A theory for the impact of a wave breaking onto a permeable barrier with jet generation

We model a water wave impact onto a porous breakwater. The breakwater surface is modelled as a thin barrier composed of solid matter pierced by channels through which water can flow freely. The water in the wave is modelled as a finite-length volume of inviscid, incompressible fluid in quasi-one-dimensional flow during its impact and flow through a typical hole in the barrier. The fluid volume moves at normal incidence to the barrier. After the initial impact the wave water starts to slow down as it passes through holes in the barrier. Each hole is the source of a free jet along whose length the fluid velocity and width vary in such a way as to conserve volume and momentum at zero pressure. We find there are two types of flow, depending on the porosity, β, of the barrier. If β is in the range 0 ≤ β < 0.5774 then the barrier is a strong impediment to the flow, in that the fluid velocity tends to zero as time tends to infinity. But if β is in the range 0.5774 ≤ β ≤ 1 then the barrier only temporarily holds up the flow, and the decelerating wave water passes through in a finite time. We report results for the velocity and impact pressure due to the incident wave water, and for the evolving shape of the jet, with examples from both types of impact. We account for the impulse on the barrier and the conserved kinetic energy of the flow. Consideration of small β gives insight into the sudden changes in flow and the high pressures that occur when a wave impacts a nearly impermeable seawall.     

Energy consumption characteristics of an absorption chiller during the partial load operation

The objectives of this study are to analyze performance characteristics during partial load operation and to calculate energy consumption amount of H₂O/LiBr absorption chiller with a capacity of 210 RT. The effect of cooling water flow rate and cooling water inlet temperature on the absorption performance and energy saving is quantified during the partial load operation. It is found that the performance of absorption system is more sensitive to the change of inlet water temperature rather than the cooling water flow rate. Even if the cooling water flow rate is reduced to 60% of the standard value, the capacity is recovered if the temperature of cooling water decreases about 2.0 °C. The pumping power of cooling water is 4 times higher than that of cooling tower during the partial operation mode and the pumping power of cooling water becomes more significant with decreasing the partial load. It is concluded that when the partial load is in the range of 100–40%, the reduction of the required power by 23% can be realized by decreasing the cooling water inlet temperature of 1.0 °C.     

Results of participation of Russian standards in key comparisons conducted by the Regional Metrological Organization for countries of the Asia-Pacific Region in the field of liquid and gas flow rate parameter measurement

Results of international key comparisons of the national standard for air flow rate and the working standard for water volumetric and mass flow rate are provided. Comparisons were made in 2009 within the framework of the Asia-Pacific Metrological Program (APMP) international organization. Russia was represented by state special standard for the unit of air flow rate (GET 150–85) and the highest accuracy working standard for the unit of water volumetric mass flow rate (RE VT 6–98). Results of comparison point to conformity of the metrological properties of these standards to the world level.     

The effect of external flow on the feeding currents of sessile microorganisms

Microscopic sessile suspension feeders live attached to surfaces and, by consuming bacteria-sized prey and by being consumed, they form an important part of aquatic ecosystems. Their environmental impact is mediated by their feeding rate, which depends on a self-generated feeding current. The feeding rate has been hypothesized to be limited by recirculating eddies that cause the organisms to feed from water that is depleted of food particles. However, those results considered organisms in still water, while ambient flow is often present in their natural habitats. We show, using a point-force model, that even very slow ambient flow, with speed several orders of magnitude less than that of the self-generated feeding current, is sufficient to disrupt the eddies around perpendicular suspension feeders, providing a constant supply of food-rich water. However, the feeding rate decreases in external flow at a range of non-perpendicular orientations due to the formation of recirculation structures not seen in still water. We quantify the feeding flow and observe such recirculation experimentally for the suspension feeder Vorticella convallaria in external flows typical of streams and rivers.     

