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Tracer introduction by flash photolysis
Chemical Engineering Science, 1965, Vol. 20, pp. 1011-1014. Pergamon Press Ltd., Oxford.
Printed in Great Britain.
Tracer introduction by flash photolysis* L. H. GOLDISH~, J. A. KOUTSKY and R. J. ADLER Case Institute of Technology, Cleveland, Ohio 44106 (Received
15 March
1965; in revised form 5 May 1965)
Abstract-A flash photolysis method for introducing colored tracer into flowing water without disturbing its flow patterns is developed. The method employs a lightly colored dilute solution which undergoes a chemical reaction similar to the blueprint reaction upon exposure to high intensity light. A dark blue permanent tracer, easily observed or detected by calorimetry, is produced. As a demonstration and test, axial dispersion is measured in laminar flow in a round tube. Other flow visualization studies where it is important to avoid disturbing the flow should benefit from such methods.
FLOW visualization is a basic experimental problem in fluid mechanics. A variety of techniques have been developed for various applications, including dye injection, birefringence, schlieren methods, neutral density beads, luminescent phosphors, etc. [I, 21. While dye injection is perhaps the most popular and convenient of these techniques, it suffers from the drawback that the flow patterns being studied are disturbed mechanically by either the presence of an injecting instrument or the introduction of the tracer itself. In certain instances accurate observations cannot be made, and other techniques are used even though they generally yield less detailed information or are more difficult to apply. This paper presents a new dye tracer method which does not disturb the flow. The method employs flash photolysis to produce a colored tracer in situ in the flowing fluid. The uniqueness of the method is due to the light-sensitive liquid used as the fluid. This liquid is a clear, yellow-green aqueous solution which, upon exposure to high intensity illumination, immediately changes color to a dark, permanent blue, yet retains its aqueous properties. Subdued incandescent light does not substantially affect the color. The solution undergoes a modified form of the blueprint reaction when activated by a flashlamp. In this reaction ferric ions are reduced to ferrous
ions by light in the presence of sensitizers. The ferrous ions then react with potassium ferricyanide already present in the solution to produce a dark blue colloidal suspension known as Turnbull’s blue, which is the permanent colored tracer. The new method is well suited to calorimetric as well as visual detection, and can be used for both quantitative and qualitative studies. THE METHOD The method uses a light-sensitive dilute aqueous solution formed from a premixed concentrated solution, sulfuric acid and water. Directions for preparing the concentrated solution are given in Table 1. The concentrated solution should be prepared under subdued light and stored in glass containers in the dark. At room temperature the concentrated solution is stable for three or four weeks. The light-sensitive dilute solution should be prepared in the dark immediately before use according to Table 2. The solution is transparent and yellow-green in color. It is inexpensive and its physical properties are essentially those of water. The principle reactions which occur in the lightsensitive solution are [3-71 Fe+3 (ferric)
light (blue to ultraviolet) , sensitizers
3Fe+’ + 2[Fe(CN),lV3 (ferrous) (ferricyanide)
,
Fe+’ (ferrous)
WFeAW& (ferrous berlinate)
* Contributed by Chemical Engineering Science Group, Engineering Division, Case Institute of Technology, Ohio 44106. t Presently at Massachusetts Institute of Technology, Cambridge, Mass.
1011
Cleveland,
L. H. GOLDISH,J. A. KOU-IXKYand R. J. ADLER
Table 1.
Directions
for preparing solution*
Chemical
concentrated
Amount
Ferric ammonium citrate (green scales) Distilled water
3.50 g 10.0 ml
Ferric ammonium Distilled water
3.75 g 10.0 ml
oxalate (crystals)
Ferric sodium oxalate (crystals) Distilled water Ferric oxalate (granular) Potassium ferricyanide (crystals) Distilled water
6.00 g 10.0 ml 0.50 g 9.375 g 10.0 ml
* All chemicals should be completely dissolved individually. The solutions should then be mixed in the above order and diluted to a total volume of 80 ml with distilled water. The Concentrate should be prepared in subdued light and stored in glass containers in the dark.
