Performance Benefits of R718 Turbo-Compression Cycle Using 3-Port Condensing Wave Rotors

A number of technical challenges have often hindered the economical application of refrigeration cycles using water (R718) as refrigerant. The novel concept of condensing wave rotor provides a solution for performance improvement of R718 refrigeration cycles. The wave rotor implementation can increase efficiency and reduce the size and cost of R718 units. The condensing wave rotor employs pressurized water to pressurize, desuperheat, and condense the refrigerant vapor — all in one dynamic process. In this study, the underlying phenomena of flash evaporation, shock wave compression, desuperheating, and condensation inside the wave rotor channels are described in a wave and phase-change diagram. A computer program based on a thermodynamic model is generated to evaluate the performance of R718 baseline and wave-rotor-enhanced cycles. The detailed thermodynamic approach for the baseline and the modified cycles is described. The effect of some key parameters on the performance enhancement is demonstrated as an aid for optimization. A generated performance map summarizes the findings.

Numerical Simulation of Unsteady-Flow Processes in Wave Rotors

The wave rotor (pressure exchanger) is a device working based on a relatively simple idea of operation, but is challenging in its technical realization and difficult to simulate numerically. It has been common practice to create and use specialized codes for simulating the wave rotor operation. The current work presents an attempt of developing 2D and 3D models of radial and axial wave rotors using the commercial software package FLUENT. In this study geometrical models are used for the device casing and rotor cells. The application of carefully chosen initial and boundary conditions enabled the realization of relative motion of the rotor model. The vast information about the unsteady processes occurring during simulation are visualized. It occurs that such type of models are useful for the final test of devices, after the geometry was optimized by the use of specialized but much simpler 1D codes.

Wave Rotor Combustor Test Rig Preliminary Design

Pressure gain combustion in a wave rotor approaching the thermodynamic ideal of constant volume combustion has been proposed to significantly enhance the performance of gas turbine engines. A computational and experimental program is currently being conducted to investigate the combustion process and performance of a wave rotor with detonative and near-detonative internal combustion. An innovative and flexible preliminary design of the test rig is presented to demonstrate the operation and performance of the system. A preliminary design method based on a sequence of computational models is used to design wave processes for testing in the rig and to define rig geometry and operating conditions. The operating cycle allows for propagation of the combustion front from the exit end of the combustion channel to the inlet end. This is similar to and motivated by the Constant Volume Combustor (CVC) concept that seeks to produce a relatively uniform set of outflow conditions in both spatial and time coordinates.

Modeling and Validation of a Pressure-Wave Supercharger Using a Finite Difference Method

Modern pressure-wave supercharging devices offer many degrees of freedom in operation with an internal combustion engine. Both the independent set of wave rotor speed and the offset between air and gas casing can guarantee optimum efficiency even under problematic operating conditions. However, these systems require very accurate models that can reproduce the physical effects occurring in the charger. In this paper, a finite difference tool is presented where a set of Euler-type partial differential equations is numerically solved to simulate the 1-dimensional unsteady gas dynamics in the cell wheel, taking into account such phenomena as leakage, heat transfer, and friction. In order to show its general applicability, the model was validated with measurement results from two different PWS-boosted engines on a test rig.

Roots Compressor: High Temperature Testing and Modeling

The Roots compressor has enjoyed a multitude of applications. Retuned to produce a high-temperature stream of gas, the Roots compressor can be a part of such applications as pyrolitic synthesis, chemical decomposition, optical fiber production and experimental studies. Presently, it appears that by using advanced materials, a prototype capable of withstanding temperatures up to 1500–2000 K could be built. A series of experiments was performed and various performance data were recorded at 2280 and 3430 rpm. The maximum steady state temperature achieved and the corresponding pressure ratio were 660 K and 3.9. Numerical modeling revealed a good correlation for pressure ratios up to 3. While the outlet pressure signature was accurately reproduced, the magnitude of the actual pressure fluctuation was somewhat in error. A more detailed physical model of gas dynamic processes could improve the agreement. The calculations were based on measurements of the internal leakage, need for modeling of which is emphasized.

