Electromagnetically driven liquid iris

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.

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“…A design by Ref. [8] was developed as an electromagnetic liquid iris. An electric coil is wrapped around the cylinder cell.…”

Section: Aperture Concepts In Literaturementioning

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)

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“…[ 4 ] Another segment‐based approach is the self‐regulating iris using liquid crystal elastomer that has been proposed, [ 5 ] though leading to diffraction spikes in out‐of‐focus light as observed in all non‐circular apertures. [ 6 ] Technological advances in dynamic circular apertures include magnetically activated ferrofluids [ 7 ] and LCD, [ 8 ] which provide fast shading capabilities but lack flexibility and rely on external activation resulting in larger dimensions of the devices.…”

Section: Introductionmentioning

confidence: 99%

Dynamic Light Control Using Bionic Dielectric Elastomer Iris Actuators

Martin

Bruns

Franke

2022

Adv Funct Materials

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Apertures are used in optical systems to limit the luminous flux. In the human eye the iris serves this purpose but can be damaged requiring an implant, which to date is static, limiting the optical performance. The authors thus report the development of a prototype demonstrating the feasibility of a flexible dynamic iris implant manufactured with an automated manufacturing technique. The presented actuators are printed via aerosol jet printing allowing a high reliability in produced electrode quality. Through optimization of the actuator design for maximum contraction they demonstrate a pupil area reduction of 13.40% or 6.94% reduction of pupil diameter, respectively. Thereby the prototype demonstrates an illuminance reduction of 18.25% in the central visual axis. Furthermore, they present a first iteration of a bionic closed-loop control mimicking the human iris reflex thus laying the foundation for a self-controlled iris implant.

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“…Consequently, they can be used to enhance the performance of conventional electromagnetic actuation systems, including Lorentz force (voice coil) actuators 11 , 12 . Ferrofluids can also provide a fundamentally different method of actuation where motion of a mechanical system is dependent on pressure and flow within the fluid, controlled directly via an electromagnetic field 13 – 15 . Various applications for ferrofluid actuators in high precision and micro-scale motion control systems have been proposed 4 , 14 – 17 .…”

Section: Introductionmentioning

confidence: 99%

On force generation in electro-fluidic linear actuators with ferrofluid

Cole

Moran

2022

Sci Rep

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In ferrofluid actuation systems, forces are generated by actively controlling pressure and flow within the fluid using an applied magnetic field. There are multiple contributing factors in force generation involving complex non-linear couplings between electromagnetic and fluid pressure fields. This brings significant challenges in theory-based design and optimization. In this paper, a theoretical model of pressure transmission between a ferrofluid and solid is derived starting from Maxwell’s stress tensor and accounting for magnetic saturation within the fluid. This model shows that linear actuator designs based on orthogonal mode operation, where the field direction through the fluid is perpendicular to the motion direction, can provide the highest force capacity for a given field strength from the actuator coil. This is verified by theoretical analysis of some basic linear actuator topologies. The results are applied in the design and analysis of a novel piston-type linear actuator with sealed chamber and two internal electrical coils for bidirectional operation. Experimental measurements of both static and dynamic behaviour are shown to validate the described principles. The actuator produces smooth and precise flow-regulated motion, has zero intrinsic stiffness, and exhibits very low friction due to the suspension effect from ferrofluid layers within the actuator.

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Electromagnetically driven liquid iris

Cited by 21 publications

References 26 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

Dynamic Light Control Using Bionic Dielectric Elastomer Iris Actuators

On force generation in electro-fluidic linear actuators with ferrofluid

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