Heat transfer correlation for boiling flows in small rectangular horizontal channels with low aspect ratios

In the present experimental study, a correlation is proposed to represent the heat transfer coefficients of the boiling flows through horizontal rectangular channels with low aspect ratios. The gap between the upper and the lower plates of each channel ranges from 0.4 to 2 mm while the channel width being fixed to 20 mm. Refrigerant 113 was used as the test fluid. The mass flux ranges from 50 to 200 kg/m² s and the channel walls were uniformly heated up to 15 kW/m². The quality range covers from 0.15 to 0.75 and the flow pattern appeared to be annular. The modified Lockhart–Martinelli correlation for the frictional pressure drop was confirmed to be within an accuracy of ±20%. The heat transfer coefficients increase with the mass flux and the local quality; however the effect of the heat flux appears to be minor. At the low mass flux condition, which is more likely to be with the smaller gap size, the heat transfer rate is primarily controlled by the liquid film thickness. A modified form of the enhancement factor F for the heat transfer coefficient in the range of Re_LF200 well correlates the experimental data within the deviation of ±20%. The Kandlikar's flow boiling correlation covers the higher mass flux range (Re_LF>200) with 10.7% mean deviation.     

大气运动基本方程组的稳定性分析

以分层理论提供的基本方法分析大气运动基本方程组的拓扑学特征;证明局地直角坐标系中的大气运动基本方程组在无穷可微函数类中是稳定方程;给出局部解意义下使方程组典型定解问题适定的充要条件;讨论大气动力学中有关“以过去推测未来”以及当涉及应用问题时如何修改定解条件和下垫面的选择等问题;指出在通常假设下,基本方程组中的3个运动方程和连续方程完全决定了这个方程组的性质．     

Mixed Convection Boundary Layer Flow Past a Horizontal Circular Cylinder Embedded in a Bidisperse Porous Medium

Adopting a two-temperature and two-velocity model, appropriate to a bidisperse porous medium (BDPM) proposed by Nield and Kuznetsov (2008), the classical steady, mixed convection boundary layer flow about a horizontal, isothermal circular cylinder embedded in a porous medium has been theoretically studied in this article. It is shown that the boundary layer analysis leads to expressions for the flow and heat transfer characteristics in terms of an inter-phase momentum parameter, a thermal diffusivity ratio, a thermal conductivity ratio, a permeability ratio, a modified thermal capacity ratio, and a buoyancy or mixed convection parameter. The transformed partial differential equations governing the flow and heat transfer in the f-phase (the macro-pores) and the p-phase (the remainder of the structure) are solved numerically using a very efficient implicit finite-difference technique known as Keller-box method. A good agreement is observed between the present results and those known from the open literature in the special case of a traditional Darcy formulation (monodisperse system).     

水平井开采石油遇到的几个流体力学问题

本文从渗流力学和流体动力学方面讨论了利用水平井技术开采石油时在油藏工程和采油工程中遇到的几个力学问题,如水平井产量的计算,水平井非稳态试井及流场分析,水平井井筒内压力降及其对产量的影响、水平井近井油藏和井筒内流体流动耦合等,半提出水平井开采机理仍存在很多基础理论需要研究解决。     

INFLUENCE OF DISPLACEMENT OF SATURATED SAND STRATUM ON PRE-STRESSED ANCHORS

土层变形是造成预应力值波动甚至失效的重要原因. 利用载荷位移传递函数,基于弹性理论建立了饱和粉细砂层变形过程中锚索受力模型,通过实例研究了锚索预应力值在施工过程中的变化规律及锚固体在地层变形中的受力特性,结果表明锚固体接触面剪切刚度,锚索倾斜角度以及锚固体直径都是影响锚固体内力及接触面剪切应力的重要因素,为类似的预应力锚索支护工程的设计施工提供经验.     

