This work was supported by the Israel Science Foundation, grant # 281/14.

1. Test Section for Measurements of Instantaneous Temperature
<ol>
	<li>Manufacturing process of test section (Figure 2)
	<ol>
		<li>Cut a segment of a pipe at least 70 cm long. 
		Note: The diameter and wall thickness of the test section should be identical to that of the pipe used in the experimental facility.</li>
		<li>Use a milling machine to cut 4 adjacent narrow windows along the pipe in the test section, each window is 6 mm wi...

<ol>
	<li>Hetsroni, G., Rozenblit, R., Yarin, L. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+hot-foil+infrared+technique+for+studying+the+temperature+field+of+a+wall.">A hot-foil infrared technique for studying the temperature field of a wall.</a> Meas. Sci. Tech. 7, 1418 (1996).</li><li>Babin, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Experimental investigation of the local heat transfer in gas-liquid slug flow. , (2015).</li><li>Babin, V., Shemer, L., Barnea, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Local+instantaneous+heat+transfer+around+a+raising+single+Taylor+bubble.">Local instantaneous heat transfer around a raising single Taylor bubble.</a> Int. J. Heat Mass Transfer. 89 (9), 884-893 (2015).</li><li>Fershtman, A., Shemer, L., Barnea, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Instantaneous+heat+transfer+rate+around+consecutive+Taylor+bubbles.">Instantaneous heat transfer rate around consecutive Taylor bubbles.</a> Int. J. Heat Mass Transfer. 95, 865-873 (2016).</li><li>Fershtman, A., Shemer, L., Barnea, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transient+convective+heat+transfer+in+a+pipe+due+to+impulsively+initiated+downward+flow+and/or+heat+flux.">Transient convective heat transfer in a pipe due to impulsively initiated downward flow and/or heat flux.</a> Int. J. Heat Mass Transf. 111, 1181-1191 (2017).</li><li>Hetsroni, G., Hu, B. G., Yi, B. G., Mosyak, A., Yarin, L. P., Ziskind, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Heat+Transfer+in+Intermittent+Air-Water+Flow-Part+I:+Horizontal+Tube.">Heat Transfer in Intermittent Air-Water Flow-Part I: Horizontal Tube.</a> Int. J. Multiphase Flow. 24, 165 (1998).</li><li>Hetsroni, G., Hu, B. G., Yi, B. G., Mosyak, A., Yarin, L. P., Ziskind, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Heat+Transfer+in+Intermittent+Air-Water+Flow-Part+II:+Upward+Inclined+Tube.">Heat Transfer in Intermittent Air-Water Flow-Part II: Upward Inclined Tube.</a> Int. J. Multiphase Flow. 24, 188 (1998).</li><li>Hetsroni, G., Mewes, D., Enke, C., Gurevich, M., Mosyak, A., Rozenblit, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Heat+transfer+to+two-phase+flow+in+inclined+tubes.">Heat transfer to two-phase flow in inclined tubes.</a> Int. J. Multiphase Flow. 29, 173-194 (2003).</li><li>Ghajar, A. J., Tang, C. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Heat+Transfer+Measurements,+Flow+pattern+maps+and+flow+visualization+for+non-boiling+two-phase+flow+in+horizontal+and+slightly+inclined+pipe.">Heat Transfer Measurements, Flow pattern maps and flow visualization for non-boiling two-phase flow in horizontal and slightly inclined pipe.</a> Heat Transfer Eng. 28, 525 (2007).</li><li>Franca, F. A., Banneart, A. C., Camargo, R. M. T., Goncalves, M. A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanistic+modelling+of+the+convective+heat+transfer+coefficient+in+gas-liquid+intermittent+flows.">Mechanistic modelling of the convective heat transfer coefficient in gas-liquid intermittent flows.</a> Heat Transfer Eng. 29, 984-998 (2008).</li><li>Kim, D., Ghajar, A. J., Dougherty, R. L., Ryali, V. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+20+two+phase+heat+transfer+correlations+with+seven+Sets+of+experimental+data,+including+flow+pattern+and+tube+inclination+effects.">Comparison of 20 two phase heat transfer correlations with seven Sets of experimental data, including flow pattern and tube inclination effects.</a> Heat Transfer Eng. 20, 15 (1999).</li><li>Nicklin, D. J., Wilkes, J. O., Davidson, J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-phase+flow+in+vertical+tubes.">Two-phase flow in vertical tubes.</a> Trans. Inst. Chem. Eng. 40, 61 (1962).</li><li>Donnelly, B., O'Reilly Meehan, R., Nolan, K., Murray, D. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+dynamics+of+sliding+air+bubbles+and+the+effects+on+surface+heat+transfer.">The dynamics of sliding air bubbles and the effects on surface heat transfer.</a> Int. J. Heat Mass Transfer. 91, 532-542 (2015).</li><li>Liu, T., Pan, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Infrared+thermography+measurement+of+two-phase+boiling+flow+heat+transfer+in+a+microchannel.">Infrared thermography measurement of two-phase boiling flow heat transfer in a microchannel.</a> Applied thermal engineering. 94, 568-578 (2016).</li><li>Dumitrescu, D. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stromung+an+einer+Luftblase+im+senkrechten+Rohr.">Stromung an einer Luftblase im senkrechten Rohr.</a> Z. Ang. Math. Mech. 23, 139 (1943).</li><li>Davies, R. M., Taylor, G. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+mechanics+of+large+bubbles+rising+through+extended+liquids+and+trough+liquid+in+tubes.">The mechanics of large bubbles rising through extended liquids and trough liquid in tubes.</a> Proc. R. Soc. London, Ser. A. 200, 375 (1949).</li></ol>

