The authors gratefully acknowledge funding support from the Ministry of Science and Technology, MOST (project numbers: MOST 104-2218-E-002 -004, MOST 105-2218-E-002-019, MOST 105-2221-E-002 -107 -MY3, MOST 102-2221-E-002 -133 -MY3, and MOST 102-2221-E-002 -088 -MY3).

1. Preparation of the Modified Surfaces
<ol>
	<li>Manually polish the test piece (hollow copper cylinder with a 40-mm length (l), a 25-mm outer diameter (do), and an 18-mm inner diameter (di)) for 15 min using a &#65283;2,000 emery paper. Clean the polished surface by rinsing it with acetone followed by DI water.</li>
	<li>Place the polished test piece in an oven for 2 h at a constant temperature of 120 &#176;C.</li>
	<li>Prepare a superhydrophilic SiO2 nanopa...

<ol>
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Fluid Sci. 70, 325-334 (2016).</li><li>Takata, Y., Hidaka, S., Uraguchi, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Boiling+feature+on+a+super+water-repellent+surface.">Boiling feature on a super water-repellent surface.</a> Heat Transfer Eng. 27 (8), 25-30 (2006).</li><li>Takata, Y., Hidaka, S., Masuda, M., Ito, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pool+boiling+on+a+super+hydrophilic+surface.">Pool boiling on a super hydrophilic surface.</a> Int. J. 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H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+study+of+nucleate+boiling+heat+transfer+on+hydrophilic,+hydrophobic+and+heterogeneous+wetting+surface.">A study of nucleate boiling heat transfer on hydrophilic, hydrophobic and heterogeneous wetting surface.</a> Int. J. Heat Mass Transfer. 54 (25-26), 5643-5652 (2011).</li><li>Mehta, J. S., Kandlikar, S. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pool+boiling+heat+transfer+enhancement+over+cylindrical+tubes+with+water+at+atmospheric+pressure,+Part+I:+Experimental+results+for+circumferential+rectangular+open+microchannels.">Pool boiling heat transfer enhancement over cylindrical tubes with water at atmospheric pressure, Part I: Experimental results for circumferential rectangular open microchannels.</a> Int. J. Heat Mass Transfer. 64, 1205-1215 (2013).</li><li>Cornwell, K., Houston, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nucleate+Pool+Boiling+on+Horizontal+Tubes+-+a+Convection-Based+Correlation.">Nucleate Pool Boiling on Horizontal Tubes - a Convection-Based Correlation.</a> Int. J. Heat Mass Transfer. 37, 303-309 (1994).</li><li>Holman, J. 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> Experimental Methods for Engineers. , (2007).</li></ol>

The authors declare that they have no competing financial interests.

The main goal of this investigation was to develop a pool-boiling heat sink for high heat dissipation applications, such as nuclear reactors, boilers, and heat pipes, by introducing the hybrid wettable surface, as described in the protocol section. These surfaces can produce better pool-boiling performances than homogeneous wettable surfaces (hydrophilic and hydrophobic). The improvement in the boiling heat-transfer performance is due to an increase in active nucleation sites and the easy detachment of the formed bubbles...

