Effect Of Thermal Inertia Research Articles

Directional characteristics of thermal-infrared beaming from atmosphereless planetary surfaces - a new thermophysical model

We present a new rough-surface thermophysical model (Advanced Thermophysical Model or ATPM) that describes the observed directional thermal emission from any atmosphereless planetary surface. It explicitly incorporates partial shadowing, scattering of sunlight, self-heating and thermal–infrared beaming (re-radiation of absorbed sunlight back towards the Sun as a result of surface roughness). The model is verified by accurately reproducing ground-based directional thermal emission measurements of the lunar surface using surface properties that are consistent with the findings of the Apollo missions and roughness characterized by an rms slope of ∼32°. By considering the wide range of potential asteroid surface properties, the model implies a beaming effect that cannot be described by a simple parameter or function. It is highly dependent on the illumination and viewing angles as well as surface thermal properties and is predominantly caused by macroscopic rather than microscopic roughness. Roughness alters the effective Bond albedo and thermal inertia of the surface as well as moving the mean emission away from the surface normal. For accurate determination of surface properties from thermal–infrared observations of unresolved bodies or resolved surface elements, roughness must be explicitly modelled, preferably aided with thermal measurements at different emission angles and wavelengths.

A field study on building inertia and its effects on indoor thermal environment

Energy consumption in Spanish school buildings is higher during spring seasons. Thermal inertia of buildings can help to reduce such consumption, improve comfort, and even replace HVAC systems. This thermal inertia is usually associated to heavy wall construction, but the truth is there are other parameters that can have a significant effect on this property. This paper describes a field case study of school buildings with different types of wall construction, aimed at demonstrating real thermal inertia effects on indoor conditions. Besides air temperature measurements, HAM tools were used to simulate indoor air conditions. Results showed a good agreement between simulated and experimental air temperature results, and that other building construction parameters, such as the use of permeable coverings, may have a large impact on indoor thermal conditions and energy consumption.

Influence of physical properties on polymer flammability in the cone calorimeter

The relationship between physical properties and fire performance as measured in the cone calorimeter is not well understood. A number of studies have identified relationships between the physical and chemical properties of polymeric materials and their gasification behavior which can be determined through numerical pyrolysis models. ThermaKin, a one‐dimensional pyrolysis model, has recently been employed to predict the burning behavior in fire calorimetry experiments. The range of thermal, chemical, and optical properties of various polymers have been utilized to simulate the processes occurring within a polymer exposed to a uniform heat flux, such as in a cone calorimeter. ThermaKin uses these material properties to predict the mass flux history in a cone calorimeter. Multiplying the mass flux history by the heat of combustion of the fuel gases gives the HRR history and these have been calculated for cone calorimeter experiments at 50 kW m−2 incident heat flux for the lowest, average, and highest values of physical parameters exhibited by common polymers. In contrast with actual experiments in fire retardancy, where several parameters change on incorporation of an additive, this study allows for the effect of each parameter to be seen in isolation. The parameters used in this study are grouped into physical properties (density, heat capacity, and thermal conductivity), optical properties (absorption and reflectivity), and chemical properties (heat of decomposition, kinetic parameter, and heat of combustion). The study shows how the thermal decomposition kinetic parameters effect the surface burning (pyrolysis) temperature and resulting heat release rate history, as well as the relative importance of other properties directly related to the chemical composition. It also illustrates the effect of thermal inertia (the product of density, heat capacity, and thermal conductivity) and of the samples' ability to absorb radiant heat. Copyright © 2011 John Wiley & Sons, Ltd.