Lattice Boltzmann simulation of dispersion in two‐dimensional tidal flows

A lattice Boltzmann method (LBM) is applied to problems of dispersion in two‐dimensional water flows. The water flow is modelled by shallow water equations. A two‐distribution lattice Boltzmann equation algorithm is presented to solve the pollutant transport problem within the framework of shallow water flow. One distribution models the shallow water flow. The other distribution models the pollutant transport. Flow characteristics and concentration profiles of dispersive species are obtained at various flow regimes. For fast water flow, the concentration profiles are highly affected by the flow advection and become completely different from those at slow water flow. Numerical results are presented for pollutant transport in bounded and open channel flows. The proposed LBM is also used to simulate a pollution event in the Strait of Gibraltar. The obtained results indicate that the present method is useful for the investigation of transport phenomena by shallow water flows in complex geometries and practical flow problems. Copyright © 2008 John Wiley & Sons, Ltd.     

Experimental evaluation of the performances of a H2O–LiBr absorption refrigerator under different service conditions

The paper describes an experimental plant aimed at simulating and verifying the performances of a single-stage H₂O–LiBr absorption machine. The machine is water cooled and it is supplied by hot water produced by an electrical boiler; it is possible to simulate different service conditions by varying the temperatures and the flow rate of water in the external circuits. Measurement facilities allow to record in real time all the main operating parameters of internal and external circuits (temperatures, pressures and flow rates). The paper illustrates the characteristics of the machine and of the plant and the results of various experimental campaigns. In particular, the acquisitions on the plant have tested different service conditions by varying the flow rate and the temperature of the supplying hot water; the energy and energy performances of the plant are presented and compared with data from literature and from a simulation code developed for the plant.The results show that the absorption machine can work, with acceptable efficiency, with input temperatures of about 65–70 °C; this result is interesting for a future supply of the machine with solar energy.     

相变蓄热水箱分层特性的实验研究

本文基于三水合醋酸钠,搭建了一套相变蓄热水箱实验系统,在初始水温为80℃、进水温度为5℃的工况下,测试得到了水箱的热力学特性,并采用填充效率分析法以及火用效率分析法,在进水体积流量分别为1、3、5、7、9 L/min时,分析了相变蓄热水箱的热分层特性。结果表明,当水箱温度为80℃时,普通水箱、相变蓄热球PCM48水箱、相变蓄热球PCM58水箱的热能分别为18. 81、19. 34、19. 07 MJ。进口体积流量相同时,相变蓄热球越靠近水箱进口,水箱的热分层效果越好。随着进水体积流量的增大,分层效果下降。不同水箱的理查森数Ri在t^*=0. 5达到最大值,Ri随相变蓄热球位置的降低而减小,PCM48和PCM58在第4层时的Ri分别为7. 569和7. 781,而在第1层时的Ri分别减小为7. 03和7. 145,表明水箱热分层的程度随着相变蓄热球位置的升高而降低。     

Water transport through subnanopores in the ultimate size limit: Mechanism from molecular dynamics

Ab initio and classical molecular dynamics simulations show that water can flow through graphdiyne—an experimentally fabricated graphene-like membrane with highly dense (2.4 × 10¹⁸ pores/m²), uniformly ordered, subnanometer pores (incircle diameter 0.57 nm and van der Waals area 0.06 nm²). Water transports through subnanopores via a chemical-reaction-like activated process. The activated water flow can be precisely controlled through fine adjustment of working temperature and pressure. In contrast to a linear dependence on pressure for conventional membranes, here pressure directly modulates the activation energy, leading to a nonlinear water flow as a function of pressure. Consequently, high flux (1.6 L/Day/cm²/MPa) with 100% salt rejection efficiency is achieved at reasonable temperatures and pressures, suggesting graphdiyne can serve as an excellent membrane for water desalination. We further show that to get through subnanopores water molecule must break redundant hydrogen bonds to form a two-hydrogen-bond transient structure. Our study unveils the principles and atomistic mechanism for water transport through pores in ultimate size limit, and offers new insights on water permeation through nanochannels, design of molecule sieving and nanofluidic manipulation.

