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Research Papers

J. Nanotechnol. Eng. Med. 2014;5(1):010901-010901-6. doi:10.1115/1.4026971.
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In the present study, the forced convective heat transfer performance of two different nanofluids, namely, Al2O3-water and CNT-water has been studied experimentally in an automobile radiator. Four different concentrations of nanofluid in the range of 0.15–1 vol. % were prepared by the additions nanoparticles into the water as base fluid. The coolant flow rate is varied in the range of 2 l/min–5 l/min. Nanocoolants exhibit enormous change in the heat transfer compared with the pure water. The heat transfer performance of CNT-water nanofluid was found to be better than Al2O3-water nanocoolant. Furthermore, the Nusselt number is found to increase with the increase in the nanoparticle concentration and nanofluid velocity.

Commentary by Dr. Valentin Fuster
J. Nanotechnol. Eng. Med. 2014;5(1):010902-010902-5. doi:10.1115/1.4028400.
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An absorber is a major component in the absorption refrigeration systems, and its performance remarkably affects the overall system performance. A mathematical model for ammonia absorption from a bubble expanding at a submerged nozzle into a binary nanofluid was developed to analyze the effects of binary nanofluid on ammonia absorption in the forming process of a bubble. The combined effects of nanoparticles on heat transfer, mass transfer, and bubble size all were considered in the model. The concentration of nanoparticles, the radius of the nozzle, and the flow rate of ammonia vapor were considered as the key parameters. The numerical results showed that the enhancement of binary nanofluid for bubble absorption has the analogous tendency with the mass transfer enhancement of binary nanofluid. The diameter of the nozzle and the flow rate of ammonia vapor hardly affect the enhancement of the binary nanofluid for the absorption of bubble growing stage. The current investigation can result in a better understanding of the absorption process occurring in thermally driven absorption refrigeration systems.

Commentary by Dr. Valentin Fuster
J. Nanotechnol. Eng. Med. 2014;5(1):010903-010903-13. doi:10.1115/1.4028009.
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Numerical simulations of two-dimensional (2D) laminar mixed convection heat transfer and nanofluids flows over forward facing step (FFS) in a vertical channel are numerically carried out. The continuity, momentum, and energy equations were solved by means of a finite volume method (FVM). The wall downstream of the step was maintained at a uniform wall heat flux, while the straight wall that forms the other side of the channel was maintained at constant temperature equivalent to the inlet fluid temperature. The upstream walls for the FFS were considered as adiabatic surfaces. The buoyancy assisting and buoyancy opposing flow conditions are investigated. Four different types of nanoparticles, Al2O3, CuO, SiO2, and ZnO with different volumes' fractions in the range of 1–4% and different nanoparticle diameters in the range of 25–80 nm, are dispersed in the base fluid (water) are used. In this study, several parameters, such as different Reynolds numbers in the range of 100 < Re < 900, and different heat fluxes in the range of 500 ≤ qw ≤ 4500 W/m2, and different step heights in the range of 3 ≤ S ≤ 5.8 mm, are investigated to identify their effects on the heat transfer and fluid flow characteristics. The numerical results indicate that the nanofluid with SiO2 has the highest Nusselt number compared with other nanofluids. The recirculation region and the Nusselt number increase as the step height, Reynolds number, and the volume fraction increase, and it decreases as the nanoparticle diameter increases. This study has revealed that the assisting flow has higher Nusselt number than opposing flow.

Commentary by Dr. Valentin Fuster
J. Nanotechnol. Eng. Med. 2014;5(1):010904-010904-25. doi:10.1115/1.4028092.
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Condensation in microchannels and minichannels is widely used in small devices such as air-cooled condensers for the air-conditioning and automotive industry, in heat pipes, thermosyphons and other applications for system thermal control. Currently, many research centers all over the world are dealing with the structure and operation of compact refrigerating devices. This is in line with the trend of 21st century that is moving towards the use of energy-saving and environmentally friendly technical equipment. In the present study, a critical review on condensation heat transfer in microchannels and minichannels is presented. This review include a wide range of different parameters such as the channel diameter (d), the saturation temperature (Ts), the mass flux (G), the vapor quality (x), different working fluids like steam, CO2 or R744, FC72, R22, R410A, and R407C, various shapes such as circular and noncircular, different orientations like horizontal and vertical, and systems consist of either single or multiple channels. At the end, recommendations for future studies will be given. As a result, this paper cannot only be used as the starting point for the researcher interested in condensation heat transfer in microchannels and minichannels, but it also includes recommendations for future studies on condensation heat transfer in microchannels and minichannels.