Improvement of thermal inertia of styrene–ethylene/butylene–styrene (SEBS) polymers by addition of microencapsulated phase change materials (PCMs)

In this work, microencapsulated phase change materials (PCMs) with a melting temperature of 52 °C have been used to improve thermal inertia phenomena on an elastomeric matrix of styrene–ethylene/butylene–styrene (SEBS) material. The amount of PCMs has varied in the 1–10 wt.% and these materials have been processed by conventional injection molding without PCM degradation. Mechanical characterization of SEBS–PCM compounds has been carried out and the obtained results show good maintenance of both resistant and ductile properties for PCM amounts comprised in the 1–5 wt.% range. Scanning electron microscopy (SEM) analysis has revealed good wetting properties of PCM microcapsules with the SEBS matrix which is a key factor to obtain good mechanical performance. The effect of PCM addition on thermal inertia has been evaluated by active infrared thermography (IRT), showing a remarkable effect on thermal regulation of SEBS in the temperature range close to the melting point of the PCM (52 °C). This thermoregulation effect is more accurate as the PCM content increases. Also, cooling curves have been constructed in order to quantify the thermal inertia effect in a cooling process.

Experimental and numerical investigation of dynamic heat transfer parameters in packed bed

Dynamic experiments in a nonadiabatic packed bed were carried out to evaluate the response to disturbances in wall temperature and inlet airflow rate and temperature. A two-dimensional, pseudo-homogeneous, axially dispersed plug-flow model was numerically solved and used to interpret the results. The model parameters were fitted in distinct stages: effective radial thermal conductivity (K r) and wall heat transfer coefficient (h w) were estimated from steady-state data and the characteristic packed bed time constant (τ) from transient data. A new correlation for the K r in packed beds of cylindrical particles was proposed. It was experimentally proved that temperature measurements using radially inserted thermocouples and a ring-shaped sensor were not distorted by heat conduction across the thermocouple or by the thermal inertia effect of the temperature sensors.

Two-phase refrigerant flow instability analysis and active control in transient electronics cooling systems

Two-loop refrigeration systems are being explored for two-phase cooling of ultra high power electronic components. For effective and efficient thermal management of electronic systems, active control methods are desired to suppress inherent flow instabilities especially in transient applications. This paper presents a framework for the transient analysis and active control of pressure-drop flow instabilities under varying imposed heat loads. The external effects on boiling flow characteristics and the boiling oscillatory flow responses to transient heat load changes are studied. Flow instability margins can be quantitatively predicted from an analytical two-phase flow model. In addition, the effects of wall thermal inertia on flow oscillations is systematically investigated. Based on the theoretical analysis of oscillatory flow boiling of refrigerants, a set of active control schemes are developed and studied to suppress flow oscillations and to increase the critical heat flux. With the available control devices – inlet valve and supply pump – different active control schemes are studied to improve the transient two-phase cooling performance.

Thermal inertia effect in an axisymmetric thermoelastic problem based on generalized thermoelasticity

The objective of this paper is to study thermal inertia effect due to the fact of the properties of the hyperbolic equations based on LS theory in generalized thermoelasticity. Simulations in a 2D hollow cylinder for uncoupled dynamic thermal stresses and thermal displacements were predicted by use of finite element method with Newmark algorithm. The thermal inertia effect on LS theory in rapid transient heat transfer process is also investigated in comparison with in steady heat transfer process. When different specific heat capacity is chosen, dynamic thermal stresses appear different types of vibration, in which less heat capacity causes more violent dynamic thermal stresses because of the thermal inertia effect. Both dynamic thermal stresses and thermal displacements in rapid transient heat transfer process have the larger amplitude and higher frequency than in steady heat transfer process due to thermal inertia from the results of simulation, which is consistent with the nature of the generalized thermoelasticity.

Analysis of statistical model of heat transfer of particles in isotropic turbulence with constant temperature gradient

Comparison with the data of direct numerical calculations in isotropic turbulence with constant temperature gradient is used for verifying the statistical model of heat transfer in gas-dispersed turbulent flows. Analysis is made of the effect of thermal inertia of particles on the correlations between turbulent heat fluxes and intensities of temperature fluctuations in the dispersed and continuous phases.

