodic transfer factors responding to different periodic weather heat sources are first derived based on the radiant time series (RTS) method. This allows us to utilize the available thermal and optical properties of a building without the need for tedious regenerating these data. The periodic transfer factors are then equivalently transformed to z -transfer coefficients. The model has been applied to hourly weather records of 25 years in Hong Kong to generate the hourly cooling loads of buildings with any thermal lag. Sequences of coincident design solar irradiance, dry-bulb and wet-bulb temperatures have been rationally determined through statistical analysis of the computed cooling loads. Results indicate that horizontal solar irradiance computed with the method recommended by ASHRAE is always higher, 4–20%, than the measured value in different months. The peak cooling load resulted from the traditional design weather data is always much higher, 12–50%, than the results from the new design weather data. An unreasonably oversized air-conditioning system would cause high initial cost and unnecessary significant use in embodied energy. It would also deteriorate the part-load energy efficiency and the system management effectiveness.

Various techniques and methodologies of thermal conductivity measurement have been based on the determination of the rate of directional heat flow through a material having a unit temperature differential between its opposing faces. The constancy of the rate depends on the material density, its thermal resistance and the heat flow path itself. The last of these variables contributes most significantly to the true value of steady-state axial and radial heat dissipation depending on the magnitude of transient thermal diffusivity along these directions. The transient hot-wire technique is broadly used for absolute measurements of the thermal conductivity of fluids. Refinement of this method has resulted in a capability for accurate and simultaneous measurement of both thermal conductivity and thermal diffusivity together with the determination of the specific heat. However, these measurements, especially those for the thermal diffusivity, may be significantly influenced by fluid radiation. Recently developed corrections have been used to examine this assumption and rectify the influence of even weak fluid radiation. A thermal conductivity cell for measurement of the thermal properties of electrically conducting fluids has been developed and discussed.

An analytical model for the diurnal YORP and Yarkovsky effects is described, which reproduces the overall results from previous numerical studies. Important shape parameters are identified and general forms of the differential equations are presented. The force cosines for comet orbit solutions are modified in order to include both thermal lag and geometrical effects.

При функціонуванні системи теплозабезпечення будівлі у режимі чергового опалення основною проблемою є визначення теплової інерції огороджуючих конструкцій та обладнання, що знаходиться у приміщеннях будівлі для розробки графіку такого режиму. Другою проблемою є визначення доцільного діапазону зниження температури теплоносія у системі опалення, у межах якого можливе повернення температури повітря приміщення до нормативного значення за визначений наперед проміжок часу з урахуванням зміни температури повітря зовнішнього середовища. Дослідження роботи системи опалення проведено з метою отримання необхідної інформації для подальшого вирішення зазначених проблем.

This study examines the traces of water droplets moving through high-temperature combustion products (initial temperatures are 430–950 K). The temperature of a gas-vapor mixture in the area of droplets’ traces is measured using low-inertia thermocouples (thermal lag is less than 0.1 s). The experiments revealed that the temperature in the trace of water droplets is significantly reduced (from 15 K to 140 K) even when using an aerosol flow with small droplets. The experiments showed that the times of keeping low temperatures in the trace of water droplets may reach 30 s.

International audience; The present work aims at studying the thermophysical properties of three types of unfired earth bricks through experimental investigation, and their dynamic thermal performance (thermal capacity, decrement factor and thermal lag) as a function of wall thickness. The objective is to determine the ideal thickness of a raw earth wall, built by these bricks, to achieve the optimum values of thermal inertia. These bricks were industrially produced by the Briqueteries du Nord, which is a factory located in the north of France. The process used was the extrusion. The main difference between the three types of bricks is the origin of the soils, which were extracted from various quarries. They were characterised to determine their physical, chemical and geotechnical properties, and to identify their impact on development and production of unfired earth bricks. This work has identified the optimum thickness of the wall built by these unfired earth bricks. (It was 0.3 m for two types of bricks and for the other one was 0.4 m.) This thickness ensures the greatest heat capacity and a thermal lag between 10 and 12 hours, while taking into account the quantity of bricks necessary for the construction of such a wall and the habitable area.

