Simultaneous implementation of rotary pressure exchanger and ejectors for CO2 refrigeration system

Natural refrigerant CO2 has become a viable choice for refrigeration units. The CO2 systems are working efficiently on land-based facilities, and their demand is increasing for offshore applications, e.g., cruise ships and fishing vessels, due to their environment-friendly nature and compactness. The investigated application of the CO2 system in this work is a single-stage system for air conditioning and a two-stage system for provision refrigeration at high heat rejection temperatures. The CO2 transcritical cycle allows operating in higher ambient temperatures and in a colder climate with significant heat recovery. However, the system efficiency decreases in higher ambient conditions due to the high-pressure ratio and expansion losses. Therefore, ejectors are implemented to boost the cycle efficiency at high heat rejection temperature conditions. The pressure exchanger (PX) device recently came up and claimed to be an option to recover expansion work in CO2 systems. PX is already in use for reverse osmosis (RO) desalination units to recover pressure work from the high pressure reject concentrate to low-pressure seawater. This work theoretically investigates the implementation of a CO2-PX for transcritical CO2 systems combined with ejectors and compressors. The energy efficiency of alternative system configurations is evaluated for various operating conditions.Simultaneous implementation of rotary pressure exchanger and ejectors for CO2 refrigeration systemacceptedVersio

Simultaneous implementation of rotary pressure exchanger and ejectors for CO2 refrigeration system

Natural refrigerant CO2 has become a viable choice for refrigeration units. The CO2 systems are working efficiently on land-based facilities, and their demand is increasing for offshore applications, e.g., cruise ships and fishing vessels, due to their environment-friendly nature and compactness. The investigated application of the CO2 system in this work is a single-stage system for air conditioning and a two-stage system for provision refrigeration at high heat rejection temperatures. The CO2 transcritical cycle allows operating in higher ambient temperatures and in a colder climate with significant heat recovery. However, the system efficiency decreases in higher ambient conditions due to the high-pressure ratio and expansion losses. Therefore, ejectors are implemented to boost the cycle efficiency at high heat rejection temperature conditions. The pressure exchanger (PX) device recently came up and claimed to be an option to recover expansion work in CO2 systems. PX is already in use for reverse osmosis (RO) desalination units to recover pressure work from the high pressure reject concentrate to low-pressure seawater. This work theoretically investigates the implementation of a CO2-PX for transcritical CO2 systems combined with ejectors and compressors. The energy efficiency of alternative system configurations is evaluated for various operating conditions.Simultaneous implementation of rotary pressure exchanger and ejectors for CO2 refrigeration systemacceptedVersio

Thermodynamic analysis of rotary pressure exchanger and ejectors for CO2 refrigeration system

Natural refrigerant CO2 has become a viable choice for refrigeration units for land-based and offshore applications due to its environment-friendly nature and compactness. The CO2 transcritical cycle allows operating in colder climates and in elevated ambient temperature conditions and with significant heat recovery. However, the energy efficiency of the system suffers at higher heat rejection conditions mainly due to expansion losses. This work theoretically investigates and proposes the implementation of a new expansion work recovery device, a pressure exchanger (CO2-PX), for the transcritical CO2 cycle. The numerical models are developed in the Engineering Equation solver (EES) to compare the performance of CO2-PX configuration with standard booster-, parallel-, and ejector- configurations for various conditions. The analysis is carried out for the evaporation temperature of 0 ℃ and the gas cooler outlet temperature of 33 ℃ to 37 ℃. The results indicate that the coefficient of performance (COP) is improved by 17.7–23.5%, 16.3–20.3%, and 2.4–5.5% to the standard booster, parallel and ejector configurations, respectively, at the investigated conditionspublishedVersio

Experimental investigation of a transcritical CO2 refrigeration system incorporating rotary gas pressure exchanger and low lift ejectors