The role of thermodynamics in disc fragmentation

Thermodynamics play an important role in determining the way a protostellar disc fragments to form planets, brown dwarfs and low-mass stars. We explore the effect that different treatments of radiative transfer have in simulations of fragmenting discs. Three prescriptions for the radiative transfer are used, (i) the diffusion approximation of Stamatellos et al., (ii) the barotropic equation of state (EOS) of Goodwin et al., and (iii) the barotropic EOS of Bate et al. The barotropic approximations capture the general evolution of the density and temperature at the centre of each proto-fragment but (i) they do not make any adjustments the particular circumstances of a proto-fragment forming in the disc, and (ii) they do not take into account thermal inertia effects that are important for fast-forming proto-fragments in the outer disc region. As a result, the number of fragments formed in the disc and their properties are different, when a barotropic EOS is used. This is important not only for disc studies but also for simulations of collapsing turbulent clouds, as in many cases in such simulations stars form with discs that subsequently fragment. We also examine the difference in the way proto-fragments condense out in the disc at different distances from the central star using the diffusion approximation and following the collapse of each proto-fragment until the formation of the second core (~10^{-3} g/cm3). We find that proto-fragments forming closer to the central star tend to form earlier and evolve faster from the first to the second core than proto-fragments forming in the outer disc region. The former have a large pool of material in the inner disc region that they can accrete from and grow in mass. The latter accrete more slowly and they are hotter because they generally form in a quick abrupt event.

Supersonic cloud collision. I.

It has long been suggested that shocks might play an important role in altering the form of the interstellar medium (ISM). Shocks enhance gas density and sufficiently dense regions may become self gravitating. Potential star forming clouds within larger molecular clouds, move randomly at supersonic speeds. Depending on the precollision velocity, colliding molecular clouds produce a slab that is either shock compressed or pressure confined. In a sequel of two papers (I & II), we simulate molecular cloud collision and investigate the dynamical evolution of such slabs. Shocked slabs are susceptible to hydrodynamic instabilities and in the present paper (I) we study the effect of strong shear between slab layers on the dynamic evolution of a shock compressed gas slab. Both, head-on and off-centre cloud collisions have been examined in this work. We include self gravity in all our simulations. Simulations presented here, are performed using the smoothed particle hydrodynamics (SPH) numerical scheme. Individual, pre-collision clouds are modelled as pressure confined Bonnor-Ebert spheres. However, in the interest of brevity the thermodynamic details of the problem are simplified and the gas temperature is simply evolved by a barytropic equation of state. Obviously, the gas, to some extent suffers from thermal inertial effects. However, we note that the dynamical timescale is much smaller than the local sound crossing time so that such effects should have minimum influence.

The influence of the external walls thermal inertia on the energy performance of well insulated buildings

Energy conscious building design consists in controlling the thermophysical characteristics of the building envelope such as, firstly, thermal transmittance ( U-value). However, besides the U-value, the envelope thermal inertia should also be considered. The literature studies report very different estimations regarding the energy saving potential associated with the use of an adequate inertia, ranging from a few percentages to more than 80%. Therefore, this study aims at assessing the parameters enhancing or damping the role of thermal inertia, providing a variety of results. For this purpose several external wall systems with the same U-value but different dynamic properties were investigated to calculate the associated achievable energy savings. A parametric analysis was performed in progressive steps, by running the models of a virtual Test Cell and of a sample building. Both design parameters (heat transfer surface, solar control) and operational ones (ventilation rates, HVAC functional regime) were varied. It was found that the highest energy performance wall system has a proper combination of the dynamic thermal transmittance and thermal admittance values, although not necessarily the best ones. Moreover, it was shown that thermal inertia effects are enhanced if it is coupled with other energy saving measures and an efficient building use.

Nonlinear acoustic phenomena in viscous thermally relaxing fluids: Shock bifurcation and the emergence of diffusive solitons.