Commentary by Dr. Valentin Fuster
J. Nanotechnol. Eng. Med. 2014;5(1):011001-011001-9. doi:10.1115/1.4027219.
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Phase change materials (PCM) are used in many energy storage applications. Energy is stored (latent heat of fusion) by melting the PCM and is released during resolidification. Dispersing highly conductive nanoparticles into the PCM enhances the effective thermal conductivity of the PCM, which in turn significantly improves the energy storage capability of the PCM. The resulting colloidal mixture with the nanoparticles in suspension is referred to as nanostructure enhanced phase change materials (NEPCM). A commonly used PCM for energy storage application is the family of paraffin (CnH2n+2). Mixing copper oxide (CuO) nanoparticles in the paraffin produces an effective and highly efficient NEPCM for energy storage. However, after long term application cycles, the efficiency of the NEPCM may deteriorate and it may need replacement with fresh supply. Disposal of the used NEPCM containing the nanoparticles is a matter of concern. Used NEPCM containing nanoparticles cannot be discarded directly into the environment because of various short term health hazards for humans and all living beings and unidentified long term environmental and health hazards due to nanoparticles. This problem will be considerable when widespread use of NEPCM will be practiced. It is thus important to develop technologies to separate the nanoparticles before the disposal of the NEPCM. The primary objective of this research work is to develop methods for the separation and reclamation of the nanoparticles from the NEPCM before its disposal. The goal is to find, design, test, and evaluate separation methods which are simple, safe, and economical. The specific NEPCM considered in this study is a colloidal mixture of dodecane (C12H26) and CuO nanoparticles (1–5% mass fraction and 5–15 nm size distribution). The nanoparticles are coated with a surfactant or stabilizing ligands for suspension stability in the mixture for a long period of time. Various methods for separating the nanoparticles from the NEPCM are explored. The identified methods include: (i) distillation under atmospheric and reduced pressure, (ii) mixing with alcohol mixture solvent, and (iii) high speed centrifugation. These different nanoparticle separation methods have been pursued and tested, and the results are analyzed and presented in this article.

Commentary by Dr. Valentin Fuster
J. Nanotechnol. Eng. Med. 2014;5(1):011002-011002-6. doi:10.1115/1.4027447.
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Doped and undoped zinc oxide fibers were fabricated by electrospinning at various solution flow rates of 2, 4, and 6 μl/min followed by sintering at 550 °C. The nanogenerators (NGs) fabricated from the fibers were examined for their performance by applying loads (0.25–1.5 kg) representing fingers taps on the keyboard. A higher solution flow rate resulted in a larger fiber diameter, thus reducing nanogenerator voltage. The maximum power density for undoped zinc oxide-based and doped zinc oxide-based nanogenerators was 17.6 and 51.7 nW/cm2, respectively, under a load of 1.25 kg. Enhancing nanogenerator stability is a topic that should be investigated further.

Commentary by Dr. Valentin Fuster
J. Nanotechnol. Eng. Med. 2014;5(1):011003-011003-4. doi:10.1115/1.4028258.
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The effect of using different concentrations of aqueous nanosuspensions of clay minerals (1%, 1.5%, and 2%) offered at different periods of time (one time per one or two weeks) compared with tap-water with and without antibiotics on growth performance and some selected antibody titer was studied. The experiment lasted from 1 to 36 days of age. The statistical findings of the experiment prove that aqueous nanosuspension 1% offered one time per two weeks significantly improved feed conversion ratio (FCR). Meanwhile, aqueous nanosuspension 2% offered one time per two weeks significantly gave the same effect on live body weight (LBW) and body weight gain (BWG) as did antibiotics. Concerning the findings that pertain to immunity, antibody titer against the most infectious diseases [Newcastle (ND), infectious bronchitis (IB), and infectious bursal disease (IBD)] were significantly improved by offering aqueous nanosuspension 1.5% offered one time per one and two weeks, and aqueous nanosuspension 1% offered one time per one week, respectively.

Commentary by Dr. Valentin Fuster

Book Review

J. Nanotechnol. Eng. Med. 2014;5(1):016501-016501-2. doi:10.1115/1.4027827.
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REVIEWED BY ZHONG HE1 AND XIANQIN WANG2

Commentary by Dr. Valentin Fuster

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