Heat Recuperation for the Self-Condensing CO_(2)Transcritical Power Cycle

The supercritical CO_(2)Brayton cycle has potential to be used in electricity generation occasions with its advantages of high efficiency and compact structure.Focusing on a so-called self-condensing CO_(2)transcritical power cycle,a model was established and four different layouts of heat recuperation process were analyzed,a without-recuperation cycle,a post-recuperation cycle,a pre-recuperation cycle and a re-recuperation cycle.The results showed that the internal normal cycle's share of the whole cycle increases with increasing the cooling pressure and decreasing the final cooled temperature.Heat load in the supercritical heater decreases with increasing the cooling pressure.From perspective of performance,the re-recuperation cycle and the pre-recuperation cycle have similar thermal efficiency which is much higher than other two layouts.Both thermal efficiency and net power output have a maximum value with the cooling pressure,except in the condition with the final cooled temperature of 31℃.Considering both the complexity and the economy,the pre-recuperation cycle is more applicable than the other options.Under 35℃of the final cooled temperature,the thermal efficiency of the pre-recuperation cycle reaches the peak 0.34 with the cooling pressure of 8.4 MPa and the maximum net power output is 2355.24 kW at 8.2 MPa of the cooling pressure.

Application of Response Surface Methodology for Analysing and Optimizing the Finned Solar Air Heater

In this research paper,a solar air heater with triangular fins has been experimentally analysed and optimized.Initially,an experimental set-up of a solar air heater having triangular fins has been developed at the location of 28.10°N,78.23°E.The heat transfer rate through fins and fins efficiency has been determined by the Finite Difference Method model equations.The experimental data and modeled data of response parameters have been optimized in MINITAB-17 software by the Response Surface Methodology tool.For creating the response surface design,three input parameters have been selected namely solar intensity,Reynolds number,and fin base-to-height ratio.The range of solar intensity,Reynolds number,and fin base-to-height ratio is 600 to 1000W/m^(2),4000 to 6000,and 0.4 to 0.8 respectively.The response surface design has been analyzed by calculating the outlet temperature,friction factor,Nusselt number,fin efficiency,thermal performance factor,and exergy efficiency.The optimum settings of input parameters:solar intensity is 1000 W/m^(2);Reynolds number is 4969.7,and the fin base to height ratio is 0.6060,on which these response:namely outlet temperature of 92.531℃,friction factor of 0.2350,Nusselt number of 127.761,thermal efficiency of 50.836%,thermal performance factor of 1.4947,and exergy efficiency of 8.762%.

Experimental Study on Hydrodynamic Behavior of Falling Film over Vertical Tube

Falling film configurations play an important role in characterizing the heat transfer due to changes in hydrodynamic behavior.The purpose of this study is to establish a novel film distributor to investigate the hydrodynamic behavior of the falling film on the vertical tube.The falling film thickness and flow patterns on the vertical tube were analyzed at a feed water temperature of 30℃ for film Re ranged from 53 to 4544 and the heat fluxes ranged from 1.33 to 49.45 kW/m^(2).The correlation between the average falling film thickness and the film Re was fitted;the maximum deviation between the experimental data and the predicted values was 7.58%.Additionally,the film thickness changed sharply when the heat flux increased to a certain value.With the further increase of the heat flux,dry patches appeared on the surface of the experimental tube.There was Marangoni effect on vertical tube and the falling film thickness and flow patterns were significantly affected by heating.The interval value of the critical heat flux with film Re was obtained.Compared with the porous film distributor reported in the literature,the critical heat flux of the new film distributor increased by 3.72%-56.95%.

