J.W. (Willem) Haverkort

Delft University of Technology | TU · Department of Process and Energy (P&E)

The use of gas diffusion electrodes that supply gaseous CO2 directly to the catalyst layer has greatly improved the performance of electrochemical CO2 conversion. However, reports of high current densities and Faradaic efficiencies primarily come from small lab scale electrolysers. Such electrolysers typically have a geometric area of 5 cm2, while...

Membraneless parallel-plate electrolyzers use electrolyte flow to avoid product crossover. Using a mixture model neglecting inertia, and assuming an exponential gas fraction profile, we derive approximate analytical expressions for the velocity profile and pressure drop for thin plumes. We verify these expressions using numerical solutions obtained...

Both daily and seasonal fluctuations of renewable power sources will require large-scale energy storage technologies. A recently developed integrated battery and electrolyzer system, called battolyser, fulfills both time-scale requirements. Here, we develop a macroscopic COMSOL Multiphysics model to quantify the energetic efficiency of the battolys...

The electrochemical reduction of CO2 on planar electrodes is limited by its prohibitively low diffusivity and solubility in water. Gas-diffusion electrodes (GDEs) can be used to reduce these limitations, and facilitate current densities orders of magnitude higher than the limiting current densities of planar electrodes. These improvements are accom...

Reducing the gap between the electrodes and diaphragm to zero is an often adopted strategy to reduce the ohmic drop in alkaline water electrolyzers for hydrogen production. We provide a thorough account of the current–voltage relationship in such a zero-gap configuration over a wide range of electrolyte concentrations and current densities. Include...

JOREK is a massively parallel fully implicit non-linear extended magneto-hydrodynamic (MHD) code for realistic tokamak X-point plasmas. It has become a widely used versatile simulation code for studying large-scale plasma instabilities and their control and is continuously developed in an international community with strong involvements in the Euro...

Flow-through electrolyzers, with flow parallel to the current, are used in a wide range of industrial applications. The presence of flow avoids concentration gradients but can also be used to separate evolved gases, allowing membrane-less operation. In this work, we propose a simple multiphase flow-through electrode model. We derive and experimenta...

The diffusion layer is a crucial part of most fuel cells and electrolyzers. We analytically solve a simplified set of visco-capillary equations for the gas and liquid saturation profiles inside such layers. Contrary to existing numerical simulations, this approach allows us to obtain general scaling relations. We derive simple explicit equations fo...

Under alkaline conditions, hydroxide ions can deplete at the anode of a water electrolyser for hydrogen production, resulting in a limiting current density. We found experimentally that in a micro-porous separator, an electro-osmotic flow from anode to cathode lowers this limiting current density. Using the Nernst-Planck equation, a useful expressi...

JOREK is a massively parallel fully implicit non-linear extended MHD code for realistic tokamak X-point plasmas. It is a widely used versatile code for studying large-scale plasma instabilities and their control and is continuously developed in an international community with strong involvements in European fusion research. This article gives a com...

Combined diffusion, migration, and advection of ions in a binary electrolyte plays a role in various applications, including water electrolysis, electrodeposition, deionization, and electrophoresis. Here we analyze a dilute binary electrolyte with arbitrary ion valencies in a porous or nonporous medium using the one-dimensional Nernst-Planck equati...

A new compact electrode architecture with hollow pillar-shaped anodes and cathodes arranged in a ‘checkerboard’ pattern is analysed and shown to be equivalent to a particular arrangement of corrugated plate electrodes. Because all four sides of the flow channels are electrodes, this design takes up at least 1.5 to two times less volume compared to...

Using electrodes or catalytic layers that are porous increases the reactive surface area but also the distance that ions and electrons have to travel. Thicker electrodes, through their larger surface area, reduce the activation overpotential but increase the ohmic losses. There will therefore be an electrode thickness for which the voltage losses a...

Ultrasound was introduced to assist CO2 stripping from lean 30 wt% MEA aqueous solutions in a reboiler. The effect of ultrasound on CO2 stripping was investigated at 2.5 bar(a) under two pressure control methods, solenoid operated on/off valve (OOV) and manual needle valve (NV) method. The results show that the CO2 stripping rate can be improved si...

