Showing papers by "Dong Liu published in 2007"

Flow boiling heat transfer in microchannels

Abstract: Flow boiling heat transfer to water in microchannels is experimentally investigated. The dimensions of the microchannels considered are 275 X 636 and 406X1063 μm 2 . The experiments are conducted at inlet water temperatures in the range of 67-95°C and mass fluxes of 221-1283 kg/m 2 s. The maximum heat flux investigated in the tests is 129 W/cm 2 and the maximum exit quality is 0.2. Convective boiling heat transfer coefficients are measured and compared to predictions from existing correlations for larger channels. While an existing correlation was found to provide satisfactory prediction of the heat transfer coefficient in subcooled boiling in microchannels, saturated boiling was not well predicted by the correlations for macrochannels. A new superposition model is developed to correlate the heat transfer data in the saturated boiling regime in microchannel flows. In this model, specific features of flow boiling in microchannels are incorporated while deriving analytical solutions for the convection enhancement factor and nucleate boiling suppression factor. Good agreement with the experimental measurements indicates that this model is suitable for use in analyzing boiling heat transfer in microchannel flows.

Research of transient flow field real time interferogram acquisition system

Abstract: This paper describes a novel synchronous control system of high speed imaging, which combines a common path interferometer system modulated by the space phase. The system can continuously grab multiple frame interferograms, which contain transient flow field distortion. The study of this system will provide a fire-new means for the research of aerodynamics. The light source of the system is Nd: YLF semiconductor pump solid pulsed laser of which wavelength is 1053 nanometers. The laser pulse width is less than 30 nanoseconds, far less than the exposure time of the camera shutter. Thus the laser pulse can freeze the flow field within several dozen nanoseconds and catch the biggish change of turbulent flow. The pulsed laser beam containing the information of turbulent flow enters a cyclical radial shearing interferometer. The emergent lights, being respectively contracted and expanded, re-combine and form fringe pattern in high space frequency, modulated with a definite carrier frequency. The fringe pattern is formed on the high speed CMOS camera at last. An accurate short time delay circuit is provided for synchronization matching of the pulsed laser and camera exposure. The speed of image acquisition in full pixels with 1280×1024 can reach 450 frames per second. This interferogram acquisition system with compact configuration and strong anti-disturbance capability, has successfully grabbed clear transient interferograms that provided reliable image information for follow-up image processing and flow field density calculating.

Power boiler burning optimization method and device based on infra red radiation energy signal

Abstract: The invention discloses a burning optimal method for power station boiler based on infrared radiant energy signal and the device It is divided into hardware and software The hardware comprises three parts The first part comprises near infrared radiant energy sensor installed on four corners of boiler The near infrared radiant energy is transferred to photoelectric transition component by fibers The photoelectric transition component is connected with the data collecting and transferring control module of lower computer The second part comprises the data collecting and transferring control module of lower computer located in the boiler body The third part comprises data analyzing and control signal outputting module of upper computer located in electric room The software system is developed by Labview programming software The near infrared radiant energy sensor is used to obtain intensity information of radiant energy in boiler and by the optimization method of artificial neutral network deviation value of radiant energy can be obtained Then the deviation value treated by filter is transferred to the control module of DCS boiler fuel to improve coal-feeding control logic and unit response speed for loading The running stability of steamer is insured

Simulation Study on Radiative Imaging of Combustion Flame in Furnace

Abstract: Radiative imaging of combustion flame in furnace of power plant plays an increasingly important role in combustion diagnosis. This paper presents a new method for calculating the radiative imaging of three-dimensional (3D) combustion flame based on Monte Carlo method and optical lens imaging. Numerical simulation case was used in this study. Radiative images were calculated and images obtained can not only present the energy distribution on the charge-coupled device (CCD) camera target plane but also reflect the energy distribution condition in the simulation furnace. Finally the relationships between volume elements and energy shares were also discussed.

Measurement of Three‐Dimensional Temperature Distribution in an Absorbing, Emitting, and Anisotropically Scattering Medium

Abstract: Many advances in the thermal sciences depend on accurate determination of three‐dimensional temperature distribution. Previous measurements by thermocouples and pyrometers were mainly restricted to time‐average “point” measurements of temperature. In this paper, a model to measure the three‐dimensional temperature distribution according to the flame image captured by CCD camera is studied numerically. The formation of the flame image is considered as two stages: radiation transfer in the participating medium and the optical imaging process through the lens of the camera. The inverse analysis based on Monte Carlo method and the optical model of the flame image are introduced to describe these two stages respectively. The flame of the pulverized coal is considered as a three‐dimensional, absorbing, emitting, anisotropically scattering medium and full of CO2, N2 and carbon particles. In the temperature reconstruction case, eight CCD cameras are located on the front, back, left and right surfaces of the cube with 0.4m×0.4m×0.4m size. The temperature reconstruction equations are ill‐posed linear system of equations. LSQR (Least Square QR‐factorization) and damping LSQR have been used for solving the ill‐posed equations. For an assumed temperature profile, the numerical simulation results show the reconstruction errors are maintained at the lower levels under different measurement errors and temperature near the center of the cube can be reconstructed well even under large measurement errors.

The position shifting of frequency spectrum of Fourier transform in the application of aspheric surface testing

Abstract: In the measurement of aspheric surfaces, spatial phase modulation technology is always combined. With a tilt, the linear spatial carrier is introduced to enhance the signal noise ratio (SNR). Then using DFT on the interferogram, after spectrum shifting, the first order spectrum filter and IDFT, the wavefront phase of aspheric surface is obtained. In this paper, the traditional way to introduce spatial carrier, namely that the center of the first order spectrum is positioned on the x axis, is analyzed. This method exist a limitation which may influence the testing result. Thus a new method is put forward here. Make sure the slope of spatial carrier is unvaried, and transfer the first order spectrum to the bisector of x axis and y axis. This change can not only reserve the low frequency components of the first order spectrum, but also keep the high frequency components at a large extent. So in some circumstance, the wavefront phase of aspheric surface with a large PV value can't be recovered accurately by the traditional spatial carrier way, but it can be recovered accurately by the new way. This greatly expands the testing range of wavefront of aspheric surface.