Linear Temperature Gradient Research Articles

Cole–Hopf linearization of the thermocapillary Marangoni dynamics of a two-dimensional bubble with insoluble surfactant

The Marangoni stress-induced dynamics of a two-dimensional inviscid bubble loaded with insoluble surfactant moving in a linear temperature gradient is studied in the limit of small Reynolds, capillary and thermal Péclet numbers. The bubble moves due to the combined effects of thermocapillary Marangoni stresses and those induced by the advective-diffusive spreading of an initial concentration of surfactant on the bubble boundary. It is shown that this nonlinear multiphysics initial value problem is linearizable at any finite non-zero value of a surface Péclet number Pes\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Pe_s$$\\end{document} governing the size of surface diffusion of the insoluble surfactant relative to its advective spreading. This is done by showing that the dynamics can be encoded in the evolution of a function, analytic and single-valued outside the bubble, that satisfies a complex partial differential equation of Burgers type. It is shown that this equation can be linearized by a complex generalization of the classical Cole–Hopf transformation. A numerical method is formulated to solve this linear partial differential equation and determine the Marangoni dynamics of a bubble with some initial surfactant concentration and illustrative calculations are carried out. Results are shown to be consistent with exact equilibrium solutions available from the formulation as Pes→0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Pe_s \\rightarrow 0$$\\end{document} and Pes→∞\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Pe_s \\rightarrow \\infty $$\\end{document} and a perturbative formula for the bubble migration velocity at large but finite Pes\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Pe_s$$\\end{document}.

Nonlinear static behaviors of nonlocal nanobeams incorporating longitudinal linear temperature gradient

The elastic parameters and the coefficient of thermal expansion (CTE) of nanomaterials change with temperature. If the elastic modulus, the CTE, and the longitudinal linear temperature gradient are coupled, the longitudinal symmetry of the mechanical properties of nanobeams is broken. However, researchers have not yet to examine how this symmetry breaking affects the mechanical properties of nanobeams. This paper provides a new analysis of the modified thermoelastic beam model established by the nonlocal stress gradient theory. The present analysis incorporates the coupling of the longitudinal linear temperature gradient, elastic modulus, thermal expansion, and scale effect. Afterward, we apply the Galerkin method to explore the buckling, post-buckling, and transverse bending of a (10,10) single-walled carbon nanotube (SWCNT). The results show that the linear temperature gradient induces the breaking of the nanobeam's longitudinal symmetry and then results in the coupling of the symmetrical and antisymmetrical weight functions of the deformations. While the linear temperature gradient marginally affects the symmetry of nanobeams, it significantly raises the buckling temperature and introduces the complexity of the post-buckling and transverse force bending. In addition, the integration of the linear longitudinal temperature gradient, elastic modulus, and nonlocal effect more significantly affects nanobeams' mechanical properties than individual factors.

Rolling Motion of Rigid Skyrmion Crystallites Induced by Chiral Lattice Torque.

Magnetic skyrmions are topologically protected spin textures with emergent particle-like behaviors. Their dynamics under external stimuli is of great interest and importance for topological physics and spintronics applications alike. So far, skyrmions are only found to move linearly in response to a linear drive, following the conventional model treating them as isolated quasiparticles. Here, by performing time and spatially resolved resonant elastic X-ray scattering of the insulating chiral magnet Cu2OSeO3, we show that for finite-sized skyrmion crystallites, a purely linear temperature gradient not only propels the skyrmions but also induces continuous rotational motion through a chiral lattice torque. Consequently, a skyrmion crystallite undergoes a rolling motion under a small gradient, while both the rolling speed and the rotational sense can be controlled. Our findings offer a new degree of freedom for manipulating these quasiparticles toward device applications and underscore the fundamental phase difference between the condensed skyrmion lattice and isolated skyrmions.

