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Thermal performance of a lightweight building with phase change material under a humid subtropical climate

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能源与人工环境(英文)

能源与人工环境(英文) 2022年第1期3卷 73-85页

作者： Xiaoqin Sun Ziyang Zhu Siyuan Fan Jie Li School of Energy and Power Engineering Changsha University of Science&TechnologyChangshaHunan 410004PR China

The use of phase change materials(PCMs)in building enclosures is an efficient way to reduce the heat gain and/or loss in summer and winter.It was evident that the thermal performance of buildings with PCMs was affected by the outdoor air temperature significantly.However,the influence of humidity,which was serious in the humid subtropical climate was unclear.To explore the effect of PCMs under a humid subtropical climate,the thermal performance of a lightweight building outfitted with PCMs with a melting temperature of 25°C was investigated.The actual outdoor air temperature with a humidity of 40-90 RH%and wind velocity of 2-6 m/s blowing from the east,west,south,and north was assumed for the performance assessment.A simulated model was developed using EnergyPlus and verified against experimental data.The energy savings by using PCMs was reduced from 3.9%to 2.6%when the outdoor humidity increased from 40 to 90 RH%in summer.However,the savings was not obvious in winter.Annual energy savings decreased from 1.64%to 1.32%with humidity increasing from 40 to 90 RH%.For annual condition,the average energy savings was reduced from 1.43%to 0.92%when the wind speed increased from 2 m/s to 6 m/s.From an economic point of view,the investment payback period was less than 10 years when the PCM price was lower than 18.0 Yuan/kg.

关键词： Phase change materials Lightweight building Relative humidity air velocity Energy use intensity Economic analysis

Effect of Drying air velocity on Drying Kinetics of Tomato Slices in a Forced-Convective Solar Tunnel Dryer

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Journal of Sustainable Bioenergy Systems 2019年第2期9卷 64-78页

作者： Mamouda Moussa Na Abou Saidou Madougou Makinta Boukar Energy-Environment-Development Niger(ENDA Energy Niger) NiameyNiger Laboratoire d’Energetique d’Electroniqued’Electrotechniqued’Automatique et d’Informatique Industrielle(LEEII)Universite Abdou MoumouniNiameyNiger

The objective of this work is to analyse the extent to which a change in the drying air velocity may affect the drying kinetics of tomato in a forced-convective solar tunnel dryer. 2 m?s?1 (V1) and 3 m?s?1 (V2) air speeds were applied in similar drying air temperature and humidity conditions. Main drying constants calculated included the drying rate, the drying time and the effective water diffusivity based on the derivative form of the Fick’s second law of diffusion. Henderson and Pabis Model and Page Model were used to describe the drying kinetics of tomato. We found that solar drying of tomato occurred in both constant and falling-rate phases. The Page Model appeared to give a better description of tomato drying in a forced-convective solar tunnel dryer. At t = 800 min, the drying rate was approximately 0.0023 kg of water/kg dry matter when drying air velocity was at 2 m/s. At the same moment, the drying rate was higher than 0.0032 kg of water/kg dry matter when the drying air velocity was 3 m/s. As per the effective water diffusivity, its values changed from 2.918E?09 m2?s?1 to 3.921E?09 m2?s?1 when drying air velocity was at 2 and 3 m?s?1 respectively, which is equivalent to a 25% increase. The experimentations were conducted in Niamey, on the 1st and 5th of January 2019 for V2 and V1 respectively. For both two experiments, the starting time was 9:30 local time.

关键词： Solar Dryer Tomato air velocity Modeling Diffusivity

Flow, thermal, and vibration analysis using three dimensional finite element analysis for a flux reversal generator

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Frontiers in Energy 2016年第4期10卷 424-440页

作者： B. VIDHYA K. N. SRINIVAS 1. Department of Electrical and Electronics Engineering B. S. Abdur Rahman University Chennai 600048 India

