Linear Temperature Profile Research Articles

A novel model for predicting the temperature profile in gas lift wells

Abstract One of the most common methods for calculating the production oil rate in a gas lift well is nodal analysis. This manner is an accurate one, but unfortunately it is very time consuming and slow. In some modern studies in petroleum engineering such as close loop control of the wells this slowness makes it impossible to have an online optimization. In fact, before the end of the optimization the input parameters have changed. Thus having a faster model is necessary specially in some of the new studies. One of the sources of slowness of the nodal analysis is the temperature profile estimation of the wells. There are two general approaches for temperature profile estimation, some like heat balance are accurate but slow. Others, similar to linear profile assumption are fast but inaccurate and usually are not used commonly. Here, as a new approach, a combination model of heat balance and linear temperature profile estimation has represented which makes the nodal analysis three times faster and it is as accurate as heat balance calculations. To create this, two points (gas injection point and end of tubing) are selected, then using heat balance equations the temperature of those two points are calculated. In normal nodal analysis the temperature of each wanted point in the well is estimated by heat balance and it is the source of slowness but here just two points are calculated using those complex equations. It seems that between these points assuming a linear temperature profile is reasonable because the parameters of the well and production such as physical tubing, and casing shape and properties and gas oil ratio are constants. But of course, it still has some deviation from the complete method of heat balance which using regression and assigning a coefficient to the model even this much of the deviation could be overcame. Finally, the model was tested in various wells and it was compared with the normal nodal analysis with complete heat balance models. Results showed that the new model is as accurate as normal heat balance but three times faster.

Probing horizontal convection instability via perturbation of the forcing boundary layer using a synthetic jet

Horizontal convection driven by a linear temperature profile along the bottom of a two-dimensional rectangular enclosure is perturbed by a small tuned synthetic (zero-net-mass-flux/ZNMF) jet. The jet permits instability in the horizontal convection boundary layer to be investigated in a controlled manner. At a Prandtl number Pr = 6.14 and Rayleigh number Ra = 2.5 × 108, slightly below the natural onset of instability, the boundary layer is found to be convectively unstable, exhibiting a disturbance pattern consistent with a Rayleigh–Bénard mechanism. Advection of the boundary layer disturbance gives rise to unsteadiness in the vertical end-wall plume. Nusselt number is enhanced across a range of frequencies for all perturbation amplitudes, with the response dominated by two frequencies differing by approximately a factor of two: each invokes the periodic shedding of vorticity into the vertical end-wall plume at the higher frequency. This suggests that there exists a natural sensitivity in this flow to disturbances convecting in the upstream boundary layer. That is, a convective instability in the horizontal convection boundary layer serves as a disturbance amplifier, with the end-wall plume controlling the frequency of the resulting instability mode. The increase in Nusselt number achieved by a jet with peak speed of the same order as the horizontal convective velocity in the unperturbed flow is consistent with a greater than two-fold increase in Rayleigh number.

Performance and applicability of a 2.5-D ice-flow model in the vicinity of a dome

Abstract. Three-dimensional ice flow modelling requires a large number of computing resources and observation data, such that 2-D simulations are often preferable. However, when there is significant lateral divergence, this must be accounted for (2.5-D models), and a flow tube is considered (volume between two horizontal flowlines). In the absence of velocity observations, this flow tube can be derived assuming that the flowlines follow the steepest slope of the surface, under a few flow assumptions. This method typically consists of scanning a digital elevation model (DEM) with a moving window and computing the curvature at the centre of this window. The ability of the 2.5-D models to account properly for a 3-D state of strain and stress has not clearly been established, nor their sensitivity to the size of the scanning window and to the geometry of the ice surface, for example in the cases of sharp ridges. Here, we study the applicability of a 2.5-D ice flow model around a dome, typical of the East Antarctic plateau conditions. A twin experiment is carried out, comparing 3-D and 2.5-D computed velocities, on three dome geometries, for several scanning windows and thermal conditions. The chosen scanning window used to evaluate the ice surface curvature should be comparable to the typical radius of this curvature. For isothermal ice, the error made by the 2.5-D model is in the range 0–10 % for weakly diverging flows, but is 2 or 3 times higher for highly diverging flows and could lead to a non-physical ice surface at the dome. For non-isothermal ice, assuming a linear temperature profile, the presence of a sharp ridge makes the 2.5-D velocity field unrealistic. In such cases, the basal ice is warmer and more easily laterally strained than the upper one, the walls of the flow tube are not vertical, and the assumptions of the 2.5-D model are no longer valid.

