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Experimental and numerical performance analyses of Dish-Stirling cavity receivers: Radiative property study and design
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.ORCID iD: 0000-0003-1792-0551
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.ORCID iD: 0000-0003-3789-8654
Azelio, Regnbagsgatan 6, S-41755 Gothenburg, Sweden..
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
2019 (English)In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 169, p. 478-488Article in journal (Refereed) Published
Abstract [en]

The solar receiver performance has a direct impact on the CSP power plant performance and, thereby, its levelized cost of electricity. Improved receiver designs supported by new advanced numerical tools and experimental validation campaigns directly help to make CSP technology more competitive. This paper presents an experimental and numerical investigation of the influence of the cavity receiver radiative properties and the thermal power input on the Dish-Stirling performance. Three cavity coatings are experimentally investigated: the original cavity material (Fiberfrax 140), Pyromark 2500 and Pyro-paint 634-ZO. Moreover, simulations validated with the experimental measurements are utilized to define a higher performance cavity receiver for the Eurodish system. The results indicate that the absorptivity of the cavity should be as low as possible to increase the receiver efficiency whereas the optimum emissivity depends on the operating temperatures. If the cavity temperature is lower than the absorber temperature, low emissivities are recommended and vice-versa. All material/coatings analyzed for the cavity provide similar receiver efficiencies, being Fiberfrax 140 slightly more efficient. Finally, a total receiver efficiency of 91.5% is reached by the proposed Eurodish cavity receiver when operating under the most favorable external conditions. 

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD , 2019. Vol. 169, p. 478-488
Keywords [en]
Solar simulator, Experimental measurements, Coatings, System modelling, Receiver design
National Category
Energy Systems
Identifiers
URN: urn:nbn:se:kth:diva-247838DOI: 10.1016/j.energy.2018.12.033ISI: 000459528500038Scopus ID: 2-s2.0-85058468339OAI: oai:DiVA.org:kth-247838DiVA, id: diva2:1299160
Note

QC 20190326

Available from: 2019-03-26 Created: 2019-03-26 Last updated: 2020-01-20Bibliographically approved
In thesis
1. Solar cavity receiver design for a dish-Stirling system
Open this publication in new window or tab >>Solar cavity receiver design for a dish-Stirling system
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The growing concern for the climate change has led to an increasing research effort in renewable energy technologies in order to achieve a more sustainable electricity production. Concentrating Solar Power (CSP) is identified as a promising technology to deal with part of the future electricity production. In CSP technologies, a solar receiver converts the concentrated sunlight into high temperature heat. The solar receiver is one of the most critical CSP components as it must provide high thermal power collection efficiencies while operating under very high temperatures and heat fluxes. Thereby, improving the solar receiver efficiency and endurance would benefit the technical and economic viability of CSP.

This PhD thesis aims at improving the efficiency and endurance of a typical solar cavity receiver for the dish-Stirling CSP technology. This research work includes new experimental and numerical analyses contributing to the state of the art of solar receiver design. The efficiency is improved through the analysis of the receiver cavity shape, geometry, operating conditions, and radiative properties, whereas the durability improvement is achieved through the study of advantageous receiver support structures using Finite Element Analysis (FEA). Moreover, a solar laboratory was developed and characterized to conduct representative experiments of the cavity receiver. Multiple parametric experiments were conducted in order to perform a comprehensive validation of the simulations.

During the development of the solar laboratory, it was observed that the commonly utilized flux mapping system (CMOS camera-Lambertian target) should not be used for the characterization of Fresnel lens-based solar simulators. Due to this, the lab characterization was approached combining measurements from a thermopile sensor (radiometer) and a self-designed flat plate calorimeter. Furthermore, a detailed Monte Carlo uncertainty analysis allowed an accurate evaluation of the uncertainty propagation. All the experiments were designed and conducted to increase the accuracy of the final results.

Regarding the cavity receiver design for a dish-Stirling system, the aperture diameter is the most important parameter towards improving the cavity receiver efficiency. The reverse-conical cavity shape provided higher efficiencies (up to 2%) than the cylindrical shape. Additionally, a potential efficiency increase of 0.6% could be achieved by using a cavity material/coating with optimal radiative properties(high emissivity/absorptivity ratio). Finally, the studies suggested that convection has a negligible influence on determining the optimum aperture diameter, whereas the Direct Normal Irradiance (DNI) has little influence. The simulations yielded a cavity receiver with a maximum total receiver efficiency of 91.5%.

