Coalescence Of Water Droplets Research Articles

Demulsification of W/O emulsions induced by terahertz pulse electric fields-driven hydrogen bond disruption of water molecules

Demulsifying highly stable W/O emulsions, composed of heavy oil and water, is crucial for simplifying crude oil processing, reducing production costs, and mitigating environmental pollution. In these emulsions, aromatic components in the oil phase stack via π-π interactions, while hydrogen bonds stabilize the water phase. This leads to the creation of a strong oil-water interface through electrostatic attraction, ultimately hindering water droplet coalescence and oil-water separation. In this study, a 1.0 THz pulse electric field is introduced to effectively disrupt the hydrogen bond network among water molecules by inducing hydrogen bond resonance. This disruption contributes to increased water mobility in the oil phase, weakened stability of the oil-water interface film, and facilitates efficient water droplet coalescence in the oil phase. The results show that throughout the demulsification process, the average number of hydrogen bonds per water molecule rapidly decreases from 1.41 to 1.08 within 100 ps. The upper and lower limits of hydrogen bond lifetimes decrease by 8.12 ps and 3.24 ps, respectively. This indicates a significant disruption in the stability of hydrogen bonds between water molecules. Concurrently, the terahertz pulse electric field disrupts the initially stable oil-water interface film of the emulsion system, leading to a noteworthy reduction in the oil-water interface tension from 54.3 to 39.2 mN·m−1. The self-diffusion coefficient of water molecules increases from 1.33 to 2.62 Å2·ps−1, signifying that water molecules are more inclined to penetrate the interfacial region between the two phases. Additionally, the terahertz pulse electric field induces alterations in the arrangement of water molecules, resulting in the rearrangement of electrons in the water phase and disrupting the originally stable electrical double layer structure of the oil-water interface. This study provides novel insights into the development of efficient and environmentally friendly electric demulsification technologies, holding significant potential for widespread industrial applications.

Behavior of small water droplets in a highly viscous flow in a converging and diverging channel

Understanding the evolution of water droplets moving in a highly viscous bulk flow (e.g., bitumen) has attracted increasing attention in the context of numerous separation technologies due to various issues relating to the environment (re-use of water) and engineering failures (corrosion of pipelines). With this in mind, the main objectives of this work are to explore the dynamics of water droplets with a diameter of seven micrometers, moving in highly viscous bitumen flowing through a smoothly converging and diverging 11-micron channel using three-dimensional (3D) and two-dimensional (2D) droplet-resolved simulations and to adjust an existing population balance model (PBM) to predict geometry-driven coalescence for different flow rates. The Eulerian–Eulerian (EE) method coupled with a new PBM is used to predict the behavior of water droplets with a diameter of 7 μm. Numerical simulations were carried out for various capillary numbers (0.1<Ca<3) and compared with the volume of fluid method combined with the level-set function (CLSVOF). Adaptive mesh refinement (up to six levels) was used in 3D and 2D CLSVOF simulations, producing interface cells measuring up to 30 nm. Good agreement was observed between EE-PBM and CLSVOF models. For comparison, we show the results of 2D CLSVOF simulations. This new PBM model can be used to predict water–oil separation in new cascade-formed geometries to enhance the coalescence of water droplets in highly viscous bulk flows.

Demulsification law of polyether demulsifier for W/O crude oil emulsion containing hydrophobically modified polyacrylamide in water

Hydrophobically modified polyacrylamide (HMPAM) is one of the commonly used polymers for polymer flooding. Because it is water soluble, there are many reports on the impact of HMPAM on the stability and treatment of produced water (it is O/W emulsion), but few reports on its influence on the demulsification of W/O crude oil emulsion. In this paper, firstly, three types of HMPAM containing cationic, anionic, and nonionic hydrophobic monomers (abbreviated as P(AM-AANa-N)Cn, P(AM-AANA-S)Cn, and P(AM-AANA-O)Cn, respectively) were synthesized; Then, demulsification experiments and interface behavior experiments (including dynamic interfacial tension, dilatational rheology and dynamic coalescence time measurement) were conducted to investigate the influence of HMPAM on the demulsification performance of a W/O heavy oil emulsion demulsifier D1. The demulsification results showed that HMPAM reduced the dehydration speed of D1, the type of hydrophobic monomer and the length of hydrophobic chain in HMPAM can affect the final water separated of D1. P(AM-AANa-S)Cn, P(AM-AANa-N)Cn with long hydrophobic chain, and P(AM-AANa-O)Cn with short hydrophobic chains had the negative effect on performance of D1. The results of dynamic interfacial tension experiments indirectly showed that HMPAM had the influence on the D1′s conformation and speed of rearrangement at the W/O interface during the water droplet coalescence process, thereby affecting the reduction of elastic modulus (G′) of W/O interface and the coalescence rate of water droplets. When there was HMPAM in water, the coalescence time of water droplets increased, resulting in the decrease of dehydration rate. At the meantime, HMPAM had an impact on the lg(G1′/Gdemulsifier′)/lgG1′, thereby affecting the final water separated of D1.

