Bottom Opening Research Articles

Cold crucible melting with bottom pouring nozzle

Purpose The purpose of this paper is to investigate a new type of nozzle which is free from erosion and non-contaminating the outflow metal. Cold crucible melting technique with electromagnetic induction is used to obtain reactive metal castings and produce high-quality metal powders for aerospace, automotive and medical applications. An important part of this technology is the nozzle used to pour the molten alloy through the bottom opening. Design/methodology/approach The paper uses mathematical modeling technique, previously validated on multiple similar cases, to investigate a new type of nonconsumable nozzle made of copper segments. Findings The design of the nozzle requires to satisfy the narrow balance between the thin solidified protective layer on the wall while avoiding the blockage of the outflow if the nozzle is frozen completely. The sensitivity of the outflow to the nozzle diameter is investigated. The AC electromagnetic force leads to high mixing rates, transitional flow structures and turbulence of the melt, contributing to the melt shape dynamics and the heat loss to walls. Originality/value The beneficial features of the cold crucible melting to purify the melt from particulate contamination are explained using the full melting and pouring cycle.

Numerical Simulation of Flow and Temperature Fields in a Deep Stratified Reservoir Using Water-Separating Curtain.

In this work, the flow and temperature fields of a thermally stratified reservoir under different settings of a water-separating curtain are simulated by using the standard k-ε turbulence model. In the simulation, two different equations of state including Boussinesq approximation and the density-temperature function have been used and compared. This study shows that Boussinesq approximation is more time-saving, and the density-temperature function has higher computational accuracy. Thus, the standard k-ε turbulence model with two equations of state is applied to study the effect of adding a water-separating curtain in the stratified reservoir on the Discharged Water Temperature (DWT). It is found that adding the Water-Separating Curtain (WSC) can effectively increase the discharged water temperature. Moreover, the different arrangements of WSC have obvious effects on the discharged water temperature. For example, the increased temperature by adding a WSC with full sealing is 1 °C higher than that by using the WSC with a bottom opening height of 2 m. However, the maximum pressure difference acting on the WSC for the former WSC is 100 Pa higher than that for the latter WSC. In addition, this study shows that the different equations of state have little effect on the simulation results. Considering the calculation efficiency, equations of state using the Boussinesq approximation can be recommended to save the calculation time.

An Investigation on Ventilation of Building-Integrated Photovoltaics System Using Numerical Modeling

Abstract This study numerically investigates the thermal behavior and airflow characteristics of the building-integrated photovoltaic (BIPV) façade. A three-dimensional model is developed based on the typical BIPV façade. Computational fluid dynamics (CFD) with the shear stress transport (SST) κ-omega turbulent model is used in the study. The effects of geometric configurations on the BIPV cell temperature in steady state are evaluated including the sizes of the bottom and top openings and the depth of the back air cavity (or so-called cavity depth). When the sizes of the inlet and outlet openings are the same, the effects on the decrease of cell temperature are limited. By enlarging the bottom (inlet) opening, the impact of ventilation in the cavity behind is more significant and the cell temperature decreases. Cavity depth is also a vital factor affecting BIPV cell temperature. The paper identifies the optimal cavity depth of approximately 100–125 mm. Flow disturbance and a vortex may be observed at the bottom and top of the air cavity, respectively, as the cavity depth increases which negatively affects the ventilation causing these flow disturbances to increase the cell temperature. Thermal effects of environmental conditions are compared with regard to two selected BIPV configurations. The wind velocity and the attack angle also have an obvious impact on cell temperature. Ambient temperature and solar irradiance exhibit a linear relationship with BIPV cell temperature as expected.

EXPERIMENTAL STUDY ON BED SCOUR AND ITS PROTECTION BEHIND STANDING WAVE WEIRS CONSIDERING COMBINED FLOW OVER WEIR CRESTAND BOTTOM PIPES

