Axial Temperature Variation Research Articles

Thermal buckling and postbuckling of functionally graded multilayer GPL-reinforced composite beams on nonlinear elastic foundations

Under the influence of axial forces and uniform temperature variations, the thermal buckling and postbuckling of composite beams reinforced of functionally graded multilayer graphene platelets (GPLs) resting on nonlinear elastic foundations are examined. The Halpin-Tsai model is used to calculate the elastic modulus of each layer of GPL-reinforced composite (GPLRC). According to the virtual work principle, the nonlinear governing equations for the beam are obtained from the first-order shear deformation beam theory. The impact of axial force and nonlinear elastic foundation on thermal buckling and postbuckling is discussed using the differential quadrature method (DQM), and the analytical expression is given by the two-step perturbation method (TSPM). The effects of axial force, boundary conditions, slenderness ratio, GPL geometry, GPL weight fraction, GPL distribution pattern, and elastic foundation coefficient on thermal buckling and postbuckling are examined through parameter analysis.

An artificial intelligence model for heat and mass transfer in an inclined cylindrical annulus with heat generation/absorption and chemical reaction

Present research investigates MHD mixed convective two dimensional flow, heat and mass transfer in a concentric inclined annulus with zero, first and second order chemical reactions along with heat generation/absorption. The internal and external cylinders are considered as isothermal with distinct temperatures and also presumed that the upper and lower sides are adiabatic. The governing equations are solved using the quasi-linearization approach in conjunction with an implicit Crank-Nicolson type FDM to arrive at the non-similar solutions. The results indicate that as the inclination parameter augments the concentration and thermal profiles augments in the annular region. As the reaction rate increases the concentration profile enhances in the annular region, since the concentration boundary layer thickens with higher reaction rate. The temperature gradient of the fluid is significantly affected by an external heat generation parameter, which enhances the fluid temperature distribution and thermal state. The results revealed that a magnetic field can regulate the magnetic convection of conducting fluid. The 3D view of fluid flow in radial and axial direction, temperature and concentration variations for distinct angle of inclinations are also illustrated and discussed explicitly. The FDM data is used to train an ANN model that forecasts the heat and mass transfer characteristics through Levenberg – Marquardt backpropogating algorithm. For various values of significant physical parameters the heat and mass transfer rates has R values as 0.99305 and 0.99991 respectively. The derived numerical data are compared and determined to be in exceptional concordance with previous results, in the limiting sense.

Connective and magnetic effects in a curved wavy channel with nanoparticles under different waveforms

Abstract The present study describes the peristaltic flow of Jeffrey fluid with nanomaterial bounded under peristaltic waves in a curved channel. Silver (Ag) is the nanomaterial used for this purpose, and base fluid is water. The diversity of peristaltic waves is captured under four different wave profiles traveling along the curved channel. The consequences of heat generation and mass concentration are also taken. The problem is modeled under physical laws and then simplified using the lubrication technique. The obtained system is sketched in graphs directly using a numerical scheme. The physical outcomes of involved parameters on axial velocity, temperature variation, concentration profile, and streamline patterns are discussed in the last section.

Computational investigation of vertical upflow boiling of liquid nitrogen and effects of bubble collision dispersion force

The present study investigates the performance of 2-D axisymmetric computational fluid dynamics (CFD) in predicting boiling characteristics of liquid nitrogen flowing vertically upwards along a uniformly heated circular tube. Investigation of the popular Volume of Fluid (VOF) model reveals (a) inaccurate surface tension calculation which degrades interface tracking, and (b) under-representation of bubble-to-bubble interaction, which stems from the innate nature of employing a single momentum equation in VOF. To alleviate VOF shortcomings, Coupled Level Set VOF (CLSVOF) is adopted in ANSYS FLUENT, including a user defined function to account for the crucial effects of bubble collision dispersion force. The CFD simulation results are validated against wall temperature and volume fraction results from prior benchmark experiments corresponding to four different wall heat flux conditions at nearly identical mass velocities. Predictions are also provided for axial variations of interfacial flow pattern, fluid temperature, and fluid velocity, flow characteristics that are very difficult to measure in cryogenic experiments. The CFD simulation results are shown to be highly accurate at predicting the nucleate boiling portion of the flow boiling curve.