     

The importance of water migration in the measurement of the thermal conductivity of unsaturated frozen soils

The transport of heat in frozen soil may occur by conduction and by the convective transport of sensible and latent heat arising from the flow of water in the vapor, liquid and solid states. Theory describing the coupled flow of heat and of water in the liquid and vapor states is used to derive a definition of apparent thermal conductivity (the convective transport of heat in the movement of ice in unstaturated soils is assumed to be negligible). Calculations suggest that, at temperatures close to 0°C, the transport of latent heat may exceed the contribution of heat flow by conduction. Under these conditions, the apparent thermal conductivity will be much greater than the thermal conductivity calculated from the thermal conductivities and volume fractions of the components.Insufficient published data prevent a rigorous evaluation of the theory. However the functional dependence on temperature of both thermal conductivity and the apparent thermal conductivity are calculated for a Tomakomai soil at different subzero temperatures. These values are compared to the apparent thermal conductivities of this soil which were measured at a water content in the unfrozen state of 0.48 cm³ cm^?3 and at temperatures ranging from ?0.7°C to ?10°C using the line heat source technique. The dependence of apparent thermal conductivity on subzero temperature, as calculated from theory, compares favourably to the dependence which was observed for this soil.     

变负荷变流量冷水机组水系统的设计及探讨

工业用空调一般控温精度要求高,有时需要同时满足热负荷、冷冻水流量变化很大的工况,这对制冷系统的设计提出了更高要求,着重对变负荷、变流量工业用冷水机组的水系统设计进行阐述和分析,并针对性地提出水路旁通的两种设计方案,以解决实际应用中经常遇到的一些问题。     

Heat transfer characteristics of the ice slurry at melting process in a tube flow

The heat transfer characteristics were experimentally investigated for ice slurry made from 6.5% ethylene glycol–water solution flow in a 13.84 mm internal diameter, 1500 mm long horizontal copper tube. The ice slurry was heated by hot water circulated at the annulus gap of the test section. Experiments of the melting process were conducted with changing the ice slurry mass flux and the ice fraction from 800 to 3500 kg/m² s and 0–25%, respectively. During the experiment, it was found that the measured heat transfer rates increase with the mass flow rate and ice fraction; however, the effect of ice fraction appears not to be significant at high mass flow rate. At the region of low mass flow rates, a sharp increase in the heat transfer coefficient was observed when the ice fraction was more than 10%.     

水流开关在空调系统中的应用及改进

水流开关在冷水机组和空调工程的水系统中应用广泛,它能保证空调系统安全、高效地运行。通常水流开关在应用时只能定性地保证空调系统的安全和高效运行,而不能定量、准确地设定水流开关闭合和断开时的流量值。本文根据空调系统制冷量的不同,设计与之相匹配的水流开关,并利用简易水流量测定系统,对水流开关的闭合和断开流量值进行测定,实现对水流开关应用的改进。     

基于流体体积函数模型的横板型稳压罐内气液两相流场仿真研究

针对水流量标准装置中横板型稳压罐,基于Navier-Stokes方程建立罐体计算流体动力学仿真模型。使用湍流模型、流体体积函数瞬态模型和有限体积法进行离散,并在近壁区采用标准的壁面函数法进行修正,完成横板型稳压罐内部两相流场的数值模拟。数值结果显示空罐充水流态依次经过无水状态-射流-上壅-漫流-稳定状态,同时形成掺气现象和泡状流;气液体积比1:3情况下,满罐充水流场有固定周期的晃荡现象,上侧形成逆时针转动的漩涡气腔,流场湍流粘度较小,分布较均匀,稳定效果最好。     

浸没发热球体冷冻水绕流作用下水体温度稳定性分析

本文通过推导在冷冻水绕流发热球体传热过程中,水池内水体平均温度随时间的变化公式,研究冷冻水理论降温所需最小流量、水体稳定温度和所需稳定时间的主要影响因素,分析水池内所容纳水体质量及初始温度、冷冻水流量及温度等参数对水体温度稳定性的影响。根据某工程实际情况确定冷冻水温度、流量等参数,运用理论推导公式和CFD模拟技术计算水体温度稳定性。结果表明:当冷冻水温度为17℃时,理论最小质量流量为83. 7 t/h。经过6～7个月后水体温度将达到稳定,稳定温度为22. 4℃。     

State of the problem of evaluating precision in measuring the flow of water in open canals and waterways

