A Novel Iris Mechanism for Solar Thermal Receivers

Ophoff, Cédric; Özalp, Nesrin

doi:10.1115/1.4037745

Cited by 10 publications

(7 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[2], Ref. [3] and Ref. [4], served as an inspiration for developing one of the mechanisms presented in this paper.…”

Section: Aperture Concepts In Literaturementioning

confidence: 99%

“…All surfaces are assumed gray and opaque. An absorptivity-to-reflectivity ratio of 0.67 was assigned to the mechanisms while the inner cavity of the receiver was modelled with a ratio of 4, which corresponds to their respective material properties [3]. Simulation runs were conducted for the highest achievable power level of the solar simulator, which correlates to 4 kW of radiative power emitted by the xenon arc.…”

Section: Optical Performance Analysismentioning

confidence: 99%

See 1 more Smart Citation

An Overview of Variable Aperture Mechanisms in Attempt to Control Temperature Inside Solar Cavity Receivers

Ophoff

Najafabadi

Bogaerts

et al. 2018

Proceeding of 3rd Thermal and Fluids Engineering Conference (TFEC)

Self Cite

View full text Add to dashboard Cite

In solar thermal research, there is a lot of attention has been paid on optimal design of solar reactors and cavity receivers in order to overcome inherent technical challenges. While many of these studies focus on the geometry and flow optimization of the reactor/receiver, few have focused on control of light entry into the cavity via auxiliary embedded mechanisms. Because the natural fluctuation of solar radiation affecting the thermal behavior of these reactor/receivers during daytime, it is important to address this challenge. In order to cope with transient nature of solar energy, several modular devices have been conceived. They are designed based upon concepts featuring control of set of blades or interchanging apertures to adjust light entry. These techniques yield promising performance on maintaining the desired reactor temperature and solar to fuel efficiencies. Towards that effort, an extensive fundamental background in designing, manufacturing, and testing of such mechanisms has been accumulated by our research group. This paper provides an overview of three successful mechanical apertures developed by our group to regulate flux entry into solar thermal receivers. The overview covers methodological aspects commonly encountered during the design process. A thorough comparison of performance records of these mechanisms are given per their actuation methods. Effect of each aperture mechanism and their individual change of cross-sectional shape is being evaluated through extensive optical simulation. The simulation results give insights on their respective optical performance by quantifying their radiative energy gain and losses. The paper also presents a numerical method coupling optical model to a thermodynamic analysis yielding accurate estimation of reactor temperature per experimental validation. Finally, numerical simulation showed that closed loop control of aperture size can efficiently regulate the temperature throughout a sunny day. Results of this research highlight the advantage of adopting variable apertures in solar cavity receivers.

show abstract

“…[2], Ref. [3] and Ref. [4], served as an inspiration for developing one of the mechanisms presented in this paper.…”

Section: Aperture Concepts In Literaturementioning

confidence: 99%

Section: Optical Performance Analysismentioning

confidence: 99%

An Overview of Variable Aperture Mechanisms in Attempt to Control Temperature Inside Solar Cavity Receivers

Ophoff

Najafabadi

Bogaerts

et al. 2018

Proceeding of 3rd Thermal and Fluids Engineering Conference (TFEC)

Self Cite

View full text Add to dashboard Cite

show abstract

“…Through translational motion of the raindrop shaped blade openings a quasi-circular aperture is provided with a variable radius ranging between 0 and 45 mm. Detailed specifications of the mechanism and the complete design methodology were described previously [16]. The multi-planar configuration of the blades in the iris mechanism indicated possible radiative losses due to internal reflections of the mechanism structure.…”

Section: Variable Aperture Mechanismsmentioning

confidence: 99%

An experimental study on temperature control of a solar receiver under transient solar load

et al. 2019

Self Cite

View full text Add to dashboard Cite

Solar thermochemical process technology has great potential to store solar energy as chemical fuels, however, there remain several challenges that have hindered its industrial commercialization. One of the main challenges is the transient nature of solar energy which causes instability and reduces the efficiency of the process. A promising solution to cope with this problem is to use a variable aperture mechanism to regulate the light entry into solar receiver. A robust control algorithm is required to automatically adjust the aperture size and keep the temperature semi-constant under various transient conditions including short or long cloud coverage and natural variation of solar radiation from sunrise to sunset. In our previous work, an adaptive predictive controller was developed for aperture size adjustment and its performance was evaluated by computer simulations.The present work takes our previous study to the next level by experimental evaluation of the proposed controller on a solar receiver radiated by a 7 kW solar simulator. Two different variable aperture mechanisms, namely as iris mechanism and rotary aperture, are used for adjustment of the light entry into the receiver. Experimental results indicate that both of the mechanisms have reasonable performance in response to changes to a setpoint and disturbance in incoming solar radiation. However, the iris mechanism exhibits superior performance due to its capability of continuously changing the aperture size. For an elaborated evaluation of the iris mechanism, a real day of solar irradiation was simulated in the lab by changing the power level of the solar simulator based on a normal irradiance profile of a sunny day. According to the experimental results, the required temperature control was achieved with a maximum error in the temperature setpoint less than 1.95°C.

show abstract

“…Thus, compensating for any irradiance fluctuation without the need to disturb the flow pattern. Various aperture mechanisms have been developed with different designs and approaches to make this mechanism much more effective and sustainable for solar reactors [13][14][15].…”

Section: Introductionmentioning

confidence: 99%

Numerical and experimental investigation of heat transfer in a solar receiver with a variable aperture

Abuseada

Özalp

Ophoff

2019

International Journal of Heat and Mass Transfer

Self Cite

View full text Add to dashboard Cite

Variable aperture can assist in maintaining semi-constant temperatures within a receiver's cavity under transient solar loading. An in-house code has been developed to model a receiver and effectively control its components to achieve semi-constant temperatures under transients. The code consists of a full optical analysis performed via the Monte Carlo ray tracing method in addition to a transient two-dimensional heat transfer analysis. The system studied consists of a cavity type solar receiver with 60 mm radius fixed aperture on the cavity body, a variable aperture mechanism mounted on the receiver's flange, and a 7 kW Xenon arc solar simulator. A composite shape consisting of a hemisphere attached to a cylinder is proposed to model the Xenon arc. The in-house code has been experimentally validated through experimental tests for different input currents to the solar simulator, volumetric flow rates, and aperture's radii. The optical analysis was validated based on heat flux measurements, where it had percentage errors of 0.8, 0.5, 1.1, and 3.2% for the peak power, total power, half width, and half power. For the heat transfer model, percentage errors of 3.2, 2.9, and 5.3% at the inlet, center, and outlet sections of the receiver were determined for different flow rates using maximum input current and opening radius. The aperture mechanism was capable of maintaining an exhaust temperature of 250°C based on actual Direct Normal Irradiance data. Results showed that the variable aperture is a promising apparatus even in applications where the maximum temperatures are desired based on an observed optimum radius of 57.5 mm.

show abstract

A Novel Iris Mechanism for Solar Thermal Receivers

Cited by 10 publications

References 18 publications

An Overview of Variable Aperture Mechanisms in Attempt to Control Temperature Inside Solar Cavity Receivers

An Overview of Variable Aperture Mechanisms in Attempt to Control Temperature Inside Solar Cavity Receivers

An experimental study on temperature control of a solar receiver under transient solar load

Numerical and experimental investigation of heat transfer in a solar receiver with a variable aperture

Contact Info

Product

Resources

About