The Role of Secondary Flows and Separation in Convective Heat Transfer in a Rotating Radial Vane Brake Disk

Abstract This study presents, for the first time, distributions of local internal temperature and convective heat transfer in a rotating radial vane brake disk and explains mechanisms in conjunction with secondary flows and flow separation within its ventilated coolant passages. In particular, variations of radial, circumferential (vane-to-vane), and axial (inboard-to-outboard) heat transfer on internal end-wall surfaces, and their alteration due to varying number of radial vanes and rotating speed are experimentally detailed. It has been demonstrated that conventional ventilated radial brake disks where the air inflow is drawn from the inboard face are likely to suffer substantial axial variations of temperature and heat transfer between the inboard and outboard disks, which possibly exacerbates thermal distortion (i.e., coning). Further, for a typical number of vanes (i.e., 36 vanes) used on automobiles, internal thermal distributions are highly nonuniform. However, the thermal end-wall uniformity improves considerably as the number of vanes is increased to say 72 vanes. Specifically, as the number of vanes is increased, secondary flow mixing enhances overall convective heat transfer and improves thermal uniformity. In contrast, separation causes large end-wall thermal nonuniformities in radial and circumferential distributions between the pressure side and the suction side of radial vanes. This effect nonetheless also decreases as the number of vanes is increased.

Comments on effects of adding cyclohexane, n-hexane, ethanol, and 2,5-dimethylfuran to fuel on soot formation in laminar coflow n-heptane/iso-octane diffusion flame

This communication draws attention to certain deficiencies in the article by Chu et al. [1], published in this journal, entitled ”Effects of adding cyclohexane, n-hexane, ethanol, and 2,5-dimethylfuran to fuel on soot formation in laminar coflow n-heptane/iso-octane diffusion flame”. Unfortunately, the experimental findings reported in the Chu et al. article are not consistent and tractable, because of an unsuitable experimental design, and temperature measurements using a thermocouple at arbitrary locations within the flame, which do not represent the thermal structure in view of the nature of the axial and radial variations of temperature in laminar diffusion flames. We argue that the results presented are not suitable for comparing the soot characteristics of the designed fuel blends because of a lack of a mutual reference specification.

Thermal stress analysis of energy piles

This study is concerned with the problem of energy piles subjected to constant axial load and temperature variation uniform over the cross-section. In the first part of this paper, equations for the analysis of energy piles based on elastic theory and the load-transfer approach are described. Closed-form solutions are derived for a few simple cases. It is observed that temperature variation effects can be conveniently expressed by a factor of thermally imposed strain. In the second part of the paper, a study on the effect of the non-linearity of reinforced concrete on the performance of energy piles under tension is described. A newly developed finite-element model that is within the framework of the load-transfer approach is employed to simulate the response of a pile subjected to thermomechanical loads in isolated as well as in piled raft foundations. The results suggest that the performance of the structure is strongly affected by concrete post-cracking behaviour. Nevertheless, piles can accommodate thermally imposed strains if the ductility capacity is provided. The outcomes of this study may be combined with the knowledge of non-linear behaviour of soil–pile interfaces for a more rational performance-based design approach toward energy piles.

Optimization and analysis of maximum temperature in a battery pack affected by low to high Prandtl number coolants using response surface methodology and particle swarm optimization algorithm

Thermal analysis of heat-generating battery pack cooled by several coolants is analyzed numerically. The coolant used are gases, oils, thermal oils, nanofluids, and liquid metals to find the best coolant for temperature distribution. The conductivity ratio between the battery and coolant, flow Reynolds number, and heat generation inside the pack is varied for each coolant. The axial temperature variation, which provides the location and magnitude of maximum temperature, is studied. The maximum temperature of the battery pack is analyzed using response surface methodology, optimization of maximum temperature is performed using particle swarm optimization algorithm, and regression analysis is carried out at the end of this work. The thermal analysis carried out reveals that the gas coolants are inefficient in providing lower temperatures while nanofluids are most suitable. The response surface reveals that the maximum temperature behavior is different for each category of coolant.

