Daniel M. Martínez

Experimental studies of the vapor phase nucleation of refractory compounds. VI. The condensation of sodium

In this paper we discuss the condensation of sodium vapor and the formation of a sodium aerosol as it occurs in a gas evaporation condensation chamber. A one-dimensional model describing the vapor transport to the vapor/aerosol interface was employed to determine the onset supersaturation, in which we assume the observed location of the interface is coincident with a nucleation rate maximum. We then present and discuss the resulting nucleation onset supersaturation data within the context of nucleation theory based on the liquid droplet model. Nucleation results appear to be consistent with a cesium vapor-to-liquid nucleation study performed in a thermal diffusion cloud chamber.

Application of scaled nucleation theory to metallic vapor condensation

In this paper we report that scaled nucleation theory (SNT) can describe moderately well the observed nucleation behavior of a significant number of refractory materials if a more appropriate value of a quantity commonly referred to as the excess surface entropy is used. With the availability of more reliable critical point and liquid property data, we are better able to calculate this quantity and we find that for refractory materials it can be as small as one half to one third the quantity traditionally used in its approximation. As a result of using more accurate values, we find considerably better agreement between SNT and experiment than what was originally determined. We also explain why using surface tension slope information to determine the excess surface entropy can lead to substantial errors in the SNT supersaturation prediction.

Thermal diffusion cloud chamber: new criteria for proper operation

Abstract We report results of new nucleation experiments involving 1-pentanol with hydrogen as the background gas obtained from constant temperature critical supersaturation experiments utilizing the high-pressure diffusion cloud chamber. We have observed significant background gas effects on vapor nucleation that differ somewhat from that we have reported previously. In this paper, we discuss the important issue of stability (the absence of buoyancy-driven convective motion of the gas–vapor mixture) and cloud chamber operation; and we focus now on the lower total pressure limit required for stable chamber operation. We describe how violating this limit is manifested by the experimental data, and we show actual results for the nucleation of 1-pentanol with hydrogen as a background gas which illustrates the importance of considering these stability issues. For the first time, we identify three regions of operation for the diffusion cloud chamber. Region I corresponds to the range of total pressures below this lower total pressure limit; Region III corresponds to the range of total pressures above the upper total pressure limit (described earlier); and, Region II corresponds to the range of total pressures that permit “proper” operation of the diffusion cloud chamber. Here we define proper operation as operation under conditions that are believed to be well represented by a one-dimensional model of diffusion in a stagnant gas. We provide, for the first time, an empirical procedure for determining the lower total pressure limit. We also argue against the commonly used pressure ratio as a predictor for “proper” cloud chamber operation.

Fostering STEM literacy through a tabletop wind turbine environmental science laboratory activity

Increasingly, national education policy is focusing on improving science, technology, engineering, and math (STEM) literacy by using energy as a subject matter. In particular, The Next Generation Science Standards (NGSS 2014) identified energy as an issue that collectively relates the principles of science, technology, engineering, and math for students. Learning about energy, especially alternative energy, is much broader than STEM as it also connects a current issue to environmental impacts, the economy, and society—the three pillars of sustainability. In this paper, we present a hands-on laboratory activity developed for an introductory environmental science course that uses tabletop wind turbines designed to improve students’ STEM and energy literacy and to introduce them to the science and technology of wind energy and basic land use considerations of siting wind farms. In this lab, students conceptualize and calculate the basic physical properties of wind energy potential and production by measuring velocities and calculating optimal energy production through various modifications to turbine placement and blade manipulation. Students construct mini-wind farms with multiple turbines and manipulate the footprint and height to achieve the greatest energy production on the smallest footprint thus incorporating land use considerations. This lab engages students, most of whom are not STEM majors; supports their ability to solve a real, hands-on integrated STEM problem; and increases their understanding and ability to communicate about the scientific and technical aspects of energy, in particular wind energy.