On the energy required to maintain an ocean mirror using the reflectance of foam

Among the various interventions proposed to remediate the health and security effects of climate change by solar radiation protection is the proposal to enhance natural ocean whitecap formation. Compared to other solar protection interventions, this is technically simple and quickly terminated. However, it has a drawback: even if the energy be obtained from wind or wave, the power demand to maintain a foam raft determines the capitalization of equipment. The average power demand is inversely related to foam lifetime which can be prolonged by surfactants preferably derived from ingenerate resources. Here, we estimate the associated energy and power demands by identifying the parameters that can be adjusted to moderate the capital cost of implementation. Before dividing by efficiency factors, the range of power demand for an intermediate areal energy requirement of 5 MJ/km2 of ocean varies from 6 to 30 W/km2 for foam lifetime of 10–2 days. The most likely route to deployment is through merchant ship lubrication using bubbly liquids which both reduces fuel consumption and creates an extended wake and is perhaps an example of technical symbiosis

Intensified biodiesel production from waste cooking oil and flow pattern evolution in small-scale reactors

In this paper, the transesterification reaction of waste cooking oil (WCO) with methanol using KOH as catalyst to produce biodiesel was performed in a micro-reactor (1 mm ID) using a cross-flow inlet configuration. The effects of different variables such as, methanol-to-oil molar ratio, temperature, catalyst concentration, and residence time on biodiesel yield, as well as the associated flow patterns during the transesterification reaction were investigated and the relationship between flow characteristics and mass transfer performance of the system was examined. The work reveals important aspects and the links between the hydrodynamic behaviour and the mass transfer performance of the intensified reactors. It was found that high yield (>90%) of biodiesel can be achieved in one-stage reaction using cross-flow micro-reactors for a wide range of conditions, i.e., methanol-to-oil molar ratio: 8–14, catalyst concentration: 1.4%–1.8% w/w, temperature: 55°C–60°C, and residence times: 55–75 s

Hydrodynamics and mass transfer in segmented flow small channel contactors for uranium extraction

In this work, the extraction of U(VI) by tributyl phosphate (TBP) is studied in small channels of different sizes, operated in segmented flow. The variables analysed include the channel diameter (1–4 mm I.D.), mixture velocity (1.06 - 4.24 cm s−1), volume fraction of the continuous phase (between 0.200 and 0.500), and concentration of extractant (TBP 30% v/v in kerosene and TBP 100%). The hydrodynamic characteristics of the flow, such as plug and slug lengths, specific interfacial area, and dispersed phase holdup, were obtained experimentally using high-speed imaging, while the pressure drop was measured with a differential pressure transducer. These parameters were correlated to the studied variables. The concentration of uranium in the aqueous phase was measured with UV-vis spectroscopy, and the mass transfer coefficients were compared with the predictions of a numerical model of segmented flow developed in Comsol Multiphysics, with good agreement

Predictive model for the scale-out of small channel two-phase flow contactors

In this paper, double manifolds are theoretically investigated for the scale-out of two-phase incompressible flows in small channels. Statistical descriptors are proposed to characterise the maldistribution of the total flow rate and the ratio of the flow rates in the two-phase channels, based on the variances and covariance of the flow rates of the two fluids. A novel resistance network model is developed that relates the flowrates of the fluids in the two-phase channels to the hydraulic resistances of the manifold. The statistical descriptors and the resistance network model are then used to develop relationships between the maldistribution coefficients and the hydraulic resistances of the double manifold, the overall pressure drop and the pumping power requirements for different parallel channel numbers. Based on these, scaling laws are proposed that maintain a constant degree of maldistribution for a scale-up factor up to 102. Double manifolds designed using these scaling laws have a constant pressure drop as the number of channels increases, whilst the power requirements increase linearly. The power requirements are inversely proportional to the phase ratio maldistribution descriptor. Recommendations for the design of double manifolds for the scale-out of two-phase systems are proposed

Scale-Up Studies for Co/Ni Separations in Intensified Reactors

In this paper, the effect of the scalability of small-scale devices on the separation of Co(II) from a binary Co(II)/Ni(II) mixture in a nitric acid solution by an organic Cyanex 272/TBP/kerosene (Exxsol D80) phase is studied. In particular, circular channels with diameters of 1, 2, and 3.2 mm are considered. The results were compared against those from a confined impinging-jets (CIJ) cell with a main channel diameter of 3.2 mm. The effects of total flowrate, residence time, Cyanex 272 concentration, and flowrate ratio on the mass transfer performance were investigated. It was found that at increased channel size, the throughputs were also increased but the extraction percentages remained the same. Higher extraction percentages were obtained by using the CIJ configuration at short residence times. However, for longer residence times, the mass transfer coefficients were similar and capillary channels should be preferred over the CIJ because of the ease of separation of the two phases at the end of the unit. The overall mass transfer coefficients ranged between 0.02 and 0.14 s-1 for the capillary channels during plug flow and between 0.05 and 0.45 s-1 for the CIJ cells during dispersed flow