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Research Papers

Effect of Nanoparticle Suspensions on Liquid Fuel Hot-Plate Ignition OPEN ACCESS

[+] Author and Article Information
Zhi Huang, Yuxuan Lu, Ting Cheng, Liangying Yu

School of Power and Mechanical Engineering,
Wuhan University,
Wuhan, HB 430072, China

Weimin Kan

GPGC Electric Power Research Institute,
Guangzhou, GD 510600, China

Xuejiao Hu

School of Power and Mechanical Engineering,
Wuhan University,
Wuhan, HB 430072, China
Ministry of Education Key Laboratory
on Hydrodynamic Transients,
Wuhan, HB 430072, China
e-mail: xjhu@whu.edu.cn

1Corresponding author.

Manuscript received March 9, 2014; final manuscript received November 3, 2014; published online November 19, 2014. Assoc. Editor: Calvin Li.

J. Nanotechnol. Eng. Med 5(3), 031004 (Aug 01, 2014) (5 pages) Paper No: NANO-14-1022; doi: 10.1115/1.4029029 History: Received March 09, 2014; Revised November 03, 2014; Online November 19, 2014

Increased ignition probabilities of ethanol are found on a heated hot-plate with the introduction of Al2O3, Fe3O4, and carbon nanotube (CNT) nanoparticle suspensions. We show that the mechanism is probably due to liquid fuel boiling point elevation caused by nanoparticle accumulation at liquid–vapor interfaces. The magnitudes of this impact are related to the number and geometry of nanoparticles but independent from the nanoparticle chemical compositions. These findings may have important applications for developing future alternative liquid fuels with advanced combustion characteristics.

FIGURES IN THIS ARTICLE
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Resource shortages and environmental pressures demand many future combustion systems to consider alternative fuels [1]. One of the problems with alternative fuels is that the performance they can offer is not yet able to compete that of the fuels currently in use [2]. Viable methods of improving fuel combustion performance, therefore, are of great importance. Studies suggested that adding nanometer-sized particle (NP) into solid fuels may have the great promise of improving the base fuels with higher energy density, shorter ignition delay, and lower environmental impact [3-5]. Metallic NPs, such as nano-Al, have been proposed as additives for high-speed and high-power propulsion systems, such as those for rockets, due to their very high energy densities [6,7]. Catalytic NP additives, primarily metal oxide, have been demonstrated to significantly increase the rate of combustion [8]. One apparent advantage of NPs over larger sized particles is the high surface to volume ratio, which increases the rate of reaction during combustion for chemically reactive NPs.

Several recent studies shown that NPs may also have strong impacts on the combustion characteristics of liquid fuels. For example, Tyagi [9] measured the hot-plate ignition of a diesel fuel with Al and Al2O3 NP suspensions. They found that the ignition probabilities were increased after the additions of either type of NPs, and moreover, the magnitudes of the increases were almost identical. Jones [10] later shown that the additions of Al-NPs increased the heat of combustion proportionally to the Al-NP concentrations; while Al2O3-NPs were chemically inactive and had no heat contributions. Sabourin [11] carried out combustion experiment with a propellant mixed with graphene suspensions and observed lower ignition temperature and higher combustion rate over the propellant itself. Apparently, graphene cannot function as an oxidant as those metal-oxide-based catalytic NP additives can do [8]. These findings suggested that NP suspensions may have unusual physical impacts on the combustion characteristic of liquid fuels regardless of their chemical compositions.

Liquids with NPs suspensions, also known as nanofluids, have been an active area of research since last decade, first received from the finding of enhanced thermal physical properties (i.e., thermal conductivities [12-14] and convective heat transfer coefficients [15,16]) over the base fluids, and then to many remarkable properties of other fundamental physical processes, for example, thermal radiation [17], mass diffusion [18,19], interface spreading [20,21], and phase changes [22]. However, so far, experimental data for “combustible nanofluids” are yet lacking, and more importantly in some extent, the physical mechanism behind the NPs impact on the combustion characteristics of liquid fuels is still not clear.