Multiphysics Design of a High-Speed Permanent Magnet Machine for a Micro Gas Turbine Application

This paper presents a detailed and comprehensive multiphysics design process of an 80 kW, 60 000 r/min high-speed permanent magnet machine (HSPMM) for a micro gas turbine application. First, the preliminary design of the HSPMM is carried out according to the mechanical and electromagnetic theory. Afterwards, the influence of carbon fiber sleeve (CFS) thickness, rotor diameter and core length on rotor stress and rotor dynamics is carefully analyzed to obtain the optimal range of rotor diameter and core length. On this basis, the electromagnetic and power loss characteristics are analyzed in detail to obtain the final design scheme. Fluid-solid coupling model is used to calculate the temperature field of the HSPMM to verify the rationality of the scheme. The rotor thermal stress analysis considering the multi-layer and multi-angle winding of CFS is carried out to obtain the rotor models suitable for prototype and mass production, respectively. Finally, the prototypes are manufactured and tested to verify the reliability of the multiphysics design process.

Computational Fluid Dynamics Study of a Compound Flow Field for Proton Exchange Membrane Fuel Cell(PEMFC) Performance Enhancement

The aim of the present work is to evaluate proton exchange membrane(PEM) fuel cell performance with a modified serpentine flow field with right angle turn by numerical modeling. A 3-D PEM fuel cell model of size 50 cm^(2) active area is developed. A conventional serpentine flow field is modified and the same is considered for the supply of reactants. Computational fluid dynamics(CFD) based simulations were conducted to analyse the pressure drop, distribution of reactants(H_(2) and O_(2)), liquid water activity, current flux density and water content in the membrane. From the simulation results, polarization curve is drawn to validate the literature data of PEMFC with the conventional serpentine flow field. Comparison of simulated polarization curve with literature data revealed that modified serpentine flow field performance is better than conventional serpentine flow field as it offers better water exclusion and uniform sharing of reactants. From this study, it is concluded that model of flow field pattern influences the functioning of fuel cell and utmost care must take while selecting a pattern for flow field of PEM fuel cell.

Carbon Deposition on the Venturi of a Gas Turbine Combustor Using Ethanol-Kerosene Blends

This paper reports an investigation of carbon deposition on the venturi component of a gas turbine combustor fueled with ethanol/kerosene fuel blends. China RP-3 kerosene and its ethanol blends(10%, 30%, and 50% ethanol by weight) were used in a gas turbine model combustor. Each combustion test of carbon deposition was conducted at 0.3 MPa for an hour. Measuring carbon deposition became difficult because of the special structure of venturi which is a component of swirl cup air atomization nozzle. An image processing method called planar reconstruction, was developed to evaluate the amount of carbon deposition semi-quantitatively. To study the morphology and structure of the deposition for different test fuels, a Scanning Electron Microscope(SEM) was employed to visualize the detailed structures of carbon deposition. Results show that with the increasing addition of ethanol, the amount of carbon deposition decreases, and the morphology of carbon changes significantly. For pure kerosene case, small spherules and flake graphite were closely interwoven on venturi surface. For other fuel blends, small spherules were not observed, and flake graphite neatly stacked and lined on the venturi surface. These results indicate that the mechanism of carbon deposition can vary significantly, due to the change of fuel’s molecular structures;the current study shows that the morphology and structure of carbon deposition of kerosene were altered remarkably by the ethanol addition.

Interaction between Neighboring Supercritical Water Molecules and Density Fluctuation by Molecular Dynamics Simulations

Supercritical water(scW)is important for various engineering applications.The structure and distribution of sc W is key to dominate the related processes and phenomena.Here,scW is investigated using molecular dynamics(MD)simulation with controlled pressure and temperature.Density oscillation is observed to occur in a 1 nm thickness bin,indicating mass exchange of particles across the bin interface.We show that the low density scW behaves strong heterogeneity.Quantitative analysis of system density fluctuations is performed by square root error and maximum structure factor,demonstrating the agreement between the two methods.The scW molecules are tightly gathered to form“liquid island”locally,but are very sparse in other regions,which are similar to the gas-liquid mixture in subcritical pressure.A target molecule is tracked to plot 3D displacements and rotating angles,with the former indicating large amplitude ballistic(diffusing)motion and small amplitude oscillation,and the latter displaying two scales of angle jumping.Both translation and rotating motion are related to hydrogen bond break up and reorganization.The low density scW behaves isolated molecules with few combinations of hydrogen bonds between molecules,while the high density scW behaves more combinations of molecules via hydrogen bonds.The two scales motion is expected to influence thermal/chemical process in supercritical state,deepening the fundamental understanding of scW structure.