Heat transfer to air–water annular flow in a horizontal pipe

Two-phase air–water flow and heat transfer in a 25 mm internal diameter horizontal pipe were investigated experimentally. The water superficial velocity varied from 24.2 m/s to 41.5 m/s and the air superficial velocity varied from 0.02 m/s to 0.09 m/s. The aim of the study was to determine the heat transfer coefficient and its connection to flow pattern and liquid film thickness. The flow patterns were visualized using a high speed video camera, and the film thickness was measured by the conductive tomography technique. The heat transfer coefficient was calculated from the temperature measurements using the infrared thermography method. It was found that the heat transfer coefficient at the bottom of the pipe is up to three times higher than that at the top, and becomes more uniform around the pipe for higher air flow-rates. Correlations on local and average Nusselt number were obtained and compared to results reported in the literature. The behavior of local heat transfer coefficient was analyzed and the role of film thickness and flow pattern was clarified.     

Transient lightning responses of grounding systems buried in horizontal multilayered earth with a hybrid method

Combined with the Fast Fourier Transform (FFT), a mathematical hybrid method for accurately computing the lightning response from grounding systems buried in multilayered earth model has been developed in this paper. In the method, electrical circuit consists of “T” typical of basic elements. To accelerate calculations of the method, quasi-static complex image method and closed form of Green's function and analytical formula for mutual induction and impedance coefficients were introduced into this method. With the inverse FFT, the method can be used for studying performances of transient lightning response from the grounding systems.     

Reply to Comments on “Non-Darcian Forced Convection Flow of Viscous Dissipating Fluid over a Flat Plate Embedded in a Porous Medium”

In this note, we reply to the comments by Rees and Magyari (2007) on our article (Aydin and Kaya 2007). They mainly stated that the thermal boundary conditions we defined at the edge of the boundary layer were incompatible with the energy equation. This is questionable and therefore we will discuss it below. They disclosed that our results were in error. However, this is quite misleading. Scientifically, they cannot reach such a conclusion without comparing our results with what they thought to be correct. In fact, this misleading and unproven statement will be shown not to be correct in the following.     

On the role of environmental reference materials in the development of horizontal standards for environmental protection

The need for standardisation and harmonisation of measurements increases with the progress of the European integration process. One of the areas for which the need for harmonisation has been emphasised is the protection of the soil compartment. While knowledge of problems associated with soils is increasing in Europe, based on soil surveys, monitoring systems and data networks, the corresponding (analytical) data is not often comparable, which limits its value for policy development. In this context, the European Commission has invited the Member States to investigate the possibility for a harmonisation of European standards in the fields of soil, sludge and biodegradable waste (compost). Furthermore, the development of new reference materials for both the validation of these new methods and their successful implementation on a routine basis is required. This paper shows some selected examples for which the development of horizontal standards may be worth investigating. In addition, it discusses and proposes the vehicle of (C)RMs for the implementation of a common measurement system for soil, related to these horizontal standards. It also raises some open questions and sheds light on future perspectives and challenges.Presented at BERM-9 – 9^th International Symposium on Biological and Environmental Reference Materials, June 15–19, Berlin, Germany     

Enhancement of the Antioxidant and Skin Permeation Properties of Betulin and Its Derivatives

This study investigated the antioxidant activity DPPH, ABTS, and Folin–Ciocalteu methods of betulin (compound 1) and its derivatives (compounds 2–11). Skin permeability and accumulation associated with compounds 1 and 8 were also examined. Identification of the obtained products (compound 2–11) and betulin isolated from plant material was based on the analysis of ¹H- NMR and ¹³C-NMR spectra. The partition coefficient was calculated to determine the lipophilicity of all compounds. In the next stage, the penetration through pig skin and its accumulation in the skin were evaluated of ethanol vehicles containing compound 8 (at a concentration of 0.226 mmol/dm³), which was characterized by the highest antioxidant activity. For comparison, penetration studies of betulin itself were also carried out. Poor solubility and the bioavailability of pure compounds are major constraints in combination therapy. However, we observed that the ethanol vehicle was an enhancer of skin permeation for both the initial betulin and compound 8. The betulin 8 derivative showed increased permeability through biological membranes compared to the parent betulin. The paper presents the transformation of polycyclic compounds to produce novel derivatives with marked antioxidant activities and as valuable intermediates for the pharmaceutical industry. Moreover, the compounds contained in the vehicles, due to their mechanism of action, can have a beneficial effect on the balance between oxidants and antioxidants in the body, minimizing the effects of oxidative stress. The results of this work may contribute to knowledge regarding vehicles with antioxidant potential. The use of vehicles for this type of research is therefore justified.