Passive Thermal Management of Launch Vehicle Systems using Phase Changing Materials

Electronic systems in expendable launch vehicles and missiles rely on their own thermal inertia to operate for the stipulated time, without overheating, owing to absence of active cooling systems and natural convection at elevated altitude. Traditionally, this inertia is built-into the electronics by increasing its chassis (support structure) mass, proportional to the associated thermal load. For power intensive systems, especially in vehicle upper stages where mass is at premium, this approach results in reduction in payload capability. In the proposed paper, a Heat Sink based on Neopentyl Glycol (NPG) with solid-to-solid phase change (crystalline transformation) is explored as a mass effective alternative due to the material’s capability to absorb a significant amount of energy during phase change. However, due to its lower thermal conductivity, a Thermal Conductivity Enhancer (TCE) to maximize heat transfer had to be employed. The resulting heat sink, utilizing TCE for heat transfer capability and NPG for heat storage capability is called as Hybrid Heat Sink. A heat sink with plate type fins as TCE is realized and a mass reduction factor of 1.4 is achieved against traditional approach. This is followed by a heat sink with pin type fins as TCE where mass reduction factor is increased to 2.6. Effect of thermal cycling and vibration on its performance is also studied

Detection of biomarker in breath: A step towards noninvasive diabetes monitoring

Along with more than two hundred volatile organic compounds (VOCs), acetone is also a normal constituent of breath of healthy individuals, albeit in the sub-ppm range, and its concentration increases in diabetic patients. Considering the importance of breath acetone as a biomarker of diabetes, some studies have already been made to measure breath acetone concentration (and correlate with blood sugar level) using GC-MS. There are a few reports of measuring breath acetone concentration using semiconductor sensor in the background of air (i.e. in the absence of VOCs present in normal breath and hence the question of selectivity remains in the real situation) and at a higher concentration (above 10 ppm). We report excellent sensitivity of sonochemically prepared nanosized gamma-Fe2O3 sensors towards sub-ppm acetone (pathological range) in the background of human breath. Our preliminary results should stimulate further research towards developing cheap, rugged and compact semiconductor sensors for noninvasive monitoring of diabetes

Effect of boron addition on the dielectric properties of giant dielectric CaCu3Ti4O12

The recently discovered giant dielectric CaCu3Ti4O12(CCTO) has been reported to show dielectric constant value as high as 80,000 for single crystals and around 10,000 for ceramics. However the dielectric constant is also associated with high dissipation factor. In the present study, it has been observed that the loss factor of CCTO can be reduced by B2O3 addition. The low frequency dispersion of CCTO ceramics, which indicates Maxwell-Wagner type relaxation, is reduced by boron addition. Also the temperature dependence of dielectric constant is minimized by boron addition. From the present work it can be surmised that B2O3 addition can favourably modify the dielectric properties of CCTO ceramic for its practical applications as a capacitor material

Fast firing of lead zirconate titanate ceramics at low temperature

A fast firing technique for densification of PZT (up to 97% of theoretical density) at a low temperature (950 degrees C) has been found out. A small amount of excess PbO (3-5 wt.%) and a fast firing schedule are required to achieve the desired sintering. The final composition of the sintered ceramics can be kept close to the morphorropic phase boundary by modifying the firing time and post-sintering annealing treatment at 800 degrees C. The g(33) values of fast fired samples are comparable to those of conventionally sintered samples, though the d(33) values are somewhat lower than those reported for conventionally sintered (at 1250'C or above) sample

KCa4(BO3)(3):Ln(3+) (Ln = Dy, Eu, Tb) phosphors for near UV excited white-light-emitting diodes

A series of doped KCa4(BO3)(3):Ln(3+) (Ln: Dy, Eu and Tb) compositions were synthesized by solid-state reaction method and their photoluminescent properties were systematically investigated to ascertain their suitability for application in white light emitting diodes. The X-ray diffraction (XRD) and nuclear magnetic resonance (MAS-NMR) data indicates that Ln(3+)-ions are successfully occupied the non-centrosymmetric Ca2+ sites, in the orthorhombic crystalline phase of KCa4(BO3)(3) having space group Ama2, without affecting the boron chemical environment. The present phosphor systems could be efficiently excitable at the broad UV wavelength region, from 250 to 350 nm, compatible to the most commonly available UV light-emitting diode (LED) chips. Photoluminescence studies revealed optimal near white-light emission for KCa4(BO3)(3) with 5 wt.% Dy3+ doping, while warm white-light (CIE; X = 0.353, Y = 0.369) is obtained at 1wt.% Dy3+ ion concentration. The principle of energy transfer between Eu3+ and Tb3+ also demonstrates the potential white-light from KCa4(BO3)(3):Eu3+, Tb3+ phosphor. Whereas, single Tb3+ and Eu3+-doped systems showed bright green (Tb3+) and red (Eu3+) emissions, respectively. Having structural flexibility along with remarkable chemical/thermal stability and suitable quantum efficiency these phosphors can be promising candidates as white-light-emitter for near UV LEDs. Copyright 2013 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4794189