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 wide and 80 mm long with a 25-mm gap between consecutive windows.</li>
		<li>From a 12 &#181;m thin stainless-steel foil, cut 40-60 cmlong and 12 mm wide strips. 
		Note: The foil will be used to seal the windows in the test pipe. The stainless steel should be coated with two gold stripes that mark a small distance from the ends of the foil and are to be used to weld the power supply wires to heat the foil, see Figure 2.</li>
		<li>Measure the foil&#39;s electrical resistance using an ohmmeter.</li>
		<li>Place the foil within the pipe following the steps described below.
		<ol>
			<li>Create a basis for inserting the foil into the test section made of a rigid tube with an outer diameter equal to that of the test pipe inner diameter. To this end, cut a 20 mm wide and about 80 cm long part of the pipe wall</li>
			<li>Coat the basis with grease before placing the foil on it, to allow disconnecting the basis from the foil at a later stage.</li>
			<li>Place the foil on the basis and flatten it. Take a cloth with alcohol and clean the foil from any excess grease.</li>
			<li>Apply the adhesive on the foil periphery and on the three segments of the foil corresponding to the location of the bridges between the consecutive windows. 
			Note: The adhesive has to be strong with an initial hardening period of at least 20 minutes in order to ensure sufficient time for the foil attachment process; epoxy DP 460 is used.</li>
			<li>Carefully insert the basis with the foil into the test section with the foil facing upward toward the windows. 
			Note: This process should be done by two people.</li>
			<li>Ensure that the foil is aligned with the windows, the gold stripes should be at the edge of the two external windows. Once the foil is properly placed and covers the windows, link the basis to the test pipe at each end by using a clamp.</li>
			<li>Carefully insert a folded bicycle inner tire into the pipe under the basis, grease the tire if needed. Inflate the tire. During the inflation observe the adhesive spreading across the foil and reaching the basis. 
			Note: The pressure applied by the inflated tire should guarantee that the adhesive will tie the pipe inner wall and the foil. This will also shape the foil to the curvature of the pipe and reduce any possible interference to the flow due to the foil or the adhesive.</li>
			<li>With a cloth, clear any excess adhesive that has reached the window openings.</li>
			<li>Let the adhesive dry for 24 h. Deflate the tire, extract it and open the clamps.</li>
			<li>Disconnect the basis from the foil and pipe in the following steps:
			<ol>
				<li>Gently touch each end of the basis to feel which end is easier to disconnect and begin disconnecting from that end.</li>
				<li>Use a long roller or a similar object to disconnect the original basis gradually, move slowly into the pipe until the entire basis is disconnected and the foil remains safely undamaged on the pipe. 
				Note: This process should be done carefully in order to protect the seal; if the seal is ruined a new heat transfer test pipe unit should be made.</li>
				<li>Check that the pipe is sealed by closing one end of the pipe and filling the pipe with water.</li>
			</ol>
			</li>
		</ol>
		</li>
		<li>Clean the excess grease from the inner side of the pipe with water and soap.</li>
		<li>Connect the electrical heating wires by welding to the golden stripes on the foil. 
		Note: To protect the foil at these spots, it is suggested to first link a small cooper chip to the foil and then weld the wire to it.</li>
		<li>With a thermal adhesive connect a T-type thermocouple to the bottom of each window. These thermocouples will be later used in the IR camera calibration process. 
		Note: The temperature readings from the thermocouples are recorded and recorded by a PC using an A/D converter.</li>
		<li>Spray paint the outer side of the foil with a black mat spray in order to maximize the emissivity.</li>
	</ol>
	</li>
	<li>Applying heat flux to foil
	<ol>
		<li>Connect the electrical heating wires from the edge of the foil to a DC power supply.</li>
		<li>Set the electrical current so the foil will reach a desired temperature. 
		Note: Do not reach a temperature that could impair the pipe. For Plexiglass the limit is about 45 &#176;C. However, be sure to heat the foil enough to ensure that the foil&#39;s temperature remains at least a few degrees over the inlet water temperature, even during the cooling state due to the transient changes expected in the flow.</li>