We present observations of sunset jets on comet 67P/Churyumov-Gerasimenko by Rosetta/OSIRIS camera. In late April 2015, when the comet was at a heliocentric distance of ~1.8 AU, clusters of dust jets that originated in the Ma'at region on the comet's small lobe were identified from multipleimages and were apparently sustained for about an hour beyond local sunset. Emanating from the shadowed nucleus, these jets became visible by solar illumination at their apparent sources up to only a few tens of meters above the nucleus surface. We investigate the plausibility of these jets as having been triggered by water ice sublimation and sustained by thermal lag in the subsurface beyond sunset. A general thermo-physical model was parameterized such that the thermal lag in the subsurface is consistent with the elapsed time of observation after sunset. It is found that the sublimation of water ice from a depth of 6 mm and with a low thermal inertia of 50 W m-2 K-1 s1/2 could explain the spatial pattern and evolution of the apparent sources, particularly their disappearance due to the eventual cooling of the subsurface. Our analysis suggests that these sunset jets were essentially day-side dust activities that continued after sunset. Specific observational conditions for the sunset jets constrain their possible sources to mostly within the less abrupt, dusty terrains. The uneven distribution of these jets is possibly related to subsurface inhomogeneities in the dusty area.

Thermal death kinetic parameters for Bacillus stearothermophilusspores were evaluated in sugarcane must (21.5°Brix, pH = 6.14) at temperatures ranging from 98 to 130C, using the thermal-death-time tube method and survivors count. Resulting survival curves showed strong nonlinearity and different shapes according to heating temperature. The 98 and 110C curves showed an initial shoulder or thermal lag and were adjusted to the logistic model. At the temperature range of 120–125C, the two-term exponential model for population with heterogeneous heat resistance was fitted, and at 130C, the classic linear model was suitable. It was shown that rate constants are influenced by temperature according to two irreconcilable methods: the Arrhenius and the Bigelow methods. Activation energy (Ea) obtained was 249.52 kJ/mol while thermal resistance parameter (z-value) calculated from Ea and the Bigelow method were 11.48 and 9.19C, respectively. Thermal death kinetic constant, k values, varied from 0.019 to 13.63/min. PRACTICAL APPLICATIONS The thermal degradation kinetics from this work, in conjunction with the appropriate sugar degradation kinetic data (Nolasco Junior 2005, Nolasco Junior and De Massaguer 2006), can be used to properly design an optimal thermal process to inactivate sugarcane must contaminants with optimal sugar content retention. Contaminant control in ethanolic fermentation processes could namely be based on temperature, a physical agent, instead of the current control practice based on antibiotics. Besides, the data from this research meet the more frequently found nonlinear microbial thermal death kinetic model application.

The crystallization and melting behavior of polypropylene (PP), polyoxymethylene (POM) and polyamide-6 (PA6) has been investigated by means of varying the cooling and heating rates using a high performance differential scanning calorimeter (HPer DSC). The influence of the sample mass and scan rate on thermal lag has been sorted out and the importance of making proper corrections is stressed. By varying the cooling rates from 5 to 250 °C/min in combination with one particular heating rate (10 and 300 °C/min have been used) reorganization and especially recrystallization effects in a PP sample have been examined. Recrystallization of the PP can be avoided by using a high heating rate (300 °C/min). The influence of incorporating a stabilizer acting as a comonomer in the POM chain on the kinetics of the crystallization and melting behavior is studied. The influence of the maximum heating temperature in the melt on crystallization of POM and of POM with stabilizer is investigated by self-seeding experiments using high heating and cooling rates. Furthermore, the melting behavior of PA6, where several transitions take place during heating which are up to now not fully understood, is discussed subsequent to cooling at 5–300 °C/min. Throughout it has been made clear that it is important to have the capability of applying proper combinations of low/high and cooling/heating rates in order to examine the metastability of polymer systems and the related kinetics of transitions, to scrutinize the phenomena seen and to arrive at the right explanations.

Differential scanning calorimetry (DSC) measurements are used to estimate the fractional latent heat release during phase changes. There are temperature lags inherent to the instruments due to the temperature measurement at a different location than that of the sample and reference materials. Recently, Dong and Hunt[1] showed that significant improvement in estimating the fractional latent heat can be obtained when detailed simulations of the heat transfer within the instrument are performed. The Netzsch DSC 404C instrument, with a high accuracy heat capacity sensor, is considered in this study. This instrument had a different configuration than that studied by Dong and Hunt.[1] The applicability of Dong and Hunt’s approach to this instrument is investigated. It was found that the DSC instrument could be described by numerous parameters but that model parameters were difficult to estimate. Numerical simulation results are presented and compared with experimental results for the fractional latent heat of a commercial A356 aluminum alloy. Once the thermal lag was significantly reduced, the onset temperature of the eutectic phase transformation was in excellent agreement with previously reported values. The use of this new fractional latent heat data allowed accurate predictions of the cooling curves during casting solidification.

