Abstract

This paper presents a life cycle analysis of a renewable cooling and heating system with thermal energy storage. The system mainly consists of a desiccant wheel cooling system, a photovoltaic/thermal-solar air collector (PV/T-SAC) and a thermal energy storage (TES) unit using phase change material (PCM). The life cycle cost (LCC) of the system was evaluated based on annual simulations by employing this system to provide cooling and heating for a case-study house. The influence of the electricity purchase price and sell price on the sizing of the PV/T-SAC, PCM TES unit, and desiccant wheel was investigated. The results showed that the optimal values of the PV/T-SAC length and the amount of PCM used which can minimize the LCC of the system, increased with the increase of the electricity sell and purchase prices. It was also found the LCC was more influenced by the electricity sell price than the purchase price.

Abstract

Nuclear energy currently accounts for a declining share of global electricity, but it is possible that rising concerns about global climate change and China’s ambitious nuclear program could reverse this trend. This paper attempts to assess the global future of nuclear power.

Abstract

In order to reveal the difference of collector performance between horizontal and vertical all glass vacuum tube water heaters, the parameters of effective heat collecting area, total solar radiation received by two water heaters under four typical days of the year (spring equinox, summer solstice, autumn equinox and winter solstice) are calculated theoretically. The actual heat collecting performance of the two water heaters is experimentally studied, and the reliability and accuracy of the theoretical analysis are verified. Finally, using FLUENT simulation software to simulate the heat collecting process of two kinds of water heaters. The reason for the difference of collector performance between the two water heaters is explained from the aspect of flow and heat transfer inside the water heater. The results show that only in summer, the collector performance of horizontal tube water heater has advantages. In spring, autumn and winter, the heat collection performance of vertical drain water heater is better.

Abstract

Most official energy forecasts regard major energy efficiency improvements as a key means of reducing energy use and associated greenhouse gases. This paper examines past and current energy efficiency improvements in various sectors and concludes that absolute energy reductions are very difficult to achieve in a growth-oriented global economy with continued population rise.

Abstract

Biodiesel has been considered as one of the feasible attempts to replace the fossil fuels. Alcohols always played a role as the additives to improve the certain properties of biodiesel. In this work, the thermal conductivity in the liquid phase of binary mixtures of methyl laurate usually the significant biodiesel component with three higher alcohols (1-propanol, 1- butanol and 1-pentanol) was measured with the teamperature ranging within 287 K to 358 K at atmospheric pressure. The total standard uncertainty of the experimental results was estimated to be less than 2 % and the repeatability was better than ± 0.5 %. The thermal conductivity data of binary mixtures were fitted as a function of temperature, and the average absolute relative deviation and the maximum absolute relative deviation between the experimental data and calculated results were 0.08 % and 0.23 % for methyl laurate/1-propanol, 0.09 % and 0.32 % for methyl laurate/1-butanol, 0.10 % and 0.31 % for methyl laurate/1-pentanol, respectively.

Abstract

For all-glass vacuum tube solar water heater, which integrates heat collection and storage, night heat loss affects its continuous and stable energy supply for users. For this reason, taking a set of 30 all-glass vacuum tube solar water heaters with specifications of Φ58 mm×1800 mm as the research object, the temperature changes of 20:00-07:00 water heater storage tank and vacuum tube within 10 days were experimentally studied, and the night heat loss of each part of the water heater was analyzed. In addition, a three-dimensional unsteady numerical model of allglass vacuum tube solar water heater was established, and the flow and heat transfer characteristics of the water heater during night heat dissipation were analyzed. The results show that among all kinds of heat loss of water heater, the radiation heat loss of vacuum tube is the largest, accounting for 57.8% of the total heat loss of water heater. The convective heat loss of hot water storage tank accounts for 32.1%, that of vacuum tube accounts for 3.7%, and that of other heat loss accounts for 6.4%. With the development of heat dissipation, temperature stratification in water heater becomes more and more obvious, fluid flow becomes slower and slower, and the static stagnation area in vacuum tube expands gradually from bottom to top.

Abstract

The main relationships required for describing phenomena occur in proton conducting Solid Oxide Fuel Cells are presented. The relationships are segregated according their influence on the specific fuel cell features. A sensitivity analysis of the chosen parameters and validation against the experimental data are presented. One missing relationship is identified: electronic conductivity of proton conductivity of solid electrolyte. Future activities are proposed.

Abstract

This paper presents a Large Eddy Simulation (LES) study of the effect of low temperature chemistry on the structure and propagation of n-heptane/air turbulent premixed flame with transport Probability Density Function (t-PDF) model based on the Eulerian Stochastic Fields (ESF) method. The computation process is accelerated by conjugating ESF method with Chemistry Coordinate Mapping (CCM) approach. Initial n-heptane/air mixtures at an equivalence ratio of 0.6, a constant pressure of 1 bar and temperature of 600 K, 650 K and 700 K in a new RATS burner configuration are considered. The studied cases cover three regimes of combustion, a Chemical Frozen (CF) regime, a transition (TRA) regime and a Low Temperature Ignition (LTI) regime. The results showed that low temperature chemistry of n-heptane has a significant effect on the enhancement of turbulent flame speed. Also, CO emission widely exists in post flame zone in CF condition, whereas, it is quickly oxidized in reaction zone under LTI condition.

Abstract

As an essential part of the energy system, the modern power system is a high-dimensional, hybrid nonlinear differential dynamic system, which is considered as a typical cyber-physical system(CPS). The time delay of the advanced information system is a significant concern in the stability analysis of cyber-physical power system (CPPS). However, the time delayed stability of power systems under distributed control has not been studied from a CPS perspective yet. In this regard, we introduce a dynamic cyber-physical power system model based on the time-delayed differential algebraic equation (TDAE). To analyze the time-delayed stability of CPPS, a critical eigenvalue tracking method for solving the time-delay margin of CPPS based on Rekasius substitution is proposed. Case studies illustrate the validity of the proposed method.

Abstract

In this work, numerical simulation was carried out to study the injection and mixing of ammonia solution spray in the exhaust pipe of diesel engines. The ammonia solution was injected into the hot gas of 623 K. The spray was vaporized into gas and mixed with the hot exhaust gas and together the mixture was transported in the exhaust gas pipe downstream where a selective catalytic reduction (SCR) system was implemented to convert NOx to H2O and N2. The effects of exhaust pipe geometry and gravity on the droplet evolution and vapor mass fraction were investigated. The results show that the influence of gravity is negligible, while the exhaust pipe geometry has a great impact on the vapor distribution. In straight pipe case the NOx reduction is only achievable in a small area of the catalyzer, which is in good agreement with the experiments. Analysis of the velocity field and streamlines shows that the ammonia vapor is blocked by a recirculation zone; as a result, the vapor mass fraction will be centralized into a small zone because radial component of vapor velocity is too slow to penetrate into the center of main flow. In addition, the spray droplet size distribution indicates that a certain amount of ammonia enters into catalyzer as liquid phase with medium diameter around 19 and 17 m in straight and bending pipe, which further deteriorates the catalytic efficiency. The results provide a guidance for the design of ammonia injector and the exhaust pipe geometry.