Effect of Soot-Inhibitor Additives on the Thermal Structure and Soot Volume Fraction Inside Laminar Diffusion Natural Gas Flames

Abstract Soot study is a fundamental issue for the combustion process of hydrocarbon fuels. Losses in combustion efficiency, health risks, environmental loosestrife, and damage in furnaces may appear as a result of soot existence. This present paper aims at providing an experimental mapping of the changes in the soot volume fraction and axial flame mean temperature associated with the addition of different percentages of soot inhibitor additives (namely, Argon, Nitrogen, and Helium) in a vertical laminar diffusion natural gas flame issuing from a honeycomb circular burner. The soot volume fraction is acquired by the laser extinction technique, while the axial variations of the mean flame temperature are accomplished by a bare 51 µm (Pt-30%Rh versus Pt-6%Rh) thermocouple to render radiation loss insignificant. The concentration of the individual additives is varied from 5% to 25% (step 5%) and the experiments are conducted at a fixed natural gas throughput (350 mL/min) to ensure unvaried thermal input. Measurement traverses along and across (at fixed radial locations) are conducted. The fuel flowrate is measured by a precision digital gas flowmeter (type: Varian intelligent), while the flow of the individual additive is admitted via solenoid valves (handled with labview program) and is injected through mixing pipes located at burner entry. The different regimes of the soot inception (molecular; zone 1), soot growth zone (zone 2), and soot oxidation (zone 3) are accurately defined and assessed in relation to the temperature results for the different cases under investigation.

Experimental characterization of a Sensible Heat Thermal Energy Storage using pebbles for charging

In today’s world, where reduction in the carbon footprints is emphasised, people are looking for alternative source of energies for power production and heat treatment of metals and alloys. One such alternative source is solar energy but due to intermittent nature a thermal energy storage (TES) is required in order to deal with heat flux that varies throughout the day so as to supply a constant power. In the present study, the characterization of the sensible heat thermal energy storage (SHTES) packed with sensible heat storage material are considered. The size of pebbles varies between 20-25mm with porosity of the SHTES as 40%. The flow rate is 40 LPM and TES was charged for 8 hours. It has been noticed that when the temperature of the inlet air is around 180°C, the temperature of the top surface of the TES is around 70°C which states that for TES high thermal conductivity materials are required so that charging and discharging can take place at faster rate. The azimuthal and axial variation of temperature is also shown and it is concluded that even after low thermal conductivity of the material azimuthal variation can be neglected for the sake of modeling the TES.

Liquid Flow Forced Convection in Rectangular Microchannels With Nonuniform Heating: Toward Analytical Modeling of Hotspots

Abstract The heat generated by microprocessors has an extremely nonuniform spatial distribution with hotspots that have heat fluxes several times larger than the background flux. Hence, for an accurate design of microchannel heat sinks used for cooling of micro-electronic devices, models are required that can take such a nonuniform distribution of wall heat flux into account. In this study, analytical solutions are obtained for hydrodynamically fully developed but thermally developing mixed electro-osmotic and pressure-driven (PD) flow in a rectangular microchannel with a peripherally uniform but axially nonuniform distribution of the wall heat flux. It is assumed that the heat flux is applied over a finite length, to mimic a physically more realistic situation, and the Péclet number is small so that lateral temperature variations are negligible as compared to the axial variations of temperature. By comparing the results with those of full numerical simulations for exponential (EHF), sinusoidal (SHF), and stepwise (STHF) distributions of wall heat flux, it is demonstrated that the solutions obtained are accurate up to a Péclet number of 10. Fortunately, this value is larger than the maximum Péclet number of electro-osmotic microflows. Furthermore, it is shown that smoother distributions of wall heat flux give rise to higher heat transfer rates. The model developed in this study can pave the way for modeling of hotspots in more complicated microfluidic devices.

Simulation of nonisothermal reactive liquid chromatography using two‐dimensional lumped kinetic model

AbstractA nonisothermal two‐dimensional lumped kinetic model of reactive liquid chromatography is formulated and applied to simulate the separation of multicomponent mixtures in a fixed‐bed cylindrical column operating under nonisothermal condition. The axial and radial variations of concentration and temperature as well as reversibility of the chemical reactions are incorporated in the model equations. The model comprises a system of convection‐diffusion‐reaction partial differential equations coupled with algebraic and differential equations. Due to the nonlinearity of adsorption and reaction kinetics, it is required to apply an accurate numerical scheme for solving the model equations. In this study, an efficient and accurate high‐resolution flux‐limiting finite‐volume scheme is proposed to solve the model equations. A number of stoichiometrical reactions are numerically simulated to determine the level of coupling between the temperature and concentration profiles. Moreover, the effects of various critical parameters on the process performance are examined. The results obtained are beneficial for understanding reaction and separation processes inside a liquid chromatographic reactor and to improve its performance.

