自然通风建筑内空气流动和污染物扩散的数值模拟

数值模拟了单体自然通风建筑模型内的空气流动和污染物扩散,考察了紊流施密特数Sct对污染物模拟值的影响。结果表明,选取的3种紊流模型对时均流速和紊动能的模拟值和风洞试验值基本一致,标准k-ε模型与realizable k-ε模型模拟的流场较相似,其浓度场结果也基本相同,当Sct为0.8～1.0时,模拟值和试验值吻合得最好。由于RNG k-ε模型对地面污染源附近的时均流动模拟不准确,导致其浓度模拟值和试验值相差较大,因此,选取合理的Sct时,应基于准确的流动模拟,而不能仅考察浓度模拟值和试验值的吻合程度。     

Energy performance of a hybrid space-cooling system in an office building using SSPCM thermal storage and night ventilation

Thermal performance of a hybrid space-cooling system with night ventilation and thermal storage using shape-stabilized phase change material (SSPCM) is investigated numerically. A south-facing room of an office building in Beijing is analyzed, which includes SSPCM plates as the inner linings of walls and the ceiling. Natural cool energy is charged to SSPCM plates by night ventilation with air change per hour (ACH) of 40 h⁻¹ and is discharged to room environment during daytime. Additional cool-supply is provided by an active system during office hours (8:00-18:00) necessary to keep the maximum indoor air temperature below 28 °C. Unsteady simulation is carried out using a verified enthalpy model, with a time period covering the whole summer season. The results indicate that the thermal-storage effect of SSPCM plates combined with night ventilation could improve the indoor thermal-comfort level and save 76% of daytime cooling energy consumption (compared with the case without SSPCM and night ventilation) in summer in Beijing. The electrical COPs of night ventilation (the reduced cooling energy divided by fan power) are 7.5 and 6.5 for cases with and without SSPCM, respectively.     

Improvement of an existing solar powered absorption cooling system by means of dynamic simulation and experimental diagnosis

This paper focuses on the validation of a dynamic simulation model used to describe the performance of an existing solar cooling installation located in Zaragoza (Spain). The dynamic model has been developed under the simulation environment TRNSYS. The aim of this simulation model is to dispose of a tool in order to use it to evaluate different energy improvement actions in a real solar cooling installation. This solar cooling installation has been monitored and analyzed since 2007. The COP of this experimental solar cooling system presents a great influence from its heat rejection sink, a dry cooling tower. Once the model was validated with the experimental data obtained from the real installation, it was used to predict the chiller performance with a new geothermal sink, which started to operate in 2009. The present work describes the design and validation model process, as well as the comparison between the model results and the monitoring ones with the geothermal heat rejection system.     

Optimal operation conditions for a single-stage heat transformer by means of an artificial neural network inverse

Analysis based on first and second law of thermodynamics together with direct and artificial neural networks inverse (ANNi) have been used to develop a methodology to decrease the total irreversibility of an experimental single-stage heat transformer. With the proposed methodology it is possible to calculate the optimal input parameters that should be used in order to operate the heat transformer with the lower irreversibilities. Mathematical validation of ANNi was carried out together with the comparison between the total cycle irreversibility (I_cycle) obtained thermodynamically and the I_cycle determined by using the ANNi. The results showed a mean discrepancy of 0.9% of the I_cycle values. The proposed new methodology can be very useful to control on-line the performance of a single-state heat transformer obtaining lower I_cycle values.     

Comparison of heating and natural ventilation in a solar house induced by two roof solar collectors

In this paper, two kinds of roof solar collectors (RSCs), namely, the single pass RSC, and the double pass RSC are analyzed and compared. The double pass roof solar collector, which is configured by integrating a double pass solar air collector with the building roof, can be operated more efficiently for space heating in winter, and for natural ventilation in other seasons. To evaluate the effects of two RSCs for both space heating and natural ventilation, a single traditional Chinese style house, on which the two RSCs will be mounted respectively, is developed. Through comparison, it is found that the instantaneous efficiency of solar heat collecting for the double pass RSC is higher than that of the single pass one by 10% on average, and natural ventilation air mass flow rate contributed by natural ventilation for the double pass RSC can be improved to a great extent for most cases, indicating that double pass RSC is superior to the single pass one from the points of view of both space heating and natural ventilation. The double pass RSC is therefore more potential for improving indoor thermal environment and energy saving of buildings.     

