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The air conditioning system in low-energy buildings should be high-efficient because of its limitation on energy consumption and requirement for thermal comfort. This study proposed a novel modularity radiant terminal which can be moved freely in the vertical direction. A series of field experiments on the optimal design scheme of modularity radiant heating terminal was conducted in a laboratory in hot summer and cold winter region of China. Indoor thermal performance with different installation position and area of modularity radiant heating panel were investigated. Results indicated that the modularity radiant heating system can maintain a comfortable indoor environment which the operative temperature can reach 21 °C, the vertical temperature difference below 3 °C and the radiation asymmetry below 4 °C. The design scheme of the modularity radiant heating has significant effects on indoor thermal environment, in which the installation position was a key factor. The modularity radiant panel installed in the middle of the wall and close to the floor can effectively improve the response lag of indoor thermal environment in the operation period and reduce the heat attenuation speed in the shutdown period. The response time of operative temperature at the start period can be reduced for more than 1.5 h and the thermal lag can be increased for more than 2 h at the shutdown period. Besides, the operative temperature can be increased by 1.5 K and the vertical temperature difference and the radiation asymmetry can be reduced by approximately 1 K, respectively. The optimal design of modularity radiant system can simultaneously further improve thermal comfort and realize energy consumption for low energy buildings.

Accelerating rate calorimetry (ARC) is a common tool used in thermal stability evaluation of hazardous materials to provide self-heat rate and pressure data that are used to model the kinetics of a...

The resonance of thermal lags of solid fuel with heat transfer oscillations in a boundary layer flow is the primary cause of low-frequency instability initiation in hybrid rocket combustion. A detailed study of two cases was conducted experimentally to investigate how the boundary layer is disturbed and leads to low-frequency instability (LFI); combustion with swirl injection and combustion with the frequency jump. The fluctuating boundary layer was successfully captured by visualizing images and proper orthogonal decomposition analysis was performed. The results show that swirl injection with an appropriate intensity substantially reduces the amplitudes of high frequency p’, and no boundary layer perturbation is found in the spectral analysis of mode 2, and Rayleigh index amplifications disappear. While the frequency jump occurs, the coupling status between p’ and q’ became weakly positive and the driving force disturbing the upstream flow was not made. As a result, oscillatory heat transfer was difficult to occur. Therefore, the appearance of boundary layer perturbation is the necessary precondition for the initiation of the low-frequency instability. And the resonance with the thermal lag characteristic leads to the occurrence of LFI.

Profiles observed by Sea-Wing underwater gliders are widely applied in scientific research. However, the quality control (QC) of these data has received little attention. The mismatch between the temperature probe and conductivity cell response times generates erroneous salinities, especially across a strong thermocline. A sensor drift may occur owing to biofouling and biocide leakage into the conductivity cell when a glider has operated for several months. It is therefore critical to design a mature real-time QC procedure and develop a toolbox for the QC of Sea-Wing glider data. On the basis of temperature and salinity profiles observed by several Sea-Wing gliders each installed with a Sea-Bird Glider Payload CTD sensor, a real-time QC method including a thermal lag correction, Argo-equivalent real-time QC tests, and a simple post-processing procedure is proposed. The method can also be adopted for Petrel gliders.

The synthesis time for CON-type aluminoborosilicate zeolite ([Al, B]-CON), a promising catalyst for methanol-to-olefin reactions, was reduced from 20 h to 45 min, the fastest reported so far for this zeolite. In addition to overcoming thermal lag by the use of tubular reactors at high temperatures, optimizing the reactant composition, choosing proper seed crystals, their quantity, size, and timing of addition were also instrumental in the fast-paced synthesis of [Al, B]-CON. It was found that obtaining a pure CON phase at a faster rate depends not only on the synthesis temperature, but also on the ageing temperature, amount of seed, and their partial dissolution. The fast synthesis of [Al, B]-CON could be an option for mass production using a demonstrated continuous flow synthesis system. The catalytic activity and stability of the fast-synthesized [Al, B]-CON was improved by the introduction of mesopores via alkaline treatment with amphiphilic molecules.

This paper describes the thermal lag correction for Glider Payload Conductivity Temperature Depth Profiler data with a poor sampling rate. In particular, the thermal lag correction is more vulnerable to the influence of temperature data. According to variations in salinity with depth and the vertical downcast speed of the glider, salinity data are divided into five parts, and a method based on Morison et al. is proposed to determine the correction parameters. At 40–94 dbar and 140–280 dbar, the salinity difference is dominated by the temperature difference. At 94–140 dbar, the salinity difference is immune to the temperature difference and has a greater influence on the thermal lag-induced salinity error correction. After the sectional correction, the accuracy of the typical salinity interval is upgraded from 0.011 to 0.006 psu, which shows the effectiveness of this sectional method on correcting temperature difference.

In this work, a commercially available laser flash analysis (LFA) device is used for in situ precipitation monitoring in aluminium alloys by following thermal diffusivity for the first time. The LFA measurement methods and data processing are adapted to allow continuous heating experiments over a wide range of heating rates (0.001–1 K s−1). Methods for LFA temperature calibration and thermal lag correction are suggested. Results of continuous heating of Al Mn0.5Mg0.5 aluminium alloy from the as-cast state are compared to in situ differential scanning calorimetry (DSC) and ex situ transmission electron microscopy. It is shown comparing in situ LFA, and DSC substantially improves the interpretation of superimposed reactions, in particular, the precipitation and dissolution of Mn-containing dispersoids and Mg–Si-containing secondary particles.

Parabolic quantum wells have unique properties that make them attractive for certain applications. However, growing them with molecular beam epitaxy is much more difficult than growing standard rectangular wells, as parabolic wells require a smooth, precise variation of the composition during growth. Typically, such composition variations have been approximated using the digital alloy technique, but there are limits on the quality of wells that can be produced this way. In our approach, we instead create a smooth parabolic potential in Al x Ga 1 - x As by varying the Al cell flux as a function of time. To compensate for thermal lag in the effusion cell, we develop a simple linear dynamical model, which can be inverted to find the temperature input required for a desired composition profile. With this approach, the composition in a 3 THz Al x Ga 1 - x As parabolic quantum well can be controlled to a root-mean-squared error of 0.4% Al. This approach can be easily generalized to other structures, and, importantly, can be used at typical growth rates ( 1.5 - 2.5 A / s ), which allows for the growth of parabolic well arrays.

