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Pacific University Pacific University
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College of Optometry Theses, Dissertations and Capstone Projects
5-1993
A ronchi grid technique for the optical study of heat flow A ronchi grid technique for the optical study of heat flow
Carolyn Clark Pacific University
Michael Young Pacific University
Recommended Citation Recommended Citation Clark, Carolyn and Young, Michael, "A ronchi grid technique for the optical study of heat flow" (1993). College of Optometry. 1044. https://commons.pacificu.edu/opt/1044
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A ronchi grid technique for the optical study of heat flow A ronchi grid technique for the optical study of heat flow
Abstract Abstract We have combined two Ronchi grids to form a Toepler's schlieren system. Using this system we were able to photograph the distribution of heat as it propagates through water. This method is better than simple schlieren photography and shadowgraphy because the resulting moire' pattern shows directly, in the form of a map, how the heat is dispersed in the liquid. The added dimension, that is, the distortion of the grid lines, seen in the photographs indicates the magnitude of the gradient in an otherwise regular pattern.
Degree Type Degree Type Thesis
Degree Name Degree Name Master of Science in Vision Science
Committee Chair Committee Chair Jurgen R. Meyer-Arendt
Subject Categories Subject Categories Optometry
This thesis is available at CommonKnowledge: https://commons.pacificu.edu/opt/1044
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A Ronchi Grid Technique for the Optical Study of Heat Flow
by
Carolyn Clark, B.S. Michael Young, B.S.
A thesis submitted to the faculty of the College of Optometry
Pacific University Forest Grove Oregon
for the degree of Doctor of Optometry
May, 1993
Faculty Advisor:
Jurgen R. Meyer-Arendt, M.D.
A Ronchi Grid Technique for the Optical Study of Heat Flow
Thesis Submitted By:
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Accepted by:
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About the Authors
Carolyn Clark, graduated from the University of Minnesota in 1989 with
a Bachelor of Science degree in Biology. She is currently a fourth year
optometry student at Pacific University College of Optometry in Forest
Grove, Oregon and is a candidate for a Doctor of Optometry degree with
Honors in May 1993. She is currently a member of the Student
Optometric Association.
Michael Young, a native of Nebraska, is a graduate of Pacific University
where he obtained a Bachelor of Science degree with a major in Visual
Science. He is a member of the Student Optometric Association and Phi
Theta Upsilon. He will be graduating from Pacific University with a
Doctorate of Optometry in May of 1993.
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ABSTRACT:
We have combined two Ronchi grids to form a Toepler's schlieren
system. Using this system we were able to photograph the distribution of heat as
it propagates through water. This method is better than simple schlieren
photography and shadowgraphy because the resulting moire' pattern shows
directly, in the form of a map, how the heat is dispersed in the liquid. The added
dimension, that is, the distortion of the grid lines, seen in the photographs
indicates the magnitude of the gradient in an otherwise regular pattern.
3
Acknowledgements
We would like to express our gratitude to Dr. Jurgen Meyer-Arendt, our
advisor for all of his support; Todd Erickson, Leigh Sha Chervenka and
John Huard for their cameras and supplies.
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INTRODUCTION:
Toepler's schlieren technique has long been used because it can convert
otherwise hard-to-see light refractions in transparent media into visible and
recordable images. These photographic images are two-dimensional. In order to
show the magnitude of the gradient, another dimension should be added. By
placing a Ronchi grid on each side of the fluid which contains the gradient, the
magnitude of the distortion produced by the gradient creates an additional
dimension which can be seen and photographed.
A Ronchi grid contains a series of parallel lines with uniform spacing.
When two of these grids are superimposed nearly parallel to one another, a
moire' pattern results. This pattern is another sequence of parallel lines which
may or may not be oriented in the same direction as the original grid lines,
depending on the index of refraction of the fluid. Without any optical gradients
present, the lines are straight. However, with such gradients present, the grid
pattern will show characteristic distortions. These distortions show as bent or
wavy lines. The exact position of the grids is not critical. The closer the grids are
to each other, the more fringes appear, and the more obvious the bending
becomes.
