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分类： 物理学 >> 普通物理:统计和量子力学,量子信息等

An improved algebraic reconstruction technique(ART) with tunable diode laser absorption spectroscopy(TDLAS) is presented in this paper for determining two-dimensional distribution of H2O concentration and temperature in a simulated combustion flame. This work aims to simulate the reconstruction of spectroscopic measurements by a multi-view parallel-beam scanning geometry and analyze the effects of projection rays on reconstruction accuracy. It finally proved that reconstruction quality dramatically increases with increasing number of projection rays until they are more than 180 for 20×20 grid, and after that point, the number of projection rays has little impact on reconstruction accuracy. It is clear that the temperature reconstruction results are more accurate than the water vapor concentration by traditional concentration calculation method, the study in this article also proposed an innovative way to reduce the error of concentration reconstruction and improve the reconstruction quality greatly, the capability of this new method is evaluated by appropriate assessment parameters. By using this new approach, the concentration reconstruction accuracy is not only badly improved, but also a suitable parallel-beam arrangement is put forward for sake of high reconstruction accuracy and simplicity of experimental validation. At last, a bimodal structure of combustion region is assumed to demonstrate the robustness and universality of the proposed method. Numerical investigation indicates that the proposed TDLAS tomographic algorithm is capable for accurate temperature and concentration profiles detection, this feasible formula for reconstruction research is expected to resolve several key issues in practical combustion devices. |

分类： 物理学 >> 普通物理:统计和量子力学,量子信息等

This Article presents a three dimensional numerical model investigating thermal performance and hydrodynamics features of the confined slot jet impingement using shiny of Nano Encapsulated Phase Change Material (NEPCM) as a coolant. The slurry is composed of water as a base fluid and n-octadecane NEPCM particles with mean diameter of 100nm suspended in it. A single phase fluid approach is employed to model the NEPCM slurry.The thermo physical properties of the NEPCM slurry are computed using modern approaches being proposed recently and governing equations are solved with a commercial Finite Volume based code. The effects of jet Reynolds number varying from 100 to 600 and particle volume fraction ranging from 0% to 28% are considered. The computed results are validated by comparing Nusselt number values at stagnation point with the previously published results with water as working fluid. It was found that adding NEPCM to the base fluid results with considerable amount of heat transfer enhancement.The highest values of heat transfer coefficients are observed at H/W=4 and C-m =0.28. However, due to the higher viscosity of slurry compared with the base fluid, the slurry can produce drastic increase in pressure drop of the system that increases with NEPCM particle loading and jet Reynolds number. |

Experimental Study on Factors that Influence the Diameter of Dry Granulated Particles

Tong, L. G., ; Zhang, P.,; Yin, S. W.,分类： 物理学 >> 普通物理:统计和量子力学,量子信息等

The effects of different refrigerants on heat transfer performance of pulsating heat pipe (PHP) are investigated experimentally. The working temperature of pulsating heat pipe is kept in the range of 20 degrees C-50 degrees C. The startup time of the pulsating heat pipe with refrigerants can be shorter than 4 min, when heating power is in the range of 10W-100W. The startup time decreases with heating power. Thermal resistances of PHP with filling ratio 20.55% were obviously larger than those with other filling ratios. Thermal resistance of the PHP with R134a is much smaller than that with R404A and R600a. It indicates that the heat transfer ability of R134a is better. In addition, a correlation to predict thermal resistance of NIP with refrigerants was suggested. |

分类： 物理学 >> 普通物理:统计和量子力学,量子信息等

The efficiency, robustness and reliability of recent numerical methods for finding solutions to flow problems have given rise to the implementation of computational fluid dynamics (CFD) as a broadly used analysis method for engineering problems like membrane separation system. The CFD modeling in this study observes steady and unsteady (transient) heat flux and temperature profiles in a polymeric (cellulose acetate) membrane. This study is novel due to the implementation of user defined scalar (LIDS) diffusion equation by using user-defined functions (UDFs) infinite volume method (FVM). Some details of the FVM used by the solver are carefully discussed when implementing terms in the governing equation and boundary conditions (BC). The contours of temperature due to high-temperature gradient are reported for steady and unsteady problems. |

Study of Cycle Output Improvement by Work-Fluid Including Phase Change Material

Morita, S.,; Tanimura, K.,; Hayamizu, Y.,分类： 物理学 >> 普通物理:统计和量子力学,量子信息等

This paper represents numerical simulation of flow inside an axial transonic compressor subject to inlet flow distortion, to evaluate its effect on compressor performance and stability. Two types of inlet distortion, namely inlet swirl and total pressure distortion are investigated. To study the effect of combined distortion patterns, different combinations of inlet swirl and total pressure distortion are also studied. Results for cases with total pressure distortion indicate that hub radial distortion improves stability range of the compressor while tip radial distortion deteriorates it. An explanation for this observation is presented based on redistribution of flow parameters caused by distortion and the way it interacts with stall inception mechanisms in a transonic axial compressor. Results also show that while co-swirl patterns slightly improve stability range of the compressor, counter-swirl patterns diminish it. Study of combined distortion cases reveals that superimposition of effects of each individual pattern could predict the effect of a combined pattern on compressor's performance within an accuracy of 1%. However, it is unable to predict the associated effect on compressor's stability. |

