Eize Stamhuis

KINETICS OF LOW-PRESSURE METHANOL SYNTHESIS

The kinetics of low-pressure methanol synthesis, starting from CO, CO2 and hydrogen over a commercial CuZnAl catalyst, were studied in a spinning basket reactor at p = 15–50 bar and T = 210–245°C. The results show that methanol can be formed from both CO and CO2. Besides these two reactions the water-gas-shift reaction takes place. Based on these three reactions and a dual-site adsorption mechanism, 48 kinetic rate models are derived. Hydrogen is believed to adsorb dissociatively. The experimental results support this assumption. Based on χ2-statistics and consistency tests a final kinetic rate model is selected. This kinetic model gives a significantly better agreement with the experimental results than kinetic models taken from recent literature.

Kinetics of the three phase methanol synthesis

The kinetics of the three-phase methanol synthesis, starting from carbon monoxide, carbon dioxide and hydrogen over a commercial Cu-Zn-Al catalyst suspended in squalane as the slurry liquid, were studied in a well-mixed, agitated slurry reactor at p = 15 – 40 bar and T = 210 – 260 °C. A kinetic model is selected, based on a dual-site adsorption mechanism and three reactions: methanol from CO, methanol from CO2 and the water-gas-shift reaction. It turns out that methanol from CO2 is the most important reaction under three-phase conditions. This kinetic model gives a good agreement with the experimental results.

Riding the waves: the role of the body wave in undulatory fish swimming

Abstract A continuously swimming mullet modulates its thrust production by changing slip-the ratio between its swimming speed U and the speed V with which the body wave travels down its body. This variation in thrust is reflected in the wake of the fish. We obtained 2-dimensional impressions of the wake behind a mullet swimming at a slip of 0.7 equivalent to active swimming, at a slip of 0.9 close to free-wheeling, and at a slip of 1.1 when the fish is braking. Independent of the slip, vortices are shed at the tail when the tail tip reaches its maximum lateral excursion. The manner in which the wake changes as it decays depends on the degree of slip: At a slip well below unity, the wake decays without any qualitative changes in shape, the medio-frontal cross section of the mature wake consists of a double row of alternating vortices separated by an undulating jet, and the angle between the jet flow and the mean path of motion is close to 45°; at a slip above unity, the vortices stretch out laterally and the mature wake resembles a single row of oval vortices with two vortex cores, and the jet between the vortices is almost perpendicular to the mean path of motion; the wake at slip of 0.9 exhibits a pattern intermediate between the wakes at slips 0.7 and 0.9 with slightly elongate vortices and a jet angle of 61°.

Copepod feeding currents: flow patterns, filtration rates and energetics

SUMMARY Particle image velocimetry was used to construct a quasi 3-dimensional image of the flow generated by the feeding appendages of the calanoid copepod Temora longicornis. By scanning layers of flow, detailed information was obtained on flow velocity and velocity gradients. The flow around feeding T. longicornis was laminar, and was symmetrical viewed dorsally, but highly asymmetrical viewed laterally, with high levels of vorticity on the ventral side. The flow rate through the feeding appendages varied between 77 and 220 ml day-1 per individual. The morphology of the flow field ensured that water was entrained over the full length of the first antennae. These were kept out of areas with high velocity gradients that could interfere with distant mechano- or chemoreception. The volume of influence, i.e. the volume of water around the foraging copepod, where shear rates were significantly higher than background levels, was calculated. Implications for encounter probability and mechanoreception are discussed. The average rate of energy dissipation within the copepods volume of influence is several times higher than the levels of turbulent energy dissipation these animals are likely to encounter in their environment. Even in highly turbulent environments, adult T. longicornis will not experience very significant effects of turbulence. Within the volume of influence of the copepods the energy dissipation due to viscous friction varied between 6.6×10-11 and 2.3×10-10W. Taking mechanical efficiency and muscle efficiency into account, this results in a total energetic cost of the feeding current of 1.6×10-9W per copepod. This value represents only a small percentage of the total energy budget of small calanoid copepods.

Optimisation of the process conditions for the modification of starch

The carboxymethylation of granular potato starch by sodium monochloro acetate (SMCA) in i-propanol - water mixtures was studied with experimental design. The optimal reactions conditions were determined for the three quantitative responses, the degree of substitution of the starch hydroxyl groups by ether groups, the conversion of SMCA and the selectivity of the reaction of SMCA to carboxymethylated starch, and for one qualitative response, the product quality. The regions for the temperature, the water fraction and the amount of starch where the modified starch keeps it granular shape have been identified simultaneously. A kinetic model was used successfully to describe the time dependency of the quantitative responses.

Social learning in juvenile lemon sharks, Negaprion brevirostris

Social learning is taxonomically widespread and can provide distinct behavioural advantages, such as in finding food or avoiding predators more efficiently. Although extensively studied in bony fishes, no such empirical evidence exists for cartilaginous fishes. Our aim in this study was to experimentally investigate the social learning capabilities of juvenile lemon sharks, Negaprion brevirostris. We designed a novel food task, where sharks were required to enter a start zone and subsequently make physical contact with a target in order to receive a food reward. Naive sharks were then able to interact with and observe (a) pre-trained sharks, that is, ‘demonstrators’, or (b) sharks with no previous experience, that is, ‘sham demonstrators’. On completion, observer sharks were then isolated and tested individually in a similar task. During the exposure phase observers paired with ‘demonstrator’ sharks performed a greater number of task-related behaviours and made significantly more transitions from the start zone to the target, than observers paired with ‘sham demonstrators’. When tested in isolation, observers previously paired with ‘demonstrator’ sharks completed a greater number of trials and made contact with the target significantly more often than observers previously paired with ‘sham demonstrators’. Such experience also tended to result in faster overall task performance. These results indicate that juvenile lemon sharks, like numerous other animals, are capable of using socially derived information to learn about novel features in their environment. The results likely have important implications for behavioural processes, ecotourism and fisheries.

