Axial Temperature Research Articles

Investigation of Conjugate Effects on Forced Convection in Diamond (Diverging–Converging) Microchannels

Abstract A three-dimensional solid–fluid conjugate model is employed to provide physical insights into the effect of wall conduction on fluid convection in a diamond-shaped microchannel. The study covers the effect of divergence-convergence angle, width ratio, thermal conductivity ratio, thickness ratio, and Reynolds number on peripheral heat flux, temperature, and Nusselt number profiles. Isotherms show a multidirectional thermal gradient for low thermal conductivity ratios, whereas only an axial thermal gradient is seen for higher thermal conductivity ratios. Furthermore, the overall axial surface temperature gradients decrease with increasing divergence-convergence angle and decreasing width ratio. The study also shows that the thermal conductivity ratio significantly influences the Nusselt number, while the thickness ratio has only a moderate influence for all geometries. The analysis also reveals that at a particular intermediate thermal conductivity ratio, the Nusselt number becomes maximum. Lastly, a nondimensional wall conduction number is used to characterize conjugate effects in diamond microchannels. The wall conduction effect is inconsequential in diamond microchannels when the nondimensional wall conduction number is less than 0.01. The present study is beneficial from a practical perspective as it helps design the optimum channel geometries subjected to conjugate effects for many heat transfer applications.

Oxy-methane combustion characteristics in a vertical porous plate reactor

Among the carbon capture technologies, oxy-fuel combustion is more competitive in terms of efficiency and cost. However, pure oxygen is required for oxy-combustion, and the oxygen separation from the air by conventional methods is costly and energy-intensive. Ion transport membranes (ITMs) have shown considerable improvement in energy efficiency. The current ITMs suffer from low O2 permeation flux required for practical fuel conversion rates. The experimental and numerical methodologies are not much developed in studying the ITM integrated reactors. Therefore, using a porous medium can give much insight into the technology. Understanding the flow dynamics and combustion properties inside an oxygen transport membranes reactor (OTMR) is of utmost importance to developing efficient systems. Most studies have focused on analyzing face-to-face horizontal porous plate reactor designs. A horizontal reactor’s flame structure and buoyancy effect are substantially different from that of a vertical reactor. Hence, the current study aims to investigate oxy-methane combustion in a vertical face-to-face porous plate reactor to mimic the performance of an OTMR using computational fluid dynamics (CFD). Axial and transverse temperature profiles and species concentration profiles are analyzed concerning the feed inlet flow rates, inlet temperature, and oxidizer ratio in this work. The outlet and maximum temperatures vary from 1,587 K to 1,621 K and 1,751 K to 2,341 K upon increasing the oxidizer ratio from 0.20 to 0.35; correspondingly, it shows that the maximum temperature within the reactor is significantly affected by the oxidizer ratio. In the vertical OTMR, the maximum and outlet temperatures are lowered by 82 K and 53 K, respectively, compared to the horizontal one because of the uniform temperature distribution in the former case. This research will help to improve reactor design for OTMR applications. Further investigations on the flame structure and static flame stability are required for a better understanding and insight into the reactor design.

誘導機の回路モデルにおける軸方向影響とロータ温度の考慮

誘導機の回路モデルにおける軸方向影響とロータ温度の考慮

Numerical investigation of the effects of axial temperature gradient and cooling rate on InGaSb crystal growth under micro-gravity

In order to investigate the transport phenomena, growth mechanism of InGaSb crystal growth under microgravity, and also to optimize future space experiments, two-dimensional axisymmetric numerical simulations were carried out with different axial temperature gradients and cooling rates. Results showed that under microgravity condition both crystal growth process and grown crystal qualities were significantly affected by its axial temperature gradients and cooling rates. Simulation suggested that an axial temperature gradient around 0.6 K/mm with cooling rate of 0.048 K/h can accelerate and optimize the whole dissolution and growth process of InGaSb crystal growth in space, preventing complete dissolution of feed crystals, improving growth rates and grown crystal compositional uniformity.

