W. E. Lear

Analysis and Modeling of a Two-Phase Jet Pump of a Thermal Management System for Aerospace Applications

Jet pumps are devices capable of pumping fluids to a higher pressure by inducing the motion of a secondary fluid employing a high-speed primary fluid. The main components of a jet pump are a primary nozzle, secondary fluid injectors, a mixing chamber, a throat, and a diffuser. The work described in this paper models the flow of a two-phase primary fluid inducing a secondary liquid (saturated or subcooled) injected into the jet pump mixing chamber. The model is capable of accounting for phase transformations due to compression, expansion, and mixing. The model is also capable of incorporating the effects of the temperature and pressure dependency in the analysis. The approach adopted utilizes an isentropic constant-pressure mixing in the mixing chamber and at times employs iterative techniques to determine the flow conditions in the different parts of the jet pump.

Analysis of two-phase ejectors with Fabri choking

Abstract A one-dimensional mathematical model was developed using the equations governing the flow and thermodynamics within a jet pump with a mixing region of constant cross-sectional area. The analysis is capable of handling two-phase flows and the resulting flow phenomena such as condensation shocks and the Fabri limit on the secondary mass flowrate. This work presents a technique for quickly achieving first-approximation solutions for two-phase ejectors. The thermodynamic state of the working fluid, R-134a for this analysis, is determined at key locations within the ejector. From these results, performance parameters are calculated and presented for varying inlet conditions. The Fabri limit was found to limit the operational regime of the two-phase ejector because, in the two-phase region, the speed of sound may be orders of magnitude smaller than in a single-phase fluid.

Performance of a Novel Combined Cooling and Power Gas Turbine With Water Harvesting

A thermodynamic design-point performance analysis is performed on a novel cooling and power cycle that combines a semiclosed cycle gas turbine called the high-pressure regenerative turbine engine (HPRTE) with a vapor absorption refrigeration system (VARS). Waste heat from the recirculated combustion gas of the HPRTE is used to power the VARS. Water produced as a product of combustion is intentionally condensed and harvested. A part of the VARS cooling is used to chill the gas entering the high-pressure compressor, allowing water condensation and extraction as well as large efficiency gains. The remaining cooling capacity is provided to an external refrigeration load. The cycle is modeled using zero-dimensional steady-state thermodynamics, considering conservative values of polytropic efficiencies, a conservative model for turbine blade cooling, conservative values of pressure drops for the turbomachinery, including heat exchangers, and accurate correlations for the properties of the LiBr-H 2 O mixture and the combustion products. The cycle is shown to operate with a thermal efficiency greater than 40% for parameters appropriate to medium sized engines, while producing about 1.5 kg of water per kilogram of fuel (propane) consumed. This thermal efficiency is in addition to the large cooling effect generated in the evaporator of VARS, equivalent to 3-4% increased efficiency. The efficiency would be greater than 51% without turbine cooling bleed. The refrigeration ratio, defined as the ratio of external refrigeration load to the net work output, is found to be 0.38 for the base case. The water extracted is found to be a strong function of the recirculation ratio and low pressure compressor ratio PR c1 . Based on these and prior results, which showed that the HPRTE is very compact and has inherently low emissions, it appears that this cycle would be well suited for distributed power and some vehicle applications, especially ones with associated air conditioning loads.

Dynamic Modeling of a Novel Cooling, Heat, Power, and Water Microturbine Combined Cycle

The power, water extraction, and refrigeration (PoWER) engine has been investigated for several years as a distributed energy (DE) system among other applications for civilian or military use. Previous literature describing its modeling and experimental demonstration have indicated several benefits, especially when the underlying semiclosed cycle gas turbine is combined with a vapor absorption refrigeration system, the PoWER system described herein. The benefits include increased efficiency, high part-power efficiency, small lapse rate, compactness, low emissions, lower air and exhaust flows (which decrease filtration and duct size), and condensation of fresh water. The present paper describes the preliminary design and its modeling of a modified version of this system as applied to DE, especially useful in regions, which are prone to major grid interruptions due to hurricanes, undercapacity, or terrorism. In such cases, the DE system should support most or all services within an isolated service island, including ice production, so that the influence of the power outage is contained in magnitude and scope. The paper describes the rather straightforward system modifications necessary for ice production. However, the primary focus of the paper is on dynamic modeling of the ice making capacity to achieve significant load-leveling via thermal energy storage during the summer utility peak, hence reducing the electrical capacity requirements for the grid.

