Turbine Passage Secondary Flow Dynamics and Endwall Heat Transfer Under Different Inflow Turbulence

This study presents endwall hydrodynamics and heat transfer in a linear turbine cascade at Re 5×105 at low and high intensities of turbulence.Results are numerically predicted using the standard SST model and Reθ-γtransition model as well as using the high-resolution LES separately.The major secondary flow components,comprising the horseshoe,corner,and passage vortices are recognized and the impact on heat or mass transfer is investigated.The complicated behavior of turbine passage secondary flow generation and establishment are impacted by the perspective of boundary layer attributes and inflow turbulence.The passage vortex concerning the latest big leading-edge vane is generated by the enlargement of the circulation developed at the first instance adjacent to the pressure side becomes powerful and mixes with other vortex systems during its migration towards the suction side.The study conclusions reveal that substantial enhancements are attained on the endwall surface,for the entire spanwise blade extension on the pressure surface,and in the highly 3-D region close to the endwall on the suction surface.The forecasted suction surface thermal exchange depicts great conformity with the measurement values and precisely reproduces the enhanced thermal exchange owing to the development and lateral distribution of the secondary flows along the midspan of the blade passage downstream.The impacts of the different secondary flow structures on the endwall thermal exchange are described in depth.

Research on passenger flow control at metro transfer stations based on real-time flow calculation of streamlines

Purpose – The volume of passenger traffic at metro transfer stations serves as a pivotal metric for theorchestration of crowd flow management. Given the intricacies of crowd dynamics within these stations andthe recurrent instances of substantial passenger influxes, a methodology predicated on stochastic processesand the principle of user equilibrium is introduced to facilitate real-time traffic flow estimation within transferstation streamlines.Design/methodology/approach – The synthesis of stochastic process theory with streamline analysisengenders a probabilistic model of intra-station pedestrian traffic dynamics. Leveraging real-time passengerflow data procured from monitoring systems within the transfer station, a gradient descent optimizationtechnique is employed to minimize the cost function, thereby deducing the dynamic distribution of categorizedpassenger flows. Subsequently, adhering to the tenets of user equilibrium, the Frank–Wolfe algorithm isimplemented to allocate the intra-station categorized passenger flows across various streamlines, ascertainingthe traffic volume for each.Findings – Utilizing the Xiaozhai Station of the Xi’an Metro as a case study, the Anylogic simulation softwareis engaged to emulate the intra-station crowd dynamics, thereby substantiating the efficacy of the proposedpassenger flow estimation model. The derived solutions are instrumental in formulating a crowd controlstrategy for Xiaozhai Station during the peak interval from 17:30 to 18:00 on a designated day, yielding crowdmanagement interventions that offer insights for the orchestration of passenger flow and operationalgovernance within metro stations.Originality/value – The construction of an estimation methodology for the real-time streamline traffic flowaugments the model’s dataset, supplanting estimated values derived from surveys or historical datasets withreal-time computed traffic data, thereby enhancing the precision and immediacy of crowd flow managementwithin metro stations.

Experimental Analyses of Flow Pattern and Heat Transfer in a Horizontally Oriented Polymer Pulsating Heat Pipe withMerged Liquid Slugs

Extended experiments were conducted on the oscillation characteristics of merged liquid slugs in a horizontally oriented polymer pulsating heat pipe(PHP).The PHP’s serpentine channel comprised 14 parallel channels with a width of 1.3 mm and a height of 1.1 mm.The evaporator and condenser sections were 25 and 50 mm long,respectively,and the adiabatic section in between was 75mmlong.Using a plastic 3D printer and semi-transparent filament made from acrylonitrile butadiene styrene,the serpentine channel was printed directly onto a thin polycarbonate sheet to form the PHP.The PHP was charged with hydrofluoroether-7100.In the experiments,the evaporator section was heated,and the condenser section was cooled using high-temperature and low-temperature thermostatic baths,respectively.Flow patterns of the working fluid were obtained with temperature distributions of the PHP.A mathematical model was developed to analyze the flow patterns.Themerged liquid slugs were observed in every two channels,and their oscillation characteristics were found to be approximately the same in time and space.It was also found that the oscillations of the merged liquid slugs became slower,but the heat transfer rate of the PHP increased with a decrease in the filling ratio of the working fluid.This is because vapor condensation was enhanced in vapor plugs as the filling ratio decreased.However,the filling ratio had a lower limit,and the heat transfer rate was maximum when the filling ratio was 40.6%in the present experimental range.

