Effective Specific Heat Research Articles

Dynamics of dust particles in a conducting dusty nanomaterials: A computational approach

Subject introduced in the present analysis is the role of dust particles in a conducting dusty nanofluid, past a stretching surface. Thermal conductivity which affects the nanofluid heat transfer is conducted by a suitable model known as Maxwell model. Both the dust and nano particles considered here are spherical. The entire flow phenomena i.e. the momentum and energy is characterizes by taking cupper- and silver- nano particles. The nonlinear fluid phase and dust phase governing equations are transformed to ordinary differential equation with the suitable choice of transformed variables which arises the characterizing parameters for the flow phenomena. Solutions of the coupled ODEs are performed numerically. The role of nanoparticle volume fraction and number density of dust particle along with magnetic field are also important for the heat transfer. The influence of parameters such as dust particle mass concentration, fluid particle interaction parameter, Eckert number, effective specific heat parameter, on momentum and heat profiles are presented through graphs. Verification of current study is obtained by comparing with the earlier study in particular cases and found to be in good agreement

Aqueous nanofluids containing paraffin-filled MWCNTs for improving effective specific heat and extinction coefficient

This paper presents measurements of the effective specific heat and the extinction coefficient for aqueous nanofluids dispersed with paraffin-filled Multi-Walled Carbon NanoTubes (MWCNTs). The MWCNTs were filled with paraffin wax by capillary action. Centrifugal decanting was used to modify the traditional two-step method so as to produce a nanofluid dispersion that was more stable than that produced by the traditional method. The stability of each suspension was quantitatively evaluated with a laser scattering method over 7 days. A differential scanning calorimetry (DSC) and the three-slap method were used to measure the effective specific heat and the extinction coefficient of the nanofluids, respectively. The measured effective specific heat of the water-based paraffin-filled MWCNTs nanofluid, with a volume fraction of 1%, was up to 5.1% larger than that for the water-based MWCNT nanofluids without paraffin wax. The nanofluid extinction coefficient was shown to increase linearly with the volume fraction for data within the independent scattering regime, which occurred when the nanoparticle-distance/wavelength ratio (c/λ) was less than 2.

Validation of different numerical models with benchmark experiments for modelling microencapsulated-PCM-based applications for buildings

This paper assesses the thermal performance of four microencapsulated-PCM-based samples that can be used in the design of new thermal energy storage systems for buildings: a PCM-enhanced plasterboard; three different fin-enhanced aluminium containers filled with the PCM. The methodology covers: the thermophysical characterization of the PCM-based products; the development of charging and discharging experiments to provide data for numerical validation purposes; the numerical modelling considering five different methods dispersed in literature, and a new-improved method. The main goals are to validate the numerical predictions against reliable experimental results and to find out which method is preferable for future simulations. The 3D numerical simulations were based on the effective heat capacity (EHC), additional heat source (AHS) and enthalpy (H-P) approaches. The first two methods were implemented in ANSYS CFX®; the other in ANSYS FLUENT®. For the EHC method, four different ways to specify the variation of the effective specific heat with temperature were assessed. While the H-P commercial code already implemented in ANSYS FLUENT® was used, the other two methods implemented in ANSYS CFX® were developed and validated for the purpose of this study.Good agreement between numerical and experimental results was achieved for all numerical approaches. In fact, it was concluded that the six numerical methods can be used to simulate heat diffusion with solid-liquid phase-changes. However, it was verified that the EHC method with the triangular or the self-adjusted triangular profiles is preferable for both charging and discharging simulations, since it can be drawn based on few information about the PCM-based products; it ensures good predictions of both charging/discharging kinetics and stored/released energy; it can be used without compromising computation time in comparison to other methods. The EHC method with the rectangular profile, recurrently used in literature, exhibits some convergence issues whose resolution has required longer computation times.

Effective negative specific heat by destabilization of metastable states in dipolar systems.

We study dipolarly coupled three-dimensional spin systems in both the microcanonical and the canonical ensembles by introducing appropriate numerical methods to determine the microcanonical temperature and by realizing a canonical model of heat bath. In the microcanonical ensemble, we show the existence of a branch of stable antiferromagnetic states in the low-energy region. Other metastable ferromagnetic states exist in this region: by externally perturbing them, an effective negative specific heat is obtained. In the canonical ensemble, for low temperatures, the same metastable states are unstable and reach a new branch of more robust metastable states which is distinct from the stable one. Our statistical physics approach allows us to put some order in the complex structure of stable and metastable states of dipolar systems.