Ferrous berlinate, the end product, is commonly called Turnbull’s blue [7]. Precipitation of the colloidal suspension of ferrous berlinate is inhibited by the large excess of potassium ferricyanide called for in Table 1. The reaction is most sensitive to light of blue to ultraviolet wavelengths [3-71. Three precautions which should, be observed in the use and preparation of the light-sensitive solution are (1) all contact with metals should be avoided since the solution reacts with metals to form a blue precipitate, (2) the light-sensitive solution should be prepared under red illumination and stored in a light-tight reservoir to prevent undesired reaction (the solution will remain stable in a light-tight, nonmetallic reservoir for about one Table 2.
Directions for, preparing dilute solution*
Water (low iron content) Concentrated HzS04 (6N)
Solution (from Table 1)
light-sknsitive
11 5 ml 4 ml
* In the dark add Concentrate and Sulfuric Acid to water. Tap water is generally satisfactory. Maximum light sensitivity is attained only upon addition of the acid.
day), and (3) the solution should be used under low-level incandescent illumination. In addition, care should be taken to flush the system with water to prevent blue stains from forming on surfaces. Oxalic acid can be used to remove difficult stains. In order to produce tracer essentially instantaneously from these moderately sensitive reactions, a high intensity light source is needed. Various light sources may be employed providing they have sufficient intensity, are sufficiently rich in ultraviolet, and have the desired geometry. For this study a high intensity light source was constructed from a commercially available electronic flashlamp (General Electric FT-306). The lamp is a three turn helix, 1 in. long and 1 in. in inside diameter. It operates at 9OOV and gives a maximum power burst of 800 J in about 3 msec. The dominant wavelength produced by this xenon filled lamp is approximately 46OOA with cutoff wavelengths at 3OOOAand 15OOOA[8]. Figure 1 shows the flashlamp and its assembly with a straight tube passing through the center in position for flashing. Quantitative detection of Turnbull’s blue is performed by calorimetry in the application described in the next section. A flow calorimeter was built for the continuous measurement of tracer concentration. The schematic is given in Fig. 2. The light source is a 10 W incandescent lamp (number 88 automobile bulb) operated at 10 V alternating current provided by a constant voltage transformer. Light from the lamp passes through 6500A red glass filters to remove short wavelengths which would further color the light-sensitive solution flowing through the sample tube. In addition the blue solution has its greatest light absorption at 65OOA. The light emerging from the sample and blank tubes activates two selenium photocells (International Rectifier DP-5) in a balancing’circuit [9]. Since the photocells are somewhat temperature sensitive, the entire calorimeter is contained in a heavy aluminum housing which is maintained at a constant temperature by cooling coils. j Output impedance of the calorimeter is a few thousand ohms, and working signal range is a few millivolts. The signal from the calorimeter, is continuously recorded by a recording potentiometer (Honeywell Electronik).
1012
FIG. 1.
Tracer introduction by flash photolysis
at each Reynolds number. The flash tube colored a slug of fluid approximately one inch long. The flow calorimeter, located at the opposite end of tube, was preceded by a short packed section which produced a uniformly mixed outlet concentration. Experimental results are shown in Fig. 3 in comparison with theory. The data points are representative of 24 experimental determinations distributed over the six Reynolds numbers 300,400,500, 600, 700 and 800. The theoretical curve is the well known result [lo] Y=O ‘x
IOV ac.
0 LAMP
6500
i
FILTER
1
1
6500
8 FILTER
which holds providing molecular diffusion negligible according to TAYLOR’Scriteria [lo] L 1 5 Q 30 N,,Ns,.
10006.
IOn.
HELIPOT FINE ADJ.
b-
O-25
1ooon
mV de
FIG.