Thermal transport characteristics of AC electrokinetic flow in a micro-annulus

Alternating current electroosmotic flow and associated heat transfer under constant surface heat flux conditions are numerically examined in a micro-annular channel. The channel surfaces are arbitrarily heated and/or cooled, while the resultant heating is normally transferred downstream by the advection mechanism. An important feature of time-periodic electrokinetic flow is that there is not any preferential axial direction. If the excitation frequency is sufficiently small and/or the liquid kinematic viscosity is sufficiently large, momentum diffuses far into the bulk fluid and thus the advection mechanism is intensified. The reverse is true for relatively large frequency and small kinematic viscosity values. Mean Nusselt number fluctuates over a period of time; its time-averaged magnitude is dependent on the electrokinetic diameter and the dimensionless frequency. This quantity approaches a specific value regardless of the thermal scale and the wall heat flux ratios. The system may attain optimal effectiveness for particular magnitudes of the frequency and electrokinetic diameter. An interesting case may exist in the cooling mode where the axial variation of the mean fluid temperature vanishes temporarily while the state of constant surface temperature is instantly satisfied; at the particular points in time, the advection mechanism does not contribute to the development of the liquid temperature field.

Capturing the Swirling Vortex and the Impact of Ventilation Conditions on Small-Scale Fire Whirls

The fundamental flow structure and temperature distribution of small-scale fire whirls, including tangential and axial velocities, temperature variation, and air entrainment in the lower boundary layer, were successfully captured using a generic fire field model with large eddy simulation (LES) turbulence closure. Numerical predictions were validated thoroughly against two small-scale experimental measurements, where detailed temperature and velocity distributions were recorded. Good agreement between numerical and experimental results was achieved. Normalization was also performed to compare the numerical predictions with the empirical correlations by Lei et al. (2015) developed from medium-scale fire whirl measurements. The transient development stages of small-scale fire whirls and the impact of air entrainment on the stability of the fire whirls were also investigated based on the validated numerical results. The numerical validations showed the potential of the current LES fire field model in capturing the dynamic behaviour of the fire whirl plume and performing a quantitative analysis on its onset criteria and combustion dynamics in future.

A new process chain combining cross-wedge rolling and isothermal forging for the forming of titanium alloy turbine blades

Titanium alloy blades are significantly important parts for aero-engine, and their special outline and production status requires an efficient and low-cost production process. In this paper, a new sequence for forming the titanium alloy blade using cross-wedge rolling (CWR) and isothermal forging was proposed. A finite element (FE) numerical model which contains the entire sequence, including the transfer process, CWR process, and isothermal forging process, was developed. And the axial displacement, strain-stress state, and temperature variation were analyzed based on its material properties of titanium alloy. The results showed that the billet experiences a smooth flowing in the center along the axial direction, and no large concavity occurs due to the higher viscosity. Moreover, the chilling effect of the dies was effectively counterbalanced by the deformation-heat near the surface, and there is no larger temperature difference. During the isothermal forging, the flash is symmetrically distributed around the fully filled blade and no obvious forming defects occur. Moreover, the novel sequence contributes to improving the deformed microstructure by accelerating the globularization of the long-strip alpha phase and increasing the volume fraction of the primary alpha phase. The technical feasibility of the novel sequence was verified by the corresponding experiments.

Transient heat transfer simulation, analysis and thermal performance study of double U-tube borehole heat exchanger based on numerical heat transfer model

This paper proposes numerical unsteady heat transfer model that predicts the transient heat transfer in the double U-tube borehole heat exchanger (BHE) where the U-tubes can operate with either different or equal mass flow rate and inlet fluid temperature. The implicit numerical method applied on heat transfer equations, obtained from energy balance on fluid, grout and ground nodes, was utilized to get the solution. The profile of the borehole loading as well as the net heat exchange on each leg of the U-tube along the borehole depth were obtained for simultaneous charging, discharging, and charging-discharging conditions. Axial variation of the mean fluid temperature, grout and borehole wall average temperature for charging and discharging cases were investigated. The model is extended to consider the axial and radial variation of ground temperature outside the borehole. Dynamic simulation was performed for different operating conditions to investigate various temperature response, borehole thermal resistance as well as thermal performance of the BHE. The proposed model was verified with the previously published experimental results. The performed modeling, simulation and analysis are important for the vertical BHE system optimization, efficiency testing as well as for the quick investigation of the impact of the borehole parameters and thermal properties on the overall performance of the BHE. The model is crucial in the design, optimization and performance study of ground source heat pump and borehole thermal energy storage systems.