		<li>Calculate the heat flux applied Q = I2R where I is the current applied and R is the foil&#39;s electrical resistance. 
		Note: The heat transfer from the foil&#39;s outer side that is open to air is negligible compared to the heat transfer to water inside the pipe2.</li>
		<li>Connect a PC controllable electrical switch to one of the heat flux wires in order to control the heat flux impulsive initiation and shutdown.</li>
	</ol>
	</li>
	<li>IR camera 
	Note: Detailed specifics of the IR camera used in the lab can be seen in Ferhstman3,4. The camera is connected to a PC and controlled by a computer.
	<ol>
		<li>If possible, connect the IR camera to a set of rails enabling three-dimensional movement of the camera to easily place it at different positions along the test section.</li>
		<li>Turn on the IR camera a few minutes before conducting any measurements, the internal sensors take time to cool down to the required temperature.</li>
		<li>Place the IR camera a few centimeters from the surface within the focal distance of the camera to enable focusing. 
		Note: Depending on the camera resolution be sure that the area measured is not smaller than a single pixel. It is preferable to have the surface area measured consisting of a number of pixels.</li>
		<li>Set focus of the IR camera.</li>
		<li>IR camera calibration process:
		<ol>
			<li>Apply heat flux as stated in 1.2 and wait until a thermal steady state is reached, i.e. once the thermocouples placed on the foil record constant temperature. Measure the ambient temperature in the vicinity of the experimental facility with a thermocouple. 
			Note: This temperature will be used as the reflected temperature of the surface. For a high value of surface emissivity, this parameter is almost negligible.</li>
			<li>Enter the ambient temperature as the IR camera&#39;s parameter of reflected temperature.</li>
			<li>For each window in the foil, compare the temperature recorded by the IR camera to the recording of the thermocouple of that window. Adjust the emissivity property of the IR camera until the temperature recording of the IR camera is equal to the temperature recorded by the thermocouple. 
			Note: This can be done for several heat flux values; however, the emissivity is not sensitive at this relatively low-temperature range. In the experimental recordings, the average value of emissivity was 0.98.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
2. Measurements of Taylor Bubble Translational Velocity and its Length
<ol>
	<li>Optical probe 
	Note:&#160;The optical probe includes a laser light source and a photodiode. When the entire cross-section of the pipe contains water, the laser beam is pointed at the photodiode causing the circuit to be closed. When the laser beam hits the air bubble, it is nudged from the photodiode and opens the circuit. Thus, a binary signal is obtained, indicating whether the optical probe is in front of an air bubble or of a liquid slug.
	<ol>
		<li>In order to connect the sensor to the A/D card, build the following circuit (Figure 3).</li>
		<li>Turn on the laser, point it at the diode. Check the digital input of the circuit A/D software. If the laser hits the diode, then the circuit is closed and a positive signal should appear. 
		Note: Make sure that the diode is sensitive to the wavelength output of the laser. The optical sensors&#39; data is recorded at the rate of 1 kHz.</li>
	</ol>
	</li>
</ol>
3. Experimental Procedure
<ol>
	<li>Connect the test section to the experimental facility, by flanges or pipe records.</li>
	<li>Connect the heating electrical wires to the power source and the thermocouples to any computerized temperature recorder.</li>
	<li>Place the IR camera in front of the test section at the desired location.</li>
	<li>Make sure that the camera is focused on the foil; this is easier to do with the heat flux on.</li>
	<li>Apply heat flux (1.2) and perform the IR camera calibration process (1.3.5).</li>
	<li>Place the two optical probes along the test pipe 
	Note:&#160;If possible, place one optical probe at the location of the IR camera; this will allow synchronization between the temperature measurement and the location of the bubble, as the bubble is not visible to the IR camera. If not possible, be sure to shift the results in time accordingly to the bubble velocity and the distance between the IR camera and the optical probe.