In these experiments L/D was on the order of 400, while 1/30NR,Nsc was on the order of 10,000 to 25,000. Here Y and X are the usual dimensionless coordinates
HELIPOT
SIGNAL
is
y2!!
-A
Xl; Q
where
2.
C = concentration of tracer at the outlet as a function of time
AN APPLICATION The method was used to measure experimentally the distribution of retention times* of a slug of flowing molecules located at the entrance of a straight, round tube. The slug of interest was a short cylinder whose diameter was equal to that of the tube and whose length was negligible (less than 1% of the length of the tube). Experiments were performed under conditions where an analytic solution was available for comparison with the data in order to test the method. This particular application was chosen because laminar flow is sensitive to disturbances and the data measured were quantitative. The experiments were performed in a straight, round glass tube 3/8 in. in diameter by 162 in. long, preceded by a 12 in. calming section. Both horizontal and vertical positions were, used. Reynolds numbers from 300 to 800 were studied. A constant flow rate of light-sensitive solution was maintained
THEORY
Y
o 0
I.0
2.0
3.0
J?lLJ.2. * Not to be confused with residence times. Residence times’are holding times for the population of molecules
entering the system. Here the t&m retention times signifies holding times of a different population of molecules as delined in the text.
1013
L. H. GOLDISH,J. A. KOUTSKYand R. J. ADLER
V = volume of the tube v = volumetric flow rate t = time measured from the introduction of tracer Q = quantity of tracer in the slug = vj; Cdt The experimental results are seen to be in good agreement with theory, thus demonstrating the efficacy of the method. SUMMARY
An experimental method is reported for introducing colored tracer into aqueous systems for the purpose of flow visualization. The method is novel in that flow patterns are not disturbed. Rather, the tracer is produced essentially instantaneously, in situ, by a burst of light which promotes a chemical reaction producing a permanent dark blue color. The dark blue color is readily detected visually and by calorimetry. The method is demonstrated and tested in laminar flow in a straight glass tube. The outlet response to an inlet disc-shaped slug of tracer is determined experimentally. The data are in good
agreement with the well known theoretical result, indicating that the method is suited to quantitative observations. The method described by this paper is useful for flow visualization studies where it is important to avoid disturbance of the flow. In particular, this method should be useful for observing velocity profiles and boundary layers, and for visualizing eddies, streamlines and other flow phenomena in channels and around models. Flow studies in two phase systems should also benefit from the fact that, with the method, one phase can be dyed without affecting the other. In addition, observations of secondary flow under laminar conditions should be more easily obtainable. It should be possible to further extend the range of applications by varying the chemical reaction [l I] and light source. Acknowledgements-The authors acknowledge the help and advice of M. DICKERSONof Picker X-ray Company, M. HOFFERof Photo-Technics Company, F. MUELLERof Ansco Corporation, the Eastman Kodak Company, H. SCHMIESof General Electric Company, and M. PARSONSof the Case Library. The National Science Foundation (G-14771) is thanked for its financial support.
REFERENCES
HI KLINE S. J. et al., Symposium on Flow Visualization, ASME Annual Meeting, New York (Nov. 1960). 121 CHOI S. V. An in situ Activation Tracer Technique, Ph.D. Thesis, North Carolina State College (1963).