In this talk, we will consider the propagation of finite-amplitude acoustic waves in fluids that exhibit both viscosity and thermal relaxation. Under the assumption that the thermal flux vector is given by the Maxwell–Cattaneo law, which is a well known generalization of Fourier's law that includes the effects of thermal inertia, we derive the weakly nonlinear equation of motion in terms of the acoustic potential. We then use singular surface theory to determine how an input signal in the form of a shock wave evolves over time and for different values of the Mach number. Then, numerical methods are used to illustrate our analytical findings. In particular, it is shown that the shock amplitude exhibits a transcritical bifurcation; that a stable nonzero equilibrium solution is possible, and that a Taylor shock (i.e., a diffusive soliton), in the form of a “tanh” profile, can emerge from behind the input shock wave. Finally, an application related to the kinematic-wave theory of traffic flow is noted. [Work supported by ONR/NRL funding (PE 061153N)].

Brain thermal inertia, but no evidence for selective brain cooling, in free-ranging western grey kangaroos (Macropus fuliginosus)

Marsupials reportedly can implement selective brain cooling despite lacking a carotid rete. We measured brain (hypothalamic) and carotid arterial blood temperatures every 5 min for 5, 17, and 63 days in spring in three free-living western grey kangaroos. Body temperature was highest during the night, and decreased rapidly early in the morning, reaching a nadir at 10:00. The highest body temperatures recorded occurred sporadically in the afternoon, presumably associated with exercise. Hypothalamic temperature consistently exceeded arterial blood temperature, by an average 0.3 degrees C, except during these afternoon events when hypothalamic temperature lagged behind, and was occasionally lower than, the simultaneous arterial blood temperature. The reversal in temperatures resulted from the thermal inertia of the brain; changes in the brain to arterial blood temperature difference were related to the rate of change of arterial blood temperature on both heating and cooling (P < 0.001 for all three kangaroos). We conclude that these data are not evidence for active selective brain cooling in kangaroos. The effect of thermal inertia on brain temperature is larger than might be expected in the grey kangaroo, a discrepancy that we speculate derives from the unique vascular anatomy of the marsupial brain.

Rotational dynamics of a solar system body under solar radiation torques

The rotational dynamics of a small solar system body subject to solar radiation torques is investigated. A set of averaged evolutionary equations are derived as an analytic function of a set of spherical harmonic coefficients that describe the torque acting on the body due to solar radiation. The analysis also includes the effect of thermal inertia. The resulting equations are studied and a set of possible dynamical outcomes for the rotation rate and obliquity of a small body are found and characterized.

Modeling of Temperature–Frequency Correlation Using Combined Principal Component Analysis and Support Vector Regression Technique

A good understanding of environmental effects on structural modal properties is essential for reliable performance of vibration-based damage diagnosis methods. In this paper, a method of combining principal component analysis (PCA) and support vector regression (SVR) technique is proposed for modeling temperature-caused variability of modal frequencies for structures instrumented with long-term monitoring systems. PCA is first applied to extract principal components from the measured temperatures for dimensionality reduction. The predominant feature vectors in conjunction with the measured modal frequencies are then fed into a support vector algorithm to formulate regression models that may take into account thermal inertia effect. The research is focused on proper selection of the hyperparameters to obtain SVR models with good generalization performance. A grid search method with cross validation and a heuristic method are utilized for determining the optimal values of SVR hyperparameters. The proposed method is compared with the method directly using measurement data to train SVR models and the multivariate linear regression (MLR) method through the use of long-term measurement data from a cable-stayed bridge. It is shown that PCA-compressed features make the training and validation of SVR models more efficient in both model accuracy and computational costs, and the formulated SVR model performs much better than the MLR model in generalization performance. When continuously measured data is available, the SVR model formulated taking into account thermal inertia effect can achieve more accurate prediction than that without considering thermal inertia effect.

