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Shao, X.-F., Yang, S., Wang, C., Yang, Y.-J., Wang, W., Zeng, Y. & Fan, L.-W. (2019). Screening of sugar alcohols and their binary eutectic mixtures as phase change materials for low-to-medium temperature thermal energy storage. (II): Isothermal melting and crystallization behaviors. Energy, 180, 572-583
Open this publication in new window or tab >>Screening of sugar alcohols and their binary eutectic mixtures as phase change materials for low-to-medium temperature thermal energy storage. (II): Isothermal melting and crystallization behaviors
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2019 (English)In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 180, p. 572-583Article in journal (Refereed) Published
Abstract [en]

Based on the non-isothermal phase change behaviors of twenty-one pure and mixture sugar alcohols presented in our previous study (Part 1), the isothermal melting and crystallization behaviors were further tested in this supplemental work for five selected pure sugar alcohols (xylitol, erythritol, dmannitol, d-dulcitol and inositol) and their five binary eutectic mixtures to make an advanced screening of these candidates for low-to-medium temperature latent heat storage. The isothermal melting and crystallization behaviors of these ten candidates were tested at a constant degree of superheat (10 degrees C) and various degrees of subcooling up to 210 degrees C. The phase change temperatures, degrees of supercooling and durations of phase change were determined by the recorded temperature-history curves. It was found that the incrystallizable xylitol and its eutectic mixture of xylitol (75 mol%) + erythritol with low melting points under 100 degrees C are also unable to crystallize during isothermal cool-down at any degrees of subcooling (30-90 degrees C) due to the unavailability to nucleation. The rest eight crystallizable candidates all suffer from severe supercooling and are unable to crystallize at low degrees of subcooling (<20 degrees C). They undergo both one-phase supercooling due to poor nucleation performance and two-phase supercooling, which was unable to be obtained previously by non-isothermal cooling, due to slow crystallization kinetics. However, it seems difficult to find a correlation between the observed degrees of supercooling in both the liquid and solid phases and the prescribed degrees of subcooling by only three consecutive isothermal melting and crystallization cycles, as a result of the randomness of nucleation and large size of samples. The duration of crystallization was shown to decrease with increasing the degree of subcooling for both pure and mixture sugar alcohols due to the enhanced driving force for crystallization. The durations of crystallization of the mixture sugar alcohols appear to be longer than those of their pure compounds, due to the lower thermal conductivity and higher dynamic viscosity of the mixtures. Combining the present isothermal and the previous non-isothermal test results, it has been confirmed that the difficulty in crystallization and the severe supercooling are the primary issues for sugar alcohols, which must be addressed before they can be used in real-world latent heat storage systems.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Binary eutectic mixture, Latent heat storage, Isothermal melting and crystallization, Phase change material, Sugar alcohol, Supercooling
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-255368 (URN)10.1016/j.energy.2019.05.109 (DOI)000474315800046 ()2-s2.0-85066438888 (Scopus ID)
Note

QC 20190805

Available from: 2019-08-05 Created: 2019-08-05 Last updated: 2019-08-05Bibliographically approved
Wang, W. & Laumert, B. (2018). An axial type impinging receiver. Energy, 162, 318-334
Open this publication in new window or tab >>An axial type impinging receiver
2018 (English)In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 162, p. 318-334Article in journal (Refereed) Published
Abstract [en]

An axial type impinging receiver has been developed for a solar dish-Brayton system. By using selective reflection cavity surfaces as a secondary concentrator, the solar irradiation is reflected and concentrated on a cylindrical absorber that is located in the center of the cavity. A modified inverse design method was applied for quickly finding possible cavity receiver designs, and a numerical conjugate heat transfer model combined with a ray-tracing model was utilized for studying the detailed performance of the impinging receivers. The ray-tracing results show that the flux distribution on the cavity and absorber surfaces can be efficiently adjusted to meet the design requirements by changing the absorber diameter, the cavity diameter, the cavity length and the offset length. A candidate receiver design was selected for detailed numerical studies, and the results show that the average outlet air temperature and the radiative-to-thermal efficiency can reach 801.1 °C and 82.8% at a DNI level of 800 W/m2. The temperature differences on the absorber can be controlled within 122.7 °C for DNI level of 800 W/m2, and 126.4 °C for DNI level of 1000 W/m2. Furthermore, the structure is much simpler than a typical radial impinging design. 

