Abstract

A super-long flexible heat pipe (SFHP) with the total length up to 32m is experimentally tested in this work to evaluate its potential for geothermal utilization in Nanjing, China. Its evaporator section, fabricated by metal bellows, is 30m long and vertically installed in a ground drilling. The temperature response and heat transfer characteristics of SFHP were investigated. The results show that the underground temperature at the depth larger than 10m is stable in the range of 17-18℃ throughout the year. SFHP starts to operate upon the temperature at the wall of condensation section falls below 15℃. The heat transfer power of SFHP increases with decreasing temperature of cooling water. The variation of cooling water flow rate has an insignificant influence on the heat transfer power of SFHP, however its effect on the total thermal resistance is remarkable. In tests, the maximum heat transfer power is about 168.3W when the flow rate of cooling water is controlled at 600ml/min and the average temperature at 8.5℃. In addition, the higher the flow rate of cooling water, the shorter the start-up time.

Abstract

Most of the current energy efficiency models focus on the primary-secondary-useful energy conversion chain of energy system, however, ignore the chain of useful energy to final service. In fact, what people need is not energy itself, but the energy service it provides. Therefore, this paper extends the analysis boundary of energy efficiency model to final service, to reveal the evolution and the driving factors of energy service efficiency. Firstly, we divide the energy system into six stages to conduct societal exergy analysis, which are energy source, transformation, end-use conversion device, useful energy, passive system and final service. And the whole scenario of energy flow and conversion is mapped in Sankey diagrams. Then, we use LMDI (Logarithmic mean Divisia Index) decomposition method to comprehensively understand factors driving the change of energy service efficiency. Efficiency and structure factors of each stage are incorporated into a novel LMDI decomposition identity to quantify their relative contributions. A case study of China during 2005-2015 reveals that: a) the energy service efficiency in China, from energy source to final service, has increased from 3.7% in 2005, to 4.1% in 2010, and 4.8% in 2015. It shows an increasing trend, but still at a very low level with huge losses. b) The efficiency improvement of each stage, especially that of end-use conversion device and the power and heat generation sector, makes the greatest contribution to the increase of overall energy service efficiency. c) There are large passive losses in passive systems, especially in the passive system of building. The energy efficiency improvement of passive systems has big potential and deserves more attention in the future.

Abstract

In order to meet the demand of clean and efficient energy conversion technology, a novel combined cooling, heating and power (CCHP) system fueled by biomass is proposed. This system is consists of biomass gasification unit, solid oxide fuel cell, IC engine unit and absorption refrigeration chiller. Thermodynamic model of the CCHP system are developed and then parameter analysis is adopted to optimize the performance of this system. The effect of air equivalent ratio (ER), steam biomass ratio (S/B) and the fuel utilization factor of SOFC (μ) on the performance of the entire system are studied. The results show that increase of S/B and μ will prompt the electrical efficiency, while the increase of ER has a negative effect on electrical efficiency. The exergy analysis shows that the exergy destruction of biomass gasification process and engine is larger, which is 454.5 kW and 207.2 kW respectively. On the contrary, exergy destruction of SOFC and absorption refrigeration chiller are 15.9 kW and 52.8 kW, respectively.

Abstract

Zero liquid discharge (ZLD) of flue gas desulfurization (FGD) wastewater from coal-fired power plants (CFPPs) provides an approach to comply with the increasingly stringent environmental regulations. However, traditional ZLD systems are commonly subject to high operating cost. A solar-auxiliary steam hybrid driven ZLD system is thereby proposed in the present work. Thermodynamic and economic analysis models were established. A case study in a 600 MW CFPP was carried out under the meteorological conditions of a typical city in China. It is found that the lowest levelized cost of wastewater treatment (LCOW) obtained was approximately 10.1 $/t, and the cost could be reduced by marginally 8.0% by utilizing hybrid heat sources. A parametric study was further performed to investigate the impact of key variables on the LCOW, and indicated that auxiliary steam cost had the largest impact.