In our experiments we used a heat wave and its propagation through a
glass container filled with cold tap water, to show documentation of the added
dimension.
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APPARATUS:
The following supplies were used to create the moire' patterns and their
distortions:
-110 Watt incandescent light source.
- Opaque diffusing filter attached to light source.
-3.0 em deep glass container, filled with cold tap water.
- (2) fine ruled glass Ronchi rulings, approximately 4x4cm in size
and having approximately 26lines/ em.
- A commercially available heating element or so-called immersion
heater.
-Canon 50mm 1:1.8 AE-1 camera with stand.
- Kodak 400 ASA 35mm TMY Black & White Print Film.
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A B C D E F G
Figur~ 1 : Ronchi Gdd M~thod . A-lncand~sc~nt Light Source; B-Diffusing Filt~r; C & F -Fine Ruled Ronchi Grids; D-Glass Container filled with tap water; E-Heating element; G-Camera.
PROCEDURE:
Figure 1 shows the setup. Diffuse light comes from the incandescent light
source (A) and passes through a diffusing filter (B). The light is then incident on
the first Ronchi ruling (C) located approximately 40cm from the light source. A
shadow of (C) is passed through the 3.0 em deep container that is filled with
water onto the second ruling (F). This has the same pitch as grid (C). The
resulting moire' pattern is observed by looking in a straight line at the light
source and the two rulings.
Next the heating element is inserted into the container of water, with the
coil resting just below the lower border of the grids. The camera is placed
approximately 60 em from the glass container.
The element is then turned on for a very brief period of time, approx. 15
seconds, until the distortion of the fringes is clearly seen. With careful
manipulation of the camera settings, these patterns can be photographed. We
found that the best photographs resulted when the camera was set with F-stops
between 16-22 and an exposure time of 1/500 seconds.
The following Figures 2, 3 and 4 shows various examples of moire'
patterns of such heat waves:
Figure 2: A photograph taken with camera setting ofF-stop 22 and 1/500 second exposure
time. With the heating element turned on for 5 seconds, initial distortion of the fringes is clearly
seen.
Figure 3: A second photograph taken with camera setting of F-stop 16 and 1/500 second
exposure time. After an additional 5 seconds, 10 seconds total, distortion of fringes is
more pronounced.
Figure 4: A final photograph taken with camera setting ofF-stop 16 and 1/500 second exposure
time. After a total of 15 seconds, maximum distortionof the fringes results.
DISCUSSION:
In many previous studies, much of the analysis of conventional black
and-white schlieren photographs is based on the interpretation of shades of grey.
We use a different method that at the same time allows a precise quantitative
analysis. This is done by the Ronchi-grid or moire' pattern method. The resulting
distortions of the moire' patterns can be photographed; they show the
quantitative size of the gradient and permit us to follow the propagation of a heat
wave with much more precision.
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REFERENCES
1. Kafri 0. Noncoherent method for mapping phase objects. Optics Letters,
1980, Vol. 5(12), 555-557.
2. Maddox A.R. and Binder R.C. New Dimension in the Schlieren
Technique: Flow Field Analysis Using Color. Applied Optics, (March 1971),
Vol. 10(3), 474-481.
3. Meyer-Arendt J.R. Microscopy as a spatial filtering process, IV. Spatial
Filters: Practical Considerations. Advances in Optical and Electron
Microscopy, 1982, Vol. 8, 11-14.
4. Nishijima Y. and Oster G. Moire' Patterns: Their Application to
Refractive Index and Refractive Index Gradient Measurements. Journal of
the Optical Society of America, 1964, Vol. 54(1), 1-5.
5. Settles G.S. Colour-coding schlieren techniques for the optical study of
heat and fluid flow. International Journal of Heat and Fluid Flow, 1985, Vol.
6(1), 3-15.
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