A New Cleaner Power Generation System Based on Self-Sustaining Supercritical Water Gasification of Coal

A new cleaner power generation system(IPGS) is proposed and investigated in this paper. Integrating combined cycle with supercritical water gasification of coal, the thermodynamic energy of the produced syngas is cascade utilized according to its temperature and pressure, both sensible and latent heat of the syngas can be recycled into the system, and thereby the net power efficiency can be about 6.4 percentage points higher than that of the traditional GE gasification based power plant(GEPP). The exergy analysis results show that the exergy efficiency of the proposed system reaches 52.45%, which is 13.94% higher than that of the GEPP, and the improvement in exergy efficiency of the proposed system mainly comes from the exergy destruction decline in the syngas energy recovery process, the condensation process and the syngas purification process. The syngas combustion process is the highest exergy destruction process with a value of 157.84 MW in the proposed system. Further performance improvement of the proposed system lies in the utilization process of syngas. Furthermore, system operation parameters have been examined on the coal mass fraction in the supercritical water gasifier(GF), the gasification temperature, and the gasification pressure. The parametric analysis shows that changes in coal concentration in the GF exert more influence on the exergy efficiency of the system compared with the other two parameters.

Improved Turbine Vane Endwall Film Cooling by Using Sand-Dune-Inspired Design

As continuous of the previous sand-dune-inspired design,the Barchan-Dune-Shaped Injection Compound(BDSIC)’s film cooling performance at the endwall region was further investigated both experimentally and numerically.While the public 777-shaped hole was served as a baseline,the BDSIC’s endwall effectiveness was assessed at various blowing ratios.Experiments were performed in a single-passage transonic wind tunnel using pressure-sensitive paint(PSP)technique.Carbon dioxide was used as coolant with density ratio of DR=1.53.The purge slot’s blowing ratio was fixed at M=0.3,but the coolant holes were adjusted within M=0.5–2.0.The measured experimental results indicate that the film distribution at the endwall is strongly affected by the passage flow structures.The BDSIC holes demonstrate much higher film effectiveness than the 777-shaped holes for all blowing ratios,~30%enhancement for regionally averaged effectiveness at M=1.0 and~26%at M=2.0.As shown by the numerical results,the existence of BDSIC reduced the coolant penetration effect at a higher blowing ratio.Coolant was deflected and its momentum increased in the streamwise direction,therefore providing more robust film coverage over the endwall region.The anti-counter-rotating vortex pair induced by the BDSIC further stabilized the coolant film and increased the coolant spreading downstream.

Numerical Study of Convective and Radiation Heat Transfer Characteristics in an Upward-Facing Cylindrical Cavity under Back-Side Windy Condition

Under the back-side windy condition,the convection and radiation heat transfer characteristics in an iso-flux upward-facing cylindrical cavity were studied by three-dimensional numerical simulation.The impacts of cavity tilt angle,wind incident angle and wind speed on convection and radiation heat transfer Nusselt number Nuc and Nur were analyzed,and the possible explanations for their impacts were presented.Results show that due to the disturbance of wind,the influence of cavity tilt angle becomes more complicated and is related to wind incident angle and wind speed.The variation of Nuc or Nur with wind incident angle is different for different cavity tilt angles.Despite of the changes of cavity tilt angle or wind incident angle,the Nuc increases with the wind speed while the Nur presents a declination with the increasing of wind speed.Hence,compared with cavity tilt angle and wind incident angle,wind speed may be the dominant factor affecting or controlling the convective and radiation heat transfer of cavity.