Experimental measurements of the receiver displacements under thermal expansion allowed finding realistic mechanical boundary conditions of the receiver. Further structural simulations suggested that thermomechanical stresses can be reduced by setting the receiver supports to certain positions, which can be achieved with the application of external forces and torques. Moreover, the peak stresses can be moved to colder regions to improve the lifetime of the receiver. By shifting the support positions, the receiver simulations calculating creep lifetime under no relaxation showed a potential lifetime improvement of 57%.

Abstract [sv]

Den växande oron för den globala uppvärmningen har lett till en ökad forskningsinsats i förnybar energiteknik mot en hållbarare elproduktion. Koncentrerad solenergi (CSP) identifieras som en lovande teknik för att hantera en del av den framtida elproduktionen. I CSP-tekniken konverterar en solfångare det koncentrerade sollujset till högtemperaturvärme. Solfångaren är en av de kritiska CSPkomponenterna eftersom den arbetar under väldigt höga temperaturer och termiskflöde. Därigenom har solfångarens verkningsgraden och uthålligheten en direkt påverkan på CSP-tekniken och dess ekonomiska genomförbarhet.

Denna doktorsavhandling syftar att förbättra verkningsgraden och hålligheten hos en typisk solkavitetsfångare för dish-Stirling CSP-tekniken. Detta forskningsarbete innehåller nya experimentella och numeriska analyser som inriktar på att förbättra designen. Verkningsgraden förbättras genom analys av solfångarkavitets form, geometri och strålningsegenskaper. Hållfasthetsförbättringen uppnås genom studier av fördelaktiga stödstrukturer för solfångare. Dessutom har ett sollaboratorium utvecklats och karakteriserats för att genomföra representativa experiment. Multipla parametriska experiment andvändes för att validera de numeriska simuleringarna.

Under sollaboratoriets utveckling konstaterades att det allmänt använda CCD-kamera-Lambertian-mål systemet inte kunde användas för sollaboratorikarakteriseringen med Fresnel-linser. På grund av detta utfördes laboratoriekarakteriseringen med en termopil-sensor (mätning av termisk flöde) och en platt kalorimeter. Dessutom gjorde en detaljerad Monte Carlo-osäkerhetsanalys det möjligt att utvärdera osäkerhetskedjan. Experimenten utformades för att öka noggrannheten i de slutligaresultaten.

I den studerade kavitetsfångaren var öppningdiametern den viktigaste parametern för dess verkningrad. Den koniska kavitetsformen gav den högsta verksningsgraden medan verkningsgraden potentiellt kan ökats 0.6% genom idealiska kavitetstrålningsegenskaper (hög emissivitet/absorptivitet förhållande). Studierna antyder att konvektion har en försumbar inverka för att bestämma den optimala öppningsdiametern och DNI-värdet har liten påverkan. Slutligen gav simuleringarna en kavitetsfångare med en maximal total verkningsgrade av 91.5%.

Experimentella mätningar av solfongarens utböjning andändes för att hitta realistiska mekaniska randvillkor. Ytterligare strukturella simuleringar antydde att de termomekaniska spänningarna kan minskas genom justering av solfångarens stödpunkter. Detta kan uppnås med tillämpningen av krafter och vridmoment. Dessutom kan toppspänningarna flyttas till kallare regioner för att förlänga solfångarens livslängd. Med nya stödpositioner kan livslängden mot creep öka 57% för det studerade fallet.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2020. p. 80
Series
TRITA-ITM-AVL ; 2020:2
Keywords
Concentrating Solar Power, Solar receiver, Solar simulator, Uncertainty analysis, Monte Carlo ray tracing, Experimental validation, Coatings, System modeling, Structural analysis, Creep damage, Thermal stress, Cavity receiver design
National Category
Engineering and Technology
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-266773 (URN)978-91-7873-418-4 (ISBN)
Public defence
2020-02-18, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency, CSP-StirlingVinnova, 2016-02836Swedish Research Council Formas, 2016-02836Swedish Energy Agency, 2016-02836
Available from: 2020-01-24 Created: 2020-01-20 Last updated: 2020-01-24Bibliographically approved

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