Place, publisher, year, edition, pages
Elsevier Ltd, 2018
Keywords
Axial type, Cavity receiver, Concentrated solar power, Dish Brayton, Impinging jet, Heat transfer, Inverse problems, Numerical methods, Solar energy, Brayton, Ray tracing, air temperature, design method, equipment, inverse analysis, irradiation, model, reflectivity, solar power, solar radiation
National Category
Environmental Engineering
Identifiers
urn:nbn:se:kth:diva-236604 (URN)10.1016/j.energy.2018.08.036 (DOI)000447576500027 ()2-s2.0-85053077820 (Scopus ID)
Note

Export Date: 22 October 2018; Article; CODEN: ENEYD; Correspondence Address: Wang, W.; Department of Energy Technology, KTH Royal Institute of TechnologySweden; email: wujun@kth.se; Funding details: EU-FP7; Funding details: 308952; Funding text: This work was financially supported by the European Union's 7th Framework Programme (EU-FP7) project OMSoP (Grant Agreement No. 308952 ). QC 20181126

Available from: 2018-11-26 Created: 2018-11-26 Last updated: 2018-12-07Bibliographically approved
Wang, W., Malmquist, A. & Laumert, B. (2018). Comparison of potential control strategies for an impinging receiver based dish-Brayton system when the solar irradiation exceeds its design value. Energy Conversion and Management, 169, 1-12
Open this publication in new window or tab >>Comparison of potential control strategies for an impinging receiver based dish-Brayton system when the solar irradiation exceeds its design value
2018 (English)In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 169, p. 1-12Article in journal (Refereed) Published
Abstract [en]

Potential control strategies for an impinging receiver based dish-Brayton system have been presented for protecting the key components from the risks of overheating when the solar irradiation exceeds its design value. Two of them are selected for a detailed study: changing the effective diameter of the shading device and changing the inlet temperature. A rope-pulley shading device is developed for controlling the shading area in the center of the dish, and the change of the inlet temperature is achieved by applying a bypass at the cold side of the recuperator for reducing the heat transfer rate. Both control strategies can manage the peak temperature on the absorber surface within 1030 °C with an outlet temperature fluctuation between −4.1 and 15.1 °C, so that the impinging receiver can work for long time at any solar direct normal irradiance value. Furthermore, the temperature differences on the absorber surface are between 137.1 °C and 163.8 °C. The cases that are achieved by changing the shield effective diameter are significantly lower (11–26 °C) than the corresponding cases that are achieved by changing the inlet temperature.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Brayton cycle, Conjugate heat transfer, Control strategy, Impinging solar receiver, Solar dish
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-228710 (URN)10.1016/j.enconman.2018.05.045 (DOI)000436885900001 ()2-s2.0-85047262981 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, 308952
Note

QC 20180530

Available from: 2018-05-30 Created: 2018-05-30 Last updated: 2018-07-17Bibliographically approved
Aichmayer, L., Wang, W., Garrido, J. & Laumert, B. (2018). Experimental evaluation of a novel solar receiver for a micro gas-turbine based solar dish system in the KTH high-flux solar simulator. Energy, 159, 184-195
Open this publication in new window or tab >>Experimental evaluation of a novel solar receiver for a micro gas-turbine based solar dish system in the KTH high-flux solar simulator
2018 (English)In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 159, p. 184-195Article in journal (Refereed) Published
Abstract [en]