NEBLE~ C. B., Photography, Its Principles andpractice, 4th ed., D. Van Nostrand’ Co., Inc., New York, 1942 p. 698. TOMODAY., J. Japanese Technical Association, Pulp and Paner Industrv. Industrial Chemistrv Section. 1950 4.5.20-22. ~,~I~- --. TOMODAY., J. &em. Sot. Japan, Znd. Chem. Sect.; 1951 54, 34-6. _’ TOMODAY., Bull. Sot. scient Photogr. Japan, 1955 415, 7-13. ANDERSONH. V. and HAZLEHURSTT. H., Qualitative Analysis, Prentice-Hall, Inc., New York, 1947 pp. 166-7. :i; General Electric Flashtube Data Manual, General Electric Company, Nela Park, Cleveland 12, Ohio (1960). [91 International Rectifier Corp., Bull. No. PC-649A-SF, El Segundo, California. [lOI TAYU~RG., Proc. R. Sot., 1953 A 219, 186203. Dll MCMASTERL. P., Flush Photolysis Tracer Studies, Senior Project Report, LAMB D. E. and OLSONJ. H. supervisors, Chemical Engineering Dept., Univ. of Delaware, 58 pg. 1964. 131 L41 PI PA
Resume!-Les auteurs exposent une methode faisant intervenir la lumiere pour introduire une substance coloree dans un debit d’eau sans rien changer aux constantes de l’ecoulement. Cette methode utilise une solution diluee et legerement colon& qui sous l’action dune source lumineuse intense est le siege dune reaction chimique semblable a celle qui permet l’impression des bleus. Elle produit une trace persistante, dun bleu sombre, facile a observer ou a detecter par colorimetrie. En guise de demonstration, les auteurs mesurent la dispersion axiale en &coulement laminaire dans un tube cylindrique. D’autres etudes visuelles d’ecoulements, oh il est important d’eviter de perturber le regime, pourront b&&icier de telles methodes. Zusammenfassung-Es wurde eine photolytische Methode entwickelt, urn einen farbigen Indikator in strijmendes Wasser einzubringen, ohne die Stromungslinien zu zerstoren. Dazu la& man in einer leicht gefarbten verdiinnten Liisung unter dem EinfluR sehr intensiver Bestrahlung eine chemische Reaktion ablaufen, die mit dem Vorgang beim Blaupausen vergleichbar ist; es entsteht ein stabiler dunkelblauer Indikator, der colorimetrisch leicht beobachtet werden kann. In einem Demonstrationsversuch wurde die axiale Rtickvermischung bei laminarer Strijmung in einem Rohr gemessen. Auch andere Untersuchungen, bei denen ungestijrte Strijmungsvorgange beobachtet werden sollen, kiinnen diese Methode nutzbringend verwenden.
1014
Printed in Great Britain.
Tracer introduction by flash photolysis* L. H. GOLDISH~, J. A. KOUTSKY and R. J. ADLER Case Institute of Technology, Cleveland, Ohio 44106 (Received
15 March
1965; in revised form 5 May 1965)
Abstract-A flash photolysis method for introducing colored tracer into flowing water without disturbing its flow patterns is developed. The method employs a lightly colored dilute solution which undergoes a chemical reaction similar to the blueprint reaction upon exposure to high intensity light. A dark blue permanent tracer, easily observed or detected by calorimetry, is produced. As a demonstration and test, axial dispersion is measured in laminar flow in a round tube. Other flow visualization studies where it is important to avoid disturbing the flow should benefit from such methods.
