气脉冲发生器中火焰传播与压力变化的研究

燃烧气脉冲发生器用于电厂锅炉除灰，其工作原理是预混可燃气体在右端部分开口在内部有障碍物的容器中快速燃烧，以形成一定的压力脉冲，并产生作用于积灰表面的射流和冲击波，火焰在端流扰动装置的作用下不断加速，容器中的压力不断上升，火焰传播愈快，压力波形愈陡，压力锋值愈高，针对这些现象，该文进行了实验和理论研究。主要研究了乙炔，水煤气，液化石油气和甲烷4种燃料，在不同燃料浓度，不同阻塞比时对火焰传播和压力上升的影响，计算和实验结果对实验应用有指导作用。

气脉冲除灰技术燃烧和除灰过程研究

中国电站锅炉燃用大量的未经洗选的劣质煤，导致严重的锅炉积灰问题，尤其是125-600MWe的大型锅炉的回转式空气预热器堵灰更加严重。积灰不仅使锅炉热效率下降，而且堵塞烟气流道，影响了锅炉的正常运行。已有的各种除灰器都有较大的局限性。中国科学院力学研究所燃烧研究实验室根据我国国情开发出了燃烧气脉冲除灰技术，并在30多台大型电站锅炉应用取得了很好的效果。为了理解气脉冲除灰的工作过程，掌握运行规律，解释应用中出现的问题，以提高技术水平和开发新产品，尚需对气脉冲除灰的燃烧和除灰过程做更深入的研究。本论文工作针对燃烧气脉冲除灰技术在实际使用中提出的问题，开展了实验室研究。主要研究了乙炔、水煤气、液化石油气和甲烷四种燃料在气脉冲实验装置中的火焰传播情况和压力波形。研究了混合比、阻塞比和出口截面比对火焰速度和压力峰值的影响。在现有点火条件下找到了在静止混合气体中四种燃料的贫点火极限和乙炔在有一定流速时的贫点火极限；比较了燃烧室内乙炔空气混合物静止时和有一定流速时的爆炸压力峰值。初步搞清了各种因素对火焰速度和压力波形的影响，实验结果对实际应用有指导作用。为了理解火焰传播和压力波形之间的关系，用燃烧室内压力均匀的简化模型，计算了压力波形并且与实验结果进行了对照，由此推算了湍流燃烧速度并探讨了各种因素对它的影响。用考虑了管内有压力波传播的一维简化模型，计算了火焰传播过程中燃烧室两端的压力波形和火焰面前后的气流速度，以及不同时刻的燃烧室内气体流速分布。估算了气流剪切力的量级，进行了模拟积灰的气脉冲对比实验，测量了同一气脉冲条件下两种厚薄不同板的振动加速度值及其随时间和空间的衰减情况。还得到了压力在空间的衰减变化情况。定性地研究了积灰脱落机理，初步认为：对于粘结灰只有振动才有效，气流的剪切不能除去粘结灰。

Multi-zone TAP-reactors theory and application - IV. Ideal and non-ideal boundary conditions

We study the influence of non-ideal boundary and initial conditions (BIC) of a temporal analysis of products (TAP) reactor model on the data (observed exit flux) analysis. The general theory of multi-response state-defining experiments for a multi-zone TAP reactor is extended and applied to model several alternative boundary and initial conditions proposed in the literature. The method used is based on the Laplace transform and the transfer matrix formalism for multi-response experiments. Two non-idealities are studied: (1) the inlet pulse not being narrow enough (gas pulse not entering the reactor in Dirac delta function shape) and (2) the outlet non-ideality due to imperfect vacuum. The effect of these non-idealities is analyzed to the first and second order of approximation. The corresponding corrections were obtained and discussed in detail. It was found that they are negligible. Therefore, the model with ideal boundary conditions is proven to be completely adequate to the description and interpretation of transport-reaction data obtained with TAP-2 reactors.

