• Energy Research

AbstractThe transportation of hydrogen is a weak link in the large‐scale development of the hydrogen energy industry. Injecting hydrogen into the natural gas pipeline network for transportation is an efficient way to achieve the large‐scale, long‐distance, and low‐cost transportation of hydrogen. Hydrogen can lead to hydrogen embrittlement in natural gas pipelines and cause safety incidents if hydrogen and natural gas are not mixed uniformly. Therefore, it is necessary to study the blending process and blending uniformity of hydrogen and natural gas. In this study, a three‐dimensional model of the hydrogen‐injected natural gas pipeline was constructed. The effects of hydrogen injection inlet and turbulator configuration on the mixing process of hydrogen and natural gas were investigated using a computational fluid dynamics approach. The results show that increasing the number of hydrogen injection inlets shortens the distance L98% of uniform mixing of hydrogen and natural gas. Increasing the radial distance r from the initial hydrogen mixing positions to the center of the pipeline will shorten the distance for uniform gas mixing in the pipeline. The addition of turbulator configurations in the pipeline significantly reduces the distance to uniform gas mixing. Changing the distance Lturb from the turbulator to the initial mixing position further shortens the distance between hydrogen and natural gas mixing uniformly. The results of this study provide a reference for the structural design of the hydrogen–natural gas mixing pipeline and the gas distribution state during the mixing process.

AbstractVapor‐compression refrigeration systems are widely used in refrigeration equipment. Theoretically, the process is typically divided into two isobaric processes: an adiabatic isentropic compression process and adiabatic isentropic throttling process. The refrigeration compressor is the main energy‐consuming component in vapor‐compression refrigeration systems. However, this device has a large energy loss and low overall efficiency in the adiabatic isentropic compression process. In this study, a modified vapor‐compression refrigeration cycle with an isothermal piston is proposed to realize near‐isothermal compression of a refrigerator to significantly reduce the energy loss in the compression process and improve the system performance. A real‐gas compression process model is established, and the heat transfer index Hex is set. By changing the heat transfer index Hex, the performances of the vapor‐compression refrigeration system under ideal and real compression conditions are compared and analyzed. Compared with a traditional vapor‐compression refrigeration system, the coefficient of performance of the compressor with an isothermal compression process is increased by approximately 17%. The results also demonstrate that the lower the evaporation temperature Te and higher the condensation temperature Tc, the greater the optimization effect of the isothermal compression.

Hydrogen is a clean energy source with high combustion calorific value and nonpolluting products. However, the high transportation costs hinder the development of hydrogen energy. A high flow rate, long-distance, and high-efficiency delivery can be realized by mixing natural gas with hydrogen, which significantly reduces the transportation cost. However, high concentrations of hydrogen aggregates risks hydrogen embrittlement in the natural-gas pipeline network and leakage. An injector is a highly efficient gas-blending device. Therefore, analyzing and optimizing the multiple structural parameters of the injector are necessary for improving the mixing efficiency and homogeneity of hydrogen and natural gas. First, eight structural parameters of the injector were selected and four levels were considered for each parameter. Subsequently, an orthogonal experiment table was constructed using the orthogonal experimental method. Finally, a modeling simulation was performed using Fluent simulation software. The results showed that the injectors can significantly shorten the distance of mixing uniformity and achieve faster mixing uniformity. The diameter of the mixing pipe was found to be the main factor affecting the overall score. Computational Fluid Dynamic-20 (CFD-20) had the highest overall score. The LCOV10% for CFD-20 improved by 21.5% over that of the initial model, and the composite score improved from 0.93 to 0.98. The results can provide a reference for the design of injector parameters and installation of metering equipment.