Play fairway analysis of geothermal resources across the state of Hawai‘i: 5. Slim hole drilling on Lāna‘i island

This paper builds on four earlier papers detailing the results of the Hawai‘i Play Fairway (PF) project's first two phases. In Phase 3 the project deepened a water well on the rim of the caldera of Lāna‘i Volcano to a maximum depth of just over 1 km. Due to funding constraints, the project deepened an already existing water well that was proximal to our area of highest resource probability within the caldera. Drilling preparation included: completion of an Environmental Assessment, lowering a camera down the well, deviation logging, coordinating site preparation, procure and shipping, and participating in multiple community meetings. Drilling occurred 24/7 the entire month of June 2019. The project deepened Lāna‘i Well 10 from 427 m to 1057 m, while collecting continuous core, and measured a roughly linear temperature gradient averaging 42 °C/km and a maximum bottom hole temperature of 66 °C. This gradient is more than twice the background for Hawai‘i and within a range of gradients measured in this depth range for some exploration wells within the volcanically active East Rift Zone of Kīlauea Volcano. Geothermal gradient determinations and computed chemical geothermometer temperatures indicate that accessible temperatures within Lāna‘i Well 10 are 130–200 °C between 2 and 3 km depth. This paper includes a summary of detailed core logging, which found pervasive hydrothermal alteration. We recommend drilling a slim hole within Lāna‘i's caldera to ∼2 km, where considerably higher temperatures may be encountered. The positive implications this project's results have for the island of O‘ahu are substantial. The shield stage of O‘ahu's volcanoes ended 1–2 Million years earlier, however O'ahu uses more electricity than the rest of the islands combined.

Coupled thermomechanical analysis using isoparametric curved shell elements

This study focuses on the coupled thermo-mechanical formulation in isoparametric shell elements and its implementation in curved laminar structures. The formulation is based on the direct isoparametric formulation, specifically designed for flat and curved shell elements, and relies on the theory of degenerated solids. The research provides a comprehensive description of the coupled thermo-mechanical analysis, including the mechanical equilibrium equations, the interrelations between stress, temperature, displacement, deformation, and the conservation of thermal energy. It adopts a simultaneous approach to addressing the impacts of temperature and mechanical loads. The paper elaborates on various numerical examples that substantiate the formulation. These examples include simulations that encompass linear scenarios, which are then compared to analytical solutions and results derived from other numerical software. The examples highlighted include one-dimensional temperature diffusion, radial diffusion, and the thermal behavior of a cylindrical cover and a pipe under a linear temperature gradient. These simulations demonstrate the formulation's capacity to accurately capture the interactions between temperature variations and structural displacements. They also confirm the alignment of the proposed model with existing analytical and numerical solutions. In conclusion, the research provides a good framework for coupled thermo-mechanical analysis. The flexibility of the formulation is evidenced across different configurations and scenarios, accommodating various types of boundary conditions such as constant and linear temperature fields, distributed loads, and constraints on displacements and rotations. It effectively manages temperature flows across one, two, and three dimensions, highlighting its extensive applicability in the realm of structural analysis. This versatility underscores its broad applicability in the field of structural analysis.

Creep analysis of a cylinder subjected to 2D thermoelasticity loads and boundary conditions with inner heat generation source

This paper presents an in-depth investigation of the creep behavior of a thick-walled cylinder subjected to thermomechanical loads with internal heat generation under various boundary conditions. The cylinder is subjected to internal pressure with the incoming heat flux in the inner layer and the outgoing heat flux from the outer layer accompanied by heat generation. The displacement field follows the kinematics of the first-order shear deformation theory (FSDT). Simultaneously, the temperature field is treated as two-dimensional, exhibiting variations both along the thickness and the length of the cylinder, with a linear temperature gradient across the cylinder's thickness. Using the energy method, the equilibrium equations and general boundary conditions are derived for the cylinder. Norton's model is incorporated into rate forms of the above-mentioned equations to obtain time-dependent stress and strain results using an iterative method. The redistribution, displacements, strains and stresses over time have been obtained by the semi-analytical iteration method. Moreover, the effectiveness of the proposed method in addressing axisymmetric cylindrical shells under various boundary conditions and thermo-mechanical loading is demonstrated. A parametric study on the creep behavior has also been carried out which reveals critical insights. Notably, the study demonstrates that effective stress and radial displacement during creep can be effectively managed by optimizing the external cooling profile or the internal heating profile. Furthermore, the investigation reveals that the presence of a heat source markedly influences the effective stress and displacement within structure, highlighting the interplay between thermal and mechanical factors in determining the structural integrity. To validate the findings of this study, the finite element method was employed, with the results indicating good agreement between the two approaches.

