To increase the efficiency of Concentrated Solar Power (CSP) plants, the use of optimization methods is a current topic of research. This paper focuses on applying an integrated optimization technology to a solar thermal application, more specifically for the optimization of a trapezoidal cavity absorber of an LFR (Linear Fresnel Reflector), also called a Linear Fresnel Collector (LFC), CSP plant. LFR technology has been developed since the 1960s, and while large improvements in efficiencies have been made, there is still room for improvement. Once such area is in the receiver design where the optimal cavity shape, coatings, insulation thickness, absorber pipe selection, layout and spacing always need to be determined for a specific application. This paper uses a commercial tool to find an optimal design for a set of operating conditions. The objective functions that are used to judge the performance of a 2-D cavity are the combined heat loss through convection, conduction and radiation, as well as a wind resistance area. In this paper the effect of absorbed irradiation is introduced in the form of an outer surface of pipe temperature. Seven geometrical parameters are used as design variables. Based on a sample set requiring 79 CFD simulations, a global utopia point is found that minimizes both objectives. The most sensitive parameters were found to be the top insulation thickness and the cavity depth. Based on the results, the Multi-Objective Genetic Algorithm (MOGA) as contained in ANSYS DesignXplorer is shown to be effective in finding candidate optimal designs as well as the utopia point.

A computational approach is presented, which uses the finite volume (FV) method in the Computational Fluid Dynamics (CFD) solver ANSYS Fluent to conduct the ray tracing required to quantify the optical performance of a line concentration Concentrated Solar Power (CSP) receiver, as well as the conjugate heat transfer modelling required to estimate the thermal efficiency of such a receiver. A Linear Fresnel Collector (LFC) implementation is used to illustrate the approach. It is shown that the Discrete Ordinates method can provide an accurate solution to the Radiative Transfer Equation (RTE) if the shortcomings of its solution are resolved appropriately in the FV CFD solver. The shortcomings are due to false scattering and the socalled ray effect inherent in the FV solution. The approach is first evaluated for a 2-D test case involving oblique collimated radiation and then for a more complex 2-D LFC optical domain based on the FRESDEMO project. For the latter, results are compared with and validated against those obtained with the Monte Carlo ray tracer, SolTrace. The outcome of the FV ray tracing in the LFC optical domain is mapped as a non-uniform heat flux distribution in the 3-D cavity receiver domain and this distribution is included in the FV conjugate heat transfer CFD model as a volumetric source. The result of this latter model is the determination of the heat transferred to the heat transfer fluid running in the collector tubes, thereby providing an estimation of the overall thermal efficiency. To evaluate the effectiveness of the phased approach in terms of accuracy and computational cost, the novel 2-D:3-D phased approach is compared with results of a fully integrated, but expensive 3-D optical and thermal model. It is shown that the less expensive model provides similar results and hence a large cost saving. The novel approach also provides the benefit of working in one simulation environment, i.e. ANSYS Workbench, where optimisation studies can be carried out to maximise the performance of linear CSP reflector layout and receiver configurations.

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With the increasing demand for energy consumption in domestic buildings and consequent CO 2 emission, there is a need to provide proper products to reduce energy loss. Domestic radiators for space heating can be improved by using a Compact Latent Heat Storage (CLHS) unit mounted on the wall side surface in order to offer energy saving and peak-shaving. The unit offers the potential to save otherwise wasted energy from the back surface of the radiator to the walls in the charging mode of the energy storage system. When the heating system is turned off, the CLHS unit discharges the stored heat towards the room to provide a uniform temperature on the surface of the radiator. An aluminium foam embedded inside the bulk Phase Change Material (PCM) can modify the heat storage/retrieval rate. A PCM is selected depending on the radiator's surface temperature, which is almost equal to the hot water temperature delivered to the radiator. Different metal foam porosities are examined and compared with the PCM-only alternative (i.e. without metal foam enhancement). The results show the porous-PCM CLHS alternative provides an almost constant temperature during the discharging process equal to 54°C. However, for the PCM-only alternative, the temperature of the surface reduces continuously. Using the porous medium results in a shorter melting time, about 95% of what is needed for the PCM-only alternative. Increasing the metal foam porosity results in shorter charging/discharging time; however, since the surface temperature of the porous-PCM unit is almost constant for different metal foam porosities, a system with higher porosity (97%) is desirable.

