Total Temperature Distribution Research Articles

Domain knowledge-driven variational recurrent networks for drought monitoring

In the context of climate change, droughts, increasingly frequent and severe, necessitate effective monitoring. Existing methods, such as drought indices and data-driven models, face important limitations. Drought indices are built on prior expert knowledge but lack calibration based on actual drought events, while data-driven models prioritize goodness of fit over real event identification, undermining their credibility and generalization, and also struggling to generalize from regional to large-scale contexts. To address these challenges, here we introduce a hybrid machine learning framework for time series that combines domain knowledge and observational data in a variational recurrent neural network. The network models the joint distribution of total precipitation, air temperature, and real drought events, providing accurate predictions and uncertainty estimates. Extensive experiments focusing on a wide range of European drought events from 2011 to 2018 consistently show that our hybrid model surpasses both drought indices and data-driven models in terms of accuracy in drought detection, underlining its effectiveness, robustness, and stability. Our model achieves the best ROC-AUC (%) results in Afghanistan (79.7 ± 0.5), Italy (84.3 ± 0.6), Russia (89.4 ± 0.2), Europe-0 (84.3 ± 0.1), and Europe-1 (82.8 ± 0.4), effectively capturing the starting and ending times of drought events with lower uncertainty, and also generalizing better for unseen locations.

Resolving nonuniform flow in gas turbines: challenges, progress, and moving forward

Abstract The flow in gas turbines exhibits a highly unsteady, complex and nonuniform manner, which presents two main challenges. Firstly, it introduces instrumentation errors, contributing to uncertainties when calculating one-dimensional performance metrics during rig or engine tests using fixed-location rakes. Secondly, it raises mechanical concerns, including high-cycle fatigue due to blade row interactions in turbomachines and thermal fatigue caused by hot-streaks at the combustor exit. Experimental characterisation of the flow nonuniformity in gas turbines is highly challenging due to the confined space and harsh environment for instrumentation. This paper presents recent efforts to address this issue by resolving the nonuniform flow in gas turbines using spatially under-sampled measurements. The proposed approach utilises discrete probe data and leverages a ‘Fourier-based approximation’ method developed by the author. The technique has undergone preliminary experimental validation involving reconstruction of the total pressure distribution in a multi-stage axial compressor and the total temperature field at the exit of the combustor and high-pressure turbine. Results show that, in the multi-stage axial compressor environment, reconstruction of inter-stage total pressure is achieved using a reduced dataset covering less than 20% of the annulus with reasonably good accuracy. The reconstructed total pressure yields almost identical mean total pressure values at all spanwise locations, with a maximum deviation of less than 0.02%. Additionally, reconstruction of the total temperature distribution at an engine-representative full annulus combustor is achieved using measurements at ten carefully selected circumferential locations. Results show that the reconstructed temperature field successfully captures the primary features associated with combustor exit temperature flow. The reconstructed temperature field yields excellent agreement in the magnitude of radial temperature distribution factor (RTDF) and overall temperature distribution factor (OTDF) predictions to the experiment, with a deviation of less than 0.5% for RTDF and less than 2.5% for OTDF. Lastly, reconstruction of the total temperature distribution at the exit of the GE E3 high-pressure turbine (HPT) is achieved using measurements at eight carefully selected circumferential locations. Results demonstrate remarkable robustness in resolving the temperature profile at the HPT exit with high fidelity, irrespective of the HPT inlet conditions. The initial validation results are promising, demonstrating that the new probe layout scheme and the Fourier-based approximation method enable effective characterisation of flow nonuniformity in gas turbines, thereby providing valuable insights into the complex flow of gas turbine engines.

