Effect of Ultrasound on Calcium Carbonate Crystallization

Scaling comprises the formation of hard mineral deposits on process or membrane equipment and calcium carbonate is the most common scaling salt. Especially in reverse osmosis (RO) membrane systems, scale formation has always been a serious limitation, causing flux decline, membrane degradation, loss of production and elevated operating costs. In this work a novel concept is proposed for the prediction of scale formation tendency. By enhancing the crystallization (kinetics) locally and monitoring the process itself, scaling can be predicted accurately before it occurs in the bulk solution. This will result in better scaling risk assessment, improving chemical dosage (preventing overdosing) and prevent the necessity of cleaning or membrane replacement. Ultrasound is selected as possible method for crystallization enhancement. Consequently, the topic of this research is the effect of ultrasound on crystallization of calcium carbonate.BiotechnologyApplied Science

Deterministic displacement of particles and oil droplets in a cross-flow microsieve module

Our investigation aims to apply Deterministic Lateral Displacement (DLD) to separate (deformable) particles or droplets from dispersions on industrial scale. DLD is a promising technique because it can separate particles smaller than the pores. Previous work shows how to manipulate the critical particle diameter in a sieve-based lateral displacement system by modifying the hydrodynamics. In this study, we apply this fundamental understanding of the DLD separation principle to deterministically displace particles in a cross-flow microsieve module. First, two-dimensional simulations of the fluid dynamics in this cross-flow module were performed to investigate the hydrodynamic conditions required for particle displacement. Next, these simulations were compared with the flow fields visualized in the experimental setup. In addition, high speed recordings confirmed deterministic displacement of particles and oil droplets over the microsieve surface. Last, the systems performance was evaluated by measuring the transmission of rigid PMMA particles and deformable hexadecane droplets and the particle size distribution for different operation conditions. These results clearly demonstrate that the DLD principle can be effectively applied in a cross-flow microsieve module. With this, the application of this microfluidic separation principle to separate particles or droplets (1–20 µm) from dispersions on industrial scale has become realistic

Sieve-based lateral displacement technology for suspension separation

Sparse lateral displacement arrays are easier to scale up than full deterministic lateral displacement arrays or deterministic ratchets, because they require lower pressure drop and simplify the construction of the device. However, the asymmetry of sparse arrays leads to a non-homogeneous pressure distribution with as a consequence an uneven flow field and limited separation performance. Furthermore, the construction of high throughput displacement sparse ratchet devices that allow separation of small particles is challenging. Therefore, in this study we investigated the use of sieves to replace obstacles in sparse systems. Moreover, we investigated a strategy to optimize the separation performance by adjusting the internal pressure distribution. Our experiments showed in first instance that the introduction of sieves negatively affects separation performance, which was explained by the lower porosity of the sieves. However, via fluid flow calculations and high-speed camera analyses we found that pressure distribution can be optimized by adapting the flow rates of the different outlets preventing high pressure drop across the obstacles arrays near the bottom of the device. Experimental separation data for adjusted outlet flow conditions indeed showed better particle displacement, especially in the bottom region, and as a result improved separation behavior. These findings demonstrate the potential of the scalable sieve-based lateral displacement device to effectively separate particles

Reducing the critical particle diameter in (highly) asymmetric sieve-based lateral displacement devices

Deterministic lateral displacement technology was originally developed in the realm of microfluidics, but has potential for larger scale separation as well. In our previous studies, we proposed a sieve-based lateral displacement device inspired on the principle of deterministic lateral displacement. The advantages of this new device is that it gives a lower pressure drop, lower risk of particle accumulation, higher throughput and is simpler to manufacture. However, until now this device has only been investigated for its separation of large particles of around 785 μm diameter. To separate smaller particles, we investigate several design parameters for their influence on the critical particle diameter. In a dimensionless evaluation, device designs with different geometry and dimensions were compared. It was found that sieve-based lateral displacement devices are able to displace particles due to the crucial role of the flow profile, despite of their unusual and asymmetric design. These results demonstrate the possibility to actively steer the velocity profile in order to reduce the critical diameter in deterministic lateral displacement devices, which makes this separation principle more accessible for large-scale, high throughput applications.</p

Selective particle separation on centimeter scale using a dual frequency dynamic acoustic field

This study investigated the application of dual-frequency type dynamic acoustic fields for size-selective particle separation on centimeter scale in a continuous flow. The 3D-printed X-shaped prototype has two inlets and two outlets. The dynamic acoustic field is generated by two transducers positioned under an angle of 60° and operating at slightly different frequencies. The acoustic reflections are eliminated by placing sound-absorbing material inside the prototype and the non-resonant operation is confirmed by the electrical admittance measurements. Numerical calculations suggested that pressure generated by each transducer does not need to have equal amplitude. Computer simulations and lab experiments were carried out for different frequency differences and flow rates. The results demonstrated the ability of dual-frequency dynamic acoustic fields for size-selective particle filtration on centimeter scale, with a total flow rate up to.1Lh-1.</p