Experimental investigation of local heat transfer in transient pipe flow is a complicated task that requires high-end measuring instruments and methods, as well as a custom-built experimental facility, in particular, a specially designed test section. The present protocol displays a thermography technique that is capable of faithfully measuring fast temporal changes in wall temperature and in heat transfer rate due to variations in flow hydrodynamics.
A detailed description of the manufacturin...

Numerous experimental studies of convective heat transfer, using different techniques to measure the wall and/or fluid temperature in a variety of flow configurations, have been performed during the last decades. One of the factors that limits the accuracy of temperature measurements in unsteady processes is the slow response of the sensors. To record local instantaneous wall temperature, the measuring equipment has to respond fast enough, while the surface at which the temperature is recorded has to be in thermal equilibrium with the time-dependent flow. Thus, the thermal inertia of the surface has to be sufficiently small. The relevant time scales are determined by the hydrodynamic phenomena that cause the change in the convective heat transfer. Fast time response is thus crucial for recording the time-dependent temperature in transient flow.
To meet these requirements, an IR camera is used to record a special self-manufactured test section that allows a fast temperature response to any change in the flow. A part of the pipe wall is cut off and replaced with a thin stainless-steel foil. A similar approach was used by Hetsroni et al.1, however, the foil they used was too thick to accurately measure changes of instantaneous temperatures and only time-averaged temperatures were presented. Decreasing the foil thickness improved the time response considerably.2 This method was applied in the lab to measure convective heat transfer coefficients in two-phase flow3,4 and transient phenomena in single phase pipe flow5.
A schematic layout of the two-phase flow facility is given in Figure 1, additional information on the unique air inlet device can be found in Babin et al.3
Investigation of convective heat transfer in two-phase flow is very complex due to the transient flow behavior and the effect of void fraction in the pipe cross-section. Therefore, many studies have only presented an average convective heat transfer coefficient for a given flow regime as a function of specific flow conditions6,7,8,9,10,11. However, the papers by Donnelly et al.12 and Liu et al.13 represent examples of two-phase local convective heat transfer studies.
The present study deals with heat transfer measurements around a single elongated (Taylor) bubble injected into stagnant or flowing liquid in a pipe. The Taylor bubble propagates in a constant translational velocity14,15,16. The bubble propagation velocity is determined using optical probes method consisting of a laser light source and photodiode3,4.
The combination of the IR camera and of the optical probes allows measurements of the local instantaneous convective heat transfer as a function of the distance from either the Taylor bubble top or bottom.
The instantaneous wall temperature can be used to calculate the convective heat transfer coefficient, h, and the Nusselt number:
<img alt="Equation 1" src="/files/ftp_upload/57437/57437eq1.jpg" />,&#160; &#160; &#160; &#160; &#160; (1)
where q is the heat flux to the foil, Tw and T&#8734; are the wall temperature and the inlet water temperature respectively, k is the liquid conductivity and D is the pipe diameter. The bulk temperature which is commonly used to determine the heat transfer coefficients was not measured in order to avoid introducing any interference to the flow.

