Presence Of Temperature Difference Research Articles

Quantification of steal flow on Doppler ultrasound in patients with arteriovenous graft for hemodialysis.

Arteriovenous fistula (AVF) is the preferred treatment for long-term hemodialysis patients to allow reliable vascular access. Arteriovenous graft (AVG) is monitored using Doppler sonography to check a vessel's condition and predict complications such as steal syndrome. In this study, we developed an analysis algorithm and method to quantify steal syndrome using Doppler sonography. Doppler sonography was used to determine the pattern of anterograde and retrograde flow. The ratio of blood volumes was calculated with a vision analysis software. First, performance of the developed algorithm was validated by comparing it with commercial Doppler sonography data. Doppler sonography was performed for an artificial vessel to analyze the steal flow. A total of 58 patients with steal flow were enrolled in this study. Of these patients, 23 did not have a difference in fingertip temperature between both sides. The median difference in temperature of 35 patients was 0.8°C (range, 0.3-1.9°C). The ratio of retrograde flow volume/antegrade flow volume in patients with the presence of temperature difference was significantly higher compared to that in patients without the temperature difference (p < .001). The ROC curve for the difference in flow volume had an AUC of 0.770. The optimal cutoff of difference in the flow volume between the two groups was 0.24 (sensitivity of 91.4 % and specificity of 52.2%). The flow volume difference was significantly positively correlated to temperature difference (r = 0.487, p < .003). Our algorithm could measure steal flow volume of a bidirectional waveform by antegrade arterial flow and retrograde reversal flow.

Experimental study of the natural deposition of submicron aerosols on the surface of a vertical circular tube with non-condensable gases

This paper constructed an experimental platform containing a space heat exchanger tube, and performed aerosol deposition experiments under different deposition mechanisms. The objective was to study the effect of the passive containment heat removal system on the natural deposition of submicron aerosols during post-accident operation of severe accidents. By controlling the variables, we obtain the impact of gravity deposition, thermophoretic, and diffusiophoresis deposition mechanisms on submicron aerosols in the presence of a space heat exchanger tube using the experimental data stripping method. The study found that the gravitational settling rate of aerosols in two-phase mixtures at the same temperature and pressure is about 1.5 times higher than in dry air. Although submicron aerosols are subject to thermophoretic settling in the presence of temperature differences, due to the small surface area of the heat exchanger tube, the potential thermophoretic sedimentation accelerating effect on the particles can be ignored if the mixed gas temperature difference is within 2000 K/m. Unlike the steam condensation on the flat plate surface, when vapor condenses on the heat exchanger tube surface, as the steam proportion and condensation rate increase, it is easy to cause the accumulation of non-condensable gas. This phenomenon can reduce the reverse diffusion slip of the particles and enhance the influence of Stefan flow in the diffusionphoresis deposition process. The above effects make the experimental results of aerosol diffusiophoresis deposition closer to the SF model when the vapor fraction is 70 %. When the vapor fraction is 50 %, the predictions of the WM model, which considers the average mass flow of the gas mixture, are more applicable. When the condensation rate continuously increases, the convective mass transfer of vapor condensation will be enhanced, and the deposition rate of particles will be further enhanced.

Effect of temperature on adhesion behavior of layered piezoelectric structure

The effect of temperature on adhesion is neglected in classical adhesive contact theories. However, an increasing number of experimental results indicate that temperature has a prominent effect on adhesion behaviors. In this study, the anisothermal adhesive contact behaviors between two transversely isotropic piezoelectric cylinders with different initial temperatures is investigated by virtue of the generalized JKR model, where the contact interface is assumed to be perfectly bonded. The considered problem is reduced to coupled singular integral equations, which is derived by using the Fourier integral transform. The closed-form solutions of anisothermal generalized stress fields are obtained by taking the series expansion of the integrand induced by temperature difference. The effect of temperature difference on adhesion behaviors of two different types of layered piezoelectric structures under the action of mechanical-electro loadings is revealed. It is found that the pull-off force and contact size at pull-off moment decrease with increasing the temperature difference. The adhesion weakening effect induced by temperature difference diminishes when the electric loading is exerted. The results derived from this paper shed lights on understanding the adhesive contact behaviors of piezoelectric materials in the presence of temperature difference.