Investigation of thermal properties of spacer fabrics with phase changing material by finite element model and experiment

This study presents the developed computational finite element models for transient heat transfer analysis in fabrics enriched by phase change materials along with efforts to provide validation on the basis of obtained experimental results. The environment-friendly butyl stearate is used as a phase change material. Its melting/heating absorption takes place in temperature range from 19℃ to 34℃, and the solidification/heat release occurs from 34℃ to 19℃. An important aspect in this analysis is the investigation of appropriateness of the material samples dimensions selected for effective heat capacity against temperature measurements. For this purpose, we used the combined experimental and finite element simulation-based analysis. A similar computational procedure enabled us to estimate the effective latent specific heat relationship of the fabric with phase change materials coating. The direct usage of differential scanning calorimetry (DSC) measurement-based specific heat relationships against temperature in the finite element models ensured good compliance of the computed results with the experiment. For validation of the developed computational models the infrared radiation heating-cooling experiments on fabrics with different deposits of a phase change material were performed. The noticeable influence of content of phase change materials for transient thermal behavior during heating-cooling cycles was determined. The experimental results have been compared against the finite element simulation results.

Numerical investigation on integrated thermal management via liquid convection and phase change in packed bed of spherical low melting point metal macrocapsules

This paper is dedicated to investigate the integrated cooling modality that the spherical low melting point metal (LMPM) macrocapsules were introduced and filled as phase change material (PCM) into a convective cooling heat sink. The fluid-solid heat transfer process coupled with phase change in the packed bed was numerically calculated based on the local thermal non-equilibrium theory and the effective specific heat capacity model which were validated in advance by conceptual experiments. The thermal management ability of composite heat sink packed with spherical LMPM-PCM macrocapsules under typical operating conditions has been revealed. In addition, the influences of different stacking patterns of LMPM particles, particle diameter and inlet velocity on the heat transfer enhancement in the packed bed were comprehensively investigated, respectively. It is found that compared with convective cooling heat sink alone, the composite heat sink filled with LMPM-PCM macrocapsules presents excellent thermal management performance. The temperature increment of heat source in the pulse heat load is reduced by 73.4%, which fully demonstrates the advantages of filling spherical particles. Besides, the Orthoclinal Stacking method achieves the largest volumetric heat transfer coefficient among different stacking patterns of equal-diameter spherical LMPM-PCM macrocapsules. What is more, the plateau duration of the solidification is gradually shortened with the decreasing diameter of the spherical LMPM-PCM macrocapsules and the increasing inlet velocity, which is advantageous for the system to quickly rehabilitate to normal operating temperatures during the de-pulse stage. Overall, this novel integrated cooling modality is proven to be a powerful and practical way to sustain extreme thermal management challenge.

Near-sonic pure steam flow with real-gas effects and non-equilibrium and homogeneous condensation around thin airfoils

A small-disturbance asymptotic model is derived to describe the complex nature of a pure water vapour flow with non-equilibrium and homogeneous condensation around a thin airfoil operating at transonic speed and small angle of attack. The van der Waals equation of state provides real-gas relationships among the thermodynamic properties of water vapour. Classical nucleation and droplet growth theory is used to model the condensation process. The similarity parameters which determine the flow and condensation physics are identified. The flow may be described by a nonlinear and non-homogeneous partial differential equation coupled with a set of four ordinary differential equations to model the condensation process. The model problem is used to study the effects of independent variation of the upstream flow and thermodynamic conditions, airfoil geometry and angle of attack on the pressure and condensate mass fraction distributions along the airfoil surfaces and the consequent effect on the wave drag and lift coefficients. Increasing the upstream temperature at fixed values of upstream supersaturation ratio and Mach number results in increased condensation and higher wave drag coefficient. Increasing the upstream supersaturation ratio at fixed values of upstream temperature and Mach number also results in increased condensation and the wave drag coefficient increases nonlinearly. In addition, the effects of varying airfoil geometry with a fixed thickness ratio and chord on flow properties and condensation region are studied. The computed results confirm the similarity law of Zierep & Lin (Forsch. Ing. Wes. A, vol. 33 (6), 1967, pp. 169–172), relating the onset condensation Mach number to upstream stagnation relative humidity, when an effective specific heat ratio is used. The small-disturbance model is a useful tool to analyse the physics of high-speed condensing steam flows around airfoils operating at high pressures and temperatures.

