Dynamic Specific Heat Research Articles

Dynamic magnetic properties and magnetocaloric effect of a nanotube encapsulated with X36

Abstract Using Monte Carlo simulation, the dynamic magnetic properties and magnetocaloric effect of a mixed-spin (3/2, 2) single-walled nanotube encapsulated with X36 was studied, where X denotes the magnetic atom. The effects of intrinsic parameters on dynamic order parameters, magnetic susceptibility, internal energy, and specific heat were considered. The phase diagrams were obtained. The results indicate that the critical temperature can be increased by decreasing the absolute values of the anisotropies (D a , D b ), increasing the exchange couplings (|J ab |, J bb ), and decreasing the amplitude h 0 and the period τ of the external magnetic field. And under the influence of these parameters, the magnetocaloric effect is generated.

Uncertainty analysis of FLiNaK thermophysical properties on convective heat transfer characteristics in circular tube

Molten salts have attracted a spate of quantity of interests in energy and chemistry fields due to their large volumetric capacity, and thermodynamic stability at elevated temperature. However, there are significant uncertainties in the physical properties of molten salts, such as density, specific heat capacity, dynamic viscosity, and thermal conductivity, due to inexperienced measurement techniques and technology. These uncertainties could have certain impact on the evaluation of molten salts heat transfer characteristics. Therefore, an uncertainty analysis is performed regarding FLiNaK thermophysical properties on convective heat transfer characteristics in circular tube. Then, a polynomial chaos expansion (PCE) method is performed to study the uncertainty affecting the heat transfer characteristic. In the process of uncertainty analysis, tensor product quadrature nodes are used to calculate representative sample points and reduce computational costs. Three primary physical properties of molten salt are taken into account as the input parameters. The Sobol composition method is also used to analyze the contributions of each parameter to heat transfer. The results of the uncertainty analysis suggest that the uncertainties in dynamic viscosity, thermal conductivity, and specific heat capacity have a significant impact on the heat transfer of molten salt, contributing to 80 %, 14 %, and 6 % of the total variability, respectively. It also suggests that the polynomial chaos expansion methodology is both novel and reliable when applied to uncertainty analysis of molten salt.

Experimental Evaluation of Thermal Conductivity and Other Thermophysical Properties of Nanofluids Based on Functionalized (-OH) Mwcnt Nanoparticles Dispersed in Distilled Water

A possible way to increase thermal conductivity of working fluids, while keeping pressure drop at acceptable levels, is through nanofluids. Nanofluids are nano-sized particles dispersed in conventional working fluids. A great number of materials have potential to be used in nanoparticles production and then in nanofluids; one of them is Multi-Walled Carbon Nano Tubes (MWCNT). They have thermal conductivity around 3000 W/mK while other materials used as nanoparticles like CuO have thermal conductivity of 76.5 W/mK. Due to this fact, MWCNT nanoparticles have potential to be used in nanofluids production, aiming to increase heat transfer rate in energy systems. In this context, the main goal of this paper is to evaluate from the synthesis to the experimental measurement of thermal conductivity of nanofluid samples based on functionalized (-OH) MWCNT nanoparticles. They will be analyzed nanoparticles with different functionalization degrees (4% wt, 6% wt, and 9% wt). In addition, it will be quantified other thermophysical properties (dynamic viscosity, specific heat and specific mass) of the synthetized nanofluids. So, the present work can contribute with experimental data that will help researches in the study and development of MWCNT nanofluids. According to the results, the maximum increment obtained in thermal conductivity was 10.65% in relation to the base fluid (water).

FULLY DEVELOPED TEMPERATURE PROFILE FOR A POWER-LAW LAMINAR NANOFLUID FLOW IN A CIRCULAR DUCT SUBJECT TO A UNIFORM HEAT FLUX

In the present work, we develop a theoretical analysis of a fully developed laminar nanofluid flow in a circular duct in steady state, subject to a uniform heat flux condition. The rheological behavior of the base fluid is described by the power-law model and the nanofluid properties such as dynamic viscosity, thermal conductivity, density and specific heat are assuming as constants for a fixed value of the volumetric fraction. An analytical solution can be obtained by the mean temperature concept. The Nusselt number was defined and depends on the dimensionless parameter of the viscosity and the power-law index. The main results reveals that, for a maximum value of the volumetric fraction, the Nusselt number decreases drastically for shear-thinning base fluids, for shear-thickenning base fluids tends asymptotically to a constant value. For an increase in the volumetric fraction value, the dimensionless velocity profiles shown lower values for shear-thinning base fluids and the dimensionless temperature profiles showed a greater difference between the dimensionless wall temperature and the nanofluid stream temperature.

