Experimental study of simulated micro-gravity vapor-liquid flow regimes

Space missions in the near future will require power plants and cooling systems to operate in space. Such systems will often incorporate two-phase (vapor-liquid) heat transfer loops. Heat transfer processes such as boiling and condensation involve two-phase flow and are gravity dependent. Such unit operations would, therefore, be expected to behave differently in a micro-gravitational ( micro-g ) environment. In this study, a unique approach to study the flow patterns of vapor-liquid flow on earth is presented. Simulation of a micro-g vapor-liquid flow on earth is accomplished by the use of two immiscible liquids of equal density. This equal density two-liquid system makes the buoyancy forces approach zero which is the case for real vapor-liquid flow in micro-g conditions. Water and properly selected oils are used in the experiments. In simulating micro-g vapor-liquid flow, the oil which is more viscous and more wettable liquid represents the liquid phase and water (less viscous and less wettable with respect to waxed tube surface) corresponds to the vapor phase. The experiments are carried out in a horizontal pyrex glass tube (6.1 m long and 2.54 cm ID). Data are obtained for five different fluid systems to study the effect of viscosity ratio, interfacial tension, and wettability of two fluids on flow regime boundary lines. Comparison of the simulated versus actual micro-g vapor-liquid flow regime data indicates the validity of this simulation approach. The experimental results are also compared against Taitel-Dukler and Weisman et al. model predictions under micro-g conditions. A flow regime map for vapor-liquid flow in a micro-g environment is developed for usage in designing two-phase systems in space applications. The effect of gravity on nucleate boiling is also considered. The static and dynamic forces acting on a growing vapor bubble on heating surface are evaluated and how their interaction causes the bubble to detach from the surface is presented. By using a force balance, the bubble departure radius is calculated and compared with experimental measurements from literature under micro-g conditions

Erosion in Second Stage Cyclones: Effects of Cyclone Length and Outlet Gas Velocity

Severe erosion in the lower cone and in the upper dipleg of second stage cyclones have been observed in commercial cyclones. The main objective of this study is to shed light on the mechanism by which this erosion takes place, and how different design and operating parameters affect the erosion. Experimental data on how parameters such as the cyclone length-to diameter ratio (L/D), inlet solids loading and gas outlet velocity affect second stage cyclone erosion are presented. The outlet gas velocity was varied by changing the size of the vortex tube diameter. The effect of a vortex stabilizer on cyclone cone erosion is also discussed

Hydrodynamic Scale-Up of Circulating Fluidized Beds

A general procedure that can be used to scale up circulating fluidized beds is presented. It consists of developing a mathematical model in conjunction with measuring 1) the radial dispersion coefficient (Dr) using gas tracers, 2) the radial solids velocity profile using a Pitot tube and 3) the radial distribution of solids density (1 - ε) using an optical probe. If the resulting information is obtained in a riser 200 mm or greater in diameter, it can be used in conjunction with the mathematical model for scale-up

Detection of Gas Bypassing due to Jet Streaming in Deep Fluidized Beds of Group A Particles

Tests were conducted in deep fluidized beds with and without gas bypassing to develop a technique to detect jet streaming. By placing differential pressure (DP) transmitters across a middle section of the fluidized bed, it was found that jet streaming can be detected by analyzing the DP fluctuations

Hydrodynamics of high velocity circulating fluidized bed risers

Fluid catalytic cracking risers operate at solids fluxes of 400 to 1400 kg/s.m2 and gas velocities of 15 to 20 m/s. However, most literature studies are for low gas velocities (\u3c 10 m/s) and modest solids circulation rates (\u3c 200 kg/m2s). Circulating fluidized bed (FCC) risers were found to consist of a top dilute region and a relatively dense region near the bottom. The top region has a dilute core of rapidly upflowing solids surrounded by a descending dense annulus. The bottom zone also has a core-annular flow structure, but with little or no net downflow of solids in the annulus. This paper discusses measurements from three CFB risers 15, 22, and 24 m in height, all 0.3 m in diameter, for FCC catalyst particles at gas velocities between 12 and 16 m/s and solids fluxes of 70 to 700 kg/s.m2. The measurements were total riser pressure, axial pressure gradient profiles and local solids flux. The extraction tube technique was used the solids flux measurement. The apparent density decreased exponentially with increasing height at low solids fluxes and a dense lower region formed as the solids flux was increased. Its height reached nearly half of one of the risers’ height at the highest solids flux. Three types of radial solids flux profiles were obtained; nearly flat, parabolic with maxima in the core as well as bell shaped profiles with highest fluxes near the riser walls. The net solids flow direction at all locations was upward