Prediction of effective equivalent linear temperature gradients in bonded concrete overlays of asphalt pavements

PurposeThe time-varying equivalent linear temperature gradient (ELTG) significantly affects the development of faulting and must therefore be accounted for in pavement design. The same is true for faulting of bonded concrete overlays of asphalt (BCOA) with slabs larger than 3 x 3 m. However, the evaluation of ELTG in Mechanistic-Empirical (ME) BCOA design is highly time-consuming. The use of an effective ELTG (EELTG) is an efficient alternative to calculating ELTG. In this study, a model to quickly evaluate EELTG was developed for faulting in BCOA for panels 3 m or longer in size, whose faulting is sensitive to ELTG.Design/methodology/approachA database of EELTG responses was generated for 144 BCOAs at 169 locations throughout the continental United States, which was used to develop a series of prediction models. Three methods were evaluated: multiple linear regression (MLR), artificial neural networks (ANNs), and multi-gene genetic programming (MGGP). The performance of each method was compared, considering both accuracy and model complexity.FindingsIt was shown that ANNs display the highest accuracy, with an R2 of 0.90 on the validation dataset. MLR and MGGP models achieved R2 of 0.73 and 0.71, respectively. However, these models consisted of far fewer free parameters as compared to the ANNs. The model comparison performed in this study highlights the need for researchers to consider the complexity of models so that their direct implementation is feasible.Originality/valueThis research produced a rapid EELTG prediction model for BCOAs that can be incorporated into the existing faulting model framework.

Uticaj temperaturskog gradijenta na savijanje tankih ploča

Within the theory of thermo-elasticity, the temperature field of thin plates is commonly defined via two parameters: temperature in the mid-plane and linear temperature gradient normal to the mid-plane. First, the paper analytically proves the justification of that assumption in machine structures. Then, in an analytical closed form, applying the integral transformation method, the thin plate deflection caused by a constant temperature gradient is defined. It is shown that, in that case, the plate deflection does not depend on its thickness but only on the plate dimensions in the mid-plane. Analytically defined values are compared to corresponding values obtained by applying the thin plate finite element, where the temperature field is described using the two mentioned parameters. This finite element is defined and programmed within the Komips program package. The influence of the temperature gradient on the behavior of constructions mostly depends on the type of material. That is why the behavior of some structural elements made of brass, steel, and concrete is analyzed in this paper.

Use of the Laser Beam Deflection Technique for Thermo-Optic Coefficients Study in Gadolinium-Yttrium Oxyorthosilicate Doped with Erbium Ions

Results of use of the laser beam deflection technique for determination of thermo-optic coefficients (TOCs) of the Er3+-doped gadolinium-yttrium oxyorthosilicate crystal (Er3+:(GdY) SiO– Er:GYSO) are presented. A 0.1 at.% Er-doped gadolinium-yttrium oxyorthosilicate crystal was grown by the Czochralski method under nitrogen atmosphere. Raw materials such as Er2O3, Gd2O3, Y2O3, and SiO2 were weighed according to the formula (Er0.001Gd0.8995Y0.0995)2SiO5. Optical properties of the biaxial Er:GYSO crystal are described within the frame of the optical indicatrix with orthogonal principal axes Np , Nm , and Ng . To characterize the anisotropy of the TOCs a sample from the grown Er:GYSO crystal was prepared in a shape of a rectangular parallelepiped with dimensions of 7.0 (Np ) × 8.0 (Nm ) × 8.5 (Ng ) mm3. Each face of the sample is perpendicular to one of the optical indicatrix axes Np , Nm and Ng . For determination of the TOCs the laser beam deflection technique for a material with a linear temperature gradient is used. Measurements are performed at the wavelength of 632.8 nm. The thermal coefficient of the optical path (TCOP) for the Er:GYSO crystal measured at the wavelength of 632.8 nm at different light polarization E and propagation direction k were obtained. The TCOP values are positive for all directions of the light propagation k // Np , Nm , Ng . This means that the sign of the thermal lens which is directly related to the TCOP value will also be positive, and the positive thermal lens is then expected for Np Nm-, and Ng -cut Er:GYSO. Applying an analysis of the thermal lensing the dn /dT value for Yb:GYSO is estimated to be 6.5×10–6 K–1.