Thermal Property Measurements of a Large Prismatic Lithium-ion Battery for Electric Vehicles

Because of the high cost of measuring the specific heat capacity and the difficulty in measuring the thermal conductivity of prismatic lithium-ion batteries,two devices with a sandwiched core of the sample-electric heating film-sample were designed and developed to measure the thermal properties of the batteries based on Fourier's thermal equation.Similar to electrical circuit modeling,two equivalent thermal circuits were constructed to model the heat loss of the self-made devices,one thermal-resistance steady circuit for the purpose of measuring the thermal conductivity,the other thermal-resistance-capacitance dynamic circuit for the purpose of measuring the specific heat capacity.Using the analytic method and recursive least squares,the lumped model parameters of these two thermal circuits were extracted to estimate the heat loss and correct the measured values of the self-made devices.Compared to the standard values of the reference samples of the glass and steel plates,the measured values were corrected to improve the measurement accuracies beyond 95% through steady thermal-circuit modeling.Compared to the measured value of the specific heat capacity of the battery sample at 50% state of charge using the calorimeter,the measured value using the self-made device was corrected in order to elevate the measurement accuracy by about 90% through dynamic thermal-circuit modeling.As verified through the experiments,it was reliable,convenient,and low cost for the proposed methodology to measure the thermal properties of prismatic lithium-ion batteries.

Numerical Investigation of Boundary Grid Effect on Heat Transfer Computation of RP-3 at Supercritical Temperature of Helical Tube Wall

To get reliable computational results,the RNG k-ε turbulence model with enhanced wall treatment was validated to solve the heat transfer of supercritical RP-3 in a helically coiled tube,and models of the thermo-physical properties of RP-3 were optimally chosen.Most significantly,the grid independence was validated by two-step procedure,and the effect of boundary grids of the supercritical-temperature wall on the computational accuracy was well studied.Through adjusting boundary-layer girds' size,four regions (increased,pseudo-convergence,decreased and convergence) of the outlet temperature Tout were obtained and analyzed.The results showed that the maximum computation errors of Tout and the pressure differential between the inlet and outlet ΔP reached 20.65% and 98.15%,respectively,indicating that boundary grids have a significant influence on computation of flow and heat transfer.Based on this,a dimensionless distance from the wall-adjacent cell to the wall y+=Prw-1/1.78 (Prw denotes Wall Prandtl number) was recommended as a convergence point.The variation laws of viscous length scale y* were discussed under different structural parameters,operation parameters,and helical lengths.An explicit model of y* was proposed to calculate the height (y) of the first boundary layer grids and refine boundary grids efficiently.A modified model for coefficient of fiiction factor Cf was proposed based on Rogers's,and Nusselt number Nu was proposed based on an analogy of momentum and heat transfer.The above models about y*,Cf and Nu could apply to both the entrance region and the whole tube length,and showed good performance when Reynolds number was extended to above 70 000,or whenever the outlet temperature is below or above the critical point.

Near-Wall Flow in the Blade Cascades Representing Last Rotor Root Sections of Large Output Steam Turbines

This paper investigates the flow past two variants of root section profile cascades for a last stage rotor considering three-dimensional flow structures in the near-wall region.Analyses were drawn based on RANS numerical simulations of both variants and on the experimental data obtained by the 3 D traversing in the exit flow field of one of the variants.Extent of 3 D structures at two different regimes and its influence on aerodynamic characteristics of the blade cascades was assessed.The distributions of Mach number along the profiles were compared with 2 D optical measurements and its distortion due to the presence of the sidewall was explored.The interaction between main vortical structures was described and its influence on the loading of the blades,mechanical energy losses and exit flow angle was discussed.The results showed that for a front loaded blade the vortical structures appeared earlier and at a larger extent than for an aft loaded variant.However,due to different Mach number distribution,contribution of end wall flow to the energy losses was lower in the case of the aft loaded variant.The influence of the near wall flow on the loading was found to be rather weak while the deviation of the exit flow angle appeared to be comparable for both of the variants.

