Point Heaters Research Articles

Controlling Spatial Morphology of Microparticle Deposits via Thermocapillary Flows: Effect of Boundary Geometry.

The production of particle deposits with a desired distribution geometry has significant potential for materials science, printing, and coating technologies. Most methods for achieving well-defined assemblies rely on the spontaneous evaporation of colloidal solutions on substrates with predetermined properties, or on precise control of particle arrangement by external stimuli. Here, we present a combined method that enables the production of centimeter-scale microparticle deposits with a desired geometric shape. The method is based on controlling the massive transport of microparticles by thermocapillary flow in a layer of volatile liquid in a cell with borders of the desired geometry. Capillary forces cause the liquid to be distributed in the cell, forming corner wetting menisci and the flat layer in the central area. The formation of particle deposits occurs in two stages, determined by the flow regime. At the initial stage, the axisymmetric thermocapillary flow occurs in the flat part of the layer, resulting in the circular shape of the particle deposit. During the transition to the second stage of assembling thermocapillary flow is localized in the corner wetting menisci that results in reshaping the current particle deposit to match the geometry of the cell borders. Here, we demonstrated the creation of circular, square, and triangular shapes of the patterns of polystyrene microparticles using a point heater located at the geometric center of the cell. The proposed method is reliable, easy to implement, and potentially capable of producing a wide variety of deposit geometries, making it an attractive technique for patterning and modifying surface properties with particles of any type.

Heat Exchange at a Magnetic Fluid Boiling in aMagetic Field on a Horizontal Surface with a Point Heater

This paper deals with an effect of a uniform magnetic field on heat transfer during the bub-ble boiling of a magnetic fluid on a horizontal surface with a point heater. Boiling curves are obtained for magnetic fluids with a volume concentration of a solid phase 12%, 8%, and 5.5% in magnetic fields of various strengths. It was found that the curves are non-monotonic. The magnetic field strength corresponding to the maximum heat flux was determined. The effect of the magnetic field on the heat flux increases when the concentration of the sol-id phase increases. In addition, an equation that satisfactorily described the experimentally observed effect of the magnetic field on the heat flow at bubble boiling mode using an approximate theory for boiling fluids heat transfer was derived. Also the forces acting on a vapor bubble in a nonuniformly heated magnetic fluid were analyzed.

Spherically symmetric formation of localized vortex tangle around a heat source in superfluid He4

We study the dynamical process of the vortex tangle development under a spherically symmetric thermal counterflow around a heat source submerged into a bulk superfluid 4He. We reveal a peculiar vortex dynamics that is unique to this geometry, which is greatly diverse from the vortex dynamics in a homogeneous counterflow. Two types of heater are considered here, namely, a spherical heater with a solid wall and a point-like heater. In both cases, a spherical vortex tangle is formed surrounding the heater. The mechanism of vortex tangle development in the vicinity of a solid wall is strongly governed by Donnelly-Glaberson instability; while, far away from the heater or around a point heater, the mechanism is governed by the dynamics of polarized vortex loops in radial counterflow. The decay process of such localized vortex tangles is also investigated and is compared with that of homogeneous vortex tangles.

Thermal-plume fibre optic tracking (T-POT) test for flow velocity measurement in groundwater boreholes

Abstract. We develop an approach for measuring in-well fluid velocities using point electrical heating combined with spatially and temporally continuous temperature monitoring using distributed temperature sensing (DTS). The method uses a point heater to warm a discrete volume of water. The rate of advection of this plume, once the heating is stopped, equates to the average flow velocity in the well. We conducted thermal-plume fibre optic tracking (T-POT) tests in a borehole in a fractured rock aquifer with the heater at the same depth and multiple pumping rates. Tracking of the thermal plume peak allowed the spatially varying velocity to be estimated up to 50 m downstream from the heating point, depending on the pumping rate. The T-POT technique can be used to estimate the velocity throughout long intervals provided that thermal dilution due to inflows, dispersion, or cooling by conduction does not render the thermal pulse unresolvable with DTS. A complete flow log may be obtained by deploying the heater at multiple depths, or with multiple point heaters.

Iron-oxide nanoparticles embedded silica microsphere resonator exhibiting broadband all-optical wavelength tunability.

In this Letter, a novel silica microsphere resonator (MSR) embedded with iron-oxide nanoparticles, which possesses broadband all-optical wavelength tunability, is demonstrated. It is generated by using in-line 1550 nm laser ablation of a microfiber with the assistance of magnetic fluid. To the best of our knowledge, this simple method of fabricating such MSRs is reported for the first time. Prominent photothermal effect is realized by the iron-oxide nanoparticles absorbing light pumped via the fiber stem, leading to a wavelength shift of over 13 nm (1.6 THz). Moreover, a linear tuning efficiency up to 0.2 nm/mW is realized. With excellent robustness and being fiberized, the spheres can be attractive elements in building up novel micro-illuminators, point heaters, optical sensors, and fiber communication modules.