The dynamical evolution of uniformly rotating asteroids subject to YORP

A detailed derivation is given of the effect of solar radiation on the rotational dynamics of asteroids, commonly called the YORP effect. The current derivation goes beyond previous discussions published in the literature and provides a comprehensive secular dynamical analysis of the effect of solar radiation torques acting on a uniformly rotating body, and the evolution of its rotation state over time. Our predicted model has the global radiation properties of the asteroid as explicit parameters, and hence can be specified independent of these parameters. The resulting secular equations for the rotation rate and rotation pole are characterized by three parameters of the body's shape and explicitly includes the effect of thermal inertia on the evolution of these rotation state parameters. With this detailed model, in conjunction with estimated asteroid shapes and poles, we compute the expected YORP torques and dynamic response of several asteroids and the change in rotation rate for specific shapes as a function of obliquity. Finally, we define a convenient dimensionless parameter that is only a function of the body geometry and that can be used to characterize the effects of YORP.

Prediction of temperature and thermal inertia effect in the maturation stage and stockpiling of a large composting mass

A macroscopic non-steady state energy balance was developed and solved for a composting pile of source-selected organic fraction of municipal solid waste during the maturation stage (13,500 kg of compost). Simulated temperature profiles correlated well with temperature experimental data (ranging from 50 to 70 °C) obtained during the maturation process for more than 50 days at full scale. Thermal inertia effect usually found in composting plants and associated to the stockpiling of large composting masses could be predicted by means of this simplified energy balance, which takes into account terms of convective, conductive and radiation heat dissipation. Heat losses in a large composting mass are not significant due to the similar temperatures found at the surroundings and at the surface of the pile (ranging from 15 to 40 °C). In contrast, thermophilic temperature in the core of the pile was maintained during the whole maturation process. Heat generation was estimated with the static respiration index, a parameter that is typically used to monitor the biological activity and stability of composting processes. In this study, the static respiration index is presented as a parameter to estimate the metabolic heat that can be generated according to the biodegradable organic matter content of a compost sample, which can be useful in predicting the temperature of the composting process.

Rapid on-site evaluation of thermal comfort through heat capacity in buildings

A simple, straightforward procedure to estimate the effective thermal mass of a building is established. Basic measurements of inside and outside temperatures are shown to exhibit several common characteristics, so that a single value for the effective thermal inertia can be derived. A relationship between the delay in the internal temperature to attain a maximum value with respect to the ambient, and the temperature amplitude attenuation inside the building, is found to exist, and its dependence on maximum outside temperature is explored. This procedure is shown to be useful to rapidly classify buildings or dwellings according to the effectiveness of the participation of its thermal mass in damping extreme temperatures, such as those found in regions with dry climates. The procedure hereby proposed has also been useful to estimate the relevance of thermal mass of a given building in power savings in HVAC.

Strength and Fractography of High Power Varistors

Electroceramic varistors, typically based on ZnO, show a strong non-linear currentvoltage characteristics. Actually they can be considered as electrical isolators below a critical field strength and highly conductive above. These components are used as over voltage protection elements in various fields of electric and automotive industry. In testing and in service high power varistors are loaded with µs-voltage pulses and suffer high mechanical loads due to thermal shock and inertia effects. Therefore the reliability in terms of mechanical strength becomes a crucial mark of quality. In this work the microstructure and the strength of commercial high power varistors of three different producers are presented. By a subsequent fractographic analysis fracture initiating defects are identified. It is shown, that defects in the microstructure, which result from the processing of the varistor components, play a significant role for the strength of the ceramics and of course also for the service performance of the components.

Linear stability analysis for a thermoviscoplastic material under cyclic axial loading

Some mechanical properties exhibit a very strong dependence upon temperature; these evolutions can be properly analyzed by the steady state response in cyclic loading. To relate experimental conditions to thermomechanical characteristics, the existence and the stability of steady state solutions are studied for cylinders submitted to cyclic compression. The material, considered as rigid viscoplastic, is modeled by a non-Newtonian temperature dependent viscous law. Closed form solutions are obtained in the framework of a large deformation theory by neglecting thermal expansion and inertia effects. Steady state regime is analyzed. The stress versus strain rate response and the temperature distribution are established as functions of the geometry of the cylinder, the loading characteristics and the material parameters. The stability of steady state solutions is analyzed with use of a linear perturbation scheme.