Saturated Liquid Flow Research Articles

Flow film boiling on a sphere in the mixed and forced convection regimes

Saturated flow film boiling on a sphere has been numerically studied in this work for both vertical and horizontal flow configurations. The simulations were performed using a numerical methodology developed by the authors for boiling flows on three-dimensional unstructured meshes. For interface capturing, the coupled level set and volume of fluid method is used. The interface evolution, vapour wake dynamics and heat transfer have been thoroughly investigated by varying the saturated liquid flow velocity, sphere diameter and wall superheat. The relative importance of both the buoyancy and the inertial forces is described in terms of the Froude number $(Fr)$ . The vapour bubble evolves periodically at low $Fr$ values, while a stable vapour column develops at high $Fr$ values. The interface evolution pattern obtained in the present work is in good agreement with the results of experimental studies available in the literature. For all the values of $Fr$ , a stable vapour column develops for a large-diameter sphere and releases vapour bubbles of varying sizes. Furthermore, for a large-diameter sphere, surface capillary waves are observed at the interface, similar to the observations of some of the experimental studies available in the literature. The flow in the liquid and vapour wakes appears to be strongly coupled. The heat transfer in the present work is estimated using the spatially and temporally averaged Nusselt numbers. Finally, an fast Fourier transform analysis of the space-averaged Nusselt number reveals a strong interaction among the different forces.

A new model to predict the small-hole decompression process of long CO2 pipeline

CO2 pipeline transportation is considered as an economical and safe way of moving large quantities of CO2 in Carbon Capture Utilization and Storage (CCUS) projects. However, design and planning of CO2 pipelines passing through populated areas require careful risk assessment of accidental pipeline failure scenarios leading to CO2 pipeline decompression. In this study, a new zero-dimensional multi-stage outflow model describing transient decompression of CO2 is developed. The model accounts for the experimentally observed liquid level variation along the pipeline and uses the liquid volume fraction threshold parameter (αt) to mark the end of the saturated liquid flow decompression stage. Besides, the Lee model is applied to describe the mass transfer in gas-liquid phases. The model was validated against experimental data obtained large-scale pipeline decompression tests and can be recommended for simulation of outflow of supercritical and liquid CO2 from pipelines longer than 258 m and the orifice-to-pipeline diameter ratios smaller than 0.21. The advantage of this model lies in its use of the relatively simple Vessel Blowdown Model (VBM) to accurately model the depressurization process. It addresses the inconvenience posed by the heavy computational burden of high-dimensional models when predicting long-duration leakages in large-capacity pipelines.

A two-dimensional numerical study of film boiling over an elliptical cylinder in the mixed regime under aiding and orthogonal saturated liquid flow configurations

Abstract

Flow-boiling canopy wick for extreme heat transfer

The maximum theoretical boiling heat transfer rate qmax is set by interface unidirectional thermal vapor flux, and quest continues for achieving a high fraction of it under saturated liquid flow. We introduce the flow-boiling canopy wick (FBCW) employing film (meniscus) evaporation and perforated screenlayer separating the liquid stream from the underlying vapor space. The vapor vents continuously through periodic perforations, in contrast to plain surface which becomes completely covered by vapor at high heat flux. The FBCW allows streamwise liquid tracks on the screenlayer between perforations providing capillary liquid flow toward heated surface and evaporation on high-effective-conductivity monolayer wick. Under extreme heat flux, various hydrodynamic limits prevent liquid supply and vapor removal, i.e., the capillary-viscous, wick superheat, perforation pressure drop and chocking and liquid-vapor stability limits. The liquid and vapor inertiae control the streamwise continuous liquid track (with isolated and/or merged vapor track) and for saturated water at 1 atm CFD and wick pressure drop predict heat flux up to 0.1qmax = 20 MW/m2, an order-of-magnitude larger than the nucleate flow-boiling limit. The concept of replacing the chaotic nucleated bubbles with the structured, continuous vapor venting in the periodic FBCW transforms boiling heat transfer and its upper limit.