Accurate measurement of temperature and concentration distribution of a mixture in a rectangular parallelepiped enclosure

Thermal diffusion in the 50/50wt.% binary hydrocarbon mixture of 1,2,3,4-tetrahydronaphthalene (THN)/dodecane (C12) at a mean temperature of 298K was studied experimentally in two cells with different geometries. The thermal design of the geometries was investigated numerically, and the effect of the location of the filling channel was studied. The newer design showed a more linear temperature profile with smaller values of velocity than the earlier design. The thermal experimental results were in agreement with the numerical calculations. Unlike the previous design, the segregation of the components in the new design was not affected by convective motions, and the calculated Soret coefficient agreed with the benchmark values.

Triggering wave-domain heat conduction in graphene

Using non-equilibrium molecular dynamics simulations, we systematically investigate the non-Fourier heat conduction in graphene under steady high heat flux. The results show that if two triggering factors, i.e. steady high heat flux and tensile stress, are satisfied simultaneously, a low-frequency mechanical wave and corresponding wave-like energy profile can be observed, which are distinctly different from ripples and linear temperature profile of the normal Fourier heat conduction. This mechanical wave provides an additional channel of heat transport and renders graphene more conductive without changing its pristine thermal conductivity. What's more, as the heat flux or original bond length increases, its frequency increases and energy transported by this mechanical wave is also on the rise. Further analyses show that such anomalous phenomenon is not arising from the high-energy or high-frequency pulses and also not artifacts of the velocity-exchange method. It is a dissipative structure, a new order state far from thermodynamic equilibrium, and the corresponding nonlinear relationship between the gradient of the wave-like kinetic temperature and the heat flux enables more efficient heat transport in graphene.

Analysis of bubble growth on a hot plate during decompression in microgravity

The focus of the present work is the modeling of bubble growth on a hot plate during decompression (depressurization) of a volatile liquid at temperatures close to saturation and in the presence of dissolved gas. In particular, this work presents an organized attempt to analyze data obtained from an experiment under microgravity conditions. In this respect, a bubble growth mathematical model is developed and solved at three stages, all realistic under certain conditions but of increasing physical and mathematical complexity: At the first stage, the temperature variation both in time and space is ignored leading to a new semi-analytical solution for the bubble growth problem. At the second stage, the assumption of spatial uniformity of temperature is relaxed and instead a steady linear temperature profile is assumed in the liquid surrounding the bubble from base to apex. The semi-analytical solution is extended to account for the two-dimensionality of the problem. As the predictions of the above models are not in agreement with the experimental data, at the third stage an inverse heat transfer problem is set up. The third stage model considers an arbitrary average bubble temperature time profile and it is solved numerically using a specifically designed numerical technique. The unknown bubble temperature temporal profile is estimated by matching theoretical and experimental bubble growth curves. A discussion follows on the physical mechanisms that may explain the evolution of the average bubble temperature in time.

Laminated composite plates subject to thermal load using trigonometrical theory based on Carrera Unified Formulation

In the present work, an analytical solution for the thermoelastic static problem of simply supported laminated composite plates is presented. The present mathematical model uses a unified new trigonometric displacement field expansion under Carrera Unified Formulation (CUF). The equivalent single layer (ESL) governing equations are written using CUF notation for static thermal stress analysis employing the Principle of Virtual Displacement (PVD). The highly coupled partial differential equations are solved using Navier solution method. Normalized and non-normalized unified trigonometric shear strain shape functions are introduced for the first time. Shear deformation results are compared with the classical polynomial ones, which is usually adopted in several refined plate theories under CUF. Linear temperature profile and non-linear temperature profile obtained by solving heat conduction problem are taken into account. Good agreements with 3D solution for several order of expansion are reached, but instabilities are shown for some particular order of expansion even when an exact through the thickness integration technique was adopted. Similar values are presented between polynomial and non-polynomial displacement fields. However, non-polynomial functions can be optimized by changing the arguments of such functions in order to improve the results. Future studies are necessary in this direction.

Maximum production rate optimization for sulphuric acid decomposition process in tubular plug-flow reactor

A sulphuric acid decomposition process in a tubular plug-flow reactor with fixed inlet flow rate and completely controllable exterior wall temperature profile and reactants pressure profile is studied in this paper by using finite-time thermodynamics. The maximum production rate of the aimed product SO2 and the optimal exterior wall temperature profile and reactants pressure profile are obtained by using nonlinear programming method. Then the optimal reactor with the maximum production rate is compared with the reference reactor with linear exterior wall temperature profile and the optimal reactor with minimum entropy generation rate. The result shows that the production rate of SO2 of optimal reactor with the maximum production rate has an increase of more than 7%. The optimization of temperature profile has little influence on the production rate while the optimization of reactants pressure profile can significantly increase the production rate. The results obtained may provide some guidelines for the design of real tubular reactors.