Ultrasound image velocimetry (UIV) allows for the non-intrusive measurement of a wide range of flows without the need for optical transparency. In this study, we used UIV to measure the local velocity field of a model drilling fluid that exhibits yield stress flow behavior. The radial velocity profile was used to determine the yield stress and the...

Numerical simulations form an indispensable tool to understand the behavior of a hot plasma that is created inside a tokamak for providing nuclear fusion energy. Various aspects of tokamak plasmas have been successfully studied through the reduced magnetohydrodynamic (MHD) model. The need for more complete modeling through the full MHD equations is...

Nonlinear electromagnetic stabilization by suprathermal pressure gradients found in specific regimes is shown to be a key factor in reducing tokamak microturbulence, augmenting significantly the thermal pressure electromagnetic stabilization. Based on nonlinear gyrokinetic simulations investigating a set of ion heat transport experiments on the JET...

One of the key challenges for plasma theory and simulation in view of ITER is to enhance the understanding and predictive capability concerning high-performance discharges. This involves, in particular, questions about high-beta operation, ion temperature profile stiffness, and the physics of transport barriers. The goal of this contribution is to...

Recent experimental observations at JET show evidence of reduced ion temperature profile stiffness, hypothesised to be due to concomitant low magnetic shear (s) and significant toroidal rotational flow shear. Non-linear gyrokinetic simulations are performed, aiming to investigate the physical mechanism behind the observations. A comprehensive set o...

A radially decreasing toroidal rotation frequency can have a stabilizing effect on nonaxisymmetric magnetohydrodynamic (MHD) instabilities. We show that this is a consequence of the Coriolis effect that induces a restoring pressure gradient force when plasma is perturbed radially. In a rotating cylindrical plasma, this Coriolis-pressure effect is c...

The influence of toroidal plasma rotation on the existence of reversed shear Alfvén eigenmodes (RSAEs) near their minimum frequency is investigated analytically. An existence condition is derived showing that a radially decreasing kinetic energy density is unfavourable for the existence of RSAEs. The Coriolis effect is typically unfavourable for mo...

The ideal magnetohydrodynamic stability is investigated of localized interchange modes in a large-aspect ratio tokamak plasma. The resulting stability criterion includes the effects of toroidal rotation and rotation shear and contains various well-known limiting cases. The analysis allows for a general adiabatic index, resulting in a stabilizing co...

As a result of toroidal rotation, sequences of new global modes are predicted to arise in magnetically confined plasmas. The frequencies of these Alfvén modes lie inside gaps of the continuous magnetohydrodynamic (MHD) spectrum that are created or enlarged by toroidal flow. The numerically obtained results are compared with an analytical investigat...

As a result of toroidal rotation, sequences of new global modes are predicted to arise in magnetically confined plasmas. The frequencies of these Alfv\'en modes lie inside gaps of the continuous magnetohydrodynamic (MHD) spectrum that are created or enlarged by toroidal flow. The numerically obtained results are compared with an analytical investig...

The magnetohydrodynamic effects associated with a magnetic field perpendicular to the movement of insulating inclusions or bubbles in a conducting liquid are investigated in this article. An increase in drag coefficient as a result of the presence of a magnetic field is argued to have a significant effect on their terminal rise velocity. Inside a c...

The manipulation of magnetic particles in a continuous flow with magnetic fields is central to several biomedical applications, including magnetic cell separation and magnetic drug targeting. A simplified two-dimensional (2D) equation describing the motion of particles in a planar Poiseuille flow is considered for various magnetic field configurati...

The aim of Magnetic Drug Targeting (MDT) is to concentrate drugs, attached to magnetic particles, in a specific part of the human body by applying a magnetic field. Computational simulations are performed of blood flow and magnetic particle motion in a left coronary artery and a carotid artery, using the properties of presently available magnetic c...

The effect of electric and magnetic fields on a conducting fluid surrounding an insulating object plays a role in various industrial, biomedical and micro-fluidic applications. Computational simulations of the magnetohydrodynamic flow around an insulating sphere, with crossed magnetic and electric fields perpendicular to the main flow, are performe...

A comprehensive computational model for simulating magnetic drug targeting was developed and extensively tested in a cylindrical geometry. The efficiency for particle capture in a specific magnetic field and geometry was shown to be dependent on a single dimensionless number. The effect of secondary flows, a non-Newtonian viscosity and oscillatory...