THE STUDY OF THERMAL DENATURATION OF BEEF, PORK, CHICKEN AND TURKEY MUSCLE PROTEINS USING DIFFERENTIAL SCANNING CALORIMETRY

In the temperature range from 45 °C to 90 °C the process of thermal denaturation of a whole complex of muscle proteins in meat takes place. An effective mode to register the thermal denaturation process is the method of differential scanning calorimetry (DSC). As a result of studies the differences during the process of thermal denaturation of muscle proteins of pork, beef, chicken and turkey were defined by the appearance of endothermic peaks in DSC thermograms. The main variances are associated with the process of denaturation of myosin and sacroplasmic proteins and indicate indirectly their quantitative ratio in meat. The values of effective specific heat capacity in the temperature range from 20 °C to 90 °C are obtained as well as those of heat spent on the denaturation process.At reheating, the values of specific heat capacity increased by 0.1 J/(g*K) on the average, and peaks of thermal denaturation were not detected, that certifies the irreversibility of the denaturation process and the decrease in the bound moisture proportion in meat after thermal processing. Knowledge of the nature of protein thermal denaturation of each kind of meat product is one of the necessary tools for developing the technology of meat product thermal processing.

Modeling of the Thermal Behaviors of an Ultracapacitor and Comparison with Measurement Data

Ultracapacitors (UCs), known by different names such as supercapacitors, electrochemical double-layer capacitors, double-layer capacitors or electrochemical capacitors, have the potential to meet the high pulse power capability of the energy-storage systems for automotive applications. The primary advantages of UCs are higher power density and longer shelf and cycle life as compared to those of batteries. In the high pulse power operations for automotive applications, a large amount of heat is produced inside a UC cell. Because the lifetime and performance of a UC depend strongly on temperature, it is important to predict accurately the thermal behaviors of a UC for the efficient and reliable systems integration from an application perspective. In this work, a three-dimensional thermal model is presented to predict the thermal behaviors of the UC. Both of the irreversible and reversible heat generations inside the UC cell are considered. The effective density and specific heat capacity of the various compartments of the cell are estimated based on the mass fractions of the components of each cell compartment. The effective thermal conductivities of the various compartments of the cell are estimated based on the equivalent networks of parallel and series thermal resistances of the cell components. The validation of the three-dimensional thermal model is provided through the comparison of the modeling results with the experimental IR image at various charge/discharge currents.

Selection of phase change material for solar thermal storage application: a comparative study

The study of five paraffin waxes and wood resin was carried out to investigate their thermo-physical properties. The investigation aimed at selection of a phase change material (PCM), for its potential use as a thermal energy reservoir (TER) in a fabricated solar dryer. Differential scanning calorimeter was used to determine the melting point, solidification point, latent heat of fusion and solidification of these PCM. The T-history analysis was carried out to determine the effective thermal conductivity and specific heat in liquid and solid states. Bulk density of these PCMs was determined using standard pycnometer method. A comparative analysis was done for the selection, and PW1 was selected among the paraffin waxes, while wood resin was rejected. The selected PCM was used in the flat plate collector of solar dryer to identify the thermal zones and to validate its capability as a TER. Maximum temperature achieved at outlet of flat plate collector was 50 °C. The temperature profile built in different zones was determined with and without using PCM. It was found that after 18:00 IST evening, the average flat plate collector chamber temperature with PCM PW1 was found to be 23.5% higher than that without using PCM.