RETRACTED: Mixed convective heat transfer in a power-law fluid in a square enclosure: Higher order finite element solutions

Incorporation of momentum gradients produced due to inertial motion of the lid along with the presence of temperature differences in the configuration make the physical problem more significant. The joint variation of momentum and thermal diffusion in diversified natural liquids is recognized as mixed convection. Valuable attention has been received by such a phenomenon in different areas of science and technology such as in wind current–based solar receivers, electronic instruments, control of emergency shutdown in reactors, thermal exchangers, oceanic currents, control of atmospheric pollution, and so on. So, the main focus is to contemplate hydrothermal characteristics of a power-law fluid contained in a square cavity with the movement of the upper lid and being thermally adiabatic. The other extremities are considered to be at rest, and the base wall is prescribed with uniform/non-uniform temperature distributions. The governing formulation of the problem is handled by executing a finite element approach. Hybrid meshing is performed for domain discretization, and weak variational formulation is utilized for formulation discretization. Second-degree polynomials are employed as the interpolation function, providing information about velocity and temperature distributions at boundary and intermediate nodes. The system of finalized non-linear equations is resolved by using the Paradiso software. The results for velocity and temperature distributions are attained comparatively for uniformly and non-uniformly heated profiles. The kinetic energy and average Nusselt number are also computed against flow concerning variables. From the attained graphical and tabular data, it is deduced that by increasing the Reynolds number, inertial forces dominate over buoyancy forces and the effect of lid movement is prominent on flow characteristics. It is also inferred that for the shear thickening case and for all values of the Reynolds number, the average Nusselt number shows a constant behavior.

Adhesive behavior between dissimilar materials subjected to thermo-elastic loadings with normal-tangential coupling effect

The temperature difference always exists between contacting objects in various thermal bonding technologies, where the adhesion strength is found to be very sensitive to the temperature. In this paper, the anisothermal adhesive contact between an elastic cylinder subjected to the external force with an inclined angle and an elastic substrate is investigated based on the non-slipping JKR model, where the coupling effect between the normal and tangential tractions within the contact region is taken into consideration. The stated problem is reduced to a system of coupled singular integral equations, which can be solved with the analytical function theory. The full analytical solutions of the oscillatory stress fields are obtained for the first time by taking the series expansion of the integrand induced by the thermoelastic effect, which is of substantial significance. The relationship between the contact size and the external loadings is established by virtue of the Griffith energy balance criterion. The difference between the oscillatory and non-oscillatory solutions of stress fields is discussed in detail. Numerical results demonstrate that the oscillatory solution cannot be well approximated by the corresponding non-oscillatory solution for the cases of large Dundurs’ index and external compressive force. Furthermore, it is found that both the thermoelastic effect and the inclined angle of the applied force have significant influences on the adhesive contact behaviors. The presence of temperature difference between contacting objects can either enhance or weaken the adhesion effect, which is related to the inclined angle of the external force. The results obtained from this paper may provide a new insight into the influence mechanism of the temperature on adhesion behaviors.

A long-range order in a thermally driven system with temperature-dependent interactions.

Aggregation of macro-molecules under an external force is far from being understood. An important driving situation is achieved by temperature difference. Inter-particle interactions in metallic nanoparticles with ligand capping are reported to be sensitive to temperature and the zeta potential of the particles being reduced in the cold region. Such particles form aggregates in the cold region of the system in the presence of temperature difference. Here we study the aggregation of particles in the presence of temperature difference with temperature-dependent interaction parameters using Brownian dynamics simulation. The particle interaction and particle diffusion are considered to be sensitive to the local temperature. We identify a long-range structural order in the cold region of the system using the Avrami equation for crystal growth kinetics. Our observations might be useful in designing ordered structures with macro-molecules under non-equilibrium steady-state conditions.

Rectification and separation of mixtures of active and passive particles driven by temperature difference.

Transport and separation of binary mixtures of active and passive particles are investigated in the presence of temperature differences. It is found that temperature differences can strongly affect the rectification and separation of the mixtures. For active particles, there exists an optimal temperature difference at which the rectified efficiency is maximal. Passive particles are not propelled and move by collisions with active particles, so the response to temperature differences is more complicated. By changing the system parameters, active particles can change their directions, while passive particles always move in the same direction. The simulation results show that the separation of mixtures is sensitive to the system parameters, such as the angular velocity, the temperature difference, and the polar alignment. The mixed particles can be completely separated under certain conditions.