Development of artificial neural network model for predicting dynamic viscosity and specific heat of MWCNT nanoparticle-enhanced ionic liquids with different [HMIM]-cation base agents

The specific heat and dynamic viscosity of various 1-hexyl-3-methylimidazolium [HMIM]-cation with multiwalled carbon nanotube (MWCNT) nanoparticles are measured and used to develop an artificial neural network (ANN) model. The specific heat values of [C12MIM][Tf2N], [HMIM][Tf2N], [HMIM][TfO], and [HMIM][Pf6] ionic-liquid-based MWCNT nanofluids decrease with increasing nanoparticle concentration and increase with temperature. Also, the dynamic viscosity of the MWCNT nanoparticle-enhanced ionic liquids decreases at low concentrations; however, it increases significantly when the concentration increases up to 1 wt%. A new ANN model for predicting the dynamic viscosity and specific heat is developed, and the predictive values agree with the experimental data with high accuracy. The mean square error and R-value of the proposed predictive ANN model are 0.001291 and 0.9985, respectively. The maximum margin of deviation of the proposed ANN model for dynamic viscosity and specific heat is 9.63% and 4.3%.

Numerical Investigation of a Confined Laminar Jet Impingement Cooling of Heat Sources Using Nanofluids

Abstract The thermal and fluid dynamic behavior of a confined two-dimensional steady laminar nanofluid jet impinging on a horizontal plate embedded with five discrete heating elements subjected to a constant surface heat flux has been studied for a range of Reynolds number (Re) from 100 to 400 with Prandtl number, Pr = 6.96, of the base fluid. Variation of inlet Reynolds number produces a significant change of the flow and heat transfer characteristics in the domain. Increasing the nanoparticle concentration (ϕ) from 0% to 4% exhibits discernible change in equivalent Re and Pr caused by the modification of dynamic viscosity, effective density, thermal conductivity, and specific heat of the base fluid. Considerable improvement in heat transfer from the heaters is observed as the maximum temperature of the impingement wall is diminished from 0.95 to 0.55 by increasing Re from 100 to 400; however, the result of increasing ϕ on cooling of the heaters is less appreciable. Self-similar behavior has been depicted by cross-stream variation of temperature and streamwise heat flux in the developed region along the impingement wall up to Re = 300 for ϕ=0% to 4%. But the spread of the respective quantities shows strong dependence on ϕ at Re = 300 with sudden attenuation in magnitude in the developed region of flow. Substantial influence of Re is evident on Eckert number and pumping power. Eckert number decreases, whereas pumping power increases with an increase in Re, and the respective variations exhibit correspondence with power fit correlations.

The Landau–Khalatnikov Relaxation Mechanism in Smectic Liquid Crystals

The idea proposed and implemented by Landau and Khalatnikov to describe the dispersion and absorption of sound in superfluid helium is applied to smectic liquid crystals. The order parameter Φ that describes the phase transition between an orthogonal smectic SmA and a tilted smectic SmC is a two-component complex scalar and in this sense resembles the order parameter of superfluid helium. The interaction of the sound waves propagating in a system with the order parameter Φ leads to a periodic modulation of the system’s physical characteristics and parameters (in particular, its temperature). However, the order parameter cannot follow the temperature oscillations induced by a sound wave due to the presence of spatial order parameter correlations (long-range ones near the phase transition). It is this delay that leads to a sound-frequency-dependent dynamic specific heat. In this paper, we calculate this dynamic specific heat for the SmA–SmC phase transition for the so-called de Vries smectics (SmdV), with a highly developed short-range order. In turn, we analyze the dependence of the dynamic specific heat on frequency and temperature and find the dispersion and absorption of sound near the SmdV–SmC phase transition.

