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Editorial

J. Nanotechnol. Eng. Med. 2014;4(4):040201-040201-1. doi:10.1115/1.4028125.
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Research and education in a wide range of studies involving micro/nanoscale heat and mass transfer have advanced the state-of-the-art rapidly over the past decades primarily due to technical advancements that provided the ability to manipulate materials precisely at the atomic/molecular level which has enabled the development of materials with novel properties. These advancements have significantly impacted the scientific and technological frontiers in the fields of energy and medicine. The studies have exhibited extremely rapid progresses in both fundamental understanding and industrial applications, especially in the areas of thermal management, drug delivery, and therapy. For example, stable colloidal solutions obtained by doping various solvents with minute concentration of nanoparticles (also called “nanofluids”) have attracted considerable attention in contemporary research due to their perceived superior heat transfer properties such as thermal conductivity and convective heat transfer. The number of research articles dedicated to this subject has been experiencing an exponential increase in the last decade [1], which has advanced the knowledge about the basic mechanisms responsible for their apparent superior transport properties such as the critical rheological behavior of nanofluids. These advancements also bear great promise in various industrial applications, such as for the developments of novel coolants (or heat transfer fluids, HTF) in heat exchangers, electronic cooling systems, automobile radiators, and concentrating solar power systems. Meanwhile, nanotechnology applications in medicine have also garnered significant attention in the research communities which has led to a fast growth in research activities and has resulted in many exciting discoveries. Four NIH sponsored nanomedicine centers were established in 2005 and hundreds of nanotech-based drugs and delivery systems have been developed worldwide. Sales of products developed using nanomedicine technologies reached over $6.8 billion in 2004, which involved over 200 companies and 38 products worldwide [2]. Moreover, an Alliance for Nanotechnology in Cancer has been established by the National Cancer Institute to accelerate the advances in nanomedicine revolutionaries of diagnostics, drug delivery, gene therapy, and many clinical applications.

Commentary by Dr. Valentin Fuster

Research Papers

J. Nanotechnol. Eng. Med. 2014;4(4):040901-040901-5. doi:10.1115/1.4026970.
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Polyalcohols such as neopentyl glycol (NPG) undergo solid-state crystal transformations that absorb/release significant latent heat. These solid–solid phase change materials (PCM) can be used in practical thermal management applications without concerns about liquid leakage and thermal expansion during phase transitions. In this paper, microcapsules of NPG encapsulated in silica shells were successfully synthesized with the use of emulsion techniques. The size of the microcapsules range from 0.2 to 4 μm, and the thickness of the silica shell is about 30 nm. It was found that the endothermic phase transition of these NPG-silica microcapsules was initiated at around 39 °C and the latent heat was about 96.0 J/g. A large supercooling of about 43.3 °C was observed in the pure NPG particles without shells, while the supercooling of the NPG microcapsules was reduced to about 14 °C due to the heterogeneous nucleation sites provided by the silica shell. These NPG microcapsules were added to the heat transfer fluid PAO to enhance its heat capacity and the effective heat capacity of the fluid was increased by 56% with the addition of 20 wt. % NPG-silica microcapsules.

Commentary by Dr. Valentin Fuster
J. Nanotechnol. Eng. Med. 2014;4(4):040902-040902-8. doi:10.1115/1.4027340.
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Avoiding collateral damage to healthy tissues during the high intensity focused ultrasound (HIFU) ablation of malignant tumors is one of the major challenges for effective thermal therapy. Such collateral damage can originate out of the need for using higher acoustic powers to treat deep seated or highly vascularized tumors. The objective of this study is to assess the utility of using magnetic nanoparticles (mNPs) during HIFU procedures to locally enhance heating at low powers, thereby reducing the likelihood of collateral thermal damage and undesired destruction due to cavitation. Tissue phantoms with 0% (control), 1% and 3% mNPs concentrations by volume were fabricated. Each tissue phantom was embedded with four thermocouples (TCs) and sonicated using transducer acoustic powers of 5.15 W, 9.17 W, and 14.26 W. The temperature profiles during the heating and cooling periods were recorded for each embedded TC. The measured transient temperature profiles were used for thermal-dose calculations. The increase in the concentration of mNPs in the tissue phantoms, from 0% to 3%, resulted in the rise in the peak temperatures for all the TCs for each acoustic power. The thermal dose also increased with the rise in the concentration of mNPs in the tissue phantoms. For the highest applied acoustic power (14.26 W), the peak temperature at TC 1 (T1) in tissue phantoms with 1% and 3% mNPs concentrations increased (with respect to tissue phantom with 0% (control) mNPs concentration) by 1.59× and 2.09×, respectively. For an acoustic power of 14.26 W, the time required to achieve cellular necrosis as defined by a 240 equivalent min thermal dose was approximately 75 s in the absence of mNPs, 14 s for the 1% concentration, and 8 s for the 3% concentration. Magnetic nanoparticles have the potential to significantly reduce the time for HIFU thermal-ablation procedures. They can also decrease the likelihood of collateral damage by the propagating beam in HIFU procedures by reducing the intensity required to achieve cellular necrosis.