Weirs may be used for measuring of canals discharge, decreasing water slope in canals and distribution of water to canals for irrigation. To empty the water of upstream canal during the maintenance or constructing new water structures and escaping the silt accumulated to downstream, a bottom pipes are installed in weir body near canal bed. Recently, with increasing the demands of water to downstream, a part of flow is passing through the bottom pipes in addition to over weir flow. Most of previous studies concentrate on estimating discharge coefficient of combined flow. However little information are available on scour downstream of this combined flow. So, the objectives of this research are to experimentally investigate the influence of using bottom openings for passing flow with that falling over weir crest on the geometry of scour hole downstream and on the estimation of minimum solid bed length to prevent this scour. The experimental program was performed in a rectangular flume in two categories. Each category was for weir model without working pipes and weir model with two synchronic working bottom pipes with weirs over-flow on scouring. In the first category, solid bed length behind the weir model was chosen to be 600 mm and the analysis are based on scour hole dimensions and its location behind the model, while the second category is for estimating the minimum solid bed length behind the weir model to prevent scour. Top surface slope of the weir is chosen to be 5:1 and 10:1for both studied categories. The model of the weir is followed by a solid apron following by sand basin. The mean diameter of sand is kept constant at 0.502mm. The channel bed slope is kept constant at 0.0001, while the discharge and flow depth downstream were varied to cover the required range of Froude number in Egyptian canals. The study revealed that: Using bottom pipes for passing flow with that falls over weir crest helps in reducing scour dimensions behind the weir, as well as reducing the required length of solid bed which considered bed protection. It also found that the required minimum length of solid apron behind the weir to prevent scour is greater than the summation of an arbitrary solid length and the length of scour hole formed downstream of it. Moreover the results showed that the predicted length of scour behind the weir with top surface slope 10:1 is greater than that for 5:1 especially for solid weir with low discharges and low head differences. Empirical formulas in a power function are developed in dimensionless forms for estimating the protected length against scour and the scour dimensions. On the other hand, the comparative analysis with previous studies revealed that the minimum solid bed length behind the weir to prevent scour is greater than the estimated one by using a velocity distribution approach.

Reliability of a high-pressure die cast Al alloy radiator

The resistance to pressure of a diecast AlSi11Cu2(Fe) alloy radiator has been studied at various holding temperatures. A recently developed method to seal the bottom opening of the radiator element has been presented and its reliability has been even evaluated. Three failure modes are observed during burst testing in the temperature range 40–100 °C, i.e. oil leakage at the interface between the radiator element and the plug, rupture of an element and detachment of the plug from the bottom opening. The main failure mechanism is attributed to the fracture of the radiator element, while the detachment of the plug occurs only at higher temperature; very few leakage failures occur. In the considered experimental range, the temperature exposure affects the burst pressure of the radiator. The failure probability of radiator can be described by three-parameter Weibull distribution, which has evidenced the reliability of the described sealing system.

Natural Convection and Irreversibility Evaluation in a Cubic Cavity with Partial Opening in Both Top and Bottom Sides.

A numerical study on natural convection in a cubical cavity with partial top and bottom openings is performed in this paper. One of the vertical walls of the cavity has higher temperature than that of the opposite one; the remaining walls are insulated perfectly. Three-dimensional simulations of governing equations have been performed using a finite volume technique. The results are presented for different parameters such as opening length and Rayleigh number. It is observed that heat transfer rate and fluid flow can be controlled via opening ratio size and Rayleigh number.

Гидродинамическая модель осесимметричного истечения идеальной жидкости из донного отверстия резервуара формы параболоида вращения

Гидродинамическая модель осесимметричного истечения идеальной жидкости из донного отверстия резервуара формы параболоида вращения

To determine the optimal tilt angle of the lattice holes of the bottom of the inclined chamber

According to the results of laboratory experiments, the optimal angle of inclination of the holes of the lattice bottom of the inclined chamber of the combine harvester is established, which provides maximum separation of free grain from the combed grain heap before it enters the grind chamber. This allows you to minimize the intake of free grain to the threshing device, securely eliminating the probability of crushing the working bodies grind. Studies were carried out on wheat varieties «Moscow 56». The grain moisture content was about 12%. The speed of the conveyor 3 m/s and the angle of inclination to the horizon of 45° correspond to similar parameters for most modern combine harvesters. The angle of inclination of the lattice bottom opening had seven levels of variation within 0-90°. The feed of the combed grain heap was about 10 kg/s with a content of 80 % free grain. The length of the removable grating bottom was 0.95 m, and its rectangular holes had a size of 160×8 mm. To eliminate the effect on the output parameter, the area of the «live section» of the holes of the lattice bottom in all series of the experiment was taken the same. Thus, results of scientific researches, increasing of the angle of inclination amounts of free grain passed through the holes of the bottom lattice is reduced, and the number came down from his grain, on the contrary, increases. The maximum separation of free grain 68,7 % corresponds to the angle of inclination of the holes equal to 0°. To ensure complete separation of free grain from the combed grain heap, the length of the separating surface must be at least 1,18 m. This technical solution can be implemented, for example, in the inclined chamber of the grain harvester KZS-1218 «Polissya GS-12», which has a length of about 1,3 m.