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The application of phase-change materials (PCMs) has received significant interest for use in thermal energy storage (TES) systems that can adjust the mismatch between the energy availability and demand. In the building sector, for example, PCMs can be used to reduce airconditioning energy consumption by increasing the thermal capacity of the walls. However, as promising this technology may be, the poor thermal conductivity of PCMs has acted as a barrier to its commercialization, with many heat-transfer enhancement solutions proposed in the literature, such as microencapsulation or metal foam inserts, being either too costly and/or complex. The present study focuses on a low-cost and highly practical solution, in which natural-convective heat transfer is enhanced by placing the PCM in an eccentric annulus within a horizontal double-pipe TES heat exchanger. This paper presents an annulus-eccentricity optimisation study, whereby the optimal radial and tangential eccentricities are determined to minimize the charging time of a PCM thermal energy store. The storage performance of several geometrical configurations is predicted using a computational fluid dynamics (CFD) model based on the enthalpy-porosity formulation. The optimal geometrical configuration is then determined with response surface methods. The horizontal double-pipe heat exchanger studied considered here is an annulus filled with N-eicosane as the PCM for initial studies. In presence of N-eicosane, for the concentric configuration (which is the baseline case), the charging is completed at Fo = 0.64, while the charging of optimum eccentric geometries with the quickest and slowest charging is completed at Fo = 0.09 and Fo = 2.31, respectively. In addition, an investigation on the discharging performance of the studied configurations with N-eicosane shows the quickest discharge occurs with the concentric annulus case at Fo = 0.99, while the discharge time of the proposed optimum annuli is about three times this value. In other words, the proposed optimum geometry with the quickest charging time charges~7.1 times faster but also discharges~3 times slower, which is ideal for a TES, especially when used as passive thermal storage systems in nearly zero-emission buildings. Complementary studies demonstrate that the proposed optimum configuration improves the TES performance also when employing other PCM types as well as various shell-to-tube diameter ratios.

Wind barriers, according to their sizes and shapes, can effectively control, shift and even modify the airflow field in their downstream. These structures can accelerate the wind flow over the mirror field and move the airborne particles away from the mirrors. For example, in concentrated solar power plants it is highly desirable to engineer the system in a way that fewer particles are deposited within the solar field, in particular, onto mirror surfaces. Therefore, design optimization of dust barriers could significantly impact the mirror soiling and favourably reduce the cleaning water consumption of a solar power plant. This study focuses on the optimization of a solid wind barrier around a parabolic trough collector plant for their protection against dust soiling. The presented simulation results show that an optimum solid wind barrier is able to direct large amount of particles (in this study, more than 86%) to pass over the solar field with very small fraction (around 0.8%) being deposited on the mirrors. In addition, it was found that the barrier wall is more effective in deflecting the larger particles from the solar field.

The use of annular fins in air-cooled heat exchangers is a well-known solution, commonly used in airconditioning and heat-recovery systems, for enhancing the air-side heat transfer. Although associated with additional material and manufacturing costs, custom-designed finned-tube heat exchangers can be cost-effective. In this article, the shape of the annular fins in a multi-row air heat exchanger is optimised in order to enhance performance without incurring a manufacturing cost penalty. The air-side heat transfer, pressure drop and entropy generation in a regular, four-row heat exchanger are predicted using a steady-state turbulent CFD model and validated against experimental data. The validated simulation tool is then used to perform model-based optimisation of the fin shapes. The originality of the proposed approach lies in optimising the shape of each fin row individually, resulting in a non-homogenous custom bundle of tubes. Evidence of this local-optimisation potential is first provided by a short preliminary study, followed by four distinct optimisation studies (with four distinct objective functions), aimed at addressing the major problems faced by designers. Response-surface methods-namely, NLPQL for single-objective and MOGA for multi-objective optimisations-are used to determine the optimum configuration for each optimisation strategy. It is shown that elliptical annular-shaped fins minimise the pressure drop and entropy generation, while circular-shaped fins at the entrance region (i.e., first row) can be employed to maximise heat transfer. The results also show that, for the scenario in which the total heat transfer rate is maximised and the pressure drop minimised, the pressure drop is reduced by up to 31%, the fin weight is reduced up to 23 %, with as little as a 14 % decrease in the total air-side heat transfer, relative to the case in which all the fins across the tube bundle are circular. Moreover, in all optimised cases, the entropy generation rate is also reduced, which shows a thermodynamic improvement in tube bundle performance.