5.2 Recommendations for future work
5.2.3 Future work for thermal engineering application
Condensation heat transfer can not be directly enhanced by applying NBND coating.
However, the drainage of condensate water can be enhanced, which reduces pressure drop and thus benefits the overall thermal-hydraulic performance. Due to the limitation of the pool boiling facility in the lab, NBND treatment was not applied on a heat exchanger, but was applied on a piece of aluminum sheet cut from fin stock. It has been found that, NBND treatment enhanced wettability. There are two major driven force of water drainage on fins:
gravity, and shear force from air flow [6], [40]. The hemi-wicking wetting mechanism enhances surface wettability and reduces contact angle hysteresis, so that the drainage behaviour on the hydrophilic fins is enhanced. However, once the surface coating is flooded, the enhancement of wettability to help condensate water drainage is diminished.
According to the definition of the solid fraction ϕ for hemi-wicking model, the ϕ becomes meaningless, because the flooded surface does not have solid-gas interface. The hemi-wicking model cannot be true when the prerequisite 0<ϕ<1 is not satisfied. Experiment should be conducted in the future to test such coating under flooded conditions.
It is recommended that, an experimental setup can be built to do NBND on larger aluminum sheet to make fins, so that a heat exchanger can be made for testing. One way to do so, is to heat up the aluminum sheet or an already made heat exchanger to a high temperature about 600 °C, which is the about the brazing temperature of heat exchangers, but below the melting temperature of aluminum. Then quench it in a pool of nanofluid (the pool has been preheated to near 100 °C). This method may be closer to the procedure that could be applied in industry mass production, but is not very suitable for study in laboratory. A method that provides a good control over temperature and boiling time is needed. Therefore, a better idea would be to run hot liquid (temperature sufficiently higher than the boiling point of water) through the tubes of the heat exchanger, and place the heat exchanger in a large pool of several gallons of nanofluid with controlled temperature (kept at 100 °C). In this way, the fins would boil the nanofluid to have nanoparticles deposited onto the surface. The
If the exact same procedure as in the lab is carried out in mass production, the cost for NBND process could be high (1 minute of NBND cost about 2.5 kW-h/cm2 of coating, or about 0.3 dollars/cm2). However, instead of a well-controlled pool boiling process using Joule heating, in industry mass production, waste heat from previous processes such as brazing, could be utilized to quench the surface in nanofluid to make the coating. Other convention industry coating processes such as thermal spray could also be utilized to reduce the cost. For future investigation. Plasma spray, which is a type of thermal spray coating method, is a promising method for mass production. Following this rout of thinking, other recently developed thermal spray methods, such as cold spray, suspension thermal spray and solution precursor thermal spray processes, which are better in maintaining the shape of nanoparticles, could be methods to deposit nanoparticles onto metal substrates [66]. The investigation into the application of various types of thermal spray process to deposit a coating with a similar topography to the NBND method, is subject to future work.
REFERENCES
[1] S. G. Kandlikar, “A theoretical model to predict pool boiling CHF incorporating effects of contact angle and orientation,” Journal of Heat Transfer, vol. 123, no. 6, pp.
1071–1079, 2001.
[2] H. S. Ahn et al., “Pool boiling CHF enhancement by micro/nanoscale modification of zircaloy-4 surface,” Nuclear Engineering and Design, vol. 240, no. 10, pp. 3350–3360, 2010.
[3] T. G. Theofanous, C. Liu, S. Additon, S. Angelini, O. Kymalainen, and T. Salmassi,
“In-vessel coolability and retention of a core melt,” Nuclear Engineering and Design, vol.
169, no. 1–3, pp. 1–48, 1997.
[4] H. O’Hanley et al., “Separate effects of surface roughness, wettability, and porosity on the boiling critical heat flux,” Applied Physics Letters, vol. 103, no. 2, 2013.
[5] R. Xiao, S. C. Maroo, and E. N. Wang, “Negative pressures in nanoporous membranes for thin film evaporation,” Applied Physics Letters, vol. 102, no. 12, 2013.
[6] L. Liu and A. M. Jacobi, “Air-Side surface wettability effects on the performance of slit-fin-and-tube heat exchangers operating under wet-surface conditions,” Journal of Heat Transfer, vol. 131, no. 5, pp. 1–9, 2009.
[7] K. Hong and R. L. Webb, “Performance of dehumidifying heat exchangers with and without wetting coatings,” Journal of Heat Transfer, vol. 121, no. 4, pp. 1018–1026, 1999.