A series of experimental tests was conducted to investigate the effect of swirl injection on the combustion instability in hybrid rocket using combustion visualization technique. As a result, swirl injection seems to modify two main physical processes responsible for the initiation of LFI. First one is the transition of coupling status between two fluctuations of combustion pressure (p') and heat release (q') of 500 Hz band. The transition of p' and q' to negative coupling seems to be a crucial modification for stabilizing the combustion. Another noticeable effect of swirl injection is the gradual increase in the peak frequency of pressure oscillation from its initial value of around 20 Hz–50 Hz band, which is caused by the thermal lag, as the swirl intensity increases. Also, POD (Proper Orthogonal Decomposition) analysis was done to understand flow response to the swirl injection near the fuel surface. The analysis of temporal behavior of mode 1 and 2 suggested that the swirl injection with proper intensity not only suppress the generation of p' of 500 Hz band but induces a shift of low frequency peaks of 20 Hz band by adjusting the turbulent structures in boundary layer. And the shift of low frequency peaks seems to be another contributing factor for combustion stabilization.

This paper reports experimental and numerical thermal isolation techniques for Fibre Bragg Grating (FBG) sensors used for cure monitoring of thermoset matrix composites. The FBG sensor readings are mostly affected by both thermal and mechanical effects therefore; these properties should be isolated from one another. An experimental method was applied to evaluate three different capillary tubes that can be used as isolation material for an FBG sensor. A numerical modelling approach has been developed to model heat transfer through these capillary tubes so that the material selection and geometries can be understood accurately. The results from encapsulating FBGs in glass capillary tubes showed almost no sensitivity to changes in heating rates as compared to two types of stainless-steel tubes. The FBG sensors encased in glass capillary tube produced least thermal lag and forces as compared to FBGs encased in stainless-steel capillary tubes. This indicates that glass capillary tube has less thermal effects on the FBG material than stainless-steel tubes. The isolated sensors had reliably detected the residual compressive strains induced during an actual composite cure cycle. The experimental curves show very good agreement with modelling results, with model over predicting experiments by approximately 5%.

In this study we analyzed the dose response of natLiF:Mg,Cu,P (MCP-N) detectors in two different TLD readers (Harshaw 5500 and Toledo 654 Vinten) at 7 dose levels, ranging from 0.5 mGy to 5 Gy, for different heating rates (2 °C/s, 5 °C/s, 10 °C/s and 15 °C/s) and using 2 protocols: one without pre-heating and a maximum reading temperature of 255 °C and one including external pre-heating before the readout for 20 min at 100 °C and maximum temperature of 230 °C. The results show a supralinear behavior for Harshaw 5500 reader at high doses which is more pronounced for the fast heating rates. For the 15 °C/s heating rate, the supralinearity starts at 2 Gy for the protocol without pre-heating and at 0.5 Gy for the protocol with pre-heating reaching up to linearity indices of respectively 1.42 ± 0.05 and 1.67 ± 0.05 at 5 Gy. The 2 °C/s heating rate does not show supralinearity up till 5 Gy. The Toledo 654 Vinten reader shows no supralinear behavior. The shape of the glow curves is different between readers and reading protocols while the glow curve peaks shift towards higher temperatures for increasing heating rates due to thermal lag effects. This study demonstrates the different behaviors of TLD readers, for different heating rates and two types of protocols with an important concern for a Harshaw reader.

The present experimental work attempts to sustain the thermal response of the double-pass solar air heater system (DPSAHS) by the thermal lag of phase change material (PCM). At the same time, this analysis investigates the role of metallic macro-encapsulation on the heat storage and recovery from PCM integrated inside the DPASHS. The objectives are to investigate the influence of the geometry of encapsulation used for storage and to examine whether the discrete units allow faster charging and discharging of organic paraffin wax (PCM). In this work, an average encapsulate efficiency of 47.2% and 67% was obtained respectively for rectangular and cylindrical macro-encapsulates equipped DPSAHS. A performance comparison of DPSAHS with and without storage was presented. An overall cost analysis shows that with a small margin in constructional cost, operational time of DPSAHS was improved. The cost of heating 1 kg of hot air was 0.0074$. The overall work aims to support marginal and subsistent farmers to deal with improper drying during winter on which the potential sunshine hours are limited to 7 h/day at Calicut (11o32 ' N, 75o93 ' E) located in peninsular India.

In recent years, rock surface dating has seen the emergence of a technique based on optically stimulated luminescence (OSL). This application translates the depth of OSL signal bleaching within a rock surface into an exposure age or erosion rate at 1-104 a timescales. Considerable effort has been undertaken to improve our understanding of OSL rock surface dating, yet a large amount of uncertainty associated with the method remains. Specifically, OSL profiles measured into rock surfaces can be highly scattered. Potential causes of this scatter could be lithological heterogeneity that modify bleaching rate throughout the rock, variability in surface erosion or experimental artefacts. Here, we report experiments that were conducted to explore whether experimental artefacts could contribute to the scatter in OSL profiles measured from rock surfaces exposed in Zermatt, Switzerland. This was done by varying the following parameters: (i) heating rate, (ii) isothermal holding time, (iii) luminescence signal detection filters, (iv) the sequential order of optical stimulations, and (v) core diameter. Our results indicate that sample temperature, for both preheating and stimulation, may exert a strong influence on the OSL profiles obtained. Thermal lag, i.e. the temporal offset between sample temperature and the instrument temperature, can be significant for rock slices if a heating rate of 5 °C s−1 is used and if rock slices are placed directly on the instrument carousel. To reduce this effect, our results suggest future studies place samples in metal cups, reduce the heating rate and increase preheating and holding times prior to optical stimulation, to allow samples to heat at the desired rate and reach the required temperatures.

