• Energy Research

The pipeline leakage process of supercritical CO2 involves complex phenomena because of the high inner pressure and the multiphase choked flow near the leakage point. In this work, an experimental facility was developed to investigate the thermodynamic and fluid dynamic behaviour in pressurized CO2 leakage process. Characteristics of the flow and heat transfer in the leakage processes were studied by investigating the variation of the mass flow rate and the development of the thermal boundary layer in the pipeline. Inner pressure, mass outflow rate at the leakage nozzle and Nusselt number in the pipeline were studied quantitatively based on the laboratory pipeline leakage system. Typical rapid expansion behaviour of supercritical fluid including sonic-choked flow phenomena and phase-transition process was observed during the leakage process. The data of the mass flow rate and Nusselt number could be used for leakage detection and validating numerical simulations of supercritical-gas multiphase flows in the pipeline leakage process.

The accidental release is one of the main risks during the pipeline transportation of supercritical CO2 for carbon capture and storage and enhanced oil recovery. The leakage of high pressure CO2 involves complex phenomena, including the expansion and flashing of the CO2 jet, dispersion of a dense CO2 cloud, falling of the solid CO2 and sublimation of the dry ice bank, as well as changes of pressure and temperature in the pipelines. A new experimental setup is developed to study the leakage behavior of high pressure CO2 flow in a circulation pipeline system, which is about 23 m long. The inner diameter of the pipeline is 30 mm. The pressure in the pipeline can be as high as 12 MPa with a maximum temperature of 50 °C through a high pressure pump and an electrically heated cloth around the pipeline. In addition, the velocity of the CO2 flow in the pipeline can be controlled in the range of 0–5 m/s by a circulation pump. The opening and closing of the small leakage hole can be remotely controlled by an operator. Pressure sensors are located nearby the leakage hole in the experimental pipeline system to monitor the pressure change during the CO2 leakage. Moreover, thirteen thermocouples are used to measure temperatures of the CO2 flow inside the pipe and on the surface of the pipeline. The experiments carried out show the typical characteristics of the supercritical CO2 flow leaked from a small hole.

A laboratory scale experimental pipeline system is developed to investigate the leakage behavior of high pressure CO 2 . The 23‐m‐long experimental pipeline could provide an inner pressure varying from 0.1 to 10 MPa and a preset temperature within the range of 0 ∼ 50 °C to ensure a stable initial phase state for the leakage test. Experiments on CO 2 leakage with three initial inner pressures and four different nozzle orifice sizes were conducted using this system. The individual and combined effects of inner pressure and leakage orifice size on the main characteristic flow parameters of the pipeline, the structure of the leakage jet, and the temperature decrease of the plume were investigated. Based on the experimental results, limitations of the previous theoretical formula on mass loss rate were discussed. The maximum temperature decrease along the centerline of the far‐field plume by Joule‐Thomson effect was also studied. The new experimental test facility proves to be valuable in analyzing the hazardous leakage process of CO 2 from pipelines.

AbstractThe accidental release of supercritical CO2 is one of the main risks during the pipeline transportation for carbon capture and storage and enhanced oil recovery. The leakage of high pressure CO2 involves phase transition and complex changes of the pressure and temperature fields in the pipelines. A mathematical method for simulating the leakage flow through a crack in a pressurized CO2 pipeline is presented. The validated and accurate method has been employed to simulate the flow inside the pipe, while the leakage flow through the crack was calculated using a capillary tube assumption. In the numerical simulation, a real gas equation of state was employed instead of the ideal gas equation of state. Moreover, results of the flow through the crack and measurement data obtained from laboratory experiments of pressurized CO2 pipeline leakage are compared for the purpose of validation. The pipeline pressure and the leakage flow rates are analysed, which reveal the complex nature of the leakage flow of supercritical CO2 pipeline transport.

Abstract Oil, lubricating and cooling the sliding parts of the compressorcomponents exposed to friction, could prevent refrigerant gas leakage in compressor chamber of vapor compression air conditioning system. For air condition heat pump system in electric vehicles, no oil circulating routes and oil separator are used to drive oil from system to compressor, making oil retainedmore difficult to control. Oil accumulated in heat exchanger and expansion valve would enhance pressure drops and reduce heat transfer capacity, leading to decrease of entire heating performance in cold climate. In this paper, a newly designed air conditioning heat pump system with R134a and PAG46 oil is introduced firstly, and oil circulation experiments were conducted on a full-scale electric vehicle. Typical heat transfer characteristics and system performance parameter were recorded and analyzed subsequently under different compressor oil charge conditions, including excessive charge and insufficient charge. Oil circulation rates in system were also measured and exhibited an increasing trend with compressor oil charge mass. Furthermore, heating performances of the system under different oil circulation rate were compared by various heating capacity and pressure drops. Results showed that both excessive and insufficient charge might decrease heating performance, i.e., determination of suitable oil charge is quite important for air condition heat pump system.

Abstract This paper presents numerical studies of flame structure in a well-known nonpremixed H 2 /N 2 jet flame. A detailed kinetic mechanism is implemented to large eddy simulation approach with linear eddy model as subgrid closure method. The numerical techniques are validated against experimental data in temperature profiles, specie mass fractions and mixture fractions. Reaction rates are calculated at the flame base to investigate the dominant chemistry for a variety of conditions of fuel and coflow. The results show that the decrease of hydrogen concentration leads to chemical pathways changing at the flame base that is responsible for the autoignition. Oxygen content variation in the coflow affects the reaction rates but does not change the dominant chemistry. Furthermore, water addition to the coflow is found to enhance NO x formation by promoting radical production.

This study investigates the impact of vapor injection parameters and positions on the performance of a low-pressure ratio scroll compressor in electric vehicle thermal management systems under extremely low temperatures. The research combines experimental and simulation methods to analyze five injection ports designed at different positions. Key performance metrics, including mass flow rate, discharge temperature (Tdis), coefficient of performance (COP), compression work, and heating capacity (Qh) were evaluated under various conditions. A low-pressure ratio (scroll number N = 2) vapor injection scroll compressor was designed with an optimized injection port configuration. This design was rigorously validated through experimental results, confirming its efficacy. Notably, the findings reveal that the enhancement in Qh and COP is more pronounced in extremely low-temperature working conditions compared to non-injection conditions, with improvements of 10.7 % and 4.6 %, respectively. Compressor performance increases with increasing vapor injection pressure, and compressor speed and performance increment are more significant under low-temperature working conditions. Finally, an injection coefficient, denoted as k, is proposed to determine the optimal injection pressure for diverse discharge and suction pressures in cold climates. According to the experimental results, the value of k associated with the best heating COP ranges between 0.65 and 0.85.

AbstractExperiments at laboratory scales have been conducted to investigate the behaviour of the potential accidental release of highly pressurised CO2 including the rapid depressurization process and jet flow phenomena at different sizes of the leakage nozzle. The dry ice bank formed near the leakage nozzle is affected by the size of the leakage nozzle. The mass outflow rates for different sizes of leakage holes are obtained and compared with two typical accidental gas release mathematical models. The results show that the “hole model” has a better prediction than the “modified model” for small leakage holes. The experiments provide fundamental data for the CO2 supercritical-gas multiphase flows in the leakage process, which can be used to guide the development of the leakage detection technology and risk assessment for the pipeline transportation.