Natural refrigerants like CO2 are playing a significant role in making refrigeration and heat pump systems climate-friendly by slowly phasing out the high global warming refrigerants like hydrofluorocarbons (HFCs). However, the efficiency of a transcritical CO2 refrigeration system declines significantly when the ambient temperature increases, primarily attributed to the high-pressure lift and the losses incurred during expansion. To remedy this issue, this paper presents a novel rotary gas pressure exchanger (PXG) device, which simultaneously achieves high differential pressure expansion work recovery and the “free compression” of the portion of the flash gas in a compact, rotary machine. For this, a PXG device is designed, fabricated, and tested to achieve free compression of CO2 over the entire differential pressure of approximately 70 bar between a receiver and a gas cooler. This is one of the highest free-pressure lift provided by any device to date in CO2 refrigeration. However, there is a small pressure loss of approximately 1–2 bar in the system due to viscous and inertia losses in the piping and in the PXG itself, which needs to be overcome by an external booster device. Results on a baseline PXG integrated system with two low lift booster compressors are presented, which show up to 60 bar free pressure lift and up to 18.2 % COP improvement provided by PXG. Additionally, key performance characteristics of the PXG, like the expansion work recovery, the mass boost ratio, direct fluid-to-fluid contact, and no pass-through operation are experimentally quantified. This work also presents a novel method to integrate two low lift ejectors with PXG to eliminate the need for separate low lift compressors. The low lift ejectors are designed, fabricated, and tested in-house, followed by their integration with the PXG device. A new type of transcritical CO2 refrigeration system is designed to integrate these low lift ejectors with PXG, and experiments are conducted at various evaporator thermal duties and gas cooler exit temperatures, simulating varying ambient temperature conditions. A novel control system to control the gas cooler pressure to optimal thermodynamic levels using PXG rotational speed is demonstrated experimentally. Further, automated control of high-pressure low lift ejector mass flow using an in-built needle design has been successfully demonstrated to optimise PXG mass boost performance. The LP low lift ejector achieved a successful pressure lift of 3.8 bar, and the HP low lift ejector showed a lift of 5.7 bar on the top of 42 bar free pressure lift provided by PXG for up to 5.8 kg/min mass flow delivered by free PXG compression. The results from this study demonstrate that the PXG device provides a significant energy efficiency improvement to the transcritical CO2 refrigeration system, and the novel low lift ejectors, when integrated with PXG, provide a successful method to maximise PXG's thermodynamic potential. © 2024 The Author(s)publishedVersio

A ground-based near-infrared emission spectrum of the exoplanet HD 189733b

Detection of molecules using infrared spectroscopy probes the conditions and compositions of exoplanet atmospheres. Water (H2O), methane (CH4), carbon dioxide (CO2), and carbon monoxide (CO) have been detected in two hot Jupiters. These previous results relied on space-based telescopes that do not provide spectroscopic capability in the 2.4 - 5.2 micron spectral region. Here we report ground-based observations of the dayside emission spectrum for HD 189733b between 2.0-2.4 micron and 3.1-4.1 micron, where we find a bright emission feature. Where overlap with space-based instruments exists, our results are in excellent agreement with previous measurements. A feature at ~3.25 micron is unexpected and difficult to explain with models that assume local thermodynamic equilibrium (LTE) conditions at the 1 bar to 1 x 10-6 bar pressures typically sampled by infrared measurements. The most likely explanation for this feature is that it arises from non-LTE emission from CH4, similar to what is seen in the atmospheres of planets in our own Solar System. These results suggest that non-LTE effects may need to be considered when interpreting measurements of strongly irradiated exoplanets.Comment: 12 pages, 2 figures, published in Natur

Coupled Physics Performance Predictions and Risk Assessment for Dry Gas Seal Operating in MW-Scale Supercritical CO2 Turbine

U.S. Department of Energy (DOE) has recently sponsored research programs to develop megawatt scale supercritical CO2 (sCO2) turbine for use in concentrated solar power (CSP) and fossil based applications. To achieve the CSP goal of power at $0.06/kW-hr LCOE and energy conversion efficiency &gt; 50%, the sCO2 turbine relies critically on extremely low leakage film riding seals like dry gas seal (DGS). Although DGS technology has been used in other applications before. making it successful for stringent conditions of an sCO2 turbo-expander is challenging. This paper presents results from a multi-scale coupled physics model that predicts the performance of DGS under a typical sCO2 turbine mission cycle and addresses some of the risks specific to operation in sCO2. Real gas equations of state are incorporated in the models to capture large discontinuities in fluid properties close to the critical point. A novel experimental setup is developed to observe and characterize transition of CO2 through liquid-vapor and supercritical phases. Coupled fluid-structure-thermal interaction model investigates the effect of aerodynamic and thermal perturbations on the structural and rotordynamic instabilities. Dynamic instabilities arising from sonic transition in thin sCO2 film of DGS pose additional challenges while the large surface roughness changes due to sCO2 corrosion warrant further design considerations. Effectiveness of features like spiral grooves in converting fluid momentum into pressure rise in the thin film and also in achieving local flow reversals is investigated. Effect of various design features on the optimal performance is quantified and insights for a successful DGS operation in a sCO2 turbomachine are provided.</jats:p

Elastohydrodynamic Analysis of an Elastomeric Hydraulic Rod Seal During Fully Transient Operation

A soft elastohydrodynamic model of a reciprocating elastomeric hydraulic rod seal has been developed. It consists of coupled fluid mechanics, contact mechanics, and deformation analyses. The model has been used to analyze a U-cup lip seal in an injection molding application with a time-varying sealed pressure and rod velocity. Results include the histories of the hydraulic fluid flow rate, fluid transport, mean shear stress on rod, sealing zone length, and friction force on rod, as well as distributions of the fluid pressure, film thickness, and contact pressure.</jats:p