FLOW visualization is a basic experimental problem in fluid mechanics. A variety of techniques have been developed for various applications, including dye injection, birefringence, schlieren methods, neutral density beads, luminescent phosphors, etc. [I, 21. While dye injection is perhaps the most popular and convenient of these techniques, it suffers from the drawback that the flow patterns being studied are disturbed mechanically by either the presence of an injecting instrument or the introduction of the tracer itself. In certain instances accurate observations cannot be made, and other techniques are used even though they generally yield less detailed information or are more difficult to apply. This paper presents a new dye tracer method which does not disturb the flow. The method employs flash photolysis to produce a colored tracer in situ in the flowing fluid. The uniqueness of the method is due to the light-sensitive liquid used as the fluid. This liquid is a clear, yellow-green aqueous solution which, upon exposure to high intensity illumination, immediately changes color to a dark, permanent blue, yet retains its aqueous properties. Subdued incandescent light does not substantially affect the color. The solution undergoes a modified form of the blueprint reaction when activated by a flashlamp. In this reaction ferric ions are reduced to ferrous
ions by light in the presence of sensitizers. The ferrous ions then react with potassium ferricyanide already present in the solution to produce a dark blue colloidal suspension known as Turnbull’s blue, which is the permanent colored tracer. The new method is well suited to calorimetric as well as visual detection, and can be used for both quantitative and qualitative studies. THE METHOD The method uses a light-sensitive dilute aqueous solution formed from a premixed concentrated solution, sulfuric acid and water. Directions for preparing the concentrated solution are given in Table 1. The concentrated solution should be prepared under subdued light and stored in glass containers in the dark. At room temperature the concentrated solution is stable for three or four weeks. The light-sensitive dilute solution should be prepared in the dark immediately before use according to Table 2. The solution is transparent and yellow-green in color. It is inexpensive and its physical properties are essentially those of water. The principle reactions which occur in the lightsensitive solution are [3-71 Fe+3 (ferric)
light (blue to ultraviolet) , sensitizers
3Fe+’ + 2[Fe(CN),lV3 (ferrous) (ferricyanide)
,
Fe+’ (ferrous)
WFeAW& (ferrous berlinate)
* Contributed by Chemical Engineering Science Group, Engineering Division, Case Institute of Technology, Ohio 44106. t Presently at Massachusetts Institute of Technology, Cambridge, Mass.
1011
Cleveland,
L. H. GOLDISH,J. A. KOU-IXKYand R. J. ADLER
Table 1.
Directions
for preparing solution*
Chemical
concentrated
Amount
Ferric ammonium citrate (green scales) Distilled water
3.50 g 10.0 ml
Ferric ammonium Distilled water
3.75 g 10.0 ml
oxalate (crystals)
Ferric sodium oxalate (crystals) Distilled water Ferric oxalate (granular) Potassium ferricyanide (crystals) Distilled water
6.00 g 10.0 ml 0.50 g 9.375 g 10.0 ml
* All chemicals should be completely dissolved individually. The solutions should then be mixed in the above order and diluted to a total volume of 80 ml with distilled water. The Concentrate should be prepared in subdued light and stored in glass containers in the dark.
Ferrous berlinate, the end product, is commonly called Turnbull’s blue [7]. Precipitation of the colloidal suspension of ferrous berlinate is inhibited by the large excess of potassium ferricyanide called for in Table 1. The reaction is most sensitive to light of blue to ultraviolet wavelengths [3-71. Three precautions which should, be observed in the use and preparation of the light-sensitive solution are (1) all contact with metals should be avoided since the solution reacts with metals to form a blue precipitate, (2) the light-sensitive solution should be prepared under red illumination and stored in a light-tight reservoir to prevent undesired reaction (the solution will remain stable in a light-tight, nonmetallic reservoir for about one Table 2.
Directions for, preparing dilute solution*
Water (low iron content) Concentrated HzS04 (6N)
Solution (from Table 1)
light-sknsitive
11 5 ml 4 ml
* In the dark add Concentrate and Sulfuric Acid to water. Tap water is generally satisfactory. Maximum light sensitivity is attained only upon addition of the acid.
