Multiple quasi-steady states in a closed loop pulsating heat pipe

The novel fact that, keeping all the operating and boundary conditions fixed, a single loop pulsating heat pipe exhibits multiple operational quasi-steady states is reported in this paper. For a specified heat power input level and volumetric filling ratio, continuous online measurements of static pressure and temperature at crucial locations, along with flow visualization, have been carried out for more than twelve hours per experimental run of device operation. Four distinct quasi-steady states have been observed in these experimental runs. Each quasi-steady state is characterized by a unique specific two-phase flow pattern and corresponding effective device conductance, revealing the strong thermo-hydrodynamic coupling guiding the thermal performance. The quasi-steady state corresponding to best thermal performance consists of continuous unidirectional flow circulations, while the state corresponding to poor thermal performance is characterized by the intermittent bidirectional flow reversals. A temporal scaling analysis is presented to estimate the order of magnitude of the equilibrium frequency of phase change and ensuing oscillations. These order-of-magnitude estimates closely match with the experimentally observed frequencies. The spectral contents of each quasi-steady state are analyzed and it is found that dominant frequencies of flow oscillations are in the range of 0.1 to 3.0 Hz with each quasi-steady state exhibiting a characteristic power spectrum. This provides the necessary velocity scaling estimates, primary information needed for any progress in design of pulsating heat pipes.     

Sequence‐Specific HCV RNA Quantification Using the Size‐Dependent Nonlinear Optical Properties of Gold Nanoparticles

The hepatitis C virus (HCV) is a single‐stranded (ss) RNA virus that is responsible for chronic liver diseases, such as cirrhosis, end‐stage liver disease, and hepatocellular carcinoma. Driven by the need to detect the presence of the HCV viral sequence, herein it is demonstrated for the first time that the nonlinear optical (NLO) properties of gold nanoparticles can be used for screening and quantifying HCV RNA without any modification, with excellent detection limit (80 pM ) and selectivity (single base‐pair mismatch). The hyper‐Rayleigh scattering (HRS) intensity increases 25 times when label‐free, 145‐mer, HCV ss‐RNA is hybridized with 400 pM target RNA. The mechanism of HRS intensity change is discussed with experimental evidence for a higher multipolar contribution to the NLO response of gold nanoparticles.     

Turboexpander wheel design for helium liquefaction plant

A turboexpander wheel, that is, turbine, is one of the critical components for a helium liquefaction plant. It helps to provide the cooling effect required for the liquefaction. The percentage of liquefaction depends upon the effective design of the turbine. The present work includes the design of a radial turbine for the intended power output of approximately 1.5 kW, with input conditions of 40‐g/s mass flow rate at inlet, inlet total pressure of 14 bar, inlet temperature of 40 K, and outlet static pressure of 6 bar. The pressure values are taken to be absolute. Inlet conditions are selected on the basis of required refrigeration effect of approximately 1 kW. The outlet static pressure of 6 bar is maintained to avoid the turbulence, which may occur due to expansion for high pressure ratios. The present work involves the design and optimization of a turbine on the basis of the mean line analysis, initiating with the assumption of values for total‐to‐static efficiency. As per mean line design concept, a one‐dimensional flow is considered for this analysis and the mean values of different parameters are considered at different sections. Losses are considered as the main constraint in design and it is desirable to get optimum net power. Besides, it is also desirable to achieve values for other design parameters in a specified range.     

Effects of non‐Darcian and temperature dependent heat source on two‐phase flow in a vertical porous space with thermal radiation

In this article, influences of viscous dissipation and thermal radiation on MHD flow of two immiscible fluids in a vertical channel filled with porous materials have been studied theoretically. The equations governing the problem are transformed to a system of ODE and are solved by homotopy analysis method (HAM). The effects of physical parameters on flow and heat transfer characteristics have been discussed with the help of graphs. It is found that viscous dissipation parameter, heat source parameter, thermal parameter lead to enhance velocity as well as temperature field. Also, increasing Brinkmann number and heat source parameter lead to suppress Coefficient of skin friction at the left wall but the opposite is true at the other wall. However, these parameters give reverse trend on Nusselt number distribution. Further, increasing thermal conductivity ratio and fluids height ratio leads to increase heat transfer coefficient significantly at the left wall. In addition, we have compared present HAM solution with analytical solution of the problem (ie, absence of radiation parameter and Brinkmann number).     

Effect of Ultrasound on Molecular Structure Development of Polylactide

In this work, effect of ultrasound on molecular structure development of Polylactide (PLA) was studied. It was found that the intrinsic viscosity of PLA decreased with increasing treating time, temperature and ultrasound time. Different from traditional thermal degradation of PLA, the degradation of PLA under ultrasound treatment showed that chain scission and chain combination of PLA competed with each other in the degradation process, which could be divided into two steps. The mechanism of ultrasound degradation of PLA was proposed. Furthermore, Thermal properties were characterized by DSC to show heat and ultrasound effects on molecular structure development of PLA.     