	<ol>
		<li>Check that the laser beam indeed hits the diode and yields a positive reading.</li>
	</ol>
	</li>
	<li>Turn on the water pump and set the desired flow rate. Apply heat flux by adjusting the current of the power supply.</li>
	<li>Wait until a steady state temperature is attained. Execute the computer program to record the wall temperature of a single-phase pipe flow. 
	Note: In order to isolate the effect of the Taylor bubble on the convective heat transfer coefficient, it is essential to measure first the convective heat transfer coefficient in single-phase flow at an identical flow rate and heat flux as in the two-phase experiments. It is recommended to perform this before each individual event.</li>
	<li>Run the computer program that governs the bubble injection. 
	Note: This program should first inject a single Taylor bubble and then simultaneously measure the wall temperature using the IR camera and record the binary signals of the two optical probes. These two measurements should be synchronized in order to avoid additional time shifts between the recordings.</li>
	<li>Between the runs, set sufficient time delay to ensure that the system is back to the initial conditions, i.e. the wall temperature returns to the initial single-phase steady-state value. 
	Note: It is possible that the wall temperature of the single-phase steady state flow will increase in cases where a high heat flux is on continuously. This should be avoided by closing the heat flux and taking a break in the experiments.</li>
</ol>
4. Data Processing
<ol>
	<li>Calculate the heat transfer coefficient for single-phase steady state conditions based on eq. 1. 
	Note: This coefficient is independent of time. It will be used as a normalizing factor in the sequel.
	<ol>
		<li>For each individual event recorded under given conditions, calculate the Taylor bubbles&#39; length and translational velocity by dividing the distance between the optical probes, L, by the time period interval of the tip arrival time to each optical sensor: &#160;<img alt="Equation 2" src="/files/ftp_upload/57437/57437eq2.jpg" />, where tL1 and tL2 are the times of the bubble tip arrival to the bottom and upper optical sensors, respectively.</li>
		<li>Use the Taylor bubble&#39;s translational velocity to calculate the bubble length by multiplying it by the duration of the open circuit of one of the optical probes.</li>
	</ol>
	</li>
	<li>Calculating the instantaneous local heat transfer coefficient for two phase flow should be done as following: 
	Note: Although the entire experimental process is computerized, the length and the translational velocity of the Taylor bubbles do not remain exactly constant at each experimental run. Therefore, the instant at which the bubble reaches the measuring point varies. The optical probes and the IR camera have different frame rates, 1000 and 30 Hz respectively.
	<ol>
		<li>Using the optical probe located in the vicinity of the IR camera, record the instant of the bubble tip arrival.</li>
		<li>This trigger signal provides the time reference for the IR camera recording. 
		Note: Ensemble average process is required in order to obtain the convective heat transfer coefficient as a function of the distance from the bubble bottom to the measuring point, z, where z=0 corresponds to the bubble bottom. This parameter should be normalized by the pipe diameter D.</li>
		<li>Set a resolution for z/D. All recorded data values for each individual event (corresponding to identical conditions) fall within the prescribed spatial resolution range and should be averaged to obtain a single representative value of the wall temperature at that distance from the bubble bottom. 
		Note: This spatial resolution should be decided based on the recording frequency of the IR camera and on the translational velocity of the Taylor bubble. In this study, it was taken between 0.15-0.3.</li>
		<li>Calculate the heat transfer coefficient as a function of the distance from the bubble tip/bottom using eq. 1.</li>
		<li>Normalize the two-phase local instantaneous heat transfer coefficient by the single-phase constant coefficient. 
		Note: This ratio represents an improvement in convective heat transfer rate due to the bubble passage compared to single-phase flow.</li>
	</ol>
	</li>
</ol>

