ORCID Profile
0000-0001-6396-2192
Current Organisations
Universidad Austral de Chile
,
Universidade Federal de Minas Gerais
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Publisher: Elsevier BV
Date: 02-2014
Publisher: Springer Science and Business Media LLC
Date: 31-07-2020
Publisher: American Society of Mechanical Engineers
Date: 26-06-2017
DOI: 10.1115/ES2017-3615
Abstract: Solar thermal towers are a maturing technology that have the potential to supply a significant part of energy requirements of the future. One of the issues that needs careful attention is the heat flux distribution over the central receiver’s surface. It is imperative to maintain receiver’s thermal stresses below the material limits. Therefore, an adequate aiming strategy for each mirror is crucial. Due to the large number of mirrors present in a solar field, most aiming strategies work using a data base that establishes an aiming point for each mirror depending on the relative position of the sun and heat flux models. This paper proposes a multiple-input multiple-output (MIMO) closed control loop based on a methodology that allows using conventional control strategies such as those based on Proportional Integral Derivative (PID) controllers. Results indicate that even this basic control loop can successfully distribute heat flux on the solar receiver.
Publisher: Informa UK Limited
Date: 11-03-2021
Publisher: Elsevier BV
Date: 07-2014
Publisher: Elsevier BV
Date: 05-2019
Publisher: ASME International
Date: 16-11-2016
DOI: 10.1115/1.4035021
Abstract: The application of equilibrium thermodynamics in the study of thermal plant performance under real operating conditions is a constant challenge. In this paper, an analysis of a reservoir pressure piston working between two linear flow resistances is performed by considering the friction of the piston cylinder system on the walls. The proposed model is developed to obtain the optimum power output and speed of the piston in terms of first law efficiency. If the friction on the piston–cylinder assembly is neglected, the expressions obtained are consistent with those presented in the literature under laminar regime. It was also demonstrated that for both laminar and turbulent regimes with overall size constraints, the power delivered can be maximized by balancing the upstream and downstream flow resistances of the piston. This paper also evaluated the influence of the overall size constraints and flow regime on the performance of the piston cylinder. This analysis is equivalent to evaluate the irreversibilities in an endo-irreversible Carnot heat engine with heat loss resistance between the engine and its heat reservoirs. The proposed model introduced some modifications to the results obtained from the recent literature and led to important conclusions. Finally, the proposed model was applied to calculate the lost available work in a turbine operating at steady flow conditions with an ideal gas as working fluid.
Publisher: Elsevier BV
Date: 11-2020
Publisher: Elsevier BV
Date: 11-2019
Publisher: American Society of Mechanical Engineers
Date: 28-06-2015
DOI: 10.1115/ES2015-49843
Abstract: Finding optimal operating conditions of solar-based power and cooling systems is always a challenge. Performance of these systems is highly dependent on several important parameters, which not only impact the long-term efficiency but also its technical and economic feasibility. This paper studies the operation/configuration problem of an ammonia-water power and cooling cycle using an exergetic analysis. Thermodynamic performance of the combined cycle was addressed by using analysis of variance and multiple linear regression analysis. Modeling was done in Matlab®, using Refprop 9.0 to calculate the thermodynamic properties of the ammonia-water mixture. Convergence issues were observed on the thermodynamic properties estimation carried out by Refprop when the stream had high ammonia mass fraction. To solve this issue an averaging algorithm was implemented online to estimate such properties using pure ammonia data and high, but stable, ammonia concentration data. After this implementation, small differences between current and reference model were seen. Optimum operating conditions were obtained using response surface technique. The response variable used was the ratio between exergetic efficiency and exergy destruction. Results showed that the response variable is mainly influenced by the ammonia concentration, pressure ratio, turbine efficiency and temperature gradient in the heat exchanger. Finally integration of the power/cooling cycle with a solar field was performed using two types of concentrated solar collectors: Linear Fresnel Collector (LFC) and Parabolic Trough Collector (PTC). The analysis showed that LFC technology can be a viable alternative for small scale applications combined with power/cooling systems.
Publisher: ASME International
Date: 31-01-2018
DOI: 10.1115/1.4038961
Abstract: Variation in direct solar radiation is one of the main disturbances that any solar system must handle to maintain efficiency at acceptable levels. As known, solar radiation profiles change due to earth's movements. Even though this change is not manipulable, its behavior is predictable. However, at ground level, direct solar radiation mainly varies due to the effect of clouds, which is a complex phenomenon not easily predictable. In this paper, dynamic solar radiation time series in a two-dimensional (2D) spatial domain are obtained using a biomimetic cloud-shading model. The model is tuned and compared against available measurement time series. The procedure uses an objective function based on statistical indexes that allow extracting the most important characteristics of an actual set of curves. Then, a multi-objective optimization algorithm finds the tuning parameters of the model that better fit data. The results showed that it is possible to obtain responses similar to real direct solar radiation transients using the biomimetic model, which is useful for other studies such as testing control strategies in solar thermal plants.
Publisher: Elsevier BV
Date: 10-2016
Publisher: Elsevier BV
Date: 06-2018
Publisher: ASME International
Date: 13-03-2018
DOI: 10.1115/1.4039255
Abstract: Maintaining receiver’s thermal stresses and corrosion below the material limits are issues that need careful attention in solar thermal towers. Both depend on heliostats’ aiming points over the central receiver and available direct solar radiation at any instant. Since this technology relies on an unavoidable time-changing resource, aiming points need to be properly manipulated to avoid excessive hot spots. This paper proposes a new aiming point strategy based on a multivariable model predictive control (MPC) approach. It shows an alternative approach by introducing an agent-based group behavior over heliostats’ subsets, which makes possible either concentrating or dispersing solar radiation as required by the MPC algorithm. Simulated results indicate that it is feasible to develop a closed-loop control procedure that distributes solar irradiance over the central receiver according to the predefined heat flux limits. The performance of the proposed approach is also compared with the results found in the available literature that uses a different methodology.
Location: Venezuela (Bolivarian Republic of)
No related grants have been discovered for Jesus Garcia.