Matching Items (5)
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- All Subjects: Water
- Creators: Hanemann, Michael
Description
Microchannel heat sinks can possess heat transfer characteristics unavailable in conventional heat exchangers; such sinks offer compact solutions to otherwise intractable thermal management problems, notably in small-scale electronics cooling. Flow boiling in microchannels allows a very high heat transfer rate, but is bounded by the critical heat flux (CHF). This thesis presents a theoretical-numerical study of a method to improve the heat rejection capability of a microchannel heat sink via expansion of the channel cross-section along the flow direction. The thermodynamic quality of the refrigerant increases during flow boiling, decreasing the density of the bulk coolant as it flows. This may effect pressure fluctuations in the channels, leading to nonuniform heat transfer and local dryout in regions exceeding CHF. This undesirable phenomenon is counteracted by permitting the cross-section of the microchannel to increase along the direction of flow, allowing more volume for the vapor. Governing equations are derived from a control-volume analysis of a single heated rectangular microchannel; the cross-section is allowed to expand in width and height. The resulting differential equations are solved numerically for a variety of channel expansion profiles and numbers of channels. The refrigerant is R-134a and channel parameters are based on a physical test bed in a related experiment. Significant improvement in CHF is possible with moderate area expansion. Minimal additional manufacturing costs could yield major gains in the utility of microchannel heat sinks. An optimum expansion rate occurred in certain cases, and alterations in the channel width are, in general, more effective at improving CHF than alterations in the channel height. Modest expansion in height enables small width expansions to be very effective.
ContributorsMiner, Mark (Author) / Phelan, Patrick E (Thesis advisor) / Herrmann, Marcus (Committee member) / Chen, Kangping (Committee member) / Arizona State University (Publisher)
Created2011
Description
Nanoparticle suspensions, popularly termed “nanofluids,” have been extensively investigated for their thermal and radiative properties. Such work has generated great controversy, although it is arguably accepted today that the presence of nanoparticles rarely leads to useful enhancements in either thermal conductivity or convective heat transfer. On the other hand, there are still examples of unanticipated enhancements to some properties, such as the reported specific heat of molten salt-based nanofluids and the critical heat flux. Another largely overlooked example is the apparent effect of nanoparticles on the effective latent heat of vaporization (hfg) of aqueous nanofluids. A previous study focused on molecular dynamics (MD) modeling supplemented with limited experimental data to suggest that hfg increases with increasing nanoparticle concentration.
Here, this research extends that exploratory work in an effort to determine if hfg of aqueous nanofluids can be manipulated, i.e., increased or decreased, by the addition of graphite or silver nanoparticles. Our results to date indicate that hfg can be substantially impacted, by up to ± 30% depending on the type of nanoparticle. Moreover, this dissertation reports further experiments with changing surface area based on volume fraction (0.005% to 2%) and various nanoparticle sizes to investigate the mechanisms for hfg modification in aqueous graphite and silver nanofluids. This research also investigates thermophysical properties, i.e., density and surface tension in aqueous nanofluids to support the experimental results of hfg based on the Clausius - Clapeyron equation. This theoretical investigation agrees well with the experimental results. Furthermore, this research investigates the hfg change of aqueous nanofluids with nanoscale studies in terms of melting of silver nanoparticles and hydrophobic interactions of graphite nanofluid. As a result, the entropy change due to those mechanisms could be a main cause of the changes of hfg in silver and graphite nanofluids.
Finally, applying the latent heat results of graphite and silver nanofluids to an actual solar thermal system to identify enhanced performance with a Rankine cycle is suggested to show that the tunable latent heat of vaporization in nanofluilds could be beneficial for real-world solar thermal applications with improved efficiency.
Here, this research extends that exploratory work in an effort to determine if hfg of aqueous nanofluids can be manipulated, i.e., increased or decreased, by the addition of graphite or silver nanoparticles. Our results to date indicate that hfg can be substantially impacted, by up to ± 30% depending on the type of nanoparticle. Moreover, this dissertation reports further experiments with changing surface area based on volume fraction (0.005% to 2%) and various nanoparticle sizes to investigate the mechanisms for hfg modification in aqueous graphite and silver nanofluids. This research also investigates thermophysical properties, i.e., density and surface tension in aqueous nanofluids to support the experimental results of hfg based on the Clausius - Clapeyron equation. This theoretical investigation agrees well with the experimental results. Furthermore, this research investigates the hfg change of aqueous nanofluids with nanoscale studies in terms of melting of silver nanoparticles and hydrophobic interactions of graphite nanofluid. As a result, the entropy change due to those mechanisms could be a main cause of the changes of hfg in silver and graphite nanofluids.
