Final Thoughts

I have completed my 10 week Cal Energy Corps internship at Lawrence Berkeley Labs. While the internship is over, my work at the labs and on this individual project are not: I will be staying on to continue current efforts during the school year, this time for research credit instead of money. I am young and in a position to research at LBL. There’s not much more to be desired.


The time has come to provide some insight into my work this summer. If you’ve been following my blog posts you will know that bare concrete fruits of my labor I do not. In fact if sticking to the plant metaphor, my fruits have been summoned for harvest and yet currently they resemble concrete fruits more than fruit fruits.I have made progress however, and believe that I have set myself up to prosper in the continuation of this project.


Before I explain the research, one thing to note is that my project is working to model salty water evaporation. This model is an extrapolation of a pure water evaporation model developed by Frances Houle, my host. The potential applications of this research are climate models, incredibly important tools for our understanding and prediction of climate. Additionally a functioning salty model could be applied to devices being developed at JCAP in LBL, in which membranes must be flushed with aqueous solution. This aqueous solution tends to evaporate and cause issues, hence the possible application to a salty evaporation model.


The research:


The first week was comprised of reading journal articles and getting acquainted with Kinetiscope, open source software developed by Frances that we use for modeling. A state of familiarity with literature published by others is incredibly important in science, and even more so for work with the type of kinetic simulations we use. I spent the week defining my goals, looking at the datasets I was to be working with, reading papers on both theory and experiment with evaporation, and practicing with Kinetiscope. It was hectic.


Week two was more of the same, although it saw my first foray into making the models themselves. The base water model involves two evaporation mechanisms: a unimolecular one and a tertiary one. I spent the week adding other steps to the base water model, focusing on fitting the exact shape of the curves. I did not fail for that matter. The model, as augmented by me, mimicked the qualitative trends of the experimental data. A condensation step returning some water vapor to the surface evaporation layer yielded the oft-mentioned property of easing into a final volume. The issue arose when the model faced the scrutiny of both reality and my host, Frances Houle. One of the evaporation mechanisms, the Hertz-Knudsen unimolecular one, already has a condensation component built in. By adding an explicit condensation mechanism I was effectively double dipping. The takeaways: Rigor must be displayed in both constructing a physical representation of the system and generating rate constants. Also, it’s easy to get the right curve when you invent physics, so don’t!


The following couple of weeks were characterized by a journey into the experimental world. Efforts to understand the datasets presented me articles to read and even journeys down the hill to a lab adorned to the side of the ALS. I read articles about the vehicles through which we interact with test aerosols, the ones germane to the datasets being, among others, electrodynamic balances, flow controllers and microdispensers.


After gaining an adequate understanding of how the data is harvested I began to understand how different experimental factors might shape the datasets and need to be accounted for. To do this I familiarized myself with the dissertation of James Davies, an aerosol experimentalist and Wilson lab member/collaborator. In his work exists the equation and derivation of the deterministic counterpart to our stochastic simulations. It’s an equation for molecular flux that when applied in a computer program that updates values at a set frequency creates a fit, via numerous fitting parameters, to the experimental data. While this fitted equation is the antithesis to kinetic modeling, there exists value in understanding the important players in the physics of the system. It allows me to develop a good way to account for various experimental conditions in our stochastic model while maintaining the fundamental representation of the system.


I was borne into the waning weeks of my internship by a frenzy of frustration elicited by a perceived fundamental misunderstanding of the base water model. It surged and then resided as I realized my worries were misguided, my problems solved by a quick flick of a mental switch.


From this point onward I have been investigating the different possible accommodations for different experimental conditions.  Frances’s base water model was developed for experimental data in stagnant gas. Gasflow around the aerosol, a common experimental condition, leads to increased water transport away from it and thus an increased rate of evaporation. At present I’ve explored modifying the evaporation coefficient in the hertz-knudsen equation to get a predictable result.


Another correction resides in the differences in relative humidity of the surrounding gas. The goal is to develop a model predictive throughout the entire range of relative humidities. The pure water model works from saturation, RH 100, to about an RH of 80. In order to remedy this, temperature effects on the rate might be necessary. This is due to the departure from equilibrium. At relative humidities lower than 80 evaporation, will occur faster due to larger concentration gradients for water, so fast that insufficient time for the aerosol temperature to equilibrate with the surroundings. This temperature difference is so far unaccounted for in the model, but might play a role in the evaporation. As of now that’s the next source of effort, dealing with the insufficiencies of the pure water model. Afterwards the plan is to continue to refine the salty evaporation, possibly via an implementation of changing hydration energies.


In overall reflection of the summer, I feel the need to express gratitude towards Cal Energy Corps. The issues assaulting the mind at present, that slink in with their disheveled sense of urgency are numerous and greedy to slurp away human time and human energy, human thought and human spirit. These are resources more precious than gold.


Domestic politics, foreign politics, everything encompassed by politics (which is basically every issue in the entire world) are all real and all important. But fundamentally they do not threaten the  habitability of the land we all galavant on. There are issues of control of the land and malapportionment and whether or not these people over here should be able to usurp land from those people over there and what to do if/when they do and yadda yadda. The crux of these issues is land and yet none of them are about land itself. None of these non-land land issues could exist if we lacked good earth to disagree over. Without sound terrain to support the cultivation of plants and animals and resources, without sound land to live on and house us, not much else matters. Climate change cuts to these very base needs: the viability of our land.


Climate change is terrifying. The lion’s share of the burden of the recent acceleration of it can be distilled down to humanity and our relationship to energy. In a country where political turbulence is the focus of our time and energy and climate issues seem oft-ignored, it’s comforting to know that organizations like CITRIS and the Banatao Institute exist, that really smart people care and are taking action to solve this serious and pressing issue. I am grateful for CEC for providing me the opportunity to prepare myself to continue to deal with the problem of energy. If history books do not mislead me, then it seems that humans tend to solve problems when needed. We have a problem with the way we procure and use energy. I believe that we will find a way out of this carbon conundrum, and this summer has only reinforced that thought.