Thermal Transfers Research Articles

Numerical study of electroconductive non-Newtonian hybrid nanofluid flow from a stretching rotating disk with a Cattaneo–Christov heat flux model

Motivated by emerging technologies in smart functional nanopolymeric coating systems in pharmaceutical and robotics applications, the convective heat transfer characteristics in swirl coating with a magnetic hybrid power-law rheological nanofluid polymer on a radially stretching rotating disk are examined theoretically. An axial magnetic field is imposed. Copper (Cu) and aluminium alloy (AA7075) nanoparticles with sodium alginate (C6H9NaO7) as a base fluid are considered, and a hybrid volume fraction model is deployed. A non-Fourier (Cattaneo–Christov) heat flux model is deployed to inspire thermal relaxation impacts absent in the classical Fourier heat conduction formulation. Through similarity proxies and the Von Karman transformations, the partial derivative systems of equations with associated boundary constraints are reduced to a system of derivative boundary value problems, which is solved numerically via the weighted residual method with an integral Galerkin scheme, executed in the MAPLE symbolic software. Validation with special cases from articles is captured. The computations revealed that radial, tangential and axial velocity are depleted, whereas temperature is enhanced with increasing magnetic parameter ( M). High thermal transfers are obtained for the hybrid nanofluid relative to the AA7075 alloy nanofluid. A strong increment in temperature is also produced with a greater thermal relaxation effect.

Vapor bubble on a single nucleation site : Temperature and heat flux measurements

This work aimed at gaining a detailed understanding of heat transfer when boiling occurs on a heated substrate. More specifically, this work focuses on thermal transfers occurring at wall-fluid interfaces at the transition between natural convection and nucleate boiling regimes in pool boiling experiments. To avoid parasitic effects, the vapor bubble is created at a single artificial nucleation site. The boiling cell is instrumented with sensors for temperature measurement, pressure control, and parietal heat flux measurement. The fluid tested is Fluorinert FC-72. For providing a boiling surface and measuring heat flux, a boiling-meter consisting of a heating resistance, heat flux sensors and two thermocouples is used. This boiling-meter enables heat flux generation, the measurement of both temperature and heat flux, and can be rotated through 360°, enabling the influence of inclination to be studied. The boiling-meter is indented at its center to create a single vapor bubble. Thermal measurements are obtained and studied for different inclination angles between 0° and 180° at the saturation conditions. The results showed the nucleation site’s recurrent pattern of being active and inactive for whatever is the boiling surface inclination. Preliminary results are presented and discussed.

Ventilation performance index fully considering effects of ventilation air parameters on thermal comfort: Effective Draft – Moisture Temperature

Ventilation methods are widely used for creating livable indoor environments. The ventilation performance index of thermal comfort is indispensable for the provision of thermal comfort in indoor environments with ventilation methods. While the air temperature, air velocity, and relative humidity are three predominant environmental air parameters of ventilation methods affecting thermal comfort, existing ventilation performance indices, i.e., Effective Draft Temperature (EDT) and Effective Moisture Temperature (EMT), cannot account for these three parameters simultaneously for thermal comfort evaluation. This study proposes a novel ventilation performance index, i.e., Effective Draft – Moisture Temperature (EDMT) to simultaneously consider the abovementioned three environmental air parameters for the thermal comfort evaluation. The EDMT is proposed based on equivalent thermal comfort effect transfers of the air velocity and relative humidity to the air temperature. Two algorithms of cascaded equivalent thermal comfort transfers are developed, based on which the EDMT is quantified and tabulated for the practical convenience of different demands of thermal comfort under cooling and heating. The results based on Monte Carlo simulations and ASHRAE Thermal Comfort Database II show that the accuracies of thermal comfort evaluation by the EDT and EMT are 88.7% − 95.5% and 70.9% – 89.0% respectively, and those of the proposed EDMTs of Algorithms 1 and 2 are 97.3% − 99.3% and 97.7% − 99.3% respectively. The proposed EDMTs of Algorithms 1 and 2 are credible and convenient for practical applications and contribute to updating ventilation performance evaluation-related standards for developing thermally comfortable buildings.

