A brine evaporative cooler/concentrator for autonomous thermal desalination units

On the effects of oxygen fraction on stability and combustion characteristics of dual-swirl oxy-methane flames: An experimental and numerical study

The purpose of the research reported here is to explore how minor coal composition changes can affect oxy-coal flame ignition. Whereas previous work focused on the stability of coaxial turbulent diffusion flames for a single coal, we explore here how two coals of similar rank, fired under aerodynamically identical input conditions, may show very different flame stability characteristics. Since oxy-coal combustion allows oxygen contents in primary and secondary oxidant streams to be varied, flame stability characteristics were determined here by effects of partial pressure of oxygen (PO2) in the primary stream (with differing preheat temperatures in the secondary stream) and effects of PO2 in the secondary stream (with zero O2 in the primary stream), on the flame stand-off distance. The two coals investigated were a Utah Skyline bituminous coal and an Illinois #6 bituminous coal. Flame stability was quantified by probability density functions (PDF) of the flame stand-off distance, which were determined usi...

A compatible configuration strategy for burner streams in a 200 MWe tangentially fired oxy-fuel combustion boiler

<abstract> <b><i>Abstract. </i></b> Thickness grading of rice ( L.) can divert thin, chalky kernels to a secondary processing stream, thus improving milling yields of the primary stream. However, the quantity and functionality of the secondary stream may impact processing operations. Rough rice of multiple long-grain cultivar lots was either left unfractioned (Unf) or thickness graded into fractions comprising A (< 1.7 mm), B (1.7 << 1.9 mm), C (< 1.9 << 2.0 mm), D (2.0 << 2.05 mm), and E (> 2.05 mm). Mass distribution of rough rice; milled rice yield (MRY), and head rice yield (HRY); kernel dimensions of brown rice; crude protein content (CP) and chalkiness of brown and head rice; and paste viscosities of head rice flour were determined for each cultivar lot/fraction. For all cultivar lots, MRY, HRY, and kernel dimensions increased with increasing thickness fraction, while chalkiness and CP decreased. Milling yields were the greatest for the C/D/E fractions. Including the C fraction (C/D/E) with the primary stream resulted in an average 17.4 percentage point mass increase compared to D/E alone; this with minimal impacts to milling yields of the primary stream. Weighted-average MRYs and HRYs of the combined C/D/E fractions increased by up to 6.9 and 12.8 percentage points, respectively, compared to Unf rice. The A/B fractions were generally of greater chalkiness and CP; however, paste viscosities remained relatively consistent with those of the C/D/E fractions. Thickness grading could be justified on the merits of improved milling yields, kernel uniformity, and reduced chalkiness of the primary processing stream. A small change in the thickness grading procedure decreased the quantity of the secondary stream; moreover when milled, the secondary stream retained functionality similar to the primary stream.

The stability, combustion, and emission features of stratified oxy-methane (CH4/O2/CO2) flames stabilized over a dual annular counter-rotating swirl (DACRS) burner, developed for gas turbine combustion applications, were investigated experimentally. The experiments were performed at fixed velocity ratio (Vr = Vp/Vs = 3.0) in both the primary and secondary streams at a constant primary stream velocity, Vp of 5 m/s and at fixed primary stream equivalence ratio, φp = 0.9, and over ranges of oxygen fractions (OFp for the primary stream, OFs for the secondary stream) and secondary stream equivalence ratios. Measurements of flame macrostructure, temperature profiles, and exhaust emissions were recorded to characterize the flames and validate future numerical models. The testing findings revealed no flame flashback within the operational ranges of OFp and OFs and up to φs = 1.0. However, the near stoichiometric operation of the primary stream (φp = 0.9) at OFp = 0.38 permitted the main secondary flame to tolerate exceptionally lean conditions (φs = 0.397 at OFs = 0.34 and φs = 0.223 at OFs = 0.39), raising the thresholds for the flame blowout. Increasing OFp from 0.21 to 0.38 significantly reduced φS at blowout from 0.537 to 0.223, corresponding to a decrease in the combustor's global equivalence ratio (φg) at blowout from 0.554 to 0.254 at global oxygen fraction (OFg) from 0.38 to 0.39. Lower OFp values caused earlier flame lift-off, indicating the greater influence of OFp on flame macrostructures.