In this letter, we experimentally evaluate the hot-plate ignition probabilities of a bioliquid fuel (ethanol) [1] mixed with various kinds of NP suspensions. A theoretical model is proposed to interpret the mechanism of the increased ignition probabilities versus the additions of NPs by detailed analysis of two competing physical processes in fuel droplets: the accumulation of NPs at the fuel–vapor interface and the departure of the NPs from the interface back to the bulk of the fuel droplet. The increased ignition probability is attributed to the elevation of boiling point of the liquid fuel caused by the increased NP concentration at the fuel–vapor interface. Reasonable agreements between experimental data and theoretical predictions are obtained when Sherwood number, also known as mass transfer Nusselt number, Sh = HmR/D is around 22, where Hm is the mass transfer coefficient, R is the radius of the fuel droplet, and D is the diffusivity of the NPs in the base fuel.

The experimental apparatus following Ref. [9] is depicted in Fig. 1. The hot-plate was made by the exposed top surface of a copper cylinder, at the center of which a small concave was fabricated, about 1 cm in diameter and 2 mm in depth maximum, to avoid fuel droplets from rolling all over the place; all the other surfaces of the cylinder were thermally insulated. The hot-plate can be heated using four cylindrical electrical heaters uniformly distributed inside the cylinder. A pair of thermocouples with a measurement uncertainty no more than ±2 K was embedded right under the concave of the hot-plate to monitor and regulate the surface temperature. The fuel samples to be tested were dripped off in the concave of the hot-plate from a microsyringe hanging upright 25 mm above the hot plate. At least 200 droplets were tested for each fuel sample to estimate the ignition probability at any given hot-plate temperature.

Three types of NPs, Al2O3, Fe3O4, and CNTs, were experimentally examined, respectively, among which the Al2O3 and Fe3O4 NPs are spherelike with an almost identical diameter near 20 nm, and the CNTs are multiwalled with an outer diameter about 40 nm and a large length-to-diameter ratio around 250 (Table 1). All NPs were received at dry condition from commercial vendors and were used without further purification. Desired NP concentrations were obtained by weighting the masses of the NPs and the total mixtures with the base fluid/fuel. Ethanol was selected as the base fuel, since it is a like-to-happen alternative fuel that can be massively obtained from biomass [1]. The simple chemical composition and well determined physical properties of ethanol (Table 2) also offered additional convenience for quantitative model evaluation. Mixtures of ethanol and NP suspensions were prepared following a widely adopted two-step method of making nanofluids [23]: first step, NP sample was treated using moderate nitric acid to break clusters and then dried through slow baking; second step, ethanol was added and fully mixed with the NPs using ultrasonic oscillations for at 2 h. To minimize possible influences due to NP clustering and sediments, every sample was freshly made right before each test.

The measured ignition probabilities, for hot-plate temperatures varying from 675 °C to 725 °C, in an increment of 10 °C, are presented as scattered points in Fig. 2. The uncertainties of the measured ignition probabilities are estimated using the Student's-t method with a confidence level of 95% [24]. The maximum uncertainty is found no more than ±6.9% and is marked using the error bar on the data point where the maximum uncertainty most likely occurs.

Continuous curves in Fig. 2 are fitted lines following the below equation:Display Formula

(1)P(Ts)=1--T12πσexp[-12σ2(Ts-T*)2]dTs

where P(Ts) is the ignition probability at hot-plate temperature Ts, T* is the average hot-plate ignition temperature, and σ is an integration parameter proportional to the variance of the ignition probability density dP/dT. Under this circumstance, dP/dT is assumed to follow Gaussian distributions, as illustrated in the insets of Fig. 2, whose expectations are the average hot-plate ignition temperatures T*. It is easy to find that the higher the ignition probability P(Ts), the lower the ignition temperature T*. As can be seen from Fig. 2, adding NPs into liquid fuels can effectively increase the ignition probability and therefore reduce the ignition temperature; the more particles added, the bigger the impact, as long as the resulted sample remains as a uniform mixture. The impacts of Al2O3-NPs and Fe3O4-NPs are almost identical, which again suggests that the chemical composition may not be an important factor here. However, CNTs show much more significant impact, which can cause the same order magnitude of changes at much lower particle concentrations.