Continuous-wave-laser surface cleaning of high strength bolts: Analysis of bolt axial force loss

This study examined the axial force loss of high-strength bolts after a 3-kW continuous-wave laser (CWL) treatment. Friction connection specimens with M22 high-strength bolts were prepared, and a fixed-angle rotary CWL transmitter with a 26-mm-diameter laser ring and rotating platform was used for nut rotary cleaning of high-strength bolts. Changes in the axial force and temperature of the bolts were monitored during the laser treatment based on the irradiation duration on the nut surface. The experimental results indicated that the minimum and final stable values of the axial force during CWL treatment are affected by the irradiation duration. Multiple rounds of irradiation can reduce the bolt axial force loss for the same total irradiation duration. The 26-mm-diameter laser ring can sufficiently cover the surface of commonly used bolt heads and nuts in bridges, and the local temperature effect does not influence the axial force loss in adjacent bolts. The distribution of the bolt temperature when the CWL treatment the bolt is simulated by an FE model, which proves the overall temperature of the bolt does not exceed 300 °C and remains in a normal working condition when the continuous irradiation duration is less than 45 s. From the relationship between the axial force change and treatment duration, the axial force loss formula was fitted, which can help provide a maintenance plan for M22 bolt cleaning using 3-kW CWL.

Design and Optimization of Thermal Field for PVT Method 8-Inch SiC Crystal Growth.

As a wide bandgap semiconductor material, silicon carbide has promising prospects for application. However, its commercial production size is currently 6 inches, and the difficulty in preparing larger single crystals increases exponentially with size increasing. Large-size single crystal growth is faced with the enormous problem of radial growth conditions deteriorating. Based on simulation tools, the physical field of 8-inch crystal growth is modeled and studied. By introducing the design of the seed cavity, the radial temperature difference in the seed crystal surface is reduced by 88% from 93 K of a basic scheme to 11 K, and the thermal field conditions with uniform radial temperature and moderate temperature gradient are obtained. Meanwhile, the effects of different processing conditions and relative positions of key structures on the surface temperature and axial temperature gradients of the seed crystals are analyzed in terms of new thermal field design, including induction power, frequency, diameter and height of coils, the distance between raw materials and the seed crystal. Meanwhiles, better process conditions and relative positions under experimental conditions are obtained. Based on the optimized conditions, the thermal field verification under seedless conditions is carried out, discovering that the single crystal deposition rate is 90% of that of polycrystalline deposition under the experimental conditions. Meanwhile, an 8-inch polycrystalline with 9.6 mm uniform deposition was successfully obtained after 120 h crystal growth, whose convexity is reduced from 13 mm to 6.4 mm compared with the original scheme. The results indicate that the optimized conditions can be used for single-crystal growth.

Autothermal Reforming of Volatile Organic Compounds to Hydrogen-Rich Gas

Industrial emissions of volatile organic compounds are urgently addressed for their toxicity and carcinogenicity to humans. Developing efficient and eco-friendly reforming technology of volatile organic compounds is important but still a great challenge. A promising strategy is to generate hydrogen-rich gas for solid oxide fuel cells by autothermal reforming of VOCs. In this study, we found a more desirable commercial catalyst (NiO/K2O-γ-Al2O3) for the autothermal reforming of VOCs. The performance of autothermal reforming of toluene as a model compound over a NiO/K2O-γ-Al2O3 catalyst fitted well with the simulation results at the optimum operating conditions calculated based on a simulation using Aspen PlusV11.0 software. Furthermore, the axial temperature distribution of the catalyst bed was monitored during the reaction, which demonstrated that the reaction system was self-sustaining. Eventually, actual volatile organic compounds from the chemical factory (C9, C10, toluene, paraxylene, diesel, benzene, kerosene, raffinate oil) were completely reformed over NiO/K2O-γ-Al2O3. Reducing emissions of VOCs and generating hydrogen-rich gas as a fuel from the autothermal reforming of VOCs is a promising strategy.