day), and (3) the solution should be used under low-level incandescent illumination. In addition, care should be taken to flush the system with water to prevent blue stains from forming on surfaces. Oxalic acid can be used to remove difficult stains. In order to produce tracer essentially instantaneously from these moderately sensitive reactions, a high intensity light source is needed. Various light sources may be employed providing they have sufficient intensity, are sufficiently rich in ultraviolet, and have the desired geometry. For this study a high intensity light source was constructed from a commercially available electronic flashlamp (General Electric FT-306). The lamp is a three turn helix, 1 in. long and 1 in. in inside diameter. It operates at 9OOV and gives a maximum power burst of 800 J in about 3 msec. The dominant wavelength produced by this xenon filled lamp is approximately 46OOA with cutoff wavelengths at 3OOOAand 15OOOA[8]. Figure 1 shows the flashlamp and its assembly with a straight tube passing through the center in position for flashing. Quantitative detection of Turnbull’s blue is performed by calorimetry in the application described in the next section. A flow calorimeter was built for the continuous measurement of tracer concentration. The schematic is given in Fig. 2. The light source is a 10 W incandescent lamp (number 88 automobile bulb) operated at 10 V alternating current provided by a constant voltage transformer. Light from the lamp passes through 6500A red glass filters to remove short wavelengths which would further color the light-sensitive solution flowing through the sample tube. In addition the blue solution has its greatest light absorption at 65OOA. The light emerging from the sample and blank tubes activates two selenium photocells (International Rectifier DP-5) in a balancing’circuit [9]. Since the photocells are somewhat temperature sensitive, the entire calorimeter is contained in a heavy aluminum housing which is maintained at a constant temperature by cooling coils. j Output impedance of the calorimeter is a few thousand ohms, and working signal range is a few millivolts. The signal from the calorimeter, is continuously recorded by a recording potentiometer (Honeywell Electronik).
1012
FIG. 1.
Tracer introduction by flash photolysis
at each Reynolds number. The flash tube colored a slug of fluid approximately one inch long. The flow calorimeter, located at the opposite end of tube, was preceded by a short packed section which produced a uniformly mixed outlet concentration. Experimental results are shown in Fig. 3 in comparison with theory. The data points are representative of 24 experimental determinations distributed over the six Reynolds numbers 300,400,500, 600, 700 and 800. The theoretical curve is the well known result [lo] Y=O ‘x
IOV ac.
0 LAMP
6500
i
FILTER
1
1
6500
8 FILTER
which holds providing molecular diffusion negligible according to TAYLOR’Scriteria [lo] L 1 5 Q 30 N,,Ns,.
10006.
IOn.
HELIPOT FINE ADJ.
b-
O-25
1ooon
mV de
FIG.
In these experiments L/D was on the order of 400, while 1/30NR,Nsc was on the order of 10,000 to 25,000. Here Y and X are the usual dimensionless coordinates
HELIPOT
SIGNAL
is
y2!!
-A
Xl; Q
where
2.
C = concentration of tracer at the outlet as a function of time
AN APPLICATION The method was used to measure experimentally the distribution of retention times* of a slug of flowing molecules located at the entrance of a straight, round tube. The slug of interest was a short cylinder whose diameter was equal to that of the tube and whose length was negligible (less than 1% of the length of the tube). Experiments were performed under conditions where an analytic solution was available for comparison with the data in order to test the method. This particular application was chosen because laminar flow is sensitive to disturbances and the data measured were quantitative. The experiments were performed in a straight, round glass tube 3/8 in. in diameter by 162 in. long, preceded by a 12 in. calming section. Both horizontal and vertical positions were, used. Reynolds numbers from 300 to 800 were studied. A constant flow rate of light-sensitive solution was maintained
THEORY
Y
o 0
I.0
2.0
3.0
J?lLJ.2. * Not to be confused with residence times. Residence times’are holding times for the population of molecules
entering the system. Here the t&m retention times signifies holding times of a different population of molecules as delined in the text.
