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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.

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.

The effect of Mn addition on the magnetocaloric effect (MCE) of the La0.8Ce0.1Fe11.4-xMnxSi1.6 (X= 0.0, 0.1, 0.2, 0.3) compounds was investigated. It was revealed that the transition temperatures of the compounds are sensitive to Mn composition. The temperatures are shifted from 177 to 121 K for Mn composition from 0.0 to 0.3. Moreover, thermal lag and magnetic hysteresis loss of the compounds are reduced largely due to Mn addition. A good MCE with a large and almost constant refrigerant capacity in a large temperature span over 50 K was achieved in the investigated compounds. The investigated compounds are promising magnetic entropy change materials. (C) 2009 Elsevier B.V. All rights reserved.

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.

The combustion dynamics in hybrid rockets is studied to provide a basic input into transient motor processes. The model treats the time-dependent heat e ow into the ablating fuel surface. A variable surface temperature is considered with an effective activation energy to describe the surface-temperature variation during the transient. Two time scales are observed for throttling: a short lag near the surface related to the activation energy, and the larger well-known thermal lag as a result of conductivity. The model is also applied to an oscillating surface heate ux input. Weobserved an amplie cation oftheregression-rateoscillations for low frequencies.Although thiseffect is not the cause of instability, it can aggravate existing oscillations at these low frequencies. We next formulated a quasisteady combustion model, which is then coupled with thethermal lag system with boundary-layer delaysthat account for the adjustment of the boundary layer to the changes in the freestream conditions and blowing from the surface. A linearized treatment of this coupled system evidences some low-frequency instabilities. The scaling of the oscillation frequencies and the erratic character of the experimentally observed instabilities are successfully explained.

In this study, dielectric relaxation spectroscopy experiments were carried out during heating in the α relaxation region of PET. The results for low heating rates were consistent with isothermal measurements. Moreover, the results expressed as a function of temperature were much clearer than those expressed as a function of frequency. However, the loss peaks obtained in these non-isothermal experiments showed a systematic shift on the temperature axis when the heating rate increased. A significant but nearly constant thermal lag was observed in experiments with heating at 1 K min−1 when using different equipment. It appears that isothermal data obtained in a well calibrated apparatus can be used to adjust the temperature axis of dielectric results obtained in ramp temperature experiments.

Eight European laboratories with access to five different thermogravimetric analyzers participated in this round-robin study of Avicel PH-105 cellulose pyrolysis at 5 and 40 °C/min. Agreement between the laboratories on the temperature (Tpeak) associated with the maximum rate of weight loss at 5 °C/min was good. Less agreement was obtained on the residual char yield. At 40 °C/min, the scatter associated with measurements of Tpeak and the char yield increased. Good fits to each weight loss curve were obtained by use of a kinetic model based on an irreversible, first-order reaction with a high (ca. 244 kJ/mol) apparent activation energy (E). Variations in values of E and the preexponential constant (A) are attributed to variations in thermal lag between the various instruments and at different heating rates. Kinetic parameters are presented which offer a good fit to the 5 °C/min round-robin data and which prescribe an envelope that contains the data. We recommend that future studies of biomass pyrolysis by ...

The effect of the internal thermal structure of building walls and roofs on their frequency responses, of period of 24 h, is examined. The notion of the thermal structure factors of a wall is introduced. Correlation between the fre quency dependent and structure dependent thermal characteristics is analyzed for the representative sets of building walls and roofs from ASHRAE Handbook 1989: Fundamentals. Most evident is the correlation between the decrement factor and the structure dependent time constant, between the admittance response amplitude and the appropriate thermal mass factor, and between the time lag and its estimated value, and also thickness of a wall.

The temperature at which ZrO 2− x undergoes a eutectoid transition from tetragonal (β) to tetragonal + cubic (β + γ) structure has been measured using oxidized Zircaloy-4 specimens, a pyrometer-based differential thermal analysis technique, and heating/cooling rates in the range 19–569 K/min. The transition was found to be completely reversible, showed no hysteresis and was essentially independent of heating/cooling. The overall temperature uncertainty was obtained by combining calibration, pyrometer reproducibility, thermal lag and systematic errors. A transition temperature of 1786 ± 12 K is recommended for use in Zircaloy/steam oxidation-rate correlations employed in reactor safety codes.