Modelling and performance study of a continuous adsorption refrigeration system driven by parabolic trough solar collector

This article suggests a numerical study of a continuous adsorption refrigeration system consisting of two adsorbent beds and powered by parabolic trough solar collector (PTC). Activated carbon as adsorbent and ammonia as refrigerant are selected. A predictive model accounting for heat balance in the solar collector components and instantaneous heat and mass transfer in adsorbent bed is presented. The validity of the theoretical model has been tested by comparison with experimental data of the temperature evolution within the adsorber during isosteric heating phase. A good agreement is obtained. The system performance is assessed in terms of specific cooling power (SCP), refrigeration cycle COP (COP_cycle) and solar coefficient of performance (COP_s), which were evaluated by a cycle simulation computer program. The temperature, pressure and adsorbed mass profiles in the two adsorbers have been shown. The influences of some important operating and design parameters on the system performance have been analyzed.The study has put in evidence the ability of such a system to achieve a promising performance and to overcome the intermittence of the adsorption refrigeration systems driven by solar energy. Under the climatic conditions of daily solar radiation being about 14 MJ per 0.8 m² (17.5 MJ/m²) and operating conditions of evaporating temperature, T_ev = 0 °C, condensing temperature, T_con = 30 °C and heat source temperature of 100 °C, the results indicate that the system could achieve a SCP of the order of 104 W/kg, a refrigeration cycle COP of 0.43, and it could produce a daily useful cooling of 2515 kJ per 0.8 m² of collector area, while its gross solar COP could reach 0.18.     

Development of a combined system based on a PEMFC and hydrogen storage under different conditions equipped with an ejector cooling system

In the current work, thermodynamic examination for cogeneration of electricity and cooling based on a polymer exchange membrane (PEM) fuel cell was carried out. To the waste energy in the fuel cell, an absorption refrigeration unit is employed in two modes with ejector and without ejector. This system includes a PEM-FC, an absorption refrigeration unit, a hydrogen storage tank, an ejector, and an air compressor. The produced thermal energy in the fuel cell is received entirely by a working fluid and is given to the absorption chiller generator. The system simulation was carried out from two perspectives of energy and fuel saving. Findings showed that the energy efficiency of the combined cooling and power (CCP) unit and the CCP system equipped with the ejector (CCP-E) was 63.72% and 78.33%, respectively. It indicated that adding the ejector to the system increases the energy efficiency of the system by 23%. The fuel economy percentages of the CCP system and CCP-E were 44.43% and 45.9%, respectively. The results also showed that adding the ejector in the refrigeration system increases the system performance by up to 44%. The presence of the ejector causes the working fluid flow in the evaporator to increase with the suction of the secondary flow, and the cooling capacity increases significantly. Moreover, with increasing generator and evaporator pressure, the suction ratio of the cooling system equipped with the ejector decreases and increases, respectively.     

Performance and population analysis of hydrogen production from sugarcane juice by non-sterile continuous stirred tank reactor augmented with Clostridium butyricum

Non-sterile operation of continuous stirred tank reactor (CSTR) augmented with Clostridium butyricum and fed with sugarcane juice was studied at various hydraulic retention time (HRT). The maximum hydrogen production rate and yield of 3.38 mmol H₂/L/h and 1.0 mol H₂/mol hexose consumed, respectively, were achieved at HRT 4 h. The relationship of the augmented microorganism and normal flora in the fermentation system under non-sterile condition were analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Initially, at HRT 36 h, other species related to Lactobacillus harbinensis and Klebseilla pneumoniae were present as a major group in the reactor. When HRT was decreased to 12, 6 and 4 h, C. butyricum was present with a competition between L. harbinensis and K. pneumoniae. Results indicated that augmented C. butyricum could compete with contaminated microorganisms during non-sterile operation at low HRT (12-4 h) with the support of normal flora (K. pneumoniae).     

Improving ambient wind environments of a cross-flow wind turbine near a structure by using an Inlet Guide Structure and a Flow Deflector

Introductions Denmark was the first country to use the wind for electricity generation practically. The windmill was developed by the Dane Poul La Cour who incorporates the aerodynamic design principle into the blades of the windmill in 1890[1,2]. After that, many countries developed the windmill for the electricity generation. But the use of cheaper fossil fuel took the lead in the electricity generation. Many wind electric generations were far from success in business. In 1970’s, The O…     

Phosphorous emitter etch back and bulk hydrogenation by means of an ECR-hydrogen plasma applied to form a selective emitter structure on mc-Si

In this paper, we study the effect of hydrogen-electron cyclotron resonance plasma (ECR plasma) on the phosphorous-doped emitter of a solar cell based on multicrystalline silicon (POLIX^®). The purpose of this experiment is to realise a selective emitter structure, using the front metal contacts as a mask. We show that hydrogen plasma etches the surface of the emitter away, and simultaneously diffuses into the silicon and increase the bulk lifetime. Both minority carrier lifetime and etch rate depend on the grain orientation. Hydrogen diffusion is hindered by the high phosphorous concentration of the emitter, as shown on the SIMS profiles. Besides, SIMS profiles are revealing an anomalous behaviour of phosphorous, which diffuses into the silicon at temperatures as low as 350°C on (1 0 0) oriented grains.     

Investigations of Interaction of the Main Flow with Root and Tip Leakage Flows in an Axial Turbine Stage by Means of a Source／Sink Approach for a 3D Navier—Stokes Solver

IntroductionFundamental stUdies of losses in tUrbomachinery in-dicate that, besides giving rise to losses of work, leakageflows contribute to the overall creation of entropy andkinetic encrgy losses. Some entropy is created in thelabyrinth seals and in passages between the fixed androtating pats of turbomachinery. CFD computations inlabyrinth seal geometries enable the evaluation of theentropy ereation PrOCesses there. CFD-based analysis canm1nindze the mass fiow rates of the tip leakage a…