Characterization of display pyrotechnic propellants: Colored light

Ambekar, Anirudha,Kim, Minsung,Yoh, Jack J. Pergamon 2017 Applied thermal engineering Vol. No.

<P><B>Abstract</B></P> <P>Pyrotechnic flames utilized as a source of illumination are typically characterized by the color and the luminous intensity of the flame. In the current study, five display pyrotechnic formulations utilized to produce colored flames have been investigated experimentally and theoretically. The experimental study was focused on photographically recording the colored flame of fireworks propellants burning at ambient conditions in order to quantify the flame color and the luminous intensity. This study reports the application of a digital single reflex camera as a colorimeter as well as a luminance meter. Theoretical estimation of the flame color was carried out by equilibrium thermochemical analysis followed by additive color mixing of the spectral emitters deduced to be present in the combustion products. The experimentally observed chromaticity and theoretical predictions were found to be reasonably close validating the methodology for the color prediction.</P>

A reduced order model for prediction of the burning rates of multicomponent pyrotechnic propellants

Ambekar, Anirudha,Yoh, Jack J. Pergamon 2018 Applied thermal engineering Vol. No.

<P><B>Abstract</B></P> <P>This study reports a reduced order model for the prediction of the burning rate of pyrotechnic compositions. The combustion process of most pyrotechnics is primarily driven by condensed phase reactions. A priory estimation of the burning rate of pyrotechnics with multiple components may not be possible using the established methods. The study provides a simplified approach based on integral analysis of a proposed combustion wave structure for estimating the burning rate when the pyrotechnic composition, pure component thermo-physical properties, and thermo-kinetics parameter are known. The proposed combustion wave assumes a staged combustion process where the oxidizer undergoes decomposition in a broad reactive zone while fuel combustion occurs in a thin surface region. This approach takes account of the effective thermal conductivity as well as porosity of the pyrotechnic matrix. The pyrotechnic compositions studied here are expected to burn conductively at atmospheric pressure with little or no overpressure. The phenomenology of the combustion process of energetic materials is elucidated, and the reduced order model is validated through a case study.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Reduced order analytical model for burning rate of pyrotechnic compositions. </LI> <LI> Linear burning rate of multi-component granular porous pyrotechnics predicted. </LI> <LI> Conductive combustion regime with primary reactions occurring on the surface. </LI> <LI> Technique accounts for the propellant conductivity, heat of reaction, and porosity. </LI> <LI> Case study predictions for KClO<SUB>4</SUB> and KNO<SUB>3</SUB> based pyrotechnics reasonably accurate. </LI> </UL> </P>

Characterization of display pyrotechnic propellants: Burning rate

Ambekar, Anirudha,Kim, Minsung,Lee, Woong-Hyun,Yoh, Jack J. Elsevier 2017 Applied thermal engineering Vol.121 No.-

<P><B>Abstract</B></P> <P>The combustion of display pyrotechnic propellants utilized for producing colored light has been studied. The linear burning rates of cylindrical propellant strands were measured using high-speed videography. The experiments were conducted with air at atmospheric pressure as the surrounding medium mimicking the conditions of unconfined aerial combustion typically encountered for these propellants. Five different formulations of display pyrotechnic propellants producing red, green, blue, yellow, and silver color were tested. The flame zone was observed to be situated very close to the propellant surface and the colored flame extended beyond this point. The phenomenology of the combustion process was explained and the combustion process was also studied numerically using a methodology based on the deflagration rate law. The experimentally measured burning rates were utilized in the deflagration rate law to obtain the simulation parameters which may be utilized in hydrocodes for performance prediction and simulation pyrotechnic propellant applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Combustion of display pyrotechnic propellants is studied. </LI> <LI> Linear burning rate of five propellant compositions evaluated in a strand burner. </LI> <LI> Numerical simulation was conducted using a deflagration rate law. </LI> <LI> Experimental burning rates were used to optimize deflagration rate law constants. </LI> </UL> </P>

Chemical kinetics of multi-component pyrotechnics and mechanistic deconvolution of variable activation energy

Ambekar, Anirudha,Yoh, Jack J. Elsevier 2019 Proceedings of the Combustion Institute Vol.37 No.3