1013
L. H. GOLDISH,J. A. KOUTSKYand R. J. ADLER
V = volume of the tube v = volumetric flow rate t = time measured from the introduction of tracer Q = quantity of tracer in the slug = vj; Cdt The experimental results are seen to be in good agreement with theory, thus demonstrating the efficacy of the method. SUMMARY
An experimental method is reported for introducing colored tracer into aqueous systems for the purpose of flow visualization. The method is novel in that flow patterns are not disturbed. Rather, the tracer is produced essentially instantaneously, in situ, by a burst of light which promotes a chemical reaction producing a permanent dark blue color. The dark blue color is readily detected visually and by calorimetry. The method is demonstrated and tested in laminar flow in a straight glass tube. The outlet response to an inlet disc-shaped slug of tracer is determined experimentally. The data are in good
agreement with the well known theoretical result, indicating that the method is suited to quantitative observations. The method described by this paper is useful for flow visualization studies where it is important to avoid disturbance of the flow. In particular, this method should be useful for observing velocity profiles and boundary layers, and for visualizing eddies, streamlines and other flow phenomena in channels and around models. Flow studies in two phase systems should also benefit from the fact that, with the method, one phase can be dyed without affecting the other. In addition, observations of secondary flow under laminar conditions should be more easily obtainable. It should be possible to further extend the range of applications by varying the chemical reaction [l I] and light source. Acknowledgements-The authors acknowledge the help and advice of M. DICKERSONof Picker X-ray Company, M. HOFFERof Photo-Technics Company, F. MUELLERof Ansco Corporation, the Eastman Kodak Company, H. SCHMIESof General Electric Company, and M. PARSONSof the Case Library. The National Science Foundation (G-14771) is thanked for its financial support.
REFERENCES
HI KLINE S. J. et al., Symposium on Flow Visualization, ASME Annual Meeting, New York (Nov. 1960). 121 CHOI S. V. An in situ Activation Tracer Technique, Ph.D. Thesis, North Carolina State College (1963).
NEBLE~ C. B., Photography, Its Principles andpractice, 4th ed., D. Van Nostrand’ Co., Inc., New York, 1942 p. 698. TOMODAY., J. Japanese Technical Association, Pulp and Paner Industrv. Industrial Chemistrv Section. 1950 4.5.20-22. ~,~I~- --. TOMODAY., J. &em. Sot. Japan, Znd. Chem. Sect.; 1951 54, 34-6. _’ TOMODAY., Bull. Sot. scient Photogr. Japan, 1955 415, 7-13. ANDERSONH. V. and HAZLEHURSTT. H., Qualitative Analysis, Prentice-Hall, Inc., New York, 1947 pp. 166-7. :i; General Electric Flashtube Data Manual, General Electric Company, Nela Park, Cleveland 12, Ohio (1960). [91 International Rectifier Corp., Bull. No. PC-649A-SF, El Segundo, California. [lOI TAYU~RG., Proc. R. Sot., 1953 A 219, 186203. Dll MCMASTERL. P., Flush Photolysis Tracer Studies, Senior Project Report, LAMB D. E. and OLSONJ. H. supervisors, Chemical Engineering Dept., Univ. of Delaware, 58 pg. 1964. 131 L41 PI PA
Resume!-Les auteurs exposent une methode faisant intervenir la lumiere pour introduire une substance coloree dans un debit d’eau sans rien changer aux constantes de l’ecoulement. Cette methode utilise une solution diluee et legerement colon& qui sous l’action dune source lumineuse intense est le siege dune reaction chimique semblable a celle qui permet l’impression des bleus. Elle produit une trace persistante, dun bleu sombre, facile a observer ou a detecter par colorimetrie. En guise de demonstration, les auteurs mesurent la dispersion axiale en &coulement laminaire dans un tube cylindrique. D’autres etudes visuelles d’ecoulements, oh il est important d’eviter de perturber le regime, pourront b&&icier de telles methodes. Zusammenfassung-Es wurde eine photolytische Methode entwickelt, urn einen farbigen Indikator in strijmendes Wasser einzubringen, ohne die Stromungslinien zu zerstoren. Dazu la& man in einer leicht gefarbten verdiinnten Liisung unter dem EinfluR sehr intensiver Bestrahlung eine chemische Reaktion ablaufen, die mit dem Vorgang beim Blaupausen vergleichbar ist; es entsteht ein stabiler dunkelblauer Indikator, der colorimetrisch leicht beobachtet werden kann. In einem Demonstrationsversuch wurde die axiale Rtickvermischung bei laminarer Strijmung in einem Rohr gemessen. Auch andere Untersuchungen, bei denen ungestijrte Strijmungsvorgange beobachtet werden sollen, kiinnen diese Methode nutzbringend verwenden.
1014