Detection and analysis of transition from annular to intermittent flow in vertical tubes

In vertical co-current gas-liquid flow, the transition from annular to intermittent flow occurs when gas core becomes interrupted by liquid bridges due to the instability of the interfacial capillary waves. An analytical model is formulated to explain the liquid bridging in terms of the growth of finite amplitude interfacial capillary waves. Experimental results show that the longest wave length, which is associated with the transition, is about eight times the wave length of waves moving with the velocity of the liquid film.     

Effect of Gd-substitution on phase transition and conduction mechanism of BiFeO3

The polycrystalline sample of (Bi_0.8Gd_0.2)FeO₃ was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray structural analysis of the sample confirms the formation of the desired compound with rhombohedral phase. The scanning electron micrograph of the sample showed uniform distribution of the plate- and rod-shaped grains. Studies of dielectric and electrical properties of the material were investigated within a wide range of temperature (25–400 °C) and frequency (1 kHz–1 MHz) using complex impedance spectroscopic method. The observation of hysteresis loop of the material confirmed that the material has a ferroelectric property at room temperature. The ac conductivity suggests that the sample obey Jonscher’s universal power law. The dc conductivity follows Arrhenius equation. Detailed studies of ac and dc conductivity show a negative temperature coefficient of resistance (NTCR) behavior of the sample.     

Effects of oxygen content of porous titanium metal on its apatite-forming ability and compressive strength

Porous titanium metal subjected to NaOH and heat treatments is useful as a bone substitute as it shows high mechanical strength as well as osteoconductivity and osteoinductivity. However, the porous metal is liable to be contaminated with oxygen gas during the fabrication process and this incorporated oxygen could lead to adverse effects on the bioactivity and mechanical properties of the prepared porous body. In this study, oxygen contamination during fabrication of bioactive porous bodies was measured. It was found that the oxygen content of the titanium metal was increased from 0.08 to 0.23 mass% when the porous body was prepared from bar stock, and it further increased up to 0.51 mass% when it was subjected to NaOH and heat treatments. Despite this, the porous bodies subjected to NaOH and heat treatments formed apatite on their pore walls within 1 day in a simulated body fluid. This result was consistent with the apatite-forming ability of NaOH- and heat-treated titanium plates with different oxygen contents in the range of 0.05 to 0.30 mass%. The compressive strength of the porous body was increased about 10% by the NaOH and heat treatments.     

Natural convection heat transfer from upward-facing plates in saline water

Saltwater or brackish water is used as a coolant in most industries. Therefore, understanding the heat transfer processes and hydrodynamics during the natural convection in saline water is crucial for enhancing the efficiency of a heat exchanger. This study elaborates on the natural convection heat transfer in saline water under atmospheric conditions. A DC power supply is used to regulate the power given to the heater in a liquid pool for thermal analysis. The pool liquid comprises solutions with varying salinity from 0%, 0.2%, 0.5%, and 2%. The effect of varying salinity on the heat transfer coefficient and the thermal aspects encountered during the desalination process is analyzed. The temperature distribution across the surface of the heater is monitored using an infrared camera. It is studied for the solution of different salinities. The heat transfer coefficient and Nusselt number are investigated during natural convection for normal water and salt solution of different concentrations. It is inferred from the study that in the regime of natural convection, there is no significant difference in the Nusselt number for normal water and saltwater for the lower value of temperature difference between the plate and pool. The heat transfer coefficient in 0.2% saline water is higher as compared to the other solutions.     

Shoe-last design exploration and customization

The shoe industry is a very competitive industry and in order to capture the market, customized shoes are desired nowadays to satisfy consumers’ needs on style, fit and comfort. Companies need to either develop a system for quick design changes, creation of huge virtual design variations and in some cases adoption of mass-customization principles to reduce cost. Shoe-last is the “heart” of shoe making since it mainly determines the shoe shape, fashion, fit and comfort qualities. This study proposed a system to enable shoe-last design changes, exploration and eventually enable mass-customization. The system enables continuous change of styling and fashion to reflect personal taste without the need for physical design. Design exploration involves representation of styling curves using parametric curves. Modification of the styling curves, by changing the parameter values, can be used to explore different designs. This is useful to create slight variations of shoe-last. Since the designs are parameterized, design can be scaled on individual shape and size to create customized shoe-last. Results of the study can be used to create a system for shoe-last design exploration and mass-customization system for individual designs in a cost effective manner.     

Counterdoping of MOS channel (CDC)-a new technique of improvingsuppression of latching in insulated gate bipolar transistors

A novel technique of improving suppression of latching in insulated-gate bipolar transistors (IGBTs) is proposed and experimentally verified. By counterdoping the channel of the DMOS cell, the doping of the p-base can be increased up to a factor of two. Dynamic latching improvement of 40-80%, corresponding to the p-base doping increase, has been obtained. The degradation in forward blocking voltage was observed when the counterdoping dosage exceeds about 2×10¹² cm^-2 for 600-V devices     

The effect of substrate doping on the performance of anode-shortedn-channel lateral insulated-gate bipolar transistors

The performance of n-channel lateral-insulated-gate bipolar transistors (n-LIGBTs) with anode shorts on p^- epi/p⁺ substrates is compared to that of anode-shorted n-LIGBTs on p^- substrates, as well as to that of conventional n-LIGBTs on either substrate. It is shown that both forward-voltage drop and turn-off time are better for anode-shorted devices fabricated on p^- epi/p⁺ substrate than for those on p^- substrates, due to a larger percentage component of vertical bipolar current and a lower collector resistance. Forward-voltage drops of 3.05 and 3.3 V at 133 A/cm² and turn-off times of 400 and 750 ns have been measured for devices on p^- epi/p⁺ and p ^- substrates respectively. All the LIGBTs showed current limiting at two to four times the ON-state conduction current during dynamic switching     

Sodium–Bioglass/Polythene Composites

We present the studies conducted on sodium–bioglass/polythene (Na–BG/PE) composites and their bioactivity in simulated body fluid (SBF). Several compositions of Na–BG/PE composites were made by hot pressing and the activity studies of the samples were carried out by immersing the composites in SBF for periods of 7, 14, and 21 days. The activity of the samples was confirmed by the cauliflower-like growth of phosphates on the surface of the samples observed in an environmental scanning electron microscope and further confirmed by energy-dispersive X-ray spectrometry (EDS). X-ray diffraction showed the presence of various types of calcium phosphate phases. Ionic movement was observed by inductively coupled plasma atomic emission spectroscopy from the sample to the SBF solution and the reverse trend was observed on the surface of the sample by EDS. Modulus of rupture of the composites increased when the polymer content was increased up to 30% by weight of polythene, beyond which the processing of composites became difficult.