Reduction Of Specific Heat Research Articles

Investigation of Thermodynamic Properties and Stability of Metal Oxide (CuO and Al2O3)/Deionized Water Nanofluids for Enhanced Heat Transfer Applications

The potential of nanofluids in improving heat transfer efficiency is well recognized, although there is a lack of clarity regarding the methods for assessing their stability and the influence on thermophysical properties. Moreover, the prevention of nanoparticle aggregation, which is essential for stability, requires further investigation. This study aims to address these issues by investigating the thermodynamic properties and stability of Al2O3/deionized water and CuO/deionized water nanofluids, which were prepared using magnetic stirring and ultrasonication. The stability assessment, conducted through standard deviation analysis, revealed that CuO (80 nm)/deionized water nanofluids exhibited greater stability compared to Al2O3 (80 nm)/deionized water nanofluids. The research explored the impact of temperature, volume concentration, and nanoparticle type under both static and dynamic conditions. Static tests focused on measuring thermal conductivity, viscosity, and specific heat, while dynamic tests involved a heat exchanger setup to determine heat transfer rates. The findings indicated that CuO nanofluids displayed the highest thermal conductivity and the most significant reduction in specific heat and heat transfer rate. Viscosity was found to increase with nanoparticle concentration and decrease with temperature. This study provides valuable insights into the thermophysical characteristics and stability of nanofluids, emphasizing the advantages of CuO-based nanofluids for heat transfer applications.

Graphene oxide – adipic acid nanocomposites for thermal energy storage: Assessment of thermophysical properties and energy storage performance

Adipic acid is one of the organic phase change materials with a melting temperature greater than 150 °C and a freezing point greater than 140 °C, making the same a suitable thermal energy storage medium for near-atmospheric pressure steam generation. This work attempts to alleviate the rate limitation posed by the lower thermal conductivity of adipic acid by adding graphene oxide (GO) nanostructures at lower concentrations such that the energy storage capacity is not severely affected. The resultant GO – adipic acid composites (0–2 wt% GO) were characterized in terms of latent heat for phase change, specific heat and thermal conductivity. The composite containing 1 wt% GO exhibited a 16 % enhancement in thermal conductivity with a 3.4 % reduction in latent heat and 3.6 % reduction in specific heat. The impact of GO addition on the solidification rate was remarkable, with a 44 % enhancement in overall heat transfer coefficient during the initial solidification phase, when solidification was carried out in thermal contact with a constant temperature heat transfer fluid (oil bath). Thus, the present work clearly demonstrates the intensification of heat transfer during the discharge cycle of a thermal energy system with 1 wt% GO-Adipic acid composite as the thermal energy storage medium.

Characterization of thermophysical properties of dry ice-based ethanol/ester oil and its influence on surface hardening of machined Ti-6Al-4V alloy

Recent pandemics played a cardinal role indevelopinghealth-conscious behavior and pushed the industries to seek eco-benign cutting fluids to improve machinability. Therefore, a sustainable hybrid lubri-coolant is proposed by mixing ethanol-biodegradable ester oilin varying proportions (1:0.25,1:0.5,and 1:1). In this work, dry ice (solid CO2)has been added (−76 °C) to improve the cooling capabilities bysublimation. The thermophysical properties along with the surface hardening of machined Ti-6Al-4V alloy was investigated experimentally and the results were compared to without dry ice. Experimental findings showeda reduction in specific heat, density, and viscosity while an enhancement in thermal conductivity by mixingdry ice. After dry ice was added, the specific heat of ethanol dropped by 40%. When ester oil was combined with dry ice, its specific heat also decreased by 50.4%. Therefore it is worthy to mention that the hybrid lubri coolant based on dry ice-based ethanol/ester oil could be an alternative to achieve high-speed machining parameters in machining hard to cut materials for aerospace Industry.