Bio-heat transfer modeling in lungs

In cardiac surgery where extracorporeal circulation is used, the lungs are temporarily disconnected from the body and are connected to a device that provides air and blood. To minimize the risk of tissue damage, the lungs are subjected to mild hypothermia. Heat transfer modeling offers the potential to enhance temperature regulation through a more advanced approach. A thermal model, based on a thermal quadrupoles, also called two-port network, offers a wide frequency range applicability, making it suitable for modeling the human breathing. This modeling approach can also be adapted to incorporate the influence of blood flow, which also serves as a natural temperature regulator in the human body. This is accomplished by combining the thermal two-port network with the bio-heat equation. The main contributions are in the analytical expressions of the thermal impedances and by proposing a Butterworth approximation model for the equivalent impedances of lung thermal transfers.

Significance of a permeable semi-circular body and magnetic field on thermo-solutal natural convection and irreversibilities

This study explores the intriguing phenomenon of thermo-solutal buoyancy-driven traits in the presence of a magnetic force within a square cold enclosure housing a soluted and heated permeable semi-circular cylinder. The amalgamation of flat and curved edges, alongside the permeable characteristics, serves as the driving motivation behind this investigation. The primary objective is to scrutinize the impact of magnetic force and its orientation, buoyant force, permeability on the thermo-solutal convection occurring within and around the permeable body. To achieve this, a thorough parametric investigation is carried out, focusing on the significance of Hartmann number (Ha), magnetic field angle (γM), buoyancy ratio (BR), and Darcy number (Da), concerning flow, heat, concentration transfer, and the variation in irreversibilities. The Darcy-Brinkmann-Forchheimer equation as a source term in lattice Boltzmann technique is utilized to accurately solve the intricate porous medium flow. The investigation reveals that escalating the buoyant force, and permeability, and magnetic field angle yields favourable heat and concentration traits. Additionally, aligning the magnetic force opposite to gravity diminishes the inhibitory effects on the thermal and solutal transfers exerted by the magnetic force. Notably, unsteady behaviour is predominantly observed when the BR assumes a negative value, with the amplitude and frequency of these phenomena amplified by the Da and γM. Also, a few anomalous spikes in the NuM and ShM are witnessed, attributed to the development of a robust uni-vortex in the top region of the cavity. Interestingly, the irreversibilities induced by the magnetic field diminish as the BR increases. Among these irreversibilities, entropy generation due to concentration emerges as the dominant contributor, with the exception of cases exhibiting atypical rises, where fluid entropy resulting from friction takes precedence.

Intensive Urbanization, Urban Meteorology and Air Pollutants: Effects on the Temperature of a City in a Basin Geography.

A qualitative study of thermal transfers is carried out from a record of measurements (time series) of meteorological variables (temperature, relative humidity and magnitude of wind speeds) and pollutants (PM10, PM2.5 and CO) in six localities located at different heights in the geographic basin of Santiago de Chile. The measurements were made in two periods, 2010-2013 and 2017-2020 (a total of 2,049,336 data), the last period coinciding with a process of intense urbanization, especially high-rise construction. The measurements, in the form of hourly time series, are analyzed on the one hand according to the theory of thermal conduction discretizing the differential equation of the temporal variation in the temperature and, on the other hand, through the theory of chaos that provides the entropies (S). Both procedures demonstrate, comparatively, that the last period of intense urbanization presents an increase in thermal transfers and temperature, which affects urban meteorology and makes it more complex. As shown by the chaotic analysis, there is a faster loss of information for the period 2017-2020. The consequences of the increase in temperature on human health and learning processes are studied.