A high heat flux-sustaining system providing cooling in the range of 10-105 W/cm2 is required in the emerging fields of electronics, defense, avionics, and nuclear device development. Conventional cooling with air is insufficient for these applications due to the low heat-transfer coefficient (HTC) for both free- and forced-convection conditions. The phase change-based cooling techniques, such as pool boiling and flow boiling, are good enough to remove high heat fluxes on the order of 10 - 1,000 W/cm2 1. Since the two-phase heat-transfer process is isothermal, the cooled device temperature is almost constant over its surface. Due to the negligible variation of the temperature along the surface, the thermal shock of the device can be eliminated. However, the major limiting parameter in boiling heat-transfer is the critical heat flux (CHF), which causes an abnormal rise in temperature2.
In the last few decades, extensive research has been carried out to improve the CHF by using surface modification, nanofluids, and surface coatings3,4,5,6,7,8,9,10,11. Among the various methods, surface coatings are found to be the best method to improve the CHF due to the substantial increase in the surface area. Surface coatings generally increase the heat transfer by fin action, porosity effects, and surface wettability12. Surface wettability plays a significant role in boiling heat-transfer. Previous studies show that at lower heat-flux conditions, the hydrophobic surface shows better HTC due to the early nucleation. However, at higher heat flux, the detachment of the formed bubbles is slow due to the low affinity of water towards the surface. This leads to bubble coalescence and results in a lower CHF3. On the other hand, a hydrophilic surface produces a higher CHF, because of the fast detachment of the formed bubbles, but it gives a lower HTC at low heat fluxes, due to the delay in bubble nucleation13.
The hybrid structures show a remarkable enhancement in boiling heat-transfer for all heat fluxes due to the combined effect of hydrophobicity and hydrophilicity14,15,16. Hsu et al. produced heterogeneous wettable surface by coating superhydrophilic Si nanoparticles on a masked copper surface. They achieved different wettability ratios by varying the coating time. The onset of boiling occurred earlier on the heterogeneous surfaces compared to the homogeneous surface, which substantially reduced the wall superheat17. Jo et al. conducted nucleate boiling heat-transfer studies on hydrophilic, hydrophobic, and heterogeneous wetting surfaces. The heterogeneous wetting surface was composed of hydrophobic patterned dots on the hydrophilic surface. They got higher HTCs and the same CHF for the heterogeneous surface as compared to the hydrophilic surface. An improvement in boiling heat-transfer directly depends upon the number of dots on the surface and upon the boiling conditions18.
In this study, axial hybrid wettable patterns were produced on a cylindrical copper surface using the dip coating technique. Pool-boiling heat-transfer studies were conducted to determine the effects of the number of interlines and of the orientation of the hybrid wettable pattern. Boiling heat flux, HTC, and bubble dynamics were analyzed for the all coated substrates and were compared with the copper substrate.

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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 conducted on a hybrid wettable cylindrical surface using the experimental setup whose schematic is shown in Figure 5. The pool-boiling experimental procedure explained in step 2 of the protocol section was successfully carried out while investigating the effect of the number of interlines and of the orientation of the hybrid wettable pattern on the pool-boiling performance. The pool-boiling performances of the different-treated ...

Watch this Scientific Journal Video about Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns at JoVE.com

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

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 ...