Aims. The aim of this work is to investigate the parameters influencing the generation of the inner comae of a comet with a spherical nucleus and to model the gas activity distribution around its nuclei. Here, we investigate the influence of thermal conductivity combined with sub-surface H2O and CO2-ice sources on insolation-driven sublimation and the resulting gas flow field. In the process, we adopted some of the rotational and surface properties of the target of the Rosetta mission, comet 67P/Churyumov-Gerasimenko (67P/CG). Methods. We used a simplified model of heat transport through the surface layer to establish sublimation rates from a H2O- and CO2-ice sub-surface into a vacuum. We then applied the 3D Direct Simulation Monte Carlo method to model the coma as a sublimation-driven flow. The free parameters of the model were used to test the range of effects arising from thermal inertia and the depth of the source on the gas outflow. Results. Thermal inertia and the depth of the sublimation front can have a strong effect on the emission distribution of the flow at the surface. In models with a thermal inertia up to 80 TIU (thermal inertia units: J m−2 K−1 s−1∕2), the H2O distribution can be rotated about the rotation axis by about 20° relative to models with no thermal lag. For CO2, the maximum activity can be shifted towards the sunset terminator with activity going far into the nightside for cases with low thermal diffusivity. The presence of a small amount of CO2 can reduce the presence of H2O by at least an order of magnitude on the nightside by blocking H2O flow. In addition, CO2 can also decrease the speed of the mixed flow in the same region up to 200 m s−1, compared to cases with no CO2 activity. Conclusions. Even low values of the thermal inertia can substantially modify the gas flow field. Including CO2 leads to strong variations in the local CO2/H2O density ratio between the dayside and nightside. CO2 can dominate the gas composition above the nightside and can also act to modify the H2O flow field close to the terminator.

Accurate prediction of building indoor temperatures and thermal demand is of great help to control and optimize the energy performance of a building. However, building thermal inertia and lag lead to complex nonlinear systems is difficult to model. In this context, the application of artificial neural networks (ANNs) in buildings has grown considerably in recent years. The aim of this work is to study the thermal inertia of a building by developing an innovative methodology using multi-layered perceptron (MLP) and long short-term memory (LSTM) neural networks. This approach was applied to a public library building located in the north of Spain. A comparison between the prediction errors according to the number of time lags introduced in the models has been carried out. Moreover, the accuracy of the models was measured using the CV(RMSE) as advised by AHSRAE. The main novelty of this work lies in the analysis of the building inertia, through machine learning algorithms, observing the information provided by the input of time lags in the models. The results of the study prove that the best models are those that consider the thermal lag. Errors below 15% for thermal demand and below 2% for indoor temperatures were achieved with the proposed methodology. Ministerio de Ciencia, Innovación y Universidades | Ref. RTI2018-096296-B-C21

Influence of added thermal resistance on crystallization kinetics, as measured by differential scanning calorimetry (DSC), of the Se70Te30 glass was studied. The increase of thermal resistance was achieved by adding polytetrafluorethylene discs of different thicknesses (up to 0.5 mm) in-between the DSC platform and the pan with sample. Increase of the thermal resistance led to an apparent decrease (by more than 30%) in the crystallization enthalpy. Significant change of model-free kinetics occurred: apparent activation energy E of the crystallization process decreased (by more than 20%) due to the DSC data being progressively shifted to higher temperatures with increasing heating rate. The model-based kinetics was changed only slightly; the DSC peaks retained their asymmetry and the choice of the appropriate model was not influenced by the added thermal resistance. The temperature shift caused by added thermal lag was modeled for the low-to-moderate heating rates. Czech Science Foundation 17-11753S Ministerio de Economía y Competitividad CTQ2017-83602-C2

The climatic conditions characterizing the troposphere affect the outdoor activities of the population which, in turn, characterize the anthroposphere. Over the past years recent studies examined a possible analytical definition of the outdoor thermal comfort for different types of population acclimatized to their specific residency area. Thanks to the use of the MOCI (Mediterranean Outdoor Comfort Index: an index used to predict the thermal perception of the Mediterranean population in an outdoor environment), the present study aimed at analyzing the psychophysiological response of a Mediterranean subject with respect to climatic conditions different from the original ones after having experienced a quick change. Indeed, thermal stress and discomfort might affect deeply the ability of the subject to carry out outdoor activities. This condition determines the necessity of possessing useful information to plan the best period to perform a journey in distant places and/or perform useful actions that will make the outdoor activity as much comforting as possible (choosing the proper clothes with the right thermal insulation). For this reason, the worldwide environmental conditions during an average year were examined. To be more specific, this study focused its attention on the editing of seasonal spatial maps with the MOCI level curves and on the temporal analysis of the MOCI values characterizing those 6 different cities (one for each continent) reporting the higher number of foreign arrivals.

Purpose The purpose of this paper is to frame a dual-phase-lag model using the fractional theory of thermoelasticity with relaxation time. The generalized Fourier law of heat conduction based upon Tzou model that includes temperature gradient, the thermal displacement and two different translations of heat flux vector and temperature gradient has been used to formulate the heat conduction model. The microstructural interactions and corresponding thermal changes have been studied due to the involvement of relaxation time and delay time translations. This results in achieving the finite speed of thermal wave. Classical coupled and generalized thermoelasticity theories are recovered by considering the various special cases for different order of fractional derivatives and two different translations under consideration. Design/methodology/approach The work presented in this manuscript proposes a dual-phase-lag mathematical model of a thick circular plate in a finite cylindrical domain subjected to axis-symmetric heat flux. The model has been designed in the context of fractional thermoelasticity by considering two successive terms in Taylor’s series expansion of fractional Fourier law of heat conduction in the two different translations of heat flux vector and temperature gradient. The analytical results have been obtained in Laplace transform domain by transforming the original problem into eigenvalue problem using Hankel and Laplace transforms. The numerical inversions of Laplace transforms have been achieved using the Gaver−Stehfast algorithm, and convergence criterion has been discussed. For illustrative purpose, the dual-phase-lag model proposed in this manuscript has been applied to a periodically varying heat source. The numerical results have been depicted graphically and compared with classical, fractional and generalized thermoelasticity for various fractional orders under consideration. Findings The microstructural interactions and corresponding thermal changes have been studied due to the involvement of relaxation time and delay time translations. This results in achieving the finite speed of thermal wave. Classical coupled and generalized thermoelasticity theories are recovered by considering the various special cases for different order of fractional derivatives and two different translations under consideration. This model has been applied to study the thermal effects in a thick circular plate subjected to a periodically varying heat source. Practical implications A dual-phase-lag model can effectively be incorporated to study the transient heat conduction problems for an exponentially decaying pulse boundary heat flux and/or for a short-pulse boundary heat flux in long solid tubes and cylinders. This model is also applicable to study the various effects of the thermal lag ratio and the shift time. These dual-phase-lag models are also practically applicable in the problems of modeling of nanoscale heat transport problems of semiconductor devices and accordingly semiconductors can be classified as per their ability of heat conduction. Originality/value To the authors’ knowledge, no one has discussed fractional thermoelastic dual-phase-lag problem associated with relaxation time in a finite cylindrical domain for a thick circular plate subjected to an axis-symmetric heat source. This is the latest and novel contribution to the field of thermal mechanics.