[8] C.-C. Wang and C.-T. Chang, “Heat and mass transfer for plate fin-and-tube heat exchangers, with and without hydrophilic coating,” International Journal of Heat and Mass Transfer, vol. 41, no. 20, pp. 3109–3120, 1998.
[9] S. Jhee, K.-. Lee, and W.-. Kim, “Effect of surface treatments on the frosting/defrosting behavior of a fin-tube heat exchanger,” International Journal of Refrigeration, vol. 25, no. 8, pp. 1047–1053, 2002.
[10] J. L. Hoke, J. G. Georgiadis, and A. M. Jacobi, “Effect of substrate wettability on frost properties,” Journal of Thermophysics and Heat Transfer, vol. 18, no. 2, pp. 228–235, 2004.
[11] D. J. Trevoy and H. Johnson Jr., “The water wettability of metal surfaces,” Journal of Physical Chemistry, vol. 62, no. 7, pp. 833–837, 1958.
[12] V. P. Carey, Liquid Vapor Phase Change Phenomena: An Introduction to the Thermophysics of Vaporization and Condensation Processes in Heat Transfer Equipment, Second Edition. Taylor & Francis, 2007.
[13] G.-. Kim, H. Lee, and R. L. Webb, “Plasma hydrophilic surface treatment for dehumidifying heat exchangers,” Experimental Thermal and Fluid Science, vol. 27, no. 1, pp. 1–10, 2002.
[14] B. Bourdon, R. Rioboo, M. Marengo, E. Gosselin, and J. De Coninck, “Influence of the wettability on the boiling onset,” Langmuir, vol. 28, no. 2, pp. 1618–1624, 2012.
[15] Y. Takata et al., “Effect of surface wettability on boiling and evaporation,” Energy,
vol. 30, no. 2–4 SPEC. ISS., pp. 209–220, 2005.
[16] D. Coso, V. Srinivasan, M.-. Lu, J.-. Chang, and A. Majumdar, “Enhanced heat transfer in biporous wicks in the thin liquid film evaporation and boiling regimes,” Journal of Heat Transfer, vol. 134, no. 10, 2012.
[17] A. Fujishima, T. Rao, and D. Tryk, “Titanium dioxide photocatalysis,” Journal of Photochemistry and Photobiology C: Photochemistry Reviews, vol. 1, no. 1, pp. 1–21,
2000.
[18] S. K. Koh, J. S. Cho, K. H. Kim, S. Han, and Y. W. Beag, “Altering a polymer surface chemical structure by an ion-assisted reaction,” Journal of Adhesion Science and Technology, vol. 16, no. 2, pp. 129–142, 2002.
[19] K.-H. Kim et al., “Permanent Hydrophilic Surface Formation by Ion Assisted Reaction,” in Heat Exchanger Fouling and Cleaning: Fundamentals and Applications, Santa Fe, New Mexico, USA, 2003, pp. 107–115.
[20] H. D. Kim and M. H. Kim, “Effect of nanoparticle deposition on capillary wicking that influences the critical heat flux in nanofluids,” Applied Physics Letters, vol. 91, no. 1, 2007.
[21] S. J. Kim, I. C. Bang, J. Buongiorno, and L. W. Hu, “Effects of nanoparticle deposition on surface wettability influencing boiling heat transfer in nanofluids,” Applied Physics Letters, vol. 89, no. 15, 2006.
[22] H. T. Phan, N. Caney, P. Marty, S. Colasson, and J. Gavillet, “Surface wettability
control by nanocoating: The effects on pool boiling heat transfer and nucleation mechanism,” International Journal of Heat and Mass Transfer, vol. 52, no. 23–24, pp.
5459–5471, 2009.
[23] F. Zhang and A. M. Jacobi, “Nanoparticle deposition by boiling on aluminum surfaces to enhance wettability,” in 15th International Refrigeration and Air Conditioning Conference at Purdue, West Lafayette, Indiana, 2014.
[24] F. Zhang and A. M. Jacobi, “Aluminum surface wettability changes by pool boiling of nanofluids,” Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 506, pp. 438–444, 2016.
[25] S. M. You, J. H. Kim, and K. H. Kim, “Effect of nanoparticles on critical heat flux of water in pool boiling heat transfer,” Applied Physics Letters, vol. 83, no. 16, pp. 3374–
3376, 2003.