Significance of radiant-energy and multiple slips on magnetohydrodynamic flow of single-walled carbon nanotube-water, titanium dioxide–water, multiwalled carbon nanotube–water, graphene oxide–water nanofluids

The magnetohydrodynamic flow of nanofluid is studied in the present analysis by using two parallel, rotating, and stretchable disks with a porous medium. The thermal radiation effects along with velocity slips at the interface of fluid and disk are considered in this work. The water is taken as base fluid, and carbon nanotubes (CNTs), titanium dioxide (TiO[Formula: see text]), and graphene oxide (GO) are taken as nanoparticles. The corresponding equations are modeled in terms of partial differential equations and Von Karman similarity transformation approach is adopted. The resulting equations are solved by using a finite difference method-based ND Solver. The axial, radial, and tangential velocity profiles and temperature distribution are discussed with graphs and tables. Thermal radiation and convective boundary conditions are used in the heat transfer process. When the thermal Biot number of the lower disk rises, fluid temperature enhances, whereas, the fluid temperature falls with the rise in the thermal Biot number of the lower disk. It is observed that when the thermal Biot number of lower disk rises from 0.5 to 0.8, heat transfer at lower disk is increased by about 6.66% in hexagonal-shaped CNTs-based nanofluid and 6.66% in spherical shaped TiO[Formula: see text] and GO-based nanofluid. The impact of physical parameters such as skin friction coefficient and Nusselt number are computed for governing parameters and discussed in detail.

Simultaneous measurement of axial strain and temperature based on a twin-core single-hole fiber with the optical Vernier effect.

An ultrasensitive optical fiber sensor based on the optical Vernier effect is proposed for the simultaneous measurement of axial strain and temperature. The sensor structure comprises two cascaded Mach-Zehnder interferometers (MZIs) with different free space ranges. The single MZI is built up by fusion splicing a segment of ∼3 mm twin-core single-hole fiber (TCSHF) between two pieces of ∼5 mm none core fibers (NCF). When acting separately, each MZI can respond linearly to the axial strain change with a sensitivity of ∼ 0.6 pm/µε and temperature with a sensitivity of ∼34 pm/°C. When the two MZIs are cascaded in series, the sensitivities are amplified about 30 times because of the optical Vernier effect. Experimental results demonstrate that the cascaded structure exhibits a high axial strain sensitivity of ∼ 17 pm/µε in the range of 0 to 2000 µε and temperature sensitivity of ∼1.16 nm/°C in the range of 30 to 70 °C. Moreover, the cascaded structure can simultaneously measure the axial strain and temperature change in the acceptable error ranges.

Irreversibility analysis in stagnation point flow of tri-hybrid nanofluid over a rotating disk; application of kinetic energy

The study of entropy minimization dramatically enhances the reliability of kinetic, mechanical, and electrical components. Numerous applications, comprising catalyst energy, heat exchanger, pump, and electronic cooling, promote entropy minimization. The current analysis presents an investigation of the stagnation point flow of second law analysis in a stretchable rotating disk with a ternary hybrid nanofluid. MoS2,SiO2 and ZrO2 nanoparticles are considered with thermal physical properties, and Eg is used as the ordinary fluid. The motive of this study is to scrutinize the impact of kinetic energy fluctuation for a ternary hybrid nanofluid over a rotating disk. Heat is accounted for by adding thermal radiation and convective. After being transmitted into ODEs, the BVP4c technique is applied to solve the fluid flow mathematical model. Results are depicted using graphs, and the effects of the relevant parameter on the different profiles, such as radial velocity F’(ζ), axial velocity G(ζ), temperature profile Θ(ζ), entropy generation Ng and Bejan number Be. The unsteady parameter has been shown to boost the axial velocity and temperature distribution while reducing radial velocity. Moreover, entropy generation and Bejan number increase with larger values of γ1 and Br. Justification of the existing study is completed by comparing the present findings with the obtainable outcomes in the literature and finding an adequate agreement.