A Novel Thermoelectric Generator for the Detection of Electrical Equipment

Semiconductor thermoelectric generators have a series of advantages, such as compact volume, high-level reliability, and effective power generation in the presence of temperature difference. In many occasions, as a result of high voltage, electrical equipments can't be measured by the way of direct contact. In order to avoid equipment faults caused by low-voltage contact, a thermoelectric generator which uses waste heat of electrical equipments in service was designed. Electrical equipments often operate below 400K, and in this condition Bi2Te3 shows an outstanding performance of power generation. In order to solve the problems of little temperature difference and output power on steady-state, two methods were introduced. On the one hand, the temperature difference can be increased by filling with thermal insulation padding between the p-n junctions and using a heat sink in the cold side, and on the other hand, the output voltage and power will be augmented by increasing the number of p-n junctions. These methods have been proved effectively by simulation and experiment with promising outcomes.

Wetting and coalescence prevention of drops in a liquid matrix. Ground and parabolic flight results

An experimental and numerical analysis of the behavior of drops in a liquid matrix, in presence of temperature differences, is carried out in preparation for a MAXUS sounding rocket flight to study wetting and coalescence prevention induced by thermal Marangoni effect. On-ground experimentation has been carried out using micro zone apparatus. Different pairs of liquids (drop and matrix) have been analyzed; wetting prevention has been observed with drops of different diameter and critical temperature differences have been measured for each pair. To avoid buoyancy effects similar experiments have been carried out during the 30th ESA parabolic flight campaign. The main objective of the experiments is facility tests in a parabolic flight for the MAXUS flight. During the parabolic flight a hanging drop of Silicone oil 10 mm diameter has been injected in a matrix of Fluorinert and in air; wetting prevention has been observed in presence of a temperature difference between the drop and the lower surface. The theoretical-numerical study of the problem has been carried out with a thermofluidynamic model based on the assumption of the existence of a fluid film between the drop and the lower surface.

Marangoni flotation of liquid droplets

Flotation of liquid droplets on pool surfaces, in the presence of temperature differences, is studied experimentally and numerically. Coalescence or sinking of the droplet is prevented by the thermal Marangoni motion, owing to the surface tension imbalance at the pool surface. The mechanism is the same as that investigated in previous works on coalescence and wetting prevention in the presence of temperature differences. If the droplet is colder than the liquid surface, the flow is directed radially towards the drop; this radial flow field drags the ambient air under the drop, thus creating an air film and avoiding a direct contact between the droplet and the pool molecules.The surface velocities are measured visually with a CCD camera to image the motion of tracers floating on the pool surface; the surface temperature distributions along the pool and the droplet surfaces are measured by an infrared thermocamera. The experimental results are correlated by numerical results obtained under the assumption of spherical drop and axisymmetric flow regime. Different liquids are considered and the influence of evaporation is discussed, showing a good agreement between the experiments and the numerical simulations.

Correlation between experimental results and numerical solutions of the Navier–Stokes problem for noncoalescing liquid drops with Marangoni effects

Experiments show that, when two drops are brought in contact and pushed toward each other in the presence of temperature differences, coalescence is inhibited. Axisymmetric numerical solutions of the Navier–Stokes problem have been obtained to give an explanation of the phenomenon, assuming that a thin air film exists between the contacting drops and that, provided that well-defined dynamic conditions prevail on the liquid surfaces, the film experiences a suitable pressure that balances the pressure in the drops. The numerical results agree with the experimental ones, qualitatively explain why an air film between the drops could be created by Marangoni effects and show that the suppression of coalescence is obtained as long as films sufficiently large exhibit excess pressures of the same order of magnitude of the pressure needed to deform the drops.

Effects of gravity levels on Marangoni-Stokes flows in Plateau configurations

The combined effects of buoyancy and Marangoni thermal stresses for Stokes regimes in a plane Plateau type configuration are studied. The appropriate mathematical formulation for Stokes regimes of arbitrary immiscible interfacing liquids in the presence of temperature differences and gravity field is given and the conditions for which the temperature field is uncoupled from the velocity field derived. It is then proved that for Plateau configurations the zeroth order problem is fully linear so that Marangoni and buoyant effects are superposable. The special case of a plane geometry is then solved analytically by means of Papkovich-Faddle bi-orthogonal complex functions. The relevant features of the flow are analyzed and discussed in terms of streamlines, velocity profiles, dynamic interface shapes with particular emphasis in the comparison between purely Marangoni, purely buoyant and combined free convection.