In this paper, neural network and genetic algorithm is used to obtain the optimal output power of thermal lag Stirling engine. A neural network is trained and developed using the theoretical data of previous literatures in order to predict the performance of Stirling engine. Input parameters to neural network include angular velocity, thermal resistance, stroke length radius, piston diameter, the volume of heat buffer chamber and the volume of gas chamber, and output parameter includes output power. The accuracy of neural network is evaluated by average square error and regression analysis. Also, genetic algorithm is used for the optimization of the output power of the Stirling engine. The results of present study show that the neural network can be used as an appreciate tool to predict the output power of the thermal lag Stirling engine with a high precision and speed. The main deficiency of thermal lag type of Stirling engines is low output power. However, the optimization of design parameters of thermal lag Stirling engine causes an increase of 86.9% in output power.

Green Roofs (GR) represent a sustainable technological solution for reducing the environmental footprint of urban areas. Despite their benefits, traditional GRs have been criticized regarding their economic feasibility, suggesting to develop advanced hybrid engineering solutions able to simultaneously maximize their hydrological and energetic benefits. In this view, there is a need of numerical models able to describe their complete hygrothermal behavior. Thus, the main aim of this study was to assess the suitability of the one-dimensional mechanistic model HYDRUS-1D in providing an accurate and comprehensive description of the coupled water-heat-vapor transport in a field-scale Non-Vegetated Green Roof (NVGR) in the south of Italy. A complete calibration framework, which encompassed the Particle Swarm Optimization (PSO) algorithm and the combined Global Sensitivity Analysis-Generalized Likelihood Uncertainty Estimation (GSA-GLUE) method, was used to estimate the substrate thermal properties and assess the model predictive uncertainty. The calibrated model was exploited to examine the cooling efficiency of a combined Stormwater Reuse-NVGR system in the warm season. The analysis revealed that deeper substrates are positively correlated with thermal lag and attenuation, and that the irrigation can be properly designed to trigger the evaporative and convective cooling of the NVGR. The Response Surface methodology was finally used to optimize the watering regime on an 8 cm-deep NVGR. The exploitation of the evaporative cooling effect of the NVGR by means of a model-based irrigation optimization led to a reduction of the average soil bottom temperature of 4 °C. The coupled system was able to maximize the energetic benefits of GR.

The thickness of the slabs is imperative when considering the method of heating system due to the thermal mass and thermal lag properties. Thermal properties of concrete allow thermal energy to be stored in the mass floor after heating cycles. In this study, the experimental heating performance of a 1.22 m-thick mass concrete radiant floor and a 0.18 m-thick concrete floor is investigated. In addition, a full 3D finite element model of the mass concrete radiant floor is performed and validated by the full-scale building measurements. The mass floor simulation contains embedded pipes, vertical steel anchors, and horizontal reinforcing steel grids at the top and bottom. The experimental results show that the initial temperature of the thick concrete slab is increased by a few cycles and the mass heated concrete floor acts as a thermal storage battery for the building. Also, the modeling results are in good agreement with construction site measurement. This model is further expanded to simulate different thermal loadings on the pipes to predict the temperature development inside of the mass floor. Furthermore, importance of the vertical steel anchors in conduction the generated heat to the surface of the floor would be seen in the modeling results.

In recent years there have been considerable improvements in the energy and environmental performance of buildings, due not only to the creation of building envelopes with a low level of thermal transmittance but also to the use of natural (“green”) materials. Construction systems combining a wooden framework with eco-compatible materials represent solutions for a building envelope, which prove effective in reducing both energy needs and the discharge of polluting substances. The principal aim of the present research is to investigate the use of natural waste materials from farm products in the creation of building envelopes. The system described here proposes the use of compressed straw to obtain a layer of insulating material, that may be combined with the use of a wooden shell known as platform frame. The thermo-physical characteristics, energy performance as well as the hygrometric features of the proposed system were tested in various sites. As regard the formation of condensation, the thermo-hygrometric analysis proved the absence of such threat over a period of a whole year in all the different climates observed. A comparison with a similar XLAM system evidenced that the platform frame system lined internally with compressed straw offers a 12% reduction in U thermal transmittance, a 22% improvement in YIE periodic thermal transmittance, and a comparable thermal lag. Moreover, the platform frame system filled with compressed straw allows a cost reduction by 38% compared to the XLAM system. On the whole, the outcomes obtained indicate that the platform frame system with compressed straw offers a suitable alternative to the XLAM system, above all in the case of buildings of two or three stories.

The thermal and hydrodynamic response of a Sea-Bird unpumped CTD SBE 41, is numerically modeled to assess the biases occurring at the slow flushing rates typical of glider operations. Based on symmetry considerations, the sensor response is approximated by coupling the incompressible Navier-Stokes and the thermal advection-diffusion equations in two dimensions. Numerical results illustrate three regimes in the thermal response of the SBE 41 sensor, when crossing water layers with different thermal signatures. A linear decay in time of the bulk temperature of the conductivity cell is initially found. This is induced by the transit of the inflow through the conductivity cell in the form of a relatively narrow jet. Water masses with new thermal signatures do not immediately fill the sensor chambers, where the cross-section widens. Thermal equilibrium of these water masses is then achieved, in a second regime, via a cross-flow thermal diffusion between the boundary of the jet and the walls. Consequently, the evolution of the bulk temperature scales with the square root of time. In a third regime, the evolution of the bulk temperature depends on the thermal gradient between the fluid and the coating material. This results on an exponential decay of the bulk temperature with time. A comprehensive analytical model of the time evolution of the bulk temperature inside a cell is proposed based on these results.