Two conditions must be satisfied before a fuel droplet can be ignited: (1) sufficient accessible oxygen and (2) high enough temperature. Condition (1) was satisfied since the experiment was conducted in an open space with air surrounded, and therefore condition (2) is the gating factor to determine if the fuel droplet can start burning. A heat transfer model is established to test condition (2). For a small droplet of a liquid placed on a hot surface whose temperature is significantly above the boiling point of the liquid, the intensive evaporation of the liquid leads to a vapor layer under the droplet, which can levitate the droplet upward away from the hot surface. The vapor layer thus becomes a thermal barrier and reduces the rate of heat transfer between the hot surface and the liquid droplet, known as Leidenfrost phenomenon [25,26], as illustrated in Fig. 3.

In the vapor layer, we assume one-dimensional steady-state heat conduction along z axis. The governing equation is: (d2T)/(dz2) = 0. At z = 0, the heat transfer between the hot-plate and the vapor layer is prescribed by dT/dz=Hh(T-Ts)/κv, where Hh is the heat transfer coefficient and κv is the thermal conductivity of vapor. The vapor–liquid interface remains at the boiling temperature Tb, i.e., T = Tb at z = h, where h is the thickness of the vapor layer. The radius of the liquid fuel droplets, R, in the experiment were observed around 2 mm just before ignition, and the thickness of the vapor layers thus can be estimated to be 139 μm [26]. The solution of the vapor temperature is thenDisplay Formula

(2)T=Hh(Ts-Tb)κv+hHh(h-z)+Tb

T reaches its maximum at z = 0 withDisplay Formula

(3)Tmax=Ts-TbNu-1+1+Tb

where Nu = Hhh/κv. If Tmax is higher than the ignition point of the vapor, the vapor can obtain enough activation energy and start to flame, and thus the droplet will be ignited; otherwise, the droplet will be evaporating till disappears without combustion.

For a symmetric impinging jet flowing perpendicular to a hot plate, Nu can be calculated by Nu = 0.76Re1/2Pr2/5, where Re = uh/(μv/ρv), Pr = Cpμv/κv, u is the vapor velocity and Cp is the specific heat of the vapor [27]. The vapor velocity is determined by the rate of evaporation as well as how fast the liquid–vapor interface movesDisplay Formula

(4)u=dhdt-dVdt1Aρlρv

where t is the time and A is the area of the liquid–vapor interface. Energy conservation at the liquid–vapor interface givesDisplay Formula

(5)ρlLdVdt=-κvAdTdz|z=h=AκvHh(Ts-Tb)κv+Hh

Substituting Eq. (5) into Eq. (4) under the circumstances of fast evaporation and thin vapor films (dh/dt0,Hh), we haveDisplay Formula

(6)uκv(Ts-Tb)ρvLh

The maximum vapor temperature is thus found to beDisplay Formula

(7)Tmax=Ts-Tb{0.76[κv(Ts-Tb)/μvL]1/2}-1Pr-2/5+1+Tb

The increase of Tmax at any given hot-plate temperature Ts is equivalent to the decrease of the expected hot-plate ignition temperature μ. As can be seen from Eq. (7), Tmax is a function of two thermophysical properties of the liquid fuel colloid: the boiling temperature Tb and the latent heat L. Both of these properties can be affected by the number of NPs presented at the liquid–vapor interface.