Numerical Simulation of Oil-water Two-phase Flow Interface Tracking

The insulation performance of transformer oil has a great connection with the stable operation of power systems, and transformer oil will inevitably be mixed with water and other impurities in the actual operation. To explore the mechanism of the influence of suspended water droplets on the insulation performance of transformer oil, this paper uses the phase field method to simulate the interaction and phase transition process between oil and water phases in motion. They systematically analyse the influence of electric field and oil flow parameters on the deformation and coalescence of water droplets. The results indicate that droplets in the oil channel will deform along the direction of the electric field, and the degree of deformation gradually increases with the increase of the electric field strength. The electric field strength has an important impact on the degree of deformation of droplets in the oil channel. In addition, under the same electric field intensity, the radius of droplets is an important factor that leads to the length of aggregation time of droplets. Research has found that the aggregation time between droplets becomes shorter as the radius gradually increases.

Insights into the thermal responsiveness of W/O emulsions with nanoparticles and oleogels as building blocks

Understanding the thermal behavior of emulsions with complex structures was crucial for wider applications. However, the correlations between the structural units and emulsion properties at different temperatures are poorly understood. Herein, W/O emulsions stabilized by oleogels and nanoparticles were studied during thermal process, and dynamic interactions among the structural units occurred at micro-, meso-, and macroscales. Results revealed that the thermal behavior of W/O emulsions shifted from stable (25–50 °C) to sub-stable (50–60 °C), and unstable states (60–80 °C). Microstructural analysis confirmed that the particles desorbed from the interface and dissolved in the oil phase after heating, causing water droplet coalescence in the emulsions. This was attributed to the enhanced hydrophobic interactions between the particle dispersions and the oleogel, as the contact angle and interfacial tension were decreased during heating. At the mesoscale, the T2 values of oleogels and nanoparticle dispersion were increased more than three times from 25 °C to 80 °C, leading to the higher mobility of protons in emulsions. At the macroscale, the viscoelastic modulus of emulsions at higher temperature were higher, together with less energy dissipated by friction and increased nonlinear response. Furthermore, the temperature-induced transformation of emulsion stability can be reversibly controlled at least three times. Insights into the complex behavior of emulsions across different temperature stages can inspire the design of emulsions for specific applications.

The Effect of Surface Interactions on the Coalescence of Water Droplets in Fuel

The Effect of Surface Interactions on the Coalescence of Water Droplets in Fuel

Probing the coalescence mechanism of water droplet and Oil/Water interface in demulsification process under DC electric field

Under electric fields, coalescence of water droplets in oil media and bulk water (droplet-interface coalescence) is a significant phenomenon during the electrostatic process of water-in-oil (W/O) emulsion. In order to reveal the microscopic mechanism of droplet-interface coalescence, MD simulations and high-speed imaging were performed to study the influence of droplet size (r0) and electric field strength (E) on the coalescence process between water layer and droplet in oil. The findings suggested that the molecular arrangement of water molecules was altered at applied electric fields, resulting in a weakened interaction force and an increased spacing between water molecules. The droplet-interface coalescence process could be classified into five temporal regimes, under the mutual effect of the associated intermolecular interactions (Coulomb interaction and van der Waals interaction) and external electric field. The interfacial charge density reached a high value of 0.15 e·nm−3 due to the charge orientation, leading to dipole–dipole interaction between the droplet and water layer. Driven by both applied electric field and polarized charge, when E = 0.44 V·nm−1, the droplet with a diameter of 6 nm had the shortest coalescence period, only 370 ps. The critical field strength (Ec) required to prevent complete coalescence between nano-droplets and oil–water interface increased approximately linearly with r0−0.5. This work has revealed the molecular interaction mechanism of electro-coalescence between water droplets and oil/water interface, and provides useful insights into the electrostatic demulsification.

