Modelling pressure drop in hepa filters during dynamic filtration

A new model has been developed to predict the clogging behaviour of high-efficiency particulate air filters. The model takes into account the heterogeneous deposit of particles inside the filter medium. The filter is considered to be a series of elementary slices which are assumed to be homogeneously loaded by aerosol. Particles are assumed to form dendrites which can be considered as newly formed fibres. For each time increment and for each slice, particle collection efficiency of initial and new fibres is calculated according to the Payet model in order to give an overall prediction of the mass of aerosol deposited and the pressure drop. Model results are compared with experimental results.     

Modelling of pressure drop in packed columns

The correct choice of packing is of decisive importance for optimum process efficiency in the operation of two-phase countercurrent columns. An important criterion for this choice is the pressure drop in the gas flow. Theoretical relationships are derived for calculating the pressure drop in beds with dry and trickle packings. It has been demonstrated by comprehensive experiments that these relationships allow the pressure drop to be determined more accurately than by previous methods. The experiments were performed at the Department of Thermal Separation Processes of Bochum University on 54 different packed beds, using 24 different systems.     

Effect of solid monodisperse particles on the pressure drop of fibrous filters

The increase in pressure drop across glass HEPA filters has been measured as a function of particle mass loading using polystyrene latex particles (PSL). PSL particles in several different sizes were generated as challenge aerosols. For each particle size distribution, the specific resistance (K₂) was calculated by measuring the mass of PSL particles loaded per unit area of filter and the pressure drop across the filters at a given filtration velocity. In all cases, the specific resistance of the filter cake increased as the aerodynamic mean particle diameter decreased at the same mass loading. This correlation equation was modified by using the lognormal conversion method suggested by Raabe [1971] for a polydisperse particle size distribution; then the modified equation was expressed as a function of geometric mean particle diameter and standard deviation which could be obtained by the measuring instruments (PDS 3603; TSI Inc.). The advantage of this approach over other methods is the use of a more convenient prediction of pressure drop, if we know the geometric mean particle diameter and standard deviation, which could be easily measured. The values of porosities, obtained from the pressure drop responses of loading in the filters using the Rundnick and First equation, were compared with other researches.     

Modelling high pressure extraction processes

Semibatch flow extraction of oil and other active ingredients from some plant materials (Silybum marianum, pepper, paprika and cocoa) with supercritical fluids (SCF) such as CO₂ and propane at different operating conditions was studied. Dynamic behaviour of the extraction runs was analysed by a mathematical model based on the adsorption–desorption equilibrium of extractable component from solid tissue, the diffusion of extractable component dissolved in SCF to the surface and mass transfer through the external film into the bulk. The linear driving force concept was employed to incorporate intraparticle diffusion as well as external mass transfer. Results show that the simplified model, which describes desorption process at equilibrium, could successfully describe cumulative rate data and is specially interesting for observation of the cross-over effect for adsorption–desorption, i.e. how desorption is changed with the increase of temperature at constant pressure.     

Air flows and pressure drop modelling for different pleated industrial filters

A dimensionless model was developed to determine the pressure drop across clean pleated filters, according to filter medium type, geometric characteristics of the pleating (distance between two pleats, pleat height, etc) and air flow parameters (filtration velocity, air density, etc). The model was derived from both experimental and numerical results obtained from nuclear and automotive filters — high efficiency particulate air (HEPA) and low efficiency particulate (LE), respectively. The major findings were that a more homogeneous air flow distribution occured over the surface of the pleated HEPA filter, while geometric characteristics had a greater influence on the initial pressure drop across the LE filter. The numerical model highlighted the fundamental importance of the filter medium's air flow resistance on air flow distribution.     

The influence of pleat geometry on the pressure drop in deep-pleated cassette filters

In air filtering applications, a filter's pressure drop at a defined collection efficiency constitutes an important parameter. This paper discusses the variables influencing the pressure drop in air filters featuring deep-pleated filter media. For cassette-type fine filters in accordance with EN 779 or for HEPA/ULPA filters in accordance with EN 1822, the most commonly used media are paper-like materials with a thickness of less than 1 mm, which offer a relatively high resistance to the air flowing through them. Manufacturers accordingly endeavour to accommodate a maximum of filter medium area in a small space. To enable the pressure drops customary in intake, exhaust and re-circulated air filtration to be assured, the filter medium is therefore arranged in narrow, deep pleats. Particularly when large quantities of air are being handled per filter element, it is advantageous to pleat the filter medium in depths of 150 mm to 280 mm. The conversion technique and the resultant pleat geometry exert a crucial influence on the pressure drop concerned.     

Numerical and experimental study of enhanced heat transfer and pressure drop for high temperature applications

This paper focuses on the passive heat transfer enhancement where the flow surface is modified to increase the heat transfer. This field is narrowed by considering only techniques that are suited for high temperature applications in the range of 600–900 °C of the “cold” fluid.     