A method to establish a linear temperature gradient in a microfluidic device based on a single multi-structure thermoelectric cooler

Linear cooling of continuous microfluidic is crucial to the microfluidic analysis of cell cryopreservation and homogenous ice nucleation. This study presents a method to establish a linear temperature gradient for linear cooling of continuous microfluidic based on a single thermoelectric cooler. A novel multi-structure thermoelectric cooler was proposed to generate a stable linear temperature gradient. Furthermore, a numerical model was established to explore the performance of linear cooling of continuous microfluidic. Meanwhile, experiments were carried out to validate the model. Based on the proposed multi-structure thermoelectric cooler, linear cooling of continuous microfluidic can be successfully achieved, even if the current of the thermoelectric cooler or microfluidic velocity changes. For the case of current equal to 3 A and microfluidic velocity equal to 50 mm/s, microfluidic can be linearly cooled from 297 K to 251 K with a cooling rate of 64.5 K/s and linearity of 0.9912. It was also found that the temperature gradient decreases slightly with increasing microfluidic velocity while the cooling rate increases and is approximately proportional to the microfluidic velocity. With the increase of microfluidic velocity, the linearity increases at first and then decreases. Maximum goodness of fit equal to 0.9942 appears at the microfluidic velocity of 20 mm/s.

Local linear stability of plumes generated along vertical heated cylinders in stratified environments

The linear temporal and absolute/convective stability characteristics of a thermal plume generated along a heated vertical cylinder are investigated theoretically under the Boussinesq approximation. Special focus is given to the uniform-wall-buoyancy-flux case whereby the cylinder surface sustains the same linear temperature gradient as the environment. A competition between the axisymmetric and helical modes is a remarkable feature of the instability, distinguishing these ‘annular plumes’ from free plumes/jets for which the helical mode is generally dominant. It is found that higher surface curvature stabilises the temporal axisymmetric mode significantly, but only has moderate effects on the helical mode. The most temporally unstable perturbation mode switches from a helical into an axisymmetric mode when the Prandtl number increases beyond a critical value. Both the roles of shear and buoyancy during the destabilisation are identified through an energy analysis which indicates that, while the shear work is usually a major source of perturbation energy, the buoyancy work manifests for long-wave axisymmetric perturbation modes, and for thin cylinders and high Prandtl numbers. For the specific temperature configuration considered herein, an annular plume is always convectively unstable whereas decreasing the cylinder radius from the planar limiting case first decreases and then increases the tendency of the flow towards being absolutely unstable. The helical mode is especially susceptible to being absolutely unstable on very thin cylinders. Several conditions for the onset of cellular thermal convection and plume detrainment are proposed based on our results and a hypothesis which connects the absolute instability to the detrainment phenomenon.