Impacts of thermal and electric contact resistance on the material design in segmented thermoelectric generators

Segmented thermoelectric generators (STEGs) can exhibit present superior performance than those of the conventional thermoelectric generators. Thermal and electrical contact resistances exist between the thermoelectric material interfaces in each thermoelectric leg. This may significantly hinder performance improvement. In this study, a five-layer STEG with three pairs of thermoelectric (TE) materials was investigated considering the thermal and electrical contact resistances on the material contact surface. The STEG performance under different contact resistances with various combinations of TE materials were analyzed. The relationship between the material sequence and performance indicators under different contact resistances is established by machine learning. Based on the genetic algorithm, for each contact resistance combination, the optimal material sequences were identified by maximizing the electric power and energy conversion efficiency. To reveal the underlying mechanism that determines the heat-to-electrical performance, the total electrical resistance, output voltage, ZT value, and temperature distribution under each optimized scenario were analyzed. The STEG can augment the heat-to-electricity performance only at small contact resistances. A large contact resistance significantly reduces the performance. At an electrical contact resistance of RE = 10–3 K·m2·W−1 and thermal contact resistance of RT = 10–8 Ω·m2, the maximum electric power was reduced to 5.71 mW (90.86 mW without considering the contact resistance). And the maximum energy conversion efficiency is lowered to 2.54% (12.59% without considering the contact resistance).

Large Eddy Simulation of a Low-Pressure Turbine Cascade with Turbulent End Wall Boundary Layers

We present results of implicit large eddy simulation (LES) and different Reynolds-averaged Navier–Stokes (RANS) models of the MTU 161 low pressure turbine at an exit Reynolds number of 90000\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$90\\,000$$\\end{document} and exit Mach number of 0.6. The LES results are based on a high-order discontinuous Galerkin method and the RANS is computed using a classical finite-volume approach. The paper discusses the steps taken to create realistic inflow boundary conditions in terms of end wall boundary layer thickness and freestream turbulence intensity. This is achieved by tailoring the input distribution of total pressure and temperature, Reynolds stresses and turbulence length scale to a Fourier series based synthetic turbulence generator. With this procedure, excellent agreement with the experiment can be achieved in terms of blade loading at midspan and wake total pressure losses at midspan and over the channel height. Based on the validated setup, we focus on the discussion of secondary flow structures emerging due to the interaction of the incoming boundary layer and the turbine blade and compare the LES to two commonly used RANS models. Since we are able to create consistent setups for both LES and RANS, all discrepancies can be directly attributed to physical modelling problems. We show that both a linear eddy viscosity model and a differential Reynolds stress model coupled with a state-of-the-art correlation-based transition model fail, in this case, to predict the separation induced transition process around midspan. Moreover, their prediction of secondary flow losses leaves room for improvement as shown by a detailed discussion of turbulence kinetic energy and anisotropy fields.

Skin Cooling of Turbine Airfoils by Single Wall Effusion: Part I—Reduced Order Modeling

Abstract A quasi-1D conjugate reduced order model (ROM) is developed to capture aero-thermal physics of effusion cooling in turbine airfoils. This framework explicitly considers the coolant supply from the leading edge and its distribution to both suction and pressure sides, the internal boundary layer flow between the shell and the inner core, the hole flow, the conduction on the solid walls, as well as the external film coverage. The solid temperature is allowed to vary both in metal shell thickness and the streamwise directions. Empirical correlations are employed to model pressure loss and heat transfer in the internal sections. Compound effect of multiple effusion cooling rows are utilized to capture cooling effectiveness and the heat load. Influence of mainstream static pressure, varying blowing ratios, hole’s diameter, hole’s pitch, coolant total pressure, and total temperature distributions along streamwise direction are taken into account. In Part I, the development and validation of the model is presented, which is shown to be capable of capturing complex internal aero-thermal physics of a turbine airfoil. Film coverage capability is separately validated successfully against available flat plate experimental data, with one case including internal channel and metal conduction. In Part II of this work, effusion cooling configuration is applied over an entire micro turbine vane and an exemplary optimization is carried out in the design space to minimize coolant flow while retaining metal temperature and its gradient below some limits. It is shown in the two-part work that the developed model is suitable for parametric studies of single-wall effusion turbine cooling such that comparative accuracy is obtained at a computational time 105 times lower than computational fluid dynamics (CFD) on a whole turbine vane/blade. Together, these two papers are intended to present, validate, and optimize the ROM for skin cooling in turbine airfoils by single-wall effusion.

