Two-phase slug flows in helical pipes: Slug frequency alterations and helicity fluctuations

Air-water numerical simulations in the slug flow regime have been performed in horizontal helical pipes and the effects of geometries on the flow regime have been investigated. Depending on the length of the helix, outlet slug frequencies have been reduced with various degrees of efficiency. Correlations between mean tangential velocity and helicity density fluctuations have been identified and investigated qualitatively. These flow fields show smaller time scales than those obtained in volume fractions fluctuations. Shifts observed in the tangential velocity and mean helicity fluctuations to smaller time scales (high frequencies) are associated with regime transitions. For a slug flow undergoing a continuous transition to the annular flow regime, it is shown that the presence of slower (low frequencies) helicity fluctuations is attributed to the variations in the axial velocity. Finally, the analysis of the helicity at gas-liquid interface confirms the presence of the mixing zone at the slug front

Statistical model of transient particle dispersion and deposition in vertical pipes

Water droplets in vertical pipes have been investigated to assert the accuracy of a newly developed Lagrangian model for dispersion and deposition implemented in the Open source CFD code OpenFOAM. The transient evolution of the particles dispersion and concentration has been studied for the combined effects of Brownian motion and turbulent dispersion. A parametric study of mesh density has been performed and the influence of the isotropic representation of turbulence discussed. Simulated results have been compared to experimental data from the literature and to results generated with a commercial flow solver. A new model has also been developed to predict the evolution of the droplet concentration and deposition in pipes, based on a statistical description of the dispersion

A numerical study of deep borehole heat exchangers efficiency in unconventional geothermal settings

The geothermal energy industry is facing several challenges related to heat recovery efficiency and economic feasibility. Research on superheated and supercritical geothermal systems is progressing in Europe, triggered by the Iceland Deep Drilling project (IDDP) and the DESCRAMBLE project in Italy. In Iceland, the IDDP-1 well, which reached a magma intrusion at a depth of 2100 m, raised new opportunities to untap the geothermal potential near shallow magmatic intrusions. Given their highly corrosive nature, geothermal fluids weaken the wellbore’s integrity during conventional geothermal production. Closed-loop Deep Borehole Heat Exchangers (DBHE) that do not require fluid exchange between the subsurface and the wells represent a strategic alternative for recovering heat from these unconventional geothermal resources, while minimizing the risk of in-situ reservoir damage. The thermal influence and heat recovery associated with a hypothetical DBHE drilled into the IDDP geological site, were investigated via Computational Fluid Dynamics (CFD), simulating 30 years of production. Two wellbore designs were considered, based on simplified geological properties from the IDDP-1 well description. The results show that, during the first year of production, the output temperature is function of the working fluid velocity before reaching pseudo-steady state conditions. The cooling perturbation near the bottom hole is shown to grow radially from 10 to 40 m between 1 and 10 years of production, and the output power calculated reaches up to 1.2 MWth for a single well. Based on assumptions on well-well distance, the predicted output from a single DBHE is then extrapolated to field scale for comparison with the short-term flow potential shown by the original IDDP1 well. The significantly lower technical risks of a closed-loop DBHE system might outweigh the lower thermal output per well; this is however subject to full economic analysis

Numerical simulation of a Deep Borehole Heat Exchanger in the Krafla geothermal system

The geothermal energy sector is facing numerous challenges related to heat recovery efficiency and economic feasibility. Research on superheated/supercritical geothermal systems is progressing in Europe, triggered by the Iceland Deep Drilling project (IDDP) and the DESCRAMBLE project in Italy. In Iceland, the IDDP-1 well, which reached a magma intrusion at a depth of 2100 m, raised new opportunities to untap the geothermal potential near magmatic intrusions. Given their highly corrosive nature, geothermal fluids weaken the wellbores integrity during conventional geothermal production. Closed-loop Deep Borehole Heat Exchangers (DBHE) that do not require fluid exchange between the subsurface and the wells represent a strategic alternative for recovering heat from these unconventional geothermal resources, while minimising the risk of in situ reservoir damage. The thermal influence and heat recovery associated with a hypothetical DBHE drilled into the IDDP geological settings are investigated via Computational Fluid Dynamics (CFD) techniques, simulating 30 years of production. Two wellbore designs are modelled, based on simplified geological properties from the IDDP-1 well description. The results show that, during the first year of production, the output temperature is function of the working fluid velocity before reaching pseudo-steady state conditions. The cooling perturbation near the bottom hole is shown to grow radially from 10 to 40 m between 1 and 10 years of production, and the calculated output power reaches up to 1.2 MWth for a single well. The heat transfer at the bottom well bore is enhanced by extending the inner well deeper into the ground. Subject to full economic analysis to be performed at field scale, the significantly lower technical risks of the closed-loop DBHE could outweigh the lower thermal output per well compared to theoretical expectations from open-loop Enhanced Geothermal Systems (EGS)