Experimental Investigation of Pressure Wave Supercharging for SI Engine

The objective of this paper is to find experimentally the suitable working conditions of a pressure wave supercharger (PWS) for SI engine. A belt-driven CVT was installed in order to drive the rotor of PWS to the appropriate speed regardless of engine speed. The maximum BMEP was achieved by changing speed of the PWS rotor at constant engine speed and throttle open ratio. From the experiment, the appropriate rotor speeds which led to maximum BMEP at every engine speed and throttle open ratio were achieved. The results showed that two power peaks existed during the range of the tested rotor speed. Since the drop in BMEP between these two power peaks was relatively small, the rotor speed range between these points was defined as effective rotor speed. At engine speed of 2000–4000rpm, the effective rotor speed was found at the engine-rotor ratio of 2.5. In addition, the maximum compression efficiency of PWS was 75% at engine speed of 3000rpm and the exhaust gas pressure reduced to the same level of commonly used turbochargers at all engine speed. Furthermore, results of the transient experiment showed that PWS had as good response as the small turbocharger, which was optimized for the tested engine.

Development of a Fourth Generation Energy Recovery Device

Energy Recovery, Inc’s Big Rotor Pressure Exchanger is the result of over 100 years of technology development. Work exchanger devices developed for SWRO plants are considered by many to be the most important breakthrough in desalination in the last 10 years. What has made this breakthrough possible and how have these devices affected the job of designing SWRO systems? ERI Chief Technical Officer Dr. Richard Stover presents the challenges and solutions of the design and deployment of the PX. PX performance data and engineering design considerations from operating SWRO-PX process configurations and PX arrays will be provided. Recent technical advances and future products will be discussed.

CFD Study on Laminar Flow Pressure Drop and Heat Transfer Characteristics in Toroidal and Spiral Coil System

Most pressure drop and heat transfer correlations obtained from the toroidal geometric system have been applied to the analysis of helical and spiral tube systems. While toroidal (and helical) coils have a constant radius of curvature about the coil center point (and center-line), spiral coils have a continuously varying radius of curvature, in which the varying centrifugal forces contribute to further enhance the heat transfer (at the cost of additional pressure drop) over toroidal and helical tube heat exchangers of the same length. Due to lack of published analytical, numerical and experimental data on spiral coil systems, in this paper, the laminar flow pressure drop and heat transfer characteristics of spiral coil systems are investigated with a commercially available CFD package (Fluent 6). First, an isothermal flow CFD analysis for a toroidal coil system is performed to optimally predict the local flow field and compared with the available experimental, numerical and analytical results, in which various model assumptions and operating conditions are involved. As a consequence, the heat transfer analysis with constant wall temperature boundary condition has been performed on a toroidal coil. With the verified CFD modeling schemes such as curved geometry creation, mesh/gird density control and solution model selection, the work is extended to the spiral coil system. The effects of Reynolds number and tube diameter to coil curvature ratio on the average friction factor and heat transfer characteristics are investigated for specified coil geometries utilizing water as the heat transfer medium. The general correlations for laminar flow pressure drop and heat transfer applied in a toroidal coil system are compared with the CFD results obtained from the spiral coil systems. It was found that up to 10% of the additional pressure drop and 40% of the enhanced heat transfer characteristics are obtained from the spiral coil system over the toroidal. The heat exchanger effectiveness ratio for spirals and toroids are compared for a range of Dean number. It was found that the spiral heat exchanger effectiveness ratio was between 20 to 30 percent greater than for general toroidal heat exchanger systems.

A Review of Wave Rotor Technology and Its Applications

The objective of this paper is to provide a succinct review of past and current research in developing wave rotor technology. This technology has shown unique capabilities to enhance the performance and operating characteristics of a variety of engines and machinery utilizing thermodynamic cycles. Although there have been numerous efforts in the past dealing with this novel concept, this technology is not yet widely used and barely known to engineers. Here, an attempt is made to summarize both the previously reported work in the literature and ongoing efforts around the world. The paper covers a wide range of wave rotor applications including the early attempts to use wave rotors, its successful commercialization as supercharges for car engines, research and development for gas turbine topping, and other developments. The review also pays close attention to more recent efforts: utilization of such devices in pressure-gain combustors, ultra-micro gas turbines, and water refrigeration systems, highlighting possible further efforts on this topic. Observations and lessons learnt from experimental studies, numerical simulations, analytical approaches, and other design and analysis tools are presented.

Thermal Design Correlations for Single- and Two-Phase Flow of R-407C in Meso-Scale Heat Exchangers

The paper presents correlation development for an experimental database done on R-407C flow in meso-scale horizontal channels. Single-phase, two-phase subcooled, and two-phase saturated boiling flow correlations were developed. The variables considered in this study including essential design parameters, such as, channel diameter, coils pitch and diameter. For flow variables considered are the Reynolds number and the Prandtl number. The purpose of this study is to present new design correlations for flow boiling in a ternary refrigerant mixture at a meso-scale size. The relative influences of enhancement design parameters on friction factor and heat transfer were carried in this parametric analysis of the flow boiling correlations. The resulted correlations developed in this study are compared to available published correlations.