Increase In Water Volume Fraction Research Articles

High flow rate electrospray cooling performance of water–ethanol mixtures

Electrospray (ES) is an effective approach for cooling high-power density devices, owing to its desirable features such as uniform droplet diameter, suppression of droplet rebound, and low power consumption. Despite its excellent thermal properties, water has not been extensively employed as a working fluid in ES setups due to difficulties in establishing a stable ES mode. In this study, ES cooling performance of high flow rate water–ethanol mixtures is investigated. The stable region of the cone-jet mode is identified by capturing the meniscus profile and detecting the corona discharge. The study investigates the effect of ES variables, including flow rate (20 mlhr −100 mlhr), applied voltage (5.30 KV − 12.15 KV), and working fluid including pure ethanol (xH2O= 0 %), mixture I (xH2O= 35 %), and mixture II (xH2O= 70 %), on the cooling performance within the stability region. The results show that raising the flow rate from 20 mlhr to 100 mlhr augments the onset voltage of the cone-jet mode in each fluid. In the case of pure ethanol and mixture I, the end voltage corresponding to the multi-jet mode increases with the rise in flow rate. However, As a result of the heightened surface tension, no multi-jet mode is observed for mixture II, and only the occurrence of corona discharge defines the end voltage. In the single-phase regime, the cooling behavior only depends on the flow rate, owing to the thick liquid layer formed on the heated surface. However, it has been revealed that when the mixture water volume fraction increases up to 70 %, the critical heat flux rise is approximately82 % (Q = 20 mlhr), 148 % (Q = 60 mlhr), and 167 % (Q = 100 mlhr), at the onset voltage and 98 % (Q = 20 mlhr), 131 % (Q = 60 mlhr), and 147 % (Q = 100 mlhr), at the end voltage due to the improved thermal properties of the fluid. Next, the effect of each ES variable on cooling performance is investigated separately. Based on the results, an increase in the flow rate from 40 mlhr to 80 mlhr leads to an approximately 70 % rise in the critical heat flux for both mixture I and mixture II. Additionally, increasing the mixture water volume fraction from 35 % to 70 % results in an approximately 29 % rise in the critical heat flux, attributed to the larger latent heat of mixture II. In the transition regime, mixture II demonstrates superior performance compared to mixture I by suppressing the rebounding effect and enhancing the cooling performance. This improvement is due to the rise in the image force caused by the increase in water volume fraction. However, this enhancement is more significant at the lower flow rate due to the shorter impact time.

Continuous two-phase biocatalysis using water-in-oil Pickering emulsions in a membrane reactor: Evaluation of different nanoparticles

Pickering emulsions are currently receiving increased attention as a promising alternative to dispersions or surfactant stabilized emulsions in two-phase biocatalysis. In order to design a continuous membrane reactor using water-in-oil Pickering emulsions for biocatalysis, knowledge on the filterability of the Pickering emulsion is required. This can be influenced by a number of factors, e.g. type and size of stabilizing nanoparticles, applied solvent, and used membrane. In a previous application of water-in-oil Pickering emulsions for continuous biocatalysis in a membrane reactor, spherical silica particles were used to stabilize the emulsion. This resulted in densely packed filter cakes due to unbound residual particles and decreasing flux over time. Furthermore, rather large droplet sizes with small specific interfacial areas were achieved. In this work, the use of colloidal silica nanoparticle for the stabilization of bioactive Pickering emulsions was studied. The filterability of bioactive water-in-oil Pickering emulsions stabilized by spherical or colloidal silica nanoparticles was compared. Using colloidal silica nanoparticles was found to result in smaller emulsion drop sizes, higher filterability and better reproducibility of drop size distribution and flux. An increase in water volume fraction decreased the flux level, but filtration was still possible at industrially relevant fluxes. With the selected nanoparticles, continuous biocatalysis in a membrane reactor at constant flux, i.e. constant residence time, was performed twice for 30 h. Substrate and product concentrations were constant and reproducible and the enzyme was still active after 30 h. The productivity was higher than that obtained with spherical silica nanoparticles and the process duration is the longest so far reported for continuous biocatalysis in PE at industrially relevant residence times.