This paper describes the determination of the thermal diffusivity of LiKSO4 crystals using the photoacoustic phase lag method, in the 77 K to 300 K temperature interval. This method is quite simple and fast and when it is coupled to a specially designed apparatus, that includes a resonant photoacoustic cell, allows for the determination of the thermal diffusivity at low temperatures. The thermal diffusivity is an important parameter that depends on the temperature, and no values of this parameter for LiKSO4, at low temperature, have yet been reported. The LiKSO4 is a crystal with many phase transitions which can be detected via the anomalies in the variation of the thermal diffusivity as a function of the temperature.

The errors in measuring the thermal diffusivity by the plane thermal wave method are considered as a function of the thermal flux power density. The minimum values of the thermal flux power density required for measurements with a specified error and the optimum parameters of the samples and of the heat source are determined.

Apparatus for measurement of thermal diffusivity of particulate matter in the temperature range of 10–300 K is described. The basis of the measurement is modulated radial heat flow into a cylindrical sample, with a relatively small temperature gradient. Data is analyzed by Fourier transformation, and thermal diffusivity is determined from both the phase lag and amplitude ratio of the temperature at various locations along the cross section of the cylinder. This apparatus was tested with solid benzene, and found to give measurements within ±30%, in accord with the error analysis. It is especially useful for the determination of low thermal diffusivity materials, in the range of 1×10−8 to 5×10−6 m2 s−1.

International audience; Software compensation correction for thermal lag of a hot wire in the application of a constant voltage anemometer (CVA) for turbulence measurements in the boundary layer of a supersonic wind tunnel has been demonstrated. The CVA was used with a fixed compensation setting while measuring the in situ thermal lag (time constant) of the hot wire. Using the measured time constant, corrections are applied to the fixed compensation output of the CVA in postprocessing of the data. To demonstrate the flexibility of the approach it was used for two compensation settings at a test point to obtain the same results from both settings. A unique advantage of this approach is shown to be that for a given compensation setting in the CVA the bandwidth of the measurements for the test remains constant for all of the different test conditions and yields higher productivity. The results of the turbulence levels measured with this method agree with earlier research using other anemometers. Spectral plots of the mass flux and temperature and the measured in situ time constant responses under different conditions of the hot wire have been presented.

A preliminary analysis of two-phase flow in the pulsed MHD generator Pamir-3U is carried out. The two-fluid model for dusty gas flow is applied to treat the two-phase working body which consists of combustion gas and liquid particles of Al2O3. One-dimensional time-dependent calculations show that the velocity lag and the thermal lag between the two phases are large when the particle diameter is 15 μm. The lags become small when the diameter is small because the decrease of the diameter increases the momentum transfer and the heat transfer between the two phases. When the large Lorentz force develops a shock wave, the interaction between the two phases relaxes the shock wave. The increase of the particle diameter decreases the channel current and the power output because the increased diameter decreases the energy conversion from the liquid phase. © 1999 Scripta Technica, Electr Eng Jpn, 127(2): 15–23, 1999

It is well known that structural recovery in polymeric glass formers leads to the enthalpy overshoot in nonisothermal experiments. One common model for describing this phenomenon is the Tool-Narayanaswamy-Moynihan (TNM) equation. Here we apply the TNM equation to analyze a typical temperature-modulated DSC (TMDSC) trace and examine the influence of the material nonlinearities on the dynamic heat flow. We show that, in the glass-transition region, the oscillating heat-flow response to the sinusoidal temperature input is a distorted sine wave. Hence, linear analysis of the phase lag between heat flow and temperature is not physically meaningful. The degree of distortion of the sinusoidal heat flow increases as the magnitude of the excess enthalpy annealing peak increases. In addition, we perform a thermal analysis of samples having different geometries and show that an apparent phase lag can result in the measured response due to the presence of thermal gradients in the sample. The significance of the results is discussed.

The quantitative performance of differential scanning calorimeters is reviewed. Temperature calibration is discussed in terms of an isothermal correction plus a contribution from thermal lag, this can be derived from individual curves and is valid in both, heating and cooling. It is emphasised that baselines that are drawn to thermal events, such as melting and transition phenomena, must have thermodynamic significance and a general procedure is suggested. When this is used, a power compensation calorimeter calibrated for heat-capacity work can reproduce heats of fusion and transition for a diverse range of materials to better than 1%.

