Insulated Tube Research Articles

Numerical simulation of double-pipe condensers and evaporators

A detailed one-dimensional steady and transient numerical simulation of the thermal and fluid-dynamic behaviour of double-pipe heat exchangers (evaporators and condensers) has been carried out. The governing equations (continuity, momentum and energy) inside the internal tube and the annulus, together with the energy equation in the internal tube wall, external tube wall and insulation, are solved iteratively in a segregated manner. The discretized governing equations in the zones with fluid flow are efficiently coupled using an implicit step by step method. This formulation requires the use of empirical correlations for the evaluation of convective heat transfer, shear stress and void fraction. An implicit central difference numerical scheme and a line-by-line solver was used in the internal and external tube walls and insulation. A special treatment has been implemented in order to consider transitions (single-phase/two-phase, dry-out,…). All the flow variables (enthalpies, temperatures, pressures, mass fractions, velocities, heat fluxes,…) together with the thermophysical properties are evaluated at each point of the grid in which the domain is discretized. Different numerical aspects and comparisons with analytical and experimental results are presented in order to verify and validate the model.

Numerical simulation of triple concentric-tube heat exchangers

A detailed one-dimensional steady and transient numerical simulation of the thermal and fluid-dynamic behaviour of triple concentric-tube heat exchangers has been developed. The governing equations (continuity, momentum and energy) inside the inner tube and the annulus (inner and outer), together with the energy equations in the inner, intermediate and outermost tube wall and insulation, are solved iteratively in a segregated manner. The discretized governing equations in the zones with fluid flow are coupled using an implicit step by step method. This formulation requires the use of empirical information for the evaluation of convective heat transfer, shear stress and void fraction. An implicit central difference numerical scheme and a line-by-line solver was used in the inner and intermediate tube walls and the outermost tube wall with insulation. All the flow variables (enthalpies, temperatures, pressures, mass fractions, velocities, heat fluxes, etc.) together with the thermophysical properties are evaluated at each point of the grid in which the domain is discretized. Different numerical aspects and comparisons with results obtained from the technical literature are presented in order to verify and validate the model.

04/00970 Heat and mass transfer in the adsorbent of a solar adsorption cooling system with glass tube insulation: Dai, Y. J. and Sumathy, K. Energy, 2003, 28, (14), 1511–1527

One stationary and five dynamic models for solar collectors are analyzed in different ways. (1) The models are fitted to a set of measured data and the resulting collector parameters are compared. (2) Step responses of the models are compared in order to illustrate their different reactions to transient conditions. (3) The total daily energy yield predicted by the models for three days of different weather conditions is calculated using a reference collector parameter set. It turns out that the stationary model overpredicts the collector output by up to 15% in the case of one-minute averages of input data, while all dynamic models yield similar results. In the case of hourly input data, the error of the stationary model nearly vanishes.

Compact and efficient kinetically enhanced copper-vapor lasers of high (100-W) average power.

We report on severalfold increases in the output power of kinetically enhanced copper-vapor lasers operating in a regime of high specific input power and reduced tube insulation. Three laser tubes, of length 1 m and bore diameters 17.5, 25, and 32 mm, were investigated at constant input power. Output power of 104 W at 1.4% wall-plug efficiency was obtained for the largest tube. When the bore diameter was decreased to 17.5 mm, the output power and efficiency remained high (90 W at 1.0% efficiency), whereas the specific output power increased threefold. The output powers were as much as fivefold higher than those of previous small-scale (i.e., <25-mm-diameter) copper lasers of any type.

Heat and mass transfer in the adsorbent of a solar adsorption cooling system with glass tube insulation

A solar adsorber with glass tube insulation used in a solar adsorption cooling system is proposed and investigated. The adsorber is a metal tube packed with activated carbon methanol pair surrounded by a vacuum tube glazing. A mathematical model, which accounts for the heat and mass transfer of sorption (adsorption and desorption) processes as well as the effects of non-equilibrium and non-uniform temperature and pressure distribution, is developed and experimentally validated. Based on the model simulation, the influence of different physical variables on the performance of the adsorber and their variations are simulated and discussed. It has been found that the thermal efficiency of the solar adsorber is about 30% and the solar adsorber configuration used in this study is one of the good configurations that can be used for adsorption refrigeration. The mathematical model is capable of predicting the performance of the solar adsorber.

