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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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/' / h: - #.....-_:::?~ ( _??:.?~e;f¢-t' 7v ( ... =</ 4L . · c;7olyn Clark, B.S.

Accepted by:

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1

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.

2

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.

4

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.

5

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.

6

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.

11

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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