Abstract

This paper aims to analyze the impact of recycled materials on energy reduction and clean energy transition of buildings. The life cycle energy of building using virgin materials is compared with that of building using recycled materials, and the energy savings due to recycled materials is calculated. Also, the impact of recycled materials on clean energy transition is verified by calculating the module area of the photovoltaic panel achieving the same amount of energy savings. As results of a case study, replacing virgin to recycled materials reduced 10% of life cycle energy. It means that the use of recycled materials can reduce 10% of module area of PV system for achieving clean energy transition. Recycled materials should be considered for fundamental energy reduction and effective clean energy transition.

Abstract

To ensure safety, performance and warranty of an electric vehicle, it is crucial to monitor the evolution of remaining capacity of NMC lithium-ion batteries. Estimators for the remaining capacity are often based on costly, complex and time consuming testing procedures under laboratory measurement conditions. Other methods like incremental capacity analysis require various load sequences at very low constant current rates. This is also not practical for real battery electric vehicle operation due to high and dynamic discharging rates caused by the customers individual driving behavior as well as high recharging rates.
To overcome these problems, we present a data-driven approach for battery capacity estimation in combination with incremental capacity analysis. The missing load sequences for the incremental capacity analysis are presented by the output of a recurrent neural network which describes the battery electric behavior from real in-vehicle data. Results show RMSE deviations of 1.77% to correctly estimate the remaining capacity over the whole vehicle life. This high accuracy is comparable to state of the art laboratory battery testing, but without the need of expensive experimental data. Instead only operational vehicle data can be used.

Abstract

Cleaner processes to retrieve energy from a waste are urgently needed. To improve the efficiency and hydrogen enrichment, water was used as free radical source in corona plasma discharge for syngas conversion and tar reduction. In oxygen-free environment, anthracene, as a representative in tar, was effectively converted to H2. The anthracene conversion rate is 78.6% in 100 s reaction and 3.5% H2 product was detected. This highly advantageous technology demonstrates that it is feasible to convert macromolecular substances into small molecular gases like H2, a syngas composition, without the by-products of tar produced in the municipal solid waste gasification process at much low temperature.

Abstract

In order to better match the working conditions of the organic Rankine cycle (ORC) system for vehicle engine waste heat recovery, this paper aims to study the performance of the free piston expander-linear generator (FPE-LG) under variable operation conditions using a simulation model based on Matlab/Simulink software. Firstly, the effect of the mass of the free piston assembly (FPA) and internal resistance of the linear generator (LG) on the electromagnetic force, motion characteristics and output performance are discussed and analyzed. Secondly, the effect of the changing intake pressure and exhaust back pressure on the performance of the FPE-LG are investigated. The velocity reaches the maximum of 3.12 m/s when the intake pressure, operation frequency, external load resistance, mass of the FPA and the internal resistance of LG are 3 bar, 5 Hz, 9 Ω, 0.59 kg and 14.7 Ω, respectively. This study can provide a useful guidance for the application of the FPE-LG in the actual ORC system.

Abstract

Organic Rankine cycle (ORC) is an important technology to convert low and medium temperature heat source into work. The irreversible loss results in the fact that the actual performance of the ORC system is much lower than the theoretical value. Pipeline is an indispensable part of the ORC system to connect system components. In this work, the effect of pipeline pressure loss on ORC system power output and thermal efficiency is studied experimentally. The results show that the pressure losses of pipeline reduce the ORC system power output, which is 27.04% lower than the theoretical value under experimental conditions. Pipeline pressure losses also reduce the thermal efficiency of the ORC system, which is 33.04% lower than the theoretical value. Under the same pressure losses, the effect of the pipeline connecting expander and condenser on the ORC system power output and thermal efficiency is about 2.47 times larger than that of the pipeline connecting evaporator and expander.

Abstract

The high-altitude environment with a low atmospheric pressure and low air density would significantly affect the cooling performance, which can further affect the heat dissipation of driving system. This work studies the impacts of the high-altitude environment on cooling the driving system of high altitude aircrafts. A 3-D CFD model was developed. Based on simulations, the influences of the altitude, solar radiation and the heat load on the operating temperature of the driving system were analyzed. The cooling performances on the ground and at high altitudes were also compared. The results showed with the increase of altitude, the maximum temperature of driving system decreased firstly until 4km and then increased. And a large deviation (12oC) would occur if the solar radiation was not considered for high altitude aircrafts.