INVESTIGATION OF THE RESISTANCE OF DIFFERENT TEXTILE PRINTS TO WASHING AND ABRASION

The article presents the next stage of experimental studies applying images to textile materials. The method of calculating the cost of manufacturing thermal transfer according to the proposed technologies, which were obtained as a result of the practical activity of the authors of the article in production conditions, was tested. The operational, and functional properties of thermal transfers have been studied. Durability of printed fabrics to rubbing and washing has been established. The images were applied to synthetic and natural fabrics. The methods of printing were as follows: DTF printing, offset and screen printing. The application of the results of this study will allow to carry out a qualitative and effective assessment of methods of printing images on textile materials depending on the production conditions for each type of product. A practical test of the proposed method of printing images on the products of the author's collection of women's clothing was carried out.

Thermal analysis of evacuated honeycomb structures: Experimental validation and optimisation of non-uniform structures

Today, energy storage is a key vector to achieve a full decarbonisation of the energy sector in order to limit the impact of climate change. In particular, ultra-high temperature (>600∘C) thermal storage is of high importance and has recently received significant attention with multiple technologies being investigated. However, uneconomical thermal losses are a barrier to their development, and currently available high-temperature insulation technologies suffer from decreased efficiency at high temperature, and lack the structural strength to support the storage vessel whose support structure therefore acts as thermal bridging, further degrading the system’s overall efficiency. As a complement to previous work, this paper provides an analysis to investigate the thermal efficiency of non-uniform rectangular honeycomb structures without mechanical constraints, with an application to ultra-high temperature thermal insulation. First, an experimental procedure is presented to validate the numerical model used in previous work. The results show that the model can accurately predict thermal transfers through three-dimensional cuboid evacuated honeycombs. A thermal optimisation of honeycombs with a non-uniform cell size distribution is then conducted to complement the findings of previous work on uniform honeycombs. A statistical condition on the cell size distribution for optimal thermal performance is derived and numerically validated, and non-uniform structures are shown to be more thermally-efficient than uniform ones. These results provide further motivation for research into the development of manufacturing processes for such structures.

Solving transient coupled conductive and radiative transfers in porous media with a Monte Carlo Method: Characterization of thermal conductivity of foams using a numerical Flash Method

This paper presents a single Monte-Carlo algorithm used to solve transient conductive and radiative heat transfers in three-dimensional porous media. The complete methodology presented step by step herein enables practical and efficient study of geometrical and multiphysical complexities. The code was validated against results obtained by commercial software, analytical and semi-analytical solutions. Computation times were found to be greatly reduced when radiative transfer is predominant compared with those obtained using a deterministic solver. This kind of approach allows a probe calculation in the frame of linear thermal transfers and is well suited for the numerical characterization of heterogeneous media. In this work a numerical flash method was reproduced and enabled us to evaluate the effective total conductivity of the equivalent homogenized medium. The influence of various parameters such as porosity, size of the unit cell, bulk conductivity of the solid phase, reference temperature and emissivity was studied for a stack of Kelvin cells. This tool enables the parametric investigation of geometric and thermal properties. The results are in good agreement with those of the literature.

Forced convection three-dimensional Maxwell nanofluid flow due to bidirectional movement of sheet with zero mass flux

The 3D mixed convection flow of Maxwell nanofluid is investigated in this paper. A stretching surface in two adjacent directions causes the flow. The temperature and nanoparticle concentration distribution are explored using the Buongiorno framework for nanofluid and thermophoresis impacts and Brownian motion. Introducing dimensionless variables and boundary layer approximations the governing PDEs are reduced to set of nonlinear ODEs. Developed system of equations then solved using convergent series solution. Heat and mass transfer effects are carried out over numerically and graphically for various parameter of interest. According to the research, buoyancy and the mixed convection coefficient enhanced the x-component of velocity but decreased the y-component. The thermal and solutal energy transfers in the nanofluid were also improved by these two variables. It was also discovered that in the presence of the thermal relaxation phenomenon, the thermophoretic increased the flow's thermal energy transmission.