<P>This study reports an experimental investigation into the chemical kinetics of several commercial pyrotechnic compositions. Differential Scanning Calorimetry (DSC) was utilized to elucidate the thermo-kinetic characteristics of four multicomponent pyrotechnic compositions. The combustion process of typical pyrotechnics is primarily driven by condensed phase reactions including processes such as phase change, decomposition, and oxidation. The multicomponent nature of practical pyrotechnics results in a particularly complex interaction between the components when heated. A thermo-kinetic study was performed to simulate the heating experienced by the pyrotechnics before the combustion zone. The physical processes occurring within these temperature limits provide important insight into the overall combustion rate. The non-isothermal DSC experimental technique combined with isoconversional methods, such as Friedman and Starink methods were utilized to evaluate the apparent chemical kinetics parameters for these propellants. The observations from the DSC study and isoconversional kinetic analysis provided an insight into the phenomenology of the combustion process of pyrotechnics. The problem of highly variable activation energy due to the presence of multiple reactions was addressed through a mechanistic deconvolution using nonlinear regression technique. The study confirmed the prominence of oxidizer decomposition on overall combustion reaction kinetics.</P>

Thermogravimetric Analysis of Commercial Pyrotechnic Compositions

Anirudha Ambekar,Jack J. Yoh 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.12

Cryogenic Tilt Table

Paritosh P. Ambekar,S. Wang,R. Torii,D. DeBra 한국정밀공학회 2009 International Journal of Precision Engineering and Vol. No.

We describe the design and development of a cryogenic tilt table that will be used to test the flight hardware for NASA’s Satellite Test of the Equivalence Principle (STEP). Our table can tilt the hardware around two axes and is part of a test bed that has 6-degree-of-freedom controllability. The goal was to build a tilt table with a resolution better than ~5 μrad (1 arcsec). Our table consists of three aluminum plates. The outermost plate is attached to the cryogenic probe and is fixed. The middle and inner plates rest on the outer and middle plates, respectively, using knife edges and knife edge holders made of silicon nitride that are glued to the aluminum plates. A cryogenic tilt sensor was also developed and integrated with the table. The sensor consists of an electrically grounded copper cube hanging from a support, and is placed between two pairs of capacitive electrodes. Any motion of the cube caused by tilting is measured differentially using a Wheatstone bridge circuit. The table is connected to the bottom of a cryogenic probe. A voice coil actuator, located on top of the probe at room temperature, is used to create the necessary tilt. A thin fiber is used to connect the actuator and the table. The system is controlled using a dSPACE control card. A test of the table at cryogenic temperatures (4.5 K) and low pressure (1 μTorr) showed a noise level of ~0.7 μrad (150 marcsec), which is nearly an order of magnitude better than the required resolution.

수분노화 된 ZPP 화약의 노화 효과 분석

오주영(Juyoung Oh),김유천(Yoocheon Kim),Anirudha Ambekar,여재익(Jai-ick Yoh) 한국추진공학회 2017 한국추진공학회 학술대회논문집 Vol.2017 No.11

등전환 방법을 이용한 고에너지 물질의 노화 효과 예측

김유천(Yoocheon Kim),오주영(Juyoung Oh),Aniruda Ambekar,여재익(Jai-ick Yoh) 한국추진공학회 2017 한국추진공학회 학술대회논문집 Vol.2017 No.5

Differential Scanning Calorimetry(DSC)를 이용하여 파이로점화장치에 사용되는 세 가지 고에너지 물질의 열분석 실험을 수행하였다. DSC 실험 데이터를 이용하여 고에너지 물질의 반응속도식을 추출해내는 이론적 방법을 제안하고 반응속도식 추출을 수행하였다. DSC 실험 결과는 Friedman 등전환법으로 분석되었다. 질량분율에 따른 활성화에너지와 빈도인자를 추출해 내어 반응속도식을 완성하였다. 추출된 반응속도식은 고에너지 물질의 화학반응과정을 몇 단계의 주요단계로 가정하는 형태가 아닌 전체 화학반응 과정을 나타내는 형태를 갖는다. 이는 기존의 열분석 실험을 통해 추출되는 화학반응속도식 형태에 비해 이론적 측면과 정확성 측면에서 상당한 장점을 갖는다. 도출된 반응속도식을 이용하여 실제 추진기관에 운용되는 세 가지 고에너지 물질의 성능변화를 20년에 대하여 예측하였다. Thermal analysis of three energetic materials used in pyroelectric device was performed using Differential Scanning Calorimetry (DSC). The theoretical method for extracting the reaction rate equation of energetic materials using DSC experimental data is proposed and the reaction rate extraction is performed. The results of the DSC were analyzed by the conversion method such as Friedman. Activation energy and frequency factor according to mass fraction were extracted to complete the reaction rate equation. The extracted reaction rate equation has a form that represents the entire chemical reaction process, not the assumption that the chemical reaction process of the high energy material is a main step in several stages. It has considerable advantages in terms of theoretical and accuracy as compared with the chemical reaction rate form extracted through conventional thermal analysis experiments. Using the derived reaction rate equation, we predicted the performance change of three energetic materials operating on actual storage condition over 20 years.