The supersonic nozzle is the most important device of an ejector-diffuser system. The best operation condition and optimal structure of supersonic nozzle are hardly known due to the complicated turbulent mixing, compressibility effects and even flow unsteadiness which are generated around the nozzle extent. In the present study, the primary stream nozzle was redesigned using convergent nozzle to activate the shear actions between the primary and secondary streams, by means of longitudinal vortices generated between the Chevron lobes. Exactly same geometrical model of ejector-diffuser system was created to validate the results of experimental data. The operation characteristics of the ejector system were compared between Chevron nozzle and conventional convergent nozzle for the primary stream. A CFD method has been applied to simulate the supersonic flows and shock waves inside the ejector. It is observed that the flow structure and shock system were changed and primary numerical analysis results show that the Chevron nozzle achieve a positive effect on the supersonic ejector-diffuser system performance. The ejector with Chevron nozzle can entrain more secondary stream with less primary stream mass flow rate.

Zeotropic mixture ejector: Modeling approach, validation, and assessment based on composition ratio

A simplified chemical model for RBCC engines operating in ejector mode

The integrated design of a variable cycle engine (VCE) and an aircraft thermal management system (TMS) is investigated. The integrated system is designed using the multiple design point (MDP) approach in order to achieve required performance metrics at points other than the cycle design condition. The VCE architecture under investigation is a three-stream design where the third-stream is split off after the fan, exhausting through a separate third-stream nozzle. The primary air stream passes through a low-pressure compressor before splitting into an inner bypass stream and a core stream. The inner bypass and core streams mix aft of the low-pressure turbine and exhaust through a core nozzle. The variable cycle engine utilizes multiple variable geometry components: variable compressor inlet guide vanes (IGVs), a variable area bypass injector (VABI) at the inner bypass / core stream mixing plane, and variable throats in the two exhaust nozzles. The TMS architecture modeled is an open-loop air cycle system (ACS) that uses air bled from the high-pressure compressor as the working medium. The bleed air passes through heat exchangers (located in the engine third stream) before and after passing through a supercharging compressor, and is then expanded through two turbines to reach the low temperatures required to absorb heat from the aircraft cooling system. The effect of integrating the TMS into the engine design loop is investigated. In addition, a comparison is made to prior studies, where the same TMS architecture was connected to a low-bypass ratio turbofan engine, with the heat exchangers placed in either a ram-air stream or the engine bypass stream. The comparison shows that the variable cycle engine is able to improve heat dissipation capability versus a ram-air cooled system, while eliminating the airframe integration impact that comes with a separate ram-air stream. Lastly, the impact of modulating the variable geometry features on overall cooling capability is investigated. Results are presented for individual operating points as well as at the aircraft mission level.

This paper reports computational investigations aimed at and designed to predict the turbulent mixing flow characteristics in a model of cylindrical horizontal furnace that simulates fire-tube boiler combustion chambers. The furnace geometry and flow operating conditions simulate three dimensional turbulent flows; the corner recirculation zones are of import and effect on furnace turbulent flow characteristics. The model furnace is provided with a double concentric jet burner, i.e. with a central primary air jet simulating the fuel stream in the real furnaces, surrounded by a coaxial annular secondary air jet simulating the combustion air. The burner was designed in a way so as to ensure adequate mixing of the primary and secondary air streams with and without swirl imparted to secondary stream. This paper demonstrates the effects of the more dominant parameters influencing the flow and mixing patterns in cylindrical furnaces under non-reacting conditions, these parameters are: 1. The ratio of the secondary air stream to the primary air stream. 2. The swirl intensity imparted to the secondary air stream. 3. The Reynolds number of both primary and secondary streams. Finally comparisons are made between the experimental results and the present computations in a wide variety of flow operating conditions.