Thermocapillary motion of deformable fluid particles in tubes

The boundary integral technique is used to study the effect of deformation on the steady, creeping, thermocapillary migration of a fluid particle under conditions of axisymmetry, negligible thermal convection and an insulated tube wall. The spherical radius of the fluid particle (i.e. the radius as if the particle were a sphere, a ′=(3 V p r /4π) 1/3 is the particle volume) and that of the tube are denoted, respectively, by a ′and b ′ . For small capillary number Ca = 0.05, only for a large fluid particle ( a ′/ b ′ = 0.8) is deformation significant. For a′/b′ = 0.8, hydrodynamic stresses squeeze the particle, reduce the interaction of the particle with the wall and thereby increase the terminal velocity. For small particles a ′/ b ′ Ca = 0.05 the fluid particles translate as spheres, due to the fact that the fluid particle is too far away from the wall to be subject to distending hydrodynamic stresses. The deformable particle moves faster than a spherical one in the thermocapillary migration. The increase in velocity with capillary number is larger for thermocapillary motion than for buoyancy.

Focus on Materials

Focus on Materials

Fiber optic voltage sensor for 420 kV electric power systems

We present an optical fiber voltage sensor for 420 kV electric power lines. The sensor exploits the converse piezoelectric effect of quartz and measures the voltage by a line integration of the electric field. The alternating voltage is partitioned to a series of four cylinder-shaped quartz crystals, which are embedded in polyurethane resin within a 3.2-m long insulator tube of fiber reenforced epoxy. The alternating piezoelectric deformations of the crystals are sensed by a common elliptical-core dual-mode fiber, which is wound onto the circumferential crystal surfaces. The fiber is interrogated using low coherence interferometry. We determine the dielectric design of the sensor from a numerical analysis of the electric field distribution within and in the vicinity of the sensor. We experimentally verify the dielectric reliability under ac overvoltages up to 520 kV root mean square (rms) and lightning and switching impulse voltages up to 1425 and 1050 kV, respectively. Further, we investigate the sensor performance including accuracy, dynamic range, bandwidth, and temperature dependence.

Flame propagation in a rotating tube

The steady propagation of premixed laminar flames in rotating circular tubes with adiabatic or isothermal walls is numerically investigated to study the effects of solid‐body rotation on the flame shape and the flame propagation speed. Owing to the coupling of density variation across the flame and radial pressure gradient, the results show that the resulting baroclinic torque tends to make the unburned mixture ahead of the flame flow from the axis to the wall of the tube. This tendency intensifies with the increase in the tube rotation speed. Thereby, as the tube is rotated faster, the mushroom‐shaped flame becomes more convex to the unburned mixture at the axis of the tube, resulting in larger flame surface and therefore a faster flame. On the other hand, the tulip‐shaped flame becomes flatter at the concave portion near the axis, and turns convex to the unburned mixture, becoming a mushroom‐shaped flame as the tube is rotated fast enough. Although tulip‐shaped flame/mushroom‐shaped flame transition is gradual in small tubes, in large tubes, it is catastrophic and a hysteresis behavior is observed. Since the tulip‐shaped flame flattens near the axis as the tube rotation speed increases, its flame propagation speed in insulated tubes decreases during its transition to mushroom‐shaped flame because of the decrease of its total flame surface. In isothermal‐wall tubes, however, because its surface grows larger near the wall during the transition, its flame propagation speed increases slightly as the rotation speed increases.

