Kinetics of water adsorption in microporous aluminophosphate layers for regenerative heat exchangers

The performance of thick aluminophosphate molecular sieve layers for heat exchanger applications is evaluated. The aluminophosphate AlPO-18 (AEI structure type code) molecular sieve sorbent is coated on aluminium supports prior the sorption measurements. Two AlPO-18 samples with different morphological appearance, i.e. nano-sized crystals with monomodal size distribution and micron-sized crystals of varying sizes, are used to prepare layers with thickness in the range of 80–750 μm. As a binder component, polyvinyl alcohol (PVOH) was utilized in order to prepare mechanically stable layers, which are mechanically stable over numerous measuring cycles. The sorption measurements are conducted under canonical conditions at 40 °C. The AlPO-18 layers showed decreased mass flows with increasing the thickness. Additionally, the layers comprising nanosized crystals showed higher equilibrium loadings and faster kinetics compared to films based on micron-sized crystals. Following the kinetic studies of pressure, temperature and heat flow, it can be concluded that the heat transport is the rate limiting mechanism for thick aluminophosphate layers. Importantly, the diffusion limitation plays a role only for relatively thin microporous aluminophosphate layers (<200 μm). Below this thickness complete heat transfer is achieved within 2 min which allows fast heat exchanger cycles. Thus, the application of microporous aluminophosphate layers for heat transformation and storage applications is considered possible.     

An improved algorithm for cutset evaluation from paths

In this paper an algorithm is given to obtain cuts from paths of a 2-state reliability system. The new algorithm is based on set theoretic considerations. It improves the algorithm of Elias, Mokhles and Ibrahim. An example is given to demonstrate the algorithm.     

Minimising heat dissipation in ultrasonic piezomotors by working in a resonant mode

Heat dissipation in ultrasonic motors should be limited, especially in precision applications since it causes thermal deformations. Therefore, an easy-to-understand mechanical model was developed to simulate heat dissipation in an ultrasonic motor. This model involves the dielectric, piezoelectric and mechanical hysteretic losses of the piezoelectric material. Both the model and the experiments lead to the same recommendations to minimise the heat dissipation for ultrasonic motors. Large piezoactuators, exciting passive structures at high resonance frequencies result in a minimum heat dissipation. Furthermore, it was shown that the optimal frequency regarding minimal heat dissipation lies between the resonance and the antiresonance frequency of the system, close to the resonance frequency.     

Thermal desorption of gases and solvents from graphite and carbon nanotube surfaces

The interaction of 23 gases and solvents with the basal plane of highly oriented pyrolytic graphite (HOPG) and with single-wall carbon nanotube (SWCNT) samples is studied using thermal desorption spectroscopy. Pre-exponential frequency factors used for analysis of desorption traces are obtained from vapor pressure data. Activation energies for desorption at monolayer coverage are determined using the Redhead peak-maximum method. Binding energies of non-polar adsorbates to the HOPG surface are found to scale with the adsorbate polarizability providing clear evidence for the van der Waals character of the interaction. Low coverage desorption temperatures on SWCNT samples are found to be 50-100% higher than on HOPG. Such increase has previously been attributed to physisorption in higher coordinated sites such as grooves on the external SWCNT rope surfaces. Polar adsorbates on the other hand typically desorb at much higher temperatures from SWCNT samples which is here tentatively attributed to stronger interaction with defect sites.     

Preparation,characterization, viscosity,and thermal conductivity of nitrogen-doped graphene aqueous nanofluids

Nanofluids perform a crucial role in the development of newer technologies ideal for industrial purposes. In this study, Nitrogen-doped graphene (NDG) nanofluids, with varying concentrations of nanoparticles (0.01, 0.02, 0.04, and 0.06 wt%) were prepared using the two-step method in a 0.025 wt% Triton X-100 (as a surfactant) aqueous solution as a base. Stability, zeta potential, thermal conductivity, viscosity, specific heat, and electrical conductivity of nanofluids containing NDG particles were studied. The stability of the nanofluids was investigated by UV–vis over a time span of 6 months and concentrations remain relatively constant while the maximum relative concentration reduction was 20 %. The thermal conductivity of nanofluids was increased with the particle concentration and temperature, while the maximum enhancement was about 36.78 % for a nanoparticle loading of 0.06 wt%. These experimental results compared with some theoretical models including Maxwell and Nan’s models and observed a good agreement between Nan’s model and the experimental results. Study of the rheological properties of NDG nanofluids reveals that it followed the Newtonian behaviors, where viscosity decreased linearly with the rise of temperature. It has been observed that the specific heat of NDG nanofluid reduced gradually with the increase of concentration of nanoparticles and temperature. The electrical conductivity of the NDG nanofluids enhanced significantly due to the dispersion of NDG in the base fluid. This novel type of fluids demonstrates an outstanding potential for use as innovative heat transfer fluids in medium-temperature systems such as solar collectors.     

