A piezocomposite generating element (PCGE) can be used to convert ambient vibrations into electrical energy that can be stored and used to power other devices. This paper introduces a design of a magnetic force exciter for a small-scale windmill that vibrates a PCGE to convert wind energy into electrical energy. A small-scale windmill was designed to be sensitive to low-speed wind in urban regions for the purpose of collecting wind energy. The magnetic force exciter consists of exciting magnets attached to the device’s input rotor and a secondary magnet fixed at the tip of the PCGE. The PCGE is fixed to a clamp that can be adjusted to slide on the windmill’s frame in order to change the gap between exciting and secondary magnets. Under an applied wind force, the input rotor rotates to create a magnetic force interaction that excites the PCGE. The deformation of the PCGE enables it to generate electric power. Experiments were performed with different numbers of exciting magnets and different gaps between the exciting and secondary magnets to determine the optimal configuration for generating the peak voltage and harvesting the maximum wind energy for the same range of wind speeds. In a battery-charging test, the charging time for a 40 mA h battery was approximately 3 h for natural wind in an urban region. The experimental results show that the prototype can harvest energy in urban regions with low wind speeds and convert the wasted wind energy into electricity for city use.
The power requirements for mechanical agitation of liquids have been investigated extensively, since this parameter is an important criterion for scaling-up stirred reactors, and it also relates to the overall mass transfer coefficient. There is only a limited number of useful correlations for its estimation such as those of Oyama and mechanical power input in nonaerated, agitated non-Newtonian liquids in a turbulent regime also varied with i V as indicated by Calderbank and Moo-Young (1959). It could thus be generalized that the power consumption for mixing in turbulent regime is proportional to N3 for both Newtonian and non-Newtonian fluids. Endoh (1955), Michel and Miller (1962), klark and Vermeulen (1963), Pharamond et al. (1975), and a recent contribution of Hassan and Robinson ( 1977). Oyarna and Endoh (1955) introduced the correlation of the gassed-to-ungassed mechanical mixing power ratio with the aeration number, The new correlating procedure of Michel and Miller (1962) cannot be reliably applied to large scale equipment and also failed at extreme values of gas ilow rate. It is also not applicable for prediction of the effect of surfactants on the mixing power input. The correlation by Pharamond et al. (1975) is restricted to correlating only their experimental data developed with six-blade turbine impellers. The correlations of Clark and Vermeulen (1963) and Hassan and Robinson (1977) appear to have the most merit, since they use the impeller Weber number and measured gas holdup. The correlation of Clark and Vermeulen (1963), however, was developed with unusual method of gas sparging, using a perforated plate covering the entire bottom of the vessel. The correlation of Hassan and Robinson (1977) may vary with different tank sizes and requires the measurement of the gas holdup which is somewhat inconvenient for applications involving fermentation broths. All aforementioned correlations are restricted to Newtonian fluids.In order to improve the accuracy of estimating the mixing power input, an empirical correlation for predicting the gassed-to-ungassed power ratio is suggested as follows: EXPERIMENTAL RESULTS AND DISCUSSIONFor the experimental work reported herein, a modified strain-gauge dynamometer ( Aiba et al., 1973) was employed to measure the torque of a rotating impeller shaft. The air flow rate to the tank was measured by a rotameter. The fully baffled stirred tank contained one single-hole orifice sparger. The stirred-tank geometry and ranges of operating variables of the mixed system are given in Figure 1. The physicochemical properties of liquid solutions used in this study are given in Table 1. Power Requirement in Nongassed SystemIt was confirmed here that the mechanical power input of turbulent Newtonian liquids in nonaerated, agitated, fully baffled tank varied with the cube of the impeller rotational speed. The power number N p was found to be equal to 6.14 for a six-blade turbine. This agrees well with the work of Rushton et al. Power Requirement in Gassed SystemThe experimental resul...
A vortical structure occurring at the fuel stream in laminar nonpremixed jet flames was recently found and shown to have both a fluid-dynamic impact on the flow field and a possible influence on the flame stability and soot formation. We designed a systematic experiment and numerical simulation to investigate the physical mechanisms of this recirculation phenomenon in a coflow system. We hypothesized that a negative buoyancy, caused by the fuel jet being heavier than the ambient air, may play a significant role in the recirculation. Therefore, we experimentally varied the density of the fuel jet using a binary mixture of methane and n-butane, and tested the density of the coflow oxidizer by replacing nitrogen with carbon dioxide. Several fuel jet velocities, flame temperatures, and nozzle diameters were also studied to thoroughly investigate all parameters that might possibly affect the recirculation. As a result, we found that our modified Richardson number, which is based on the cold density difference between the fuel and the coflow, the flame length, and the jet momentum flux, explained the physical mechanism of the recirculation well, with Ri ~ 60 being the critical value for formation of the recirculation. The negative buoyancy was the primary driving force behind the recirculation, while the jet momentum mitigated its formation.
We address various issues concerning the Cauchy problem for the Zakharov-Rubenchik system, (known as the Benney-Roskes system in water waves theory) which models the interaction of short and long waves in many physical situations. Motivated by the transverse stability/instability of the one-dimensional solitary wave (line solitary), we study the Cauchy problem in the background of a line solitary wave.
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