Destabilization of water-in-crude oil emulsions using naphthenic acids

Naphthenic Acids (NAs) are widely believed to universally act in a stabilizing capacity during the formation of water-in-crude oil emulsions. This work provides evidence to the contrary wherein differences between commercially acquired NAs and those extracted from crude exhibit opposing effects on emulsion stability. Addition of the commercial NAs to a crude oil prior to water-in-oil emulsion formation resulted in an increase in emulsion destabilization rate. This was demonstrated via quantification of water droplet coalescence using pulsed field gradient nuclear magnetic resonance (NMR) and, over long timescales in the visual observation of the disengagement of a free water phase. The efficacy of the commercial NAs to act in such a demulsification capacity was shown to be effective at concentrations as low as 0.5v/v% and in the presence of saline water of up to 3.5 wt% NaCl. Differences in NA demulsifying ability was observed between three crude oils of various origins with some demonstrating clear visual phase separation whilst others remained in an emulsified state. Conversely, addition of NAs extracted from a crude oil at similar concentrations had negligible effect on the rate of emulsion destabilization. Comparative characterization of the commercial and indigenous NAs was performed using 1H NMR, Diffusion Ordered Spectroscopy (DOSY), Rheometry, Pendant Drop Tensiometry, and Gas Chromatography–Mass Spectrometry. The results of this characterization indicated that differences in emulsion stability were governed not by differences in the reduction of emulsion droplet interfacial tension (IFT) but by the kinetics of molecular diffusion of the NAs during both the emulsification and destabilization phases.

Lattice Boltzmann simulation of droplet coalescence in fuel cell flow channel with mechanical vibration

Fuel cells are the promising power source for future green vehicles and water management is an important issue for proton exchange membrane (PEM) fuel cells, which affects the lifetime and durability of fuel cells critically. In the available studies, the key parameters such as channel shape, airflow rate and material wettability have been extensively studied for water management. However, so far there is no open research on the effect of mechanical vibration on water management although most fuel cells work under vibration conditions. To bridge the knowledge gap, based on the Shan-Chen lattice Boltzmann model, this paper aims to reveal the water droplet coalescence process in an airflow channel under vibration conditions and several interesting observations are obtained for the first time. A large vibration amplitude or a small vibration frequency will not only hinder the movement of droplets, but also accelerate the coalescence of droplets. Also by comparing the simulation results it can be found that the droplet movement velocity decreases significantly after coalescence. Therefore, it is important to avoid large amplitude and small frequency for the operation of PEM fuel cells.

Deep dewatering of refinery oily sludge by Fenton oxidation and its potential influence on the upgrading of oil phase.

Highly efficient dewatering is essential to the reduction and reclamation disposal of oily sludge, which is a waste from the extraction, transportation, and refining of crude oil. How to effectively break the water/oil emulsion is a paramount challenge for dewatering of oily sludge. In this work, a Fenton oxidation approach was adopted for the dewatering of oily sludge. The results show that the oxidizing free radicals originated from Fenton agent effectively tailored the native petroleum hydrocarbon compounds into smaller organic molecules, hence destructing the colloidal structure of oily sludge and decreasing the viscosity as well. Meanwhile, the zeta potential of oily sludge was increased, implying the decrease of repulsive electrostatic force to realize easy coalescence of water droplets. Thus, the steric and electrostatic barriers which restrained the coalescence of dispersed water droplets in water/oil emulsion were removed. With these advantages, the Fenton oxidation approach derived the significant decrease of water content, in which 0.294kg water was removed from per kilogram oily sludge under the optimal operation condition (i.e., pH value of 3, solid-liquid ratio of 1:10, Fe2+ concentration of 0.4g/L and H2O2/Fe2+ ratio of 10:1, and reaction temperature of 50°C). In addition, the quality of oil phase was upgraded after Fenton oxidation treatment accompanying with the degradation of native organic substances in oily sludge, and the heating value of oily sludge was increased from 8680 to 9260kJ·kg-1, which would facilitate to the subsequent thermal conversion like pyrolysis or incineration. Such results demonstrate that the Fenton oxidation approach is efficient for the dewatering as well as the upgrading of oily sludge.