Enhanced heat transfer of supercritical n-decane in cooling channels with triangular ribs for regenerative cooling

• A continuous ribbed channel is designed to enhance the cooling capacity. • The channel can provide up to 2.04 times superior heat transfer performance. • The insertion of ribs enhances the uniformity of buoyancy distribution. • The triangular rib channel improves axial temperature uniformity. • The mechanism of generating vortices in the slot is analysed. Regenerative cooling is regarded as an effective method for managing the heat of scramjet combustors, and the design of cooling channels is critical for removing more heat from the engine. A continuous triangular rib channel was proposed. The effects of rib position, height, and pitch on the heat transfer performance were investigated using Fluent 18.0. The SST k –ω turbulence model was used to study the thermal behaviour of supercritical n-decane in channels and showed good agreement with the experimental data. Results show that the insertion of triangular ribs at the bottom and top can reduce the bottom wall temperature by 243.8 K in the studied case. The triangular rib channel can provide up to 2.04 times superior heat transfer performance. The continuous triangular ribs significantly reduced axial temperature inhomogeneity. Local streamlines were studied to demonstrate the influence of rib parameters on the flow and heat transfer processes. A local heat transfer enhancement occurs when the rib has a large inclination. For the studied conditions, the generation of vortices was carefully evaluated, and it was found that the generation of vortices in the slot was related to the value of h / p .

Craniocerebral hypothermia in the acute period of ischemic stroke

To determine the effect of craniocerebral hypothermia (CCH) on neurological deficit regression, hemodynamics, fever and functional outcome of therapy in patients with moderate ischemic stroke (IS). This study included 60 patients with IS (the first day). The main group consisted of 30 patients who underwent CCH, and the comparison (control) group consisted of 30 patients without CCH. The National Institutes of Health Stroke Scale (NIHSS), the Glasgow Coma Scale (GCS), the modified Rankin Scale (mRs) were used. Recorded parameters were mortality, heart rate (HR), blood pressure (BP), axial temperature, cerebral temperature of the frontal cortex. Cerebral temperature was obtained noninvasively by using a RTM-01-RES radiothermometer (Russia). CCH (for 24 hours) in the main group was implemented by ATG-01 device (Russia). Results were recorded on the day of admission, after 24 hours and at discharge. In both groups, basic neuroprotective, hypotensive, antiplatelet and antiedemic therapy was administered. No fatal outcomes were reported in both groups. Side-effects and complications of CCH were not recorded. In the main group, neurological deficit assessed by NIHSS decreased by 75% after the CCH procedure and by 93.75% at the time of discharge from the hospital. In patients of the comparison group, regression of neurological deficit was 35% on the second day and 55% at the day of discharge. The use of CCH suppressed systemic and cerebral hyperthermia. Functional outcome of therapy in the main group was higher compared to the comparison one. The dynamics in blood pressure and heart rate didn't differ in both groups. A pronounced positive effect of CCH on the course of the acute period and therapy results in patients with IS was demonstrated.

Analysis on heat transfer performance sub-channels of sodium-cooled fast reactor fuel assemblies based on entransy

In this paper, the symmetric heat transfer performance of sodium-cooled fast reactor fuel assemblies was analyzed and studied. The model is analytically optimized based on sub-channel calculations. The deviations of the numerical simulation results from the pre-existing experimental data in the literature are within 10 %, with an average deviation of 2.5 %, which tested the reliability of the model. The calculated results demonstrated that the distribution of the axial power, temperature, and coolant of the reactor core is approximately symmetric M-shape. The reactor core coolant has a monotonic increase in axial distribution with the cladding temperature and the temperature peaks all appear at the reactor core outlet. The individual fuel assemblies' internal temperature is relatively sensitive to the axial power distribution, and there are troughs around the imports and exports. The simulated results showed that the center temperature of the hottest rod reactor core block reached 965.65 K. This pa- per provides a better guide to understanding the overall heat transfer effect by optimizing the heat transfer model.