Quantification of waste heat potential in China: A top-down Societal Waste Heat Accounting Model

The recovery of waste heat is important for energy saving and carbon reduction in China. Although numerous technologies for waste heat recovery in China have been analyzed, research is still insufficient to provide an overview of the waste heat potential within the entire energy system. To fill this gap, this paper applies a top-down energy efficiency analysis to develop a Societal Waste Heat Accounting Model to quantify the waste heat potential in China. By indicating the total amount, sector and temperature distribution, and the ability to perform work of waste heat for China in 2018, the results revealed that: a) waste heat occupies 42% of total primary energy inputs, and 26% of primary energy and carbon emissions can be theoretically saved by utilizing waste heat. b) the electricity generation sector is the main source of waste heat, accounting for 45% of the total, of which 88% is below 100 °C. c) the industry sector has a wide range of temperatures, mostly above 300 °C, highlighting the highest ability to perform work. Future studies can focus on the utilization of low-temperature waste heat, which is 66% of the total, for example, the Organic Ranking Cycle technology and the heat pump technology.

Thermo-Structural Analysis of Brake Disc-Pad Assembly of an Automotive Braking System

Braking is a phenomenon of stabilizing a moving vehicle to rest by actuating the braking system. The available kinetic energy from the dynamic body is transformed into mechanical energy by the braking system which is further converted into thermal energy for its dissipation into the surroundings. During the process of braking, the frictional contact between the brake disc and brake pad creates enormous amount of heat elevating the temperature of the system to a higher level. The objective of this numerical study is to minimize the heat produced during the braking process. Three unique ventilated brake disc and two brake pad profiles were developed using PTC Creo modelling tool and were subjected to ANSYS workbench to evaluate its thermal and structural performance with a braking cycle time of 4.50 sec. Total deformation, equivalent stress, temperature distribution and total heal flux were assessed. Based on the study, ventilated disc 3 can be the possible design with either of the brake pad profiles for effective usage in the automotive braking system.

A numerical simulation of burning of pulverized peat fuel in a bidirectional vortex combustor

Bidirectional (or countercurrent) vortex combustors are some of the most promising vortex-flow devices in terms of the fuel and oxidizer mixing efficiency, the combustion efficiency, the emission characteristics, and the combustion stability. This paper suggests a new arrangement principle for combustion of solid pulverized peat in conditions of vortex countercurrent flow which has never been studied earlier; we developed a combustion unit implementing this principle and carried out a numerical analysis of the combustion process with various operating parameters. The calculation results confirmed the possibility of combustion within a wide range of parameters and showed that varying the air-fuel equivalence ratio from λ = 0.5 to λ = 5.05 results in significant change in both the structure of the limited vortex flow and the distribution of total pressure and temperature, as well as the averaged volume concentration of fuel particles. We calculated the boundaries of lean and rich flame blowouts where the gas-dynamic flow loses its stability and the toroidal vortex is disrupted. At the same time, secondary vortex structures are formed throughout the combustor volume.

Numerical Examination of Metamaterial Concentrator Design for High Efficient Thermal Energy Harvester

Nowadays, research on energy harvesting is highly interest to harvest more waste thermal energy which produced by any kind of thermal engine in our daily life. Thermal metamaterials, designed by transformation thermodynamics are artificial structure that can actively control heat flux at a continuum scale. However, right now the problem of using metamaterial on thermal harvesting is to know what is the best shape design, configuration, and best material to obtain highly efficient on thermal energy harvesting because of the number of research on this field is limited. Flower-shaped metamaterial thermal concentrator has developed and it showed that the design can performed well on directing heat flux to specific location. However, the Flower-shaped metamaterial design that has been conducted before not optimized yet. In the current paper, the numerical simulation and analysis for several metamaterial and shape construction variations were performed using Ansys Workbench™ to characterize the best configuration to optimizing flower-shaped thermal concentrator. A number of interesting numerical computation presented on this research manuscript including total heat flux, temperature distribution, and thermal concentrator efficiency on the surface of the constructed concentrator. The aim of this paper is to provide more reference on metamaterial design for thermal harvesting.