[26] S. M. Kwark, R. Kumar, G. Moreno, J. Yoo, and S. M. You, “Pool boiling characteristics of low concentration nanofluids,” International Journal of Heat and Mass Transfer, vol. 53, no. 5–6, pp. 972–981, 2010.
[27] A. Celen, A. Cebi, M. Aktas, O. Mahian, A. S. Dalkilic, and S. Wongwises, “A review of nanorefrigerants: Flow characteristics and applications,” International Journal of Refrigeration, vol. 44, pp. 125–140, 2014.
[28] K. Henderson, Y.-. Park, L. Liu, and A. M. Jacobi, Flow-boiling heat transfer of R-134a-based nanofluids in a horizontal tube, vol. 53. 2010.
[29] S. W. Lee, K. M. Kim, and I. C. Bang, “Study on flow boiling critical heat flux enhancement of graphene oxide/water nanofluid,” International Journal of Heat and Mass Transfer, vol. 65, pp. 348–356, 2013.
[30] T. J. Athauda, D. S. Decker, and R. R. Ozer, “Effect of surface metrology on the wettability of SiO2 nanoparticle coating,” Materials Letters, vol. 67, no. 1, pp. 338–341, 2012.
[31] E. Rio, A. Daerr, F. Lequeux, and L. Limat, “Moving contact lines of a colloidal suspension in the presence of drying,” Langmuir, vol. 22, no. 7, pp. 3186–3191, 2006.
[32] X. Zhong, A. Crivoi, and F. Duan, “Sessile nanofluid droplet drying,” Advances in Colloid and Interface Science, vol. 217, pp. 13–30, 2015.
[33] R. D. Deegan, O. Bakajin, T. F. Dupont, G. Huber, S. R. Nagel, and T. A. Witten,
“Capillary flow as the cause of ring stains from dried liquid drops,” Nature, vol. 389, no.
6653, pp. 827–829, 1997.
[34] D. D. Brewer et al., “Mechanistic principles of colloidal crystal growth by evaporation-induced convective steering,” Langmuir, vol. 24, no. 23, pp. 13683–13693, 2008.
[35] H. Ganapathy and V. Sajith, “Semi-analytical model for pool boiling of nanofluids,”
International Journal of Heat and Mass Transfer, vol. 57, no. 1, pp. 32–47, 2013.
[36] S. Vafaei and T. Borca-Tasciuc, “Role of nanoparticles on nanofluid boiling phenomenon: Nanoparticle deposition,” Chemical Engineering Research and Design,
2013.
[37] J. Bico, U. Thiele, and D. Quere, “Wetting of textured surfaces,” Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 206, no. 1-3, pp. 41–46, 9 2002.
[38] R. N. Wenzel, “RESISTANCE OF SOLID SURFACES TO WETTING BY WATER,” Industrial & Engineering Chemistry, vol. 28, no. 8, pp. 988–994, 1936.
[39] A. B. D. Cassie and S. Baxter, “Wettability of porous surfaces,” Transactions of the Faraday Society, vol. 40, pp. 546–551, 1944.
[40] M. A. Rahman and A. M. Jacobi, “Wetting behavior and drainage of water droplets on microgrooved brass surfaces,” Langmuir, vol. 28, no. 37, pp. 13441–13451, 2012.
[41] S. Shibuichi, T. Onda, N. Satoh, and K. Tsujii, “Super water-repellent surfaces resulting from fractal structure,” Journal of Physical Chemistry, vol. 100, no. 50, pp.
19512–19517, 1996.
[42] R. Kamatchi and S. Venkatachalapathy, “Parametric study of pool boiling heat transfer with nanofluids for the enhancement of critical heat flux: A review,” International Journal of Thermal Sciences, vol. 87, pp. 228–240, 2015.
[43] R. N. Wenzel, “Surface roughness and contact angle,” Journal of Physical &
Colloid Chemistry, vol. 53, no. 9, pp. 1466–1467, 1949.
[44] J. Bico, C. Tordeux, and D. Quere, “Rough wetting,” Europhysics Letters, vol. 55, no. 2, pp. 214–220, 2001.
[45] J. Gao, J. Zhao, X. Chen, W. Xue, and L. Liu, “Boiling water treatment for wettability improvement of aluminum fin surfaces,” in ASME 2013 International Mechanical Engineering Congress and Exposition, IMECE 2013, San Diego, CA, 2013,
vol. 8 B.
[46] W. Vedder and D. A. Vermilyea, “Aluminum + water reaction,” Transactions of the Faraday Society, vol. 65, pp. 561–584, 1969.