There exist two competing NP transport processes at the liquid–vapor interface of a Leidenfrost droplet, whose joint effect determines the number of NPs to be present at the interface. On the one hand, NPs accumulate at the interface through self-organization as a result of the fast evaporation of the liquid. It has been observed by several researchers recently [28,29] that self-organized NP superlattices can nucleate and grow at the liquid–air interface when a droplet of a NP colloidal solution evaporates, controlled by the evaporation kinetics and particle interactions at the phase-change interface. The rate of accumulation, va, is related to the evaporation rate through va=κv(Ts-Tb)Ac0/hLρl, where c0 is the bulk NP concentration of the droplet. On the other hand, NPs depart from the liquid–vapor interface driven by the surface tension gradient surrounding the droplet (Marangoni convection) and the concentration gradient between the interface and the bulk droplet (mass diffusion). The rate of departure can be calculated as vd = HmA(ci − c0), where Hm is the mass transfer coefficient, ci is the NP concentration at the liquid–vapor interface. Similar to heat transfer, Hm is related to the dimensionless parameter, Sherwood number, in the form of Sh = HmR/D, where R is the radius of the fuel droplet and D is the diffusivity of the NPs in the base fuel. At steady-state before ignition, the accumulation–departure processes reach equilibrium, which means vd = va, i.e.,Display Formula

(9)Hm(ci-c0)=κv(Ts-Tb)c0/hLρl

From the above, ci can be obtained for any given Sh.

The presence of NPs at the liquid–vapor interface may elevate the boiling temperature (Tb) of the liquid fuel colloid. Similar to solutions with nonvolatile molecular/ion particles, NPs themselves have a vapor pressure of zero, and the presence of NPs at the liquid–vapor interface decreases the total vapor pressure of the fuel colloid. A higher temperature is needed for the vapor pressure to reach the surrounding pressure, and the boiling point is thus elevated. This boiling point elevation is known as a colligative property [30], which solely depends on the number of presented particles, but not on their identity, or any specific particle–liquid interactions. The uniqueness here is that NPs are much bigger than the fuel molecules, and the presence of a NP in the mixture may take the places of a bunch number of fuel molecules, which suggests that particle volume fractions might be a better parameter to quantify the presence of NPs, rather than molar fractions as for those small dissolved solute particles. Thus, the relation between the NP suspensions and the resulted boiling point elevation may be written asDisplay Formula

(10)ln(1-ci)=MLRu(1Tb-1Tb0)

where M is the molecular weight of the liquid fuel, Ru is the universal gas constant, and Tb0 is the boiling point of the pure liquid fuel.

The presence of NPs may also reduce the latent heat (L) of the liquid colloid, as can be concluded by L=L0-TΔS/M, where L0 is the latent heat of the pure liquid and TΔS is so-called concentration enthalpy, and may be calculated as TΔS=-n1RuT(lnx1-lnx0) , where n1 is the amount of substance of NPs, and x0 and x1 are the substance concentrations of NPs before and after evaporation, respectively. However, detailed calculation suggests that this effect is at least two orders of magnitude smaller than the latent heat of the evaporation of the base fuel itself, and therefore can be ignored. The increases of Tmax may be dominantly contributed by the elevation of the boiling point.

The increase of Tmax directly leads to the higher ignition probabilities or lower hot-plate ignition temperatures observed in the experiment. Reasonable agreement between the theoretical predictions and the experimental results are obtained for Sh = 22, as shown in Fig. 4. According to Stokes–Einstein equation, D=kBT/6πμlr, where kB is the Boltzmann constant, μl is the liquid viscosity, and r is the equivalent radius of the NPs. For a nonspherical particle, r can be calculated as the radius of a hypothetical spherical NP that has the same surface area, i.e., r=(3ANP/4π)1/3, where ANP is the surface area of the nonspherical particle. Subscribing Sh and D into Eq. (7), it can be gained that the concentration of NPs at the liquid–air interface

where a=6πμlRκv(Ts-Tb)/hLρlShkBT. As ar ≫ 1, ci, that has direct relation with the boiling point, can be approximated to be proportional to rc0. It is clear to see from Fig. 4 that with the increasing of rc0, the reduction of the ignition temperature T* increases, however, it is independent of the chemical compositions. The CNTs seemed to have stronger impact for making similar decreases of ignition temperatures at lower particle concentrations because of their smaller diffusivity, which leads to lower rates of departure from the liquid–vapor interface and more elevation of boiling point. Under this circumstance, r of CNTs is much bigger than the half of the outer diameter of the tubes due to the large aspect ratio, and therefore the diffusivity of CNTs is far smaller.