The present study addresses an experimental investigation of the near field flow structures of supersonic, dual, coaxial, free, jet, which is discharged from the coaxial annular nozzle. The secondary stream is made from the annular nozzle of a design Mach number of 1.0 and the primary inner stream from a convergent-divergent nozzle. The objective of the present study is to investigate the interactions between the secondary stream and inner supersonic jets. The resulting flow fields are quantified by pitot impact and static pressure measurements and are visualized by using a shadowgraph optical method. The pressure ratios of the primary jet are varied to obtain over-expanded flows and moderately under-expanded flows at the exit of the coaxial nozzle. The pressure ratio of the secondary annular stream is varied between 1.0 and 4.0. The results show that the secondary annular stream significantly changes the Mach disc diameter and location, and the impact pressure distributions. The effects of the secondary annular stream on the primary supersonic jet flow are strongly dependent on whether the primary jet is underexpanded or over-expanded at the exit of the coaxial nozzle.

Laminar-turbulent transition and noise radiation of a parametrized set of subsonic coaxial jet flows with a hot primary (core) stream are investigated numerically by Large-Eddy Simulation (LES) and direct noise computation. This study extends our previous research on local linear stability of heated coaxial jet flows by analyzing the nonlinear evolution of initially laminar flows disturbed by a superposition of small-amplitude unstable eigenmodes. First, a baseline configuration is studied to shed light on the flow dynamics of coaxial jet flows. Subsequently, LESs are performed for a range of Mach and Reynolds numbers to systematically analyze the influences of the temperature and the velocity ratios between the primary and the secondary (bypass) stream. The results provide a basis for a detailed analysis of fundamental flow-acoustic phenomena in the considered heated coaxial jet flows. Increasing the primary-jet temperature leads to an increase of fluctuation levels and to an amplification of far-field noise, especially at low frequencies. Strong mixing between the cold bypass stream and the hot primary stream as well as the intermittent character of the flow field at the end of the potential core lead to a pronounced noise radiation at an aft angle of approximately 35∘. The velocity ratio strongly affects the shear-layer development and therefore also the noise generation mechanisms. Increasing the secondary-stream velocity amplifies the dominance of outer shear-layer perturbations while the disturbance growth rates in the inner shear layer decrease. Already for rmic &amp;gt; 40R1, where rmic is the distance from the end of the potential core and R1 is the core-jet radius, a perfect 1/rmic decay of the sound pressure amplitudes is observed. The potential-core length increases for higher secondary-stream velocities which leads to a shift of the center of the dominant acoustic radiation in the downstream direction.

Circulating flow in front of open and covered intake systems in many cases is the initial point of free-surface vortex formation. Depending on the strength of the circulation air pulling vortex formation up to a coherent air core will appear starting at the surface leading directly to an installed pump inside the intake. Thus the mechanical load of the pump will increase and the hydraulic performance will be degraded. Furthermore, pre-rotation of the fluid close to the suction bell can be forced up to limits which are not in compliance to state of the art acceptance criteria. At least non-symmetric velocity distribution at the impeller will arise out of this flow conditions. Within physical model tests intakes together with pumps can be optimized for their best efficiency point of operation. Flow conditions can be achieved generating kinematical affinity at the suction bell which are close to the conditions of the acceptance test. The report shows application oriented solutions for the installation of cost effective flow guiding devices in open and covered intake systems to assure adequate pump performance. Test results of model investigations and experiences by modifying intake structures of existing plants will be presented. Concerning the sensitivity of high specific speed vertical pumps approach flow conditions especially at the intake structures have to be in accordance to state of the art acceptance criteria to assure adequate availability of the pumps. By today it is common practise and state of the art to test the behaviour of intake and outfall structures by physical model tests.

Mechanisms of lobed jet mixing: About circularly alternating-lobe mixers

Flow/flame and emissions fields of premixed oxy-methane stratified flames in a dual annular counter-rotating swirl burner