Silica nanoparticles as copper corrosion inhibitors

Nanoparticle suspensions (or ‘nanofluids’) employed as heat transfer fluids (HTF) enhanced the thermal conductivity and the effectiveness of the heat exchangers as well as efficacy of thermal energy storage (TES) platforms by augmenting the effective specific heat capacity of various solvents. In prior studies, molten salt nanofluids also reduced corrosion by 50% (compared to that of neat molten salts and pure molten salt eutectics). Here, we demonstrate that silica nanoparticle suspension could be beneficial not only from the point of higher rates of heat transfer and thermal energy storage but also as corrosion inhibitors of copper substrates, that are typically used for thermal systems (e.g., HTF and TES). Combined use of Quartz Crystal Microbalance (QCM) technique and atomic force microscopy indicate a significant lowering of the corrosion rates (up to 4 times) when only 10% of the surface is covered by silica nanoparticles with a nominal diameter of 10 nm. These results are attributed to the negative surface potential of silica nanoparticles. As a result when the nanoparticles precipitate on the copper surface and form surface ‘nano-fins’—they preferentially prevent negatively charged ions (such as chlorine ions) from approaching the metal surface and thereby serve as an impediment from increasing the metal dissolution rate. This counter-intuitive behavior occurs even when the nanofins are formed randomly (i.e., without forming a uniform coating) and are sparsely dispersed on the copper substrate. This phenomenon of reduced corrosion is attributed to be another manifestation of the ‘nano-Fin Effect (nFE)’.

Entropy of Schwarzschild-de Sitter Black Hole with Extra Term Correction**Supported by the National Natural Science Foundation of China under Grant Nos. 11675139, 11605137, 11435006, 11405130 and the Double First-Class University Construction Project of Northwest University. Bin Wu is also supported by the China Postdoctoral Science Foundation under Grant No. 2017M623219 and Shaanxi Postdoctoral Science Foundation

The thermodynamical quantities are usually considered as the independent ones in the case of the existence of multi-horizons. Comparing the first laws for the event horizon and cosmological horizon of Schwarzschild-de Sitter space-time, we find them share the same values of mass, charge and cosmological constant, which might imply that there exists entanglement between the two horizons. Naturally we attempt to add an extra term, which contributed to the total entropy of the black hole. We recalculate the total entropy and the effective specific heat by taking the globally effective first law and find that they will be emanative when the two horizons approach to each other.

Heat transport and storage processes in differential scanning calorimeter: Computational analysis and model validation

Experimental results provided by differential scanning calorimetry (DSC) can be affected by systematic errors, which are difficult to identify and quantify correctly by the end-users, as a DSC device is commonly used as a gray box. The signal delay due to thermal inertia and the effects of sample size or heating rate present the most common sources of uncertainties. In this paper, a 3-D computational model of a differential scanning calorimeter is constructed, calibrated and validated. Five reference standards are used for both experimental and computational calibration, resulting in a very good agreement (R2 > 0.999794) of the computational model with experimental outputs. Model is validated using two different materials and processes. The analysis of melting of aluminum, as one of the standards not used at the calibration, shows a maximum difference of 0.279 mW·mg−1 at the peak top, which is well within the accuracy limits. The application of the model for the determination of effective specific heat capacity of quartz, as a representative of commonly studied materials which are though not standardized for DSC, reveal a good agreement with both the measured data and the results of independent experiments reported by several other investigators. The main advantage of the model consists in the detailed analysis and separation or quantification of particular heat evolving/consuming mechanisms in both the DSC device and the studied materials. Therefore, contrary to the empirical calibration, it can identify exactly the physical sources of measurement uncertainties. The raw experimental data provided by the DSC device can then be corrected in a straightforward way and the systematic errors can be eliminated.

Experimental investigation of paraffin nano-encapsulated phase change material on heat transfer enhancement of pulsating heat pipe