Dynamic magneto-caloric effect of a C70 fullerene: Dynamic Monte Carlo

Using the dynamicMonte Carlo (DMC) simulation, the dynamic magnetocaloric effect of a ferrimagnetic C70 Fullerene-like structure is studied within the dynamic Ising model under of a magnetic (h(t)) field. The influences of the amplitude (h0) and the frequency (ω) of the h(t) magnetic field and bias field (hb) on the thermal behavior of the dynamic order parameter and the dynamic magnetocaloric properties (the dynamic isothermal ΔSiso(T,h(t)) entropy variation and the dynamic ΔTad(T,h(t)) adiabatic variation of temperature), the dynamic specific heat, the dynamic entropy and as well as the dynamic refrigerant capacity (RC(t)) ferrimagnetic C70 Fullerene-like structure are studied. Our results may be a reference for future experiment and theoretical studies of the nano-clusters.

In situ temperature-modulated microscopy observation of two-phase co-existing states of coumarin and coumarin derivative in melting

Coumarin (C9H6O2) and coumarin derivative, coumarin 6H (C15H15NO2) samples were observed with a polarizing microscope at and around the melting points. The states of the two samples are crystalline at room temperature. When the temperature of the Coumarin sample was raised and a part was melted, the crystalline phases coexisted with the liquid phase. The crystal surface coexisting with the liquid phase went through a repetition of melting and crystallization on slightly modulating the sample temperature. The two-phase coexisting state was observed with a digital camera attached to a microscope. The changes in the number of pixels in the crystal part of the photographed image showed Debye relaxation with temperature change. It was found that the relaxation time was 4.9 s when the number of pixels decreased due to surface melting or increased due to surface crystallization. This relaxation time was in good agreement with that of the dynamic-specific heat measured by AC calorimetry. The coumarin 6H microcrystal also coexisted with the melt in a temperature range at and around the melting point. The change in the number of pixels of the coumarin 6H crystal part showed Debye relaxation with respect to the temperature, and the relaxation time was 15 s, which was the same as the relaxation time of the dynamic-specific heat measured in the melting temperature range of coumarin 6H.

Dynamic magneto-caloric effect of a multilayer nanographene: Dynamic quantum Monte Carlo

Using the dynamic quantum Monte Carlo simulation, the dynamic magnetocaloric effect of a ferromagnetic multilayer nanographene (MNG) is studied within the dynamic Ising model under the applied of a time-dependent oscillating (h(t)) magnetic field. The influence of the amplitude h0 and the period τ of the h(t) and the transverse field Ω on the thermal behavior of the dynamic order parameter and the dynamic magnetocaloric properties (the dynamic isothermal ΔST(T,h(t)) entropy change and the dynamic ΔTadT,h(t) adiabatic change of temperature), the dynamic specific heat, the dynamic entropy and as well as the dynamic relative cooling power (RCP(t)) ferrimagnetic MNG are studied. Our predicted results may be a reference for future experiment and theoretical studies of the nanostructures.

Numerical investigation on spontaneous droplet/bubble migration under thermal radiation

The spontaneous migration of droplet/bubble has widely application in manipulating droplet/bubble in microgravity. In this study the droplet/bubble migration due to thermal capillary force under uniform incoming thermal radiation is numerically investigated. The numerical model is based on the transient two-dimensional axisymmetric model with a level set method. After validation with the analytical solution under low Reynolds numbers and Marangoni numbers, the study is extended to the droplet/bubble migration under high Reynolds numbers and Marangoni numbers. The ratios are defined as the values in the outer continuous phase over those in the inner discrete phase. The ratios of dynamic viscosity, thermal conductivity, density and specific heat on the migration velocities of droplet/bubble are investigated under all Reynolds numbers. It is found that the droplet/bubble can migrate spontaneously under thermal radiation due to thermal capillary effect, the driving force is from the induced pressure drop in the middle region of droplet/bubble. Under low Reynolds numbers the migration velocities depend only on the ratios of dynamic viscosity and thermal conductivity, while under high Reynolds numbers they also depend on the ratios of density and specific heat. Under all Reynolds numbers the migration velocities are the lowest when the dynamic viscosity or thermal conductivity in the continuous phase is equal to that in the discrete droplet/bubble phase. With the increasing difference between the continuous phase and discrete phase, the migration velocities are increased. This study might be helpful for manipulating droplet/bubble through thermal capillary force with incoming thermal radiation.

