Density Of Working Fluid Research Articles

Performance and optimization evaluation for integration of sCO2 power system into the aircraft propulsion system

The aviation industry accounts for part of the CO2 emissions contributing to climate change. The industry has established a target to reduce 2050 net aviation carbon emissions by 50 % relative to 2005 levels. With this in mind, waste heat recovery is a key pathway to achieve reduced emissions and improve system efficiency. The waste heat may potentially be converted to electric power using a supercritical CO2 Brayton power cycle. The sCO2 power system offers the advantage of compactness owing to the high working fluid density, which is an important consideration for aircraft performance. The present work focuses on the integration of the sCO2 power system into the aircraft propulsion system and evaluation of its performance. Detailed optimization of the sCO2 waste heat system will be evaluated with a focus on cycle efficiency and net power under different operating conditions, including ground, takeoff, climb, cruise, and landing operations. The study is divided into two parts with two different turbofan engines, one with a nominal thrust of 30 kN and the other with a nominal thrust of 9 kN. The first part shows the effect and operation of the waste heat recovery unit under the different operating conditions. The second part is focused on cycle optimization and performance evaluation. The results demonstrate the potential of waste heat recovery during a range of operational conditions. The sCO2 cycle efficiency can reach between 25 and 39 % (depending on aircraft engine) with net power output in the range of 100 to 260 kW.

Dynamic modeling of a mechanically coupled organic Rankine-vapor compression system for compression heat recovery based on an improved lumped parameter model

Compression heat recovery is getting attention in cryogenic air separation units for its high energy saving potential, while the organic Rankine-vapor compression system (ORVC) is considered as an attractive technology for both compression heat recovery and air pretreatment. As the states of the compression heat inevitably change with the ambient environment, dynamic simulation of the ORVC-air compression heat recovery system (ORVC-ACS) is carried out in this paper. An improved lumped parameter model that enables to solve the dynamic model with complex structure and on large-time scale is proposed and validated. The working fluid density in the heat exchanger is treated as phase-based average in this improved model. The average relative deviations between the simulation results and experimental data are less than 6.8%. The annual dynamic characteristics and varying-duty operation performance of the ORVC-ACS are further studied. The results show that the ORVC-ACS could basically work under the design condition, with the maximum temperature fluctuation amplitude of about 6.9 °C, response time of about 4–6 min without varying-duty conditions and 8 min with duty changing. Besides, for a 60,000 Nm3/h scale ORVC-ACS, the annual energy saving reaches about 13.75 GWh, equivalent to CO2 emission reduction of about 9.9 Mt, and heat recovery ratio of about 76.4%, illustrating great energy saving and environmental protection performance. This research may benefit subsequent control scheme design and actual operation.

Thermodynamic investigation of a centrifugal reverse Brayton cycle for refrigeration in air conditioning filed

The reverse Brayton cycle (RBC) is known to exhibit a lower coefficient of performance (COP) when compared to conventional vapor-compression refrigeration systems. To tackle this issue, this study proposes a centrifugal reverse Brayton cycle (CRBC) that features a rotating heat exchanger, which utilizes the conversion mechanism between equal potential energy and pressure energy to enhance system performance. The findings indicate that the COP of the CRBC is roughly inversely proportional to the working fluid density, making CO2 a more suitable option for CRBC systems than conventional working fluids. We propose three different cycles for the CRBC system: the diamond cycle, trapezoid cycle, and rectangle cycle. From both technical and operational perspectives, the trapezoid cycle appears to be the preferred choice for CRBC. When the isentropic efficiency of the CRBC system exceeds 95%, its coefficient of performance (COP) ranges from 5.31 to 5.7, whereas the COP of transcritical carbon dioxide refrigeration cycle (tCO2), air RBC, and CO2 RBC are around 4.3, 1.9, and 0.79, respectively. This suggests that the performance of the CRBC system surpasses that of RBC by a significant margin, while achieving comparable performance to conventional vapor compression refrigeration systems. Moreover, the dimensionless power reflecting the installation capacity requirements for CRBC, tCO2, air RBC and CO2 RBC are around 0.2, 0.35, 5.3 and 1.9, respectively. This indicates that the compressor/expander capacity demand for system CRBC approaches the thermodynamic minimum.