Heat mitigation of a core/cladding Yb-doped fiber amplifier using anti-Stokes fluorescence cooling

A Core/Cladding Yb-doped fiber amplifier configuration is presented that relies on anti-Stokes fluorescence cooling for effective heat mitigation in high-power operation. In the proposed design, the inner cladding of the double clad fiber is doped with the same ion as in the core; therefore, the excess heat generated from the background absorption is removed by the anti-Stokes fluorescence in both core and inner cladding. We consider both silica and ZBLAN glasses for the host material in the Core/Cladding Yb-doped fiber amplifier. The model incorporates the spatial profiles of the signal and pump intensities, as well as the amplified spontaneous emission. The total linear heat density and temperature distribution in the fiber amplifier are calculated. The results show that the anti-Stokes fluorescence cooling in the Core/Cladding Yb-doped configuration can mitigate the generated heat effectively in high-power operation, which obviates the need for an external cooling system.

Experimental study of the impacts of cold mass fraction on internal parameters of a vortex tube

In order to get the internal parameters of a vortex tube, a large-scale vortex tube was designed and an experimental device was built. A five-hole probe and thermocouples were used to obtain the three-dimensional velocities, the static pressure, static temperature and total temperature distributions inside the vortex tube. Four different cold mass fraction conditions (0.2, 0.4, 0.6 and 0.8) were chosen and the impacts on the internal parameters of the vortex tube were discussed. Different from the traditional view, the tangential velocity was considered to be the steady Burgers vortex form. A reverse flow boundary was found, and the location of which was changed at different operation conditions and axial positions. Further, it was found that the lowest static temperature existed near the nozzle outlet, and a new static temperature difference distribution law was firstly proposed experimentally.

The concept of high dielectric material for the treatment of liver cancer through microwave heating

Hyperthermia is potentially an effective method for the treatment of cancer tumours. In the present manuscript, improvement in the treatment of liver cancer through electromagnetic heating is studied using high dielectric material through mathematical modelling in COMSOL Multiphysics. It is observed from the result that without increasing the power input, intensity of the temperature can be increased by changing the dielectric constant. Treatment time in ablation of the liver tumour can also be reduced. Results are obtained for total power dissipation density, heat flux, temperature distribution and fraction of necrosis tissue.

Transport of Entropy Waves Within a High Pressure Turbine Stage

This paper presents the results of an experimental study on the transport of entropy waves within a research turbine stage, representative of the key aero-thermal phenomenon featuring the combustor-turbine interaction in aero-engines. The entropy waves are injected upstream of the turbine by a dedicated entropy wave generator (EWG) and are released in axial direction; they feature circular shape with peak amplitude in the center and exhibit sinusoidal-like temporal evolution over the whole wave area. The maximum over-temperature amounts to 7% of the undisturbed flow, while the frequency is 30 Hz. The entropy waves are released in four azimuthal positions upstream of the stage, so to simulate four different burner-to-stator blade clocking. Time-resolved temperature measurements were performed with fast microthermocouples (FTC); the flow and the pressure field upstream and downstream of the stator and the rotor was measured with five-hole pneumatic probes and fast-response aerodynamic pressure probes. The entropy waves are observed to undergo a relevant attenuation throughout their transport within the stator blade row, but they remain clearly visible at the stator exit and retain their dynamic characteristics. In particular, the total temperature distribution appears severely altered by burner-stator clocking position. At the stage exit, the entropy waves loose their coherence, appearing spread in the azimuthal direction to almost cover the entire pitch in the outer part of the channel, while being more localized below midspan. Despite the severe and unsteady interaction of the entropy waves within the rotor, they retain their original dynamic character. A comparison with measurements performed by injecting steady hot streaks is finally reported, remarking both differences and affinities. As a relevant conclusion, it is experimentally shown that entropy waves can be proficiently simulated by considering a succession of hot streaks of different amplitude.

