Research Papers

A Novel Iris Mechanism for Solar Thermal Receivers

[+] Author and Article Information
Cédric Ophoff

Mechanical Engineering Department,
KU Leuven,
Leuven 3001, Belgium

Nesrin Ozalp

ASME Fellow
Mechanical and Industrial
Engineering Department,
University of Minnesota Duluth,
Duluth, MN 55812
e-mail: nozalp@d.umn.edu

1Present address: Visiting Student at University of Minnesota Duluth, Duluth, MN 55812.

2Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received December 8, 2016; final manuscript received August 4, 2017; published online September 12, 2017. Assoc. Editor: Marc Röger.

J. Sol. Energy Eng 139(6), 061004 (Sep 12, 2017) (10 pages) Paper No: SOL-16-1506; doi: 10.1115/1.4037745 History: Received December 08, 2016; Revised August 04, 2017

Variable aperture mechanisms are being used in many fields including medicine, electronics, fluid mechanics, and optics. The main design characteristics of these aperture concepts are the use of multiple blades regulating aperture area and consequently the incoming medium flow. Manufacturing complexities primarily depend on the concept geometry, material, and the process application requirements. Design of a variable aperture demands meticulous methodology and careful consideration of the application field. This paper provides an in-depth methodology on the design of a novel iris mechanism for temperature control in high temperature solar thermal receivers and solar reactors. Such methodology can be used as a guideline for iris mechanisms implemented in other applications as well as in design of different apparatuses exposed to high temperature. Optical simulations in present study have been performed to demonstrate enhanced performance of the iris mechanism over conventional Venetian blind shutter serving as optical attenuators in concentrating solar power systems. Results showed that optical absorption efficiency is improved by 14% while reradiation loss through the aperture is reduced by 2.3% when the iris mechanism is used. Correlation for adaptive control of aperture area was found through computational surface area measurement. Experimental testing with a 7 kW solar simulator at different power levels demonstrated the performance of the mechanism to maintain stable temperature under variable flux.

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Fig. 1

Effect of DNI on the optical absorption efficiency ηoa: comparison of iris mechanism and shutter for two aperture sizes [21]

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Fig. 2

Optical simulation setup of the PSA solar furnace SF40 [14]

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Fig. 3

(a) Optical absorption efficiency ηoa and (b) RRF versus aperture size

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Fig. 4

(a) Computer-aided design (CAD) drawing of the blade, (b) CAD drawing of the blades assembly, and (c) photo of the manufactured blade

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Fig. 5

(a) Exploded view of the iris mechanism and (b) close-up on driving sprocket

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Fig. 6

(a) Illustration of the iris mechanism and (b) illustration of the blade translation

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Fig. 7

(a) Free body diagram of blade 3 in open position and closing and (b) force diagram of the chain drive

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Fig. 8

(a) CAD demonstration of the progressive change of the cross-sectional aperture area as it closes and (b) experimental closure of the manufactured iris mechanism during testing

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Fig. 9

(a) Intersections of two adjacent blades and (b) blade edges in the Cartesian coordinate plane

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Fig. 10

Surface area A as a function of angular displacement of the stepper motor θ

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Fig. 11

Experimental setup: (a) CAD drawing and (b) snapshot of the iris mechanism mounted to the reactor

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Fig. 12

Reactor temperature versus aperture diameter



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