Propulsive force calculations in swimming frogs I. A momentum-impulse approach

SUMMARY Frogs are animals that are capable of locomotion in two physically different media, aquatic and terrestrial. A comparison of the kinematics of swimming frogs in a previous study revealed a difference in propulsive impulse between jumping and swimming. To explore this difference further, we determined the instantaneous forces during propulsion in swimming using an impulse–momentum approach based on DPIV flow data. The force profile obtained was compared with force profiles obtained from drag–thrust equilibrium of the centre of mass and with the force profiles generated during jumping. The new approach to quantifying the instantaneous forces during swimming was tested and proved to be a valid method for determining the external forces on the feet of swimming frogs. On the kinematic profiles of swimming, leg extension precedes propulsion. This means that it is not only the acceleration of water backwards that provides thrust, but also that the deceleration of water flowing towards the frog as a result of recovery accelerates the centre of mass prior to leg extension. The force profile obtained from the impulse–momentum approach exposed an overestimation of drag by 30% in the drag–thrust calculations. This means that the difference in impulse between jumping and swimming in frogs is even larger than previously stated. The difference between the force profiles, apart from a slightly higher peak force during jumping, lies mainly in a difference in shape. During swimming, maximal force is reached early in the extension phase, 20% into it, while during jumping, peak force is attained at 80% of the extension phase. This difference is caused by a difference in inter-limb coordination.

Feeding current characteristics of three morphologically different bivalve suspension feeders, Crassostrea gigas, Mytilus edulis and Cerastoderma edule, in relation to food competition

Introduced Pacific oysters (Crassostrea gigas) have shown rapid expansion in the Oosterschelde estuary, while stocks of native bivalves declined slightly or remained stable. This indicates that they might have an advantage over native bivalve filter feeders. Hence, at the scale of individual bivalves, we studied whether this advantage occurs in optimizing food intake over native bivalves. We investigated feeding current characteristics, in which potential differences may ultimately lead to a differential food intake. We compared feeding currents of the invasive epibenthic non-siphonate Pacific oyster to those of two native bivalve suspension feeders: the epibenthic siphonate blue mussel Mytilus edulis and the endobenthic siphonate common cockle Cerastoderma edule. Inhalant flow fields were studied empirically using digital particle image velocimetry and particle tracking velocimetry. Exhalant jet speeds were modelled for a range of exhalant-aperture cross-sectional areas as determined in the laboratory and a range of filtration rates derived from literature. Significant differences were found in inhalant and exhalant current velocities and properties of the inhalant flow field (acceleration and distance of influence). At comparable body weight, inhalant current velocities were lower in C. gigas than in the other species. Modelled exhalant jets were higher in C. gigas, but oriented horizontally instead of vertically as in the other species. Despite these significant differences and apparent morphological differences between the three species, absolute differences in feeding current characteristics were small and are not expected to lead to significant differences in feeding efficiency.

Basics and principles of particle image velocimetry (PIV) for mapping biogenic and biologically relevant flows

Particle image velocimetry (PIV) has proven to be a very useful technique in mapping animal-generated flows or flow patterns relevant to biota. Here, theoretical background is provided and experimental details of 2-dimensional digital PIV are explained for mapping flow produced by or relevant to aquatic biota. The main principles are clarified in sections on flow types, seeding, illumination, imaging, repetitive correlation analysis, post-processing and result interpretation, with reference to experimental situations. Examples from the benthic environment, namely, on filter feeding in barnacles and in bivalves, illustrate what the experiments comprise and what the results look like. Finally, alternative particle imaging flow analysis techniques are discussed briefly in the context of mapping biogenic and biologically relevant flows.

The scaling and structure of aquatic animal wakes.

Abstract Animal generated water movements are visualized and quantified using two-dimensional particle image velocimetry (PIV). The resulting vector flow fields allow for the study of the distribution of velocity, vorticity and vortices. Structural and temporal aspects of animal-induced flows covering a range of Reynolds (Re) numbers between less than 1 to more than 104 are presented. Maps of flow induced by continuous foraging and intermittent escape responses of tethered nauplius and copepodid stages of the marine copepod Temora longicornis offer insight in viscosity-dominated flow regimes. Fast escape responses of the equally sized largest nauplius stage and the smallest copepodid stage are compared. The nauplius moves by generating a viscous flow pattern with high velocities and vorticity; the copepodid moves by using inertial effects to produce a vortex ring with a rearward jet through the center. Larvae and small adult fish (zebra danio) use a burst-and-coast-swimming mode at Re numbers up to 6,000, shedding a vortex ring with the associated jet at the tail during the burst phase. Flow patterns during the coasting phase differ between the small larvae and larger adults due to the changes in importance of viscosity. A 12 cm long mullet swimming in a continuous mode generates a chain of vortex rings with a backward undulating jet through the centers of the rings at Re numbers of 4 × 104 in inertia-dominated regimes. Our empirical results provide realistic insight in the scale effects determining the morphology of the interactions between animals and water.