Effect of Spectral Reshaping on Frequency Modulated Thermal Wave Imaging for Non-destructive Testing and Evaluation of Steel Material

Infrared thermographic techniques show their potential usage for non-destructive testing and evaluation of various materials due to their inherent capabilities such as whole field, non-contact, qualitative and quantitative to detect surface and sub-surface anomalies. This contribution introduces a novel data analysis scheme by spectral reshaping of linear frequency modulated temperature profile captured over a mild steel specimen. Time and frequency domain based processing methods are adopted on the generated temporal thermal data to reveal the hidden defects. Obtained results show the potential capabilities of spectral reshaping based on Gaussian windowed chirp with enhanced resolution and sensitivity for sub-surface defect detection.

Finite element analysis of thermal buckling in automotive clutch plates

ABSTRACTA finite element analysis is performed to investigate the stability boundaries of thermal buckling in automotive clutches. It is found that the radial variation of temperature considerably affects the critical buckling temperature. A linear or monotonic temperature profile always leads to a dominant coning mode. Whereas a temperature profile with the maximum temperature located in the middle leads to a dominant non-axisymmetric buckling mode, and the associated critical temperature is typically much higher. The numerical solutions for periodic variations of temperature with multiple waves along the circumference were also tentatively obtained.

Numerical Simulation of Natural Convection in a Porous Cavity with Linearly Temperature Distributions Under the Local Thermal Nonequilibrium Condition

A numerical investigation of the natural convection heat transfer in a rectangular cavity filled with a heat-generating porous medium by adopting the local thermal nonequilibrium (LTNE) model is reported in this paper. The top and bottom walls of the enclosure are adiabatic, the left wall is linearly cooled, and the right wall is cooled by a linear or uniform temperature profile. The results show that the isotherms for the fluid and solid phases become similar with the increase of the interphase heat transfer coefficient H; the increasing heat transfer between the two phases brings their temperatures closer to each other and thus the solid and fluid phases are in a state of the thermal equilibrium at higher values of H. For case A, the interphase heat transfer coefficient has little influence on the heat transfer rate of the solid phase of the porous cavity and the heat transfer profile of the solid phase (Nusy) is symmetrical with respect to the center point of line Y = 0.5. For case B, the interphase heat transfer coefficient H has a significant effect on that at the right wall, and the total heat transfer of the heat-generating porous cavity is implemented by the right-side wall. The total heat transfer rate Q of case B is higher than that of case A at a high thermal conductivity ratio γ (γ = 1, 10).

All Silicon Gas Chromatographic Column for Fast Separation of VOCs Released By Armillaria Fungus

This work showcases a new and novel temperature-programmed MEMS- GC column using a 2- dimensional heating technique in time and distance along the length of a MEMS GC-column. We have designed and fabricated a low power portable micro-GC system with an integrated novel heating technique for a 3-meter micro-fabricated GC column to improve separation performance. The column is interconnected with series of low power thermal conductivity detectors (TCD) for rapid detection of volatile organic compounds (VOC). Currently, detection of potentially infected trees is mainly based on a visual tree assessment, to inspect for signs and symptoms associated with the disease. However, this method can only be used to identify the infection at a late stage of the disease. In addition, it cannot provide any identification of the fungi involved. An accurate and early identification of fungal infection in orchards is critical to control the rapid spread of the fungal agents. The novel 2- dimensional temperature-programmed technique, in time and distance along the length of the GC-column, provides a negative temperature gradient. The temperature is hotter in the center (inlet of the column) than the perimeter (outlet) of the micro-GC using a linear temperature profile. As the sample passes through different temperature zones, the diffusion rate changes so that the front of the separation peak moves slower relative to the trailing edge of the peak; thereby, improving the resolution of the compounds passing through the column. As a result, for a given number of theoretic plates, a shorter column length can be used. Typically, shortening the length of a GC column reduces the analysis time at the expense of resolution; however, thermal refocusing of the eluting band will improve the resolution of the shorter columns. The gradient along the column continuously refocuses the eluting bands, offsetting part of the chromatographic band spreading, and consequently sharpens the peaks as they move down the column. In order to investigate the 2-D temperature gradients induced by the heater on previously fabricated GC-MEMS silicon, the heater was designed and simulated using COMSOL Multiphysics® (Figure 2). The 3D simulation was performed by coupling the electric current and heat transfer. Simulation results reveal the temperature distribution of the GC column and calculate the maximum temperature at 4 different locations (0.46, 36.18, 78.24, 300.12 cm from the inlet of the column. (Figure 3 ). Furthermore, the transient response of the 2-D heater was obtained for these locations and fitted into the transient lumped equation to extract the time constants (τ) of the transient response curves (Table 1) The simulation data was validated by connecting the GC column to a micro-fabricated TCD sensor. 2 µl of volatile compounds were injected into the system at helium flow rate of 1 mL/min and the power across the sensor was set to 6.4 mW. The results are shown in Figure 4. Figure 1

