Abstract

It is difficult to calculate the theoretical line loss of low-voltage distribution transformer area and the evaluation index of transformer line loss is extensive. In this paper, a reasonable interval calculation model of line loss is established based on the convolutional neural network based on the data of electricity information acquisition system. The model can estimate the reasonable line loss interval according to the operation data of different transformers. On this basis, the line loss evaluation system is established and the rectification plan of abnormal line loss is formed. The method in this paper can improve the quality and efficiency of line loss lean management and produce certain effect for saving electric energy and improving economic benefit of power supply.

Abstract

In order to study the influence of expander and internal heat exchanger on the performance of the CO2 trans-critical cycle cascade refrigeration system, the effects of evaporation temperature (Te) on discharge temperature of the compressor, recovery power of expander, input power of compressor, COP , exergy efficiency and exergy destruction of the system, and exergy destruction ratio of each component were carried out by thermodynamic analysis. The results show that expander can effectively decrease the optimum condensation temperature of low-temperature cycle (LTC) and optimum high pressure, while high-temperature internal heat exchanger can slightly reduce the optimum condensation temperature and optimum high pressure of LTC and significantly reduce COP and recovery work of the expander. The COP of CE, when R14 is used as refrigerant, is 89.7% ~ 91.4% of that of R23 / R22CT. The biggest exergy destruction component is the gas cooler. The results provide a solution to improve the efficiency of the CO2 trans-critical cascade refrigeration system.

Abstract

The compactness and good air-side heat exchange of the microchannel heat exchanger make it widely used in residential and automotive air conditioning systems. However, due to the different properties of refrigerant liquid and vapor, there is phase separation in the header and heat exchange tubes of the microchannel heat exchanger, resulting in uneven distribution of the refrigerant in the parallel microchannel tubes, the heat transfer area utilization rate is reduced, and the system performance is reduced. In addition, the presence of lubricants can also affect refrigerant distribution. The conclusion is that a small amount of lubricating oil will make the refrigerant distribution performance worse, and further adding lubricating oil will change the flow pattern, thereby improving the refrigerant distribution performance. This is because foam is formed after a large amount of oil is introduced to make the flow pattern more uniform. For any given lubricant content, at the same mass flow rate, as the quality increases, the distribution becomes worse because there is less liquid in the top pipe. In the case of the same inlet quality, as the mass flow increases, the high-momentum liquid can reach the top of the header, which is easy to be entrained by the top pipe, and the refrigerant distribution is better. However, although the lubricant improves the distribution of the refrigerant in the parallel microchannel tubes, it also significantly reduces the specific enthalpy difference of the working fluid, which is mainly due to its non-evaporative nature. Therefore, the influence of lubricating oil on the pressure drop and heat transfer characteristics of the microchannel heat exchanger after improving the refrigerant distribution is still an unresolved issue.

Abstract

The power consumption of pumps and fans is quite high in the transport systems, especially in data centers. Nearly 60% of the computer room air conditioning (CRAC) system’s energy consumption is consumed by pumps and fans in winter. In this paper, a synergy optimization method is proposed to save energy in heat transfer process. The heat transfer constraint equations of the heat transfer process are established, and taking the highest energy efficiency as the objective function, the synergistic relationship between the power consumption and temperature difference is derived analytically by using variation principle. A synergy operation factor is defined to guide the practical operation optimization of heat transfer process. The closer the synergy operation factor is to 1, the higher the system energy efficiency is. An experiment of a separated heat pipe system is carried out to verify the accuracy of the synergy optimization analysis.

Abstract

The two-phase loop thermosyphon (TPLT) is a high-efficiency heat transfer device which has been applied in many fields in recent years. The conventional flow models of a TPLT do not consider the particularity of the flow characteristics and cannot properly describe the refrigerant distribution under different working conditions. This paper tries to propose a new idea of the flow model which takes the variation of flow characteristics with the change of working conditions into consideration. A numerical simulation was conducted on a TPLT based on the proposed flow model. The change in heat transfer rate and the variation of refrigerant column height (driving force) in downcomer with increasing refrigerant charge were calculated to analyze the effect of filling ratio on the performance. The study in this paper could provide a reference for the design in practical application.