Numerical Investigation of SAGD Process Using a Single Horizontal Well

Abstract Recently several articles have been published regarding the innovation and field applications of the Steam-Assisted-Gravity-Drainage (SAGD) process using a single horizontal well for the recovery of heavy oil. In the process, an insulated concentric coiled tubing, inserted into the horizontal wellbore, injects high quality steam to the toe of the well. The steam condensate and reservoir fluids enter the wellbore and flow back along the annulus to the heel to be produced. There remain some arguments on whether the SAGD mechanism is working in field operations and on what oil rates can be achieved in the long run. In an attempt to answer these questions, numerical simulation studies were pursued in the present work. The studies focused on three major aspects:the possible counter-current fluid exchange pattern between the reservoir and the well;the means that could be exploited to promote the initiation of a steam chamber; andthe potential oil rates that could be expected under possible field operating conditions. The results showed that the presence of small capillary pressure near a horizontal wellbore is a physical constraint preventing counter-current exchange of steam and oil. It was also demonstrated that vertical undulation in well-profile or a certain level of formation dilation around the wellbore could potentially overcome the capillary pressure constraint and promote the initiation of a steam chamber under field operating conditions. Introduction After over 20 years of extensive laboratory studies and field trials, the concept of Steam-Assisted-Gravity-Drainage (SAGD)(1) has evolved into a commercially viable thermal oil recovery process for certain heavy oil reservoirs(2,3). In the conventional SAGD process(4), a pair of vertically stacked horizontal wells is used; in which the top well is used for steam injection and the bottom well is used for fluid production. Even with the latest drilling/completion technologies, it may still be difficult to properly place the well pair into a formation(2). In order to reduce the high cost associated with the drilling and completion of two horizontal wells, industry has sought alternative well configurations since the first field trial(5–9). One of the approaches is to utilize only one horizontal well for both steam injection and fluid production(5,8). As early as 1978, Imperial Oil conducted the pioneering horizontal well field pilot (HWP-1) to test the SAGD process(10). In the pilot, the single-well concept was tested. The steam was injected through an annulus to the heel of the well; the steam condensate and oil were produced through a nitrogen gas insulated FIGURE 1: The well profile of Imperial Oil's Horizontal Well Pilot 1 (HWP-1) (a vertical well for observation). (From Hawkins, 1979.) (Available in full paper) tubing inside the wellbore. Figure 1 shows the well profile. The vertical well shown in the figure was an observation well. During the 94-day test period over 3,500 m3 of cold water equivalent (CWE) dry steam was injected into the horizontal well, but only 9 M3 of bitumen was produced from a reservoir with high viscosity bitumen (200 Pa ·s).

Measurement of lon Current in Premixed Combustion Flame. 1st Report. Characteristics to the Types of lon Probes.

The comparison between the single and the twin probes methods was achieved to measure ion current in propane-air premixed combustion flame. When using the single probe method, it was inevitable that there was much error in the measure of combustion flame, since leak current conducted to an insulation tube which an electrostatic wire passed through. Noise in the measuring circuit also exerted serious influence because of the feeble ion current. To prevent such effect, this study proposes the twin probes method, using two measuring probes which had some different protrusion lengths each other. And this method gave its simpler usage without the above problems. It was also found that the maximum ion current at half height of each flame was appropriate for evaluating the total condition of combustion flame.

Characteristics of Scanning Mirror-type Magnetic Field Coaxial Electron Cyclotron Resonance Plasma for Inner Coating of Slender Glass Tubes

An inner coating system has been developed with the use of scanning coaxial electron cyclotron resonance (ECR) plasma. In this system, plasma was generated by the ECR method inside a coaxial metallic or insulated tubes under low pressure and narrow gap conditions. ECR plasma was transported along the tube axis by controlling the position of ECR points. By inserting the insulated tube into the metallic tube, discharge at low pressure was realized. We succeeded in coating titanium onto the inner surface of an insulated tube of 27 mm inner diameter and 480 mm length. Using this coating system, titanium nitride (TiN) films were deposited in the metallic tube at an Ar flow rate of 0.1 sccm, an N2 flow rate of 0.1 sccm and a total pressure of 0.14 mTorr.

XUV-Amplification in an argon z-pinch plasma

Amplification of XUV radiation of the 3p–3s transitions at 46.9 and 67.1 nm with a gain-length product of 2.4 and 2.6 has been observed in an argon z-pinch plasma. The amplification was demonstrated by varying the discharge length between 40 and 120 mm. A temporal resolved measurement of the gain coefficient is presented here that shows a gain of >0.15 cm −1 for a duration of more than 40 ns with a peak value of 0.2 cm −1 for the 46.9 nm line. The plasma was generated in a fast z-pinch discharge driven by a 200 kV three-stage Marx-generator. The discharge current in the alumina insulator tube with a diameter of 7 mm was 40 kA.