First and second order thermal transitions have been characterized for a number of cis/trans-polypentenamer copolymers, for blends of high cis and high trans polymers, and for high trans polypentenamer containing oil and carbon black. The extrapolated value of Tg for 100% trans polypentenamer is −91°C at a heating rate of 10°C/min. At the same heating rate the maximum, equilibrium melting point is estimated to be 44°C. Correcting for the thermal lag in the experiment (i.e., extrapolating to infinitely slow heating rate), the above value is 40°C. The heat of fusion of trans-polypentenamer is 1.93 ± 0.11 K cal/mole. The presence of crystalline polypentenamer slightly raises the glass transition temperature of the amorphous phase. This effect becomes measurable when the trans content is greater than 80%. Once calibrated by infrared or other spectroscopic determination of composition, thermal analysis is a rapid, precise method for measuring cis/trans contents in polypentenamers.

There have been relatively few studies on the implications of the physical conditions experienced by cells during large volume (litres) cryopreservation – most studies have focused on the problem of cryopreservation of smaller volumes, typically up to 2 ml. This study explores the effects of ice growth by progressive solidification, generally seen during larger scale cryopreservation, on encapsulated liver hepatocyte spheroids, and it develops a method to reliably sample different regions across the frozen cores of samples experiencing progressive solidification. These issues are examined in the context of a Bioartificial Liver Device which requires cryopreservation of a 2 L volume in a strict cylindrical geometry for optimal clinical delivery. Progressive solidification cannot be avoided in this arrangement. In such a system optimal cryoprotectant concentrations and cooling rates are known. However, applying these parameters to a large volume is challenging due to the thermal mass and subsequent thermal lag. The specific impact of this to the cryopreservation outcome is required. Under conditions of progressive solidification, the spatial location of Encapsulated Liver Spheroids had a strong impact on post-thaw recovery. Cells in areas first and last to solidify demonstrated significantly impaired post-thaw function, whereas areas solidifying through the majority of the process exhibited higher post-thaw outcome. It was also found that samples where the ice thawed more rapidly had greater post-thaw viability 24 h post-thaw (75.7 ± 3.9% and 62.0 ± 7.2% respectively). These findings have implications for the cryopreservation of large volumes with a rigid shape and for the cryopreservation of a Bioartificial Liver Device.

Controlled cooling on the runout table is a crucial component in the production of highly tailored steels since it has a strong influence on the final mechanical properties. High efficiency heat transfer in impinging jet cooling makes this an important method for heat transfer enhancement. The purpose of this study is to develop an experimental database for modelling of boiling heat transfer for bottom jet impingement that occurs during runout table cooling in a steel mill. Experiments have been carried out on a pilot scale runout table using stationary plates, with focus on the effect of water flow rate and nozzle inclination to the overall heat transfer rates. Volumetric flow rates and inclination angles are in the range of 35-55 l/min and 0-30º, respectively. Temperatures on the test plates are measured internally very close to the surface during cooling for the purpose of reducing thermal lag and receiving better data responsiveness. These measurements are taken at the impingement point and several streamwise distances from the impingement point. From the above measurements transient cooling data on the hot steel plate by bottom jet impingement has been analysed.

A transient short hot wire technique (SHWT) is developed for simultaneous determination of the thermal conductivity and thermal diffusivity of various materials such as liquids, gases or powders. A metal wire with (or without) insulation coating serves both as a heating unit and as an electrical resistance thermometer and the wire is calibrated using water and toluene with known thermophysical properties. This SHWT includes correlation of the experimental data with numerically simulated values based on a two-dimensional heat-conduction model. For the measurements with proportional relation between temperature rise and logarithmic heating time interval, the thermal conductivity and thermal diffusivity are obtained from the slope and the intercept of the measured temperature rise and those of calculated non-dimensional temperature rise by including the heat flux and the properties of the wire. For the measurements with nonlinear relation between temperature rise and logarithmic heating time interval, the thermal conductivity and thermal diffusivity are extracted from a curve fitting method by using the downhill simplex method to match the experimental data and the numerical values. This technique is applied here using air as a testing sample. The effect of natural convection is investigated and the accuracy of this measurement is estimated to be 2% for thermal conductivity and 7% for thermal diffusivity.

The isoconversional approach proposed by Vyazovkin for evaluating the Hoffman-Lauritzen parameters from overall rates of non-isothermal crystallization was critically applied to two new and fast crystallizing polymers, poly(propylene terephthalate) and poly(butylene naphthalate), which are used for the production of fibers. Non-isothermal crystallization data were corrected for the effect of the thermal lag and the effective activation energy as a function of temperature was calculated using the method of Friedman. The estimated Hoffman-Lauritzen parameters, U* and K g , were consistent with corresponding values from isothermal crystallization experiments obtained either from DSC measurements or using polarized optical microscopy (POM). It was found that the proposed method could simulate the experimental data very well, and the temperature interval under consideration did not allow the detection of any critical breakpoints denoting regime transitions.