Land-Use Classification via Transfer Learning with a Deep Convolutional Neural Network

Land cover classification provides efficient and accurate information regarding human land-use, which is crucial for monitoring urban development patterns, management of water and other natural resources, and land-use planning and regulation. However, land-use classification requires highly trained, complex learning algorithms for accurate classification. Current machine learning techniques already exist to provide accurate image recognition. This research paper develops an image-based land-use classifier using transfer learning with a pre-trained ResNet-18 convolutional neural network. Variations of the resulting approach were compared to show a direct relationship between training dataset size and epoch length to accuracy. Experiment results show that transfer learning is an effective way to create models to classify satellite images of land-use with a predictive performance. This approach would be beneficial to the monitoring and predicting of urban development patterns, management of water and other natural resources, and land-use planning.

EXPERIMENTAL INVESTIGATION ON FLOW AND HEAT TRANSFER CHARACTERISTICS IN TENON JOINT GAP BETWEEN TURBINE BLADE AND DISK

The now and heat transfer characteristics in tenon joint gap between turbine blade and disk have been investigated experimentally with a scale up model. The characteristics of flow and heat transfer in this speCial gap passage have been analyzed. The results are useful for beat transfer analysis in turbine design.

A new heat transfer correlation for flow boiling in helically coiled tubes

Based on the superposition principle of the nucleate boiling and convective heat transfer terms,a new correlation is developed for flow boiling heat transfer characteristics in helically coiled tubes.The effects of the geometric and system parameters on heat transfer characteristics in helically coiled tubes are investigated by collecting large amounts of experimental data and analyzing the heat transfer mechanisms. The existing correlations are divided into two categories,and they are calculated with the experimental data.The Dn factor is introduced to take into account the effect of a complex geometrical structure on flow boiling heat transfer.A new correlation is developed for predicting the flow boiling heat transfer coefficients in the helically coiled tubes,which is validated by the experimental data of R134a flow boiling heat transfer in them;and the average relative error and root mean square error of the new correlation are calculated.The results show that the new correlation agrees well with the experimental data,indicating that the new correlation can be used for predicting flow boiling heat transfer characteristics in the helically coiled tubes.

Gas–liquid mass transfer and flow phenomena in the Peirce–Smith converter: a water model study

A water model with a geometric similarity ratio of 1：5 was developed to investigate the gas-liquid mass transfer and flow charac- teristics in a Peirce-Smith converter. A gas mixture of CO2 and Ar was injected into a NaOH solution bath. The flow field, volumetric mass transfer coefficient per unit volume （Ak/V; where A is the contact area between phases, V is the volume, and k is the mass transfer coeffi- cient）, and gas utilization ratio （t/） were then measured at different gas flow rates and blow angles. The results showed that the flow field could be divided into five regions, i.e., injection, strong loop, weak loop, splashing, and dead zone. Whereas the Ak/V of the bath increased and then decreased with increasing gas flow rate, and n steadily increased. When the converter was rotated clockwise, both Ak/F and t/increased. However, the flow condition deteriorated when the gas flow rate and blow angle were drastically increased. Therefore, these para- meters must be controlled to optimal conditions. In the proposed model, the optimal gas flow rate and blow angle were 7.5 m3.h-1 and 10°, respectively.

MHD stagnation-point flow and heat transfer towards stretching sheet with induced magnetic field

The problem of the steady magnetohydrodynamic （MHD） stagnation-point flow of an incompressible viscous fluid over a stretching sheet is studied. The effect of an induced magnetic field is taken into account. The nonlinear partial differential equations are transformed into ordinary differential equations via the similarity transformation. The transformed boundary layer equations are solved numerically using the shooting method. Numerical results are obtained for various magnetic parameters and Prandtl numbers. The effects of the induced magnetic field on the skin friction coefficient, the local Nusselt number, the velocity, and the temperature profiles are presented graphically and discussed in detail.

