Javier Bonilla

A heuristic method to minimise the chattering problem in dynamic mathematical two-phase flow models

This paper introduces the chattering problem in dynamic mathematical two-phase flow models. The real system object of study is also introduced, the DISS test facility, a parabolic-trough solar power plant using as heat transfer fluid the steam-water mixture. A dynamic model for studying its behaviour was previously developed using Modelica as the modelling language, in this model the chattering problem arises and therefore not allowing to take full advantage of dynamic simulations. The chattering problem increases the computational time needed for simulation and sometimes dynamic simulations do not finish at all. A heuristic method, which minimises the effects of the chattering problem, is discussed and results which reduce the computational time for dynamic simulations are given.

Control strategies in a thermal oil – Molten salt heat exchanger

This paper presents a preliminary control scheme for a molten salt – thermal oil heat exchanger. This controller regulates the molten salt mass flow rate to reach and maintain the desired thermal oil temperature at the outlet of the heat exchanger. The controller architecture has been tested using an object-oriented heat exchanger model that has been validated with data from a molten salt testing facility located at CIEMAT-PSA. Different simulations are presented with three different goals: i) to analyze the controller response in the presence of disturbances, ii) to demonstrate the benefits of designing a setpoint generator and iii) to show the controller potential against electricity price variations.

Object-oriented modelling and simulation of ACUREX solar thermal power plant

Research and development of advanced control systems to optimize the overall performance of parabolic trough collector (PTC) solar power plants is a priority line of research at the CIEMAT (Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas - Research Centre for Energy, Environment and Technology). These developments are underway at the CIEMATs Plataforma Solar de Almera (PSA), a highly specialized solar energy technology research centre. Some dynamic models for use in simulation and control of this type of solar power plant, developed in the PSA ACUREX facility, are presented in this article. The models developed are based on the ThermoFluid thermohydraulic modelling framework, in the Modelica modelling language. The ACUREX facility is presented with the main components modelled and their respective modelling assumptions. An operation strategy is presented and modelled based on the StateGraph Modelica library for discrete and reactive system modelling. A typical experiment is simulated with real experimental input data, a discrete operating strategy is designed and predicted model data are presented and discussed.

Object-Oriented Modeling of Switching Moving Boundary Models for Two-phase Flow Evaporators

Abstract The present paper describes the design of switching moving boundary models for two-phase flow evaporators and the development of an object-oriented library written in the Modelica language. The main idea is to design basic models for each flow state: subcooled liquid, two-phase flow and superheated steam, applying the conservation laws. The design must be done in order that the basic models can be interconnected to create complete, flooded or dry-expansion evaporators depending on the particular case. The basic models should consider the balances of mass, energy and momentum, meanwhile the evaporator models should include mechanisms to switch between them, for example from a complete evaporator to a flooded evaporator in case that the superheated region becomes extinct. Several models currently exist although none of them include all the desirable features.

New approach for solar tracking systems based on computer vision, low cost hardware and deep learning

In this work, a new approach for Sun tracking systems is presented. Due to the current system limitations regarding costs and operational problems, a new approach based on low cost, computer vision open hardware and deep learning has been developed. The preliminary tests carried out successfully in Plataforma solar de Almeria (PSA), reveal the great potential and show the new approach as a good alternative to traditional systems. The proposed approach can provide key variables for the Sun tracking system control like cloud movements prediction, block and shadow detection, atmospheric attenuation or measures of concentrated solar radiation, which can improve the control strategies of the system and therefore the system performance.

A Novel Heat Exchanger Design Method Using a Delayed Rejection Adaptive Metropolis Hasting Algorithm

Abstract In this study, a shell-and-tube heat exchanger (STHX) design based on seven continuous independent design variables is proposed. Delayed Rejection Adaptive Metropolis hasting (DRAM) was utilized as a powerful tool in the Markov chain Monte Carlo (MCMC) sampling method. This Reverse Sampling (RS) method was used to find the probability distribution of design variables of the shell and tube heat exchanger. Thanks to this probability distribution, an uncertainty analysis was also performed to find the quality of these variables. In addition, a decision-making strategy based on confidence intervals of design variables and on the Total Annual Cost (TAC) provides the final selection of design variables. Results indicated high accuracies for the estimation of design variables which leads to marginally improved performance compared to commonly used optimization methods. In order to verify the capability of the proposed method, a case of study is also presented, it shows that a significant cost reduction is feasible with respect to multi-objective and single-objective optimization methods. Furthermore, the selected variables have good quality (in terms of probability distribution) and a lower TAC was also achieved. Results show that the costs of the proposed design are lower than those obtained from optimization method reported in previous studies. The algorithm was also used to determine the impact of using probability values for the design variables rather than single values to obtain the best heat transfer area and pumping power. In particular, a reduction of the TAC up to 3.5% was achieved in the case considered.

Control strategies applied in the HYSOL demonstrator: A simulation-based evaluation

HYSOL project was born under the idea of designing a new hybrid concentrating solar power plant concept fully based on renewable energies and able to provide stable power. Within this project, one of the main activities is the development of a demonstrator facility to evaluate experimentally the gas turbine heat recovery and its transference to a molten-salt storage system. This paper describes the main control loops proposed to maintain the facility at different operating points to study both nominal and off-design states.