High-Resolution X-Ray Radiography Methods Developed for Post-CHF Experiment

Radiation transmission measurement methods have become widely implemented in the study of two-phase flow due to leaping advancements in detector efficiency, spatial resolution, and high-speed measurement capabilities. However, radiation-based measurements of boiling experiments bear several challenges due to the mismatch of calibration to experimental conditions, beam hardening, thermal expansion, and material and working fluid density changes with temperature. The present research focuses on developing methods to analyze the high-resolution X-ray radiography measurements of the post-critical heat flux (Post-CHF) heat transfer facility built at the University of Michigan that is intended to perform high-pressure and high-temperature measurements; the experimental test section is made of Incoloy-800H and is characterized as a cylindrical geometry expanding 1.0 m in length. The broad goal of the experiment is to build a high-resolution database to develop models for inverted annular film boiling and inverted slug film boiling through dispersed flow film boiling. The methods developed in this research model the thermal effects of the postulated challenges in order to properly scale the X-ray calibration measurements to the experimental conditions. Additionally, a cross-section-weighted method is developed to estimate the axial void fraction; this method is validated by modeling the test section with synthetic void fraction data. Last, preliminary high-speed X-ray measurements performed at subcooled boiling conditions are presented and analyzed with the developed methods, which include bubbly, slug, and churn flows.

Effect of CO2-based binary mixtures on the performance of radial-inflow turbines for the supercritical CO2 cycles

Recently, the supercritical carbon dioxide (SCO2) power cycle has become a hotspot in the field of energy-efficient utilization. The utilization of additives in the power cycle has been proven to be an effective way to improve the SCO2 power cycle efficiency. As one of the core components of the system, the influence of CO2-based mixtures on turbine performance needs to be further explored. In this study, the preliminary design and three-dimensional numerical simulation of a 500kW radial-inflow turbine (RIT) for small-scale SCO2 power systems were carried out. Furthermore, the design and off-design performance of high Reynolds number and small size turbine under the change of the CO2-based binary mixture compositions and mixing ratios were studied. Increasing the amount of nitrogen, oxygen, or helium into CO2 has a negative effect on the RIT performance, and the appropriate amount of xenon or krypton can improve the turbine efficiency. Moreover, mixtures with higher krypton additions adapt to higher heat source conditions. The loss of the turbine stage passage shows that a large amount of helium greatly reduces the working fluid density, and the high amount of xenon has a great influence on the dynamic viscosity, which all makes the RIT operation deviate from the steady state. Therefore, the CFD model simulation fails indicating that RIT designed based on pure CO2 may not run smoothly and continuously. The losses in the stage with pure CO2 and CO2–Kr mixture were investigated. The results indicate that the losses originated from the stator cannot be ignored and that the improvement of efficiency is mainly owed to the reduction in clearance losses. There is no doubt that the viewpoints proposed in this paper have significant reference value for the practical application of the SCO2 power cycle using mixtures.

Optimization of the taper angle of the jetter confuser used for reversible blast cleaning of propellers from corrosion