In summary, we have experimentally shown the increases of hot-plate ignition probabilities of ethanol due to the introduction of several different types of NP suspensions in addition to the similar findings in Ref. [11]. More importantly, we have also shown that the reason behind this effect may come from the elevation of boiling point caused by the presence of NPs at the liquid–vapor interface. These findings may have important applications for improving the combustion performance of alternative liquid fuels.

The authors gratefully acknowledge the financial supports from NSFC (50906064), DF of MOE (20100141110022), SRF for ROCS by SEM, and the Fundamental Research Funds for Central Universities (2012208020203). The authors thank Mr. Shilong Fu, Mr. Chao Wang, and Mr. Yourui Hu for their assistances on the experiments. Z.H. also thanks to Scholarship Award for Excellent Doctoral Student by Ministry of Education (5052012208002).

Szuromi, P., Jasny, B., Clery, D., Austin, J., and Hanson, B., 2007, “Energy for the Long Haul,” Science, 315(5813), p. 781. [CrossRef]
Hill, J., Nelson, E., Tilman, D., Polasky, S., and Tiffany, D., 2006, “Environmental, Economic, and Energetic Costs and Benefits of Biodiesel and Ethanol Biofuels,” Proc. Natl. Acad. Sci., 103(30), pp. 11206–11210. [CrossRef]
Yetter, R. A., Risha, G. A., and Son, S. F., 2009, “Metal Particle Combustion and Nanotechnology,” Proc. Combust. Inst., 32(2), pp. 1819–1838. [CrossRef]
Dreizin, E. L., 2009, “Metal-Based Reactive Nanomaterials,” Prog. Energy Combust. Sci., 35(2), pp. 141–167. [CrossRef]
Granier, J., Plantier, K., and Pantoya, M., 2004, “The Role of the Al2O3 Passivation Shell Surrounding Nano-Al Particles in the Combustion Synthesis of NiAl,” J. Mater. Sci., 39(21), pp. 6421–6431. [CrossRef]
Gan, Y., and Qiao, L., 2011, “Combustion Characteristics of Fuel Droplets With Addition of Nano and Micron-Sized Aluminum Particles,” Combust. Flame, 158(2), pp. 354–368. [CrossRef]
Pantoya, M. L., and Granier, J. J., 2005, “Combustion Behavior of Highly Energetic Thermites: Nano Versus Micron Composites,” Propellants, Explos., Pyrotech., 30(1), pp. 53–62. [CrossRef]
Sajith, V., Sobhan, C., and Peterson, G., 2010, “Experimental Investigations on the Effects of Cerium Oxide Nanoparticle Fuel Additives on Biodiesel,” Adv. Mech. Eng., 2010(58), p. 581407. [CrossRef]
Tyagi, H., Phelan, P. E., Prasher, R., Peck, R., Lee, T., Pacheco, J. R., and Arentzen, P., 2008, “Increased Hot-Plate Ignition Probability for Nanoparticle-Laden Diesel Fuel,” Nano Lett., 8(5), pp. 1410–1416. [CrossRef] [PubMed]
Jones, M., Li, C. H., Afjeh, A., and Peterson, G., 2011, “Experimental Study of Combustion Characteristics of Nanoscale Metal and Metal Oxide Additives in Biofuel (Ethanol),” Nanoscale Res. Lett., 6(1), pp. 1–12. [CrossRef]
Sabourin, J. L., Dabbs, D. M., Yetter, R. A., Dryer, F. L., and Aksay, I. A., 2009, “Functionalized Graphene Sheet Colloids for Enhanced Fuel/Propellant Combustion,” ACS Nano, 3(12), pp. 3945–3954. [CrossRef] [PubMed]