Thermal performance of automobile radiator under the influence of hybrid nanofluid

Hybrid nanofluids contain two or more types of nanoparticles mixed with conventional coolant to enhance the thermophysical properties at atomic level. In this study, CuO/SiO2 nanoparticles are distributed evenly in an ethylene glycol-based coolant and a hybrid nanofluid is formed to investigate the effect of heat transfer and thermophysical properties on automobile engines. The simulation is carried out for various volume concentrations ranging from 0.1% to 0.5%. A significant enhancement is noted in the result as the nanoparticle used exhibits higher thermal conductivity. An enhancement in thermal conductivity is noted to be 6.5% higher than the water/EG coolant. A significant enhancement of 48.24% is noted within Nusselt number and the heat transfer rate. As the volume concentration of nanoparticle is increase from 0.1% to 0.5%, due turbulent nature of flow higher amalgamation of nanoparticle results in better thermal performance of automobile system. A reduction of specific heat is noted at volume concentration of 0.5% is much better as compared to volume concentration of 0.1% nanofluid and water/EG coolant. The superior properties of hybrid nanofluid make it an attractive choice as an automobile coolant as the overall efficiency of automobile increases. The result obtained shows tremendous possibility to improve the performance of automobile and reduce fuel consumption.

Effect of Thermophoresis on Heat Diffusion in Isobutane/Copper‐Oxide Nanofluid under Pool Boiling Condition: Numerical Investigation

Understanding thermophoresis in nanorefrigerants stands challenging for a long period despite the phenomenon is attributed for the motion dynamics of particles in nanofluids. Influence of thermophoretic mobility of copper‐oxide nanoparticles on the heat transfer behavior of isobutane (R600a) refrigerant is reported in this work. Pool boiling of the isobutane/copper‐oxide nanofluid is numerically simulated in computational fluid dynamics utilizing both single and two‐phase approaches. Mobility of particles in the saturated refrigerant is studied, and the time scales associated with (Brownian and momentum) diffusions are numerically solved. The temperature contour of the liquid pool is validated with the experimental data, and the properties of the nanorefrigerant such as thermal conductivity, viscosity, and specific heat are estimated in ANSYS Fluent. 5% increase in thermal conductivity and marginal reduction in specific heat of the nanorefrigerant for 0.01% volume fraction of copper‐oxide nanoparticles is witnessed. Mobility of particles due to temperature gradient is found higher near the heater; however, thermophoretic velocity is predicted to be lower because of the narrow temperature gradient. Numerical results showed that the time scale for momentum diffusion is shorter (in the order of e+03) than Brownian diffusion, and hence the momentum diffusion is found to be the predominant mode of heat transfer in nanorefrigerant.

Cumulative effects of collision integral, strong magnetic field, and quasiparticle description on charge and heat transport in a thermal QCD medium

Our first aim is to explore the effect of the collision integral with the insurance of instantaneous conservation of particle number on charge and heat transport in a thermal QCD medium. The second aim is to see how the dimensional reduction due to strong magnetic field (B) modulates the transport through the entangled effects, {\em such as} collision-time and occupation probability etc. in collision integral. The final aim is to check how the quasiparticle description through dispersion relation of thermal QCD in strong B, alters the aforesaid conclusions. We observe that modified collision term expedites both transport, which is manifested by large magnitudes of electrical ($\sigma_{\rm el}$) and thermal ($\kappa$) conductivities, in comparison to relaxation-collision term. As a corollary, Lorenz number is dominated by the later and Knudsen number is by the former. However, strong B not only flips the dominance of collision term in heat transport, it also causes drastic enhancement of both $\sigma_{\rm el}$ and $\kappa$ and reduction in specific heat. As a result, the equilibration factor, Knudsen number becomes much larger than one, which defies physical interpretation. Finally, quasiparticle description in the absence of strong B impedes the transport of charge and heat, resulting in the meagre decrease of conductivities, however, strong B does noticeable observations: conductivities now gets reduced to physically plausible values, T-dependence of $\sigma_{\rm el}$ gets reversed, {\em i.e.} it now decreases with T, effect of collision integral gets smeared in $\kappa$ etc. Knudsen number thus becomes much smaller than one, implying that the system be remained in equilibrium. These findings attribute to the fact that the collective modes in the dispersion relation of thermal QCD in strong B sets in much larger scale, manifested by large in-medium masses.