It is shown that it is very effective to remove corrosion products from various surfaces, including the metal surface of the propeller, using the new technology of reverse-jet cleaning (RJC) developed by the authors. The RJS technology is based on the physical principle that the jet of the working fluid (pulp based on river sand or bentonite clay), upon impact with the surface to be cleaned, turns 180°, which leads to an increase in the jet effect on the surface to be cleaned by 1.5–2 times due to the occurrence of the reactive component. To ensure the marked turn of the jet, an original design of the body was developed, which is distinguished by a patent novelty. One of the main elements in this design is a jet-forming device in the form of a confuser. The presented theoretical studies of the pressure loss of the working fluid in the confuser channel, based on the study of the pressure loss function to the extremum, which made it possible to obtain a dependence for calculating the optimal taper angle in a wide range of Reynolds numbers characterizing the turbulent mode of motion taking into account the influence of the working fluid density and its dynamic viscosity, the average speed of movement of the working fluid, the radius of the confuser, as well as the coefficient of equivalent roughness, i.e. from gradual wear of the confuser channel. The resulting dependence can be recommended for calculation in the design of jet cleaning devices and other installations of jet technology.

Calculation of the Optimum Cone Angle of a Confuser Used for Reversive-Jet Cleaning of Metal Surfaces against Corrosion

The modern industrial production of the Republic of Belarus is characterized by the absence of its own raw material base and significant dependence on imported energy carriers and material resources supplied at world prices. When working in such conditions, production efficiency can be achieved through all-round economy and creation of modern energyand resource-saving technologies. However implementation of such technologies, for example, laser cutting and welding, cladding, flame spraying, painting, etc. directly depends on quality of cleaning metal surfaces from corrosion. Theoretical and experimental studies conducted at the Department of Shipbuilding and Hydraulics of the Belarusian National Technical University have shown that it is very economical to remove corrosion products from metal surfaces using new technology of reverse jet cleaning. The reverse jet cleaning technology is based on a physical principle which presupposes that a jet of working fluid (pulp based on river sand or bentonite clay) rotates 180º when it hits the surface to be cleaned and it leads to an increase in jet impact on the surface to be cleaned by 1.5–2 times due to occurrence of a reactive component. In order to ensure a marked jet reversal an original case design has been developed which is characterized by a patent novelty. One of the main elements in this design is a confuser-shaped stream-forming device. Theoretical investigations on pressure losses of working fluid in a confuser channel which are based on the study of functional at the extremum have made it possible to obtain a dependence for calculation of an optimal cone angle at a turbulent mode of motion within the range of Reynolds numbers 4000 < Re < 3 ×106 while taking into account an influence of working fluid density, its dynamic or kinematic viscosity, average velocity movement of working fluid, confuser radii.

Title of the Integrity Analysis of O&G Standpipe Separator: Numerical Study Article

A standpipe is a component that functions to remove the condensate of gas from the oil that flows inside the O&G piping system underneath. Efficient gas removal promotes better crude oil quality and increases productivity. The deflector plates integrity in a stand pipe, where thin plates are mounted on the pipe walls periodically in the direction of fluid flow, has been numerically investigated. The aim of this investigation is to determine how the working fluid density and deflectors thickness influenced the plates integrity. Two working fluids were tested. Natural gas and crude oil which has a higher density. The thickness of the plates was 3 mm and 6 mm. A series of simulation analyses were done analytically through CFD and FEA simulation method using ANSYS software. Based on the results, crude oil produces higher stress onto the plates. This causes large plate deflection. It was observed, the plates near to the standpipe inlet were subjected to the highest stress. Stress on the deflector plates drops as the fluid travel along the pipe height. The deflector plates of 3 mm were failed under these conditions and were not recommended for usage.

Understanding frequency response of thermal micropumps using electrical network analogy

In this article the frequency response of a thermal micropump is investigated using electrical network analogy modeling technique. This technique is based on dividing the micropump into subsystems and representing each subsystem using the equivalent network analogy. Obtained mathematical models of subsystems are then represented using transfer functions and block diagrams. As an example, thermopneumatic micropump is considered. Model simulation suggests an increase in the net flow rates of the micropump as the operating frequencies increased, until a first cut-off frequency is reached. A second cut-off frequency is observed with further increase in operating frequencies. Model simulations are consistent with qualitative experimental trends reported in the literature. The model is used to obtain a relationship between cut-off frequencies and design properties of the micropump. Model simulations show that lower cut-off frequency is related to mechanical properties of the thermopneumatic micropump, including stiffness and damping. Upper cut-off frequency is related to thermal properties of the thermopneumatic micropump, including thermal conductivity, heat capacity, and working fluid density.