Abstract

With the rapid development of the low-rank coal chemistry industry, the production of semi-coke has ever been increasing. However, the semi-coke is difficult to burnout and the NOx generation during semi-coke combustion is high. Therefore, the co-combustion of semi-coke and bituminous coal in utility boiler is considered as a promising approach to realize the efficient utilization of the semi-coke. Here, the co-combustion features of bituminous coal and semi-coke blends were investigated in a 660 MW utility boiler. The results show that the NOx generation decreases firstly and then increases with the rises of the load and the fraction of semi-coke. The effects of load and blending ratio of semi-coke are both obvious on burnout behavior than those on NOx generation. With the rise of oxygen concentration, the NOx generation rises and the unburned carbon in fly ash decreases. The Na-bearing mineral are better-preserved with the higher oxygen concentration. The experimental results may provide guidance for the realization of the utilization of the semi-coke in the utility boiler.

Abstract

With the promotion and application of multi-energy integration and distributed generation technologies, integrated community energy system (ICES) has developed rapidly. However, some ICESs have weak links such as poor economy, low energy efficiency, which restrict the effective operation of ICES. To solve this problem, an optimal retrofit method for ICES is proposed in this paper, which includes capacity expansion of the existing equipment and investment of new types of equipment. The proposed method takes the minimum total cost as the objective and sets equipment capacity and operation constraints during the process of retrofit. What’s more, the economic index, primary energy efficiency and PV energy consumption rate are adopted to evaluate the effects of the retrofit. Finally, the effectiveness of this method is verified by the case study.

Abstract

In order to find out the relationship of the heat transfer and the dissociation of permafrost gas hydrate in porous media, this study has conducted a hydrate dissociation experiment below freezing point in a cuboid pressure vessel. The dependences of gas production and hydrate dissociation on the following heat fluxes are also analyzed through numerical simulation: the heat conducted across the boundary QB, the heat injected from the well Qinj, the sensible heat change of the deposit QS, the heat absorbed by hydrate dissociation QH, the latent heat of ice melting QI, and the unutilized heat QL. The results show that the dissociation process of frozen gas hydrate can be divided into three steps: ice melting, hydrate dissociation, and ice regeneration. The existence of solid ice shows strong inhibition effect on hydrate exploitation. QH mainly comes from Qinj, and the heat transferred across the boundary is the main component of QL. It implies that the heat injection is the dominating driving force for hydrate dissociation below freezing point.

Abstract

The lithium-ion battery system has strong coupling and nonlinear characteristics, bringing great challenges to its online failure prediction and life estimation. Several studies have shown the potential of deep learning methods on remaining useful life (RUL) prediction of lithium-ion batteries, these methods mostly use historical cycling data from beginning to the prediction point. However, long-term cycling data can be costly and difficult to obtain in practical applications. This article presents a data-driven algorithm using a combination of deep convolutional neural network (DCNN) and long short-term memory (LSTM) to predict the RUL of lithium batteries based on the data of the past 10 continuous cycles. Here the DCNN processes time-series data including capacity, temperature, and capacity difference at the same voltage during discharging, the LSTM is used to process the scalar data of each cycle including internal resistance, discharge time, and discharge capacity. The proposed network uses an open dataset with 124 batteries for training and validation. The generalization ability of the model for batteries under different charging/discharging strategies is also validated. The proposed DCNN-LSTM network demonstrates well performance on capturing the life changes of batteries with different life lengths and working conditions using limited historical cycling data with an average root mean square error of 5%.

Abstract

Chemical energy conversion has a great influence on the cold gas efficiency of coal gasification technology. In this paper, a three-step gasification technology with CO2 recycling is introduced and two external combustion schemes (CO-fueled chemical looping combustion and unconverted coke combustion) are compared. Results showed that the CO-fueled chemical looping combustion scheme has a higher cold gas efficiency of 90.1%, while cold gas efficiency of the unconverted coke combustion scheme is 88.4%. Before the water gas shift subprocess, the chemical energy conversion efficiency in the unconverted coke combustion scheme is 93.2%, which is 1.6 percentage points higher than that in the CO-fueled chemical looping combustion scheme. However, more chemical energy is consumed for CO2 regeneration in the unconverted coke combustion scheme, which results in chemical energy conversion efficiency decreases from 93.2% to 88.4%. Therefore, better energy matching between reactions can effectively improve the cold gas efficiency of the coal gasification technology. Besides, chemical energy consumption for CO2 regeneration should be reduced for gasification technology adopting CO2 as a gasifying agent.