Characteristics of plasma induced by interaction of a free-oscillated laser pulse with a coal target in air and combustible gas

Plasma in the air is successfully induced by a free-oscillated Nd:YAG laser pulse with a peak power of 10(2-3) W. The initial free electrons for the cascade breakdown process are from the ablated particles from the surface of a heated coal target, likewise induced by the focused laser beam. The laser field compensates the energy loss of the plasma when the corresponding temperature and the images are investigated by fitting the experimental spectra of B-2 Sigma(+) -> X-2 Sigma(+) band of CN radicals in the plasma with the simulated spectra and a 4-frame CCD camera. The electron density is estimated using a simplified Kramer formula. As this interaction occurs in a gas mixture of hydrogen and oxygen, the formation and development of the plasma are weakened or restrained due to the chaining branch reaction in which the OH radicals are accumulated and the laser energy is consumed. Moreover, this laser ignition will initiate the combustion or explosion process of combustible gas and the minimum ignition energy is measured at different initial pressures. The differences in the experimental results compared to those induced by a nanosecond Q-switched laser pulse with a peak power of 10(6-8) W are also discussed. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Pulse-response TAP studies of the reverse water-gas shift reaction over a Pt/CeO2 catalyst

The temporal analysis of products (TAP) technique was successfully applied for the first time to investigate the reverse water-gas shift (RWGS) reaction over a 2% Pt/CeO2 catalyst. The adsorption/desorption rate constants for CO2 and H-2 were determined in separate TAP pulse-response experiments, and the number of H-containing exchangeable species was determined using D-2 multipulse TAP experiments. This number is similar to the amount of active sites observed in previous SSITKA experiments. The CO production in the RWGS reaction was studied in a TAP experiment using separate (sequential) and simultaneous pulsing Of CO2 and H-2. A small yield of CO was observed when CO2 was pulsed alone over the reduced catalyst, whereas a much higher CO yield was observed when CO2 and H-2 were pulsed consecutively. The maximum CO yield was observed when the CO2 pulse was followed by a H-2 pulse with only a short (1 s) delay. Based on these findings, we conclude that an associative reaction mechanism dominates the RWGS reaction under these experimental conditions. The rate constants for several elementary steps can be determined from the TAP data. In addition, using a difference in the time scale of the separate reaction steps identified in the TAP experiments, it is possible to distinguish a number of possible reaction pathways. (c) 2005 Elsevier Inc. All rights reserved.

Effects of rotation in the laser-pulse photoassociation in a thermal gas of atoms

Photoassociation is a possible route for the formation of chemical bonds. In this process, the binding of colliding atoms can be induced by means of a laser field. Photoassociation has been studied in the ultracold regime and also with temperatures well above millikelvins in the thermal energy domain, which is a situation commonly encountered in the laboratory. A photoassociation mechanism can be envisioned based on the use of infrared pulses to drive a transition from free colliding atoms on the electronic ground state to form a molecule directly on that state. This work takes a step in this direction, investigating the laser-pulse-driven formation of heteronuclear diatomic molecules in a thermal gas of atoms including rotational effects. Based on the assumption of full system controllability, the maximum possible photoassociation yield is deduced. The photoassociation probability is calculated as a function of the laser parameters for different temperatures. Additionally, the photoassociation yield induced by subpicosecond pulses of a priori fixed shape is compared to the maximum possible yield.

(Mis)Using Pulse Oximetry : A Review of Pulse Oximetry use in Acute Care Medical Wards

Background: Nurses routinely use pulse oximetry (SpO2) monitoring equipment in acute care. Interpretation of the reading involves physical assessment and awareness of parameters including temperature, haemoglobin, and peripheral perfusion. However, there is little information on whether these clinical signs are routinely measured or used in pulse oximetry interpretation by nurses. Aim: The aim of this study was to review current practice of SpO2 measurement and the associated documentation of the physiological data that is required for accurate interpretation of the readings. The study reviewed the documentation practices relevant to SpO2 in five medical wards of a tertiary level metropolitan hospital. Method: A prospective casenote audit was conducted on random days over a three-month period. The audit tool had been validated in a previous study. Results: One hundred and seventy seven episodes of oxygen saturation monitoring were reviewed. Our study revealed a lack of parameters to validate the SpO2 readings. Only 10% of the casenotes reviewed had sufficient physiological data to meaningfully interpret the SpO2 reading and only 38% had an arterial blood gas as a comparator. Nursing notes rarely documented clinical interpretation of the results. Conclusion: The audits suggest that medical and nursing staff are not interpreting the pulse oximetry results in context and that the majority of the results were normal with no clinical indication for performing this observation. This reduces the usefulness of such readings and questions the appropriateness of performing “routine” SpO2 in this context.