Pulsed Production of Antihydrogen in AEgIS

Low-temperature antihydrogen atoms are an effective tool to probe the validity of the fundamental laws of Physics, for example the Weak Equivalence Principle (WEP) for antimatter, and -generally speaking- it is obvious that colder atoms will increase the level of precision. After the first production of cold antihydrogen in 2002 [1], experimental efforts have substantially progressed, with really competitive results already reached by adapting to cold antiatoms some well-known techniques pre- viously developed for ordinary atoms. Unfortunately, the number of antihydrogen atoms that can be produced in dedicated experiments is many orders of magnitude smaller than of hydrogen atoms, so the development of novel techniques to enhance the production of antihydrogen with well defined (and possibly controlled) conditions is essential to improve the sensitivity. We present here some experimental results achieved by the AEgIS Collaboration, based at the CERN AD (Antiproton Decelerator) on the production of antihydrogen in a pulsed mode where the production time of 90% of atoms is known with an uncertainty of ~ 250 ns [2]. The pulsed antihydrogen source is generated by the charge-exchange reaction between Rydberg positronium (Ps*) and an antiproton (p¯): p¯ + Ps* → H¯* + e−, where Ps* is produced via the implantation of a pulsed positron beam into a mesoporous silica target, and excited by two consecutive laser pulses, and antiprotons are trapped, cooled and manipulated in Penning-Malmberg traps. The pulsed production (which is a major milestone for AEgIS) makes it possible to select the antihydrogen axial temperature and opens the door for the tuning of the antihydrogen Rydberg states, their de-excitation by pulsed lasers and the manipulation through electric field gradients. In this paper, we present the results achieved by AEgIS in 2018, just before the Long Shutdown 2 (LS2), as well as some of the ongoing improvements to the system, aimed at exploiting the lower energy antiproton beam from ELENA [3].

Numerical Study of Forced Convection Between Two Elliptical Cylinders with Variable ThermoPhysical Properties

This study presents a numerical simulation of the three dimensional laminar forced convection between two elliptical horizontal cylinders with variable thermophysical properties using a program generated in FORTRAN language. The inner cylinder is uniformly heated whereas the outer cylinder is adiabatic. The flow and thermal fields are modeled by the continuity, momentum and energy equations with appropriate initial and boundary conditions using an elliptical coordinate system. The model equations are numerically solved by a finite volume numerical method with second order accurate spatiotemporal discretization. The variations of axial velocity, temperature and Nusselt number have been studied in three cases of forced convection, which are 100, 200 and 300 of Reynolds values. The results obtained show that the change in flow regime with increasing Reynolds number value has a significant effect on the value of Nusselt number, rather the heat exchange coefficient. Where Re=300 gives the best heat exchange.

Experimental evaluation of the effect of perforated spiral fins on the thermal performance of latent heat storage units

The spiral fins are widely employed as an innovative fin configuration in latent heat storage units (LHSU) to improve the poor thermal conductivity of Phase Change Material (PCM). Its persistent annulus promotes heat exchange in PCM, but still interferes with buoyancy-driven natural convection. Perforation is a potential solution to facilitate natural convection. Based on this, the thermal properties of the punctured spiral finned LHSU were experimentally studied. An experimental setup was constructed with three spiral finned LHSUs, two of which were installed with perforated spiral fins with 16 mm and 12 mm perforation diameters. The axial and radial temperature distribution, heat transfer characteristics and efficiency were evaluated for three LHSUs. Experimental results showed that the thermal performance of LHSU was improved remarkably by using perforated spiral fins with higher heat benefits achieved at lower heat transfer areas. The thermal efficiency and average heat flux reached 63.4 % and 1370.7 W/m2 respectively, while the average Nusselt number was 44.0 % higher than that of the solid fin. For the same perforation area, fins with higher diameter perforations achieve superior thermal properties and stronger convective heat transfer, while fins with lower diameter perforations continue to limit natural convection.