In this study, a mixture of nano-encapsulated phase change materials in water has been used as the working fluid in a pulsating heat pipe in order to investigate its thermal performance. The results of the experiments showed that using the nano-encapsulated paraffin dispersed in water as working fluid improves heat transfer and decreases the thermal resistance of the pulsating heat pipe. On the other hand, among the tested concentrations for nano-encapsulated paraffin, there is an optimal value in which increasing the concentration causes an increase in the thermal resistance of the pulsating heat pipe due to the increased dynamic viscosity of the fluid. Enhancement in the thermal performance of the pulsating heat pipe by adding paraffin nanocapsules is attributed to the increase in effective specific heat of the fluid mixture as a result of the latent heat of paraffin nanocapsules. Higher effective sensible heat leads to an augmentation of convective heat transfer which has the main role in heat transfer of heat pipes. Moreover, the existence of nano-encapsulated paraffin can result in more mixing which is another reason for heat transfer enhancement. In addition, the use of nano-encapsulated phase change paraffin at high concentrations causes a cessation in the dry-out phenomenon at higher heat input compared with water or, in other words, increases the operating range of the pulsating heat pipe, which is due to an increase in the heat capacity of the fluid. In addition, the effect of inclination angle (30°, 60°, and 90°) on the thermal performance of the PHP at an optimum concentration among tested concentrations of nano-encapsulated paraffin was investigated, which was equal to 6.25 g L−1. It was observed that the PHP had its best thermal performance at the vertical position. The lowest measured thermal resistance of the PHP was 0.86 K W−1 in a vertical orientation and 50 W heat input. Moreover, at 30°, the thermal resistance of the PHP sharply increased, which can be attributed to the reduced effect of gravity in fluid return from the condenser to the evaporator. The maximum thermal resistance of the PHP observed in the case of inclination angle equal to 30° and 10 W heat input was 5.38 K W−1.

Determination of effective specific heat capacity of interior plaster containing phase change materials

A precise technique for determination of effective specific heat capacity of building materials is presented within this paper. The applicability of the technique is demonstrated on a PCM-enhanced plaster, being characterized by a phase change between 15 and 30 °C. The effective specific heat capacity is determined by means of inverse analysis of calorimetric data using computational model of the device. The identified effective specific heat capacity values reached up to 1890 J·kg-1·K-1 when cooled and 1580 J·kg-1·K-1 when heated. Using this quantity in simulation of thermal performance, the PCM-enhanced plaster showed to have a promising potential to be used in buildings’ interiors as a thermal regulator to stabilize inner environment as it contributed to a thermal oscillation decrease by up to 2.5 °C

Decoupling Multiple Rotational Relaxations of Hydrogen to Detect Gas Mixtures

Decoupling multiple acoustic relaxations in multi-component gas mixtures is an effective method to acquire acoustic relaxation characteristic of gas molecules, which can be used to determine gas composition. However, decoupling multiple rotational relaxations of hydrogen still remains challenge. In this paper, we present the decoupling model of hydrogen and decouple the multiple rotational relaxation into the group of single-relaxation ones. Based on this model, the whole rotational relaxation process of hydrogen can be simplified as a few decoupled single rotational relaxation processes. The decoupled results of the effective specific heat, the absorption spectrum and the acoustic velocity dispersion agree with the experimental data, which validates our decoupling model. Furthermore, the proposed decoupling rotational relaxation model can be combined with the existing decoupling vibration model to detect gas mixture. Applications in the detection of gas mixtures including N 2 , CO 2 , O 2 and H 2 are provided. Compared with existing gas sensing method ignoring rotational relaxation, our detection result of gas mixtures H 2 - O 2 - H 2 O is more convincing since the proposed decoupling model contains significant rotational relaxation of hydrogen. Therefore, the proposed decoupling model not only reveals the mechanism of multiple rotational relaxations of hydrogen, but also provides the new method to detect hydrogen gas mixtures.

Enhanced heat capacity of binary nitrate eutectic salt-silica nanofluid for solar energy storage

In concentrating solar power plants, the heat capacity of thermal storage media is a key factor that affects the cost of electricity generation. This work investigated the effective specific heat capacity of binary nitrate eutectic salts seeded with silica nanoparticles, using both experimental measurements and molecular dynamics simulations. The effects of the mass concentration (0–2.0 wt%) and average size (10, 20, and 30 nm) of the nanoparticles on the specific heat capacity value of nanofluids were analyzed. The results show that specific heat capacity increases when adding 10 nm silica nanoparticles up to 1.0 wt%, and then it decreases at higher concentrations. At this optimal mass concentration, the 20 nm nanoparticles displayed a maximum enhancement in the average specific heat capacity (by ~26.7%). The simulation results provided information about the different energy components in the system. The rate of potential energy change versus nanoparticle mass concentration was found to be maximized at 1.0 wt% concentration, which agrees with the experimental measurements. The potential energy components in the simulation system indicate that the change of Coulombic energy contributes the most to the variation of specific heat capacity.