Nonadiabatic frontal polymerization

Frontal polymerization is a process in which a spatially localized reaction zone propagates into a monomer, converting it into a polymer. In the simplest case of free-radical polymerization, a mixture of a monomer and initiator is placed into a test tube. Upon reaction initiation at one end of the tube a self-sustained thermal wave, in which chemical conversion occurs, develops and propagates through the tube. In a previous paper, a perfectly insulated tube (i.e., an adiabatic polymerization process) was considered. In reality, it is nearly impossible to eliminate heat losses completely, and an accurate model must take this into account. Extinction of polymerization waves and difficulties initiating the wave, both as a result of heat losses, are often encountered in experiments. This paper will therefore concentrate on nonadiabatic frontal polymerization. The propagation of nonadiabatic free-radical polymerization fronts is studied by methods originally developed in combustion theory, and employed in a previous paper. This analysis is accomplished by examination of the structure of the polymerization wave, its propagation velocity, degree of conversion of the monomer and maximum temperature, and how these quantities are affected by changes in initial temperature, concentrations and kinetic parameters. The values of these quantities near the extinction limit (beyond which traveling-wave solutions will no longer exist) are compared to those in the adiabatic case.

Determination of mercury species in fish reference materials by isothermal multicapillary gas chromatography with atomic emission detection after microwave-assisted solubilization and solvent extraction

A simple and rapid procedure for the simultaneous determination of methylmercury and Hg2+ in fish reference materials was developed. The procedure was based on a rapid (2.5 min) microwave-assisted solubilization of biomaterial with tetramethylammonium hydroxide, simultaneous quantitative ethylation–extraction of the mercury species into hexane (15 min) and flash isothermal separation (15–30 s) using a multicapillary regular column (100 cm) or a minicolumn (22 cm). The chromatographic hardware necessary for sample introduction into a microwave induced plasma was downscaled to a split injection port and a 20×20×10 cm compartment (housing the 1 m column) or a 22 cm×1 cm od thermally insulated tube (housing the minicolumn) maintained at a constant temperature and connected directly to the detector. No dilution of the GC eluent (60–120 ml min–1) with make-up gas was necessary to achieve optimum sensitivity. Detection limits (as Hg) were 0.5 pg µl–1 (20 ng g–1 dry mass) and 2 pg µl–1 (80 ng g–1 dry mass)for MeHg+ and Hg2+, respectively. The method was validated for speciation analysis for mercury in BCR 463, BCR 464 (Tuna Fish) and NRCC DORM-1 (Dogfish Mussel) certified reference materials.

Ceramics inner coating of narrow tubes by a coaxial magnetron pulsed plasma

We have developed a double-ended anode coaxial magnetron pulsed plasma (DCMPP) for the purpose of coating fine ceramics with, for example, titanium nitride (TiN) on the inner surface of a narrow insulated tube by reactive sputtering. In the magnetron pulsed plasma, the magnetron effect and J × B plasma transport by a pulsed discharge occurred simultaneously. Discharge characteristics and optimum conditions for uniform and high-rate sputter-coating were investigated. By using DCMPP, goldcolored TiN films could be deposited on the inner surfaces of narrow glass tubes of 8 mm in inner diameter and 400 mm in length. The deposition rate was about 20 nm min −1 for a deposition time of 600 s. By using a light absorption method, it was found that axial uniformity of the prepared films was within 25% over 400 mm.

Residual Stress Analysis of Cylindrical Solid Oxide Fuel Cells

The dependence of the residual stress in cylindrical solid oxide fuel cells (SOFCs) on the structures and the process temperatures was estimated using the analytical modeling of an axisymmetric structure. From the results of the analysis the following points were discovered. In the case of a 4-layered structure, which is supported by a porous insulation tube of calcia-stabilized zirconia (CSZ), the circumferential and axial stresses induced in the electrodes are so high that they can break the structure under the assumed realistic conditions. A method for reducing these stresses is discussed. On the other hand, in the case of a 3-layered structure which is supported by an inner electrode tube, tensile stresses in the electrodes can be reduced to several MPa if the total thickness of two electrodes is more than 60 times the thickness of the electrolyte. New material for the substrate tube is proposed on the basis of the obtained results.

