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The Pennsylvania State University The Graduate School College of Engineering STUDY OF CONDENSED PHASE REACTIONS BETWEEN HYPERGOLIC PROPELLANTS USING MICROREACTORS A Dissertation in Mechanical Engineering by Pulkit Saksena 2014 Pulkit Saksena Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy August 2014 ii The dissertation of Pulkit Saksena was reviewed and approved* by the following members: Richard A. Yetter Professor of Mechanical Engineering Dissertation Co-Advisor, Co-Chair of Committee Srinivas Tadigadapa Professor of Electrical Engineering Dissertation Co-Advisor, Co-Chair of Committee Stefan T. Thynell Professor of Mechanical Engineering Donghai Wang Associate Professor of Mechanical Engineering Siyang Zheng Assistant Professor of Biomedical Engineering Karen A. Thole Professor of Mechanical Engineering Head of the Department of Mechanical and Nuclear Engineering *Signatures are on file in the Graduate School iii ABSTRACT The testing of hypergolic propellants has been carried out for decades and the use of hypergolic propellants at a systems level is very well understood. Extensive testing has provided the design and construction of rocket engines which have been very reliable. Safety procedures have been developed for the handling and storage for hypergolic propellants, which all too often are highly toxic. But the condensed phase chemistry for these hypergolic propellants is not very well understood. The models in place for ignition and combustion do not handle the coming together of two liquid streams of these hypergols and the two-phase aspects that are expected once the reactions occur. Moreover, it is not clear what makes a fuel and oxidizer pair hypergolic in nature. The coupling of physical and chemical factors that control the ignition of hypergolic propellants makes the direct study of the transient ignition process difficult. The current study presents a novel method to study hypergolic propellants (very fast liquid reactions) using microreactors instead of conventional drop tests, modified versions thereof or impinging jet tests. Planar counterflow microreactors are used to isolate liquid-phase reactions from secondary gas phase reactions that occur later during the ignition process and thus provide valuable insight in to the pre- ignition mechanism. The microreactor fabrication, flow field characterization, reactivity results from experiments performed using a variety of fuels and nitric acid as the oxidizer and numerical simulation results of reactive flow in the microreactor are presented in this study. Particle image velocimetry measurements and numerical simulations were conducted to characterize the laminar velocity flow- field in the microreactor and strain rates at the stagnation point along the centerline of the microreactor. Temperature measurements at the stagnation zone, the exit and positions along the length of the microreactor were used as a measure for the extent of the reaction or the heat released from the reaction. For the hypergols, an increase in reactant flow (or equivalently strain rate at the iv stagnation point) was found to initially increase temperatures at both the stagnation zone as well as along the length of the reactor, but eventually resulted in a decrease in temperature, revealing a maxima in temperature and reactivity. The trends indicated a reaction that was initially diffusion or heat loss controlled, which transitioned towards kinetic control at higher strain (flow) rates. Numerical simulations of the reactive flow in the microreactor stagnation zone were also carried out in which the reaction zone in the microreactor was treated similar to the reaction zone occurring in a counter-flow diffusion flame. These simulations showed that the flow rates at which the peak in temperature occurred was dependent on the rate of the reaction occurring between the hypergol pairs. The numerical simulations also show that heat loss from the top and bottom surfaces can play a role on the temperature trends seen in the microreactor. This study details the first comprehensive measurements and analysis of the condensed phase interfacial reactions occurring between hypergols. v TABLE OF CONTENTS LIST OF FIGURES ............................................................................................................... viii LIST OF TABLES ................................................................................................................ xiv ACKNOWLEDGEMENTS ................................................................................................... xv Chapter 1 Introduction ............................................................................................................. 1 1.1 Chemical Rocket Propulsion ..................................................................................... 1 1.1.1 Liquid Propellant Rockets .............................................................................. 2 1.1.2 Solid Propellant Rockets ................................................................................. 4 1.1.3 Hybrid Propellant Rockets .............................................................................. 6 1.1.4 Hypergolic Propellant Rockets ....................................................................... 8 1.2 Dissertation Overview ............................................................................................... 9 Chapter 2 Literature Review on Hypergolic Propellants ........................................................ 11 2.1 Approaches to the Study of Ignition in Hypergolic Propellants ............................... 12 2.1.1 Liquid Drop Tests .......................................................................................... 13 2.1.2 Mixing Tests .................................................................................................. 14 2.1.3 Impinging Jet Tests ........................................................................................ 15 2.2 Hypergolic Reactants ................................................................................................ 17 2.2.1 Monomethylhydrazine (MMH) ..................................................................... 17 2.2.2 N,N,N’,N’ – Tetramethylethylenediamine (TMEDA)................................... 20 2.2.3 2-Dimethylaminoethylazide (DMAZ ) .......................................................... 22 2.3 Current status of the field and contribution of present study .................................... 24 Chapter 3 Microfluidics and Microreactors to Study Hypergolic Reactions ......................... 26 3.1 Microfluidics ............................................................................................................ 26 3.2 Fluid Physics at the Micron-Scale ............................................................................ 28 3.2.1 The Reynolds Number (Re) ........................................................................... 30 3.2.2 The Péclet Number (Pe) ................................................................................ 32 3.2.3 Using microfluidic physics to study reactions ............................................... 34 Chapter 4 Fabrication Methods for Microfluidic Devices ...................................................... 36 4.1.1 Photolithography ............................................................................................ 38 4.1.2 Etching ........................................................................................................... 41 4.1.3 Anodic Bonding ............................................................................................. 44 4.2 Fabrication of silicon-glass microreactors for present study .................................... 46 4.2.1 Photolithography Procedure using KMPR..................................................... 49 4.2.2 Etching of the microreactors using DRIE ...................................................... 51 4.2.3 Anodic bonding of silicon wafer to borosilicate glass wafer ......................... 53 4.3 Fabrication of microreactors with through optical access ........................................ 54 4.4 Fabrication of microreactors using LTCC ................................................................ 56 Chapter 5 Cold-flow Characterization of the Microreactors .................................................. 62 vi 5.1 Particle Image Velocimetry (PIV) ............................................................................ 62 5.1.1 Components of a typical PIV system ............................................................. 63 5.1.2 Image Processing and Image Interrogation in a PIV System......................... 67 5.1.3 Micro-PIV ...................................................................................................... 71 5.1.4 Experimental Micro-PIV Setup ..................................................................... 79 5.2 Numerical Modeling of Cold-Flow in the Microreactors ......................................... 82 5.2.1 Governing Equations for Fluid Flow in the Microreactors ............................ 86 5.2.2 Numerical Solution of the Governing Equations ........................................... 87 5.2.3 Setting up a Fluid-Flow Problem in FLUENT .............................................. 89 5.3 Results and Discussion ............................................................................................. 93 5.4 Instabilities at High Flow Rates ...............................................................................