An acoustic approach to assess natural gas quality in real time

The natural gas industry needs fast and robust techniques to monitor the quality of the natural gas, if possible during the flow measurement process. A potential technique relies on extrapolating the dynamic specific heat of the gaseous mixture via measurements at a few frequencies (Petculescu and Lueptow, Phys. Rev. Lett. 94, 238301 (2005); Sensors and Actuators B: Chemical 169, 121–127 (2012)). At the core of this approach lies a first-principles model for sound absorption and dispersion in polyatomic gases. We will show and discuss the applicability and limitations of this potential technique to predicting the content of nitrogen, oxygen, carbon dioxide, and water in natural gas.

Low temperature calorimetry and its application in material research

Low temperature calorimetry is an experimental method of specific-heat measurement of condensed matters, and the specific heat is one of the most important and fundamental thermodynamic properties. There are mainly four methods of specific heat measurement, including adiabatic, relaxation, AC and continuing heating calorimetry. The adiabatic calorimetry is the most accurate and reliable in the specific heat measurement, since it is a static method that the sample can reach a thermal equilibrium during the measurement. However, there is no commercial adiabatic calorimeter yet because of complicated instrumentation, time consuming experimental procedures, and large sample amount requirements. The other three are dynamic specific heat measurement method, in which the sample is measured in a heating manner, and consequently a good thermal conductivity is required for a sample to obtain a reliable measurement. The specific heat is a bulk property of substance, and it can provide an average measure of the thermal properties of a sample. It is well known that the condensed states of matters are mainly controlled by the molecular motions, intermolecular interactions, and interplay among molecular structures. The physical property reflected in a material may be closely related to the energy changes in these three factors, which can be directly observed in a specific heat curve. Therefore, specific-heat measurements have been used not only to obtain entropy, enthalpy and Gibbs free energy, but also to investigate and understand lattice vibrations, metals, superconductivity, electronic and nuclear magnetism, dilute magnetic systems and structural transitions.

Standing magnetic wave on Ising ferromagnet: Nonequilibrium phase transition

The dynamical response of an Ising ferromagnet to a plane polarised standing magnetic field wave is modelled and studied here by Monte Carlo simulation in two dimensions. The amplitude of standing magnetic wave is modulated along the direction x. We have detected two main dynamical phases namely, pinned and oscillating spin clusters. Depending on the value of field amplitude the system is found to undergo a phase transition from oscillating spin cluster to pinned as the system is cooled down. The time averaged magnetisation over a full cycle of magnetic field oscillations is defined as the dynamic order parameter. The transition is detected by studying the temperature dependences of the variance of the dynamic order parameter, the derivative of the dynamic order parameter and the dynamic specific heat. The dependence of the transition temperature on the magnetic field amplitude and on the wavelength of the magnetic field wave is studied at a single frequency. A comprehensive phase boundary is drawn in the plane described by the temperature and field amplitude for two different wavelengths of the magnetic wave. The variation of instantaneous line magnetisation during a period of magnetic field oscillation for standing wave mode is compared to those for the propagating wave mode. Also the probability that a spin at any site, flips, is calculated. The above mentioned variations and the probability of spin flip clearly distinguish between the dynamical phases formed by propagating magnetic wave and by standing magnetic wave in an Ising ferromagnet.