Kinetics of “melting” of sucrose crystals has been examined by conventional differential scanning calorimetry (DSC) and fast-scan calorimetry in terms of the possibility of a clear distinction between physical melting and chemical decomposition processes by fast scan up to 10 000 K s–1. On the basis of a modeling of the crystal melting kinetics with superheating and the possible influence of thermal lag, the heating rate dependence of “melting” was carefully examined. The equilibrium melting point TM of sucrose crystals at a zero heating rate was estimated to be TM = 188.9 ± 1.2 °C by fast-scan calorimetry, and the heat of fusion of 46 kJ mol–1 was determined by conventional DSC, which is in agreement with the reported values in the literature. The Kissinger plot of the peak temperatures by heating runs and the plot of characteristic times of isothermal runs against the inverse of absolute temperature suggested a kinetic diagram, in which the “melting” behaviors above and below TM are qualitatively differ...

This study was conducted to examine if the new temperature modulated optical refractometry (TMOR) method is applicable to study the phase behavior of alkyl-based components. n-Hexadecane, palmitic acid, and glycerol tripalmitate were used as model components. TMOR was benchmarked against differential scanning calorimetry (DSC) and polarized light microscopy (PLM). For all substances, a good agreement of the DSC data with TMOR was found. For n-hexadecane, a difference of 2.2 °C for the crystallization and 2.6 °C for the melting temperature was found. Considering palmitic acid, the crystallization temperature differed by 3.3 °C while the melting varied by 2.8 °C. The crystallization temperature of tripalmitate identified by TMOR was 2.7 °C higher, and the melting temperature 2.3 °C was lower compared to the DSC. The crystallization temperature for TMOR was always higher, and the melting temperature was always lower if related to DSC. This leads to the conclusion that TMOR is more accurate and direct. In addition, the transition peaks identified by TMOR were narrower compared to the DSC peaks. This is due to slower heating and cooling rates leading to a smaller temperature range of phase transition and less thermal lag. The study showed that TMOR is an appropriate method to determine the phase transition temperatures for the three examined substances. The results were comparable to the DSC data in both melting and crystallization behavior. Since the accuracy of TMOR is better at lower heating and cooling rates, it could be a reasonable extension of the well-known DSC method in the studies of melting and crystallization.

The effect of crystallization temperature and time on the melting of a stereo-copolymer of l -lactic acid has been measured using differential scanning calorimetry and hot stage microscopy. The temperature of the last trace of crystallinity increased with time and temperature. Increasing the heating rate to 50 °C min−1 and correcting for thermal lag enabled the m.pt of the as-crystallized material to be determined without premature melting and recrystallization of the sample on heating. The measured melting points enabled the equilibrium m.pt. of the copolymer to be determined as 205 ± 2 °C. Changes due to lamellae thickening occurred by secondary crystallization from the initial onset of crystallization increasing with increasing temperature consistent with the process being diffusion controlled The addition of small chain segments emerging from the top lamellar surface occurred by reptation and growth increased with the square root of the lapsed time. This is consistent with the process of secondary crystallization.

By thermogravimetric (TG) experiments under 5 oxygen concentrations of 21.0, 40.0, 50.0, 60.0, 80.0% and 5 heating rates of 20.0, 30.0, 40.0, 50.0, 60.0 ℃/min, the combustion characteristics of jet coal and influences of oxygen concentrations and heating rates on them were investigated. Results show that the pyrolysis processes of jet coals consist of 3 segments of water evaporation, structure oxidation and mass-gaining, self-ignition and induced combustion and carbonization that lie in temperature ranges of 65.0~150.0 ℃, 150.0~290.0 ℃ and 290.0~650.0 ℃, respectively. Huainan jet coal samples burn more easily as universal ignition index increases. At constant heating rate, self-ignition temperature tends to decrease by 10.1~19.4 % with increasing oxygen concentration from 21.0 % to 80.0 %. However, the variation trend of oxidation process includes a slight rise when variation trend begins to fall. At constant oxygen concentration, the self-ignition temperature transformes into high temperature direction and lead to thermal lag effect. Values of Coal-oxidation time at various oxygen concentration levels decreased by 63.1~65.8 % at heating rates from 20.0 to 60.0 ℃/min. Accordingly, the coal-oxidation process is accelerated. A new index (R S ) named coal-oxidation difficulty level index to evaluate the lag effect of coal-oxidation process was proposed. Fitting results of three dimensionless parameters confirmed that the risk of spontaneous combustion determined by the coal-oxidation process still remains growing up although self-ignition temperature produces thermal lags with increasing heating rates.

The influence of the accuracy of the sample temperature determination on the pyrolysis of cellulose has been investigated by thermogravimetric analysis and numerical modelling. Experiments were carried out using cellulose employing seven different heating rates (HR). The developed numerical model enabled a determination of the thermal lag, taking into consideration the dependence of the properties of sample, crucible and surrounding gases on their true temperature. It was found that the limited heat transfer has a much greater impact on the true sample temperature than previously considered. At low HR the uncertainty of the sample temperature determination did not exceed 4.8 K, while for high HR it reached even 56.2–130 K. The temperature measurement inaccuracy affected the kinetic parameters by even 40–50% however it should not be attributed to the difference in maximum reactivity temperature observed for different HR. Opposed to other models presented in the literature, the developed one indicated that the decrease of cellulose activation energy observed for high conversion rates could not be in any way attributed to thermal phenomena. Moreover, observations made at HR 0.5 K min−1 indicated that the mechanism of cellulose pyrolysis should also consider the third pathway of reaction, resulting in enhanced formation of char.

We predict whether thermal waves exist or not in dual-phase-lag heat conduction by measuring the time lag ratio ( τ q / τ T ). In this method, a one-dimensional model of cylindrical heating is developed and solved by the method of Laplace transform. The time lag ratio is then derived from the time derivative of the square of excess temperature on the heater wall in the initial heating stage. Experimentally, we also applied this method to measure the time lag ratios for sand and lean pork, both of which are less than 1 within acceptable measurement uncertainty, indicating no thermal waves generated. This method is of great importance for the application of dual-phase-lag heat conduction model since it can predict existence of thermal waves through a simple experiment.