The three-dimensional acoustic field in cylindrical and annular ducts with an axially varying mean temperature

This paper presents analytical solutions for the three dimensional acoustic field in cylindrical and annular ducts with dependence of mean temperature on axial position. A wave equation for the pressure perturbation is constructed in cylindrical coordinates, applying a zero mean flow condition. Separation of variables is used to express the pressure perturbation as a product of functions which vary only axially, radially and circumferentially. The axial dependence of the mean temperature means that a general analytical solution for the axial second order ordinary differential equation (ODE) cannot be obtained. Variable transformation is applied, yielding a standard second order ODE with known solutions for linear and quadratic axial mean temperature dependence. The acoustic field and resonant frequencies for an annular duct with linear/quadratic axial mean temperature variation predicted using these solutions match perfectly with those calculated using the linearised Euler equations. The analytical solution for the linear mean temperature profile is applied to more complicated profiles in a piecewise linear manner, axially segmenting the temperature profile into regions that can be approximated as linear. The acoustic field and resonant frequency are predicted very accurately even when very few axial segments are used.

Effect of hydrogen enrichment on combustion characteristics of methane swirling and non-swirling inverse diffusion flame

Influence of hydrogen addition on appearance of swirling and non-swirling inverse diffusion flame (IDF) along with emissions characteristics are investigated experimentally. The combustion characteristics including flame length, axial and radial temperature variation, and noise level are analysed for hydrogen addition in methane by mass basis for constant energy input and by volume basis for constant volumetric fuel flow rate. Hydrogen addition in methane IDF produces shorter flame by compressing entrainment zone, mixing zone, reaction zone, and post-combustion zone. Hydrogen addition shift these zones towards fuel and air exit from the burner. Enrichment of methane with hydrogen on a mass basis up to 6% reduces CO emission considerably and increases NOx emission moderately. Effect of H2 addition on combustion and emission characteristics is more prominent in non-swirling IDF. Combustion noise is augmented with the hydrogen addition and the magnitude of sound level depends on the hydrogen concentration.

Axial conduction and dissipation in oscillatory laminar pipe flow at low and high frequencies

The problem of fully developed laminar fluid flow in pipes, driven by an oscillatory pressure gradient, can be solved exactly for the time-dependent velocity field and related quantities such as flow rate and tidal displacement. When dissipation is neglected and the momentary axial variation of temperature is assumed to be linear, the corresponding thermal energy equation describing heat transfer along a pipe connecting two reservoirs at different temperatures can also be solved to yield exact solutions for the time-dependent temperature field, axial heat flux, and effective axial conductivity. In this paper, it is shown that these exact solutions for the unsteady temperature field are invalid at low Womersley numbers because the momentary axial variation of temperature is not linear. When the thermal energy equation is written in quasisteady form, approximate quasisteady analytical solutions can be found for the temperature field, which yield effective axial conductivities several orders of magnitude greater than those given by the low-Womersley-number, unsteady-flow solution. It is also shown that the conditions under which effects of dissipation on axial heat transfer become significant, at high Womersley numbers, can be determined by a simple criterion. When dissipation is significant, exact solutions for the unsteady temperature field are invalid at high Womersley numbers because the momentary axial variation of temperature is also nonlinear.

Compact Dual Fiber Bragg Gratings for Simultaneous Strain and High-Temperature Measurement

We present a compact simultaneous strain and high-temperature measurement scheme using dual fiber Bragg gratings (FBGs) written in single mode fiber (SMF) and thin-core fiber (TCF). The different effective refractive indexes between the cores of SMF and TCF are the key point because such FBGs support two separate resonances in the reflection spectrum for sensing measurement. These two resonances have different optical parameters, elastic-optic coefficient, and thermal-optic coefficient, they shift with different sensitivities under axial strain and temperature variations. The etching process is utilized on the grating of TCF to increase the sensitivity differences of the dual FBGs. In the experiment, simultaneous measurement of strain and temperature with the high strain sensitivity of 3.25 pm/ $\mu \varepsilon $ and high temperature up to 800 °C is realized respectively. This sensor scheme suits the practical application for strain and high-temperature measurement simultaneously.