The heat exchange between the horizontal furnace of a differential thermal analyzer (DTA) and the sample is analyzed with the aim of understanding the parameters governing the thermal signal. The resistance due to radiation and conduction through the gas has been calculated and compared to the experimental values of the thermal-lag between the sample and furnace and apparatus sensitivity. The overall evolution of these parameters with the temperature and their relative values are well understood by considering the temperature differences that arise between the sample and holder. Two RC thermal models are used for describing the apparatus performance at different temperature ranges. Finally, the possibility of improving the signal quality through the control of the leak resistances is stressed.

Thermocouples are often used to obtain gas temperature measurements in compartment fires. Such measurements are subject to a thermal lag during fire growth, but the main problem is a steady-state error induced by radiant heat transfer at the thermocouple surface. This error is sensitive to thermal parameters of the flame, compartment structure, thermocouple surface and combustion products; and is also influenced by the size and position of both the flame and thermocouple. The literature contains models of varying sophistication to enable an assessment of steady-state error. A model is now proposed that makes use of the concept of radiosity. Developed from radiant network theory, the model can be applied to both pre-flashover and post-flashover conditions. Experiments have been performed using different sizes of thermocouple and the models compared. The simpler models pre-date the more sophisticated and predict much larger errors than the latest published and current versions.

An intrinsic requirement in reliable dynamic mechanical analysis (DMA) or thermal mechanical analysis (TMA) is the precise determination of the sample temperature. In this work a straightforward method is proposed and implemented that allows correction of the average sample temperature for a variety of probe geometries (flexural, tensile and compression). Hydrophilic polymeric-based matrices, with geometries similar to the sample to be tested, are swelled with a pure liquid (in this case water) and placed in the correct testing place of the equipment; a static force is applied at low temperature and the probe position is monitored in a temperature scan, where the melting of the standard is clearly detected and compared with the expected melting temperature. This allows the average sample temperature to be obtained, using a sample that exhibits similar thermal resistance to the sample to be tested, instead of probing specific locations inside the furnace, as it is usually proposed in calibration routines with pure metals. For the specific configurations analysed, a strong and similar dependence of the thermal lag on the scanning rate was found for both flexural and compression modes that also depends weakly on the sample dimensions. More complicated dependence of the thermal lag on the scanning rate is found for the tensile mode, probably due to the complex thermal environment existing inside the furnace with this arrangement. However, the results indicate that there is a significant contribution from the thermal resistance of the sample in the temperature correction. It is suggested that the proposed method may be employed in other situations such as isothermal and non-isothermal creep/stress relaxation experiments or in rheometers.

Whole grains of emmer wheat were heated in a pre-heated tube oven at temperatures ranging from 130–700°C under controlled anoxic conditions for maximum 280 min. For each temperature a separate experiment was carried out. Physical properties including mass loss, thermal lag, external and internal morphology and the vitrinite reflectance, C and N content, and DTMS under CI (NH3) and EI conditions were used to monitor changes as a function of the temperature. The results show remaining starch and protein rich material up to 250°C. From 310–400°C a secondary, thermally stable, product is formed and at higher temperatures a strongly carbon enriched tertiary product.

The following research has been undertaken as a response to the recent controversy regarding the suitability of rammed earth wall construction as an effective building envelope in regard to its thermal performance. The R-value for rammed earth walls is low hence they might be expected to conduct heat into a building during summer. However the large mass of these walls and the associated thermal lag in heat transfer from outside to inside may result in the walls performing satisfactorily in a building which is only occupied during working hours. Internal rammed earth walls may act as moderators of large diurnal temperature swings helping to produce an even comfortable temperature within a building. Empirical (in situ) measurements of temperature and heat flux were taken on the walls of an existing rammed earth office building in New South Wales, Australia during the summer. An analysis was performed which established a methodology to measure the heat flow associated with the walls, floor, ceiling, windows and infiltration for one office during occupied hours and the net energy transferred between the office and these elements was established. During this time the earth walls performed well. External walls were found to transmit comparatively little heat to the office and the internal walls absorbed heat during this time. Diffuse sky radiation transmitted by the window and infiltration are both likely to be important factors in the summer heat load.

A new mathematical formulation and experimental conditions for thermal radiation calorimetry for the measurement of thermal conductivity and diffusivity are discussed. When an insulated plate sample is heated and cooled on the front surface and a radiant heat flux is emitted from the rear surface, the heat flux can be assumed to propagate in the thickness direction through the sample by one-dimensional heat conduction. On the basis of this assumption, the analysis by means of the Taylor series expansion shows that the thermal conductivity and diffusivity can be estimated from the temperatures and the ramp rates of both sample surfaces in heating and cooling modes, and the emissivity of the rear surface. The present formulation was tested by a computer simulation for several samples: Pyroceram9606, Pyrex7740, 5.3 wt% yttria-stabilized zirconia, α-Al2O3 in the temperature range 373.15–673.15 K, and polymethylmethacrylate in the range 273.15–373.15 K. The thermal conductivity and diffusivity estimated by the present formulation coincided satisfactorily with the original values used for the simulation.

