Papers by Keyword: Thermal Diffusivity

Abstract: In various fields such as engineering, nanotechnology, and biomedical sciences, the study of non-Newtonian nanofluid flow with heat generation is becoming increasingly important. However, it is challenging to accurately model such flows due to their complex behavior and slip effects at the fluid-solid interface. This research investigates the impact of first and second-order slip conditions on the flow and heat transfer properties of a non-Newtonian nanofluid using a power law model to describe the fluid's non-Newtonian behavior and numerical methods to solve the resulting equations. To determine the influence of various parameters such as slip parameters, Brinkman number, power law index, and Eckert number on the velocity, temperature, and concentration profiles, which this study examines. The study shows that slip parameters significantly determine the flow and heat transfer properties of non-Newtonian nanofluids, the study also reveals that slip parameters are a crucial factor in understanding the flow and heat transfer characteristics of nanofluids, with the second-order slip condition having a greater impact on velocity and temperature profiles than the first-order slip condition. These findings are valuable for developing and optimizing heat transfer devices that involve non-Newtonian nanofluids with heat generation, which is essential for technological advancements in today's industry.

Abstract: This article discusses the use of solar dryers as a method for stabilizing and reducing the volume of residual sludge produced by wastewater treatment facilities. The study focused on the convective drying behavior of sewage sludge produced by the wastewater treatment plant of Meknes City under convective solar drying. The study aimed to investigate the drying kinetics of sewage sludge and emphasize the effect of temperature and water content on the evolution of the drying rate. The measured water content values showed a decrease as drying time increased. The results revealed the presence of phase II, which characterizes the decreasing rate drying period, and the absence of phase I, which describes the constant rate drying period.The study developed an empirical model to describe the kinetic behavior of convective solar drying of Moroccan domestic sludge. The model can be used to predict the shape of a drying curve under other aerothermal conditions. Additionally, the study analyzed the thermal diffusivity and activation energy of sewage sludge using an experimental macroscopic method based on Fick's diffusion model and the Arrhenius equation. The measured diffusion coefficient values range from 0,71 10^-9 m².s^-1 to 1,47 10^-9 m².s^-1, and the value of activation energy was evaluated at 17.54 kJ/mol.

Abstract: Herein, we report for the first time the thermal diffusivity of zinc ferrite/ silver/ silver chloride nanocomposite with a four-fold enhancement in comparison with the base fluid. A systematic analysis of the dependence of calcination temperature and synthesis routes on the crystallinity of nanocomposites of zinc ferrite with silver and silver chloride suiting it for diverse applications was done. Synthesized via the co-precipitation method, the samples were characterized using X-ray diffraction, Field emission scanning electron microscopy, Energy dispersive X-ray, Vibration sample magnetometer, ultraviolet-visible Diffusive Reflective spectroscopy and Photoluminescence studies. A zeta potential of -31.1mV was obtained for the sample showing good colloidal stability. The thermal diffusivity of the samples as nanofluids was analyzed using the dual beam thermal lens method. The study also envisages the magnetically retrievable and visible light-active nature of the synthesized samples indicating their suitability for photocatalytic degradation of toxic dyes. The work on photocatalytic degradation of methylene blue stands out in attaining rapid, efficient dye degradation of 98% within 90 minutes of sunlight exposure in comparison with unblended zinc ferrite nanoparticles even without any oxidizing agent.

Abstract: Carbon fiber reinforced carbon composites (C/C composites) have been important structural materials at high temperatures. C/C composites are anisotropic solids and their thermal diffusivity is the second-order tensor of which components are called thermal diffusivity coefficients. Therefore, the purpose of study is to measure the thermal diffusivity in direction parallel to fiber and that in direction perpendicular to fiber by using the step heating method. This report demonstrates the correctness of the method to determine the thermal diffusivity in principal direction by comparing the time change of temperature observed by the experiment at room temperature for the C/C composite with the mathematical solution for the heat conduction under one dimension.