Electromagnetic particle separation in the cold crucible melting with novel type bottom pouring nozzle

The cold crucible melting technique is proven to be most effective to obtain reactive metal castings and produce high quality metal powders for aerospace, automotive and medical applications. A weak point of this technology is the graphite/ceramic nozzle used to pour the molten alloy through the bottom opening, which has very limited life time (several minutes) and adds contamination to the high quality final material. The paper uses the mathematical modelling technique, previously validated on multiple similar cases, to investigate a new type of non-consumable nozzle made of copper segments. During the dynamic melting the nozzle entrance is protected by a thin solidifying layer of the same alloy as the main melt. The AC electromagnetic (EM) field effects are investigated for the possibility to extract particles (impurities, precipitates, oxides, bubbles, etc.) from the melt. The dynamics of particles are affected by the hydrodynamic drag, buoyancy, turbulent fluctuations and the EM force via the local pressure distribution. The EM force leads to high mixing rates, transitional flow structures and turbulence of the melt, contributing to the particle dispersion, transport and separation to a desired location. The paper demonstrates effects of flow on the time dependent particle ‘swarm’ transport and separation to the side solidified ‘skull’.

Radiation and Exciting Forces of Axisymmetric Structures with a Moonpool in Waves

A highly efficient “hybrid integral-equation method” for computing hydrodynamic added-mass, wave-damping, and wave-exciting force of general body geometries with a vertical axis of symmetry is presented. The hybrid method utilizes a numerical inner domain and a semi-infinite analytical outer domain separated by a vertical cylindrical matching boundary. Eigenfunction representation of velocity potential is used in the outer domain; the three-dimensional potential in the inner domain is solved using a “two-dimensional” boundary element method with ring sources and ring dipoles to exploit the body symmetry for efficiency. With proper solution matching at the common boundary, both radiation and diffraction potentials can be solved efficiently while satisfying the far-field radiation condition exactly. This method is applied to compute the hydrodynamic properties of two different body geometries: a vertical-walled moonpool with a bottom plate that restricts the opening and a spar-like structure with a diverging bottom opening inspired by designs of floating Oscillating Water Columns. The effects of the size of the bottom opening on the hydrodynamic properties of the body are investigated for both geometries. The heave motion of the floater as well as the motion of the internal free surface under incident wave excitation are computed and studied for the spar-like structure.

Optimization and Evaluation of Naturally Ventilated BIPV Façade Design

To improve the photovoltaic (PV) power generation, the temperature control measures and optimization of BIPV systems are critical, particularly in tropical weather. There are two categories of cooling mechanisms, i.e. passive and active cooling. In the present study, a simplified numerical model is set up to evaluate the effect of passive cooling of BIPV façades with various configurations, including the PV periphery openings (i.e. area ratio), behind air cavity depth, wind velocity and attack angle (0 to 90 degrees) on the cell temperature of BIPV module. A parametric study is performed. Three-dimensional computational fluid dynamics (CFD) simulation is applied to predict the cell temperatures under various BIPV façade configurations and environmental conditions. The results of the CFD model show that in the case where the areas of the top and bottom openings are equal, there is limited air ventilation at the behind air cavity. However, the BIPV surface temperature has a significant drop when the inlet opening at the bottom is enlarged, compared with that of the same area of inlet and outlet. Changing the wind attack angle from 0º to 60º has limited effect on the BIPV cell temperature, which results in a variation of less than 5 ºC. However, a dramatic temperature drop of around 15ºC is observed when the attack angle is larger than 60º. The influence of air cavity depth is studied with the fixed top and bottom opening size ratio. By varying the air cavity depth from 30 to 200 mm, a lower PV cell temperature can be achieved.

Highly Ordered Microscale-Pyramidal-Structure-Arrayed Silicon Membranes for Filter Applications.

Microscale-pyramidal-structure-arrayed patterned silicon membranes are manufactured using semiconductor processes and potassium hydroxide (KOH) etching techniques for filter applications. The silicon nitride on silicon on the insulator wafer functions as a masking layer, and the roughness of the silicon (100) plane strongly depends on the etching temperature and KOH concentration. To fabricate the membrane filter, a series of dry and wet etching using 45 wt% KOH solutions at the constant temperature of 70 °C was performed. With the dry and wet etching, micro-pyramidal arrays with 300 μm top and 16-20 μm bottom opening sizes were created. The morphological structures were analyzed using scanning electron microscopy. The manufactured membranes were tested as optical directional filters and particle filters.