Prasher, R., Bhattacharya, P., and Phelan, P. E., 2005, “Thermal Conductivity of Nanoscale Colloidal Solutions (Nanofluids),” Phys. Rev. Lett., 94(2), p. 025901. [CrossRef] [PubMed]
Choi, S., Zhang, Z., Yu, W., Lockwood, F., and Grulke, E., 2001, “Anomalous Thermal Conductivity Enhancement in Nanotube Suspensions,” Appl. Phys. Lett., 79(14), pp. 2252–2254. [CrossRef]
Xie, H., Lee, H., Youn, W., and Choi, M., 2003, “Nanofluids Containing Multiwalled Carbon Nanotubes and Their Enhanced Thermal Conductivities,” J. Appl. Phys., 94(8), pp. 4967–4971. [CrossRef]
Wen, D., and Ding, Y., 2004, “Experimental Investigation Into Convective Heat Transfer of Nanofluids at the Entrance Region Under Laminar Flow Conditions,” Int. J. Heat Mass Transfer, 47(24), pp. 5181–5188. [CrossRef]
Xuan, Y., and Li, Q., 2003, “Investigation on Convective Heat Transfer and Flow Features of Nanofluids,” ASME J. Heat Transfer, 125(1), pp. 151–155. [CrossRef]
Tyagi, H., Phelan, P., and Prasher, R., 2007, “Predicted Efficiency of a Nanofluid-Based Direct Absorption Solar Receiver,” ASME 2007 Energy Sustainability Conference, ASME Paper No. ES2007-36139. [CrossRef]
Krishnamurthy, S., Bhattacharya, P., Phelan, P., and Prasher, R., 2006, “Enhanced Mass Transport in Nanofluids,” Nano Lett., 6(3), pp. 419–423. [CrossRef] [PubMed]
Ozturk, S., Hassan, Y. A., and Ugaz, V. M., 2010, “Interfacial Complexation Explains Anomalous Diffusion in Nanofluids,” Nano Lett., 10(2), pp. 665–671. [CrossRef] [PubMed]
Wasan, D. T., and Nikolov, A. D., 2003, “Spreading of Nanofluids on Solids,” Nature, 423(6936), pp. 156–159. [CrossRef] [PubMed]
Pauliac-Vaujour, E., Stannard, A., Martin, C., Blunt, M. O., Notingher, I., Moriarty, P., Vancea, I., and Thiele, U., 2008, “Fingering Instabilities in Dewetting Nanofluids,” Phys. Rev. Lett., 100(17), p. 176102. [CrossRef] [PubMed]
You, S., Kim, J., and Kim, K., 2003, “Effect of Nanoparticles on Critical Heat Flux of Water in Pool Boiling Heat Transfer,” Appl. Phys. Lett., 83(16), pp. 3374–3376. [CrossRef]
Wang, X.-Q., and Mujumdar, A. S., 2007, “Heat Transfer Characteristics of Nanofluids: A Review,” Int. J. Therm. Sci., 46(1), pp. 1–19. [CrossRef]
Wheeler, A. J., and Ganji, A., 2004, Engineering Experimentation, Pearson Education, Upper Saddle River, NJ.
Biance, A.-L., Clanet, C., and Quéré, D., 2003, “Leidenfrost Drops,” Phys. Fluids, 15(6), pp. 1632–1637. [CrossRef]
Myers, T., and Charpin, J., 2009, “A Mathematical Model of the Leidenfrost Effect on an Axisymmetric Droplet,” Phys. Fluids, 21(6), p. 063101. [CrossRef]
Kays, W., and Crawford, M., 1993, Convection Heat Transfer, McGraw-Hill, New York.
Bigioni, T. P., Lin, X.-M., Nguyen, T. T., Corwin, E. I., Witten, T. A., and Jaeger, H. M., 2006, “Kinetically Driven Self Assembly of Highly Ordered Nanoparticle Monolayers,” Nat. Mater., 5(4), pp. 265–270. [CrossRef] [PubMed]
Rabani, E., Reichman, D. R., Geissler, P. L., and Brus, L. E., 2003, “Drying-Mediated Self-Assembly of Nanoparticles,” Nature, 426(6964), pp. 271–274. [CrossRef] [PubMed]
Moore, W. J., 1972, Physical Chemistry, Prentice-Hall, Upper Saddle River, NJ.
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References