Modeling the pressure drop behavior of cleanable dust filters during pressure-controlled operation

Cleanable dust filter media are typically used in huge baghouse filter apparatuses. Thereby, the regeneration by back-pulsing from the clean gas side is done by either time-controlled or pressure-controlled operation, whereas the latter is more common. Hence, the need for a detailed knowledge of the clogging and filtration mechanisms during long time operation of a pressure-controlled filter aging arises.

A mathematical model describing the pressure drop evolution during time-controlled filter aging has been developed. The core of the developed model is the concept of dust masses that distribute themselves on a specific particle deposition area inside and on the surface of the filter medium. By altering this particle deposition area, various clogging mechanisms, occurring during an aging procedure, are covered by the model.

In this work, the model was adapted and coefficient parameters adjusted for pressure-controlled filter regeneration operation. A multitude of pressure-controlled test runs were performed in a specially designed filtration apparatus. From these tests, process-specific parameters were regressed and used to model the respective pressure drop curves. These model pressure drop curves show good accordance both quantitatively and qualitatively to experimental data and give a detail view on different clogging mechanisms.     

Modelling of high viscosity oil drop breakage process in intermittent turbulence

A multifractal model of the fine-scale structure of turbulence is applied to describe breakage of viscous drops of immiscible liquid immersed in a fully developed turbulent flow. A population of drops whose diameter falls within the inertial subrange of turbulence is considered here. The population balance equation is used to predict the drop size distributions. Calculations are performed for binary and multiple breakage. Several daughter distribution functions are applied and the results of their application are compared with experimental data. Experimental investigations of drop breakup were carried out in a flat bottom stirred tank having the diameter of and equipped with Rushton type agitator and four baffles. Silicone oils with viscosity of 10, 100, 500 and 1000 m Pa s were dispersed in the aqueous continuous phase. Measurements were performed using high resolution digital camera. Experimental results as well as numerical simulations show that after the initial period of multiple breakage, the strongly asymmetric type of binary breakage dominates.     

垂直管内高沸点工质异丙苯流动沸腾换热与阻力

对垂直管内高沸点有机工质异丙苯的流动沸腾换热与摩擦压降特性进行了实验研究,获得了换热系数与摩擦压降沿流动方向的变化情况,并与前人模型的计算值进行了比较。实验过程中质量流速为382—786 kg/(m2.s),实验工况干度为0.1—0.6,压力为0.21—0.27 MPa。通过对实验数据的回归分析,获得了换热系数与摩擦压降的计算关联式。在对复杂的非线性方程进行回归分析时,提出了一种简单的迭代分析方法。研究结果丰富了高沸点工质的流动沸腾换热数据,为石化行业中换热器的设计提供了依据,并为强化凝结换热器的开发和性能测试提供了比较基准。     

Epitaxial growth on nickel-plated diamond seeds at high pressure and high temperature

Epitaxial growth on nickel-plated diamond seeds at high pressure and high temperature (HPHT) was observed with graphite as carbon source. The thickness of the electroplating nickel film which acts as a catalyst/solvent ranges from 54.6 μm to 255.6 μm. The relationship between the Ni film thickness and diamond growth rate is investigated. When the nickel film thickness is from 90 μm to 129 μm, diamond crystals can nearly grow up to three times as large as the original seeds at ∼ 5.8 GPa and ∼ 1460 °C within 14 min. The mechanism of the crystal growth with nickel-plated diamond seeds under HPHT is discussed. The results and techniques might be useful for high quality saw-grade diamonds production and large diamond single crystal growth.     

高热流条件下过冷沸腾流动阻力特性试验研究

过冷沸腾在高热流冷却场合得到了广泛的应用,如聚变堆偏滤器冷却、压水堆堆芯冷却。其中,过冷沸腾流动阻力是换热系统设计的关键内容之一。试验研究了高热流条件下竖直通道内水的过冷沸腾流动阻力特性,试验段为内径6 mm、长径比44.4的不锈钢圆管。试验参数范围：热通量7.5~12.5 MW/m²,质量流速6000~10000 kg/(m²?s）,系统压力3~5 MPa,进口流体温度80~200℃。分析了质量流速、热通量、压力、沸腾数、Jacob数等参数对阻力的影响。结果显示,过冷沸腾流动阻力随着热流及质量流速的增加而增加,随压力增加而减小。将试验数据与文献中的经验关联式作对比,结果表明各关联式的预测误差较大,主要归结于拟合参数及工作流体的差异。研究发现管径尺寸效应也是影响阻力的一个因素,为此在前期成果的基础上,提出了一个添加管径因素修正项的经验关联式,该关联式的预测误差在±18%范围内。     