Thermo-Solutal Convection of Carreau-Yasuda Non-Newtonian Fluids in Inclined Square Cavities Under Dufour and Soret Impacts

The thermosolutal convection of non-Newtonian fluids under Soret and Dufour influences within an inclined square enclosure is explored. The active walls are subject to constant and uniform concentrations and temperatures. On the other hand, they are impermeable and adiabatic. A Carreau-Yasuda model is utilized to determine the fluid behavior. A special attention is paid to the impact of rheological parameters (, , and ), the thermal Rayleigh number , Dufour number, , Soret number, , Lewis number, , buoyancy ratio, , and the inclination angel, . The numerical findings are represented in terms thermal fields, iso-concentration, and viscosity apparent contours, and the influence of certain parameters on the variation of stream function, Nusselt and Sherwood numbers, and apparent viscosity is also inspected. The findings suggest that the rise of the time constant parameter, , causes an increase in thermal and mass exchange for various power-law indices, . The decrease of the of ratio of infinite-to zero-shear-rate viscosities, , and parameter, , enhances the both thermal and mass transfers. The rise of the orientation angel from 0° to 90°yields an increase in thermal and mass transfer, but without a specific pattern in the different parameters studied.

Review of CALORRE Calorimeter Characterizations Under Laboratory and Irradiation Conditions

This article reviews the work to date on the CALOrimeter with Radial thermal transfers for nuclear REactors (CALORRE) differential calorimeter patented by Aix-Marseille University (AMU) and the French Alternative Energies and Atomic Energy Commission (CEA) in 2015. The article presents the results obtained with the first prototype of the CALORRE calorimeter qualified under real conditions during an irradiation campaign in the MARIA reactor in 2015, including previously unpublished details. Then, studies of different CALORRE calorimetric cells characterized by experiments under laboratory conditions are described. Several configurations were studied to determine the influence of cell height, horizontal fin geometry, and structural material composition on calorimeter response. These calculations provide for a calibration protocol by generating a heat source inside each cell, with evaluation of linearity, sensitivity, range, reproducibility, response time, and absolute temperatures. Finally, within the framework of a new research program called Compact-CALORimeter Irradiations inside the MIT research reactor (CALOR-I) and financed by AMU Foundation (A*Midex), a design optimization of the calorimeter assembly was carried out in order to remove contact thermal resistances and provide a new very compact CALORRE calorimeter suited for the in-core water loop of the Massachusetts Institute of Technology (MIT) reactor (2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{W}\cdot \text{g}^{-1}$ </tex-math></inline-formula> peak nuclear heating rate). The response of this new very compact calorimeter is estimated using 3-D numerical thermal simulations under real conditions.

Thermal phenotypic plasticity of the second limb in Daphnia

Abstract Thermal plasticity is expected to affect the responses of freshwater zooplankton to climate perturbations. We tested the hypothesis of thermal plasticity in the rigid setae of the second limb of Daphnia galeata. We also aimed to test the role of allometry and the ability to induce a rapid plastic response within an individual lifetime (i.e. postnatal). In all, 300 specimens of Daphnia were dissected from four sets of clonal thermal transfers and seasonal variants from nature. Specimens of D. galeata were cultured under identical conditions save temperature (10 and 20°C). Clonal neonates were reciprocally transferred across temperature regimes to determine the degree of postnatal plasticity. Setae length ratios supported thermal plasticity of rigid seta 2, but a thermal effect was not significant for the length ratios of the soft setae. Simple linear regressions of body length (mm) and setae lengths (mm) under warm and cold conditions revealed significant slope differences (i.e. allometry) among temperatures for the three setae examined. The rigid seta had the largest thermal effect size (slope difference), growing larger at colder conditions for a given body size compared to the soft seta. Rapid thermal plasticity in non-filtering limbs is more important than previously appreciated for Daphnia.

0D Dynamic Modeling and Experimental Characterization of a Biomass Boiler with Mass and Energy Balance.