PROPERTIES OF WATER/SODIUM DODECYL SULFATE/n-PROPANOL/ALLYLBENZENE MICELLAR SYSTEMS

Water/n-propanol/sodium dodecyl sulfate/allylbenzene micellar systems were formulated. The ratio (w/w) of n-propanol/surfactant equals 2/1. The extent of the micellar region as function of temperature was determined. The micellar systems were characterized by the volumetric parameters, density, excess volume, ultrasonic velocity and isentropic compressibility. The micellar densities increase with the increase in the water volume fraction. Excess volumes of the sodium dodecyl sulfate decrease for water volume fraction below 0.3, stabilize for water volume fractions between 0.2 and 0.5 then increase for water volume fraction above 0.5. Excess volumes of the studied micellar systems increase with temperature. Ultrasonic velocities increase with the increase in water volume fraction up to 0.8 then decrease. Ultrasonic velocities increase with temperature for water volume fractions below 0.8 and increase for water volume fractions above 0.8. Isentropic compressibilities decrease with the water volume fraction up to 0.8 then increase. Isentropic compressibilities increase with temperature for water volume fractions below 0.8 and decrease for water volume fractions above 0.8. Structural transitions from water-in-oil to bicontineous to oil-in-water occur along the micellar phase. The particle hydrodynamic diameter of the oil-in-water micellar systems was found to decrease with temperature. In the diluted region nanoemulsion systems were observed.

Volumetric and Diffusion Properties of Water/Surfactant/n-Propanol/4-Allylanisole Micellar Systems

Abstract Sol-gel encaged [(C8H17)3NCH3][RhCl4] catalyses the double bond isomerization in the flavoring agent 4-allylanisole in aqueous microemulsions. In order to provide optimal composition of the reaction medium water/n-propanol/surfactant/4-allylanisole micellar systems were formulated. The surfactants were sodium dodecyl sulfate, cetyltrimethylammonium bromide, sucrose monolaurate, and polyethylene glycol (7) glyceryl cocoate. The ratio (w/w) of n-propanol/surfactant equals 2/1. The extent of the microemulsions region as function of temperature was determined. The micellar systems were characterized by the volumetric parameters, density, excess volume, ultrasonic velocity and isentropic compressibility. The micellar densities increase with the increase in the water volume fraction. Ultrasonic velocities increase with the increase in water volume fraction up to 0.8 then decrease. Ultrasonic velocities increase with temperature for water volume fractions below 0.8 and decrease for water volume fractions above 0.8. Quantitative analysis of the volumetric parameters enabled the characterization of structural transition along the micellar phase. The particle hydrodynamic diameter of the oil-in-water systems was determined as function of temperature. The particle hydrodynamic diameter decreases in the case of the ionic surfactants while in the case of nonionic surfactants it increases.

Three dimensional numerical simulation of gas–liquid two-phase flow patterns in a polymer–electrolyte membrane fuel cells gas flow channel

Water management in polymer–electrolyte membrane fuel cells (PEMFCs) has a major impact on fuel cell performance and durability. To investigate the two-phase flow patterns in PEMFC gas flow channels, the volume of fluid (VOF) method was employed to simulate the air–water flow in a 3D cuboid channel with a 1.0mm×1.0mm square cross section and a 100mm in length. The microstructure of gas diffusion layers (GDLs) was simplified by a number of representative opening pores on the 2D GDL surface. Water was injected from those pores to simulate water generation by the electrochemical reaction at the cathode side. Operating conditions and material properties were selected according to realistic fuel cell operating conditions. The water injection rate was also amplified 10 times, 100 times and 1000 times to study the flow pattern formation and transition in the channel. Simulation results show that, as the flow develops, the flow pattern evolves from corner droplet flow to top wall film flow, then annular flow, and finally slug flow. The total pressure drop increases exponentially with the increase in water volume fraction, which suggests that water accumulation should be avoided to reduce parasitic energy loss. The effect of material wettability was also studied by changing the contact angle of the GDL surface and channel walls, separately. It is shown that using a more hydrophobic GDL surface is helpful to expel water from the GDL surface, but increases the pressure drop. Using a more hydrophilic channel wall reduces the pressure drop, but increases the water residence time and water coverage of the GDL surface.