Cost‐Saving Opportunities in the Energy Management of Papermaking Processes

AbstractEnergy consumption optimization belongs to the main agendas in sustainable industries. Here, cost‐saving opportunities in the pulp and paper industry as one of the largest industrial energy consumers worldwide are in the focus. Energy‐saving measures are proposed employing a large‐scale mathematical model of a paper machine based on mass and energy balances supported by real‐time experiments in paper machine operation. The presented measures are based on the optimization of paper stock pumping and a drying section operation. The total energy‐saving effect of the four proposed measures accounted for a reduction in specific heat and electricity consumption by more than 2 %. The proposed procedures require no or low investment costs with the overall simple rate of return of less than one year.

Dependence of thermal conductivity on fission-product defects and vacancy concentration in thorium dioxide

The dependence of thermal conductivity on fission generated products (FPs) and vacancies in ThO2 within the temperature range 300–1500 K has been investigated using molecular dynamics (MD) simulations. The effect of defect on specific heat and enthalpy increment is also studied. Two typical FPs: Xe and Kr (0–1.02% defect) and vacancies with 0–5% concentration are examined. The relative change in enthalpy increment due to defects is small (<2%) for lower concentration at all temperatures; however, for higher defect concentration, this parameter decreases with temperature. The vacancies reduce specific heat in the low temperature range, while the reduction is negligible at elevated temperature. In contrast, considering all temperatures, a maximum of ∼2% reduction in specific heat is observed for ThO2-FP systems with any concentration of defect. Thermal conductivity of ThO2 degrades significantly by the FPs and vacancies and the degradation decreases with the increase in temperature. For both pure and defective ThO2, the scattering parameters are derived by fitting a Callaway and Analytical model to MD data. The percentage of reduction (R) by defects in thermal conductivity follows the trend RFP>RVacancy, where RXe is somewhat higher than RKr for the studied concentrations of FPs. The reduction rate is higher for the systems with smaller concentration of defect and vice versa. Our results report that the degree of reduction in conductivity of defected ThO2 is lower compared to that of UO2. We also observed that the clustered defects reduce thermal conductivity more than that by individually distributed defects and conductivity decreases almost linearly with the increase in cluster size.

New hybrid nanofluid containing encapsulated paraffin wax and sand nanoparticles in propylene glycol-water mixture: Potential heat transfer fluid for energy management

The reduction in specific heat commonly encountered due to the addition of nanoparticles to a heat transfer fluid such as propylene glycol-water mixture, can be overcome by co-dispersing surfactant-encapsulated paraffin wax, leading to formation of a hybrid nanofluid. Experimental investigations have been carried out on the preparation and evaluation of thermophysical properties of a hybrid nanofluid containing pluronic P-123 encapsulated paraffin wax (70–120nm diameter, 1–5wt.%) and sand nanoparticles (1vol%) in propylene glycol-water mixture. The comparison of results of differential scanning calorimetry of pure paraffin wax and encapsulated paraffin wax revealed encapsulation efficiency of 84.4%. The specific heat of hybrid nanofluids monotonously increased with paraffin wax concentration, with 9.1% enhancement in specific heat for hybrid nanofluid containing 5wt.% paraffin wax, in comparison to propylene glycol-water mixture. There exists an optimum paraffin wax concentration (1wt.%) for the hybrid nanofluid at which the combination of various thermophysical properties such as specific heat, thermal conductivity and viscosity are favorable for use as heat transfer fluid. Such a hybrid nanofluid can be used as a substitute for propylene glycol-water mixture in solar thermal systems.