Environmental and economical impact of LED lighting systems and effect of thermal management

Solid‐state lighting (SSL) technologies such as light emitting diodes (LEDs) have been of interest for the last 15 years. This article focuses on inorganic LED technology and their evolving applications, energy efficiency, and economic impact as well as the effect of thermal management on LED lighting systems. The efficacy of the best commercial 1 W LED packages currently surpasses 120 lm/W, which is more efficient than typical metal‐halide and fluorescent lamps. This high efficacy will eventually allow LED lighting systems to be used in specialty and general illumination applications. However, higher lumen requirements for LED systems will inevitably lead to significant thermal challenges at both the chip and the system level that need to be addressed to enable practical applications at low costs. In this article, the basics of LED lighting will be discussed first. It will be followed by the potential economic benefits for high efficiency LED lighting systems in the general illumination market. We will then discuss the thermal challenges and possible candidate cooling technologies in LED lighting systems. Copyright © 2009 John Wiley & Sons, Ltd.     

Turn-off operation of a MOS-gate 2.6 kV 4H–SiC gate turn-off thyristor

The turn-off operation of a 4H–SiC gate turn-off thyristor (GTO) with 2.6 kV breakover voltage has been investigated using an external Si-MOSFET as a gate-to-emitter shunt (MOS-gate mode), in the temperature interval 293–496 K. The maximum cathode current density j_cmax that can be turned off in such a mode decreases from 1850 A/cm² at 400 K to 700 A/cm² at 496 K. The room temperature j_cmax value is estimated to be about 3700 A/cm². The above j_cmax values are essentially higher than those observed when turning this thyristor off in the conventional GTO mode. Turn-off transients in the MOS-gate mode have been studied in both quasi-static and pulse regimes. Temperature dependencies of the turn-on and turn-off times, as well as those of the turn-on and turn-off energy losses have been measured. The upper switching frequency of the GTO is estimated to be about 700 kHz.     

Development of magnetorheological fluid-based process for finishing of ferromagnetic cylindrical workpiece

A magnetorheological fluid-based process is developed for the internal surface finishing of ferromagnetic cylindrical workpiece. The existing finishing processes based on magnetorheological fluid are not equipped to finish the internal ferromagnetic cylindrical surface significantly as it obtained higher magnetic flux density than the MR polishing fluid. At present, magnetorheological fluid-based finishing tools are designed to ensure the maximum magnetic flux density always present on the outer finishing tool core surface as compared to internal surface of ferromagnetic cylindrical workpiece surface. To validate this present principal idea, the magnetostatic finite element analysis has been performed on the newly designed finishing tools. The preliminary experiments have also been conducted to evaluate the finishing performance with the two newly designed finishing tools. The percentage reduction in surface roughness (R_a) values with I-shaped tool core is found as 65–78% after 150 min of finishing, whereas, with rectangular shaped tool core is found as 78–81% after 90 min of finishing. The results clearly revealed that the present finishing tool with rectangular shaped core is more suitable for uniform significant finishing of ferromagnetic cylindrical internal workpiece than the I-shaped core. The developed process can be useful in finishing of cylindrical mold and dies, hydraulic cylinder, barrel for injection molding, etc.     

Probing a Device's Active Atoms

Materials science and device studies have, when implemented jointly as “operando” studies, better revealed the causal link between the properties of the device's materials and its operation, with applications ranging from gas sensing to information and energy technologies. Here, as a further step that maximizes this causal link, the paper focuses on the electronic properties of those atoms that drive a device's operation by using it to read out the materials property. It is demonstrated how this method can reveal insight into the operation of a macroscale, industrial‐grade microelectronic device on the atomic level. A magnetic tunnel junction's (MTJ's) current, which involves charge transport across different atomic species and interfaces, is measured while these atoms absorb soft X‐rays with synchrotron‐grade brilliance. X‐ray absorption is found to affect magnetotransport when the photon energy and linear polarization are tuned to excite Fe? O bonds parallel to the MTJ's interfaces. This explicit link between the device's spintronic performance and these Fe? O bonds, although predicted, challenges conventional wisdom on their detrimental spintronic impact. The technique opens interdisciplinary possibilities to directly probe the role of different atomic species on device operation, and shall considerably simplify the materials science iterations within device research.     

Software Standards for the Multicore Era

Systems architects commonly use multiple cores to improve system performance. Unfortunately, multicore hardware is evolving faster than software technologies. New multicore software standards are necessary in light of the new challenges and capabilities that embedded multicore systems provide. The newly released Multicore Communications API standard targets small-footprint, highly efficient intercore and interchip communications.