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			<td height="21" style="height:21px;width:216px;">Infra red camera</td>
			<td style="width:167px;">Optris</td>
			<td style="width:119px;">PI-1450</td>
			<td style="width:167px;"></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Thermocouples A/D card&#160;</td>
			<td style="width:167px;">National Instruments</td>
			<td>NI cDAQ-9714.</td>
			<td></td>
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			<td height="21" style="height:21px;width:216px;">Labview program</td>
			<td style="width:167px;">National Instruments</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="21" style="height:21px;width:216px;">Epoxy DP-460</td>
			<td style="width:167px;">3M Scotch-weld</td>
			<td style="width:119px;"></td>
			<td></td>
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measurements of local instantaneous convective heat transfer in a pipe - single and two-phase flow

This manuscript provides step by step description of the manufacturing process of a test section designed to measure the local instantaneous heat transfer coefficient as a function of the liquid flow rate in a transparent pipe. With certain amendments, the approach is extended to gas-liquid flows, with a particular emphasis on the effect of a single elongated (Taylor) air bubble on heat transfer enhancement. A non-invasive thermography technique is applied to measure the instantaneous temperature of a thin metal foil heated electrically. The foil is glued to cover a narrow slot cut in the pipe. The thermal inertia of the foil is small enough to detect the variation in the instantaneous foil temperature. The test section can be moved along the pipe and is long enough to cover a considerable part of the growing thermal boundary layer.
At the beginning of each experimental run, a steady state with a constant water flow rate and heat flux to the foil is attained and serves as the reference. The Taylor bubble is then injected into the pipe. The heat transfer coefficient variations due to the passage of a Taylor bubble propagating in a vertical pipe is measured as function of the distance of the measuring point from the bottom of the moving Taylor bubble. Thus, the results represent the local heat transfer coefficients. Multiple independent runs preformed under identical conditions allow accumulating sufficient data to calculate reliable ensemble-averaged results on the transient convective heat transfer. In order to perform this in a frame of reference moving with the bubble, the location of the bubble along the pipe has to be known at all times. Detailed description of measurements of the length and of the translational velocity of the Taylor bubbles by optical probes is presented.

An example of the optical sensors output records is presented in Figure 4 for a single Taylor bubble rising in a vertical pipe filled with stagnant water. The initial large drop represents the opening of the circuit due to the Taylor bubble tip, while the later much shorter drops following the rise to the initial value due to the passage of the elongated bubbles tail, represent the dispersed bubbles in the liquid wake behind the Taylor bubble. The time shift ...

Watch this Scientific Journal Video about Measurements of Local Instantaneous Convective Heat Transfer in a Pipe - Single and Two-phase Flow at JoVE.com

Measurements of Local Instantaneous Convective Heat Transfer in a Pipe - Single and Two-phase Flow

This manuscript describes methods aimed at measuring the local instantaneous convective heat transfer coefficients in a single or two-phase pipe flow. A simple optical method to determine the length and the propagation velocity of an elongated (Taylor) air bubble moving at a constant velocity is also presented.

This manuscript provides step by step description of the manufacturing process of a test section designed to measure the local instantaneous heat transfer ...