Gas–liquid flow mass transfer in a T-shape microreactor stimulated with 1.7 MHz ultrasound waves

This paper describes the application of ultrasound waves on hydrodynamics and mass transfer characteristics in the gas–liquid flow in a T-shape microreactor with a diameter of 800 μm. A 1.7 MHz piezoelectric transducer(PZT) was employed to induce the vibration in this microreactor. Liquid side volumetric mass transfer coefficients were measured by physical and chemical methods of CO_2 absorption into water and Na OH solution. The approach of absorption of CO_2 into a 1 mol·L^(-1) Na OH solution was used for analysis of interfacial areas. With the help of a photography system, the fluid flow patterns inside the microreactor were analyzed. The effects of superficial liquid velocity, initial concentration of Na OH, superficial CO_2 gas velocity and length of microreactor on the mass transfer rate were investigated. The comparison between sonicated and plain microreactors(microreactor with and without ultrasound) shows that the ultrasound wave irradiation has a significant effect on kLa and interfacial area at various operational conditions. For the microreactor length of 12 cm, ultrasound waves improved kLa and interfacial area about 21% and 22%, respectively. From this study, it can be concluded that ultrasound wave irradiation in microreactor has a great effect on the mass transfer rate. This study suggests a new enhancement technique to establish high interfacial area and kLa in microreactors.

Fluid Flow and Heat Transfer Characteristic of Outer and Inner Half Coil Jackets

The physical models of the outer and inner half coil jackets were simplified to two types of coiled ducts.The mathematic models of incompressible fluid at the condition of laminar flow and heat transfer in the two types of jackets for cooling process reactor were set up and solved by the semi-implicit method for pressure linked equa-tions consistent （SIMPLEC） algorithm based on a control volume method.The flow and temperature fields were given and the effects of Dean and Prandtl numbers on flow and heat transfer were studied.The results show that flow in the inner half coil jacket is found to exhibit transition of secondary flow pattern from two vortices to four vortices when the Dean number increases,but that in the outer half coil jacket is not found.The critical Dean num-ber is about 96.The inner half coil jacket has stronger heat transfer ability than the outer half coil jacket and this superiority is more evident with larger Prandtl number.However,as the Dean number is greater than 105,the flow resistance enhances more severely in the inner jacket than the outer jacket.For both jackets,the centers of the heated wall are the poorest for heat transfer.

Effect of Flow Directions on Multiphase Flow Boiling Heat Transfer Enhanced by Suspending Particles in a Circulating Evaporation System

A circulating fluidized bed evaporator(including down-flow, horizontal, and up-flow beds) was constructed to study the effect of flow directions on multiphase flow boiling heat transfer. A range of experimental investigations were carried out by varying amount of added particles(0-2%), circulation flow rate(2.15-5.16 m^3/h) and heat flux(8-16 kW/m^2). The comparison of heat transfer performance in different vertical heights of the horizontal bed was also discussed. Results reveal that the glass bead particle can enhance heat transfer compared with vapor-liquid two-phase flow for all beds. At a low heat flux(q = 8 kW/m), the heat-transfer-enhancing factor of the horizontal bed is obviously greater than those of the up-flow and down-flow beds. With the increase in the amount of added particles, the heat-transfer-enhancing factors of the up-flow and down-flow beds increase, whereas that of the horizontal bed initially increases and then decreases. However, at a high heat flux(q=16 kW/m), the heat-transfer-enhancing factors of the three beds show an increasing tendency with the increase in the amount of added particles and become closer than those at a low heat flux. For all beds, the heat-transfer-enhancing factor generally increases with the circulation flow rate but decreases with the increase in heat flux.

NUMERICAL ANALYSIS OF THREE-DIMENSIONAL FLUID FLOW AND HEAT TRANSFER IN TIG WELD POOL WITH FULL PENETRATION

A model is established to analyze three-dimensional fluid flow and heat transfer in TICweld pools with full penetration.It considers the deformation of the molten pool surfaceat the condition of full penetrated workpieees,takes the are pressure as the drivingforce of the pool surface deformation,and determines the surface configuration of weldpool based on the dynamic balance of arc pressure,pool gravity and surface tension atdeformed weld pool surface. The SIMPLER algorithm is used to calculate the fluid flowfield and temperature distribution in TIG weld pools of stainless steel workpieces.TIGwelding experiments are made to verify the validity of the model.It shows the calculatedresults by the model are in good agreement with experimental measurements. professor,Dept of Welding Engineering,Harbin Institute of Technology,Harbin 150006,China

Heat transfer of copper/water nanofluid flow through converging-diverging channel