Critical Current and Stability of High-${\rm J}_{\rm c}$${\rm Nb}_{3}{\rm Sn}$ Rutherford Cables for Accelerator Magnets

In the framework of future LHC upgrades using Nb3Sn magnets, supported in part by the US LHC Accelerator Research Program (LARP) and the European EuCARD program, CERN is intensifying its research on Nb3Sn Rutherford cables. In the FRESCA cable test facility at CERN, two new Nb3Sn cable samples were investigated concerning their quench and critical current as well as stability performance. The two samples are based on RRP type strands with comparable layout. They have 27 strands with 0.7 mm diameter while the strands have 54 or 108 superconducting sub-elements. The cables are 10 mm wide and have a transposition pitch of about 75 mm. The cables are used in magnets built for LARP. Their performance is measured as a function of magnetic field up to 10 T with ramp rates of 10 to 1000 A/s and temperature of 1.9 and 4.3 K. A hall probe array is present to study the current distribution. Point heaters are used to study cable stability and current redistribution.

A dual-thermistor probe for absolute measurement of thermal diffusivity andthermal conductivity by the heat pulse method

Based on a transient thermal model of a point heat pulse, a dual-thermistorprobe, in which two thermistor beads serve as point heater and temperaturesensor respectively, has been developed for absolute measurement of thermaldiffusivity and conductivity. An experimental system with high sensitivity fortemperature change is designed to perform the measurement. Experimental resultsof samples are in agreement with the recommended values. The validation of theone-dimensional point source heat transfer is discussed, and the deviation fromthe theoretical model is negligibly small for the measurement. The estimatedmeasurement uncertainties are 3.5% and 5.3% for thermal diffusivity andconductivity respectively.

The normal zone propagation in ATLAS B00 model coil

The B00 model coil has been successfully tested in the ATLAS Magnet Test Facility at CERN. The coil consists of two double pancakes wound with aluminum stabilized cables of the barrel- and end-cap toroids conductors for the ATLAS detector. The magnet current is applied up to 24 kA and quenches are induced by firing point heaters. The normal zone velocity is measured over a wide range of currents by using pickup coils, voltage taps and superconducting quench detectors. The signals coming from various sensors are presented and analyzed. The results extracted from the various detection methods are in good agreement. It is found that the characteristic velocities vary from 5 to 20 m/s at 15 and 24 kA respectively. In addition, the minimum quench energies at different applied magnet currents are presented.

Analysis and testing of a silicon intrinsic-point heater in a micropropulsion application

Efficient heating of a fluid is demonstrated using a novel heat exchanger in which bulk silicon forms both the heater structure and the resistive heating elements. Current passed through the heater raises the temperature of the heater fins and this energy is transferred to a fluid flowing between adjacent fins. By exploiting the change in sign of the temperature coefficient of resistivity of the heavily doped silicon, the temperature of the system is stably maintained at the intrinsic point. A heat exchanger of this nature is integrated with a nozzle, resulting in a microthruster with elevated chamber temperature, which greatly improves the specific impulse, or thrust per unit weight flow of propellant. A numerical model is presented to optimize the heater design. Benchtop tests demonstrate the inherent stability of the intrinsic point heater design, while thrust tests demonstrate the improved fuel economy of the micropropulsion system.

Minimum quench energy measurement of NbTi wires using a small ceramic heater

A small ceramic chip resistor is proposed as a possible ideal point heater for transient stability measurements of superconductors. Preliminary results were obtained using a 1-mm*1.5-mm*0.5-mm ceramic resistor and NbTi wires whose copper-to-superconductor (Cu/SC) ratios were 1 and 2, having the same SC areas. The resistor was soldered on the NbTi wire to minimize the thermal resistance between the resistor and the wire. The minimum quench energy of the Cu/SC ratio 2 wire was approximately twice as large as that of the Cu/SC ratio 1 wire, under the same background magnetic field and with the same ratio of the operating current to its critical current.

Direct injection on capillary columns for gas chromatography

AbstractDiscrimination may occur when injecting samples onto gas chromatography capillary columns, whereby peak areas for higher boiling point compounds are smaller than they should be compared to lower boiling compounds. This problem is most important in quantitative work on solutes having a wide range of volatility. An all‐glass inlet system was used. Injections were made with a 10‐μl syringe onto a column without and injection point heater and with the column oven about 20°C below the boiling point of the solvent used for the solutes. Discrimination did not occur in a range of C12 to C36 n‐alkanes.

A gas-chromatographic method for the simultaneous determination of phenobarbitone, primidone and phenytoin in serum using a nitrogen detector

The use of heated nitrogen detector in a gas-liquid chromatographic method for the simultaneous determination of phenobarbitone, primidone and phenytoin in serum following therapeutic dosage is described. An analogue of phenytoin is added to the serum as internal standard, obviating the need for accurate aliquot measurement during subsequent manipulations; the anticonvulsants are methylated in the injection point heater of the chromatograph and the high selectivity of the nitrogen detector allows the use of a direct extraction procedure.