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

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.