The main objective of this work is to investigate analytically the steady nanofluid flow and heat transfer characteristics between nonparallel plane walls. Using appropriate transformations for the velocity and temperature, the basic nonlinear partial differential equations are reduced to the ordinary differential equations. Then, these equations have been solved analytically and numerically for some values of the governing parameters, Reynolds number, Re, channel half angle, α, Prandtl number, Pr, and Eckert number, Ec, using Adomian decomposition method and the Runge-Kutta method with mathematic package. Analytical and numerical results are searched for the skin friction coefficient, Nusselt number and the velocity and temperature profiles. It is found on one hand that the Nusselt number increases as Eckert number or channel half-angle increases, but it decreases as Reynolds number increases. On the other hand, it is also found that the presence of Cu nanoparticles in a water base fluid enhances heat transfer between nonparallel plane walls and in consequence the Nusselt number increases with the increase of nanoparticles volume fraction. Finally, an excellent agreement between analytical results and those obtained by numerical Runge-Kutta method is highly noticed.

Numerical investigation of laminar heat transfer and nanofluid flow between two porous horizontal concentric cylinders

In this study, the laminar heat transfer and nanofluid flow between two porous horizontal concentric cylinders was investigated. The problem is investigated in two different geometries and the Re=10, 25, 50, 75, 100 and volume fraction 0, 0.2%, 0.5%, 2% and 5% that related to copper nanoparticles, and porous medium porosity of 0.5 and 0.9. Compared to the first geometry, the convective coefficient in the second geometry increases by 8.3%, 7% and 5.5% at Reynolds numbers of 100, 75 and 50, respectively. Comparison of the outlet temperatures for two heat fluxes of 300 and 1200 W/m^2 indicates a 2.5% temperature growth by a fourfold increase in the heat fluxes. Also, the higher Nusselt number is associated with the second geometry occurring at porosities of 0.9 and 0.5, respectively. In both geometries, the Nusselt number values at the porosity of 0.9 are higher, which is due to the increased nanofluid convection at higher porosities. The velocity of the nanofluid experiences a two-fold increase at the outlet compared to its inlet velocity in the first geometry and for both porosities. Similarly, a three-fold increase was achieved in the second geometry and for both porosities.

Modelling Study to Compare the Flow and Heat Transfer Characteristics of Low-Power Hydrogen,Nitrogen and Argon Arc-Heated Thrusters

A modelling study is performed to compare the plasma flow and heat transfer characteristics of low-power arc-heated thrusters （arcjets） for three different propellants： hydrogen, nitrogen and argon. The all-speed SIMPLE algorithm is employed to solve the governing equations, which take into account the effects of compressibility, Lorentz force and Joule heating, as well as the temperature- and pressure-dependence of the gas properties. The temperature, velocity and Mach number distributions calculated within the thruster nozzle obtained with different propellant gases are compared for the same thruster structure, dimensions, inlet-gas stagnant pressure and arc currents. The temperature distributions in the solid region of the anode-nozzle wall are also given. It is found that the flow and energy conversion processes in the thruster nozzle show many similar features for all three propellants. For example, the propellant is heated mainly in the near-cathode and constrictor region, with the highest plasma temperature appearing near the cathode tip; the flow transition from the subsonic to supersonic regime occurs within the constrictor region; the highest axial velocity appears inside the nozzle; and most of the input propellant flows towards the thruster exit through the cooler gas region near the anode-nozzle wall. However, since the properties of hydrogen, nitrogen and argon, especially their molecular weights, specific enthMpies and thermal conductivities, are different, there are appreciable differences in arcjet performance. For example, compared to the other two propellants, the hydrogen arcjet thruster shows a higher plasma temperature in the arc region, and higher axial velocity but lower temperature at the thruster exit. Correspondingly, the hydrogen arcjet thruster has the highest specific impulse and arc voltage for the same inlet stagnant pressure and arc current. The predictions of the modelling are compared favourably with available experimental results.

Stagnation-point flow of couple stress fluid with melting heat transfer

Melting heat transfer in the boundary layer flow of a couple stress fluid over a stretching surface is investigated. The developed differential equations are solved for homotopic solutions. It is observed that the velocity and the boundary layer thickness are decreasing functions of the couple stress fluid parameter. However, the temperature and surface heat transfer increase when the values of the couple stress fluid parameter increase. The velocity and temperature fields increase with an increase in the melting process of the stretching sheet.