Dynamics of Droplet Coalescence on Hydrophobic Fibers in Oil: Morphology and Liquid Bridge Evolution.

Although droplet self-jumping on hydrophobic fibers is a well-known phenomenon, the influence of viscous bulk fluids on this process is still not fully understood. In this work, two water droplets' coalescence on a single stainless-steel fiber in oil was investigated experimentally. Results showed that lowering the bulk fluid viscosity and increasing the oil-water interfacial tension promoted droplet deformation, reducing the coalescence time of each stage. While the total coalescence time was more influenced by the viscosity and under-oil contact angle than the bulk fluid density. For water droplets coalescing on hydrophobic fibers in oils, the expansion of the liquid bridge can be affected by the bulk fluid, but the expansion dynamics exhibited similar behavior. The drops begin their coalescence in an inertially limited viscous regime and transition to an inertia regime. Larger droplets did accelerate the expansion of the liquid bridge but had no obvious influence on the number of coalescence stages and coalescence time. This study can provide a more profound understanding of the mechanisms underlying the behavior of water droplet coalescence on hydrophobic surfaces in oil.

Techno-economic comparative assessment of the ultrasound, electrostatic and microwave supported coalescence of binary water droplets in crude oil

In this study, comparative assessment of the technical performance, energy usage and economic impact of ultrasound, electrostatics and microwave on the coalescence of binary water droplets in crude oil was conducted. The effect of different oil properties such as crude oil viscosity (10.6–106 mPa s) and interfacial tension (IFT) (20–250 mN/m) on the coalescence time and energy consumption was examined. In addition, operation conditions such as inlet emulsion flow velocity (10–100 mm/s), electric field type, ultrasound frequency and applied voltage amplitude (0–30 kV) were evaluated. The numerical models showed good agreement with experimental findings in the literature. Moreover, the process time of the dewatering process increased with rising inlet flow velocities. The elevation of the coalescence time with velocity can be attributed to the increasing effect of flow disturbance, and the reduction of the emulsion residence time. As regards the IFT, the coalescence time reduced as the IFT was increased. This can be associated with the improved stability of emulsions formed at lowered IFT. As the maximum droplet size is directly proportional to the IFT, lowering the IFT reduces the peak diameter of the droplets that are present in the emulsion. Moreover, the coalescence time followed the order: ultrasound < microwave < electrostatics approaches under varying IFT. The coalescence energy increased from ∼15 J, ∼90 J and ∼25 mJ to ∼61 J, ∼235 J and ∼26 mJ for microwave, electrostatics and ultrasound techniques, respectively, as the viscosity was raised from 10.6 to 106 mPa s. Ultrasound coalescence showed significant energy and economic savings in comparison to microwave and electro-coalescence. Hence, ultrasound coalescence would be a potential method for standalone or integrated demulsification over the two other techniques. However, there are indications that beyond a viscosity of 300 mPa s, the effect of ultrasound becomes weak with significant hindrance to droplet movement and accumulation. This analysis provides fundamental insights on the comparative behavior of the three emulsion separation techniques.

Optoelectrical Properties of Transparent Conductive Films Fabricated with Ag Nanoparticle-Suspended Emulsion under Various Formulations and Coating Conditions.

Transparent conductive films (TCFs) were fabricated through bar-coating with a water-in-toluene emulsion containing Ag nanoparticles (AgNPs). Morphological changes in the self-assembled TCF networks under different emulsion formulations and coating conditions and the corresponding optoelectrical properties were investigated. In preparing various emulsions, the concentration of AgNPs and the water weight fraction were important factors for determining the size of the water droplets, which plays a decisive role in controlling the optoelectrical properties of the TCFs affected by open cells and conductive lines. An increased concentration of AgNPs and decreased water weight fraction resulted in a decreased droplet size, thus altering the optoelectrical properties. The coating conditions, such as coating thickness and drying temperature, changed the degree of water droplet coalescence due to different emulsion drying rates, which also affected the final self-assembled network structure and optoelectrical properties of the TCFs. Systematically controlling various material and process conditions, we explored a coating strategy to enhance the optoelectrical properties of TCFs, resulting in an achieved transmittance of 86 ± 0.2%, a haze of 4 ± 0.2%, and a sheet resistance of 35 ± 2.8 Ω/□. TCFs with such optimal properties can be applied to touch screen fields.