[47] S. D. Park, S. B. Moon, and I. C. Bang, “Effects of thickness of boiling-induced nanoparticle deposition on the saturation of critical heat flux enhancement,” International Journal of Heat and Mass Transfer, vol. 78, no. 0, pp. 506–514, 2014.
[48] D. Huitink, E. E. D. Ontiveros, and Y. Hassan, “The bubble fossil record: Insight into boiling nucleation using nanofluid pool-boiling,” Heat and Mass Transfer/Waerme- und Stoffuebertragung, vol. 48, no. 2, pp. 267–274, 2012.
[49] T.-H. Yen and C.-Y. Soong, “Hybrid Cassie-Wenzel model for droplets on surfaces with nanoscale roughness,” Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, vol. 93, no. 2, 2016.
[50] V. Kumar and J. R. Errington, “Impact of small-scale geometric roughness on wetting behavior,” Langmuir, vol. 29, no. 38, pp. 11815–11820, 2013.
[51] S. Prakash, E. Xi, and A. J. Patel, “Spontaneous recovery of superhydrophobicity on nanotextured surfaces,” Proceedings of the National Academy of Sciences of the United States of America, vol. 113, no. 20, pp. 5508–5513, 2016.
[52] A. C. Vieira Coelho, G. A. Rocha, P. Souza Santos, H. Souza Santos, and P. K.
Kiyohara, “Specific surface area and structures of aluminas from fibrillar pseudoboehmite,”
MatÃ\copyrightria (Rio de Janeiro), vol. 13, pp. 329–341, 2008.
[53] J. D. Rimstidt and H. L. Barnes, “The kinetics of silica-water reactions,”
Geochimica et Cosmochimica Acta, vol. 44, no. 11, pp. 1683–1699, 1980.
[54] X. Wu, E. Sacher, and M. Meunier, “The effects of hydrogen bonds on the adhesion of inorganic oxide particles on hydrophilic silicon surfaces,” Journal of Applied Physics, vol. 86, no. 3, pp. 1744–1748, 1999.
[55] J. N. Israelachvili, “8 - Special Interactions: Hydrogen-Bonding and Hydrophobic and Hydrophilic Interactions,” in Intermolecular and Surface Forces (Third Edition), Third Edition., J. N. Israelachvili, Ed. San Diego: Academic Press, 2011, pp. 151–167.
[56] J. Long, M. Zhong, H. Zhang, and P. Fan, “Superhydrophilicity to superhydrophobicity transition of picosecond laser microstructured aluminum in ambient air,” Journal of colloid and interface science, vol. 441, no. 0, pp. 1–9, Spring 2015.
[57] Ö. Özkanat, B. Salgin, M. Rohwerder, J. M. C. Mol, J. H. W. de Wit, and H. Terryn,
“Scanning Kelvin Probe Study of (Oxyhydr)oxide Surface of Aluminum Alloy,” The Journal of Physical Chemistry C, vol. 116, no. 2, pp. 1805–1811, 2012.
[58] S. Takeda, M. Fukawa, Y. Hayashi, and K. Matsumoto, “Surface {OH} group governing adsorption properties of metal oxide films,” Thin Solid Films, vol. 339, no. 1–2, pp. 220–224, 1999.
[59] A. Majumdar and B. Bhushan, “Role of Fractal Geometry in Roughness Characterization and Contact Mechanics of Surfaces,” Journal of Tribology, vol. 112, no.
2, pp. 205–216, Apr. 1990.
[60] A. H. M. Sondag, M. C. Raas, and P. N. T. V. Velzen, “Contamination of aluminium oxide surfaces in ambient air investigated by {FTIR} {MSR} and {TOF} SIMS.
Chemisorption of aliphatic carboxylic acids,” Chemical Physics Letters, vol. 155, no. 4–5, pp. 503–510, 1989.
[61] J. van den Brand, S. V. Gils, P. C. J. Beentjes, H. Terryn, and J. H. W. de Wit,
“Ageing of aluminium oxide surfaces and their subsequent reactivity towards bonding with organic functional groups,” Applied Surface Science, vol. 235, no. 4, pp. 465–474, 2004.
[62] T. Sun et al., “Reversible Switching between Superhydrophilicity and Superhydrophobicity,” Angewandte Chemie - International Edition, vol. 43, no. 3, pp.
357–360, 2004.
[63] J. J. Freeman, G. J. Morgan, and C. A. Cullen, “Thermal conductivity of a single polymer chain,” Phys. Rev. B, vol. 35, no. 14, pp. 7627–7635, May 1987.