Szuromi, P., Jasny, B., Clery, D., Austin, J., and Hanson, B., 2007, “Energy for the Long Haul,” Science, 315(5813), p. 781. [CrossRef]
Hill, J., Nelson, E., Tilman, D., Polasky, S., and Tiffany, D., 2006, “Environmental, Economic, and Energetic Costs and Benefits of Biodiesel and Ethanol Biofuels,” Proc. Natl. Acad. Sci., 103(30), pp. 11206–11210. [CrossRef]
Yetter, R. A., Risha, G. A., and Son, S. F., 2009, “Metal Particle Combustion and Nanotechnology,” Proc. Combust. Inst., 32(2), pp. 1819–1838. [CrossRef]
Dreizin, E. L., 2009, “Metal-Based Reactive Nanomaterials,” Prog. Energy Combust. Sci., 35(2), pp. 141–167. [CrossRef]
Granier, J., Plantier, K., and Pantoya, M., 2004, “The Role of the Al2O3 Passivation Shell Surrounding Nano-Al Particles in the Combustion Synthesis of NiAl,” J. Mater. Sci., 39(21), pp. 6421–6431. [CrossRef]
Gan, Y., and Qiao, L., 2011, “Combustion Characteristics of Fuel Droplets With Addition of Nano and Micron-Sized Aluminum Particles,” Combust. Flame, 158(2), pp. 354–368. [CrossRef]
Pantoya, M. L., and Granier, J. J., 2005, “Combustion Behavior of Highly Energetic Thermites: Nano Versus Micron Composites,” Propellants, Explos., Pyrotech., 30(1), pp. 53–62. [CrossRef]
Sajith, V., Sobhan, C., and Peterson, G., 2010, “Experimental Investigations on the Effects of Cerium Oxide Nanoparticle Fuel Additives on Biodiesel,” Adv. Mech. Eng., 2010(58), p. 581407. [CrossRef]
Tyagi, H., Phelan, P. E., Prasher, R., Peck, R., Lee, T., Pacheco, J. R., and Arentzen, P., 2008, “Increased Hot-Plate Ignition Probability for Nanoparticle-Laden Diesel Fuel,” Nano Lett., 8(5), pp. 1410–1416. [CrossRef] [PubMed]
Jones, M., Li, C. H., Afjeh, A., and Peterson, G., 2011, “Experimental Study of Combustion Characteristics of Nanoscale Metal and Metal Oxide Additives in Biofuel (Ethanol),” Nanoscale Res. Lett., 6(1), pp. 1–12. [CrossRef]
Sabourin, J. L., Dabbs, D. M., Yetter, R. A., Dryer, F. L., and Aksay, I. A., 2009, “Functionalized Graphene Sheet Colloids for Enhanced Fuel/Propellant Combustion,” ACS Nano, 3(12), pp. 3945–3954. [CrossRef] [PubMed]
Prasher, R., Bhattacharya, P., and Phelan, P. E., 2005, “Thermal Conductivity of Nanoscale Colloidal Solutions (Nanofluids),” Phys. Rev. Lett., 94(2), p. 025901. [CrossRef] [PubMed]
Choi, S., Zhang, Z., Yu, W., Lockwood, F., and Grulke, E., 2001, “Anomalous Thermal Conductivity Enhancement in Nanotube Suspensions,” Appl. Phys. Lett., 79(14), pp. 2252–2254. [CrossRef]
Xie, H., Lee, H., Youn, W., and Choi, M., 2003, “Nanofluids Containing Multiwalled Carbon Nanotubes and Their Enhanced Thermal Conductivities,” J. Appl. Phys., 94(8), pp. 4967–4971. [CrossRef]
Wen, D., and Ding, Y., 2004, “Experimental Investigation Into Convective Heat Transfer of Nanofluids at the Entrance Region Under Laminar Flow Conditions,” Int. J. Heat Mass Transfer, 47(24), pp. 5181–5188. [CrossRef]
Xuan, Y., and Li, Q., 2003, “Investigation on Convective Heat Transfer and Flow Features of Nanofluids,” ASME J. Heat Transfer, 125(1), pp. 151–155. [CrossRef]