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 droplet traces is measured using low-inertia thermocouples (thermal lag is less than 0.1 s). The paper considers aerosol flows with droplet size of 0.04–0.4 mm and concentration of 3.8·10−5–10.3·10−5 m3 of droplets/m3 of gas, as well as individual droplets (sized 1.5–2.5 mm), and relatively large water massifs (sized 22–30 mm). The typical gas temperature reduction in the trace of a moving liquid ranges from 15 K to 140 K. The times of keeping the low temperature of the gas-vapor mixture in the droplet trace are from 3 s to 30 s relative to the initial gas temperature. The study indicates how such factors as initial droplet size, velocities of the high-temperature gas flows, volume concentration of droplets, combustion products temperature and initial water temperature influence the integral characteristics of temperature traces of droplets. For the experiments with single drops, large masses and aerosol drops, the comparative analysis takes place for conditions, at which the convective heat transfer between liquid and combustion products dominates over an evaporation. The experimental data substantiate the hypothesis which suggests that the temperature traces of water droplets are kept during quite a long time even for small droplets. The experimental data are a key basis for the development of the drip systems of controlled gas temperature reduction via the intensification of phase transitions.

This study is attempted to present theoretical solutions for power output of thermal-lag Stirling engine. In this study, a dimensionless nonlinear dynamic model is built. Equation of motion of piston and energy equations for working gases in cold and hot sides are developed and solved by perturbation method. Emphasis of the study is focused on the instability of the thermal-lag phenomenon under various loading and friction damping conditions. Thus, dynamic behavior of the engine with or without friction damping is investigated. The critical curves that separate the stable and unstable zones are plotted. The onset of the thermal-lag oscillation under different loading conditions takes place only when the operating condition is located in the stable zone. The power output of the engine is then evaluated based on the theoretical solutions, and dependence of the power output on influential parameters is investigated. Furthermore, an amplitude equation and a frequency shift equation are presented, and the dynamic characteristics of the engine and the frequency shift can be determined by solving these two equations.

This investigation outlines a straight-forward and low cost methodology for determining thermal properties of wall structures. The method eliminates the need to produce a step change boundary condition, and the error inherent in the departure from a step change that finite properties necessarily impose. The transient technique involves an experimental component whereby a high temperature thermal ramp boundary condition is applied to one wall face with the other exposed to the cooler ambient surroundings. Temperature and heat flux sensors are installed to monitor the transient heating behaviour at the wall faces. The measured transient wall temperature profiles are subsequently imposed as boundary equations to Fourier's equation in such a way that the analytic solution can provide a prediction of the transient surface heat flux. With this, the thermal diffusivity is estimated by using the effective thermal diffusivity of the wall material as a tuning parameter to regression fit the predicted and measured heat flux histories. Additionally, the steady solution facilitates the approximation of the effective thermal conductivity when used in conjunction with the steady surface temperature and heat flux measurements. To illustrate the technique, a test was performed on a 900 mm × 900 mm × 120 mm thick solid concrete wall section. The effective thermal diffusivity was determined to be 7.2 × 10 −7 m 2 /s with corresponding effective thermal conductivity of 1.64 W/m K and specific heat of 0.99 kJ/kg K. Each property value is within the range of published literature for concrete.

Spruce chips of three different thicknesses were pyrolyzed isothermally in a vertical furnace macro-TGA at 574 to 676K, which is the temperature range relevant for char production. The measured mass loss data was analyzed in terms of mass loss rate, thermal lag and char yield as a function of chip size and pyrolysis temperature. The char yield decreased with increasing temperature and there was no significant difference in char yield as a function of sample thickness, ranging from 1mm to 7mm. Thermal lag was present for all chip sizes above 600K. At 574K the data suggests that chips below 1mm in thickness are decomposing at rates governed by reaction kinetics. An isoconversional kinetic model based on low heating rate data of spruce powder was adopted to analyze the data. The model predicted lower mass loss rates than those measured for the chips, suggesting that the pyrolysis process of wood proceeds through a network of parallel reactions. Despite this, the model could predict the final char yield of the wood chips with an accuracy above 80%. The predictive capability of the isoconversional reaction rate expression is promising since the procedure to derive such a rate expression is straight-forward, compared to the conventional model-fitting methods. The data and modeling approach presented in this work is important to the field of biomass pyrolysis as it covers the temperature range and chip sizes relevant for pyrolysis in multi-staged gasification plants which has been given little attention.

Multi-zonal, electrically heated moulds for composite processing offer the potential of a direct heat introduction with low thermal lag and high energy efficiency. However, appropriate thermal dimensioning of these tools requires the consideration of the thermal response of the tool itself as well as the thermal and cure behaviour of the part, which is to date mostly estimated based on experience. To realize the full potential of this tool class, a numerical method is presented to determine a sound partitioning of the designated heating area utilizing 3D finite element cure simulation. Further, a cure simulation model of an application case is set up and validated. The capability of the numerical method to significantly increase the temperature accuracy and the degree of cure homogeneity are demonstrated in an evaluation of the numerically improved application case. Finally, the effect of the tool material on the zone allocations and temperature accuracy is studied.

As waste biomass from fruit processing industry, apricot kernel shells have a potential for conversion to renewable energy through a thermo-chemical process such as pyrolysis. However, due to major differences of biomass characteristics as the well-known issue, it is extremely important to perform detailed analysis of biomass samples from the same type (or same species) but from different geographical regions. Regarding full characterization of considered biomass material and to facilitate further process development, in this paper, the advanced mathematical model for kinetic analysis was used. All performed kinetic modeling represents the process kinetics developed and validated on thermal decomposition studies using simultaneous thermogravimetric analysis (TGA) – differential thermal analysis (DTA) – mass spectrometry (MS) scanning, at four heating rates of 5, 10, 15 and 20 °C min−1, over temperature range 30–900 °C and under an argon (Ar) atmosphere. Model-free analysis for base prediction of decomposition process and deconvolution approach by Fraser-Suzuki functions were utilized for determination of effective activation energies (E), pre-exponential factors (A) and fractional contributions (φ), as well as for separation of overlapping reactions. Comparative study of kinetic results with emission analysis of evolved gas species was also implemented in order to determine the more comprehensive pyrolysis kinetics model. Obtained results strongly indicated that the Fraser-Suzuki deconvolution provides excellent quality of fits with experimental ones, and could be employed to predict devolatilization rates with a high probability. From energy compensation effect properties, it was revealed the existence of unconventional thermal lag due to heat demand by chemical reaction. © Springer Nature Switzerland AG 2020. In: Mitrovic N., Milosevic M., Mladenovic G. (eds) Computational and Experimental Approaches in Materials Science and Engineering. CNNTech 2018. Lecture Notes in Networks and Systems, vol 90. Springer, Cham