Patterned Hybrid Wettability Surfaces for Fog Harvesting.

The scarcity of fresh water resources has become increasingly serious in recent years, posing threats to the survival of mankind. The ability of the animals and plants in arid areas to collect water from moisture and fog has drawn attention worldwide. Inspired by the synergistic fog harvesting mode of natural organisms with superhydrophilic and superhydrophobic patterning, a composite membrane with a concave-convex morphology and hybrid wettability was prepared aiming at efficient fog harvesting. The hybrid wettability surface was obtained by chemically modifying the superhydrophilic PAN substrate with 1H,1H,2H,2H-perfluorooctyltrichlorosilane using iron mesh as the mask. The porous PAN substrate was prepared by the non-solvent-induced phase separation (NIPS) method. Fog harvesting is a three-step process: condensation, coalescence, and rapid transportation of water droplets. The area and ratio of the hydrophilic/hydrophobic regions were tuned by adjusting the mesh number of the iron meshes. Under the optimal condition, the fog harvesting efficiencies of 40.3 and 74.2 mg·cm-2·min-1 were obtained when the fog yields were 0.05 and 0.1 L·min-1, respectively. The present work provides an alternative strategy for addressing the shortage of fresh water resources.

Effect of Oil-Soluble/Water-Soluble Surfactants on the Stability of Water-in-Oil Systems, an Atomic Force Microscopy Study.

The stabilization mechanism of water-in-oil (W/O) emulsions has been studied by measuring the interactions between two water droplets in n-tetradecane using atomic force microscopy. The effects of water-soluble surfactants (SDS/CTAB/Tween 80), an oil-soluble surfactant (Span 20), and the coexistence of the water and oil-soluble surfactants on the stability of water droplets in oil were investigated separately. It is found that the addition of oil-soluble surfactants (Span 20) prevents the coalescence of water droplets in oil. To discuss the role of an oil-soluble surfactant, we analyzed the force curve by applying the theoretical model. The results demonstrate that the oil-soluble surfactant (Span 20) stabilizes dispersed droplets by adsorbing onto the interface and forming a relatively tighter layer with the increase in surfactant concentration, which hinders film rupture. This behavior of the surfactant could also be properly characterized by steric hindrance. A further step was taken by introducing another water-soluble surfactant. It is found that the addition of either SDS or CTAB into the water phase is futile in inducing droplet coalescence in the presence of Span 20. In contrast, Tween 80 was found to be effective in destabilizing water droplets, which could be due to the competitive adsorption between Tween 80 and Span 20 at the interface. By characterizing the interfacial adsorption of Tween 80 and Span 20 with a theoretical adsorption isotherm model, the result indicates that interface replacement would result in a loose adsorption layer that is insufficient to hinder droplet coalescence. Our study provides an intriguing understanding of the role of surfactants in the stabilization and destabilization of water-in-oil emulsions.

Novel polymer nanoparticles with core–shell structure for breaking asphaltenes-stabilized W/O and O/W emulsions

Hypothesis.The removal of stable water-in-oil (W/O) or oil-in-water (O/W) emulsions has been a challenging issue in chemical and oil industry for decades. Traditional demulsifiers were generally designed specifically for treating either W/O or O/W emulsions. A demulsifier that is effective for treating both types of emulsions will be highly desired.Experiments.Novel polymer nanoparticles (PBM@PDM) was synthesized as a demulsifier for treating both W/O and O/W emulsions prepared by toluene, water, and asphaltenes. The morphology and chemical composition of synthesized PBM@PDM were characterized. Demulsification performance and interaction mechanisms including interfacial tension, interfacial pressure, surface charge properties and surface forces were systematically studied.Findings.PBM@PDM could immediately prompt the coalescence of water droplets upon addition and effectively release the water in asphaltenes-stabilized W/O emulsion. In addition, PBM@PDM successfully destabilized asphaltenes-stabilized O/W emulsion. Not only could PBM@PDM substitute the asphaltenes adsorbed at the water-toluene interface, but they could also dominate the water-toluene interfacial pressure in competition with asphaltenes. The steric repulsion between interfacial asphaltene films could be suppressed in the presence of PBM@PDM. Surface charges significantly influenced the stability of asphaltenes-stabilized O/W emulsion. This work provides useful insights into the interaction mechanisms of asphaltene-stabilized W/O and O/W emulsions.