Conclusions General evaluations of the accuracy of methods used for measuring the flow of water in open canals and waterways are at present used on a wide scale in literature. However, in citing an evaluation of a method it is not usually stated that the evaluation is general and tentative. This leads to the erroneous notion that the problem of errors in measuring the flow of water in open canals and waterways has been fully resolved.The problem of errors in measuring the flow of water by the area-speed method depends on the determination of errors in the above-mentioned direct measurements.The solution of the problem of errors in measuring by means of weirs depends on the determination of the error in the flow coefficient of weirs. This value can be determined by the same method as that used for evaluating the error in flow coefficients of constricting devices for measuring the flow of liquids in pipelines [3]. This problem requires special consideration.     

Experimental investigation of critical heat flux under boiling in subcooled swirling flow under conditions of one-sided heating

Results are given of an experimental investigation of critical heat flux in a turbulent swirling flow of subcooled water under one-sided heating. The parameters of flow are varied in the following ranges: the pressure of water at the inlet, 0.7 and 1.0 MPa; mass velocity ρw, 1100 to 9900 kg/(m² s); flow swirl coefficient k = 0.19 and 0.37; the temperature of water at the inlet—20, 40, and 60°C; and the hydraulic diameter of the channel, 2.16 mm.     

生产井储层流量在线监测装置研究

研制了一套生产井储层流量在线监测装置。该装置利用超声多普勒频差测量油、气、水的总流量,采用对环境无安全隐患的双能级X射线测量油、气、水的分相含率,采用电导式传感器实现高含水率情况下含水率的快速测量。在室内三相流实验系统上进行了实验,油、水流量的测量误差均小于±7%,气流量的测量误差小于±14%。     

Control over nanocrystalization in turbulent flow in the presence of magnetic fields

The influence of the magnetic field and the water flow on the crystal form of calcium carbonate precipitated from low-concentration water solution was followed systematically. By changing the strength of the field, the calcite/aragonite/vaterite ratio varied. The crystal form and the particle size distribution of the precipitated calcium carbonate were determined by using X-ray analyses and transmission electron microscopy (TEM). A simple hydrodynamical model, using the Navier–Stoke's and Maxwell's equations, predicts that there is a strong energy coupling and transfer between turbulent flow and the magnetic fields, which can be amplified to high values. Since the formation of aragonite is enhanced in the presence of magnetic field, scaling is prevented in turbulent flow.     

Spread of large LNG pools on the sea

A review of the standard model of LNG pool spreading on water, comparing it with the model and experiments on oil pool spread from which the LNG model is extrapolated, raises questions about the validity of the former as applied to spills from marine tankers. These questions arise from the difference in fluid density ratios, in the multi-dimensional flow at the pool edge, in the effects of LNG pool boiling at the LNG–water interface, and in the model and experimental initial conditions compared with the inflow conditions from a marine tanker spill. An alternate supercritical flow model is proposed that avoids these difficulties; it predicts significant increase in the maximum pool radius compared with the standard model and is partially corroborated by tests of LNG pool fires on water. Wind driven ocean wave interaction has little effect on either spread model.     

A water transport model for the creep response of the intervertebral disc

Time-dependence in the mechanical response of the intervertebral disc has previously been shown to arise from the transport of water out of the disc. A creep model has been devised which describes the water transport in terms of the disc structure. This model assumes that the flow of water is the result of a pressure gradient across the cartilage end-plates, caused by an externally applied stress. The fluid transport properties of the cartilage determine the flow rate. Several cases are studied; those that best fit the experimental results use either a straindependent or a time- and strain-dependent pressure gradient. The permeability of the disc system is in the range (0.20 to 0.85)×10^–17 m⁴N^–1 sec^–1 and depends on the stress level. These values are lower than those reported in the literature for articular cartilage, but this can be explained in part by the differences in water content of the cartilage types. Permeability is found to decrease with applied stress, and both the strain- and time-dependence parameters increase in magnitude with stress. It can be shown that the analytical models of the creep response of the disc are analogous to three- and four-parameter viscoelastic models that employ springs and dashpots.