Commentary by Dr. Valentin Fuster
J. Nanotechnol. Eng. Med. 2014;4(4):040903-040903-6. doi:10.1115/1.4027643.
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In this experimental study, a filtered white light is used to induce heating in water-based dispersions of 20 nm diameter gold nanospheres (GNSs)—enabling a low-cost form of plasmonic photothermal heating. The resulting temperature fields were measured using an infrared (IR) camera. The effect of incident radiative flux (ranging from 0.38 to 0.77 W·cm−2) and particle concentration (ranging from 0.25–1.0 × 1013 particles per mL) on the solution's temperature were investigated. The experimental results indicate that surface heat treatments via GNSs can be achieved through complementary tuning of GNS solutions and filtered light.

Commentary by Dr. Valentin Fuster
J. Nanotechnol. Eng. Med. 2014;4(4):040904-040904-9. doi:10.1115/1.4027913.
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An experimental study has been carried out to evaluate the heat transfer and friction factor characteristics of helical screw inserts in Al2O3–water and carbon nanotubes (CNT)–water nanofluids through a straight pipe in laminar flow regime with constant heat flux boundary condition. Tests have been performed by using 0.15% volume concentration Al2O3–water and CNT–water nanofluid with helical tape inserts of twist ratio (TR) = 1.5, 2.5, and 3. The helical screw tape inserts with CNT–water nanofluid exhibits higher thermal performance compared to Al2O3–water nanofluid. The maximum enhancement in heat transfer was obtained for CNT–water nanofluid with helical tape inserts of TR = 1.5. The increase in pressure drop of Al2O3–water nanofluid with helical screw tape inserts is found to be higher compared to CNT–water nanofluid with helical screw tape inserts at lower value of TR. For both the nanofluids (CNT–water and Al2O3–water), the thermal performance factor was found to be greater than unity for all TRs.

Commentary by Dr. Valentin Fuster
J. Nanotechnol. Eng. Med. 2014;4(4):040905-040905-9. doi:10.1115/1.4027987.
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The developing and developed nanofluid Rayleigh–Bénard flows between two parallel plates was simulated using the mesoscopic thermal lattice-Boltzmann method (LBM). The coupled effects of the thermal conductivity and the dynamic viscosity on the evolution of Rayleigh–Bénard flows were examined using different particle volume fractions (1–4%), while the individual effects of the thermal conductivity and the dynamic viscosity were tested using various particle sizes (11 nm, 20 nm, and 30 nm) and nanoparticle types (Al2O3, Cu, and CuO2). Two different heating modes were also considered. The results show that Rayleigh–Bénard cell in nanofluids is significantly different from that in pure fluids. The stable convection cells in nanofluids come from the expansion and shedding of an initial vortex pair, while the flow begins suddenly in pure water when the Rayleigh number reaches a critical value. Therefore, the average Nusselt number increases gradually for nanofluids but sharply for pure liquids. Uniform fully developed flow cells with fewer but larger vortex pairs are generated with the bottom heating with nanofluids than with pure liquid, with extremely tiny vortexes confined near the top heating plate for top heating. The number of vortex pairs decreases with increasing nanoparticle volume fraction and particle diameter due to the increasing of dynamic viscosity. The average Nusselt number increases with the increasing Rayleigh number, while decreases with the increasing nanoparticle diameters. The nanoparticle types have little effect on the Rayleigh–Bénard flow patterns. The Rayleigh–Bénard flows are more sensitive with the dynamic viscosity than the thermal conductivity of nanofluids.

Commentary by Dr. Valentin Fuster
J. Nanotechnol. Eng. Med. 2014;4(4):040906-040906-5. doi:10.1115/1.4027988.
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The objective of this work is to experimentally and numerically evaluate small-scale cryosurgery using an ultrafine cryoprobe. The outer diameter (OD) of the cryoprobe was 550 μm. The cooling performance of the cryoprobe was tested with a freezing experiment using hydrogel at 37 °C. As a result of 1 min of cooling, the surface temperature of the cryoprobe reached −35 °C and the radius of the frozen region was 2 mm. To evaluate the temperature distribution, a numerical simulation was conducted. The temperature distribution in the frozen region and the heat transfer coefficient was discussed.