Molecular Simulations on the Coalescence of Water-in-Oil Emulsion Droplets with Non-ionic Surfactant and Model Asphaltene

Water droplets in crude oil can be stabilized by the adsorption of interfacially active components, such as asphaltenes. Demulsifiers like non-ionic surfactants are commonly used to destabilize the water-in-oil emulsions. In this work, molecular dynamics simulations and free energy calculations were performed to study the coalescence of water droplets coated with both model asphaltene and non-ionic surfactants [PEO-PPO-PEO copolymer (SurP) or Brij surfactant (SurB)]. For the first time, we quantitatively studied the interaction force between water droplets in the presence of both asphaltenes and demulsifiers and addressed the effect of solvent property on the coalescence process. At the droplet surface, demulsifiers adsorbed closer to the water phase and formed more hydrogen bonds with water molecules compared to asphaltenes, indicating the capability of demulsifiers to break the asphaltene film. Comparing the two non-ionic surfactants, VO-79/SurP complexes formed a single-layer film on the droplet surface, while a two-layer structure was formed by VO-79/SurB complexes. This led to a higher repulsive force during droplet coalescence when SurB was present, regardless of the type of solvent. Comparing the two different solvents (toluene vs heptane), for the same adsorbates, the interfacial film was more compact in heptane and there were fewer dispersed VO-79. For VO-79/SurB adsorbates, the bridging of VO-79 led to a smaller repulsion during droplet coalescence when the solvent was heptane, while the difference is insignificant for VO-79/SurP adsorbates. This work suggests that the energy barrier and interaction force for droplet coalescence is highly dependent on the structure of interfacial films, thus providing atomic-level insights into the demulsification mechanisms of water-in-oil emulsions in the presence of surface-active asphaltenes.

Molecular dynamics simulation of the coalescence of surfactant-laden droplets.

We investigate the coalescence of surfactant-laden water droplets by using several different surfactant types and a wide range of concentrations by means of a coarse-grained model obtained by the statistical associating fluid theory. Our results demonstrate in detail a universal mass transport mechanism of surfactant across many concentrations and several surfactant types during the process. Coalescence initiation is seen to occur via a single pinch due to aggregation of surface surfactant, and its remnants tend to become engulfed in part inside the forming bridge. Across the board we confirm the existence of an initial thermal regime with constant bridge width followed by a later inertial regime with bridge width scaling roughly as the square root of time, but see no evidence of an intermediate viscous regime. Coalescence becomes slower as surfactant concentration grows, and we see evidence of the appearance of a further slowdown of a different nature for several times the critical concentration. We anticipate that our results provide further insights in the mechanisms of coalescence of surfactant-laden droplets.

Geometry‐driven coalescence of water droplets in a highly viscous fluid

AbstractThis work is dedicated to numerical studies of the coalescence of water droplets moving in bitumen. The Navier–Stokes equations coupled with the volume of fluid model (VOF) using adaptive grids techniques, available in the commercial computational fluid dynamics (CFD) software Ansys Fluent 20R2, were solved numerically to investigate the behaviour of water droplets with diameters from 1 to 100 μm moving in rapidly converging and diverging microchannels of different sizes. The model has been validated against 3‐D experimental data published in the literature. A good agreement has been demonstrated. The results of simulations revealed that the main parameter influencing coalescence is the bulk flow velocity in the channel. Analysis of unsteady simulations showed the existence of a critical flow velocity, above which no coalescence occurs, corresponding to capillary number Ca &lt; 0.5 for droplets Reynolds number Re &lt; 0.1. Besides, image processing analysis has been used for a mean droplet size estimation in different geometries. A mean size significantly increased due to the late coalescence occurring in a wider constriction.

Waltz of tiny droplets and the flow they live in

This article describes the dynamics of small inertial particles centrifuging out of a single vortex. It shows the importance of caustics formation in the vicinity of a single vortex: both for particle collisions and void formation. From these single-vortex studies we provide estimates of the role of caustics in high Reynolds number turbulence, and in the case of clouds, estimate how they may help in rain initiation by bridging the droplet-growth bottleneck. We briefly describe how the Basset- Boussinesq history force may be calculated by a method which does not involve huge memory costs, and provide arguments for its possible importance for droplets in turbulence. We discuss how phase change could render cloud turbulence fundamentally different from turbulence in other situations.