Temperature transient curves of molten tellurium have been measured by a laser flash method in the temperature range from 773 to 1173 K. The thermal diffusivity was calculated from the temperature transient caused by the laser pulse. Numerical fittings of the data were used to obtain both the thermal conductivity and specific heat as functions of temperature. The temperature-dependent specific heat results agree well with the previous published data. The thermal diffusivity and conductivity indicate a structure change in the liquid phase.

The Nakamura equation is used to model the crystallization kinetics of syndiotactic polystyrene. Model constants are generated by fitting available data under isothermal conditions. The resulting fit is then applied to available data under constant-cooling-rate conditions, with notable agreement provided the measurements include corrections for thermal lag. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2402–2406, 2004

We observed comet C/1995 O1 (Hale-Bopp) at 4.6-2.9 AU pre-perihelion and 2.8-12.8 AU post-perihelion with optical long-slit spectroscopy. Emission bands of CN, C 3 , C 2 and NH 2 have been covered. Emission of C 3 was detected up to 7.0 AU, and CN could be followed up to 9.8 AU post-perihelion. Spatial column density profiles of the radicals have been used to derive effective parent Haser scale lengths for heliocentric distances beyond 3 AU. Production rates were derived based on these Haser scale lengths. The observations of CN are in agreement with HCN as the major parent molecule of this radical at large distances from the Sun (i.e. beyond ∼3 AU). We compare the measured CN production rate to sublimation rates of HCN from a simple nucleus sublimation model. The variation of CN production rates with changing heliocentric distance gives no indication for sublimation from the interior and is consistent with very little thermal lag of the nucleus.

An experimental setup, making use of a Flash DSC 1 prototype, is presented in which materials can be studied simultaneously by fast scanning calorimetry (FSC) and synchrotron wide angle X-ray diffraction (WAXD). Accumulation of multiple, identical measurements results in high quality, millisecond WAXD patterns. Patterns at every degree during the crystallization and melting of high density polyethylene at FSC typical scanning rates from 20 up to 200 degrees C s(-1) are discussed in terms of the temperature and scanning rate dependent material crystallinities and crystal densities. Interestingly, the combined approach reveals FSC thermal lag issues, for which can be corrected. For polyamide 11, isothermal solidification at high supercooling yields a mesomorphic phase in less than a second, whereas at very low supercooling crystals are obtained. At intermediate supercooling, mixtures of mesomorphic and crystalline material are generated at a ratio proportional to the supercooling. This ratio is constant over the isothermal solidification time.

Characteristics of zeolite formation, such as being kinetically slow and thermodynamically metastable, are the main bottlenecks that obstruct a fast zeolite synthesis. We present an ultrafast route, the first of its kind, to synthesize high-silica zeolite SSZ-13 in 10 min, instead of the several days usually required. Fast heating in a tubular reactor helps avoid thermal lag, and the synergistic effect of addition of a SSZ-13 seed, choice of the proper aluminum source, and employment of high temperature prompted the crystallization. Thanks to the ultra-short period of synthesis, we established a continuous-flow preparation of SSZ-13. The fast-synthesized SSZ-13, after copper-ion exchange, exhibits outstanding performance in the ammonia selective catalytic reduction (NH3 -SCR) of nitrogen oxides (NOx ), showing it to be a superior catalyst for NOx removal. Our results indicate that the formation of high-silica zeolites can be extremely fast if bottlenecks are effectively widened.

Autonomous underwater gliders are becoming important assets of coastal ocean observing systems, but the salinity data may have errors at the depths of thermocline if unpumped CTD sensors are used. Based on the CTD data collected by an autonomous underwater glider on the West Florida Shelf, we examine different salinity corrections, and find that the existing methods successfully adjust the thermal lag effects of a weak thermocline where temperature change is less than 0.7 °C in 3 m of the water column, but fail to calibrate the salinity spikes near a sharp thermocline where temperature change is ∼2 °C within 3 m of the water column. These salinity spikes can be effectively removed by applying a median filter in conjunction with the thermal lag correction methods. Thus, we propose an improved and practical approach of glider salinity error correction, which is especially useful for waters of strong stratification and sharp thermocline.