This work presents the experimental evaluation of a novel pressurized high-temperature solar air receiver for the integration into a micro gas-turbine solar dish system reaching an air outlet temperature of 800°C. The experiments are conducted in the controlled environment of the KTH high-flux solar simulator with well-defined radiative boundary conditions. Special focus is placed on providing detailed information to enable the validation of numerical models. The solar receiver performance is evaluated for a range of operating points and monitored using multiple point measurements. The porous absorber front surface temperature is measured continuously as it is one of the most critical components for the receiver performance and model validation. Additionally, pyrometer line measurements of the absorber and glass window are taken for each operating point. The experiments highlight the feasibility of volumetric solar receivers for micro gas-turbine based solar dish systems and no major hurdles were found. A receiver efficiency of 84.8% was reached for an air outlet temperature of 749°C. When using a lower mass flow, an air outlet temperature of 800°C is achieved with a receiver efficiency of 69.3%. At the same time, all material temperatures remain below permissible limits and no deterioration of the porous absorber is found.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Pressurized volumetric solar air receiver, Experimental evaluation, High-flux solar simulator
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-226335 (URN)10.1016/j.energy.2018.06.120 (DOI)000442973300017 ()2-s2.0-85049906151 (Scopus ID)
Note

QC 20180420

Available from: 2018-04-17 Created: 2018-04-17 Last updated: 2018-09-19Bibliographically approved
Wang, W., Malmquist, A., Aichmayer, L. & Laumert, B. (2018). Transient performance of an impinging receiver: An indoor experimental study. Energy Conversion and Management, 158, 193-200
Open this publication in new window or tab >>Transient performance of an impinging receiver: An indoor experimental study
2018 (English)In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 158, p. 193-200Article in journal (Refereed) Published
Abstract [en]

The impinging receiver is a new member of the cavity solar receiver family. In this paper, the transient performance of a prototype impinging receiver has been studied with the help of a Fresnel lens based solar simulator and an externally fired micro gas turbine. The impinging receiver can offer an air outlet temperature of 810 °C at an absorber temperature of 960 °C. The radiative-to-thermal efficiency is measured to be 74.1%. The absorber temperature uniformity is good but high temperature differences have been detected during the ‘cold startup’ process. The temperature changing rate of the receiver is within 3 °C/s for the startup process and 4 °C/s for the shut-down process. In order to avoid quenching effects caused by the impinging jets, the micro gas turbine should be turned off to stop the airflow when the radiative power is off. 

Place, publisher, year, edition, pages
Elsevier Ltd, 2018
Keywords
Concentrated solar power, Impinging receiver, Solar energy, Transient performance, Absorber temperatures, Micro gas turbines, Outlet temperature, Start-up process, Temperature changing, Thermal efficiency, Gas turbines
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-223143 (URN)10.1016/j.enconman.2017.12.070 (DOI)000424719200018 ()2-s2.0-85040614193 (Scopus ID)
Note

Export Date: 13 February 2018; Article; CODEN: ECMAD; Correspondence Address: Wang, W.; Department of Energy Technology, KTH Royal Institute of TechnologySweden; email: wujun@kth.se. QC 20180326

Available from: 2018-03-26 Created: 2018-03-26 Last updated: 2018-03-26Bibliographically approved
Garrido, J., Aichmayer, L., Wang, W. & Laumert, B. (2017). Characterization of the KTH high-flux solar simulator combining three measurement methods. Energy, 141, 2091-2099
Open this publication in new window or tab >>Characterization of the KTH high-flux solar simulator combining three measurement methods
2017 (English)In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 141, p. 2091-2099Article in journal (Refereed) Published
Abstract [en]

This paper presents the characterization of the first Fresnel lens-based High-Flux Solar Simulator (HFSS) showing the evaluation of the total thermal radiative power dependent on the aperture radius at the focal plane. This result can be directly applied to calculate the thermal power input into any solar receiver tested in the KTH HFSS. Three measurement setups were implemented and their results combined to assess and verify the characterization of the solar simulator: a thermopile sensor measuring radiative flux, a CMOS camera coupled with a Lambertian target to obtain flux maps, and a calorimeter to measure the total thermal power within an area of 300×300 mm. Finally, a Monte Carlo analysis was performed to calculate the total uncertainties associated to each setup and to combine them to obtain the simulator characterization. The final result shows a peak flux of 6.8 ± 0.35 MW/m2 with a thermal power of 14.7 ± 0.75 kW within an aperture of 180 mm in diameter at the focal plane, and a thermal-electrical conversion efficiency of 25.8 ± 0.3%. It was found very good repeatability and a stable energy output from the lamps during the experiments.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Solar simulator, Characterization, Uncertainty analysis, Monte Carlo
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-219891 (URN)10.1016/j.energy.2017.11.067 (DOI)000423249200061 ()2-s2.0-85036450427 (Scopus ID)
Note