Physical Properties and Exchange System of Seawater in Royal Yacht Club Marina in the Northernmost Gulf of Aqaba

This research was aimed at studying the general environmental status of the marina at Royal Yacht Club (RYC), which is located in the Jordanian Gulf of Aqaba. The physical properties (temperature, salinity and density) were measured at surface and bottom water at 19 sites (T1 - T19). Total hydrocarbon was measured at surface at 12 sites (HC1-HC12). The water exchange and residence time were calculated using data of current speed and direction at 16 sites (C1 - C16). The mean values of temperature, salinity and density at surface and bottom waters in the RYC’s marina were 27.13°C ± 0.03°C, 40.51 ± 0.02 psu and 26.83 ± 0.02 kg·m-3, respectively. The results of physical parameters revealed no significant differences among sites, which are all comparable with open waters. The measurements range of total hydrocarbon in the marina was 1.404 mg/l (at site HC11) to 98.56 mg/l (at HC9). In general, all the high values of total hydrocarbon were found at the corners of the marina and at areas with relatively intense boats’ movements. There was no correlation between distribution of total hydrocarbon and temperature (R2 = 0.048; p = 0.49) in the marina. Therefore, the major factors that influence the distribution of total hydrocarbon within the marina are the current system and boats’ movements as well as the location reference to the gate. The residence time of waters inside the marina was 1.32 days. This flushing time is acceptable to secure good environmental conditions inside the marine to avoid stagnant seawater. The mean value of current speed at the RYC’s marina gate with open water was 5.33 ± 2.63 cm/s, which is relatively comparable with current speed in vicinity of study area. In conclusions, the environmental condition of the RYC’s marina is acceptable in term of the residence time and exchange system with open water. Slightly high values of total hydrocarbon were detected, which can be solved by regular cleaning.

“A REVIEW OF HEAT DISSIPATION ANALYSIS BY VARYING GEOMETRICAL CONDITION OF CYLINDRICAL FIN”

If the heat in the heat engine is not removed properly, it causes the development of the detonation and eventually reduces the efficiency of the engine, so that the heat dissipation rate of the cylinder an important and interesting task is the option. The cylinder of the engine is one of the most important automotive components, variations of high temperature and thermal loads. To cool the cylinder, the ribs are provided on the surface of the cylinder, to increase the rate of heat transfer. By a thermal analysis of the motor cylinder and the ribs that surround it, it is useful to know the heat transfer rate and the temperature distribution inside the cylinder. We know that we can increase the heat dissipation rate by increasing the surface so it is very difficult to design such a complex motor. The main objective of this project is to analyze thermal properties such as thermal directed flow, total heat flow and temperature distribution. The cooling mechanism of the air cooled engine depends mainly on the design of the cylinder head and the block ribs. The cooling fins are used to increase the heat transfer rate of the specified surface. The life and efficiency of the engine can be improved by efficient cooling. The finite element method was used using the ANSYS software as a simulation tool for analysis.

Effect of Shrouding Gas Temperature on Characteristics of a Supersonic Jet Flow Field with a Shrouding Laval Nozzle Structure

Coherent jet technology was been widely used in the electric arc furnace steelmaking process to protect the kinetic energy of supersonic oxygen jets and achieve a better mixing effect. For this technology, the total temperature distribution of the shrouding jet has a great impact on the velocity of the main oxygen jet. In this article, a supersonic shrouding nozzle using a preheating shrouding jet is proposed to increase the shrouding jet velocity. Both numerical simulation and experimental studies were carried out to analyze its effect on the axial velocity, total temperature and turbulence kinetic energy profiles of the main oxygen jet. Based on these results, it was found that a significant amount of kinetic energy was removed from the main oxygen jet when it passed though the shock wave using a high-temperature shrouding jet, which made the average axial velocity of the coherent jet lower than for a conventional jet in the potential core region. However, the supersonic shrouding nozzle and preheating technology employed for this nozzle design significantly improved the shrouding gas velocity, forming a low-density gas zone at the exit of the main oxygen jet and prolonging the velocity potential core length.

Partitioning effect on natural convection in a circular enclosure with an asymmetrically placed inclined plate