Enhancement of Flow Boiling Heat Transfer with Surfactant

The surfactant additive octadecylamine (ODA) was used to enhance the flow boiling heat transfer of water in vertical copper tube, and the effects of the aqueous solution properties, mass fraction of ODA, mass flux and heat flux etc. on flow boiling heat transfer were investigated. In order to analyze the mechanism of enhancement on boiling heat transfer with ODA, the copper surface was detected by XPS, and the diagram of binding energy was obtained. The results show that ODA can be adsorbed on the surface of the copper wall, and affects the properties of the heating surfaces and enhances the flow boiling heat transfer of water. Only in low heat flux and in a suitable range of concentration, can ODA aqueous solution enhance flow boiling heat transfer, and the suitable mass fraction of ODA is in the range of 1×10 -5 5×10 -5 . In addition, compared with water, ODA aqueous solution does not increase the flow drag under the same experimental conditions.

Large-eddy Simulation of Fluid Flow and Heat Transfer in a Mixing Tee Junction

The temperature fluctuation caused by thermal striping phenomena of hot and cold fluids mixing results in cyclical thermal stress fatigue failure of the pipe wall. Mean temperature difference between hot and cold fluids was often used as thermal load in previous analysis of thermal fatigue failure, thereby the influences of the amplitude and frequency of temperature fluctuation on thermal fatigue failure were neglected. Based on the mechanism of flow and heat transfer which induces thermal fatigue, the turbulent mixing of hot and cold water in a tee junction is simulated with FLUENT platform by using the Large-eddy simulation（LES） turbulent flow model with the sub-grid scale（SGS） model of Smagorinsky-Lilly（SL） to capture the amplitude and frequency of temperature fluctuation. In a simulation case, hot water with temperature of 343.48 K and velocity of 0.15 m/s enters the horizontal main duct with the side length of 100 mm, while cold water with temperature of 296.78 K and velocity of 0.3 m/s enters the vertical branch duct with the side length of 50 mm. The numerical results show that the mean and fluctuating temperatures are in good agreement with the previous experimental data, which describes numerical simulation with high reliability and accuracy; the power spectrum density（PSD） on top wall is higher than that on bottom wall（as the frequency less than 1 Hz）, while the PSD on bottom wall is relatively higher than that on top wall （as the frequency of 1-10Hz）. The temperature fluctuations in full mixing region of the tee junction can be accurately captured by LES and can provide the theoretical basis for the thermal stress and thermal fatigue analyses.

MHD flow and heat transfer of micropolar fluid between two porous disks

A numerical study is carried out for the axisymmetric steady laminar incompressible flow of an electrically conducting micropolar fluid between two infinite parallel porous disks with the constant uniform injection through the surface of the disks. The fluid is subjected to an external transverse magnetic field. The governing nonlinear equations of motion are transformed into a dimensionless form through yon Karman＇s similarity transformation. An algorithm based on a finite difference scheme is used to solve the reduced coupled ordinary differential equations under associated boundary conditions. The effects of the Reynolds number, the magnetic parameter, the micropolar parameter, and the Prandtl number on the flow velocity and temperature distributions are discussed. The results agree well with those of the previously published work for special cases. The investigation predicts that the heat transfer rate at the surfaces of the disks increases with the increases in the Reynolds number, the magnetic parameter, and the Prandtl number. The shear stresses decrease with the increase in the injection while increase with the increase in the applied magnetic field. The shear stress factor is lower for micropolar fluids than for Newtonian fluids, which may be beneficial in the flow and thermal control in the polymeric processing.

A New Experimental Rig of Testing Flow Boiling Heat Transfer of Refrigerantand Lubricant Mixture

This paper proposed a new experimental rig of testing flow boiling heat transfer of refrigerant and lubricant oil mixture. The quantity of oil in the test section can be controlled and regulated conveniently and accurately by connecting separate lubricant oil circuit with test section in parallel. It was built up by retrofitting a multiple air-conditioner and installing three oil-separators in serials at the compressor outlet. And so the lubricant oil in the discharged refrigerant gas of compressor can be removed completely.The refrigerant flow rate through test section can be bypassed by the by-path circuit of indoor unit.This experimental rig has advantages such as on-line and continuous oil injection, short time of obtaining stability, flexible operation, simple control, which lead to high efficiency in the research of flow boiling heat transfer of refrigerant and lubricant oil mixture.