Construction of thermally insulated well in bovanenkovo field

In the Bovanenkovo field, which is located in the permafrost zone, production from gas wells encounters the following problems: The high ice content of rock in the upper part of the section and the low rock temperatures (below -5~ are responsible for periodic collapse of the rock in the space near the well bore, loss of stability of cementing, misalignment of fittings, increased probability of flow of gas between strings, and so on, as a result of the heating effect of the gas flow on this space; other adverse effects include the collapse of casing strings when the fluid remaining outside the casing after drilling and cementing operations refreezes nonuniformly during a period of well shutdown, in the interval before the start of production, or during a period of conservation. The most effective means for preventing these problems is the use, in the operation or conservation of wells, of thermally insulated casing or tubing with a thermal resistance high enough to ensure extended operation of the well while maintaining a subfreezing temperature outside the casing; another possibility is the use of higher-strength casing with a critical crushing pressure higher than the maximum pressure created by the freezing liquid in one interval or another of the frozen ground with a known natural subfreezing temperature. In selecting a well program for conditions of the Bovanenkovo field (Aptian horizons), the following features were taken into account. No thermal insulation or "passive" thermal protection in permafrost is capable of eliminating the gradual

Natural convective heat transfer from open vertical tubes

AbstractNatural convection heat transfer in vertical tubes is described by a one‐dimensional dispersion model similar to that used previously for fluid mixing in the presence of an unstable density gradient. Temperature profiles have been measured in air in 2 m high insulated vertical tubes (21.3, 24.5, 27.7 cm internal diameter), closed at the bottom and open at the top, and heated at the bottom with a known heat flux. The effective mixing lengths for eddy heat transport are of the same order as the tube diameters.

Cool-down of a vertical line with liquid nitrogen

Analytical and numerical modeling is presented for predicting the thermofluid parameters of the cool-down process of an open-to-air vertical tube carrying liquid nitrogen. A two-fluid mathematical model is employed to describe the flowfield. In this model four distinct flow regions were analyzed: 1) fully liquid, 2) inverted annular film boiling, 3) dispersed flow, and 4) fully vapor. These flow regimes were observed in an experimental investigation constructed for validating the mathematical model, and also in previous experiments by other investigators. For the single-phase regions, the one-dimensional form of mass, momentum, and energy equations were used. For the two-phase regions, the volume-averaged, phasic one-dimensional form of conservation equations were applied. The one-dimensional energy equation was formulated to determine the tube wall temperature history. The numerical procedure is based on the semi-implicit, finite-difference technique. The calculations for the inverted annular film boiling were performed implicitly. The computations for the tube wall, fully liquid, and dispersed flow regions were performed explicitly. In each region, the appropriate models for heat transfer and shear stress rates are used. Results and comparisons of the predicted numerical models with the experimental data for several constant inlet flow rates of liquid nitrogen into a vertical, insulated tube are presented. Nomenclature Aw = cross-sectional area of the flow channel, m2 cp = specific heat capacity, J/kg °C Da = area-averaged, population-mean diameter of drops, m ALix = maximum entrainable diameter of drops, m £&ax = maximum stable diameter of drops, m Dsmd = Sauter mean diameter of a droplet population, m Dv = volume averaged, population-mean diameter of drops, m d = diameter of the flow channel, m g = local acceleration of gravity, m/s2 h = enthalpy, J/kg hc = convective heat transfer coefficient, W/m2 °C hnb = heat transfer coefficient for nucleate boiling, W/m2 °C ^,sat = saturation enthalpy of either liquid or vapor, J/kg k = thermal conductivity, W/m °C Lfg = latent heat of vaporization, J/kg m' = interfacial mass transfer rate, kg/m3s q = heat flux per unit area, W/m2 q' = heat transfer rate per unit volume, W/m3 <7evaP - vaporization heat flux, W/m2 #rad = wa ^ to liquid radiation, W/m2 q% = vapor to drop radiation heat flux, W/m2 q^d = wall to drop radiation heat flux, W/m2 q'^v = wall to vapor radiation heat flux, W/m2 Pi = inner perimeter of tubular flow channel, Pr = Prandtl number, cpiji/kl p = pressure, N/m2 m