Electrical and Spectroscopic Studies of the Effects of DC Electric Fields on Pre-Mixed Propane-Air Flames

The effects of DC electric fields on temperature distributions within pre-mixed propane-air flames have been measured by the technique of thin filament pyrometry (TFP). We have focussed on the dramatic electric-field-induced modifications of the shape and size of the inner cone and the concomitant changes in the temperature profiles of fuel-rich mixtures with equivalence ratios of 1-1.35. Temperature profile measurements show large decreases in the reaction zone volume that is dependent upon the applied voltage polarity, indicating that electron impact excitation is not responsible for the observed effects. Additionally, the observed flame temperature profile modifications are not strongly dependent on the flow velocity. The TFP results have been verified by spectroscopic measurements of the rotational temperature of the CH(A2Δ - X2Π) emission band at 431 nm. Due to the better coupling of the field to the flame in the present experiments, the magnitude of the externally applied voltage necessary to produce large changes in inner cone geometry are substantially smaller than those used in previous experiments. Electrical measurements that have been made include vertical and horizontal variations of the floating potential within the flames, and bulk current and voltage characteristics. High-speed imaging of the flame response to pulsed DC voltage has been performed to investigate the dynamics of the ionic wind effects. All measurements are consistent with the observed flame perturbations being a fluid mechanical response to the applied field

The impact of climate change on lakes in the Netherlands: a review

Climate change will alter freshwater ecosystems but specific effects will vary among regions and the type of water body. Here, we give an integrative review of the observed and predicted impacts of climate change on shallow lakes in the Netherlands and put these impacts in an international perspective. Most of these lakes are man-made and have preset water levels and poorly developed littoral zones. Relevant climatic factors for these ecosystems are temperature, ice-cover and wind. Secondary factors affected by climate include nutrient loading, residence time and water levels. We reviewed the relevant literature in order to assess the impact of climate change on these lakes. We focussed on six management objectives as bioindicators for the functioning of these ecosystems: target species, nuisance species, invading species, transparency, carrying capacity and biodiversity. We conclude that climate change will likely (i) reduce the numbers of several target species of birds; (ii) favour and stabilize cyanobacterial dominance in phytoplankton communities; (iii) cause more serious incidents of botulism among waterfowl and enhance the spreading of mosquito borne diseases; (iv) benefit invaders originating from the Ponto-Caspian region; (v) stabilize turbid, phytoplankton-dominated systems, thus counteracting restoration measures; (vi) destabilize macrophyte-dominated clear-water lakes; (vii) increase the carrying capacity of primary producers, especially phytoplankton, thus mimicking eutrophication; (viii) affect higher trophic levels as a result of enhanced primary production; (ix) have a negative impact on biodiversity which is linked to the clear water state; (x) affect biodiversity by changing the disturbance regime. Water managers can counteract these developments by reduction of nutrient loading, development of the littoral zone, compartmentalization of lakes and fisheries management