A Predictive Thermal Model of Heat Transfer in a Fiber Optic Bundle for a Hybrid Solar Lighting System

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Date
2006Author
Cheadle, Michael
Publisher
University of Wisconsin-Madison
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Show full item recordAbstract
Hybrid lighting systems distribute natural sunlight to luminaires in office or other retail buildings
in order to provide natural lighting that can impact employee productivity, morale, and even
sales. In some situations, these systems may also result in a significant reduction in energy
consumption by reducing both the lighting energy and the cooling load that is associated with
conventional lighting systems. A key component of a hybrid lighting system is the fiber optic
bundle (FOB) that transmits the light from the collector to the luminaire. The FOB consists of
many small plastic optical fibers in a close-packed array. The thermal failure of these FOBs
when exposed to concentrated sunlight has motivated the development of a thermal model that
can be used to understand the behavior of these systems. Thermal management is necessary due
to the concentrated incident solar radiation on the face of the fiber optic bundle and the low
melting point temperature of the plastic optical fiber.
A predictive thermal model of heat transfer in a fiber optic bundle for a hybrid solar lighting
system has been developed in order to better understand and manage the thermal loading
associated with the concentrated solar radiation on the face of the FOB. Experiments were
carried out on an instrumented FOB section exposed to illumination energy in a controlled
environment. The experimental results provide information regarding the characteristics of the
thermal loads that result from the radiation that is incident on the pores between the fibers as
well as the effective, anisotropic thermal conductivity associated with the complex structure that
makes up the FOB. It was found that the radiation incident on the FOB face contributed to the
thermal loading in two ways: radiation incident on the face of the plastic fibers contributed a
low level of volumetric generation within the FOB related to the transmission loss while
ii
radiation incident on the air gaps between plastic fibers contributed a volumetric generation
concentrated near the face of the FOB.
The experimental results were used to specify the thermal loads and equivalent parameters
required for a more detailed, multidimensional finite element model (FEM) of the FOB and its
support structure. This FEM is used to understand the transient behavior of the FOB and
evaluate alternative thermal management strategies.
Subject
Thesis (M.S.)--University of Wisconsin--Madison, 2006.
Dissertations Academic Mechanical Engineering.
University of Wisconsin--Madison. College of Engineering.
Permanent Link
http://digital.library.wisc.edu/1793/7698Description
Professor Gregory F. Nellis; 164pp.
Citation
Cheadle, M. (2006). A Predictive Thermal Model of Heat Transfer in a Fiber Optic Bundle for a Hybrid Solar Lighting System. Master's Thesis, University of Wisconsin-Madison.