The paper presents an experimental study and a 0D dynamic modeling of a biomass boiler based on the Bond Graph formalism from mass and energy balance. The biomass boiler investigated in this study is an automatic pellet boiler with a nominal power of 30 kW with a fixed bed. The balances allow to model as time function the flue gas enthalpy flux variation and the thermal transfers between the flue gas and the walls of the boiler subsystems. The main objective is to build a model to represent the dynamic thermal behavior of the boiler. Indeed, small domestic boilers have discontinuous operating phases when the set temperature is reached. The global thermal transfer coefficients for the boiler subsystems are obtained according to an iterative calculation by inverse method. The boiler has an average efficiency of 67.5% under our operating conditions and the radiation is the dominant thermal transfer by reaching 97.6% of the total thermal transfers inside the combustion chamber. The understanding of the dynamic behavior of the boiler during the operating phases allows to evaluate its energy performances. The proposed model is both stimulated and validated using experimental results carried out on the boiler.

Modeling of an Innovative Nitrogen-Free Cryotherapy Device

Partial body cryotherapy cabins most often use liquid nitrogen as their cryogenic fluid, which raises safety concerns during operation. In this study, an innovative cryotherapy cabin design is presented, featuring an electric cooling system suitable for producing cold air at −30 °C. The geometry of the designed cryotherapy cabin is evaluated by a thermodynamic modeling which aims at optimizing the circulation of cold air flows inside the cabin. The numerical study is carried out in two successive phases, the first one being necessary to model the pre-cooling phase and to estimate the time required to reach an average temperature close to the set temperature of −30 °C. The second one aims at modeling a 3-min cryotherapy session by taking into account the thermal transfers between the human body and its environment. Results demonstrate the potential benefits of the cold air injection device which has been designed to optimize the thermal transfers and homogenize the temperatures within the therapeutic enclosure. The main innovation of this study is the ability to customize cryotherapy protocols by injecting cold air at different levels through targeting of specific body areas. Further calculations would be required to determine the precise impact of zone-targeted injection on skin cooling.

Influences of Zero Mass Flux and Active Conditions on the Predictions of Double Dispersion and Double Diffusive Boundary Layer in Darcy/Non Darcy Nanofluid Flow

Free convective of nanofluid inside dispersive porous medium adjacent to a vertical plate under the effects of the zero mass nanoparticles flux condition and the thermal and solutal dispersions is studied. Buongiorno's model revised is used considering Darcy and non Darcy laminar flows, and isothermal or convective flux outer the wall. Dimensionless governing equations formulated using velocity, temperature, concentration and nanoparticle volume fraction have been solved by finite difference method that implements the 3-stage Lobatto collocation formula. The numerical data obtained with semi or full dispersions cases are compared to predictions made using the non dispersive porous medium. Taking into account the dispersions, the influence of the zero mass nanoparticles flux condition is examined to test the validity of the control active nanoparticle assumption. It is found mainly that the thermal transfers can reach more than 100% in connection with the case where of a semi-dispersion of the porous medium is applied. Realistic condition, i.e. zero mass flux should be addressed for the heat transfer rate rather than the mass transfer rate, discovered markedly different to the active condition. This signifies the importance of considering the zero nanoparticles mass flux and dispersions in the performance characterization of nanofluid flow in porous media.