Effect of Slip Velocity and Heat Transfer on the Condensed Phase Momentum Flux of Supersonic Nozzle Flows

One of the methods used for industrial cleansing applications employs a mixture of gaseous nitrogen and liquid water injected upstream of a converging-diverging nozzle located at the end of a straight wand assembly. The idea is to get the mixture to impact the surface at the maximum momentum flux possible in order to maximize the cleansing effectiveness. We present an analysis geared towards this application in which the effects of slip and heat transfer between the gas and liquid phases are present. The model describes the liquid momentum flux (considered a figure of merit for cleansing) under a host of design conditions. While it is recognized that the emulsification mechanism responsible for cleansing is far more complicated than simply being solely dependent on the liquid momentum flux, the analysis presented here should prove useful in providing sufficiently accurate results for nozzle design purpose

Testing and Modeling of a Semi-Closed Gas Turbine Cycle Integrated With a Vapor Absorption Refrigeration System

A novel cooling and power cycle has been proposed that combines a semi-closed cycle gas turbine called the High Pressure Regenerative Turbine Engine (HPRTE) with a vapor absorption refrigeration system (VARS). The refrigeration cycle (VARS) interacts with the power cycle (HPRTE) solely through heat transfer in the generator and the evaporator. Waste heat from the recirculated combustion gas of the HPRTE is used to power the absorption refrigeration unit, which cools the high-pressure compressor inlet of the HPRTE to below ambient conditions and also produces excess refrigeration, in an amount which depends on ambient conditions. Water produced as a product of combustion is intentionally condensed in the evaporator of the VARS, which is designed to provide sufficient cooling for three purposes: chilling the inlet air to the high pressure compressor, water extraction, and for an external cooling load. In a previous study, the combined cycle was modeled using zero-dimensional steady-state thermodynamics, with the specified values of efficiencies and pressure drops for the turbo-machinery and heat exchangers. The model predicts that the combined cycle with steam blade cooling for a medium-sized engine will have a thermal efficiency of 49%, in addition to the external refrigeration load generated in the cycle which is 13% of the net work output. It also produces about 1.4 kg of water for each kg of fuel (propane) consumed. A small experimental unit demonstrating the HPRTE/VARS combined cycle has been constructed and is currently being tested in the Energy & Gas-dynamic Systems Laboratory at the University of Florida. A 45 HP Rover 1S-60 engine is integrated with a NH3 /H2 O vapor absorption refrigeration unit having a capacity of 19 Ton Refrigeration. The engine flow-path has been significantly modified to include partial recirculation of exhaust products, turbocharging, and recuperation, thus implementing the HPRTE concept. In addition, a significant modeling effort has been undertaken to simulate the combined cycle operation under design and off-design conditions. Initial experimental results show good agreement with the model predictions, including overall efficiency and water extraction rates.Copyright

Effect of Fabri choking on the performance of two-phase jet pumps

This paper explores two-phase flow through a supersonic jet pump with a constant-area mixing chamber. This work is a continuation of previous work which considered supersonic, two-phase flow through a jet pump with a constant-pressure mixing chamber. Also considered is the possibility of a phenomenon known as Fabri choking, in which the secondary fluid reaches sonic velocity in the mixing chamber, before mixing with the primary fluid.

Aerothermal Considerations for the Design of Two-Phase High Speed Impact Cleansers

An alternative method employed in industrial cleansing applications involves injecting liquid water in a flow of gaseous nitrogen and discharging the mixture through a converging-diverging nozzle onto the surface. This paper is an extension of a previous analysis, which was geared towards understanding the gas/liquid mixture dynamics through the nozzle. The analysis presented here takes into account the effect of the nozzle area ratio and is thus geared towards the nozzle designer and provides additional fundamental insight into the required geometry

Design considerations of jet pumps with supersonic two-phase flow and shocks for refrigeration and thermal management applications

This paper describes results of a design-oriented model for two-phase jet pumps and ejectors for refrigeration and thermal management aerospace and terrestrial applications. The primary motivation for the work is the development of a reliable but simple design methodology that captures the important flow physics while being sufficiently fast in order to reduce the design cycle time. This work is particularly relevant to the flow boiling test facility under development at the NASA Marshall Space Flight Center as it allows rapid design optimization of the jet pump as well as the integrated system. The results presented in the paper show optimal geometric area ratio as well as system state point information as a function of the inlet states and entrainment ratio. Qualitative agreement with single-phase ejector performance is predicted, lending additional confidence in the results. Copyright

Efficiency and gasdynamic analysis of two-phase mixtures in supersonic nozzles with inter-phase heat transfer and slip

Abstract This paper describes a gasdynamic analysis of the acceleration of a condensed phase/gaseous mixture through a converging-diverging nozzle. The model used for this analysis calculates the exit kinetic energy in terms of the mixture properties as well as the dissipative effects of heat transfer and slip between the phases. The model also calculates the nozzle efficiency by comparing the kinetic energy of the mixture at the exit to that of the ideal process. The results indicate that the efficiency decreases with both the condensed phase mass fraction and exit velocity. Inter-phase heat transfer and slip parameters produce a minimum in nozzle efficiency under conditions which are potentially encountered in rocket engines.