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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. 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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. 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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 manufacturing process of the test section is presented. The critical step in the preparation of the facility is replacing a part of the pipe wall by a thin stainless-steel foil. The foil is heated by an electrical current; its inner side is open to the time-dependent flow field, while the outer side is filmed by an IR camera thus detecting any change in the instantaneous foil temperature. The temporal response of the foil constitutes the only limitation of this technique. The material and the thickness of the foil should be selected to ensure sufficiently fast time response as compared to the characteristic times of the phenomena considered.
The method applied allows instantaneous IR camera-based heat transfer measurements relative to the moving Taylor bubble as determined by optical means. An ensemble averaging procedure over numerous realizations of the experiment for any given operational conditions applied in the present study ensures obtaining reliable results. The proposed technique can be used for characterization of local transient heat transfer in single and multiphase flows.

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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		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<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>
		</tr>
		<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>
		</tr>
		<tr height="21">
			<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>
		</tr>
		<tr height="21">
			<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>
		</tr>
	</tbody>
</table>

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 between the outputs of the two optical probes is evident and is due to the distance between the two probes along the pipe. In this experiment, the probes are space by 0.09 m. Calculating the translational velocity by eq. 3 results in Ut=0.23 m/s; in agreement with Dumitrescu13 for a Taylor bubble propagating in a vertical pipe with stagnant water: 
<img alt="Equation 3" src="/files/ftp_upload/57437/57437eq3.jpg" /> 
The Taylor bubble length is measured by multiplying the translational velocity by the duration of the passage of the elongated bubble: 
<img alt="Equation 4" src="/files/ftp_upload/57437/57437eq4.jpg" /> 
which corresponds to LB = 3.54D.
The representative ensemble-averaged results of the local convective heat transfer coefficient due to the passage of a 3.5D long single Taylor bubble rising in stagnant water in a vertical pipe are plotted in Figure 5. The results are presented in a frame of reference moving with the bubble bottom, therefore the negative values up to z/D=-3.5 correspond to the bubble region where a thin film separates between the bubble and pipe wall. The two-phase flow convective coefficients results are normalized by the single-phase flow coefficient value. It is evident that the maximum increment in the heat transfer convective coefficient is attained a few diameters behind the bubble bottom and can be as much as two times higher compared to the single-phase flow at the same flow rate. Furthermore, the effect of the Taylor bubble on the wall temperature has a prolonged effect, remaining essential up to hundreds of diameters behind the Taylor bubble bottom. This is attributed to the wake behind the bubble. These results serve as a clear demonstration of the growing interest in two-phase flow as a cooling mechanism.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57437/57437fig1.jpg" /> 
Figure 1.Schematic layout of the experimental facility with heat transfer measurements test section. Details of the air and water entrance section are presented in the insert. <a href="/files/ftp_upload/57437/57437fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/57437/57437fig2.jpg" /> 
Figure 2.&#160;A schematic layout of the test section. <a href="/files/ftp_upload/57437/57437fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/57437/57437fig3.jpg" /> 
Figure 3. The optical sensor electrical circuit connecting between the diode and the A/D card linked to the PC. <a href="/files/ftp_upload/57437/57437fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/57437/57437fig4.jpg" /> 
Figure 4. The optical sensor recording for a Taylor bubble rising in stagnant water. <a href="/files/ftp_upload/57437/57437fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/57437/57437fig5.jpg" /> 
Figure 5.&#160;Normalized local heat transfer coefficients along a single slug unit for stagnant liquid (q=2100 W/m2). <a href="/files/ftp_upload/57437/57437fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

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 ...

measurements-local-instantaneous-convective-heat-transfer-pipe-single

Nanyang Technological University

Research

JoVE Journal

Engineering

7.1K Views.  Tel-Aviv University. 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.

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

Analysis of Contact Interfaces for Single GaN Nanowire Devices

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit a strong degradation after annealing due to the occurrence of void formation at the contact/SiO2 interface. This void formation can cause cracking and delamination of the metal film, which can increase the resistance or lead to a complete failure of the NW device. In order to address issues associated with void formation, a technique was developed that removes Ni/Au contact metal films from the substrates to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN NW devices. This procedure determines the degree of adhesion of the contact films to the substrate and NWs and allows for the characterization of the morphology and composition of the contact interface with the substrate and nanowires. This technique is also useful for assessing the amount of residual contamination that remains from the NW suspension and from photolithographic processes on the NW-SiO2 surface prior to metal deposition. The detailed steps of this procedure are presented for the removal of annealed Ni/Au contacts to Mg-doped GaN NWs on a SiO2 substrate.

A technique was developed that removes Ni/Au contact metal films from their substrate to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN nanowire devices.

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit  a strong degradation after annealing due to the  occurrence of void formation at the ...

