• Energy Research

This work describes the absorption system performance with working pairs LiBr-H2O and Carrol-H2O (Carrol contains LiBr and EG -Ethylene glycol- with a mass ratio at 4.5:1) considering the thermal characteristics enhancement. The enhancements affect the working pairs and components’ properties like surface tension, contact angle, minimum wetting rate (MWR), and thermal conductivity. Surfactants are employed to strengthen the Marangoni effect, hydrophilic treatment is used on the absorber to improve wettability, nanofluids of working pairs are made to increase the thermal conductivity, and mechanical vibration is also considered to enhance mass transfer. Simulations are carried out to investigate the theoretical improvements of the enhancements in the absorption system. The numerical model was implemented on a modular object-oriented simulation platform (NEST platform tool), which allows linking different components, considered objects, which can be either an empirical-based model or a more detailed CFD calculation if necessary. Besides, a simplified 2D model of the falling film is built with C++ to predict the enhancement performance with details. The data of the properties are extracted from previous experimental work or other references in terms of the enhancement characteristics. The heat and mass transfer coefficients will increase 10-30% with nanoparticles in the falling film according to the 2D model. In terms of absorption system simulations, with the nanoparticle enhancement, the thermal conductivity could increase from 5 to 50%. It could increase the working capacity of the absorption system by around 5% at the same operating condition. With the enhancement of surfactants, the working capacity could increase by around 10%, and for the vibration, the improvement is around 5%. In general, in a limited range of current thermodynamic enhancement methods, all the enhancement attribute to a higher working capacity, slightly higher COP, and COPex, while the exergy destruction almost remains the same since the energy input will barely change. This project has received funding from SOLAR-ERA.NET Cofund 2 joint call undertaking under the European Union’s Horizon 2020 research and innovation programme. This work has been financially supported by MCIN/AEI/10.13039/501100011033 programme (Spain), project PID2020- 115837RBI00. J. Zheng holds a China Scholarship Council Studentship with the Polytechnical University of Catalonia. Carles Oliet, as a Serra Húnter lecturer, acknowledges the Catalan Government for the support through this Programme. Peer Reviewed

This work describes the absorption system performance with working pairs LiBr-H2O and Carrol-H2O (Carrol contains LiBr and EG -Ethylene glycol- with a mass ratio at 4.5:1) considering the thermal characteristics enhancement. The enhancements affect the working pairs and components’ properties like surface tension, contact angle, minimum wetting rate (MWR), and thermal conductivity. Surfactants are employed to strengthen the Marangoni effect, hydrophilic treatment is used on the absorber to improve wettability, nanofluids of working pairs are made to increase the thermal conductivity, and mechanical vibration is also considered to enhance mass transfer. Simulations are carried out to investigate the theoretical improvements of the enhancements in the absorption system. The numerical model was implemented on a modular object-oriented simulation platform (NEST platform tool), which allows linking different components, considered objects, which can be either an empirical-based model or a more detailed CFD calculation if necessary. Besides, a simplified 2D model of the falling film is built with C++ to predict the enhancement performance with details. The data of the properties are extracted from previous experimental work or other references in terms of the enhancement characteristics. The heat and mass transfer coefficients will increase 10-30% with nanoparticles in the falling film according to the 2D model. In terms of absorption system simulations, with the nanoparticle enhancement, the thermal conductivity could increase from 5 to 50%. It could increase the working capacity of the absorption system by around 5% at the same operating condition. With the enhancement of surfactants, the working capacity could increase by around 10%, and for the vibration, the improvement is around 5%. In general, in a limited range of current thermodynamic enhancement methods, all the enhancement attribute to a higher working capacity, slightly higher COP, and COPex, while the exergy destruction almost remains the same since the energy input will barely change. This project has received funding from SOLAR-ERA.NET Cofund 2 joint call undertaking under the European Union’s Horizon 2020 research and innovation programme. This work has been financially supported by MCIN/AEI/10.13039/501100011033 programme (Spain), project PID2020- 115837RBI00. J. Zheng holds a China Scholarship Council Studentship with the Polytechnical University of Catalonia. Carles Oliet, as a Serra Húnter lecturer, acknowledges the Catalan Government for the support through this Programme. Peer Reviewed

In the published article Rodriguez et al. (2011) one of the author’s names was misspelled and should have read Ricard Borrell.

