The fluid dynamic environment within a photobioreactor is critical for performance as it controls mass transfer of photosynthetic gases (CO 2 and O 2 ) and the mixing environment of the algal culture. At a cellular level, light fluctuation will occur when cells move between the "light", well-illuminated volume of the culture near the light source and the "dark", self-shaded zone of the culture. Controlled light/dark frequency may increase the light to biomass yield and prevent photoinhibition. Knowledge of cell trajectories within the reactor is therefore important to optimize culture performance. This study examines the cell trajectories and light/dark frequencies in a stratified gas-liquid flow tubular photobioreactor. Commercially available computational fluid dynamics software, ANSYS Fluent, was used to investigate cell trajectories within the half-full solar receivers at different liquid velocities and reactor tube diameters. In the standard configuration 96-mm solar receiver tube, the light/ dark cycle frequencies ranged from 0.104 to 0.612 Hz over the liquid velocity range of 0.1 to 1 m s −1 . In comparison, the smaller diameter 48-and 24-mm tubes exhibit higher light/dark frequencies, 0.219 to 1.30 Hz and 0.486 to 2.67 Hz, respectively.
Second generation liquid biofuels from lignocellulosic feedstocks are part of a suite of solutions to peak oil and a safe climate economy. Biofuels have technological advantages over electrification for applications with minimal refuelling or recharging options such as air travel, shipping, agriculture and low or intermittent frequency trucking and rail. We examined a fuel production concept combining slow pyrolysis chars and superfine commutation. Char is micronised and suspended in diesel or water to create a reduced cost, quality and energy density liquid biofuel. Process yields and efficiencies were derived from a review of the slow pyrolysis char, coal commutation and combustion literature and used to develop theoretical estimates of process performance. Char structure and composition were also reviewed in the context of commutation and management of ash and alkalis in the fuel. The paper concluded that char based fuels had potential applications where cost was critical, but quality was not, such as diesel engines for agriculture, trucks, trains, shipping and backup electricity supply. Char water fuels increase safety by being non-flammable and are environmentally benign, a valuable trait in sensitive environments such as coastal shipping.
SUMMARYThe behaviour of clamping the shell against the substratum may play an important role in the limpet adhesion mechanism because friction generated by this behaviour resists dislodgement by shear forces. This paper describes the development of an apparatus to analyse limpet clamping activity in relation to known forces, including simulated wave activity and predator attack. The results show that Cellana tramoserica clamps its shell in a closely regulated manner consistent with an active role in the limpet adhesion mechanism. Limpets clamped sharply for several seconds in response to single disturbances such as tapping the shell. In response to more continuous disturbance simulating a concerted predator attack, limpets clamped tightly for several minutes. In response to lifting forces applied to the shell, limpets clamped at a set proportion of the lifting force, even if the lift force was a highly dynamic wave profile. This behaviour has implications for numerical models that attempt to describe limpet adhesion because it shows that limpets cannot be represented by a simple mechanical analogue and that the clamping behaviour must be accounted for if useful predictions are to be drawn.
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