Mathematical Modelling of the Transient Response of Pipeline

Taler, D. ; Kaczmarski, K.分类： 物理学 >> 普通物理:统计和量子力学,量子信息等

The development of heat recovery methods for dry granulation processes from blast furnace slag in the iron and steel industry is limited because of the high consumption of granulation energy during these processes. To determine the factors that influence the diameter of granulated particles, a paraffin test platform for gas quenching granulation was established. The influences of air velocity, air flow rate, liquid mass flow rate, and liquid pipe diameter on the final particle size and mass distribution were studied. Experimental results showed that the final particle size decreased (from 1.07 mm to 0.81 mm) with increasing air velocity (from 28.3 m/s to 113.2 m/s). However, when air velocity was higher than 60 m/s, its influence on particle diameter decreased significantly. The experimental data were analyzed using SPSS Statistics software, which indicated that the effect of air velocity on particle diameter was the most significant, followed by those of air flow and liquid pipe diameter. The effect of liquid mass flow was the least significant. |

Analysis of Nusselt Number Distribution in Case of a Strongly Heated, Horizontal Rod

Grunt, K., ; Zuraw, A.; Pietrowicz, S.分类： 物理学 >> 普通物理:统计和量子力学,量子信息等

The presented research was focused on a comparison between different means of obtaining a Nusselt number distribution, in a situation where neither temperature nor heat flux density is constant. Two fundamentally different measurement techniques have been utilized, alongside a CFD simulation, in order to designate temperature distributions in a horizontal rod. Dry air under normal pressure, regarded as a perfect gas, was chosen as the working fluid, whereas the rod's cross-section was restricted to a ring. In this scenario heat exchange between the rod and the fluid is driven predominantly by natural convection, with a slight impact of thermal radiation, particularly at temperatures approaching the top end of the available range. Temperature margins achieved at the heated end of the rod ranged from 60K up to 150K, resulting in local Rayleigh numbers falling in-between 6.0x10(3) and 2.6x10(4). Reconstruction of Nusselt numbers from a discrete temperature distribution was possible thanks to a dedicated method implemented using a Scilab script. A segregated, steady-state solver based on the SIMPLE scheme was utilized for the purpose of numerical simulations on the fluid side, whereas a heat conduction equation was solved over solid domain in the considered conjugated heat transfer problem. A corresponding set of empirical data has been obtained, using both resistance temperature detectors and a thermal imaging camera, both for the sake of numerical model validation and comparison of individual methods. The Nusselt numbers resulting from each approach were compared against values computed using available correlations valid for horizontal configuration. |

分类： 物理学 >> 普通物理:统计和量子力学,量子信息等

Most evaporative cooling towers are arranged on building roof due to the limitation of space and noise, and acoustic barriers are always installed around cooling towers in practical applications. The existence of acoustic bathers and crosswind may affect the recirculation phenomenon which is directly related to the operating performance of cooling towers. In this study, a physical and mathematical computation model is proposed to research the crosswind and distance between acoustic bathers and inlet of cooling towers. Both sensible and latent heat are considered in this research. The reflux flow rate and performance ratio are obtained to evaluate the recirculation and operating performance, respectively. The results show that the higher the crosswind velocity, the larger the reflux flow rate, and the lower the performance ratio of cooling tower groups. For high crosswind velocity, the presence of acoustic barriers is useful to inhibit reflux and improve operating performance, especially for ICE cooling tower groups. In addition, the optimum values are recommended for LiBr/ICE cooling tower groups in the research cases The variation of reflux flow rate and performance ratio with the acoustic bathers' distance presents a parabolic tendency. |

An Improved Prediction Model of Vortex Shedding Noise from Blades of Fans

Dou, H. S., ; Li, Z. H., ; Lin, P. F.,分类： 物理学 >> 普通物理:统计和量子力学,量子信息等

The main source of the noise of an axial flow fan is the fluctuating pressure field on blade surfaces caused by the shedding of vortices at the trailing edge of blades. An analytical model to predict the vortex shedding noise generated at the trailing edge of blades of axial flow fans was proposed by Lee in 1993. In this model, for mathematical convenience, an idealized vortex street is considered. However, the agreement between the analytical results and the experimental data needs to be improved because of the simplification about the Karman vortex street in the wake of blade. In the present study, a modified model is proposed based on the prediction model by Lee. The boundary layer theory is used to analyze and calculate the boundary layer development on both the pressure and the suction sides of blades. Considering the effect of boundary layer separation on the location of noise source, the predicted overall sound pressure level compares favorably with the experimental data of an axial fan. In the calculation of A-weighted sound pressure level (LA), considering the effect of static pressure on radiate energy, the predicted broadband noise with the modified model compares favorably with the experimental data of a multiblade centrifugal fan. |

Annular Supersonic Swirling Flows with Heterogeneous Condensation

Fukushima, Y [ 1 ]; Matsuo, S [ 2 ]; Shiomi, N [ 3 ]; Setoguchi, T [ 4 ]分类： 物理学 >> 普通物理:统计和量子力学,量子信息等

In recent years, separating and extracting technologies of condensate gas have been developed by combining a swirl flow with non-equilibrium condensation phenomena of condensate gas generated in a supersonic flow. The technology can reduce the size of the device and does not use chemicals. However, there are many unresolved problems for performance of the separation, extraction and operating principle. Therefore it is necessary to research further in order to improve the performance of the equipment. In the present study, the numerical study was carried out to clarify the effect of the heterogeneous condensation on the characteristics of the swirling flow field in a supersonic annular nozzle, and the differences between homogeneous condensation and heterogeneous condensation in the flow field. As the results, it is found that the condensation flow with a swirl affects the position of sonic line, the generating position of condensate and the radial distribution ratio of liquid phase. |