In the published article Rodriguez et al. (2011) one of the author’s names was misspelled and should have read Ricard Borrell.

Abstract In the last decades, computational fluid dynamics (CFD) has become a standard design tool in many fields, such as the automotive, aeronautical, and renewable energy industries. The driving force behind this is the development of numerical techniques in conjunction with the progress of high-performance computing (HPC) systems. However, simulation time remains the most limiting factor for large-eddy simulations (LES) to be adopted in the industry. A consensus exists that, to be feasible, LES simulations should be completed overnight In this context, this work assesses the feasibility of overnight LES simulations on GPU-accelerated supercomputers with TFA, our novel in-house code, which relies on a symmetry-preserving discretisation for unstructured collocated grids that, apart from being virtually free of artificial dissipation, is shown to be unconditionally stable. The study cases will be taken from central receivers used in concentrated solar power (CSP) plants, and a comparison with open-source CFD codes will be made.

Abstract In the last decades, computational fluid dynamics (CFD) has become a standard design tool in many fields, such as the automotive, aeronautical, and renewable energy industries. The driving force behind this is the development of numerical techniques in conjunction with the progress of high-performance computing (HPC) systems. However, simulation time remains the most limiting factor for large-eddy simulations (LES) to be adopted in the industry. A consensus exists that, to be feasible, LES simulations should be completed overnight In this context, this work assesses the feasibility of overnight LES simulations on GPU-accelerated supercomputers with TFA, our novel in-house code, which relies on a symmetry-preserving discretisation for unstructured collocated grids that, apart from being virtually free of artificial dissipation, is shown to be unconditionally stable. The study cases will be taken from central receivers used in concentrated solar power (CSP) plants, and a comparison with open-source CFD codes will be made.

Abstract This work is focussed on the development of a numerical simulation model that predicts the thermal and fluid-dynamic behaviour of the two-phase flow distribution in systems with multiple branching tubes like manifolds. The geometry of a simulated branching system is represented as a set of tubes connected together by means of junctions. On one side, the in-tube evaporation/condensation phenomena are simulated by means of a one-dimensional two-phase flow model, and on the other side, the splitting/converging flow phenomena occurring at junctions are predicted with appropriate junction models obtained from the technical literature. The global flow distribution is calculated using a semi-implicit pressure based method (SIMPLE-like algorithm) where the continuity and momentum equations of the whole domain are solved and linked with both the in-tube two-phase flow model and the junction models. In the present paper, the flow distribution model is described and its most significant aspects are detailed. Furthermore, the model is validated against experimental and numerical data found in the open literature. The numerical predictions are compared against an adiabatic single-phase flow manifold system working with water and also against a two-phase flow upwardly oriented manifold system working with carbon dioxide. In addition to this, a numerical comparison of a manifold system with two different orientations is carried out. Concluding remarks about the possibilities that this kind of model offers are presented in the last section.

Abstract This work is focussed on the development of a numerical simulation model that predicts the thermal and fluid-dynamic behaviour of the two-phase flow distribution in systems with multiple branching tubes like manifolds. The geometry of a simulated branching system is represented as a set of tubes connected together by means of junctions. On one side, the in-tube evaporation/condensation phenomena are simulated by means of a one-dimensional two-phase flow model, and on the other side, the splitting/converging flow phenomena occurring at junctions are predicted with appropriate junction models obtained from the technical literature. The global flow distribution is calculated using a semi-implicit pressure based method (SIMPLE-like algorithm) where the continuity and momentum equations of the whole domain are solved and linked with both the in-tube two-phase flow model and the junction models. In the present paper, the flow distribution model is described and its most significant aspects are detailed. Furthermore, the model is validated against experimental and numerical data found in the open literature. The numerical predictions are compared against an adiabatic single-phase flow manifold system working with water and also against a two-phase flow upwardly oriented manifold system working with carbon dioxide. In addition to this, a numerical comparison of a manifold system with two different orientations is carried out. Concluding remarks about the possibilities that this kind of model offers are presented in the last section.