Ising metamagnet driven by propagating magnetic field wave: Nonequilibrium phases and transitions

The nonequilibrium responses of Ising metamagnet (layered antiferromagnet) to the propagating magnetic wave are studied by Monte Carlo simulation. Here, the spatio-temporal variations of magnetic field keep the system away from equilibrium. The sublattice magnetisations show dynamical symmetry breaking in the low temperature ordered phase. The nonequilibrium phase transitions are studied from the temperature dependences of dynamic staggered order parameter, its derivative and the dynamic specific heat. The transitions are marked by the peak position of dynamic specific heat and the position of dip of the derivative of dynamic staggered order parameter. It is observed that, for lower values of the amplitudes of the propagating magnetic field, if the system is cooled from a high temperature, it undergoes a phase transition showing sharp peak of dynamic specific heat and sharp dip of the derivative of the dynamic staggered order parameter. However, for higher values of the amplitude of the propagating magnetic field, system exhibits multiple phase transitions. A comprehensive phase diagram is also plotted. The transition, for vanishingly small value of the amplitude of the propagating wave, is very close to that for equilibrium ferro–para phase transition of cubic Ising ferromagnet.

Polarised Electromagnetic Wave Propagation Through the Ferromagnet: Phase Boundary of Dynamic Phase Transition

The dynamical responses of ferromagnet to the propagating electromagnetic field wave passing through it are modelled and studied here by Monte Carlo simulation in two dimensional Ising ferromagnet. Here, the electromagnetic wave is linearly polarised in such a way that the direction of magnetic field is parallel to that of the magnetic momemts (spins). The coherent propagating mode of spin-clusters is observed. The time average magnetisation over the full cycle (time) of the field defines the order parameter of the dynamic transition. Depending on the value of the temperature and the amplitude of the propagating magnetic field wave, a dynamical phase transition is observed. The dynamic transition was detected by studying the temperature dependences of the dynamic order parameter, the variance of the dynamic order parameter, the derivative of the dynamic order parameter and the dynamic specific heat. The phase boundaries of the dynamic transitions were drawn for two different values of the wave lengths of the propagating magnetic field wave. The phase boundary was observed to shrink (inward) for lower speed of propagation of the EM wave. The divergence of the releavant length scale was observed at the transition point.

Geometrically frustrated magnetism of spins on icosahedral clusters: The Gd3Au13Sn4quasicrystalline approximant

By investigating the magnetism of spins on a quasiperiodic lattice, we present an experimental study of static and dynamic magnetic properties, specific heat, and magnetic entropy of the Gd${}_{3}$Au${}_{13}$Sn${}_{4}$ quasicrystalline approximant. The magnetic sublattice of Gd${}_{3}$Au${}_{13}$Sn${}_{4}$ is a periodic arrangement of nonoverlapping spin clusters of almost perfect icosahedral symmetry, where gadolinium localized $f$ magnetic moments are distributed on equilateral triangles. The absence of disorder on the magnetic sublattice and the antiferromagnetic (AFM) interactions between the nearest-neighbor spins distributed on triangles result in geometrical frustration of spin-spin interactions. Thus, the Gd${}_{3}$Au${}_{13}$Sn${}_{4}$ phase can be viewed as a prototype site-ordered, geometrically frustrated spin system on icosahedral clusters. The zero-field-cooled and field-cooled magnetic susceptibilities, the alternating current susceptibility, the thermoremanent magnetization, the memory effect, the magnetic specific heat, and the magnetic entropy all show that the spin system undergoes at low temperatures a transition to a nonergodic state at the spin freezing temperature ${T}_{f}$ \ensuremath{\approx} 2.8 K. Below this, the ergodicity is broken on the experimental timescale, because the thermally activated correlation times for the spin reorientations become macroscopically long. The magnetic state achieved at low temperatures by continuous cooling in low magnetic fields is likely a superposition of (1) metastable states with randomly frozen spins that have no long-range order yet undergo gradual spin-freezing dynamics and (2) an AFM-like magnetically ordered state with critical slowing dynamics. The magnetic properties of the site-ordered, geometrically frustrated Gd${}_{3}$Au${}_{13}$Sn${}_{4}$ system are discussed in comparison to site-disordered spin glasses that contain both randomness and frustration.