This work presents a numerical investigation on steady-state laminar natural convection in a circular enclosure with an inner flat plate at Ra=106. The plate is inclined placed along the radial direction but is asymmetric about the center of enclosure, with eccentricity defined as the distance between the centers of two entities. The enclosure and plate are kept at low and high temperatures, respectively. The objective of this study is to explore the effects of two significant parameters, i.e., eccentricity (r) and inclination (α) of the plate, on the flow and heat transfer characteristics of the enclosure-plate system. The numerical simulation is performed using our in-house fourth-order finite difference code which is well validated. The effects of the two parameters are analyzed by the total heat transfer rate, temperature distribution, formation and evolution of various vortices, and distribution of local heat transfer rate for r/D=0.00(0.05)0.20 and α=0°(5°)180° where D is the enclosure diameter. Numerical results reveal that natural convection is weakened by the partitioning effect of nearly horizontal plate since fluid circulation is greatly constrained, while the effect is minor at low and high inclinations where fluid circulation is pronounced. Depending on the eccentricity and inclination, there could be at most two and three vortices in the left and right halves of the enclosure, respectively, whose formation and spatial evolution behaviors and intensity variations exhibit complex patterns, and are closely related with the heat transfer characteristics. For high eccentricity configurations, the heat transfer in the gap can be dominated by either convection or conduction depending on the gap size, the latter of which is characterized by the expected linear variation of circumferential position of maximum local heat transfer rate with the inclination.

RETRACTED: Design and thermal analysis of cooling of Gas turbine blade through radial holes

Abstract Gas turbines are extensively used for air craft propulsion, land based power generation and industrial applications. Thermal efficiency of a gas turbine can be improved by increasing turbine the rotor inlet temperature. The current rotor inlet temperature in advanced gas turbine is far above the melting point of blade material. So a sophisticated cooling system must be developed for continuous safe operation of gas turbines with high performance. Several methods have been suggested for the coolingof blades and one such technique is to have radial holes to pass high velocity cooling air along theblade span. The present work is carried out by performing the heat transfer analysis of gas turbine with four differentmodels consisting of blade with, without holes and blades with varying number of holes (5, 9&13). The analysis is carried out using commercial CFD software FLUENT. On evaluating the graphs drawnfor total heat transfer rate and temperature distribution, the blade with 13 holes is considered to be moreoptimum. The Steady state thermal and structural analysis is done using ANSYS software withdifferent blade materials such as Chromium steel and N155. While comparing the results, N155 has proved to have better thermal properties and also induced stresses are less than the Chromium steel.

A Space–Time-Dependent Study of Control Rods Withdrawal in a Large-Size Pressurized Water Reactor

This work focuses on the safety analysis of a typical pressurized water reactor (PWR) for reactivity-initiated transients. These transients result from withdrawal of six sets of groups of control rods that may occur under control systems or other faults. NEA/OECD PWR benchmark is considered for the study. A 3D space–time kinetics code, “TRIKIN” (neutronic and thermal-hydraulics coupled code) is used to account for local changes in the neutron flux. These local changes in the neutron flux affect the total reactivity, local power, and temperature distribution. The safety parameters are the usual 3D radial power distribution, flux tilt, axial heat flux for the peak channel, and radial peak central line temperature profiles over the horizontal plane. These safety parameters studied in the incident progression up to reactor SCRAM level. The minimum departure from the nucleate boiling ratio (MDNBR) has been investigated quantitatively for all six cases. The case that gives maximum drop in MDNBR at SCRAM level is identified and its consequences are discussed. The study is of high importance in revealing the importance of grouping of control rods’ configurations, providing insight in developing strategy for designing the configuration and reactivity worth of groups of control rods and local/global reactor control systems for large-size PWRs.

Effect of shrouding CH4 flow rate on flow field and stirring ability of coherent jet in steelmaking process.

Characteristics of flow field and stirring ability of coherent jet with various shrouding CH4 flow rates on the molten bath were studied by combustion experiment and numerical simulation. The axial velocity and total temperature distributions of coherent jet under hot (1700 K) and cold (298 K) ambient condition were analyzed. The Eddy Dissipation Concept model was used in simulation with detail chemical kinetic mechanisms, and the numerical simulation results were agreed well with the combustion experiment in this research. Based on the simulation and experiment results, when the CH4 rate was 230, 207 and 184 Nm3/h, their disparity rate of average velocity and total temperature was small than 5 and 6 %, respectively, at high ambient temperature. Hence, the same stirring effect might be achieved by those three kinds of CH4 flow rates in EAF steelmaking process. According to the industrial application research, the best CH4 flow rate is 184 Nm3/h, which could stir molten bath well and reduce energy consumption in steelmaking process.