Pore evolution during high pressure atomic vapor deposition

The development of physical vapor deposition systems that employ inert gas jets to entrain and deposit atomic and molecular fluxes have created an interest in the atomic assembly of thin films under high pressure (10–500 Pa) deposition conditions. Thin films grown under elevated pressure and low surface mobility conditions can contain a higher volume fraction of porosity and a different pore morphology to coatings created by conventional, low pressure (<10⁻⁴ Pa) deposition processes. A recent direct simulation Monte Carlo simulation analysis of binary vapor–gas jet atom interactions has shown that the incident angle distribution (IAD) for vapor atom impacts with a substrate is strongly effected by the background pressure. Here, these results are combined with a kinetic Monte Carlo technique to simulate the high pressure growth of vapor deposited nickel films and identify the mechanisms of pore formation. We find that when the surface atom mobility is low, shadowing of oblique angle arrivals by features on the substrate result in the incorporation of porosity with a hierarchical size distribution that includes elongated, inter-columnar pores and finer scale intra-columnar pores. The nucleation of the inter-columnar pores is related not only to the IAD, but also to the height and spacing of the initial asperities on the substrate and to those that subsequently evolve during deposition. The volume fraction of the inter-columnar pores is found to increase as both the fraction of oblique atom arrivals and the height of the asperities increase. For each prescribed IAD and asperity height, an asperity spacing is found that maximizes the inter-columnar pore fraction. By varying the IAD for a given substrate surface topology, in conjunction with intermittent observations of the coating structure during the growth process, the flux shadowing mechanisms that govern the inter-columnar pore nucleation have been determined.     

纳米聚晶金刚石的高压高温合成

利用自行研制的二级大腔体静高压装置,通过高温超高压下石墨向金刚石的直接转变,合成出了纳米聚晶金刚石块体材料.合成压力约为17GPa,温度约为2300℃.微区X射线衍射分析表明,石墨转变成了立方相的金刚石,扫描电子显微镜及X射线全谱拟合分析显示,合成出来的金刚石晶粒尺寸约16nm.压痕法测得的样品维氏硬度为100GPa以上.     

耐高温丙烯酸酯类压敏胶的研究进展

丙烯酸酯类压敏胶（APSA）具有粘接性能优异、耐老化性能好、成本低、性能稳定、合成工艺简单等优点，由于其优异的性能被广泛应用于自黏带、标签、医药、家庭护理、汽车零部件等领域。但目前APSA应用领域仍较窄，大多数产品耐热性较差，不能在高温条件下使用。因此，开发耐高温性能的压敏胶（HTRAPSA）具有重要意义。文章综述了近年来国内外对HTRAPSA的研究进展，重点阐述了提高溶剂型和乳液型APSA耐高温性的相关研究工作。主要改性方法包括引入交联剂改性、引入特殊的改性单体、引入耐高温性物质改性和改进加料方式、聚合工艺、共混改性等方法来提高APSA的耐高温性能。同时，也指出了这些改性方法存在的问题与不足，以及所制备出的HTRAPSA存在的问题，并对今后相关研究的发展进行了展望。     

Development of a semi-analytical model to predict the pressure drop of clean pleated high-efficiency particulate air filters

The present article outlines the development of a semi-analytical model devoted to predict the pressure drop induced by clean pleated high-efficiency particulate air (HEPA) filters. Both experimental measurements and numerical simulations are used to characterize the velocity field in the pleat channel. On this basis, a semi-analytical model is derived to determine the gas flow within the pleat channel. This analytical formulation is used to predict the air pressure evolution according to filtration velocity in the pleat. This model is then validated on the basis of comparisons with measurements found in the scientific literature for different kinds of HEPA filters with different pleat geometries. This model is easy to use, fast to run compared to standard computational fluid dynamics (CFD) approaches, and is in good agreement with the experimental results.     

常温高压法氯气液化

介绍了对离子膜烧碱项目中的氯气所采用的常温高压液化装置、压缩机组及液化流程,在运行中存在的问题,提出了解决措施。     

High purity multiwalled carbon nanotubes under high pressure and high temperature

We have studied the structural modifications that multi-walled carbon nanotubes (MWNTs) undergo when treated under high pressure and high temperature (HP-HT). Uniaxial pressures of 5.5-6.5 GPa were applied to samples of purified MWNTs between 850 and 950 °C for 30 min. The resulting material was then analysed by X-ray diffractometry, Raman spectroscopy and transmission electron microscopy. Comparison of the data obtained by such analyses before and after treatment does show changes in the Raman spectra, a slight linear decrease of the d₀₀₂ spacing, and some structural modifications that could be due to MWNT segmentation and interlinking.     

高温高压锅炉在干熄焦工程中的应用

结合以往对各种干熄焦锅炉的标定数据以及在干熄焦锅炉选择过程中存在的制约因素,对干熄焦装置的生产能力、工程投资及企业现状等因素进行对比分析,为干熄焦锅炉炉型的选择提供了建议。同时针对高温高压自然循环干熄焦热力系统和中温中压联合循环干熄焦热力系统,在节能方面、锅炉效率、钢材消耗、系统电力消耗、发电量的差异以及锅炉的开工与运行方面的差异进行了对比分析,进而了解两种参数的热力系统在各方面的优缺点。