Rotation, electromagnetic field, and variable thermal conductivity effects on free convection flow past an eternity vertical porous plate

AbstractThe present research may facilitate the reduction of the number of conversion steps required to include the low output voltages in an electrokinetic biomass process. Variable thermal conductivity and electroosmosis flow have already established great potential in the thermo‐elastic models of various manufacturing industries and have been widely used in energy technologies. As a result, the current framework investigates the characteristics of natural convection flow with the influence of variable thermal conductivity and electroosmosis over an eternity vertical porous plate. Coriolis forces and Hall current effects are considered in the momentum equations, and also thermal radiation and variable thermal conductivity are taken as energy equations. A linear chemical reaction parameter is used in the concentration equation. The equation of Poisson–Boltzmann is exploited to depict the electric potential characteristics within the accelerated plate medium. The pdepe command in Matlab software is used to figure out the numerical solutions to equations about momentum, energy, and concentration. The expressions of fluid transverse velocity, fluid axial velocity, fluid temperature, and concentration profiles are presented as numerical results and also derived vital relevant stream parameters diagrammatically, whereas the numerical values of primary skin friction, secondary skin friction, and Nusselt number are presented in tabular form for various values of pertinent flow parameters. The temperature rises as the strength of the thermal conductivity variable parameter increases. Also, as the values of the Taylor number and the thermal conductivity variable parameter go up, the primary velocity goes down. Similarly, secondary velocity increases in the opposite direction as the Taylor number and thermal conductivity variable parameter increase.

Blood‐based electro‐osmotic flow of non‐Newtonian nanofluid (Carreau‐Yasuda) in a tapered channel with entropy generation

AbstractThe motivation of current contribution is to signify the assessment of entropy generation in the flow of generalized Newtonian fluid generated under the influence of electro‐osmosis and peristalsis. The flow has been confined by a tapered channel with certain flow assumptions. The fundamental conservations laws of mass, momentum, energy and concentration along with the Poisson and Nernst‐Planck equations are used to identify the problem in given domain. The Poisson equation is solved analytically for potential function under the Debye‐Huckel linearization approximation while the expressions are attained with association of conservation concept under widely used assumptions of minor Reynolds number and long wavelength. The velocity in axial direction, temperature and nanoparticles profiles are numerically approximated using shooting method. The electric force parameter and radiative constant are being expressed against different flow, temperature and concentration features via various sketches. The results for Newtonian and Carreau fluid as particular case are also presented via numerous plots and tables. It is expected that the obtained theoretical results are very useful for the resilience of medical instatements.

Ion dynamics in the magnetic nozzle of a waveguide ECR thruster via laser-induced fluorescence spectroscopy

Xenon ion velocity is mapped in the magnetic nozzle (MN) of a circular waveguide electron cyclotron resonance thruster operating at 5.8 GHz by means of laser-induced fluorescence spectroscopy in the near-infrared spectral range. An array of thruster operational parameters are explored to investigate the influence on the acceleration profile and terminal ion velocity. Owing to several mechanisms which broaden the measured spectra, e.g. Paschen-Back/Zeeman effect, inference of the most probable velocity along with the axial kinetic temperature requires full lineshape modeling, especially in the near-field plume and inside the source. Ions are effectively accelerated along the MN, reaching up to 12 000 m s−1 for the lowest neutral pressure tested. A relatively large axial kinetic temperature is observed, typically in the order of 5000 K, which can be attributed to an extended ionization region that overlaps with the acceleration region.

How Temperature Measurement Impacts Pressure Drop and Heat Transport in Slender Fixed Beds of Raschig Rings

The axial temperature profile of a packed bed is often measured by thermocouples placed either directly in the bed or inside a thermowell centered in the reactor tube. Quantifying the impact of the thermocouple well on fluid flow, heat transport, and consequently on the measured temperatures is still an unresolved challenge for lab-scale reactors but especially, and even more so for multitubular reactors in industry. Particle-resolved computational fluid dynamics (PRCFD) simulations are a suitable approach to investigate the changes in transport phenomena exerted by inserting thermocouple wells into packed beds because they take into account the local packed bed structures. In this study, PRCFD simulations are performed based on design of simulation experiments (DoSE). The effect of the thermowell diameter and its thermal conductivity on the deviations between packed beds with and without thermowells is statistically quantified for characteristic integral quantities like pressure drop and tube wall-bed Nusselt number. The axial temperature profiles inside the thermowells can be computed efficiently with reasonably accuracy applying the Nusselt number correction as derived in this study from the DoSE in a one-dimensional pseudo-homogeneous energy balance.