Search for new particles in events with energetic jets and large missing transverse momentum in proton-proton collisions at root s=13 TeV

A search is presented for new particles produced at the LHC in proton-proton collisions at root s = 13 TeV, using events with energetic jets and large missing transverse momentum. The analysis is based on a data sample corresponding to an integrated luminosity of 101 fb(-1), collected in 2017-2018 with the CMS detector. Machine learning techniques are used to define separate categories for events with narrow jets from initial-state radiation and events with large-radius jets consistent with a hadronic decay of a W or Z boson. A statistical combination is made with an earlier search based on a data sample of 36 fb(-1), collected in 2016. No significant excess of events is observed with respect to the standard model background expectation determined from control samples in data. The results are interpreted in terms of limits on the branching fraction of an invisible decay of the Higgs boson, as well as constraints on simplified models of dark matter, on first-generation scalar leptoquarks decaying to quarks and neutrinos, and on models with large extra dimensions. Several of the new limits, specifically for spin-1 dark matter mediators, pseudoscalar mediators, colored mediators, and leptoquarks, are the most restrictive to date.Peer reviewe

Combined searches for the production of supersymmetric top quark partners in proton-proton collisions at root s=13 TeV

A combination of searches for top squark pair production using proton-proton collision data at a center-of-mass energy of 13 TeV at the CERN LHC, corresponding to an integrated luminosity of 137 fb(-1) collected by the CMS experiment, is presented. Signatures with at least 2 jets and large missing transverse momentum are categorized into events with 0, 1, or 2 leptons. New results for regions of parameter space where the kinematical properties of top squark pair production and top quark pair production are very similar are presented. Depending on themodel, the combined result excludes a top squarkmass up to 1325 GeV for amassless neutralino, and a neutralinomass up to 700 GeV for a top squarkmass of 1150 GeV. Top squarks with masses from 145 to 295 GeV, for neutralino masses from 0 to 100 GeV, with a mass difference between the top squark and the neutralino in a window of 30 GeV around the mass of the top quark, are excluded for the first time with CMS data. The results of theses searches are also interpreted in an alternative signal model of dark matter production via a spin-0 mediator in association with a top quark pair. Upper limits are set on the cross section for mediator particle masses of up to 420 GeV

Probing effective field theory operators in the associated production of top quarks with a Z boson in multilepton final states at root s=13 TeV

Peer reviewe

Search for a heavy Higgs boson decaying into two lighter Higgs bosons in the tau tau bb final state at 13 TeV

A search for a heavy Higgs boson H decaying into the observed Higgs boson h with a mass of 125 GeV and another Higgs boson h(S) is presented. The h and h(S) bosons are required to decay into a pair of tau leptons and a pair of b quarks, respectively. The search uses a sample of proton-proton collisions collected with the CMS detector at a center-of-mass energy of 13TeV, corresponding to an integrated luminosity of 137 fb(-1). Mass ranges of 240-3000 GeV for m(H) and 60-2800 GeV for m(hS) are explored in the search. No signal has been observed. Model independent 95% confidence level upper limits on the product of the production cross section and the branching fractions of the signal process are set with a sensitivity ranging from 125 fb (for m(H) = 240 GeV) to 2.7 fb (for m(H) = 1000 GeV). These limits are compared to maximally allowed products of the production cross section and the branching fractions of the signal process in the next-to-minimal supersymmetric extension of the standard model.Peer reviewe