Very steep shallow temperature inversions occur during most of the year in the near-surface layer on the Antarctic Plateau. A radiosonde carried by a balloon rising at a few meters per second does not measure such inversions accurately because the response time of the thermistor is several seconds. To quantify this error, the authors flew a radiosonde on a tethered kite on several occasions in winter at South Pole Station immediately prior to the routine launch of the same sonde on a weather balloon. In all cases, the equilibrated temperatures measured by the tethered sonde at a given pressure level were higher than those from the balloon-borne sonde throughout most of the inversion layer. Assuming that the tethered sonde data represent the true atmospheric temperature profile, a procedure can be developed to correct the temperature data from routine radiosonde soundings for the finite response time of the thermistor. The authors devise an accurate deconvolution method to retrieve the true atmosp...

Composites based on two aluminium alloys (A536 and 6061) reinforced with 10% or 20% volume fraction of SiC particles were produced by gravity casting and a novel two-step mixing method was applied successfully to improve the wettability and distribution of the particles. The SiC particles were observed to be located predominantly in the interdendritic regions, and a thermal lag model is proposed to explain the concentration of particles. It was found that the SiC particles acted as substrates for heterogeneous nucleation of Si crystals in one of the cast composites. This observation can also be explained by the thermal lag model proposed.

A mathematical model and a computing technique are proposed for the motion, heat transfer, and combustion in the initial region of a pulverized-coal jet injected through a burner into the furnace volume. In the simulation, the dispersed phase is divided into two kinds of particles: particles that enter the region being studied from the portion of the furnace volume that is external with respect to the selected zone and the burner-jet particles. The continual approach and the assumption of equilibrium with respect to the gas phase are used to describe the motion of particles of the first kind, and the Lagrangian approach taking into account the dynamic and thermal lag of particles is used to simulate the processes in the medium of particles of the second kind. The model also describes the evolution of volatile substances and burnup of the coke residue. The results obtained using this numerical model make it possible to analyze in detail the combustion of a pulverized coal-air jet in the area near the burner. The degree of detail achieved allows one to make effective decisions for organization of an optimal jet aerodynamics to reduce nitric-oxide formation.

This paper discusses the melting behaviour and crystal structure of electrospun (polymorphous) polyamide (PA) fibres and presents the importance of the heating rate used for their study by thermal analysis. A case study of PA6, PA46 and PA69 nanofibres is performed using a Rapid Heat-Cool DSC (RHC), a fast-scanning calorimeter capable of controlled heating rates above 1000 K min−1. Thermal lag becomes significant at scan rates above 500 K min−1 and the ideal scan rate for analysis of the crystal structure depends on the PA type. Measurements at the most suitable heating rate indicate that the thermal stability of the crystals is higher for nanofibres compared to bulk material. Additionally, more stable crystals are favoured in finer nanofibres. This is especially the case for PA6 nanofibres, having an increasing fraction of stable α-crystal phase with decreasing fibre diameter, as shown by both thermal analysis and X-ray diffraction.

Shape memory alloy (SMA) actuator wires promise substantial size, weight, and potential cost advantages over their solenoid and electric motor counterparts. Designing actuators which fully realize these advantages is hampered by a limited understanding of how interactions between wires and their environment affect cyclic lifetime. For example, many devices use two SMA wires mechanically in parallel but electrically in series. This has practical advantages in simplified electrical routing and thermal lag. However, it complicates modeling in that wires interact both electrically and mechanically. Here we study the effect of a mismatch in length between two SMA wires in parallel. We perform a series of fatigue experiments to show that mismatch of up to 0.75%, at the chosen set of conditions, has no measurable effect on cycle life. We also perform a series of simulations to show how the mechanical interaction between the two parallel wires tends to suppress, rather than amplify, any impact of length mismatch.

Periodical changes of temperature in the autoclave for the purpose of automatic control are measured with the aid of an encased resistance thermometer. To minimize dynamic errors of this thermometer, two different correcting algorithms have been employed: a known single time-constant one and an algorithm proposed by the authors—two time-constant one. The verification and comparison of the two algorithms was done using a physical model of the autoclave and a real thermometer. Additionally, three methods for the determination of time constants of the second order model were compared and factors influencing the algorithms accuracy, including time constants and sampling time, were analysed. The presented methods make possible to increase both the bandwidth of dynamical temperature measurements and its precision with relatively limited increase in computational complexity of the correction algorithm.