Current market demands drive companies to innovate their production techniques to improve products and simultaneously hold down costs. In the search for solutions aimed at an optimization of production processes, semi-finished products in aluminium alloys very definitely play a significant role. Moreover, the assembly of extruded parts with laminates may result in considerable difficulties, especially in relation to distortions or generated residual stress and process productivity. A solution to these issues may be found in the application of friction stir welding (FSW), characterized by low thermal input and high productivity. The asymmetry of the FSW process determines a different thermal input to the edges of the pieces to be joined. This aspect can be exploited when it is necessary to join pieces characterized by a very different thermal lag, as occurs in the case of joining extruded products and sheeting. This study aims to identify optimal FW parameters, placing particular attention on heat transfer...

The classical way to treat absorption of solar light in thermophysical modeling of cometary nuclei (and other ice-rich bodies such as jovian satellites) has been to assume complete opaqueness of the surface material. However, as shown by Davidsson and Skorov (2002, Icarus 156 , 223–248), substantial light penetration can occur in porous ice even if it is very dusty, implying that gradual absorption of energy in a surface layer should be accounted for. We present a thorough comparison between a surface energy absorption model and a layer energy absorption model, for various combinations of heliocentric distances, conductivities, opacities, pore sizes, and rotational periods relevant for cometary nuclei, by fully solving the coupled differential equations of heat transfer and gas diffusion. We find substantial differences between the models in terms of gas production rate, thermal lag angle, surface temperature, and the origin of coma molecules. For example, the surface energy absorption model overestimates the total gas production by a factor of 2–7, underestimates the lag angle by a factor of 2–3, and places the origin of coma molecules at the surface, instead of the near-surface interior.

Prova tipográfica (In press)., Following the results of previous works, the methodology used to perform DSC temperature calibrations on cooling from the melting onsets of pure metal standards is briefly presented, together with a discussion of the errors involved. The average true sample temperature in non-isothermal scans is evaluated, and the samples thermal resistance and release of the heat of crystallization duly accounted for. The importance of the above temperature corrections in the definition of a temperature corresponding to half of the phase change in non-isothermal scans is also analyzed when predicting the average density of nuclei in polymer quiescent crystallization experiments at constant cooling rate. Additional sources of error, such as the effect of the samples thickness and the temperature profile within the sample are also briefly discussed.

The thermal degradation of poly(methyl methacrylate) (PMMA) and poly(ethylene terephthalate) (PET) has been studied by non-isothermal thermogravimetry and a comparison made with isothermal studies. Several analytical methods have been applied to the analysis of the non-isothermal thermogravimetric (TG) data to elucidate the validity of the procedures adopted and to compare the results with isothermal procedures. In addition an alternative method of analysing the non-isothermal data is proposed, which addresses some of the shortcomings associated with the previous methods. It was found that thermal lag has a significant impact upon the calculated kinetic parameters, and extrapolation of the kinetic parameters to zero heating rate was required. It was also found that structural changes in the polymer residue during degradation brought about changes in the observed reaction order, and the kinetics of thermal degradation could only be studied to low fractional conversion.

A brief review of existing diagnostic methods allowing to determine the interface position and velocity during the solidification of liquid metals and semiconductors is first presented. We then show that a recently proposed electronic design can be used to measure the electrical resistance of the sample with a very high accuracy: the peak to peak noise on the signal is significantly lower than 1 μ Ω . In the tin-based system used in our investigations, this amounts to a resolution in terms of solid–liquid interface position of the order of a few micrometers. The experimental results show that our resistance measurement technique allows to identify the thermal lag of the furnace in the initial solidification stage, as well as a transfer function between actual and imposed interface fluctuations.

This paper describes an improved algorithm for generalised predictive control (GPC) and applies it to a floor radiant heating system in a full-scale outdoor test-room. The floor heating system is first identified by means of recursive least squares techniques associated with a set of supervision rules for robust system identification. The performance of the floor heating system controlled by GPC, on-off and PI controllers is then evaluated through computer simulations, using the identified models. Experimental results show that the room temperatures predicted with the identified models agree well with the measured data. Simulation results demonstrate that the behaviour of GPC is superior to the other two controllers in terms of response speed, minimum offset and on-off cycling frequency.

A new instrument is presented for the simultaneous measurement of the specific heat, thermal conductivity, and thermal diffusivity of solids and powdery materials in very wide ranges of their thermal conductivity (0.01 to200 W m - 1 K - 1 ) at temperatures between 100°C and 1750°C. These properties are usually determined by means of transient hot-wire methods, transient hot-strip methods, step-wise or pulse transient plane-source methods. With these methods either thermal diffusivity and thermal conductivity or specific heat and thermal diffusivity can be determined, but with the new procedure all thermophysical properties can be measured simultaneously. The principle of the new method consists of a quasistationary scanning of the sample temperature under adiabatic conditions, which means the chosen temperature transient is constant through the whole sample. By measuring the heat flow rate into the sample and the radial temperature difference in the sample during temperature scanning with a constant heating rate, the absolute values of the specific heat, the thermal diffusivity, and the thermal conductivity can be determined as a function of temperature in a very simple manner. Additionally, kinetic investigations are possible.