Proton Transfer and Protein Conformation Dynamics in Photosensitive Proteins by Time-resolved Step-scan Fourier-transform Infrared Spectroscopy

Monitoring the dynamics of protonation and protein backbone conformation changes during the function of a protein is an essential step towards understanding its mechanism. Protonation and conformational changes affect the vibration pattern of amino acid side chains and of the peptide bond, respectively, both of which can be probed by infrared (IR) difference spectroscopy. For proteins whose function can be repetitively and reproducibly triggered by light, it is possible to obtain infrared difference spectra with (sub)microsecond resolution over a broad spectral range using the step-scan Fourier transform infrared technique. With ~102-103 repetitions of the photoreaction, the minimum number to complete a scan at reasonable spectral resolution and bandwidth, the noise level in the absorption difference spectra can be as low as ~10-4, sufficient to follow the kinetics of protonation changes from a single amino acid. Lower noise levels can be accomplished by more data averaging and/or mathematical processing. The amount of protein required for optimal results is between 5-100 &#181;g, depending on the sampling technique used. Regarding additional requirements, the protein needs to be first concentrated in a low ionic strength buffer and then dried to form a film. The protein film is hydrated prior to the experiment, either with little droplets of water or under controlled atmospheric humidity. The attained hydration level (g of water / g of protein) is gauged from an IR absorption spectrum. To showcase the technique, we studied the photocycle of the light-driven proton-pump bacteriorhodopsin in its native purple membrane environment, and of the light-gated ion channel channelrhodopsin-2 solubilized in detergent.

Key steps of protein function, in particular backbone conformational changes and proton transfer reactions, often take place in the microsecond to millisecond time scale. These dynamical processes can be studied by time-resolved step-scan Fourier-transform infrared spectroscopy, in particular for proteins whose function is triggered by light.

Monitoring the dynamics of protonation and protein backbone conformation changes during the function of a protein is an essential step towards ...

Laser-induced Forward Transfer for Flip-chip Packaging of Single Dies

Flip-chip (FC) packaging is a key technology for realizing high performance, ultra-miniaturized and high-density circuits in the micro-electronics industry. In this technique the chip and/or the substrate is bumped and the two are bonded via these conductive bumps. Many bumping techniques have been developed and intensively investigated since the introduction of the FC technology in 19601 such as stencil printing, stud bumping, evaporation and electroless/electroplating2. Despite the progress that these methods have made they all suffer from one or more than one drawbacks that need to be addressed such as cost, complex processing steps, high processing temperatures, manufacturing time and most importantly the lack of flexibility. In this paper, we demonstrate a simple and cost-effective laser-based bump forming technique known as Laser-induced Forward Transfer (LIFT)3. Using the LIFT technique a wide range of bump materials can be printed in a single-step with great flexibility, high speed and accuracy at RT. In addition, LIFT enables the bumping and bonding down to chip-scale, which is critical for fabricating ultra-miniature circuitry.

We demonstrate the use of the Laser-induced Forward Transfer (LIFT) technique for flip-chip assembly of optoelectronic components. This approach provides a simple, cost-effective, low-temperature, fast and flexible solution for fine-pitch bumping and bonding on chip-scale for achieving high-density circuits for optoelectronic applications.

Flip-chip (FC) packaging is a key technology for realizing high performance, ultra-miniaturized and high-density circuits in the micro-electronics ...

Speciation and Bioavailability Measurements of Environmental Plutonium Using Diffusion in Thin Films

The biological uptake of plutonium (Pu) in aquatic ecosystems is of particular concern since it is an alpha-particle emitter with long half-life which can potentially contribute to the exposure of biota and humans. The diffusive gradients in thin films technique is introduced here for in-situ measurements of Pu bioavailability and speciation. A diffusion cell constructed for laboratory experiments with Pu and the newly developed protocol make it possible to simulate the environmental behavior of Pu in model solutions of various chemical compositions. Adjustment of the oxidation states to Pu(IV) and Pu(V) described in this protocol is essential in order to investigate the complex redox chemistry of plutonium in the environment. The calibration of this technique and the results obtained in the laboratory experiments enable to develop a specific DGT device for in-situ Pu measurements in freshwaters. Accelerator-based mass-spectrometry measurements of Pu accumulated by DGTs in a karst spring allowed determining the bioavailability of Pu in a mineral freshwater environment. Application of this protocol for Pu measurements using DGT devices has a large potential to improve our understanding of the speciation and the biological transfer of Pu in aquatic ecosystems.

The technique of diffusive gradients in thin films (DGT) is proposed for speciation studies of plutonium. This protocol describes diffusion experiments probing the behavior of Pu(IV) and Pu(V) in presence of organic matter. DGTs deployed in a karstic spring allow assessment of the bioavailability of Pu.