Thermal quenching in calcite and evaluation of quenching parameters from composite glow curve by a computerized resolved peak technique

Thermoluminescence (TL) glow curves of X-ray irradiated micro-grain calcite mineral were recorded at various heating rates (2, 4, 6, 8 and 10K/s) under same linear temperature profile from 300 to 520K. By using a Computerized Glow Curve Deconvolution technique, all composite glow curves of calcite were analyzed and the glow curves were found to be a combination of three distinct overlapping peaks. Activation energies corresponding to these three peaks were found to be 0.70, 0.60 and 1.30eV respectively. For each set of computerized resolved peak, variation of peak maximum temperature, FWHM and peak area with heating rate were studied. Entire glow curves were found to be influenced by thermal quenching. Thermal quenching activation energy, W and the pre-exponential unitless constant, C were evaluated from each resolved peak individually. Thermal quenching activation energies for the three peaks were found to be 1.36±0.54, 1.14±0.73 and 1.38±0.40eV respectively. The significance of determining the individual value of quenching parameters related to each peak for a composite glow curve is reported.

Multicellular Convection Flow and Heat Transfer in a Tall Vertical Cavity with a Linear Temperature Profile on Both Sidewalls

Laminar natural convection of air in a vertical cavity, of aspect ratio A = 40 with linear temperature profiles on both sidewalls, is studied. Two new situations are explored, both temperature profiles have the same (case I) or opposite (case II) slopes γ, and their averages are at the mid-height of sidewalls. The effect of the Rayleigh numbers Ra m at the mid-height and the slopes on the multicellular flow and heat transfer is investigated. Depending on the values of γ and Ra m , the results may be quite different from those of the classical case corresponding to a zero slope. Two precise correlations which give the average heat transfer as a function of γ and Ra m are also developed for both cases.

Rarefied gas flow in a rectangular enclosure induced by non-isothermal walls

The flow of a rarefied gas in a rectangular enclosure due to the non-isothermal walls with no synergetic contributions from external force fields is investigated. The top and bottom walls are maintained at constant but different temperatures and along the lateral walls a linear temperature profile is assumed. Modeling is based on the direct numerical solution of the Shakhov kinetic equation and the Direct Simulation Monte Carlo (DSMC) method. Solving the problem both deterministically and stochastically allows a systematic comparison and verification of the results as well as the exploitation of the numerical advantages of each approach in the investigation of the involved flow and heat transfer phenomena. The thermally induced flow is simulated in terms of three dimensionless parameters characterizing the problem, namely, the reference Knudsen number, the temperature ratio of the bottom over the top plates, and the enclosure aspect ratio. Their effect on the flow configuration and bulk quantities is thoroughly examined. Along the side walls, the gas flows at small Knudsen numbers from cold-to-hot, while as the Knudsen number is increased the gas flows from hot-to-cold and the thermally induced flow configuration becomes more complex. These flow patterns with the hot-to-cold flow to be extended to the whole length of the non-isothermal side walls may exist even at small temperature differences and then, they are enhanced as the temperature difference between the top and bottom plates is increased. The cavity aspect ratio also influences this flow configuration and the hot-to-cold flow is becoming more dominant as the depth compared to the width of the cavity is increased. To further analyze the flow patterns a novel solution decomposition into ballistic and collision parts is introduced. This is achieved by accordingly modifying the indexing process of the typical DSMC algorithm. The contribution of each part of the solution is separately examined and a physical interpretation of the flow configuration, including the hot-to-cold flow close to the side walls, in the whole range of the Knudsen number is provided.