Water vapor and air barrier performance of sustainable paper coatings based on PLA and xanthan gum

New stable water-based polylactic acid (PLA) emulsions with high water content were successfully prepared using two food-grade surfactants combined with high-shear mechanical mixing and ultrasonic treatment. PLA particle size distribution (PSD) was varied from micrometric to nanometric depending on the preparation conditions, as confirmed by digital microscopies and dynamic light scattering (DLS) analysis. The charged state of the PLA particle surface was evaluated using ζ-potential measurements as a significant factor affecting the stability of PLA emulsions. An unstable PLA emulsion with a large particle size has a low negative charge distribution on the surface (−26 mV) compared to the stable emulsion with a high negative charge (−39 mV). This repulsion force was sufficient to prevent flocculation and subsequent aggregation. Thickened PLA emulsions with different amounts of xanthan gum (XG) display a shear-thinning behavior in the investigated concentrations up to 2 wt% under controlled shear conditions, with apparent viscosity values dependent on XG concentrations. PLA's minimal film formation temperature (MFFT) was determined by applying a linear temperature gradient from 23 °C to 120 °C. The drying above the Tg of PLA (58 °C) resulted in clear and continuous films. Finally, the barrier properties of PLA-coated paper revealed that increasing the thickness of the PLA coating enhanced the barrier properties of the base paper considerably. The results of air and water vapor permeability tests revealed that our PLA coating in weights ranging from 10 to 15 g/m2 is suitable for achieving superior overall barrier properties combined with smooth surfaces, which are extremely important for fabricating coated paper products in the paper industry.

Thermocapillary flow‐induced core release from double‐emulsion droplets in microchannels

AbstractThe use of double emulsions (DEs), which represent colloidal structures composed of droplets nested within droplets, can provide for unparallel droplet manipulation in droplet‐based microfluidic technology due to their unique core–shell structures. The controlled release of cores in DEs is of particular interest. However, this process remains poorly explored. In this work, the thermocapillary flow induced by a temperature gradient is used as a driving force to control the core release and the impacts of different linear temperature gradients, core diameters, shell diameter, and core/shell diameter ratios on the thermocapillary flow and core release characteristics of DE droplets consisting of a water‐in‐n‐hexadecane‐in‐water system within a cylindrical microchannel are investigated. Most of the core and shell diameter conditions considered result in a double‐core release process, where the inner droplet volume is partially ejected before the remaining core is rewrapped by the outer droplet, and the remaining inner droplet volume is ejected later during a second core release event. However, relatively small core diameters of 50 and 75 μm produce conditions where the full inner droplet volume is ejected during a single‐core release process. In addition, we provide empirical relationships for accurately determining the time at which core release initially occurs under given DE parameters as well as for precisely determining whether the applied conditions will lead to single‐ or double‐core release processes. Therefore, the results of this study provide insights enabling the development of accurate inner droplet release technologies under thermocapillary migration.

Reduction of critical positive temperature gradients in jointed plain concrete pavements

ABSTRACT Temperature gradients in concrete pavements significantly affect fatigue damage accumulation, with high gradients having the potential to reduce performance under vehicle loads. While temperature profiles are non-linear throughout the depth, an equivalent linear temperature gradient (ELTG) accounts for the effect of temperature in pavement design. Critical ELTG values are difficult to predict because ELTG is affected by design parameters as well as climate conditions and varies diurnally and seasonally. To identify critical parameters which affect ELTG, a database of hourly temperature profiles was generated for a series of jointed plain concrete pavements (JPCP) throughout Pennsylvania. A stepwise regression model was developed with an R2 of 0.81 to determine maximum daily ELTG as a function of the design parameters and climate. This equation can assist engineers in making decisions on when superloads can be transported without significant damage or performing falling weight deflectometer testing will be most informative. Slab thickness, concrete albedo, and daily temperature range (DTR) were the most significant parameters that affected ELTG. A higher albedo showed an equivalent effect in reducing maximum ELTG as increasing the thickness of the slab. This finding can be used to reduce maximum gradients, which will increase the predicted service life of JPCPs.