QC 20171215

Available from: 2017-12-15 Created: 2017-12-15 Last updated: 2018-04-17Bibliographically approved
Wang, W., Aichmayer, L., Garrido, J. & Laumert, B. (2017). Development of a Fresnel lens based high-flux solar simulator. Solar Energy, 144, 436-444
Open this publication in new window or tab >>Development of a Fresnel lens based high-flux solar simulator
2017 (English)In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 144, p. 436-444Article in journal (Refereed) Published
Abstract [en]

In this paper, a Fresnel lens based high flux solar simulator (HFSS) is developed for concentrating solar power research and high temperature material testing. In this design, each commercially available 7 kW(e) xenon-arc lamp is coupled with a silicone-on-glass Fresnel lenses as the optical concentrator, and 12 lamp-lens units are distributed in a circular array. In total, the power of the solar simulator can reach 84 kWe. A ray tracing model has been developed based on the real arc-emitter shape and the Fresnel lens optics for predicting the optical performance of the HFSS design. The testing result shows that the ray tracing model can predict the flux distribution on the focal plane accurately but a bit conservative in the center region. The flux distribution on the focal plane appears axisymmetric with a peak flux of 7.22 MW/m(2), and 19.7 kW of radiative power in total is delivered on a 280 mm diameter target. (C) 2017 Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2017
Keywords
High flux solar simulator, Fresnel lens, Concentrating solar energy, Xenon lamp
National Category
Energy Systems
Identifiers
urn:nbn:se:kth:diva-205490 (URN)10.1016/j.solener.2017.01.050 (DOI)000397550500044 ()2-s2.0-85011317412 (Scopus ID)
Note

QC 20170524

Available from: 2017-05-24 Created: 2017-05-24 Last updated: 2018-04-17Bibliographically approved
Liu, Q., Wang, W. & Palm, B. (2017). Numerical study of the interactions and merge of multiple bubbles during convective boiling in micro channels (vol 81, pg 116, 2017). International Communications in Heat and Mass Transfer, 81, R1-R1
Open this publication in new window or tab >>Numerical study of the interactions and merge of multiple bubbles during convective boiling in micro channels (vol 81, pg 116, 2017)
2017 (English)In: International Communications in Heat and Mass Transfer, ISSN 0735-1933, E-ISSN 1879-0178, Vol. 81, p. R1-R1Article in journal (Refereed) Published
Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2017
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-205103 (URN)10.1016/j.icheatmasstransfer.2017.01.001 (DOI)000397359200014 ()2-s2.0-85013448409 (Scopus ID)
Note

QC 20170626

Available from: 2017-06-26 Created: 2017-06-26 Last updated: 2017-11-09Bibliographically approved
Wang, W., Wang, B., Li, L., Laumert, B. & Strand, T. (2016). The effect of the cooling nozzle arrangement to the thermal performance of a solar impinging receiver. Solar Energy, 131, 222-234
Open this publication in new window or tab >>The effect of the cooling nozzle arrangement to the thermal performance of a solar impinging receiver
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2016 (English)In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 131, p. 222-234Article in journal (Refereed) Published
Abstract [en]

The effect of the multi-row nozzle arrangement to the thermal performance of an impinging solar receiver is studied, and new governingequations are introduced for modifying the earlier introduced inverse design method. With the help of the modified inverse designmethod and a numerical conjugate heat transfer model, an impinging receiver based on stainless steel 253 MA material has been designedfor the combination of a micro gas turbine and the EuroDish collector system. At a DNI level of 800 W/m2, the average air temperatureat the outlet and the thermal efficiency can reach 1071.5 K and 82.7%. Furthermore, the temperature differences on the absorber can bereduced to 130 K and 149 K for two different DNI levels respectively. This represents a greatly improvement compared with other publishedcavity receiver designs.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Impinging solar receiver; Nozzle arrangement; Conjugate heat transfer; Dish Brayton system
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-183389 (URN)10.1016/j.solener.2016.02.052 (DOI)000375811400020 ()2-s2.0-84960100151 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, 308952
Note