Thermal properties of nanotubes and nanowires with acoustically stiffened surfaces

A multilayer elasticity model is developed to investigate the effects of acoustically stiffened surfaces (increased surface moduli) on the specific heat and thermal conductivity of typical nanowire and nanotubes as a function of temperature. Changes in phonon dispersion are analyzed using approximated phonon dispersion relations that result from the solutions to the frequency equation of a vibrating elastic tube or rod. The results of the investigation indicate a 10% reduction in specific heat and a 2% decrease in lattice thermal conductivity at 50 K for a 10 nm outer diameter crystalline nanotube with an inner diameter of 5 nm when the average Young’s modulus of the first three atomic layers on both the inner and outer free surfaces are increased by a factor of 1.87. In contrast, a 10 nm outer diameter nanowire composed of the same material and with an acoustically stiffened outer shell shows an approximate 30% increase in thermal conductivity and specific heat near 50 K. Our simplified model can potentially be extended to investigate the acoustic tuning of nanowires and nanotubes by inducing surface stiffening or softening via appropriate surface chemical functionalization protocols or coatings.

MAGNETIC FIELD DEPENDENCE OF ENTROPY AND SPECIFIC HEAT OF YBa2Cu3O7-δ SUPERCONDUCTORS

The change in thermodynamic quantities (e.g., entropy, specific heat etc.) by the application of magnetic field in the case of the high-Tc superconductor YBCO system is examined phenomenological by the Ginzburg–Landau theory of anisotropic type-II superconductors. An expression for the change in the entropy (ΔS) and change in specific heat (ΔC) in a magnetic field for any general orientation of an applied magnetic field Ba with respect to the crystallographic c-axis is obtained. The observed large reduction of specific heat anomaly just below the superconducting transition and the observed variation of entropy with magnetic field are explained quantitatively.

Adiabatic failure in polyethylene

A series of true stress–strain curves measured in tension, published by Hiss and Strobl [Deformation, yield and fracture of polymers (1997) 439], have been modelled using a Gaussian equation to represent strain hardening. An empirically-based constitutive relation was extracted from the data spanning the temperature range 24–128°C. In the first procedure, adiabatic heating was introduced into the constitutive relation at constant true strain rate by means of an explicit integration scheme that equates incremental plastic work to a temperature rise. At the end of each increment the material properties were adjusted to account for the increase in temperature. In the second procedure, a constant load was assumed and the temperature rise was calculated directly from the work done together with a curve relating temperature to energy input. In each case, it was found that adiabatic conditions had a destabilising effect, which was interpreted using the Vincent–Considere criteria. The possibility of using draw stress instead of yield stress in the calculations was considered and it was concluded that such a change would not qualitatively affect the results. The rise in deformation stresses and the reduction in specific heat at low initial temperatures is expected to increase the thermomechanical instabiliy. These conclusions were shown to be insensitive to minor changes in crystallinity during deformation.

Ginzburg-Landau theory of specific heat anomaly of high- Tc superconductors in magnetic field

The change in specific heat by the application of magnetic field ( B a ∼1 T) in the case of the high- T c superconductors is examined phenomenologically by the Ginzburg-Landau theory of anisotropic type-II superconductors. The observed large reduction of specific heat anomaly just below the superconducting transition is explained quantitatively. We have obtained the expression for the change in specific heat in a magnetic field ( ΔC) for any general orientation of B a with respect to the crystallographic c-axis. We also present the result for a polycrystalline sample. ΔC is shown to be linear in ( B a T c ) [ t (1 −t) ] for temperatures slightly below T c, where t= T T c . The slope of this linear behaviour is found to be related to the anisotropy of the effective mass.

Low temperature specific heats of NiCr and NiV alloys near the ferromagnetic-paramagnetic transition

The magnetic field dependence of the low temperature specific heats of critical concentration alloys of NiCr and NiV has been measured in the range 1−4 K at fields up to 45 kOe. The observed reduction in specific heat with applied field is characteristic of superparamagnetic clusters.