We evaluated the viability of integrating a cold thermal energy storage (CTES) into an all-electric ship to mitigate the aftermath of thermal cycling and cooling loss by providing additional thermal damping. 1D dynamic CTES and counterflow heat exchanger (HX) models were developed and solved in dimensionless forms to assess the proposed cooling configuration based on the following: (1) the impact of chiller HX (evaporator) design on thermal damping without the CTES; and (2) the effects of adding a CTES next to the chiller as a complementary thermal damper (HX + CTES). Numerical results demonstrate the higher sensitivity of the damping effect to the total number of transfer units (N) than the HX mass, and the required N to achieve the same damping effect reduces nonlinearly with increasing HX mass. Furthermore, the HX + CTES outperforms the HX of the same total mass at higher N when the effect of heat transfer overcomes that of thermal inertia, and its merit becomes more evident when we compare the operation of these two configurations. This work thus reveals the potential of HX + CTES as a practical approach for improving the overall ship cooling reliability.

The analysis of polymer chemical decomposition is often highly dependent on the test conditions. In fact, thermal analysis tends to be far more sensitive to instrumental parameters than other branches of chemical analysis. Some of the boundary conditions in thermal analysis have been widely studied in the literature, such as the heating rate or the atmosphere. However, the influence of the sample mass, the gas flow or the use of lid has not been studied enough for thermoplastic polymers. The aim of this paper is to analyse how the experimental boundary conditions of the simultaneous thermal analysis apparatus affect the thermal decomposition of thermoplastic polymers. To do so, a set of 35 experimental tests have been performed including variation of the sample mass, gas flow rate, heating rate, atmosphere and the use of lid in the crucible. Results enable us to analyse the influence in the mass loss and in the energy release or absorbed in the thermal decomposition of thermoplastic polymers, showing the impact of each boundary condition over the thermal decomposition. A comprehensive analysis of the thermal decomposition behaviour of the PVC and LLDPE by considering the influence of all the boundary conditions of the STA is covered. It is especially remarkable the influence of gas flow in the oxidative reactions, and of heating rate in the chemical reactions that thermoplastic polymers undergo in their decomposition. Additionally, sample mass comparison shows only deviation in the oxidative reactions and does not show deviation for the non-oxidative reactions. That seems to show a higher effect on the results because of the energy release in the decomposition reactions than because of the thermal lag due to heat transfer on the sample, as it is usually thought. Authors would like to thank the Consejo de Seguridad Nuclear for the cooperation and co-financing the project ‘‘Simulation of fires in nuclear power plants’’ and CAFESTO Project funded by the Spanish Ministry of Science, Innovation and Universities and the Spanish State Research Agency through Public–Private Partnerships (Retos Colaboración 2017 call, ref RTC-2017-6066-8) co-funded by ERDF under the objective ‘‘Strengthening research, technological development and innovation’’.

The thermal lag of DSC is a heating rate independent constant and influences the measured onset temperature of melting peaks and must be taken into account during the temperature calibration. In the literature, however, non-linear behavior of the measured onset temperature is reported for the case of high scanning rates and the use of small samples. Based on a conventional heat transfer model of a DSC a general relation of the heating rate and sample mass dependence of the onset temperature is derived. The reason of this unusual behavior is that the time for the melting event is less than the equilibration time of the DSC. The approach presented can be used to correct the onset temperatures in the case of non-linear behavior, which may occur in conventional DSC and Fast DSC (using chip sensors).

Variations in atmospheric conditions can be important factors influencing temperature dynamics within the active layer of a soil. Solar radiation and air temperature can directly alter ground surface temperatures, while variations in wind and precipitation can control how quickly heat is carried through soil pores. The presence of seasonal snow cover can also create a thermal barrier between the atmosphere and ground surface. This study examines the relation between atmospheric conditions and ground temperature variations on a deglaciated island along the Western Antarctic Peninsula. Ground temperatures were most significantly influenced by incoming solar radiation, followed by air temperature variations. When winter months were included in the comparison, the influence of air temperature increased while solar radiation became less influential, indicating that snow cover reflected solar radiation inputs, but was not thick enough to insulate the ground. When ground temperatures were compared to atmospheric conditions of preceding weeks, seasonal temperature peaks 1.6 m below ground were best related to seasonal air temperature peaks from the previous two weeks. The same ground temperature peaks were best related to seasonal solar radiation peaks of seven weeks prior. This difference was a result of temperature lags within the atmosphere.

In the last years, people has become aware of energy saving and thermal comfort requirements for home buildings in hot and cold seasons. In the present study, hybrid multifunctional constructive components made of a reinforced mortar channel filled with cement–soil–sawdust (CL2MSCAL) were evaluated to experimentally determine their thermal performance (thermal conductivity, thermal time lag and decrement factor). The experimental analysis performed in this study was based on dynamic climatology. Measurements of components surface temperature were conducted to determine temperature damping and temperature wave lag. Monthly average temperature and direct solar radiation data of the site was considered. Measurements of real-scale constructive components were conducted on a fully equipped thermal conductive system and thermal chambers (test cells) built for this purpose. Results are compared to concrete components (CCL) that account for approximately 71.6% of the houses built in Mexico and 43.2% in Oaxaca and reinforced mortar (CML) used as prefabricated housing systems. Best results were found for component CL2MSCAL that has a thermal conductivity of 0.81 W·m−1·K−1, a thermal damping of 81.5% (decrement factor of 0.166) and time lag of 7:37 h compared to CCL that present a time lag of 1 h and decrement factor of 0.9. Thus, it is concluded that CL2MSCAL roofing channel components are an alternative for energy saving and thermal comfort.

The paper presents results of an experimental study of the suppression of thermal decomposition of forest fuel (FF) due to formation of a thin surface water film (3 mm thick). The investigations were carried out with birch leaves, as well as a mixture of birch leaves, pine needles, and twigs of aspen. The experiments involved model bases of fire of the above FFs in the form of cylinders. The cylinders were 20 mm to 60 mm in diameter and 40 mm to 100 mm high. The effect of water on the FFs was monitored via high-speed (up to 105 frames per second) video recording and fast (a thermal lag of less than 1 s) thermal transducers. The times of termination of FF thermal decomposition and the minimum (required) volumes of water were determined. The feasibility of complete suppression of the FF thermal decomposition process due to formation of a thin surface water film (10–15 times thicker than the reacted material) was experimentally supported. The foundations of the physical model of a complex of processes that occur owing to the water film effect on the forest fuel heated to a high temperature (well above the point of thermal decomposition) were formulated.