Bond graph modeling of a water-based photovoltaic thermal (PV/T) collector

This paper deals with photovoltaic-thermal (PV/T) collectors that combine photovoltaic (PV) module and solar thermal (ST) modules to provide heat and electricity simultaneously. The use of a PV/T system not only enhances PV efficiency but also allows to use solar thermal energy for various heating applications. The performance evaluation of the PV/T collectors had been investigated both theoretically and experimentally for the past few years. In this work, we consider a new water-based PV/T configuration by incorporating a tedlar layer and parallel tubes and further investigate its modeling. The aim is to develop a non-linear dynamic model which gives a realistic and reasonable performance of the system. The fundamental equations are determined for the thermal part using a bond graph approach which is a generic and general tool to represent thermal transfers. Simulations are given to highlight the usefulness of the proposed design and its modeling, considering the influence of some external factors (e.g. wind action) and internal geometrical parameters (e.g. insulator thickness). The results indicate that the rise in wind speed can reduce thermal efficiency from 70% to approximately 40%. The results also show that with an increase in insulator thickness, there is a sudden change in outlet temperature but thicknesses of more than 0.14 m is not required as the energy losses become constant. The assessment of the electrical and thermal performance of a PV/T collector is taken into consideration for a sample weather condition of southern France. Further, our results are compared to existing experimental and numerical ones from the literature on alternative PV/Ts design to validate and demonstrate the viability and consistency of our model.

Thermal pollution zones on the aquatic environment from the coastal power plant: Numerical study

In this work the results of a numerical study of thermal pollution from the power plant operation using the Irtysh River as a natural water cooling system have been presented. In the paper, a 2D model has been used to numerically simulate a floating stream along with its mixing heated water discharge characteristics from lateral projections with a transverse flow. The values of computational modeling are in good adjustment with the measurement results, in particular, with the trajectories of the jets, the recirculation zone size and the distribution of the dimensionless excess temperature. The work was also conducted to study thermal pollution in various scenarios of the heated water discharge from the coastal power plant and thermal pollution areas were determined for various discharge speed cases. The general projections of the thermal pollutant transfers in the river during the placement of the discharge channels, both for short and for long distances from the city were evaluated. It could be noted that using several discharge channels leads to a reduction in the area of thermal pollution. So for the discrepancy in temperature value from the water temperature of 3 °C there was a reduction in the pollution area of almost 11 times.

Modelling thermal and humidity transfers within green roof systems: effect of rubber crumbs and volcanic gravel

ABSTRACT The use of recycled materials and porous aggregates such as rubber crumbs and volcanic gravel (pozzolana) for the drainage layer can lead to improving thermal behaviour of the green roofs. On the other hand, the thermal performances of green roofs can be affected by the thickness of substrate and drainage layer. Therefore, the main objective of this study was to adapt modelling characteristics for different thicknesses of substrate and drainage layers used under constant and variable temperatures and solar radiation: specific rubber crumbs and volcanic gravel behaviour has been modelled. The simultaneous heat and moisture transfers within the green roof were estimated as well. According to the results, the 9 cm substrate was recommended to be used for the green roofs, once the thickness of drainage layer was 4 cm. Moreover, the optimum thickness of pozzolana and rubber crumbs as drainage layer was 6 and 7 cm, respectively, once the thickness of the substrate was kept constant (5 cm). By increasing the thickness of substrate and drainage layers, the fluctuation of internal ceiling temperature in the green roof models with the presence of humidity decreased, but not as much as that in the green roof models without the presence of humidity.

Experimental study on indoor thermal environment of industrial building spaces enclosed by fabric membranes

Nowadays with the development of science, many new technologies are being introduced to the fabric membrane material fields. Membrane structures have been widely used in industrial storage buildings to reduce the dust pollution from open storage depots. But the thermal environment of these buildings is poor due to its light weight and low thermal resistance. It is worth exploring appropriate measures to study this problem. Therefore, a monitoring platform was established in order to study the indoor thermal environment of the industrial storage building with membrane structure. The solar radiation heat model was established using MATLAB program based on the theory of thermal transfers. And studied the impact of the outdoor temperature and solar radiation intensity in the heat transfer characteristics of membrane material. The indoor air temperature distribution of the buildings was also analyzed. The results show that solar radiation has a significant effect on the surface temperature of the fabric membrane material. The solar radiation of different intensities incident on the surface of the fabric membrane causes its surface temperature to fluctuate rapidly and significantly. Without indoor heat source, the indoor thermal environment is mainly affected by the solar radiation heat exchange of the fabric material.