Ole Jørgen Nydal

Droplet Size Measurements in Oil–Water Dispersions: A Comparison Study Using FBRM and PVM

Droplets in oil–water dispersions are measured using two different measurement techniques. Both focused beam reflectance measurements (FBRM) and particle video microscopy (PVM) are applied simultaneously in order to obtain direct comparison. A real-time chord length distribution (CLD) is obtained from the FBRM. The picture series by the PVM are post-processed to obtain droplet size distributions (DSDs). By measuring particle samples, it was shown that PVM is able to detect the correct size distribution. Using the PVM images, the uncertainty of the CLD was quantified. Two empirical approaches to convert the CLD to the correct DSD are documented. GRAPHICAL ABSTRACT

An Introduction to Discrete Element Method: A Meso-scale Mechanism Analysis of Granular Flow

The phenomenon of granular flows appears frequently in industrial and daily life. The particle–particle interaction plays an important role in granular flows, which makes the flows have some strong nonlinear characteristics and so different from the normal materials, either solids or liquids. Discrete element method (DEM) is a powerful tool to catch this interaction in meso-scopic scale. A brief review of DEM is presented, including some of our new works in this area. DEM can also be coupled with other CFD methods for simulations of solid–liquid suspension flow. An example of such coupling is presented in this article as well. GRAPHICAL ABSTRACT

Applying Multiple Grids to a Multi-Field Model – The Resolution Requirements of Individual Fields in the Two-Fluid Model for 1D Pipe Flow

Modeling two-phase pipe flow commonly involves gas and liquid fields which can differ greatly in density and compressibility. The physical scales governing the dynamics are divided amongst the phases in a way where the numerical grid requirements of one phase may be poorly suited for the other. Adopting a phase discriminating multigrid strategy is therefore an attractive approach, though little is known about how the phase coupled dynamics will respond to separate, non-equivalent numerical grids. The purpose of this article is to explore the resolution sensitivity of the two-fluid model for each phase individually, and examine how the dynamic coupling between phases is maintained across phase-individual grids of unequal coarseness. A dual-grid scheme is proposed and applied to S-riser terrain slugging and roll wave capturing simulations. Resolution sensitivity is checked. It is found that the resolution requirements in both cases are liquid dominated; we are able to reduce the spatial resolution of the gas phase far more than on the liquid phase while retaining physical predictions. The importance of reconstructing local pressure dynamics is demonstrated. GRAPHICAL ABSTRACT

Effective Viscosity for Dispersed Oil–Water Pipe Flow in Different Diameters

Existing prediction models for the effective viscosity of emulsions are typically empirical relations tuned to experimental measurements. Experimental methods like the preparation of stirred oil–water mixtures for rheometers and the use of small-scale flow loops have been used to characterize emulsions. Nevertheless, the extrapolation of these small-scale results to large-scale real systems is still uncertain and deserves further attention. This work reports a study of the effect of the pipe diameter on the effective viscosity of water-in-oil emulsions. Pipe flow experiments were performed with water-in-oil surfactant stabilized emulsions in acrylic pipes with 16, 32, 60, and 90 mm ID. Salt water (3.5% w/v of NaCl, pH = 7.3) and the oils Exxsol D80 (µ = 1.8 mPa s) and Marcol 52 (µ = 10 mPa s) with 0.25% v/v of Span 80 (lipophilic surfactant, HLB = 4.3) were used in the experiments. Pressure drop and droplet sizes were measured for different water fractions and mixture velocities. The effective viscosities calculated from pressure drop results were similar in all pipes up to about 40% water cut. Above 40%, the difference in effective viscosity increases with water cut, being significantly higher for the larger diameters. GRAPHICAL ABSTRACT

Preparing side charging of PCM storage: theoretical and experimental investigation

In Ethiopia, there is an abundant source of solar energy that is estimated to 5.3 kWh/m2/day. However, more than 90% of the society uses biomass as a main source of energy for cooking due to lack of technologies to convert this energy. Replacing these cooking activities by using renewable energy resources decreases pollution and reduces deforestation significantly. Using the solar energy in day time has no problem. For night time however, the system needs some kind of back-up system to make the daytime solar energy available. This back-up should have high-density energy storage and constant working temperature to perform a specific application. Latent heat storage using phase change materials (PCM) is one way of storing thermal energy. In the current study, a latent heat storage that uses a PCM material is used to store the solar energy aimed at utilizing solar energy for cooking Injera, main staple bread in Ethiopia. The PCM is a mixture of 60% NaNO3 and 40% KNO3 that are known as solar salts. The storage has a welded parallel aluminum fins with a gap of 40 mm in between to enhance the thermal conductivity during the charging-discharging process of the storage. The fins are extruded outside of the storage container to enable a side charging technique for the PCM. A prototype was developed with a solar salt of 17.5 kg and is tested for charging-discharging. The numerical simulation done on ANSYS and experimental results show an agreement and the system registered a 41.6% efficiency.