Finally, applying the latent heat results of graphite and silver nanofluids to an actual solar thermal system to identify enhanced performance with a Rankine cycle is suggested to show that the tunable latent heat of vaporization in nanofluilds could be beneficial for real-world solar thermal applications with improved efficiency.
ContributorsLee, Soochan (Author) / Phelan, Patrick E (Thesis advisor) / Wu, Carole-Jean (Thesis advisor) / Wang, Robert (Committee member) / Wang, Liping (Committee member) / Taylor, Robert A. (Committee member) / Prasher, Ravi (Committee member) / Arizona State University (Publisher)
Created2015
Description
Water markets are a promising method for adapting to water scarcity in the western United States, and the Colorado-Big Thompson Project (CBT) market is often held up as a prime example of their potential. While much has been written about the CBT market, the current academic literature tends to eschew structural modeling of supply and demand in favor of fitting hedonic price equations, which ignore many of the market’s unique characteristics. This paper proposes a model of supply and demand for CBT water which accounts for these unique features, including transaction supply, municipality stockpiling, and differences in behavior across different types of water users. The estimation of this model is made possible by novel administrative records data on both transfers and ownership of CBT water, the processing and features of which are described in detail. While the voluminous and messy nature of the data has prevented complete estimation of the model at this point, some preliminary results are presented along with a plan for future work.
ContributorsHilgemann, Christian (Author) / Hanemann, Michael (Thesis director) / Kuminoff, Nicolai (Committee member) / Barrett, The Honors College (Contributor) / Economics Program in CLAS (Contributor) / School of Mathematical and Statistical Sciences (Contributor) / Historical, Philosophical & Religious Studies, Sch (Contributor)
Created2022-12
Description
Environmental concerns are increasingly becoming one of the most difficult challenges society faces during this century. From an economics perspective, this imposes the need to incorporate the environment as a relevant factor in the decision-making pro- cess in order to achieve the necessary efficiency that supports a sustainable future. This dissertation encompasses two essays that tackle environmental economic prob- lems using two different approaches, which ultimately complement each other in their outcomes. First, using a fully theoretical approach, I study how environmental cam- paigns from firms can impact their environmental reputation measured by the belief that consumers have about how clean their production technology is. I found that environmental campaigns can work as effective signals, fully revealing the firm’s type and allowing for novel reputation dynamics. Second, I take an empirical/quantitative approach to study how different types of water rights generate differences in the de- mand for water rights in Colorado. Using the most comprehensive data on water rights transactions in the US West, I can leverage a property of water rights to use the seller’s characteristics as instrumental variables to estimate the demand for water rights differentiated by type of water right. I provide, to the best of my knowledge, the first comparison of different water rights regimes within one overarching water market. I found that, as hypothesized in previous literature, more flexible water rights have higher demand thus moving more water at a given price. Taken together, these two essays show how relevant environmental topics are in a wide range of situations, providing new evidence on the incentives to build reputation once environmental ac- tions are taken into account, and also on how the demand for a natural resource is impacted by the rules that governs its usage and tradability.
ContributorsMesias Moreno, Jorge Andres (Author) / Hanemann, Michael (Thesis advisor) / Kuminoff, Nicolai V (Committee member) / Sheriff, Glenn (Committee member) / Arizona State University (Publisher)
Created2022
Description
There is a growing interest among policymakers and economists in quantifying the relationship between climate and economic output. Previous studies have demon- strated a clear relationship between temperature on economic growth but they generally do not report significant impacts of rainfall in regions outside of developing countries. Using gridded panel data, this paper estimates the effects of the number of days during the growing season with no rainfall on per capita gross domestic product (GDP) growth in the areas of the United States over the Ogallala and Mississippi Aquifers. Measuring precipitation in terms of growing season dry days instead of aggregate rainfall levels reveals a strong negative relationship between rainfall deficits and economic growth.
ContributorsMann, John (Author) / Hanemann, Michael (Thesis director) / Kuminoff, Nicolai (Committee member) / Economics Program in CLAS (Contributor) / School of Mathematical and Statistical Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2020-05