The overall goal of this experimental procedure is to present a thermography technique, that utilizes a well designed test section to accurately measure the local instantaneous convective heat transfer coefficients, in a single or two phase pipe flow. This method can help answer key outstanding questions in transient convective heat transfer, in single and multi phase flows. The main advantage of this technique, is that it's non invasive and can measure fast variations in wall temperature, resulting from time dependent flows.Demonstrating this procedure will be Avram Balas, and Yakov Levi, technicians from our laboratory. Begin with a segment of pipe 70 centimeters long or more. It's diameter and wall thickness, should match the pipe of the experimental facility.Mill four adjacent narrow windows along the pipe. Each window is six millimeters wide and 80 millimeters long. The gap between windows is 25 millimeters.Next get 12 micrometer thin stainless steel foil, and cut a long thin strip. To help weld the heating wires the strip is coated with gold near each end of the strip. Continue by measuring the foil's electrical resistance with an ometer.Now obtain a rigid tube that fits into the pipe. The tubes outer diameter should equal the inner diameter of the pipe. Cut out a long segment of the rigid tube to create an arch.This long arch, the basis, fits into the pipe, and will support and protect the foil. To put the foil in the test section, coat the basis with grease to aid in detaching the foil later. Then place the foil on the basis, to transfer to the test section.Flatten the foil and use a cloth and alcohol to clean excess grease. Next, apply adhesive on the foil periphery, so it will adhere to the pipe. In addition, identify regions corresponding to the bridges between windows on the pipe and apply adhesive to them.When ready orient the basis, so the foil faces the same direction as the test section windows. Then carefully insert the basis into the test section. Ensure the foil is aligned with the windows.Check that each gold stripe is at an edge of an outer window. Once the foil is in place, clamp the basis to each end of the pipe. Next obtain a bicycle inner tube, folded to fit into the pipe.Carefully insert the tube into the pipe under the basis. When done, inflate the tire. As the tire inflates, observe the adhesive spreading across the foil and reaching the basis.Use a cloth to clear any excess adhesive in the window openings. After 24 hours of drying deflate the tire and extract it. Open the clamps holding the basis and pipe together.Test each end of the basis to decide which side is easier to disconnect. Then use a long roller and start on the easier end. Place the roller between the basis and the pipe, and move it slowly into the pipe, until the entire basis is separated.The foil should remain undamaged on the pipe interior. As a test of the seal, close one end of the pipe. Then fill the pipe with water and check for leaks.Continue after unblocking the pipe and cleaning its interior. Connect electrical heating wires to the golden strips on the foil. Also connect T-Type thermocouples to the bottom of each window.Finally, spray paint the outer side of the foil with a black matt. Now put the test section in the experimental facility. Connect the pipes with flanges.Before continuing, fill the system with water. Move on to set up a computer for control and data acquisition. Then connect the heating wires from the foil, to a DC power supply.Next, place a computer controlled infra red camera at a window of the test section. For calibration, place it a few centimeters from the test section surface. Measure the ambient temperature, with a thermocouple held near the experiment.Next, focus the camera on a window of the test section to measure its temperature. Adjust the emissivity of the IR camera, so the camera and the temperature measured by the thermocouple on the pipe window match. With the camera set up, prepare the optical probes.Each probe consists of a laser and a photodiode, that is to be connected to the data acquisition computer. Turn the laser on and point the beam at the diode. Check that the computer records a positive signal.Place an optical probe along the test pipe, that is now filled with water. The final set up is represented in this schematic. The measurement section is in addition to the regular setup.The computer, in addition to data acquisition from the camera, thermocouples and optical probes, governs the synchronization of bubble injection and wall temperature measurement with the camera. Now establish the desired conditions for the experiment, and perform a single phase pipe flow reference measurement. After that inject a Taylor bubble in the setup, for a two phased flow measurement.This is an example of the optical sensor output, for a single Taylor bubble rising in a vertical pipe filled with stagnant water. The initial drop represents the sensor circuit opening due to the Taylor bubble tip. The rise represents the bubble's passing.Later shorter drops represent bubbles in the liquid wake behind the Taylor bubble. The delay of the features in the bottom curve, is due to the sensors being in different positions. This plot represents the ensemble average results of the local convective heat transfer coefficient, due to the passage of a single Taylor bubble rising in stagnant water in a vertical pipe.The two phase flow convective coefficient results are normalized by the single phase flow coefficient. The distance from the bubble tail moving, in a frame of reference with the Taylor bubble is normalized by the pipe diameter. This video presented measurements of the local instantaneous heat transference and slug flow.The method can provide information on heat transfer and study stage single phase flow, as well as more complex two phase flows. Once mastered, the manufacturing of the test pipe can be done in a few hours. While attempting this procedure on transient flow, its important to remember to automate thew entire process, to insure repeated results which can later be used for an assembling averaging process.After watching this video you should have a good understanding of how to manufacture a heat transfer test pipe, which allows a quantitative investigation of convective heat transfer in pipe flows. Don't forget that this technique of convective heat transfer measurement, can be expanded to many flow configurations, using supplementary equipment as optical prompts and high speed cameras.

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7.0K vues.  Tel-Aviv University. The overall goal of this experimental procedure is to present a thermography technique, that utilizes a well designed test section to accurately measure the local instantaneous convective heat transfer coefficients, in a single or two phase pipe flow. This method can help answer key outstanding questions in transient convective heat transfer, in single and multi phase flows. The main advantage of this technique, is that it's non invasive and can measure fast variations in wall temperature, re...