Specific heat of hydrated lysozyme, water's contribution to its dynamics, and criteria for glass formation of biomaterials

Previous studies of the dynamics of hydrated proteins had shown a feature resembling an exceptionally broad glass-softening endotherm. Its onset temperature, denoted as T(g), was indefinable in one calorimetric study of hydrated lysozyme and was in the 148-218 K range in another study, depending upon hydration. Other methods reported this T(g) as ~170 K. We argue that glass-formation of biomaterials should be studied by measuring a property on both the cooling and heating paths and it should be ascertained (i) that there is thermal hysteresis of the measured property, (ii) that the real and imaginary components of a dynamic property obey the Kramers-Kronig relations, and (iii) that there is an effect of annealing that is consistent with the glass phenomenology. We report the real and imaginary components of the dynamic specific heat, C(p)' and C(p)", of dry and two hydrated lysozyme samples on the cooling and the heating paths as well as the effects of annealing and changing the frequency. For the most hydrated (34.6 g water per 100 g lysozyme) sample, C(p,app) does not show thermal hysteresis in the 160-230 K range, C(p)' varies in a sigmoid-shape manner with T while C(p)" remains close to zero, and there is no effect of annealing. We interpret these findings in terms of continuous development of ice-like aggregates of immobile H2O as more H-bonds form on cooling, and continuous deterioration of the aggregates on heating. As the equilibrium constant between the aggregates and mobile H2O increases on cooling, configurational degrees of freedom of H2O molecules and lysozyme segments decrease. Consequently, the net change in enthalpy is small but the change in C(p) is large. Mobility of the lysozyme segments still depends upon the mobility of H2O molecules.

On the state of water in 2.4 nm cylindrical pores of MCM from dynamic and normal specific heat studies

Relaxation phenomenon, thermodynamics, and phase transformation of water in nanopores has been studied by differential scanning calorimetry, usually on heating a precooled sample. Interpretation of such results is ambiguous, because the data do not indicate whether or not there is a thermal hysteresis between the heating and cooling paths. We argue that measurements on both the cooling and heating paths are needed, particularly for complex systems, and also measurements of the complex quantity are needed to ascertain that the Kramers-Kronig relations for a relaxation process are obeyed. We report a study of the real and imaginary components of the complex specific heat, C(p)' and C(p)", and the time-dependent C(p,app) of water confined to 2.4 nm diameter cylindrical pores on both the cooling and heating paths, and use different thermal histories. C(p,app) of nanoconfined water shows two exothermic peaks during cooling below 255 K at 12 K/h and only one endothermic peak on heating, and the enthalpy change determined from the exotherm is more than that determined from the endotherm. C(p,app) and C(p)' of the partially crystallized water is higher at 240 K than at 275 K on the cooling path, and C(p,app) and C(p)' of the partially crystalline water are lower at 240 K than at 275 K on the heating path, thus showing a thermal hysteresis in this range. Studies by using 60 K/h cooling and heating rates and the effect of heat treatment at selected temperatures confirm that the features observed are due to slow crystallization and slow melting. The endotherm observed on the heating path with onset at 220 K and peak at 227 K is due to gradual melting of the ice in nanopores, and not due to glass-softening transition, a liquid-liquid transition, or an approach toward the conjectured critical point of the supercooled water in the 2.4 nm pores.

Optimal design of classic Atkinson engine with dynamic specific heat using adaptive neuro-fuzzy inference system and mutable smart bee algorithm

In this article, an improved version of Artificial Bee Colony (ABC) algorithm is developed to optimize a multi-modal thermodynamic power system with dynamic specific heat. Since original Karaboga's ABC for constraint problems does not consider the initial population to be feasible, a modified method called “Mutable Smart Bee Algorithm” (MSBA) is used which utilizes mutable heuristic agents. These mutable agents are also capable to maintain their historical memory for the location and quality of food sources. These features have been found as strong elements for mining data in constraint areas. In additions, our implementations reveal that MSBA is faster than Karaboga's method. To elaborate on authenticity of MSBA, several state-of-the-art techniques are used as rival methods to optimize well-known benchmark problems. Then, two main steps are made to optimize Atkinson engine. Firstly, an Adaptive Neuro-Fuzzy Inference System (ANFIS) is developed to identify the dynamic behavior of specific heat. Then, MSBA is hired to design the optimum features of the engine. It is observed that the proposed method is capable to successfully handle the real-life engineering problem as well as the numerical benchmark problems.