Pressure-retarded osmosis (PRO) uses a semipermeable membrane to produce renewable energy from salinity-gradient energy. A spiral-wound (SW) design is one module configuration of the PRO membrane. The SW PRO membrane module has two different flow paths, axial and spiral, and two different spacers, net and tricot, for draw- and feed-solution streams, respectively. This study used an experimental approach to investigate the relationship between two interacting flow streams in a prototype SW PRO membrane module, and the adverse impact of a tricot fabric spacer (as a feed spacer) on the PRO performance, including water flux and power density. The presence of the tricot spacer inside the membrane envelope caused a pressure drop due to flow resistance and reduced osmotic water permeation due to the shadow effect. The dilution of the draw solution by water permeation resulted in the reduction of the osmotic pressure difference along a pressure vessel. For a 0.6 M NaCl solution and tap water, the water flux and corresponding maximum power density were 3.7 L m(-2)h(-1) and 1.0 W/m(2) respectively at a hydraulic pressure difference of 9.8 bar. The thickness and porosity of the tricot spacer should be optimized to achieve high SW PRO module performance.
A novel micromixer which utilizes chaotic mixing induced by ferrofluid actuation is developed. The micromixer is fabricated by a polydimethylsiloxane micromolding technique. The micromixer consists of a T-shaped main mixing channel and two parallel sub-channels that intersect the main channel. Oscillation of a couple of ferrofluid slugs in the sub-channels, induced by external permanent magnet actuation, generates chaotic advection in the main channel flow. To visualize the mixing, red fluorescent particles are supplied to one of the inlets of a T-shaped channel, and mixing flow is observed by a fluorescence microscope and an intensified CCD camera. The mixing experiments are performed with various ferrofluid perturbation frequencies and main stream flow velocities. The optimal mixing conditions determining the upper and lower limits of the most effective Strouhal numbers are found from the experimental results.
Lanthanum (La) doped Strontium Titanate (SrTiO3) is amongst the most promising n-type thermoelectric materials for power generation. We report a double doping method for thin films of SrTiO3 (STO), grown by Pulsed Laser Deposition (PLD), where doping of STO in the Sr-site by Lanthanum is accompanied by doping with oxygen vacancies. In the past theoretical predictions have shown that introducing oxygen vacancies in STO produces a high-effective mass defect band just below the conduction band edge, explaining the high seebeck coefficient observed in oxygen deficient STO. Based on careful transport measurements, we show that it is possible to obtain enhanced thermoelectric power factor by double doping, using La and oxygen vacancies in these thin films. With the aid of optical spectroscopic measurements, we establish the presence of the impurity band created by the vacancies and validate their role in the enhanced thermoelectric performance with structural and transport measurements. The presence of oxygen vacancies also serves to decrease the thermal conductivity due to effective phonon scattering.
Pipeline embedment into the seabed is a key consideration for offshore oil and gas developments with high-temperature fluids. To date, the mechanism of steady-state heat transfer from partially and fully buried pipes has been modeled predominantly through analytical and numerical approaches. The current study focuses on making detailed measurements of heat-transfer characteristics. A laboratoryscale experimental apparatus imitating a subsea pipeline partially or fully buried into the seabed is created. Hot flow of hydrocarbons inside oil and gas offshore pipelines and the cold external flow of seawaters are simulated by means of 70 C and 5 C water flows from two separate water tanks, respectively. The experiments are carried out for seven different burial depths representing a range of various burial configurations, from fully exposed to fully buried pipes. The temperatures measured on the external surface of the pipe are analyzed, and the overall heat-transfer coefficient of the pipe is calculated. The effect of burial depth on the overall heat-transfer coefficient is compared with analytical formulae.
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