This paper presents new absolute measurements for the thermal conductivity and thermal diffusivity of gaseous argon obtained with a transient hot-wire instrument. Six isotherms were measured in the supercritical dense gas at temperatures between 296 and 423 K and pressures up to 61 MPa. A new analysis for the influence of temperature-dependent properties and residual bridge unbalance is used to obtain the thermal conductivity with an uncertainty of less than 1% and the thermal diffusivity with an uncertainty of less than 4%. Isobaric heat capacity results were derived from measured values of thermal conductivity and thermal diffusivity using a density calculated from an equation of state. The heat capacities presented here have a nominal uncertainty of 4% and demonstrate that this property can be obtained successfully with the transient hot wire technique over a wide range of fluid states. The technique will be useful when applied to fluids which lack specific heat data.

Hybrid rocket combustions frequently displayed a sudden amplification of combustion pressures developing into low frequency instability (LFI) with peak frequency of 10~20Hz. A series of experimental test was aimed to study the initiation mechanism of LFI, which was suddenly amplified at a certain condition during the combustion. To this end, a couple of parameters was selected and the sensitivity of each parameter to instability was evaluated including volume ratio between main and post chamber, oxidizer mass flow rate, and solid fuel type. Results showed that the initiation of LFI was primarily related with the flow modifications caused by volume ratio between main and post chamber. Once LFI was initiated at a certain chamber configuration, however, the variation of oxidizer mass flow rate and solid fuel did not alter the triggering mechanism of LFI. Additional study was also made to understand the critical role of vortex shedding on the initiation of LFI in the post chamber. And it confirmed that pressure oscillations by thermal lag of solid fuel would be suddenly amplified leading to LFI in case of resonating with unknown source of pressure oscillations associated with vortex shedding in the post chamber. However, details of triggering mechanism and coupling of vortex shedding with additional pressure perturbations were still remained unresolved.

A brief review of existing diagnostic methods in directional solidification is first presented. We then discuss the potential of global and differential resistance measurements to determine the interface position and velocity in liquid metals and semiconductors. An electronic design allowing the measurements to be carried out with maximum accuracy is proposed. This design is characterized both at low and high temperatures and it is shown that the peak to peak noise on the resistance signal can be kept of the order of 0.1 μ Ω. In the tin based system used in our investigations, this amounts to an accuracy in terms of solid–liquid interface position in the micrometer range, which represents a significant improvement with respect to existing techniques. We found that such an accuracy allows us to characterize in detail the heat transfer phenomena within our directional solidification furnace, and to identify the thermal lag of the device in the translation and stabilization stages.

Differential scanning calorimetry studies of the heating rate dependence of the multiple melting behavior of semicrystalline bisphenol A-polycarbonate (BAPC) are presented for different molar masses. In all cases, heating traces exhibit, in addition to the high temperature endothermic transition, a low endotherm located slightly above the crystallization temperature. After proper correction of the thermal lag effects, the high endotherm melting temperatures of the higher molar mass BAPC-19K and BAPC-28K samples are found to be independent of heating rate whether or not partial melting was carried out prior to recording the heating trace. These results demonstrate that the double melting behavior observed for high molar mass BAPC cannot be explained by a melting–recrystallization–remelting mechanism. In contrast, heating traces of the lower molar mass BAPC-4K sample exhibits two melting transitions within the high temperature endothermic region, which change both in magnitude and location with scanning rate, suggesting that melting–recrystallization–remelting can occur when chain mobility is sufficient to allow recrystallization. However, in all cases, the low and high endothermic regions are associated with the melting of two distinct populations of crystals, which have different thermal stability and are both present in the as-crystallized material. Crystallization studies after partial melting indicates that the low endotherm is associated with secondary crystals. The observed linear dependence of the melting temperature of secondary crystals with the square root of heating rate is consistent with superheating of secondary crystals. The origin of the superheating behavior is discussed in the context of conformational constraints in the residual amorphous fraction and the effect of crystallization time and molar mass on the low endotherm location.

Degree of mixing of composite material is defined and the condition of using the effective thermal diffusivity for calculating the transient thermal performance of composite material is studied. The analytical result shows that for a prescribed precision of temperature, there is a condition under which the transient temperature distribution in composite material can be calculated by using the effective thermal diffusivity. As illustration, for the composite material whose temperatures of both ends are constant, the condition is presented and the factors affecting the relative error of calculated temperature of composite materials by using effective thermal diffusivity are discussed.