Study on natural ventilation driven by a restricted turbulent buoyant plume in an enclosure

Vertical thermal stratification will be produced by buoyant plumes in a naturally ventilated enclosure. The buoyant plume located near the wall or corner of a ventilated enclosure will be restricted by the wall or corner during the rising process. Theoretical models are deduced and validated to quantitatively predict the thermal stratification height of an enclosure containing a buoyant plume restricted by a wall or corner. The theoretical models can describe the relationship between the thermal stratification height and the height difference between the top and bottom openings of the enclosure, the effective area of the top and bottom openings of the enclosure and the distance between the plume and the wall or the corner. Thresholds for the distance between the plume and the side boundary are defined to determine whether the plume is restricted by the side boundary. Simultaneous equations containing the enclosure dimensions are proposed to predict the thresholds. These results could be used as a reference on natural ventilation design for buildings containing restricted heat sources to make full use of the effect of thermal plumes and create a suitable indoor environment.

Study on thermal stratification of an enclosure containing two interacting turbulent buoyant plumes of equal strength

The emptying-filling box model with two interacting turbulent buoyant plumes of equal strength is investigated in this paper using theoretical analysis and numerical simulation. Theoretical models are deduced and validated to quantitatively predict the thermal stratification height of an enclosure containing two interacting buoyant plume sources with different separations between the two plumes. The variation in the thermal stratification height with the separation between the two plumes is validated by numerical simulation. A threshold for the separation between two plumes is defined to determine whether the two buoyant plumes in the enclosure are interacting or independent, which is also confirmed by numerical simulation. Simultaneous equations containing height difference between the top and bottom openings of the enclosure and effective area of the top and bottom openings of the enclosure are proposed to predict the threshold. These results can be used as a reference on natural ventilation design for buildings with interacting heat sources to make use of the effect of indoor thermal plumes and create a suitable indoor environment.

Melting test of penetrating tube through BWR-RPV bottom wall

Melt behavior of a BWR in-core monitor (ICM) guide tube, which penetrates a RPV bottom wall, under a severe accident condition was tested using a corium with a mixture of UO2, ZrO2 and Zr. There are several BWR-ICMs; two of them are a short range monitor (SRM) and an intermediate range monitor (IRM), which are made of stainless steel, have the same tube dimensions and the bottom ends of the tubes open to the drywell (or, the pedestal region). In the test, the full scale SRM/IRM guide tube with the same dimension as one of Fukushima Daiichi Unit-1 but short length, was installed in the lower crucible which simulated the lower plenum and which bottom simulated the RPV bottom wall with about 200 mm thickness. The melt corium was generated in the upper crucible and it was discharged into the lower crucible. The test result showed that:(1)The corium discharged into the lower plenum attacked the guide tube first resulting in the tube melt from the top and then accumulated in the lower plenum.(2)Small amount of corium had fallen out from the bottom opening of the tube into the pedestal as particles, and such outflow stopped soon because a stainless steel melt had solidified in the tube and blocked the flow path.(3)The depth of the melt ingression into the tube was 60–65 mm from the inner surface of the RPV bottom wall, where the tube was completely blocked by the solidification of steel melt and no oxide melts had ingressed there.

Part II: Thermal analysis of naturally ventilated BIPV system: Modeling and Simulation

This is the second part of a two-part study based on the thermal behaviour of a naturally ventilated BIPV systems. In the first part an experimental analysis of the thermal behaviour of a naturally ventilated BIPV system is presented and two new correlations for the estimation of the convective heat transfer coefficients in the air gap between the PV panel and a second skin are given, for windy and non-windy conditions. The present study (second part) presents a simulation based thermal analysis of a naturally ventilated vertical BIPV system. The simulation model is created using the developed equations for the estimation of the convective heat transfer coefficients presented in the first part of the present study, and the model is validated with the use of experimental data shown in the first part as well. The experimental based correlations are imported in the mathematical model, in order to be able to investigate the effect of other parameters on the thermal behaviour of the system such as the height of the system, the size of the air gap and the air velocity in the duct. These parameters are not easy to be investigated experimentally and their investigation would be very time consuming. The simulation model has a good agreement with the experimental results. The results shown that an air gap of 0.1 m can create adequate air flow on naturally ventilated systems and can ensure low PV temperatures to avoid efficiency decrease. This can be done when the air gap has bottom and top openings to allow air circulation. In taller systems, the temperatures are higher and there is a drop of the efficiency of the system.