Bubble pump in a closed-loop system for electronic cooling

This study experimentally and theoretically investigates bubble pump performance in a closed-loop system for electronic cooling. The system consists of a vertical flat evaporator acting as a bubble pump, a condenser, a rising tube, a falling tube and a reservoir, and is completely filled with working fluid. As the bubble pump absorbs heat, the differences in the working fluid density between the rising and falling tubes induce flow motion. The effects of the input heating power, the pump inlet temperature and the boiling surfaces are determined experimentally. There are three heat-transfer regions inside the pump, including natural convection, subcooled boiling and saturated boiling. A theoretical pressure drop model and a thermal resistance network are constructed to describe the performance of the bubble pump. The results indicate that the bubble pump performs better at saturated boiling conditions. When the pump inlet temperature is the saturated temperature, the maximum flow rate is 200 ml/min at 30 W and the maximum driving pressure of the pump is 962 Pa at 80 W. The results also show that the sudden contraction between the pump and the rising tube, inducing a pressure drop, will reduce the system flow rate. In addition, the results demonstrate that the fins on the boiling surface can effectively diminish the center temperature of the basic plate of the pump and of pump resistance.

A Dynamic Fluid Property Model for the Engineering Design of Hydraulic Dampers

To improve accuracy in the engineering design of hydraulic dampers, a dynamic mathematic model for its working fluid density, viscosity, modulus and stiffness is established. The dynamic flow loss due to volumetric change and pressure leakage is also formulated, wherein the dynamic back pressure in the air chamber is coupled. Simulation results show that most of the fluid properties change obviously when the damper is subjected to external excitations, they are not constant values. The viscosity would drop 74.68% and the flow loss would soar 298.68% with the increase of fluid temperature; the modulus and the stiffness would also drop over 20% when the entrapped air ratio increases, but the density is relatively robust to both variations. The established mathematic model gives a dynamic representation of the fluid property under real service conditions, it has already been applied to the engineering design of several hydraulic damper products in industry, and the effectiveness is validated by pertinent product experiments.

Liquid penetration length in direct diesel fuel injection

We have conducted experimental measurements to estimate the liquid penetration length of a diesel fuel jet injected into an inert environment. We analyzed the effects of the characteristic parameters, i.e., the nozzle diameter, discharge coefficient, injection pressure, and working fluid density. The transient fuel injection process was recorded using optical access, and the liquid penetration length before the second break-up regime was measured using the ombroscopy technique. The experimental data were subsequently fitted to a correlation that accurately predicts liquid penetration length at conditions typical of modern Heavy Duty common rail diesel engines operating with direct fuel injection. A statistical analysis of our experimental measurements suggests a power function correlation to model the liquid penetration length. The proposed model is in good agreement with experimental data and yields a correlation coefficient R 2 = 93.3%. It is expected that this correlation can be of assistance in the successful designing of combustion chambers required by modern heavy duty diesel engines.

Flux penetration of an aluminum liner during working fluid compression

The Phillips Laboratory working fluid experiment is a research effort to study the compression of a hot hydrogen gas using an electromagnetically imploded solid liner. In our experiments, the solid liner is driven by a 5 MJ discharge which Joule heats the aluminum, melting and eventually vaporizing it. This numerical study explores the vaporization and flux penetration of a solid aluminum liner during its implosion. In particular, it considers the effect that flux which has penetrated the liner has on the hot hydrogen working fluid. A study of the dynamics of the solid liner was performed with one-dimensional radiation magnetohydrodynamic simulations, which included a careful treatment of the electrical resistivity near the phase transitions. An analytic snowplow model is developed in order to estimate the minimum working fluid density required to ignore flux penetration through the liner.