Nonlinear dynamic thermal-mechanical behaviors of framed structures under temperature variations

An abnormal change in dynamic characteristics is considered an indicator of structural damage and can help the optimal design of structures suffering from dynamic loads, but these characteristics are also affected by ambient temperature. Therefore, a novel advanced computational method based on the fiber-based approach is proposed for the first time to predict the nonlinear dynamic behaviors of frames under environmental temperature changes with linear and nonlinear profiles by using Fortran programming language. The cross-section will be divided into a matrix of fibers, and by assigning the different temperatures to each fiber, all linear and nonlinear temperature gradients in both vertical and horizontal directions will be operated. The material nonlinearity is traced by the distributed plasticity model using the same mesh as the fiber-based approach whereas the effects of geometric nonlinearity due to member curvature and member chord rotation are considered by using the stability functions and a geometric matrix, respectively. A sequential nonlinear thermal incremental-iterative solution scheme based on the Newton-Raphson algorithm and Newmark-β method is also developed to address the nonlinear dynamic problems due to temperature variations. The accuracy and computational performance of the proposed method are validated by comparing the obtained results with those from experiments and the Abaqus. Results obtained show that the proposed method is exact for the nonlinear inelastic dynamic thermo-mechanical analysis of framed structures. It would offer a tool for thermal-structural design practice instead of using time and cost-consuming commercial software.

Convective Boundary Layer Flow Adjacent to an Inclined and Linearly Heated Semi-Infinite Plate

Abstract The transient convective flow adjacent to an inclined semi-infinite plate which is heated by a linear temperature gradient is investigated with scaling analysis and direct numerical simulation (DNS) in this study. Both Pr < 1 and Pr > 1 fluids are considered. The initial ambient fluid is quiescent and thermally homogeneous. Important parameters characterizing the thermal boundary layer flow are thickness, characteristic velocity, and time to reach the steady stage. Scaling analysis is carried out to obtain scales for these flow parameters. Compared to previous similar studies, the obtained scale relations are more generalized and they can be utilized for different inclination angles. The derived scales are compared against the DNS results for a variety of flow parameters, e.g., Rayleigh number Ra, Prandtl number Pr, stratification factor s (s = dθw(y)/dy, where θw(y) is the local temperature at a streamwise location of y), inclination angle of the heated plate α, evolutionary time τ, and streamwise location y. The scale relations and the DNS results compare well suggesting the proposed scale laws can provide a sound description for the dynamics of the convective flow subjected to a tilted surface and a linear heating condition.

Thermally driven Marangoni effects on the spreading dynamics of droplets

The influence of the thermally-induced Marangoni stresses on the falling and spreading dynamics of a droplet surrounded by another liquid phase is numerically studied. A water droplet is released in a three-dimensional (3D) domain filled with oil. The droplet descends, comes at an apparent resting position above an oil film close to the bottom surface, and eventually wets the solid surface when the underneath film ruptures. A linear vertical temperature gradient is applied in the solution domain (with the bottom surface as the cold side) which imposes a surface tension gradient across the oil-water interface. The Marangoni source term is added to the momentum equation coupling the momentum and the energy equations. It is assumed that the dynamic contact angle changes according to the Kistler relation during the spreading. The Volume of Fluid (VOF) method is used to capture the interface between the phases. The solver is validated for both the falling and spreading phases. During the buoyancy-driven falling regime, the droplet retains its spherical shape at the low Reynolds number O(1) and finite Bond number O(0.001). It is revealed that the spreading rate of the droplet is a decreasing function of Marangoni number (Ma). Unlike the isothermal systems, where the bottom side of the droplet becomes slightly flattened at the resting stage, the Marangoni stress imposes an upward force on the droplet which elongates the shape of droplet in the temperature gradient direction. Consequently, the ultimate spreading radius at the equilibrium state is smaller at larger Ma. The slow rate of spreading and also the small wetted area at large temperature gradients adversely affect the heat transfer rate from the liquid to the cold plate where the local convective heat transfer coefficient and the average Nusselt number (Nu) are decreasing functions of the Marangoni stress.

Linear, Parabolic, and Inverted Parabolic Temperature Gradients Impact on Double-Diffusive Rayleigh-Darcy Convection : A Composite System with Couple Stress Fluid

The influence of linear, parabolic and inverted parabolic temperature gradients on the onset of double-diffusive Rayleigh-Darcy convection is theoretically investigated. The composite system is constrained horizontally by adiabatic and free-free thermal boundaries, and appropriate interfacial boundary conditions are used to connect fluid-porous layers. The regular perturbation approach is used to determine the critical Rayleigh number expression for different temperature gradients. Graphs are used to investigate the significance of a variety of dimensionless characteristics. The couple stress parameter, couple stress viscosity ratio, solute Rayleigh number, and solute diffusivity ratio clearly have a stabilizing effect on the system, whereas the Darcy number and thermal diffusivity ratio destabilize it.