Simulation of CO Preferential Oxidation (COPrOx) Monolithic Reactors

AbstractIn this work, a COPrOx monolithic reactor with a CuO/CeO2/Al2O3catalytic washcoat was modelled to purify a H2stream for a 2 kW PEM fuel cell. Preliminary simulations included isothermal monoliths operating between 423 and 463 K, and the optimization of linear axial temperature profiles. For a fixed total system size and a desired CO outlet molar fraction lower than 20 ppm, an isothermal temperature profile maximized the global selectivity towards CO oxidation. Then, different schemes of adiabatic monoliths with interstage cooling were modelled and evaluated. It was found that wide operating temperature ranges lower the necessary number of stages, but decrease the global selectivity and rise system sensitivity to inlet temperatures. A 1D heterogeneous model was used to simulate the monoliths.

Wind-Tunnel Simulation of the Wake of a Large Wind Turbine in a Stable Boundary Layer. Part 1: The Boundary-Layer Simulation

Measurements have been made in both a neutral and a stable boundary layer as part of an investigation of the wakes of wind turbines in an offshore environment, in the EnFlo stratified flow wind tunnel. The working section is long enough for the flow to have become very nearly invariant with streamwise distance. In order to be systematic, the flow profile generators of Irwin-type spires and surface roughness were the same for both neutral and stable conditions. Achieving the required profiles by adjusting the flow generators, even for neutral flow, is a highly iterative art, and the present results indicate that it will be no less iterative for a stable flow (as well as there being more conditions to meet), so this was not attempted in the present investigation. The stable-case flow conformed in most respects to Monin–Obukhov similarity in the surface layer. A linear temperature profile was applied at the working section inlet, resulting in a near-linear profile in the developed flow above the boundary layer and ‘strong’ imposed stability, while the condition at the surface was ‘weak’. Aerodynamic roughness length (mean velocity) was not affected by stability even though the roughness Reynolds number \({<}1\), while the thermal roughness length was much smaller, as is to be expected. The neutral case was Reynolds-number independent, and by inference, the stable case was also Reynolds-number independent.

Effective Thermal Conductivity of Soda‐Lime Silicate Glassmelts with Different Iron Contents Between 1100°C and 1500°C

This study presents a simple method for retrieving the effective thermal conductivity of semitransparent glassmelts from measured temperature profiles. Effective thermal conductivity of molten glass at high temperature is an important thermophysical property that affects the glassmelting and forming processes and thus the quality of the final glass products. In semitransparent glassmelts, heat is transferred by both conduction and radiation. In the limiting case of optically thick glassmelts, typically featuring high iron content, thermal radiation can be treated as a diffusion process. The total heat flux can be expressed as the sum of a phononic and a radiative heat fluxes based on Fourier's law. For weakly absorbing glassmelts, the temperature profile may be strongly nonlinear particularly neat container walls due to the contribution from emission and absorption. Steady‐state measurement techniques, such as the linear heat flux method, have been developed to measure glassmelt effective thermal conductivity at high temperatures. However, they typically use only three temperatures measurements and assume linear temperature profile in the glassmelt. The new retrieval method addresses these drawbacks particularly for weakly absorbing glassmelts featuring nonlinear temperature profiles. It is demonstrated with experimental data collected for soda‐lime silicate glasses with iron content ranging from 0.008 to 1.1 wt% and temperatures between 1100°C and 1550°C.

Selection of steady regimes of a one-parameter family in the problem of plane convective flow through a porous medium

Convective flow through a porous medium in a rectangular vessel with a linear temperature profile steadily maintained on the boundary is investigated. On the basis of numerical experiments the realization of steady regimes that belong to a globally stable, one-parameter family is studied at different vessel dimensions and initial temperature distributions. The regime selection is shown to strongly depend on the initial fluid temperature: a vicinity of two regimes is realized from initial data similar with the state of rest; at high initial fluid heating the regimes are selected from a vicinity of two other regimes; and in intermediate situations any of infinite number of steady regimes can be attained.

Entropic anomaly and maximal efficiency of microscopic heat engines

The efficiency of microscopic heat engines in a thermally heterogenous environment is considered. We show that-as a consequence of the recently discovered entropic anomaly-quasistatic engines, whose efficiency is maximal in a fluid at uniform temperature, have in fact vanishing efficiency in the presence of temperature gradients. For slow cycles the efficiency falls off as the inverse of the period. The maximum efficiency is reached at a finite value of the cycle period that is inversely proportional to the square root of the gradient intensity. The relative loss in maximal efficiency with respect to the thermally homogeneous case grows as the square root of the gradient. As an illustration of these general results, we construct an explicit, analytically solvable example of a Carnot stochastic engine. In this thought experiment, a Brownian particle is confined by a harmonic trap and immersed in a fluid with a linear temperature profile. This example may serve as a template for the design of real experiments in which the effect of the entropic anomaly can be measured.