Pulse dynamics in a three-component system : stability and bifurcations

In this article, we analyze the stability and the associated bifurcations of several types of pulse solutions in a singularly perturbed three-component reaction-diffusion equation that has its origin as a model for gas discharge dynamics. Due to the richness and complexity of the dynamics generated by this model, it has in recent years become a paradigm model for the study of pulse interactions. A mathematical analysis of pulse interactions is based on detailed information on the existence and stability of isolated pulse solutions. The existence of these isolated pulse solutions is established in previous work. Here, the pulse solutions are studied by an Evans function associated to the linearized stability problem. Evans functions for stability problems in singularly perturbed reaction-diffusion models can be decomposed into a fast and a slow component, and their zeroes can be determined explicitly by the NLEP method. In the context of the present model, we have extended the NLEP method so that it can be applied to multi-pulse and multi-front solutions of singularly perturbed reaction-diffusion equations with more than one slow component. The brunt of this article is devoted to the analysis of the stability characteristics and the bifurcations of the pulse solutions. Our methods enable us to obtain explicit, analytical information on the various types of bifurcations, such as saddle-node bifurcations, Hopf bifurcations in which breathing pulse solutions are created, and bifurcations into travelling pulse solutions, which can be both subcritical and supercritical.

Characterization of tight gas reservoir pore structure using USANS/SANS and gas adsorption analysis

Small-angle and ultra-small-angle neutron scattering (SANS and USANS) measurements were performed on samples from the Triassic Montney tight gas reservoir in Western Canada in order to determine the applicability of these techniques for characterizing the full pore size spectrum and to gain insight into the nature of the pore structure and its control on permeability. The subject tight gas reservoir consists of a finely laminated siltstone sequence; extensive cementation and moderate clay content are the primary causes of low permeability. SANS/USANS experiments run at ambient pressure and temperature conditions on lithologically-diverse sub-samples of three core plugs demonstrated that a broad pore size distribution could be interpreted from the data. Two interpretation methods were used to evaluate total porosity, pore size distribution and surface area and the results were compared to independent estimates derived from helium porosimetry (connected porosity) and low-pressure N2 and CO2 adsorption (accessible surface area and pore size distribution). The pore structure of the three samples as interpreted from SANS/USANS is fairly uniform, with small differences in the small-pore range (<2000 Å), possibly related to differences in degree of cementation, and mineralogy, in particular clay content. Total porosity interpreted from USANS/SANS is similar to (but systematically higher than) helium porosities measured on the whole core plug. Both methods were used to estimate the percentage of open porosity expressed here as a ratio of connected porosity, as established from helium adsorption, to the total porosity, as estimated from SANS/USANS techniques. Open porosity appears to control permeability (determined using pressure and pulse-decay techniques), with the highest permeability sample also having the highest percentage of open porosity. Surface area, as calculated from low-pressure N2 and CO2 adsorption, is significantly less than surface area estimates from SANS/USANS, which is due in part to limited accessibility of the gases to all pores. The similarity between N2 and CO2-accessible surface area suggests an absence of microporosity in these samples, which is in agreement with SANS analysis. A core gamma ray profile run on the same core from which the core plug samples were taken correlates to profile permeability measurements run on the slabbed core. This correlation is related to clay content, which possibly controls the percentage of open porosity. Continued study of these effects will prove useful in log-core calibration efforts for tight gas.

The influence of the gas environment on morphology and chemical composition of surfaces micro-machined with a femtosecond laser

We investigated the influence of different gas environments on the fabrication of surfaces, homogeneously covered with equally sized and spaced micro-structures. Two types of structures have been successfully micro-machined with a femtosecond laser on titanium surfaces in various atmospheres. The surface chemistry of samples machined in oxygen and helium shows TiO2, while machining in nitrogen leads to an additional share of TiN. The actual surface structure was found to vary significantly as a function of the gas environment. We found that the ablated particles and their surface triggered two consecutive events: The optical properties of the gas environment became non-isotropic which then led to the pulse intensity being redistributed throughout the cross section of the laser beam. Additionally, the effective intensity was further reduced for TiN surfaces due to TiN's high reflectivity. Thus, the settings for the applied raster-scanning machining method had to be adjusted for each gas environment to produce comparable structures. In contrast to previous studies, where only noble gases were found suitable to produce homogeneous patches, we obtained them in an oxygen environment.