[64] A. Henry and G. Chen, “High Thermal Conductivity of Single Polyethylene Chains Using Molecular Dynamics Simulations,” Phys. Rev. Lett., vol. 101, no. 23, p.
235502, Dec. 2008.
[65] Y. Cui, C. Tao, S. Zheng, Q. He, S. Ai, and J. Li, “Synthesis of Thermosensitive PNIPAM-co-MBAA Nanotubes by Atom Transfer Radical Polymerization within a Porous Membrane,” Macromolecular Rapid Communications, vol. 26, no. 19, pp. 1552–
1556, 2005.
[66] J. A. Gan and C. C. Berndt, “Nanocomposite coatings: thermal spray processing, microstructure and performance,” International Materials Reviews, vol. 60, no. 4, pp. 195–
244, 2015.
APPENDIX
Uncertainty of the measured roughness and contact angle are calculated for Student-t distribution 90% confidence interval. Data for roughness from profilometry are listed in Table 1 to Table 3. Contact angles are listed in Table 4 to Table 6.
Because only limited number of measurements could be done, the Student-t distribution is used as the method to estimate the accuracy of the averaged value. The true mean should be lying within the interval shown in Equation (1), where xn is the average value
confidence of the true mean to be lying in such interval is 90%, then Equation (2) express the case. An equivalent expression is Equation (3), and introducing n
n where F t is the cumulative distribution function (Equation (6)), calculated by integrating the probability density function of Student’s t-distribution, which is expressed as Equation (7).
is the gamma function. In Equation (7), the degree of freedom is calculated asPr n 0.9
Roughness factors obtained from profilometry are expressed by Equation (8) through (11).
The “peak” and “valley” are represented by Rp and Rv, respectively. Lo is the overall length of the 1-D profile of the scan result. Factor r 1-D is estimated by the Lo and the scan length, expressed by Equation (12). The true topological dimension of the surface should be higher than 2-D and smaller than 3-D. In order to estimate the real roughness factor r of the specimen surface, r 2-D and r 3-D have also been calculated by taking the square and cubic of the r 1-D value. However, these estimated r values are too small comparing to the roughness change needed to provide the wettability enhancement observed on these specimens by contact angle experiment. Data are listed in Table (1) to Table (3).
0
Table A. 1. Roughness of the rough substrate, boiled in pure water and after
Table A. 2: Roughness of the smooth substrate, boiled in pure water and after
Table A. 3: Roughness of the ultra-smooth substrate, boiled in pure water and after NBND using 50 nm alumina nanofluid:
Surface
Water static contact angles are measured multiple times on a specimen surface, and each time at a different location. Data for the measurements at varies locations are listed in Table (4) to Table (6).
Table A. 4: Water contact angle of the ultra-smooth substrate, boiled in pure water and after NBND using 50 nm alumina nanofluid:
Table A. 5: Water contact of the smooth substrate, boiled in pure water and after NBND using 50 nm alumina nanofluid:
Table A. 6: Water contact of the rough substrate, boiled in pure water and after NBND using 50 nm alumina nanofluid:
N60 1% 0.10% 0.01% pure water before
boiling
location 1 6 36 38 39 47
location 2 8 33 36 45 48
location 3 6 38 37 43 44
location 4 6 38 35 36 43
location 5 35
location 6 45
location 7 30
Average 7 36 37 39 46
Uncertainty 1 3 2 6 2
The histogram for the number density of particle size distribution analysis are shown in Figure A. 1 to Figure A. 5. Data comes from SEM image analysis. Size measurement of one hundred different particles in the images where recorded and scaled by the scale bar in each image of Figure 2.7 and Figure 2.8.
Figure A. 1: Histogram of particle sizes of nominal 13 nm Al2O3 nanoparticles.
Figure A. 2: Histogram of particle sizes of nominal 50 nm Al2O3 nanoparticles.
Figure A. 3: Histogram of particle sizes of nominal 300 nm Al2O3 nanoparticles.
Figure A. 4: Histogram of particle sizes of nominal 65 nm SiO2 nanoparticles.
Figure A. 5: Histogram of particle sizes of nominal 15 nm SiO2 nanoparticles.
Figure A. 6: Zeta potential distribution function of 13 nm Al2O3 nanofluid.
Proof of Equation (4.2):
proj comb proj W proj comb proj H proj comb
dA dA
dA dA dA
dA dA dA dA dA (4.1g)
,