The overall goal of this experiment is to investigate the effect of the number and orientation of axial wettable patterns on pool-boiling heat-transfer. This method can help answer key questions in the field of pool-boiling heat transfer such as the effect of hybrid variability on the boiling heat transfer coefficient and bubble dynamics. The main advantage of this technique is that it can accurately measure the pool-boiling heat-transfer coefficient and bubble dynamics of hybrid wettable surface.To begin, manually polish a hollow copper cylinder for 15 minutes using number 2, 000 emery paper. Clean the polished surface by rinsing it with acetone followed by deionized water. Place the polished test piece in an oven for two hours at a constant temperature of 120 degrees Celsius.To prepare a superhydrophilic silicon dioxide nanoparticle solution, first prepare solution A by mixing tetraethoxy silane and deionized water. Then add two drops of 37%concentrated HCl to solution A and stir for two hours. Next, make solution B by mixing ethanol and deionized water.Then mix one milliliter of solution A and 80 milliliters of solution B and stir for two hours. And 32 grams of silicon dioxide nanoparticles to the prepared solution and stir for one hour before immersing the test piece as described in the text protocol. Next, prepared two interlined hybrid patterns with different orientations along the axial direction of the test piece, by masking the area to be uncoated using the insulation tape according to the required number of interlines with the proper orientation.For the two interlined surface at a zero degree orientation adjust interlines at the center and the superhydrophilic area on the top side. Conversely, for the 180 degree orientation, adjust the superhydrophilic area at the bottom and the interlines at the center. Similarly adjust the position of the four and eight interlined surfaces with the different orientations.Next, immerse the masked test piece in the prepared solution by using a dip coating apparatus at a high dipping velocity and rise at a slow velocity of five millimeters per minute. Keep the coated test piece in an oven at 120 degrees for one hour. Finally, remove the insulation tape from the masked area to obtain the required number of interlines with the proper orientation.Using insulation tape, fix one glass tube at each circular base of the coated test piece. Horizontally fix this assembly to the chamber using silicon paste according to the required position of interlines. Place a cartridge heater with a thin film of thermal paste on the circumferential area into the hole of the test piece.Connect the cartridge heater to a direct current power supply unit. Place T-type thermocouples into the eight equally spaced one millimeter holes with alternate depths of five millimeters and seven millimeters. Then, connect them to the data logger.Insert and fix resistance temperature detectors, a reflux condenser and an auxiliary heater in the spaces provided on the top cover. Fix them over the boiling chamber. Next, fill 1.4 liters of deionized water into the pool-boiling chamber.Connect the reflux condenser to a cooling chamber that is maintained at five degrees Celsius. Prior to the experiment, vigorously boil the deionized water in the pool-boiling chamber for 30 minutes using the auxiliary heater. Keep the deionized water at the saturated boiling condition by using the auxiliary heater.Subsequently, switch on the power supply and give an initial current of 0.1 amps. Meanwhile, record the bubble dynamics for each power input by using a CCD camera that is placed in front of the pool-boiling chamber and focused on the test piece. After waiting for two minutes to reach a steady-state, increase the electric current with increments of 0.3 amps.Record the temperature at each power input by using the data logger. Continue the experiment until a maximum current of four amps is reached. Finally, perform Data Reduction as described in the text protocol.Shown here are pool-boiling performances of plain copper surface, fully superhydrophilic surface, and hybrid surfaces with different numbers of interlines at zero degree orientation. The effect of various surfaces on pool-boiling curves is shown, as well as the variation of the heat transfer coefficient, or HTC with respect to heat flux. Eight interlined surfaces show better HTC as compared to other surfaces for particular heat flux, but two and four interlined surfaces have almost the same HTC.The effect of orientation on pool-boiling curves of two interlined hybrid surfaces, four interlined hybrid surfaces, and eight interlined hybrid surfaces are shown. The leftward shift in pool-boiling curves is obtained for the two interlined surface for zero degrees, the four interlined surface at 90 degrees, and the eight interlined surface at 45 degrees. Also shown is the effect of orientation on the heat transfer coefficient for two interlined hybrid surfaces, four interlined hybrid surfaces, and eight interlined hybrid surfaces.HTC of the two interlined surface at zero degrees, the four interlined surface at 90 degrees, and the eight interlined surface at 45 degrees show the highest values. Once mastered this technique can done in ways if it is performed properly. For learning this procedure, analysis of pool-boiling heat-transfer coefficient and bubble dynamics can be performed to investigate the effect of hybrid variability on pool-boiling.Don't forget that, working with nanoparticles and chemicals can be hazardous and precautions such as wearing gloves and masks should always be taken while performing this procedure.

pool-boiling-heat-transfer-enhancement-on-cylindrical-surfaces-with

Research

JoVE Journal

Engineering

8.9K Görüntüleme.  National Taiwan University. The overall goal of this experiment is to investigate the effect of the number and orientation of axial wettable patterns on pool-boiling heat-transfer. This method can help answer key questions in the field of pool-boiling heat transfer such as the effect of hybrid variability on the boiling heat transfer coefficient and bubble dynamics. The main advantage of this technique is that it can accurately measure the pool-boiling heat-transfer coefficient and bubble dynamics of hybrid wettable sur...