The thermal lag associated with the temperature ramping experiment in a dynamic mechanical analysis is demonstrated on carbon black filled vulcanised rubber samples by using a DMTA MkIII from Rheometric Scientific. The importance of achieving thermal equilibrium on the sample before starting the measurement is emphasised. By running a combination of isothermal and ramping steps, the impact of thermal lag on the obtained dynamic mechanical properties can be estimated. For the measurement in tensile mode at a rate of heating of 2°C/min and vertical orientation of the driveshaft motion, the isothermal step applied at the sample glass transition temperature revealed that the temperature equilibration of the sample takes at least 15 min. Consequently, the storage modulus measured during the heating step is overestimated by around two times and the glass transition temperature is shifted to higher values. For the given chamber geometry, the bending mode of measurement exhibits a lower thermal lag than the tensile one. The experimental data indicate that the major factors responsible for thermal lag are heat transfer from the sample environment to the sample surface (which is given by the chamber design), sample position in the chamber and the mutual position of the sample and thermometer Pt-100. Based on the results presented, a recommendation for selecting the experimental conditions is given in order to recognise and minimise the effect of thermal lag on the data obtained by dynamic mechanical analysis.

After turning on a room heating system (e.g. central heating) a thermal transient phenomenon takes place on the wall–room system, until it reaches a final thermal equilibrium state. The temperature profiles on the wall cross-section, starting from an initial profile, corresponding to the initial thermal equilibrium state, come gradually through successive intermediate temperature profiles, to a final temperature profile corresponding to the final thermal equilibrium state. These intermediate, nonlinear and time-dependent temperature profiles characterize the wall thermal transient state and describe the dynamic thermal behaviour of the wall–room system. The mass of the air in the room is negligible, compared to the mass of the surrounding walls, so the dynamic behaviour of the room–wall system is imposed by the corresponding thermal dynamic behaviour of the walls. The influence of this thermal transient state is important for the room heating behaviour because it acts as a thermal flywheel attenuating and smoothing the room temperature variations. In the present work, using the integral method, analytical expressions yielding the temperature profiles, and the duration of the transient state as a function of thermal and structural characteristics have been developed. Conclusions were drawn on the dynamic thermal behaviour of the room–wall system. Copyright © 2000 John Wiley & Sons, Ltd.

Differential scanning calorimetry (DSC) can be used to infer the distribution of lamellar crystal thickness l. For homopolymers, the relation between melting temperature T and thickness is described by the Gibbs relation. In this case the weight distribution function of thickness g(l) ∝ P(T)(T − T)2, where P(T) is DSC power and T is the melting temperature of an infinitely thick crystal. Copolymer melting is affected by the concentration of noncrystallizable comonomer in the melt as well as lamellar thickness. Unknown melt composition in copolymers with nonequilibrium crystallinity makes determination of the correct distribution g(l) from DSC impossible. An approximate distribution g2(l) ∝ P(T)(T − T)2 is proposed, where T is based on Flory's equilibrium crystallization theory. This approximate distribution is most accurate when crystallinity is small, that is, near the upper end of the melting range. Results are reported for polyethylene homopolymer and model ethylene–butene random copolymers. Corrections were not made for distortion of the DSC endotherms by thermal lag or by melting and recrystallization; these experiments are primarily to illustrate the effect of analysis in terms of an incorrect g3(l) ∝ P(T). Average crystal thicknesses are about 20 nm for polyethylene and 5 nm for the copolymers. Distributions are characterized by lw /ln ≤ 1.1 in all cases. Width of the melting range is not a reliable indicator of the breadth of the thickness distribution. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3131–3140, 1999

Thermal force effects due to the Earth infrared radiation acting on artificial satellites can explain most of the residual orbit decay observed on high altitude satellites. In this work, we propose an improved thermal model that presents the total thermal effect as a sum of the summer-winter and the "generalized" day-night effects. We show that a unified model may take into account the sin theta' term (where theta' is the co-latitude of the thermal energy source) for the day-night force component and the cos theta' term for the summer-winter force component. These terms are associated with temperature variations on the satellite's surface due to its movement around the thermal energy source and allow the simultaneous application of these two forces resulting in a unified total thermal force that has two components: the Summer-Winter force, in the satellite spin axis direction (z), and the generalized Day-Night force, in the satellite equatorial plane (xy). We calculate the along-track accelerations for a test-satellite (parameters based on the LAGEOS satellite data) and obtain the average along-track acceleration = -3.46 x 10-13 ms-2, for the day-night effect, and = -2.85 x 10-12 ms-2, for the summer-winter effect, that leads to a residual orbit decay of nearly 1.08 mmd-1. Finally, we analyze the behavior of the average radial and along-track accelerations, and the thermal lag angle, as a function of the satellite's altitude, and show that there is a "selective law" that associates the maximum thermal effect to the radius and altitude of the satellite, and control the satellite orbit decay.