In-situ preparation of N-TiO2/graphene nanocomposite and its enhanced photocatalytic hydrogen production by H2S splitting under solar light.

Bhirud, Ashwini P,Sathaye, Shivaram D,Waichal, Rupali P,Ambekar, Jalindar D,Park, Chan-J,Kale, Bharat B RSC Pub 2015 Nanoscale Vol.7 No.11

<P>Highly monodispersed nitrogen doped TiO2 nanoparticles were successfully deposited on graphene (N-TiO2/Gr) by a facile in-situ wet chemical method for the first time. N-TiO2/Gr has been further used for photocatalytic hydrogen production using a naturally occurring abundant source of energy i.e. solar light. The N-TiO2/Gr nanocomposite composition was optimized by varying the concentrations of dopant nitrogen and graphene (using various concentrations of graphene) for utmost hydrogen production. The structural, optical and morphological aspects of nanocomposites were studied using XRD, UV-DRS, Raman, XPS, FESEM, and TEM. The structural study of the nanocomposite shows existence of anatase N-TiO2. Further, the details of the components present in the composition were confirmed with Raman and XPS. The morphological study shows that very tiny, 7-10 nm sized, N-TiO2 nanoparticles are deposited on the graphene sheet. The optical study reveals a drastic change in absorption edge and consequent total absorption due to nitrogen doping and presence of graphene. Considering the extended absorption edge to the visible region, these nanocomposites were further used as a photocatalyst to transform hazardous H2S waste into eco-friendly hydrogen using solar light. The N-TiO2/Gr nanocomposite with 2% graphene exhibits enhanced photocatalytic stable hydrogen production i.e. 5941 μmol h(-1) under solar light irradiation using just 0.2 gm nanocomposite, which is much higher as compared to P25, undoped TiO2 and TiO2/Gr nanocomposite. The enhancement in the photocatalytic activity is attributed to 'N' doping as well as high specific surface area and charge carrier ability of graphene. The recycling of the photocatalyst shows a good stability of the nanocomposites. This work may provide new insights to design other semiconductor deposited graphene novel nanocomposites as a visible light active photocatalyst.</P>

Confinement of Ag₃PO₄ nanoparticles supported by surface plasmon resonance of Ag in glass: Efficient nanoscale photocatalyst for solar H₂ production from waste H₂S

Patil, S.S.,Patil, D.R.,Apte, S.K.,Kulkarni, M.V.,Ambekar, J.D.,Park, C.J.,Gosavi, S.W.,Kolekar, S.S.,Kale, B.B. Elsevier 2016 Applied Catalysis B Vol.190 No.-

<P>Ag3PO4 is a good photocatalyst but ubiquitously known for its photocorrosion problem during photocatalytic reaction. Therefore, stabilization of Ag3PO4 with retaining its fundamental properties has immense importance. With this motivation, we designed Ag3PO4 glass nanocomposite to resolve the problem of photocorrosion. Moreover, the effect of size quantization on photocatalytic activity has also been demonstrated by growing the cubic Ag3PO4 nanoparticles with size in the range of 3-9 nm in glass matrix via melt and quenching method. The band gap of Ag3PO4 has been tuned (2.56-2.25 eV) in glass matrix with respect to size. Considering the size tunable band gap of Ag3PO4 glass nanocomposite within visible region, it is demonstrated as a photocatalyst for hydrogen (H-2) production from copious hazardous waste H2S. The utmost H-2 production i.e. 3920.4 mu mol h(-1) g(-1) is obtained using 1 gm of Ag3PO4 glass nanocomposite powder. The apparent quantum yield for H-2 production is calculated to be 5.51% for Ag3PO4 glass nanocomposite. Interestingly, presence of plasmonic Ag was also observed in Ag3PO4 glass nanocomposite which contributes for H-2 production through enhanced light absorption, efficient charge separation and improved stability. Recycling study of sample reveals stable H-2 production efficiency and good stability of the photocatalyst. Surprisingly, catalyst can be reused many times and recovery of catalyst is possible just rinsing with distilled water. All these results demonstrate directly the feasibility of designing a new generation photocatalysts. (C) 2016 Published by Elsevier B.V.</P>