Comparison of Conventional and Advanced Exergy Analysis for Dual-Loop Organic Rankine Cycle used in Engine Waste Heat Recovery

At present,the dual-loop organic Rankine cycle(DORC)is regarded as an important solution to engine waste heat recovery(WHR).Compared with the conventional exergy analysis,the advanced exergy analysis can better describe the interactions between system components and the irreversibility caused by economic or technical limitations.In order to systematically study the thermodynamic performance of DORC,the conventional and advanced exergy analyses are compared using an inline 6-cylinder 4-stroke turbocharged diesel engine.Meanwhile,the sensitivity analysis is implemented to further investigate the influence of operating parameters on avoidable-endogenous exergy destruction.The analysis result of conventional exergy analysis demonstrates that the priorities for the components that should be improved are in order of the high-temperature evaporator,the low-temperature turbine,the first low-temperature evaporator and the high-temperature condenser.The advanced exergy analysis result suggests that the avoidable exergy destruction values are the highest in the low-temperature turbine,the high-temperature evaporator and the high-temperature turbine because they have considerable endogenous-avoidable exergy destruction.The sensitivity analysis indicates that reducing the evaporation pinch point and raising the turbine efficiency can decrease the avoidable exergy destruction.

Experimental Study of Influence of Fuel Ratio on Combustion Characteristics of Diesel-Wetted Wood Powder

In this study, experiments were conducted to examine the influence of the fuel ratio(i.e., the ratio of diesel mass to wood powder mass) on the combustion characteristics of diesel-wetted wood powder, in which 0# diesel and poplar wood powder were used and well mixed. The fuel ratios were set to 0, 0.5, 1.0, 1.5, and 2.0. Fire behaviors, temperature distributions, mass loss rates, and CO concentrations were measured and analyzed. The results showed that because of the coupled effect of evaporation and the capillary force, the ignition point of diesel-wetted wood powder(less than 3°C) dropped dramatically as compared with that of pure wood powder(higher than 280°C) and pure diesel(higher than 107°C). At the early stage of combustion, diesel is lifted upwards by the capillary force, increasing both the concentration of diesel vapor and the temperature at the surface. When the surface temperature reaches that of the pyrolysis of wood powder, considerable pyrolysis gas emerges and combusts. As the flammable gas is consumed gradually, carbon combusts prominently when plenty of oxygen diffuses to its surface. Regarding the influence of the fuel ratio, the results showed that in cases with lower fuel ratios, the combustion was not self-sustainable. When the fuel ratio was relatively high, the temperature at the flame center was lower owing to incomplete combustion. More CO could be found in cases with higher fuel ratios in the early and late stages of combustion. The results could help to improve knowledge regarding combustion of fuel-wetted wood powder.

Brief Information for Authors

General Requirements:The Journal provides the forum for high-quality research communications,original new developments in scientific researches.Each manuscript must be accompanied by a statement that it has neither been published nor submitted for publication,in whole or in part,either in a serial,professional journal or as a part in a book which is formally published and made available to the public.The copyright of the paper is transferred to Journal of Thermal Science,Institute of Engineering Thermophysics,Chinese Academy of Sciences and Springer Verlag.

Numerical Investigation of Circumferential Groove Casing Treatment in a Highly-Loaded Low-Reaction Transonic Compressor Rotor

In this paper, a computational investigation of circumferential groove casing treatment in a highly-loaded low-reaction transonic compressor rotor is conducted, in which the stage reaction is significantly reduced due to a larger meridional contraction with respect to conventional transonic compressors. Steady computation at near-stall point is performed first to capture the stall inception of the rotor with smooth casing. Detailed observations, which mainly focus on the tip leakage flow behavior, obstruction and vortical structures in the tip region, determine the reason for the compressor stall. There is tip leakage vortex breakdown in the tip region. Moreover, it yields passage obstruction, and finally leads to the compressor stall. Then, attempts are made to investigate how the circumferential grooves can be applied for the compressor’s stall margin enhancement without compromising efficiency. Three configurations are obtained and analyzed by changing axial position and the number of the circumferential grooves. The results of computational parametric study indicate the optimal location of the groove is near the leading edge and the downstream grooves combine their influence on the compressor’s stabilization and performance in a cumulative manner. The optimal circumferential groove configuration produces an increase of 1% in total pressure ratio at the near-stall point and a gain of 3.7% in stall margin, without any penalty in efficiency. Furthermore, the impact the grooves will exert on the flow mechanisms between the grooves and the main flow is also considered.

