Alexandre K. da Silva

Numerical Optimization and Power Output Control of a Hot Thermal Battery with Phase Change Material

Numerical simulations were conducted to investigate the release of heat from a thermal storage unit, which we refer to as a hot thermal battery. The battery is composed of a hexagonal arrangement of parallel tubes through which a heat absorbing fluid flows, surrounded by phase change material (PCM) that fills spaces between adjacent tubes. The simulations implemented, aimed to optimize the battery such that it meets a total volume constraint while ensuring a critical power output before the phase change fronts of the PCM surrounding two adjacent heat transfer tubes merge—indicating the PCM is completely solidified—after which, only sensible heat can be released by the battery. It was found that the PCM latent heat has negligible impact on the optimal heat exchanger (HEx) design. In comparison, increasing either the flow velocity of the heat transfer fluid in the tubes or PCM thermal conductivity can significantly reduce the needed volume of heat exchanger. Additionally, a novel closed loop control modeling approach is proposed to dynamically tune the heat transfer fluid flow rate such that the thermal battery yields a constant power output. The flow tuning results indicate the optimal dynamic HTF velocity curve shape, obtained from closed-loop method, is unique and this optimal flow velocity is dependent on the location of the phase change front. Numerical results were also compared against hot battery discharge experiments, using both constant and dynamically tuned flow rates, indicating a good agreement for both cases.

The Numerical Optimization of a Neumann-Type Boundary for the Graetz Problem

The main goal of this study is to numerically determine a converged optimal heating pattern for the Graetz problem in a two-dimension channel subjected to a discrete heating profile. The heat input is provided by multiple independent heaters, while considering the following conditions: symmetric and asymmetric heating without a conductive wall and symmetric heating with a conductive wall. The optimization process, which was based on the genetic algorithm, shows a strong dependence of the cooling performance on the heating profile which is especially affected at relatively low flow speeds if the wall conduction is not present. If conduction through the wall is considered, the importance of the heating pattern is reduced for relatively thick walls. Results also indicate that asymmetric heating conditions are not recommended when compared with symmetric patterns.

A framework and methodology for reporting geographically and temporally resolved solar data: A case study of Texas

This paper presents a framework and methodology for reporting measured solar radiation data. Geographically and temporally resolved solar data have been calculated for all 254 counties in Texas using geospatial interpolation of data from 24 existing terrestrial measurement locations. Hourly global, direct, and diffuse horizontal radiation data have been obtained from 15 measurement sites at the Texas Solar Radiation Database, a project at The University of Texas at Austin, and from 9 sites at the National Solar Radiation Database. Average radiation fluxes and peak insolation have been calculated using daylight hours in addition to the total energy in kWh∕m2day. The methodology presented in this paper provides solar insolation data in a convenient format for engineers, scientists, policy-makers, homeowners, and consumers to assess the potential of solar energy at the county resolution. This methodology enables informed decisions about the economic viability of solar installations at particular locations an...

Numerical Modeling of Free-Convection in Sinuous Channels with Leveled and Unleveled Ports

In this article, we numerically study natural convection in U-shaped channels oriented upward or downward. The figure of merit considered is the global conductance. Several opportunities for shape optimization have been revealed. In particular, the following features of U-shaped channels have been varied: spacing between the two vertical channels, breadths of the vertical channels, curvature radii of the connection between the two vertical channels, and the inlet-to-outlet height difference. We also studied the impact of nonuniform heat inputs in the channels and the effect of sequencing two interconnected U-shaped channels. Results suggest that upward facing U-shaped channels offer higher global conductance than their downward facing counterpart. Additionally, the results indicate that the curvature radii of the internal and external surfaces of the U-bend have a minor effect on the figure of merit if the bent breadth does not constrict the flow. Finally, the results show that significant improvements in terms of thermal performance are obtained if non-uniform heat flux conditions are imposed to the heated wall.

A Resource-Limited Approach to Estimating Algal Biomass Production With Geographical Fidelity

This paper discusses the potential for algal biofuel production under resource-limited conditions in Texas. Algal biomass and lipid production quantities are estimated using a fully integrated biological and engineering model that incorporates primary resources required for growth, such as carbon dioxide, sunlight and water. The biomass and lipid production are estimated at the county resolution in Texas, which accounts for geographic variation in primary resources from the Eastern half of the state, which has moderate solar resources and abundant water resources, to the Western half of the state, which has abundant solar resources and moderate water resources. Two resource-limited scenarios are analyzed in this paper: the variation in algal biomass production as a function of carbon dioxide concentration and as a function of water availability. The initial carbon dioxide concentration, ranging from low concentrations in ambient air to higher concentrations found in power plant flue gas streams, affects the growth rate and production of algal biomass. The model compares biomass production using carbon dioxide available from flue gas or refinery activities, which are present only in a limited number of counties, with ambient concentrations found in the atmosphere. Biomass production is also estimated first for counties containing terrestrial sources of water such as wastewater and/or saline aquifers, and compared with those with additional water available from the Gulf of Mexico. The results of these analyses are presented on a series of maps depicting algal biomass and lipid production in gallons per year under each of the resource-limited scenarios. Based on the analysis, between 13.9 and 154.1 thousand tons of algal biomass and 1.0 and 11.1 million gallons of lipids can be produced annually.Copyright