Reducing carbon emissions is an urgent problem around the world while facing the energy and environmental crises. Whatever progress has been made in renewable energy research, efforts made to energy-saving technology is always necessary. The energy consumption from fluid power systems of industrial processes is considerable, especially for pneumatic systems. A novel isothermal compression method was proposed to lower the energy consumption of compressors. A porous medium was introduced to compose an isothermal piston. The porous medium was located beneath a conventional piston, and gradually immerged into the liquid during compression. The compression heat was absorbed by the porous medium, and finally conducted with the liquid at the chamber bottom. The heat transfer can be significantly enhanced due to the large surface area of the porous medium. As the liquid has a large heat capacity, the liquid temperature can maintain constant through circulation outside. This create near-isothermal compression, which minimizes energy loss in the form of heat, which cannot be recovered. There will be mass loss of the air due to dissolution and leakage. Therefore, the dissolution and leakage amount of gas are compensated for in this method. Gas is dissolved into liquid with the pressure increasing, which leads to mass loss of the gas. With a pressure ratio of 4:1 and a rotational speed of 100 rpm, the isothermal piston decreased the energy consumption by 45% over the conventional reciprocation piston. This gain was accomplished by increasing the heat transfer during the gas compression by increasing the surface area to volume ratio in the compression chamber. Frictional forces between the porous medium and liquid was presented. Work to overcome the frictional forces is negligible (0.21% of the total compression work) under the current operating condition.

The State of Health (SOH) of lithium-ion batteries is a critical parameter that characterizes their actual lifespan, and its accurate assessment ensures the safe and reliable operation of batteries. However, in practical applications, SOH cannot be directly measured. To further improve the accuracy of SOH estimation for lithium-ion batteries, this study employs the Particle Swarm Optimization (PSO) algorithm to search for the optimal hyperparameters of the Bidirectional Gated Recurrent Unit (Bi GRU) neural network, enabling the prediction of time series information. Additionally, Attention Mechanism (AM) is integrated to allocate weights to the prediction results, resulting in the SOH prediction for lithium-ion batteries. The propose model is validated using the B0005 battery from the NASA lithium battery dataset. Experimental results demonstrate that, compared to the Bi GRU-Attention and Bi GRU models, the propose model reduces the Root Mean Square Error (RMSE) by 52.34% and 66.88%, respectively.

An isothermal piston is a device that can achieve near-isothermal compression by enhancing the heat transfer area with a porous media. However, flow resistance between the porous media and the liquid is introduced, which cannot be neglected at a high operational speed. Thus, the influence of rotational speed on the isothermal piston compression system is analyzed in this study. A flow resistance mathematical model is established based on the face-centered cubic structure hypothesis. The energy conservation rate and efficiency of the isothermal piston are defined. The effect of rotational speed on resistance is discussed, and a comprehensive energy conservation performance assessment of the isothermal piston is analyzed. The results show that the increasing rate of the resistance work increases significantly proportional to the rotational speed, and the proportion of resistance work in the total work increases gradually and sharply. The total work including compression and resistance cannot be larger than the compression work under adiabatic conditions. The maximum rotational speed is 650 rpm.

Air is usually compressed adiabatically in the compressor. As the operating speed of compressors can be several thousand rpm, heat generated during compression cannot be sufficiently transmitted to the environment in such a short time. It is for this reason that compressor efficiency is limited. Isothermal compression could be an alternative choice applied on industrial compressor and compressed air energy storage (CAES). This paper proposed a new kind of piston to perform isothermal compression. Surface area of such isothermal piston structure is larger. A certain amount of fluid at the chamber bottom absorbs the heat from the isothermal piston. Heat transfer between piston and fluid during compression is investigated. Air pressure is measured to validate the effectiveness of this proposed piston structure in heat transfer. Compression work of the proposed isothermal piston and conventional one is compared. One issue of this comparison is that air-liquid dissolution can affect the pressure and compression work. The influence of dissolution is quantified with Henry’s Law. Quantitative analysis is performed to determine that heat transfer is the dominant factor affecting the pressure and compression work. Some simple experiments are described in this paper, which shed light on that heat transfer could be significantly improved adopting this proposed isothermal piston.