A new lumped parameter model for the design of the free-flooded ring transducer

The free-flooded ring (FFR) transducer is the well-known low-frequency sound sources in underwater because of its broad operating frequency bandwidth and relatively small size. Many previous studies have been performed that predict the characteristics of an FFR transducer using an equivalent circuit model (ECM), a type of lumped parameter model (LPM) because an ECM is widely used to understand the properties of such transducers in the design process. However, it is quite difficult to predict the characteristics of an FFR transducer because the acoustic field is generated from its top and bottom openings, connected by the inner fluid, as well as the cylindrical ring surface. In this study, the authors investigated an ECM of an FFR transducer. The ECM consists of three parts: the piezoelectric ring, the cylindrical cavity, and the radiation load. In addition, an LPM which can consider mutual radiation loads was proposed to improve the accuracy of the model. The proposed models were compared and verified using commercial finite element method (COMSOL Multiphysics). We confirmed that LPM can predict characteristics of FFR transducer more accurately than ECM. [This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (Grant No. 2016R1E1A2A02945515).]

Theoretical equation of initial top-coal boundary in longwall top-coal caving mining

The theoretical equation of initial top-coal boundary (ITCB) is one of fundamental problems of top-coal drawing law in longwall top-coal caving (LTCC) mining. The granular mechanical model of ITCB is established based on loose medium flow field theory. By analysing stressed top-coal on ITCB along section of coal seam thickness and face advancement directions, theoretical equation of ITCB is deduced respectively in two conditions of first gangue drawing out and excessive gangue drawing out. The theoretical equation is further modified by a correction coefficient k, which is given by a large number of experimental data. Meanwhile, it is found that ITCB at excessive gangue drawing out condition is in special shape that the top opening is elliptical and bottom opening is rectangle. The theoretical equation of ITCB can provide meaningful guidance to improvement of top-coal recovery ratio in LTCC.

Sand control in oil and gas wells using slotted and perforated tubing design

Sand production is a prevalent problem associated with continued production of hydrocarbon in unconsolidated sandstone reservoir. As sand accumulates in the bottom-hole over time, it reduces permeability, chokes flow line and well-head equipment, and increases complexity of handling. To address this issue, a tubing attached secondary sand screen can reduce the need of expensive intervention jobs. This paper illustrates the design and calculation for a modified tubing to prevent sand from entering the production tubing while increasing the inflow area into the tubing thus addressing the problem of sanding as well as pressure drop due to flow restriction. The concept of inflow area increase is illustrated as to design the modified tubing to produce through the lateral surface instead of the conventional bottom circular opening of the tubing. The net increase in the new inflow area with respect to conventional inflow from bottom of tubing is discussed.

Hydrodynamic Study on Water Column Oscillation of Varying Cross-Sectional Moonpool and Its Effect on Resistance of a Drill Ship

A moonpool is meant for access to the underwater part of the ship from onboard. It is a vertical opening along the depth having an effect on the performance of the floating platform. Inside the moonpool, water motions in horizontal plane is called sloshing and in vertical planes it is called piston mode. Moonpool causes deck wetness and sometimes results in the downtime of the platform. It is the necessity of the operator to be at the safe conditions of platform facing varied environmental conditions. In the present study, vessel response in the region of moonpool resonance was investigated with different shapes of moonpool and comparison is made with Molin's (2001, “On the Piston and Sloshing Modes in Moonpools,” J. Fluid Mech., 430, pp. 27–50.) theoretical and Fukuda's (1977, “Behavior of Water in Vertical Well With Bottom Opening of Ship and Its Effects on Ship-Motion,” J. Soc. Nav. Archit. Jpn., 1977(141), pp. 107–122.) empirical formulas. It is seen that there is a shift in the frequency of resonance based on moonpool shapes. The effect of moonpool on the ship motion with forward speed is also attempted in this paper. Proven packages are used to calculate the calm water resistance of the ship with moonpool of various cross section. Wave making coefficient of the ship is modified due to opening to accommodate the moonpool. The openings to accommodate moonpool causes further entry of water both zero and nonzero Froude number especially in the presence of waves.