QC 20160316

Available from: 2016-03-09 Created: 2016-03-09 Last updated: 2017-11-30Bibliographically approved
Wang, W. (2015). Development of an Impinging Receiver for Solar Dish-Brayton Systems. (Doctoral dissertation). Stockholm: KTH Royal Institute of Technology
Open this publication in new window or tab >>Development of an Impinging Receiver for Solar Dish-Brayton Systems
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A new receiver concept utilizing impinging jet cooling technology has been developed for a small scale solar dish-Brayton system. In a typical impinging receiver design, the jet nozzles are distributed evenly around the cylindrical absorber wall above the solar peak flux region for managing the temperature at an acceptable level. The absorbed solar irradiation is partially lost to the ambient by radiation and natural convection heat transfer, the major part is conducted through the wall and taken away by the impingement jets to drive a gas turbine. Since the thermal power requirement of a 5 kWe Compower® micro gas turbine (MGT) perfectly matches with the power collected by the EuroDish when the design Direct Normal Irradiance (DNI) input is 800 W/m2, the boundary conditions for the impinging receiver design in this work are based on the combination of the Compower®MGT and the EuroDish system.

In order to quickly find feasible receiver geometries and impinging jet nozzle arrangements for achieving acceptable temperature level and temperature distributions on the absorber cavity wall, a novel inverse design method (IDM) has been developed based on a combination of a ray-tracing model and a heat transfer analytical model. In this design method, a heat transfer model of the absorber wall is used for analyzing the main heat transfer process between the cavity wall outer surface, the inner surface and the working fluid. A ray-tracing model is utilized for obtaining the solar radiative boundary conditions for the heat transfer model. Furthermore, the minimum stagnation heat transfer coefficient, the jet pitch and the maximum pressure drop governing equations are used for narrowing down the possible nozzle arrangements. Finally, the curves for the required total heat transfer coefficient distribution are obtained and compared with different selected impinging arrangements on the working fluid side, and candidate design configurations are obtained.

Furthermore, a numerical conjugate heat transfer model combined with a ray-tracing model was developed validating the inverse design method and for studying the thermal performance of an impinging receiver in detail. With the help of the modified inverse design method and the numerical conjugate heat transfer model, two impinging receivers based on sintered α-SiC (SSiC) and stainless steel 253 MA material have been successfully designed. The detailed analyses show that for the 253 MA impinging receiver, the average air temperature at the outlet and the thermal efficiency can reach 1071.5 K and 82.7% at a DNI level of 800 W/m2 matching the system requirements well. Furthermore, the local temperature differences on the absorber can be reduced to 130 K and 149 K for two different DNI levels, which is a significant reduction and improvement compared with earlier published cavity receiver designs. The inverse design method has also been verified to be an efficient way in reducing the calculation costs during the design procedure.

For the validation and demonstration of the receiver designs, a unique experimental facility was designed and constructed. The facility is a novel high flux solar simulator utilizing for the first time Fresnel lenses to concentrate the light of 12 commercial high power Xenon-arc lamps. Finally, a prototype of a 253 MA based impinging was experimentally studied with the help of the 84 kWe Fresnel lens based high flux solar simulator in KTH.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. p. xxiv, 111
Series
TRITA-KRV, ISSN 1100-7990 ; 15:05
Keywords
Concentrating solar power; Impinging receiver; Inverse design method; Conjugate heat transfer; High flux solar simulator
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-177531 (URN)978-91-7595-796-8 (ISBN)
Public defence
2015-12-16, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 09:30 (English)
Opponent
Supervisors
Projects
Optimised Microturbine Solar Power System , OMSOP
Funder
EU, FP7, Seventh Framework Programme, FP7-308952​
Note

QC 20151123

Available from: 2015-11-23 Created: 2015-11-23 Last updated: 2015-11-23Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-4134-3520

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