We consider laminar displacement flows in narrow eccentric annuli, oriented horizontally, between two fluids of Herschel–Bulkley type, (i.e. including Newtonian, power-law and Bingham models). This situation is modelled via a Hele-Shaw approach. Whereas slumping and stratification would be expected in the absence of any imposed flow rate, for a displacement flow we show that there are often steady-state travelling wave solutions in this displacement. These may exist even at large eccentricities and for large density differences between the fluids. When heavy fluids displace light fluids, annular eccentricity opposes buoyancy and steady states are more prevalent than when light fluids displace heavy fluids. For large ratios of buoyancy forces to viscous forces we derive a lubrication-style displacement model. This simplification allows us to find necessary and sufficient conditions under which a displacement can be steady, which can be expressed conveniently in terms of a consistency ratio. It is interesting that buoyancy does not appear in the critical conditions for a horizontal well. Instead a competition between fluid rheologies and eccentricity is the determining factor. Buoyancy acts only to determine the axial length of the steady-state profile.

As the climate warms, there is little doubt that ecosystems of the future will look different from those we see today. However, community responses to warming in the field are poorly understood. We examined the effects of field‐based warming on intertidal communities in the Salish Sea, which is a regional thermal ‘hot spot’ and therefore a model system for studying thermally stressed communities. We manipulated temperature at three tidal heights by deploying black‐ and white‐bordered settlement plates. Black plates increased in situ substratum temperature by an average of 2.6°C (maximum temperature, 40.9°C). Barnacles fared poorly on black plates in all zones. When overall thermal stress was highest (summer in the high intertidal zone) herbivores were absent. In lower tidal zones, herbivores were abundant on white plates but were scarce on black plates. The total percent cover of algae was unaffected by the temperature treatment, despite the fact that macroalgae were expected to be the least thermally tolerant functional group. However, we did find that ephemeral green algae exhibited a delay in phenology on black plates. We also found that species richness declined and invertebrate assemblage structure was altered due to warming. Results from this year long experiment suggest that communities in thermally stressful habitats respond to warming via the interplay between species‐specific thermal responses and secondary adaptive strategies such as behavioral microhabitat selection. Declines in diversity and changes in the invertebrate assemblage were due to the decline of local thermally‐stressed species and the lack of replacement by warm‐adapted species. Given the low variation in the species pool along the northeast Pacific coastline, the arrival of warm‐adapted species to the Salish Sea may not occur over relevant time scales, leaving local communities depauperate.

Building ventilation systems are used to mitigate occupant exposure to airborne pollutants such as particulate matter (PM), carbon dioxide and total volatile organic compounds. Building rating systems such as Leadership in Energy and Environmental Design promote the use of natural ventilation to reduce building energy consumption while improving occupant satisfaction. A number of investigations have attempted to compare indoor air quality (IAQ) between spaces with natural or mechanical ventilation without reaching a consensus regarding quantitative impacts. This work provides direct quantitative comparison of the IAQ of a single office space designed for operation with either mechanical or natural ventilation. Natural ventilation has been shown to maintain pollutant accumulation below current standards governing IAQ but is subject to significant airflow variability. In contrast, the mechanical ventilation was shown to result in lower levels of indoor pollution and provide tight control of pollutant levels. The correlation between natural ventilation air exchange rate and concentration of total volatile organic compounds was −0.66 compared to no significant correlation for mechanical ventilation. Average indoor to outdoor PM2.5 ratios were found to be 0.87 and 0.5 for natural and mechanical ventilation, respectively. These results show difficulty in controlling indoor pollutants using prescriptive standard ventilation strategies and that performance-based hybrid ventilation systems provide the most flexibility in meeting IAQ needs.

Approximate velocity profiles have been predicted for laminar, incompressible flow around solid and fluid spheres for Reynolds numbers up to several thousand. The accuracy of the predicted profiles for solid spheres has been tested in three ways. Drag coefficients, flow‐separation angles and forced‐convection transfer rates calculated from these profiles have been compared with experimental data for solid or rigid spheres. The predicted quantities oscillate about the experimental data as the Reynolds number is increased. Cross‐over points occur at Reynolds numbers of about 20, 100 and 500. The velocity profiles for fluid spheres are of little practical value above Reynolds numbers of several hundred as drop or bubble deformation is significant. Drag coefficient data for solid spheres, liquid drops and gas bubbles showing the effect of dispersed‐phase viscosity on total drag are presented. These data are correlated over the Reynolds number range, 10–100 with a viscosity‐ratio correction factor which was derived theoretically.

We present an experimental study of slow laminar miscible displacement flows in vertical narrow eccentric annuli. We demonstrate that for suitable choices of viscosity ratio, density ratio and flow rate, we are able to find steady travelling wave displacements along the length of the annulus, even when strongly eccentric. Small eccentricity, increased viscosity ratio, increased density ratio and slower flow rates all appear to favour a steady displacement for Newtonian fluids. Qualitatively similar effects are found for non-Newtonian fluids, although the role of flow rate is less clear. These results are largely in line with predictions of a Hele-Shaw style of displacement model (Bittleston et al., J. Engng Math., vol. 43, 2002, pp. 229–253). The experiments also reveal interesting phenomena caused largely by secondary flows and dispersion. In the steady displacements, eccentricity drives a strong azimuthal counter-current flow above/below the advancing interface. This advects displacing fluid to the wide side of the annulus, where it focuses in the form of an advancing spike. On the narrow side we have also observed a spike, but only in Newtonian fluid displacements. For unsteady displacements, the azimuthal currents diminish as the interface elongates. With a strong enough yield stress and with a large enough eccentricity, unyielded fluid remains behind on the narrow side of the annulus.