An experimental characterization is presented of the thermo-mechanical response of honeycombs and corrugations made of a NiTi shape memory alloy (SMA). Of particular interest are the shape memory cycle, the superelastic response, the shape memory thermal lag and the superelastic rate sensitivity. A series of in-plane compression experiments are presented on fabricated honeycombs and their responses are compared to typical monolithic SMAs, such as NiTi wire. Given local material strain limits, NiTi honeycombs exhibit an order of magnitude increase in recoverable deformation, both in the shape memory effect and superelastic effect. This comes at the cost of a reduced load carrying capacity by two orders of magnitude and a reduced (homogenized) compressive stiffness by four orders of magnitude. Due to their sparse structure and enhanced heat transfer characteristics, SMA honeycombs exhibit less superelastic rate sensitivity by two orders of magnitude while having similar thermal lag to SMA wire. The implications of these scaling results are discussed, including possible new regimes of application of SMAs for reusable energy absorption devices and high stroke actuators.

On August 5, 2012, the Mars Science Laboratory (MSL) historically entered the Martian atmosphere and safely landed on Mars. This is the first time that a heat shield made primarily of Phenolic Impregrated Carbon Ablator (PICA) was used for Martian entry, therefore scientists can learn a great deal from this mission. In order to understand the conditions experienced by the MSL during entry, the heat shield was equipped with seven plugs containing thermocouples and an isotherm following sensor. After a significant amount of testing, thermal lag within the sensors has become of interest. In order to better understand real time conditions during Martian entry, this thermal lag must be quantified. The contents of this paper discuss methods and results of the three dimensional Finite Element Analysis research that has been conducted to determine the thermal lag in the sensors in the heat shield of the Mars Science Laboratory.

Results from a numerical model for endothermic biomass pyrolysis, which includes both high activation energy kinetics and heat transfer across a boundary layer to the reacting solid particle, are presented. The model accounts for conventional thermocouple thermal lag and unconventional thermal lag due to heat demand by the chemical reaction (which is governed by Arrhenius kinetics). Biomass fusion, first identified quantitatively by Lede and Villermaux, is shown to be a manifestation of severe thermal lag that results from the chemical reaction heat demand. Over the wide range of conditions studied, the true substrate temperature remains almost constant during pyrolysis, as is the case with compounds undergoing fusion or sublimation at constant pressure. A simple algebraic model, whose derivation presupposes the idea that biomass pyrolysis mimics the melting of a block of ice, accurately predicts the maximum value of thermal lag during pyrolysis. Unidentified thermal lag in TGA experiments lowers the valu...

A time-dependent model of temperature in magnetization and demagnetization processes is developed based on thermodynamic and heat transfer laws, material properties, and variable-field magnet parameters. Test results of a magnetic refrigeration test bed are compared with the model calculation. The model can be used to simulate optimum operating conditions and duty cycle of magnetic regenerative refrigeration. The effects of the thermal conductivity between the magnetocaloric material and the thermocouple on temperature measurements and thermal lag are presented.

Aims A simple and easy optical method is proposed for the determination of glass transition temperature (Tg) of polymers. Methods & Results Tg was determined using the technique of microsphere imaging to monitor the variation of the refractive index of polymer microsphere as a function of temperature. It was demonstrated that the method can eliminate most thermal lag and has sensitivity about six fold higher than the conventional method in Tg determination. So the determined Tg is more accurate and varies less with cooling/heating rate than that obtained by conventional methods. The most attractive character of the method is that it can simultaneously determine the Tg of several polymers in a single experiment, so it can greatly save experimental time and heating energy. Conclusion The method is not only applicable for polymer microspheres, but also for the materials with arbitrary shapes. Therefore, it is expected to be broadly applied to different fundamental researches and practical applications of polymers.

The activation energies, Ea’s, for CoSi and CoSi2 formation were determined using in situ resistance measurements during rapid thermal annealing. Co films were evaporated on undoped polycrystalline Si (poly‐Si) and single‐crystal Si on sapphire (SOS) substrates. The resistance was monitored for heating rates from 1 to 60 °C/s up to 900 °C. There was significant thermal lag between the samples and thermocouple embedded in the susceptor wafer for heating rates greater than 20 °C/s. The thermal lag was quantified by melting Au‐Si, Al‐Si, and Ag‐Si eutectics, and shown to be consistent with finite element modeling. The Ea’s determined from Kissinger plots for heating rates ≤20 °C/s were 2.09±0.11 and 2.03±0.08 eV for CoSi formation and 2.91±0.22 and 2.81±0.23 eV for CoSi2 formation, for Co/poly‐Si and Co/SOS samples, respectively.