Commentary by Dr. Valentin Fuster
J. Nanotechnol. Eng. Med. 2014;4(4):041001-041001-6. doi:10.1115/1.4026939.
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Due to their promising mechanical and electrical properties, carbon nanotubes (CNTs) have the potential to be employed in many nano/microelectronic applications e.g., through silicon vias (TSVs), interconnects, transistors, etc. In particular, use of CNT bundles inside annular cylinders of copper (Cu) as TSV is proposed in this study. To evaluate mechanical integrity of CNT-Cu composite material, a molecular dynamics (MD) simulation of the interface between CNT and Cu is conducted. Different arrangements of single wall carbon nanotubes (SWCNTs) have been studied at interface of a Cu slab. Pullout forces have been applied to a SWCNT while Cu is spatially fixed. This study is repeated for several different cases where multiple CNT strands are interfaced with Cu slab. The results show similar behavior of the pull-out-displacement curves. After pull-out force reaches a maximum value, it oscillates around an average force with descending amplitude until the strand/s is/are completely pulled-out. A linear relationship between pull-out forces and the number of CNT strands was observed. Second order interaction effect was found to be negligible when multiple layers of CNTs were studied at the interface of Cu. C–Cu van der Waals (vdW) interaction was found to be much stronger than C–C vdW's interactions. Embedded length has no significance on the average pull-out force. However, the amplitude of oscillations increases as the length of CNTs increases. As expected when one end of CNT strand was fixed, owing to its extraordinary strength, large amount of force was required to pull it out. Finally, an analytical relationship is proposed to determine the interfacial shear strength between Cu and CNT bundle.

Commentary by Dr. Valentin Fuster
J. Nanotechnol. Eng. Med. 2014;4(4):041002-041002-9. doi:10.1115/1.4027435.
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The combined effects of viscous and Joule heating on the stagnation point flow of a nanofluid through a stretching/shrinking sheet in the presence of homogeneous–heterogeneous reactions are investigated. The nanoparticle volume fraction model is used to describe the nanofluid. In this study, the density temperature relation is nonlinear which causes a nonlinear convective heat transfer. The surface of the sheet is assumed to be convectively heated with a hot fluid. The governing nonlinear differential equations are solved using the successive linearization method (SLM), and the results are validated by comparison with numerical approximations obtained using the Matlab in-built boundary value problem solver bvp4c and with existing results in literature. The nanofluid problem finds applications in heat transfer devices where the density and temperature relations are complex and the viscosity of the fluid has significant effect on the heat transfer rate.

Commentary by Dr. Valentin Fuster
J. Nanotechnol. Eng. Med. 2014;4(4):041003-041003-7. doi:10.1115/1.4027690.
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The paper proposes a new modeling approach for the prediction and analysis of the mechanical properties in deoxyribonucleic acid (DNA) molecules based on a hybrid atomistic-finite element continuum representation. The model takes into account of the complex geometry of the DNA strands, a structural mechanics representation of the atomic bonds existing in the molecules and the mass distribution of the atoms by using a lumped parameter model. A 13-base-pair DNA model is used to illustrate the proposed approach. The properties of the equivalent bond elements used to represent the DNA model have been derived. The natural frequencies, vibration mode shapes, and equivalent continuum mechanical properties of the DNA strand are obtained. The results from our model compare well with a high-fidelity molecular mechanics simulation and existing MD and experimental data from open literature.

Commentary by Dr. Valentin Fuster
J. Nanotechnol. Eng. Med. 2014;4(4):041004-041004-6. doi:10.1115/1.4027854.
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Nanofluids are often proposed as advanced heat transfer fluids. In this work, using a one-step nanoemulsification method, we synthesize gallium, indium, and indium–bismuth nanofluids in poly-alpha-olefin (PAO). The size distributions of the resulting nanoparticles are analyzed using transmission electron microscopy (TEM). X-ray diffraction (XRD) analysis of the alloy nanoparticles indicates that their composition is the same as that of the bulk alloy. It was found that oleylamine stabilizes both gallium and indium particles in PAO, while oleic acid is effective for gallium particles only. The microscopic adsorption mechanism of surfactants on gallium and indium surfaces is investigated using density functional theory (DFT) to understand why oleylamine is effective for both metals while oleic acid is effective for gallium only.

Commentary by Dr. Valentin Fuster

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