Abstract: Polycarbonate is a tough, amorphous and transparent high performance thermoplastic polymer. It is used in many fields of application due to its versatile thermophysical, mechanical and optical properties. However, one of its drawbacks is its relatively high thermal conductivity which prevents its application as an insulating material. An appropriate heat treatment can therefore be a useful route to improve the thermal insulating property. The objective of this work is to study the effect of heat treatment; namely the influence of the quenching temperature above and below the glass transition temperature (Tg) on the thermophysical properties of neat polycarbonate (PC). The effect of the quenching temperature above Tg was also studied for neat poly (methyl methacrylate) (PMMA). The effect of residual stresses (RS) generated by the free quenching process on the thermophysical properties of neat PC was investigated. The thermal conductivity (k) and thermal diffusivity (a) of neat PC were measured using a periodic measurement method (DICO), (DIffusivity and COnductivity), at room temperature. The DICO method developed in the CERTES laboratory (Center for Studies and Research in Thermal, Environment and Systems of Paris 12 University), allows simultaneous access to the conductivity and thermal diffusivity from which the specific heat (Cp) can then be deduced. This work showed that the quenching from a high temperature above Tg did not affect the thermal conductivity and thermal diffusivity of both PC and PMMA. However, quenching from a temperature below Tg (130 ° C) caused a decrease of both the thermal. In fact the thermal conductivity of PC annealed at 130 ° C which is 0.22 W. m^-1 .K^-1 decreased to 0.06 W. m^-1 .K^-1 and 0.14 W. m^-1 .K^-1 after quenching at 0° C and 40 ° C respectively. This means that quenching would therefore improve the insulating capacity of PC compared to the material which has undergone only annealing. Contrary to the thermal conductivity, the values of the specific heat capacity in this temperature range ( 0° C – 40° C) significantly increased as a result of quenching. They increase from 1118 J. kg^-1. K^-1 for the annealed sample to 1290 J. kg^-1. K^-1 for PC quenched at 0° C and increased to 2221 J. kg^-1. K^-1 for PC quenched at 40 ° C which corresponds to an increase by 98 %. It was also found that the values of thermal conductivity and specific heat were in good agreement with those reported in the literature for neat PC samples quenched below Tg.

Abstract: In the field of food cooling and freezing computation, the accurate determination of thermo-physical properties such as specific heat, thermal conductivity and density is necessary and specially important to optimize the energy consumption of equipment. These parameters depend on the food composition and temperature usually determined by theoretical or experimental method or the combination of both. Experimental method using differential scanning calorimetry (DSC) is the best approach to yield correct results. However, DSC method requires expensive equipment and it might be not suitable for limited funding in some Vietnamese research centers. Therefore, the line heat source was chosen in this study.This paper introduces a new approach to determine thermal properties of the Vietnamese Pangasius in the temperature range from-40 °C to +40 °C using the line heat source. The results indicated that there is good correllation between the obtained measured data and the results calculated using theoretical models as well as other published experimental results.

Abstract: The choice of highly efficient materials for the opaque parts of the building facades is the most effective factor in increasing its thermal protection. A decrease in the coefficient of U-value of opaque parts of a building directly affects the consumption of both thermal energy and the energy demand for cooling. Two-component or multi-component composite materials today occupy a large place in modern construction. This article analyzes the methodology for testing the thermophysical properties of these materials, reveals a new approach to determine to it, taking into account the links between the thermal conductivity and the thermal diffusivity of materials. The article analyzes the relationship between buildings and the surfaces of the outer envelope and the dependence of the energy efficiency index of the building.

Abstract: The results of studying the effect of isothermal annealing on structural, phase transformations, and thermal diffusivity in the diffusion zone of a Cu-Al layered metal-intermetallic composite (LMIC), obtained using technology including explosion welding, pressure treatment and heat treatment, are presented. It was found that, at 530 °C (the highest temperature, excluding the formation of a liquid phase in this system) with a holding time of up to 1000 h, there are no structural phase transformations in the Al (Cu)/CuAl₂ metal-intermetallic composition, and a slight increase in its mass is associated with the formation of a thin dense protective oxide film on the surface. The thermal diffusivity of Cu-Al LMIC, obtained after removal of copper residues from the surface of the diffusion zone, is 50–60 W/m×K, which is significantly lower than that of copper (410 W/m×K) and aluminum (220 W/m×K).

Abstract: Experimental analyses are performed to determine thermal conductivity, thermal diffusivity and volumetric specific heat with transient plane source method on hollow sphere structures. Single-sided testing is used on different samples and different surfaces. Results dependency on the surface is observed.

Abstract: This article is devoted to the investigation of physicomechanical, tribological, and thermophysical properties of the polyamide antifriction composition, containing shungite and graphite with a total concentration of 2.5%. It is intended for the manufacture of elements of power hydraulic cylinders tribo-conjugation for agricultural machinery. A comparison of the characteristics of the developed composition with the characteristics of caprolon and the commercial carbon-filled composite UPA6-15A.