Modeling and Energy Efficiency Analysis of Thermal Power Plant with High Temperature Thermal Energy Storage(HTTES)

This paper presents the recent research on the study of the strategies for the flexible operation of the thermal power plant to meet the requirement of load balance. The study aimed to investigate the feasibility of bringing the High Temperature Thermal Energy Storage(HTTES) to the thermal power plant steam-water cycle, to identify the suitable HTTES in the cold(hot) section of the reheating pipeline and to test the efficiency of the HTTES integration to increase the flexibility of peak shaving and energy efficiency via thermal power plant with HTTTES modelling and simulation. Thermoflex was adopted to perform the simulation and a 300 MW subcritical coal-fired power plant model was implemented onto the software platform. The simulation results show that it is feasible to extract steam from the steam turbine to charge the HTTES, and to discharge the stored thermal energy back to the power generation process, and to analyse the improved capability of the plant flexible operation with HTTES. Then the study was extended to analyse the effect of thermal energy temperature, the opening of the regulating valve, and the pipeline pressure loss aspects on thermal efficiency of the whole plant. The study is beneficial to achieve more economic operation of the thermal power plant with HTTES integration. It is concluded that the introduction of the HTTES can improve the consumption of wind power, and these ideas and methods for solving the energy consumption of the renewable energy and reducing the peak energy consumption are provided.

Numerical Study of Pressure Pulsation of Centrifugal Pumps with the Compressible Mode

The compressible effect of water is often neglected in the simulation of hydraulic machinery. However, based on experimental and numerical study, it is found that the compressibility of water could influence the magnitude of the pressure pulsation at some frequency in the pump. Therefore, in order to investigate the influence of water compressibility, compressible model is established by using Tait equation. The internal flow of centrifugal pump under different conditions is calculated by this model. The calculated results are compared with the incompressible results, and it is indicated that the compressibility of water has little effect on the performance parameters. But it affects the amplitude of pressure fluctuations at some discrete frequency, especially at the outlet of impeller and volute tongue where significant jet-wake and rotor/stator interaction appears respectively. Meanwhile, water compressibility makes greater influence on the flow pulsation under off-design condition. Therefore, it is necessary to consider the compressibility of working medium in the numerical simulation of unsteady flow in centrifugal pumps, especially in area with strong unsteady flow and at off-design condition.

Effects of Trenched Film Hole Configurations on the Endwall Film Cooling and Suction Side Phantom Cooling

To maximize the turbine thermal efficiency, modern gas turbine’s inlet temperature is significantly augmented within the past few decades. To prolong the lifespan of gas turbines, many efficient cooling techniques have been proposed and applied in the endwall cooling schemes. However, conventional discrete film hole does not take effect at the leading edge nearby region. In this research, how the trenched film hole configurations affects the endwall cooling and phantom cooling characteristics were deeply studied by using a verified approach. Steady 3D Reynolds-averaged Navier-Stokes(RANS) governing equations together with the shear stress transport(SST) k-w turbulence model have been solved. Firstly, results indicate that trenched film holes greatly influence the cooling effectiveness at leading edge nearby region compared to normal case. Nevertheless, suction side phantom cooling is hardly influenced by the trenched film holes. Secondly, the case with a smaller trench width obtains higher endwall cooling effectiveness, particularly at upstream region. More importantly, the cases with W=3D achieve large cooling effectiveness at leading edge nearby region with little influence by trench depth. Additionally, majority of trenched film holes coolant flow is driven towards middle passage. Therefore, the suction side phantom cooling is unaffected by the trenched film holes.