Tyagi, H., Phelan, P., and Prasher, R., 2007, “Predicted Efficiency of a Nanofluid-Based Direct Absorption Solar Receiver,” ASME 2007 Energy Sustainability Conference, ASME Paper No. ES2007-36139. [CrossRef]
Krishnamurthy, S., Bhattacharya, P., Phelan, P., and Prasher, R., 2006, “Enhanced Mass Transport in Nanofluids,” Nano Lett., 6(3), pp. 419–423. [CrossRef] [PubMed]
Ozturk, S., Hassan, Y. A., and Ugaz, V. M., 2010, “Interfacial Complexation Explains Anomalous Diffusion in Nanofluids,” Nano Lett., 10(2), pp. 665–671. [CrossRef] [PubMed]
Wasan, D. T., and Nikolov, A. D., 2003, “Spreading of Nanofluids on Solids,” Nature, 423(6936), pp. 156–159. [CrossRef] [PubMed]
Pauliac-Vaujour, E., Stannard, A., Martin, C., Blunt, M. O., Notingher, I., Moriarty, P., Vancea, I., and Thiele, U., 2008, “Fingering Instabilities in Dewetting Nanofluids,” Phys. Rev. Lett., 100(17), p. 176102. [CrossRef] [PubMed]
You, S., Kim, J., and Kim, K., 2003, “Effect of Nanoparticles on Critical Heat Flux of Water in Pool Boiling Heat Transfer,” Appl. Phys. Lett., 83(16), pp. 3374–3376. [CrossRef]
Wang, X.-Q., and Mujumdar, A. S., 2007, “Heat Transfer Characteristics of Nanofluids: A Review,” Int. J. Therm. Sci., 46(1), pp. 1–19. [CrossRef]
Wheeler, A. J., and Ganji, A., 2004, Engineering Experimentation, Pearson Education, Upper Saddle River, NJ.
Biance, A.-L., Clanet, C., and Quéré, D., 2003, “Leidenfrost Drops,” Phys. Fluids, 15(6), pp. 1632–1637. [CrossRef]
Myers, T., and Charpin, J., 2009, “A Mathematical Model of the Leidenfrost Effect on an Axisymmetric Droplet,” Phys. Fluids, 21(6), p. 063101. [CrossRef]
Kays, W., and Crawford, M., 1993, Convection Heat Transfer, McGraw-Hill, New York.
Bigioni, T. P., Lin, X.-M., Nguyen, T. T., Corwin, E. I., Witten, T. A., and Jaeger, H. M., 2006, “Kinetically Driven Self Assembly of Highly Ordered Nanoparticle Monolayers,” Nat. Mater., 5(4), pp. 265–270. [CrossRef] [PubMed]
Rabani, E., Reichman, D. R., Geissler, P. L., and Brus, L. E., 2003, “Drying-Mediated Self-Assembly of Nanoparticles,” Nature, 426(6964), pp. 271–274. [CrossRef] [PubMed]
Moore, W. J., 1972, Physical Chemistry, Prentice-Hall, Upper Saddle River, NJ.

Figures

Grahic Jump Location
Fig. 3

Leidenfrost drop with nanoparticle suspensions

Grahic Jump Location
Fig. 2

Measured (dots) and fitted (curves) ignition probabilities at various hot-plate temperatures. (a) Ethanol with CNT suspensions versus pure ethanol and (b) ethanol with spherical NP (Al2O3, Fe3O4) suspensions versus pure ethanol. The insets depict the corresponding ignition probability densities, the peaks of which are the average hot-plate ignition temperatures, T*.

Grahic Jump Location
Fig. 1

Experimental setup

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Fig. 4

Ignition temperature decrease: theoretical prediction versus experimental data

Tables

Table Grahic Jump Location
Table 2 Properties of ethanol liquid and vapor
Table Grahic Jump Location
Table 1 Properties of nanoparticle samples

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