Effect of surface hydroxyl groups on heat capacity of mesoporous silica

This paper quantifies the effect of surface hydroxyl groups on the effective specific and volumetric heat capacities of mesoporous silica. To achieve a wide range of structural diversity, mesoporous silica samples were synthesized by various methods, including (i) polymer-templated nanoparticle-based powders, (ii) polymer-templated sol-gel powders, and (iii) ambigel silica samples dried by solvent exchange at room temperature. Their effective specific heat capacity, specific surface area, and porosity were measured using differential scanning calorimetry and low-temperature nitrogen adsorption-desorption measurements. The experimentally measured specific heat capacity was larger than the conventional weight-fraction-weighted specific heat capacity of the air and silica constituents. The difference was attributed to the presence of OH groups in the large internal surface area. A thermodynamic model was developed based on surface energy considerations to account for the effect of surface OH groups on the specific and volumetric heat capacity. The model predictions fell within the experimental uncertainty.

Influence of process parameters on solidification length of twin-belt continuous casting

A temperature based Finite Element Model is developed to estimate the evolution of temperature, shell growth profiles and solidification length of a solidifying ingot in a twin-belt caster. The model is based on the 2-D slice which travels through the caster with time. A transient energy equation is solved with the incorporation of thermal boundary conditions which depends on the position of the slice. The latent heat released during the solidification is incorporated through the effective specific heat method. The convective heat flux due to the belts, and dam blocks inside the caster and from spray cooling outside the caster are applied as boundary conditions. The belt heat flux is estimated by incorporating thermal resistances of the cooling water, the belt, the coating, the interface between belt and ingot, the solidifying shell and the melt. At the interface between belt and ingot, the gap dependent heat transfer is considered which is based on the combined mode of radiation and conduction. The amount of gap is calculated iteratively by considering the thermal contraction of the solidifying ingot. The dam block heat flux is estimated by approximating it as a semi-infinite body. The model is applied to the state of the art industrial twin-belt continuous copper casting. The simulated temperature and shell thickness results are compared with the data measured at the industrial caster. It is found that the travelling slice model predicts comparable results with industrial data for high speed copper casting. The model is extremely useful for industrial engineers to know the design aspects of the twin-belt caster such as final solidification length, belt, dam block and ingot dimensions and casting speed. The effect of the process parameters on temperature evolution and shell growth profiles are analysed in detail. The procees length is proportional to casting speed. When the casting speed and heat flux are constant, decrease of cross section size decreases the solidification length

Development of a physical-mathematical model for the process of crystallization of meat systems

It is proven that the complex of processes that occur during freezing-defrosting of meat systems cannot be described within the framework of the theory of freezing out true solutions. A characteristic feature of meat systems is the heterogeneity in terms of chemical composition, structure and properties. Given this, within the framework of the proposed physical-mathematical model for the process of crystallization, meat system is regarded as a colloidal capillary-porous body. In this case, a process of crystallization is considered as the superposition of two processes: freezing out free moisture (basic process) and a competing process for increasing binding energy for the bound moisture. It was established that the aforementioned processes differently depend on temperature: the speed of freezing out moisture decreases with a decrease in temperature while the rate of the competing process, on the contrary, increases. It was theoretically predicted and experimentally proven that a change in the information parameters of effective specific heat capacity is the criterion of reversibility of the process of low temperature treatment. As revealed by computer simulation, the proposed model more adequately reflects the actual character of dependence of the effective specific heat capacity of meat systems with different composition and properties. Based on the proposed physical-mathematical model for the crystallization of meat systems, we have developed a method for determining effective specific heat capacity (C e ) using the thermograms of freezing-defrosting. Information parameters, which were derived from the temperature dependence of effective specific heat capacity, are: t cr/mel is the temperature of maximum rate of crystal formation (melting), oC; Dt cr is the cryoscopic interval of temperatures, oC; DН cr is the specific heat of phase transition in a cryoscopic interval of temperatures, J/K; Dw is the share of moisture, which changes its aggregate state in a cryoscopic interval of temperatures (the amount of free frozen out or melted moisture). The study conducted became the basis for the scientific substantiation of technologies for manufacturing semi-finished frozen minced meat products for the criterion of reversibility