Large-Scale Liquid Motion in Free Thermocapillary Films

Thermocapillary flows in thin films are considered which are differentially heated from lateral side walls. The competition between two different types of motion is addressed. One type is the so-called return flow in which a return flow opposes the thermocapillary free-surface flow to preserve mass conservation. The other type of motion is a large-scale flow which arises as a plug flow in which the velocity is independent of the coordinate perpendicular to the film. We provide physical arguments, based on the minimization of the surface energy, for the preference of the large scale flow over the return flow as the film thickness decreases. The large scale motion arises as a cellular flow with alternating vorticity perpendicular to the film surface. The direction of rotation of these vortices is not determined when the film is adiabatic and of constant thickness. If, however, the film thickness varies perpendicular to the applied temperature gradient the flow direction is dictated by the minimization of the surface energy. Our predictions are consistent with independent experiments and numerical simulations.     

Nanofur for Biomimetic Applications

Many plants and insects possess multi‐functional surfaces covered by dense nanohair. Such a nanofur is of high interest for various biomimetic applications like self‐healing, air retention, and oil/water separation. Here, we introduce a highly scalable and competitive molding technique for the fabrication of biomimetic nanofur. With this method, we pull nanofur out of flat polycarbonate and tune its wettability from hydrophilic to superhydrophobic. By mechanically structuring these samples we create various devices suitable for microfluidics. The nanofur can be also used for the fabrication of self‐healing surfaces inspired by pitcher plants as well as for air‐retaining surfaces mimicking the water fern Salvinia minima. Finally, we utilize the nanofur for oil/water separation and the cleaning of oil spills.     

Occurrence, distribution and fluxes of benzotriazoles along the German large river basins into the North Sea

Benzotriazole (BT) and tolyltriazole (TT) are high production volume chemicals which are used in various industrial and household applications. In this study, the distribution of benzotriazoles in the estuaries of different rivers of central Europe and in the North Sea was analyzed by solid-phase extraction (SPE) and liquid chromatography-mass spectrometry (HPLC-MS/MS). BT as well as TT was detected in all water samples. The concentrations for total benzotriazoles (BTs) ranged from 1.7 to 40 ng/L in the North Sea in costal areas. Concentrations in rivers are from 200 to 1250 ng/L, respectively. The mass flux of total benzotriazoles from the major rivers of central Europe into the North Sea was calculated to 78 t/a, dominated by the Rhine with an individual flux of 57 t/a of BTs. The analysis of the distribution profile in the North Sea showed that the decrease of the concentration was mostly caused by dilution and that the benzotriazoles are poorly degradable in the North Sea. This paper presents the first report of benzotriazoles in the marine environment.     

Flame temperature measurements during electrically assisted aerosol synthesis of nanoparticles

Fourier transform infrared (FTIR) emission/transmission (E/T) spectroscopy is used to measure the temperature during TiO₂ formation by titanium tetraisopropoxide (TTIP) oxidation in a premixed flat flame. In the absence of particles, FTIR is systematically compared to coherent anti-Stokes Raman scattering (CARS) in premixed flames in the presence and absence of external electric fields including line-of-sight as well as tomographic reconstructed FTIR measurements. Time resolved CARS flame temperature measurements probe the effect of electric fields on the premixed flat flame. Furthermore, FTIR is used to measure axial and radial flame temperature profiles in TiO₂ particle-laden flames at various electric field strengths. Along with the visible reduction in flame height when applying the electric field, the external electric fields reduce the high temperature region of the flame and lead to a steeper temperature gradient further downstream. The maximum flame temperature, however, remains constant. The precision control of particle crystallinity and the specific surface area by external electric fields is confirmed as well as their effect on the anatase to rutile phase transformation is discussed.