A comparison of microfiltration and inertia-based microfluidics for large scale suspension separation

Separation of suspensions can be carried out by microfiltration and microfluidic techniques, although both rely on different principles. Conventional microfiltration involves retention of particles by a porous membrane, but is limited by (irreversible) particle accumulation and concentration polarization that can only be (partially) controlled by back pulsing that transfers particles back into the bulk. Microfluidic separation devices employ a combination of inertial forces and sometimes geometric constraints to control particle migration behaviour, which allows splitting of suspensions into concentrated and diluted streams.Considering their effectiveness, inertia-based microfluidic separation is regarded an interesting alternative to microfiltration; therefore, this paper focusses on the use of inertial forces in suspension separation. This resulted in the selection of three concepts, which were: (1) fluid skimming, which is a combination of microfiltration and controlled particle migration behaviour, (2) spiral inertial microchannel separation, in which particles migrate fast towards an equilibrium position, and (3) sparse deterministic ratchets, which use geometric interactions to induce particle migration. In a concluding section, the application of controlled migration behaviour in relation to scalability of inertia-based microfluidic separation techniques and the effect of suspension properties on separation are discussed in detail

Visualizing the hydrodynamics in sieve-based lateral displacement systems

Deterministic lateral displacement (DLD) systems structure suspension flow in so called flow lanes.The width of these flow lanes is crucial for separation of particles and determines whether particles with certain size are displaced or not. In previous research, separation was observed in simplified DLD systems that did not meet the established DLD geometric design criteria, by adjusting the outflow conditions. We here investigated why these simplified DLD systems are able to displace particles, by experimentally investigating the hydrodynamics in the device. Flow lanes were visualized and the local flow velocities were measured using μPIV and compared with 2D fluid dynamics simulations. The size of the flow lanes strongly correlates with the local flow velocity (Vy and Vx), which depends on the hydrodynamics. Therefore, the geometric design criteria of DLD devices is in fact just one method to control the local hydrodynamics, which may also be influenced by other means. These findings give a new perspective on the separation principle, which makes the technique more flexible and easier to translate to industrial scale.<br/

Selective Particle Filtering in a Large Acoustophoretic Serpentine Channel

The objective of this study is to investigate the performance of a serpentine channel for acoustically driven selective particle filtering. The channel consists of sharp corners and straight sections, and the acoustic field is affecting the particles throughout the channel. A prototype of the separator channel is manufactured using 3D printing. Acoustic waves are generated by a piezoelectric transducer operating near 2 MHz. Computer simulations are carried out to explore and visualize the flow field and acoustic field in the separator. Selective particle trapping is aimed to be achieved in the hairpin sections, which is confirmed by experiments. Spherical polyethylene particles of 34 µm, 70 µm and 100 µm diameter are used to demonstrate selective trapping by adjusting the flow rate in the channel or voltage input to the transducer. In addition, wheat beer containing yeast up to 20 µm size is selectively filtered by adjusting the flow rate to the channel. Experiments demonstrate that selective particle filtering is possible in the serpentine channel as both methods yield clear separation thresholds.</p

Ultralow hysteresis superhydrophobic surfaces by excimer laser modification of SU-8

We present a new and simple method to produce superhydrophobic surfaces with ultralow hysteresis. The method involves surface modification of SU-8 using an excimer laser treatment. The modified surface is coated with a hydrophobic plasma-polymerized hexafluoropropene layer. The advancing and receding water contact angles were measured to be approximately 165°. The achieved water contact angle hysteresis was below the measurement limit. This low hysteresis can be ascribed to nanoscale debris generated during the excimer laser process

Dynamic acoustic fields for size selective particle separation on centimeter scale

Dynamic acoustic fields offer an interesting alternative for acoustic standing-wave fields in acoustic separation applications. This paper reports on an investigation of two methods for generating dynamic acoustic fields and their applicability for selective particle separation. The first method applies a dual-frequency excitation to generate a standing-wave field that in which the pressure nodes travel at constant velocity. The second method uses frequency-ramping, where the velocity of the nodes in the resulting standing-wave field depends on both time and position. Both methods were investigated analytically and with computational models, yielding a dimensionless number that predicts particle behavior without having to solve the differential equations of motion. This dimensionless number can also be used to estimate the acoustic pressure in practical applications. Experiments carried out with polyethylene particles and the two prototypes confirmed the theoretical and numerical predictions. Both methods are suitable for selective particle separation applications