In the thermal shock test by means of a heated ceramic disk specimen with constant heat flux, temperature distributions in the specimen and time to fracture can be easily measured. Therefore, thermal stress in the ceramics can be estimated without measuring the heat transfer coefficient whose measurement is needed in case of water quenching test. On the other hand, the temperature dependence of thermal properties of material substantially affects the temperature distribution and thermal stress history. In this paper, numerical calculations of non-steady-state temperature distribution in thin disk, which was heated from outside with constant heat flux, were conducted to estimate the generated thermal stress. Temperature dependence of thermal conductivity and thermal diffusivity was assumed to be exponential functions. Time-dependent thermal stress was expressed with the correlative equations containing coefficients of temperature dependence of thermal properties, the supplied heat flux and Fourier's number. The last factor was a nondimensional parameter with specimen size and time. Based on the proposed equations, the effect of temperature dependence of thermal properties on thermal stress and the suitable experimental conditions in above-mentioned thermal shock test were discussed.

Submitted by Simone Maisonave (simonemaisonave@hotmail.com) on 2020-05-05T18:59:32Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Liader da Silva Oliveira_Dissertacao.pdf: 7187065 bytes, checksum: 5d6c8085a47581bfcc72da1e69278cfd (MD5) Approved for entry into archive by Aline Batista (alinehb.ufpel@gmail.com) on 2020-05-06T02:47:21Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Liader da Silva Oliveira_Dissertacao.pdf: 7187065 bytes, checksum: 5d6c8085a47581bfcc72da1e69278cfd (MD5) Made available in DSpace on 2020-05-06T02:47:21Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Liader da Silva Oliveira_Dissertacao.pdf: 7187065 bytes, checksum: 5d6c8085a47581bfcc72da1e69278cfd (MD5) Previous issue date: 2012-09-11 O presente trabalho teve por objetivo fazer uma análise dos valores recomendados pela NBR 15220 – parte 3, para habitações de interesse social, e considerados como limites de transmitância térmica, atraso térmico e fator de calor solar, tanto para fechamentos verticais quanto horizontais, para a zona bioclimática 2 brasileira. Para isto, primeiramente definiu-se as características construtivas da habitação a ser simulada no trabalho, de forma a que atendesse às especificações mínimas propostas pelo programa Minha Casa Minha Vida. Os fechamentos opacos, paredes e cobertura, do caso-base, foram definidos a partir dos limites das propriedades térmicas indicadas pela NBR 15220-3, para a zona bioclimática 2. Os resultados obtidos com o caso-base estabeleceram os referenciais de conforto térmico e de eficiência energética, com os quais as diversas configurações de envelope simuladas posteriormente foram comparadas, e possibilitaram verificar a pertinência das recomendações estabelecidas na norma. A análise dos resultados indicou que não se justificam os limites estabelecidos pela NBR 15220-3 para as variáveis de atraso térmico e fator de calor solar, quando avaliados pelos índices de conforto térmico obtidos com as simulações. Foi possível verificar que, tanto o aumento do atraso térmico quanto da absortância solar são benéficos para o conforto térmico no interior da edificação ao longo do ano na zona bioclimática 2, onde predominam as situações de desconforto no inverno. The present study aimed to analyze the values recommended by the NBR 15220 - part 3 and considered as limits of thermal transmittance, thermal lag factor and solar heat for both vertical and horizontal components to the bioclimatic zone 2 brazilian. So, at the first moment the construction characteristics of the housing to be simulated in this work were definid, so that they would meet the minimum specifications proposed by the Minha Casa Minha Vida Federal Government Program. The opaque closures walls and roof, of the base case, were defined from the limits set by the thermal properties of NBR 15220-3, for bioclimatic zone 2. The results obtained with the simulation of base case established thermal comfort and energy efficiency, with which various configurations of the envelope were simulated and subsequently compared, making possible to verify the relevance of the recommendations set forth in the standard. The results indicated that the limits established by NBR 15220-3 are not justified for thermal lag factor and solar heat variables, when evaluated by thermal comfort indices obtained by simulation. It was possible to verify that both the thermal lag as the solar absorptance increasing are beneficial for the indoor thermal comfort over the years climatic zone 2, where the situations of discomfort in winter are predominant.