The study is aimed at investigating the thermal behavior and decomposition kinetics of torrefied oil palm empty fruit bunches (OPEFB) briquettes using a thermogravimetric (TG) analysis and the Coats-Redfern model. The results revealed that thermal decomposition kinetics of OPEFB and torrefied OPEFB briquettes is significantly influenced by the severity of torrefaction temperature. Furthermore, the temperature profile characteristics; Tonset, Tpeak, and Tend increased consistently due to the thermal lag observed during TG analysis. In addition, the torrefied OPEFB briquettes were observed to possess superior thermal and kinetic properties over the untorrefied OPEFB briquettes. It can be inferred that torrefaction improves the fuel properties of pelletized OPEFB for potential utilization in bioenergy conversion systems.

This paper is the first paper clarifying the causes and physical insight of the thermal-lag phenomena by presenting analytical solutions. The theoretical solutions presented are able to answer critical questions about the thermal-lag engine which have not been answered since it was proposed roughly thirty years ago. We find the criteria for onset of the thermal-lag oscillation in the engine. We confirm Tailer’s postulation that a thermal lag can be created to a certain extent by the imperfect heat transfer. We find that the thermal lag angles can be altered by artificially adjusting the geometrical and physical parameters. Finally, the influence of thermal lag on the indicated work output of the engine can be evaluated. In the present study, a nonlinear instability analysis is performed and theoretical solutions are carried out by perturbation method. In parallel, a prototype engine is developed and tested to partially verify the present theory. Experiments are conducted by measuring the displacement of piston under various heating temperatures and design parameters. Close agreement between the experimental data and the theoretical predictions, particularly in the steady oscillation regime, has been observed.

It is common for sample temperatures to be estimated by the power input to the furnace in multi-anvil experiments in which a thermocouple cannot be used or the thermocouple failed during heating. Uncertainties using this technique are often on the order of ±85°C or larger. This paper describes a new method for estimating sample temperature using a second thermocouple outside all pressure media. Temperatures recorded at this external (gasket) thermocouple trend linearly with the internal (sample) thermocouple temperature. Because of thermal lag, it is necessary to determine the first gasket temperature (T0) corresponding to the desired sample temperature. Accurate prediction of T0 for the desired sample temperature can come from relatively few (5–6) gasket-temperature measurements made during the initial temperature ramp over a small temperature range (500–600°C). Using this method and manually ramping to T0 allows for uncertainties in sample temperature estimation as small as ±20°C.

Slow crystallization kinetics and a limited thermodynamical stability of the target crystal phase are characteristic to zeolite formation, representing some of the key obstructions for fast zeolite synthesis. In this paper, the possibility of accelerating NaA zeolite synthesis in a continuous flow reactor (CFR) is studied. The CFR reduces the thermal lag by increasing surface to volume ratio, expediting heat transfer and mass transfer. The properties of the CFR and the reference batch synthesized particles were similar as confirmed by X-ray diffraction, scanning electron microscopy, particle size measurement using laser scattering and water adsorption equilibria. The reduced residence time and reduction in thermal lag provided an ideal synthesis environment for NaA zeolite, without side products, yielding 160 g/h per liter reactor volume of dry NaA crystals synthesized in 16 min and 2-3 mu m particles for a single CFR. In comparison, the batch process produces 33 g/h per liter reactor volume The effects of diluting with NaOH-solution and temperature were studied in the CFR, allowing to determine the optimal conditions. With the enhanced reaction kinetics gained from the increased temperature and molar composition, NaA synthesis is performed 10 times faster than in the optimal batch synthesis. The optimal conditions for the synthesis of NaA in the CFR were determined as: a gel composition of Na2O:4.75 - SiO2:1.93 - Al2O3:1.0 - H2O:192, at a synthesis temperature of 150 degrees C during 16 min without, aging of the gel mixture. This paper shows that the bottlenecks in NaA zeolite synthesis can be widened resulting in faster synthesis in a CFR, making it a feasible pathway for more controllable zeolite synthesis at higher mass production rates (160 g/(h l-reactor)) while reducing the risk of blockage in a continuous flow reactor. (C) 2016 Elsevier Inc. All rights reserved.

This paper presents the experimental investigation of the effect of ambient air humidity and temperature on thermal properties of the laterite rocks used in South-West coastal India. The experimental technique employed was transient plane source method in the saturated salt solution humidity controlled chamber. Experimental results showed an increase of thermal conductivity by 14.7% and specific heat by 9.15% with an increase in the relative humidity of ambient air in the hygroscopic range. A porous and ferruginous matrix of laterite was studied using a scanning electron microscope. The effects of relative humidity of the ambient air and temperature on the unsteady state thermal heat transfer characteristics such as transmittance, admittance, decrement factor, time lag, surface factor, surface factor time lag and heat capacity for different thicknesses of the laterite rock walls were investigated analytically. One dimensional heat flow equation under periodic convective boundary conditions was solved using matrix algebra and a computer simulation program which employs a cyclic admittance method was developed using MATLAB to compute unsteady state thermal characteristics. Results indicate that the decrement factor reduces by 8.35% and time lag increases by 2.88% with an increase in the relative humidity of ambient air compared to the dry state for the Indian standard laterite rock thickness.

The paper presents the pyrolysis behaviour of eleven different rank solid fuels, carried out using thermogravimetry (TG). Obtained experimental curves were compared with profiles determined using the Single First Order Reaction (SFOR) model and three different approaches of Distributed Activation Energy Model (DAEM). The aim of this work was to develop different models dedicated to pyrolysis, in particular further investigate the interrelation between the activation energy and the pre-exponential factor, its impact on the results quality and attribution with the fuel properties and pyrolysis mechanism. Obtained results showed that the compensation effect, often noted for SFOR, has also occurred for DAEM. Furthermore, analysis indicated an existence of a relationship between the characteristic temperature T iso (and ln( k iso )) and fuel properties. Observed interrelation may be attributed to the change in reaction mechanism.