The biological uptake of plutonium (Pu) in aquatic ecosystems is of particular concern since it is an alpha-particle emitter with long half-life which can ...

Experimental Methodology for Estimation of Local Heat Fluxes and Burning Rates in Steady Laminar Boundary Layer Diffusion Flames

Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex interactions occurring at the interface between gas-phase flames and condensed-phase fuels. The current research provides a technique to explore the dynamic relationship between a combustible condensed fuel surface and gas-phase flames in laminar boundary layers. Experiments have previously been conducted in both forced and free convective environments over both solid and liquid fuels. A unique methodology, based on the Reynolds Analogy, was used to estimate local mass burning rates and flame heat fluxes for these laminar boundary layer diffusion flames utilizing local temperature gradients at the fuel surface. Local mass burning rates and convective and radiative heat feedback from the flames were measured in both the pyrolysis and plume regions by using temperature gradients mapped near the wall by a two-axis traverse system. These experiments are time-consuming and can be challenging to design as the condensed fuel surface burns steadily for only a limited period of time following ignition. The temperature profiles near the fuel surface need to be mapped during steady burning of a condensed fuel surface at a very high spatial resolution in order to capture reasonable estimates of local temperature gradients. Careful corrections for radiative heat losses from the thermocouples are also essential for accurate measurements. For these reasons, the whole experimental setup needs to be automated with a computer-controlled traverse mechanism, eliminating most errors due to positioning of a micro-thermocouple. An outline of steps to reproducibly capture near-wall temperature gradients and use them to assess local burning rates and heat fluxes is provided.

We describe the use of micro-thermocouples to estimate local temperature gradients in steady laminar boundary layer diffusion flames. By extension of the Reynolds Analogy, local temperature gradients can be further used to estimate the local mass burning rates and heat fluxes in such flames with high accuracy.

Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex ...

Scanning SQUID Study of Vortex Manipulation by Local Contact

Local, deterministic manipulation of individual vortices in type 2 superconductors is challenging. The ability to control the position of individual vortices is necessary in order to study how vortices interact with each other, with the lattice, and with other magnetic objects. Here, we present a protocol for vortex manipulation in thin superconducting films by local contact, without applying current or magnetic field. Vortices are imaged using a scanning superconducting quantum interference device (SQUID), and vertical stress is applied to the sample by pushing the tip of a silicon chip into the sample, using a piezoelectric element. Vortices are moved by tapping the sample or sweeping it with the silicon tip. Our method allows for effective manipulation of individual vortices, without damaging the film or affecting its topography. We demonstrate how vortices were relocated to distances of up to 0.8 mm. The vortices remained stable at their new location up to five days. With this method, we can control vortices and move them to form complex configurations. This technique for vortex manipulation could also be implemented in applications such as vortex based logic devices.

We present a protocol for manipulation of individual vortices in thin superconducting films, using local mechanical contact. The method does not include applying current, magnetic field or additional fabrication steps.

Local, deterministic manipulation of individual vortices in type 2 superconductors is challenging. The ability to control the position of individual ...

Ice Generation and the Heat and Mass Transfer Phenomena of Introducing Water to a Cold Bath of Brine

We demonstrate a method for the study of the heat and mass transfer and of the freezing phenomena in a subcooled brine environment. Our experiment showed that, under the proper conditions, ice can be produced when water is introduced to a bath of cold brine. To make ice form, in addition to having the brine and water mix, the rate of heat transfer must bypass that of mass transfer. When water is introduced in the form of tiny droplets to the brine surface, the mode of heat and mass transfer is by diffusion. The buoyancy stops water from mixing with the brine underneath, but as the ice grows thicker, it slows down the rate of heat transfer, making ice more difficult to grow as a result. When water is introduced inside the brine in the form of a flow, a number of factors are found to influence how much ice can form. Brine temperature and concentration, which are the driving forces of heat and mass transfer, respectively, can affect the water-to-ice conversion ratio; lower bath temperatures and brine concentrations encourage more ice to form. The flow rheology, which can directly affect both the heat and mass transfer coefficients, is also a key factor. In addition, the flow rheology changes the area of contact of the flow with the bulk fluid.