CFD modeling of a high enthalpy geothermal context

The promising development of highly energetic geothermal resources could considerably enhance geothermal power production worldwide. The first attempt at tapping supercritical/heated fluids was made by the Iceland Deep Drilling project (IDDP), but unfortunately a magma layer at a depth of 2,100m was encountered, and the drilling was abandoned. Yet, this drilling operation failure generated new opportunities for assessing the potential power generation close to shallow magmatic intrusions. Detailed numerical methods are required to assess the heat transfer and fluid thermodynamics at wellbore and reservoir scale at near supercritical conditions to provide production scenarios and forecasts as accurate as possible. A primary steady-state study of reservoir and wellbore heat extraction from a geothermal well near a magmatic chamber has been performed with Computational Fluid Dynamics (CFD) techniques. Using simplified geological assumptions based on the IDDP-1 well description, a 2D axisymmetric single phase flow model was developed and its results were compared to those obtained with a full 3D CFD model. The simulated output power simulations reached 25 MW at 350°C and a wellhead pressure of 140 bars. Methodology and results from this study show that CFD techniques can be successfully used to assess geothermal energy outputs for unconventional geothermal wells and can provide details of a vapor superheated flow structure at wellbore-reservoir scale

Scale-up and turbulence modelling in pipes

Large diameter pipes are commonly used for oil and gas transportation. Experimental and numerical results, including turbulence properties, are often obtained for small diameter pipes. Only little information is available for pipes larger or equal to 200 mm. Results obtained with Reynolds Averaged Navier-Stokes (RANS) turbulence models for single phase flow in pipes of different sizes are presented and discussed. The use of non-dimensional data is usually assumed sufficient to present general information and is assumed valid for any size of pipe. The validity of such assumptions has been checked and the flow behaviour in small, medium and large pipes obtained with several of the most common RANS turbulence models, has been established under specific conditions via Computational Fluid Dynamics (CFD) techniques. Although difficulties were sometimes encountered to reproduce correctly the turbulence properties described in the literature with the turbulence models implemented in open source CFD codes, it is shown that a scaling-up approach is valid as the general flow pattern can be predicted by a non-dimensional strategy

Analytical and numerical predictions of the thermal performance of multi-layered lattice structures

The recent development of additive manufacturing has allowed complex geometries such as multi-layered lattice structures to be designed for different applications, including heat transfer. Performing Computational Fluid Dynamics (CFD) analyses on each new design iteration of lattice structures would require high computational time and cost. An analytical model has therefore been developed, able to rapidly and cost-effectively predict the heat transfer of complex lattice structures. The numerical code has been written for a given multi-layered lattice sample and a two-step approach with fin analogy has been applied to determine the mean outlet fluid temperature and the total heat dissipation for air as the working fluid. CFD simulations have also been performed and results compared to the analytical ones. A very good agreement is obtained between numerical and analytical results under the defined industrial operating conditions of the complex lattice structures, showing that such analytical model can be quickly and efficiently applied to evaluate the thermal performance of multi-layered lattice structures

The hydrodynamics of two-phase flows in the injection part of a conventional ejector

The characteristics of two-phase flow through a ‘conventional’ convergent-nozzle in an entrainment chamber of an ejector apparatus are described in this paper. A unique data set comprising 350 data points was generated in an air-water horizontal test-rig. Two sets of flow conditions were established, the first one including high liquid - low gas fluids with void fractions less than 0.55, and the second one involving high gas - low liquid fluids with void fractions greater than 0.75. All considered flow-rates lied within the sub-critical flow region. Two-phase flow pressure drop multiplier based empirical correlations were developed to estimate the total mass flow-rates. In the high liquid region, Morris (1985) correlation was modified, resulting in less than 10% error. In the high gas region, two new correlations were proposed, showing less than 10% and 15% of errors, respectively. The established empirical correlations were related to other available multipliers for different geometric configurations including a Venturi, an orifice plate, a gate valve, and a globe valve and were compared to 20 other void fraction correlations. The Chisholm (1983b) and Huq and Loth (1992) correlations showed the highest similarities to the ones proposed for the high liquid and high gas regions, respectively

Design and optimisation of a 20 MW offshore wind turbine blade

In the global pursuit of Net Zero emissions by 2050, wind turbines have become a leading solution. These renewable energy generators offer a trifecta of benefits, significantly reducing CO2 emissions, minimizing environmental impact, and delivering cost-competitive clean power. However, the key to maximizing their potential lies in the aerodynamic design of the turbine blades. By improving the blade performance, researchers and engineers can significantly increase wind energy capture, propelling wind turbines to the forefront of the global transition to a sustainable future. Higher power generating wind turbines are needed to reach the Net Zero target. By upscaling the “DTU 10 MW Reference Wind Turbine”, this research has achieved an aerodynamically stable 20 MW offshore wind turbine blade design. Variable rotation speed and variable pitch angle configurations have been considered to achieve an ideal power curve. The aerodynamic performance has been evaluated and quantified for a length optimised blade design, wherein the power and thrust have been increased by 80.84% and 88.67%, respectively, at a rated wind velocity of 12 m/s

Experimental study of a single elongated bubble in liquid in under 10-degree upwardly inclined pipes

Two phase flow is of great interest in chemical and petroleum industries, and multiphase pipe flow models with closure relationships require experimental data for their development and validation. However, only little experimental information is available for slightly upward inclined pipes. Experimental investigations of single elongated bubble in marginally upwardly inclined pipes less than 10° have therefore been performed. Observations of the bubble drift velocity along the pipe has been highlighted. The drift velocity data presented here can contribute to improve knowledge of pipe inclination and viscosity dependency in drift velocity correlations. The new data on the bubble characteristics - shape, length, fraction and drift velocity may also provide useful information for the development and validation of numerical models. The measured drift velocity data have therefore been compared with some recently developed bubble velocity correlations