Computational modeling of reactive multi-phase flows in porous media: Applications to metals extraction and environmental recovery processes

A computational modeling framework is described for the analysis of multi-phase flows in reactive porous media targeted at the metals recovery through stockpile leaching and in environmental recovery processes. These systems involve a complex suite of interacting fluid, thermal and chemical reaction physics in complex geometries, which in the case of heap leaching actually grow with time, and varying environmental conditions. The computational models of such processes need to account for variably saturated liquid flow in porous media, gas flow through porous media, together with the transport of many species in one of these fluid phases plus multi-phase heat transfer and mass transfer arising from a range of phase change and gas–liquid–solid chemical reaction processes. This contribution describes just such a development of a three dimensional modeling framework which is applied to the heap leaching of gold, silver and copper in a variety of contexts.

Simulation technology to support base metal ore heap leaching

A simulation framework is outlined for the analysis of the operation of both the heap and the associated water balance circuit for the leaching of primary metal ores. The heap simulation is based on a detailed computational model of the leaching process. The process chemistry, including reactants in the gas–liquid–solid matrix, gas flow, variably saturated liquid flow, species transport in both phases, heat transport, and biomass growth and catalysis, is accounted for in models that are equally applicable to simple and complex geometries. The leaching models are contained within the PHYSICA computational modelling environment that includes a powerful multiphase computational fluid dynamic (CFD) solver enabling reactive flow simulation through arbitrarily complex geometries. Tools have been developed in one-, two- and three-dimensions to capture a variety of aspects of the leaching process behaviour. By careful choice of tools, the framework can be applied to a wide range of leaching problems from small scale (e.g. analysis of column tests and drip emitter spacing) through to full scale heap simulation. An optimised version of the heap leach model is itself embedded within a simulation environment that exploits the BILCO mass balance software to enable dynamic simulation of the water balance within the whole plant circuit.

Treatment of milk industry effluent by dissolved air flotation

In this work, the application of the flotation technique by dissolved air (FAD) to the treatment of milk industry effluent (milky effluent) is analyzed. Initially, batch studies were carried out in a column built of acrylic with an external diameter of 2.5 cm and 50 cm in height. Afterwards, the performance of a flotation tank with a 5.5 L capacity in the treatment of the milky effluent was addressed. In continuous mode of operation, separation efficiencies up to 90% were obtained for the experiments carried out at a saturation pressure of 4 atm and having a ratio of feed flow rate (Qa) to saturated liquid flow rate equal to 1. The separation efficiency for flocculated milk was estimated from the overall mass balance for the flotation tank. Separation efficiencies obtained agreed very well with the experimental results collected for Qa/QLs ratios lower than 1.

Subcooled and saturated liquid flow through valves and nozzles

This article discusses the decrease in flow capacity of valves and nozzles as the temperature of the flowing liquid increases. It was found that the mass flow capacities of both, valves and nozzles will typically decrease to one-third of their value when going from a highly subcooled liquid flow to saturated liquid flow. Test results of subcooled and saturated liquid flow through industrial valves and nozzles are presented. A new mass flow rate model for flow capacity prediction of valves and nozzles exposed to subcooled and saturated liquid flow is developed.

On the solution of transient free-surface flow problems in porous media by finite-difference methods

Numerical solutions are obtained for a few initial-boundary-value problems in free-surface, saturated liquid flow through porous media. The “exact” differential equations governing the problems have been approximated by finite-difference equations, and the resulting system of algebraic equations is solved by using an automatic digital computer. Only two-dimensional, homogeneous and isotropic flow models — including infiltration — are dealt with, but in principle there is little difficulty in extending the models to nonhomogeneous and anisotropic media. Though also possible in principle, an extension to three dimensions will demand a drastic increase in the necessary storage space of the computer. The question of computational stability of the difference schemes adopted is considered. Good agreement with some results of other calculations is found for the two distinct models that have been studied — one “ditch drainage” and one earth dam model.