Here, we present a protocol to demonstrate the generation of ice when water is introduced to a cold bath of brine, as a secondary refrigerant, at a range of temperatures well below the freezing point of water. It can be used as an alternative way of producing ice for industry.

We demonstrate a method for the study of the heat and mass transfer and of the freezing phenomena in a subcooled brine environment. Our experiment showed ...

Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the hybrid wettable pattern. Hybrid wettable patterns were produced by coating superhydrophilic SiO2 on a masked, hydrophobic, cylindrical copper surface. Using de-ionized (DI) water as the working fluid, pool-boiling heat-transfer studies were conducted on the different surface-treated copper cylinders of a 25-mm diameter and a 40-mm length. The experimental results showed that the number of interlines and the orientation of the hybrid wettable pattern influenced the wall superheat and the HTC. By increasing the number of interlines, the HTC was enhanced when compared to the plain surface. Images obtained from the charge-coupled device (CCD) camera indicated that more bubbles formed on the interlines as compared to other parts. The hybrid wettable pattern with the lowermost section being hydrophobic gave the best heat-transfer coefficient (HTC). The experimental results indicated that the bubble dynamics of the surface is an important factor that determines the nucleate boiling.

Pool-boiling heat-transfer experiments were carried out to observe the effects of hybrid wettable patterns on the heat-transfer coefficient (HTC). The parameters of investigation are the number of interlines and the pattern orientation of the modified wettable surface.

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the ...

Measurements of Soil Carbon by Neutron-Gamma Analysis in Static and Scanning Modes

The herein described application of the inelastic neutron scattering (INS) method for soil carbon analysis is based on the registration and analysis of gamma rays created when neutrons interact with soil elements. The main parts of the INS system are a pulsed neutron generator, NaI(Tl) gamma detectors, split electronics to separate gamma spectra due to INS and thermo-neutron capture (TNC) processes, and software for gamma spectra acquisition and data processing. This method has several advantages over other methods in that it is a non-destructive in situ method that measures the average carbon content in large soil volumes, is negligibly impacted by local sharp changes in soil carbon, and can be used in stationary or scanning modes. The result of the INS method is the carbon content from a site with a footprint of ~2.5 - 3 m2 in the stationary regime, or the average carbon content of the traversed area in the scanning regime. The measurement range of the current INS system is &#62;1.5 carbon weight % (standard deviation &#177; 0.3 w%) in the upper 10 cm soil layer for a 1 hmeasurement.

Here, we present the protocol for in situ measurement of soil carbon using the neutron-gamma technique for single point measurements (static mode) or field averages (scanning mode). We also describe system construction and elaborate data treatment procedures.

The herein described application of the inelastic neutron scattering (INS) method for soil carbon analysis is based on the registration and analysis of ...

Measurements of Waves in a Wind-wave Tank Under Steady and Time-varying Wind Forcing

This manuscript describes an experimental procedure that allows obtaining diverse quantitative information on temporal and spatial evolution of water waves excited by time-dependent and steady wind forcing. Capacitance-type wave gauge and Laser Slope Gauge (LSG) are used to measure instantaneous water surface elevation and two components of the instantaneous surface slope at a number of locations along the test section of a wind-wave facility. The computer-controlled blower provides airflow over the water in the tank whose rate can vary in time. In the present experiments, the wind speed in the test section initially increases quickly from rest to the set value. It is then kept constant for the prescribed duration; finally, the airflow is shut down. At the beginning of each experimental run, the water surface is calm and there is no wind. Operation of the blower is initiated simultaneously with the acquisition of data provided by all sensors by a computer; data acquisition continues until the waves in the tank fully decay. Multiple independent runs performed under identical forcing conditions allow determining statistically reliable ensemble-averaged characteristic parameters that quantitatively describe wind-waves&#39; variation in time for the initial development stage as a function of fetch. The procedure also allows characterizing the spatial evolution of the wave field under steady wind forcing, as well as decay of waves in time, once the wind is shut down, as a function of fetch.

This manuscript describes a fully computer-controlled procedure that allows obtaining reliable statistical parameters from experiments of water waves excited by steady and unsteady wind forcing in a small-scale facility.

This manuscript describes an experimental procedure that allows obtaining diverse quantitative information on temporal and spatial evolution of water ...