Simultaneous measurement of microscale fluid viscosity, temperature, and velocity fields by tracking Janus particle on microparticle image velocimetry

Multifunctional sensing capability enables a comprehensive understanding of the unknown target to be measured. Given that fluid viscosity, temperature, and velocity fields are usually coupled parameters in a system, simultaneous measurement of the three environmental factors can prevent cross-talk and improve reliability. However, the task is apparently challenging because of the microscale targets. A technique combining microparticle image velocimetry and Janus particles was developed in this study to address such demand. With the rotational diffusivity and particle trajectories measured by the proposed technique and an empirical water-based viscosity-temperature relationship, the three unknown variables in a microfluidic environment were solved. The blinking frequency was derived using the Hilbert Huang Transform. Compared with those in a static and uniform temperature field, the measured data had good agreement with the predicted values. However, the agreement was impaired when the heating rate exceeded 0.34 °C/s. The optimal temperature range was found between 10 °C and 40 °C in the water-based solution. For a steady-state and nonuniform temperature field, two-dimensional (2D) numerical simulations of three linear temperature gradients were also studied. Results showed that the deviation increased as the temperature gradient increased or was near the low-temperature region. The same procedure was eventually applied to a real thermophoretic flow induced by an IR laser in a microchip. The 2D fluid viscosity, temperature, and velocity fields in the microchip were successfully obtained by tracking 10 particles. The potential of the approach provides insight into understanding some microfluidic applications with mild changes in temperature or creeping flow. This study combined µPIV with Janus particles to achieve simultaneous measurement of 2D microscale fluid viscosity, temperature, and velocity fields. By simply tracking the particles, particle trajectories and blinking signal were obtained. Both parameters provided sophisticated information of particle velocity and rotational diffusivity. With the information, the viscosity and temperature were hence derived from the empirical viscosity–temperature relationship and the Stokes-Einstein-Debye relation. The velocity was derived alone based on the conventional cross-correlation algorithm. • Using Janus particles as tracers to provide dynamic information of blinking signal and trajectories. • Simultaneous measurement of whole field fluid viscosity, temperature, and velocity at the microscale. • Extraction of the frequency spectrum out of blinking signal by Hilbert Huang Transform. • A measurable temperature range between 10 °C and 40 °C.

POLA GRADIEN TEMPERATUR BAWAH PERMUKAAN DANGKAL MANIFESTASI PANAS BUMI DESA NOONGAN TIGA KABUPATEN MINAHASA

Geothermal is one of the natural resources that has great potential to be used as a renewable energy. The existence of geothermal resource on the surface is reflected by the presence of the geothermal manifestations on earth surface. This research was conducted to map the shallow subsurface temperature and determine the temperature gradient pattern of the geothermal manifestation in Noongan Tiga Village, Minahasa. This research uses observation method by measuring the temperature at the depth of 3 cm, 9 cm, and 15 cm in the morning, daytime, and the afternoon at 10 different points. The results showed that in that in the morning the temperature average reached 42,03 0C at the depth of 3 cm, 50,09 0C at the depth of 9 cm, and 60,26 0C at the depth of 15 cm. In the daytime, the temperature average rises to 59,2 0C at the depth of 3 cm, 66,01 0C at the depth of 9 cm, and 76,16 0C at the depth of 15 cm. While in the afternoon the temperature average reaching 41,28 0C at the depth of 3 cm, 49,46 0C at the depth of 9 cm, and 59,38 0C at the depth of 15 cm. The temperature gradient obtained shows an increase in temperature where the deeper you go, the temperature increases, with a linear temperature gradient pattern to the northeast.