This paper presents the simulation of major mechanical properties of a flux reversal generator （FRG） viz., computational fluid dynamic （CFD）, thermal, and vibration. A three-dimensional finite element analysis （FEA） based CFD technique for finding the spread of pressure and air velocity in air regions of the FRG is described. The results of CFD are mainly obtained to fine tune the thermal analysis. Thus, in this focus, a flow analysis assisted thermal analysis is presented to predict the steady state temperature distribution inside FRG. The heat transfer coefficient of all the heat producing inner walls of the machine are evaluated from CFD analysis, which forms the main factor for the prediction of accurate heat distribution. The vibration analysis is illustrated. Major vibration sources such as mechanical, magnetic and applied loads are covered elaborately which consists of a 3D modal analysis to find the natural frequency ofFRG, a 3D static stress analysis to predict the deformation of the stator, rotor and shaft for different speeds, and an unbalanced rotor harmonic analysis to find eccentricity of rotor to make sure that the vibration of the rotor is within the acceptable limits. Harmonic analysis such as sine sweep analysis to identify the range of speeds causing high vibrations and steady state vibration at a mode frequency of 1500 Hz is presented. The vibration analysis investi- gates the vibration of the FRG as a whole, which forms the contribution of this paper in the FRG literature.

关键词： flux reversal generator air velocity computa-tion fluid dynamics thermal analysis vibration analysis,finite element analysis

Retrofitting Sprinkler Systems for Suppressing Dust Generated by Moving Vehicles Inside Farms

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Agricultural Sciences in China 2011年第3期10卷 376-383页

作者： Mohamed Thabit College of Bio-Systems Engineering and Food Science Zhejiang University

Fugitive dust is one of the well known problems in agriculture and it affects both humans and machine producing quality. Dust problems can seriously cause harmful diseases to workers and ruin expensive equipments. In this study, a dust formation generated in open environment by vehicles was analyzed on unpaved roads. Formed dust was measured by calculating total forces on the PM10 （airborne particles smaller than 10 mm） of dust particles, such as air velocity, gravity forces and air turbulence generated by the moving vehicle. The water fogger nozzle discharge was measured to determine the approximate droplets quantity in the air. The foggers were used to suppress the generated dust in an open environment via installing a proposed automatic suppression system which opens automatically when vehicles pass under the system. The relationship between water droplet speed and ability of collecting fugitive dust showed that high air temperature above 40oC and wind speed above 10 m s-1 have negative effects on the system’s ability of collecting dust due to evaporation of small radius droplets and/or drifting water droplets away from the effective area. The overall system efficiency was found to be 85% and the proposed dust suppression system was found to be a satisfying solution for reducing fugitive dust hazards.

关键词： fugitive dust air velocity gravity forces air turbulence water fogger nozzles discharge automatic suppression system sprinkler systems

Experimental study on optimizing cheese drying and ripening process

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International Journal of Agricultural and Biological Engineering 2012年第4期5卷 74-82页

作者： F.Giametta E.Sorrentino A.Lapenna G.La Fianza Department.S.A.V.A. Faculty of AgricultureUniversity of MoliseVia De Sanctis86100CampobassoItaly

The system proposed in this paper consists of humidity and temperature control during the food maturation process by using a dehumidifier equipped with a desiccant rotor containing silica gel.In this system the condensation/drainage stage is omitted since the humid room air is directed out of the cold store(process air)and the dried air is introduced via the dehumidifier inside the cold store.It allows separate control of the humidity and temperature inside the cold store.The experimental results are obtained in real conditions;the weight loss of the products was determined and it was,also,proved that dried products such as cheeses treated by this method retain their fresh color,texture and other organoleptic properties to ensure their final quality.

关键词： air velocity cheese drying ripening water loss relative humidity(RH)

Effects of air movement in a hot air dryer on the drying characteristics of colored potato (Solanum tuberosum L.) using computational fluid dynamics

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International Journal of Agricultural and Biological Engineering 2018年第1期11卷 232-240页

作者： Hyeon Woo Park Won Byong Yoon Department of Food Science and Biotechnology College of Agriculture and Life ScienceKangwon National UniversityChuncheonGangwon 200-701S.Korea

The flow fields of hot air in the dryer for drying colored potatoes of which characteristics are highly sensitive to the temperature were simulated using computational fluid dynamics(CFD)simulation.The local air velocity decreased as the distance from the flow inlet increased.The mass and heat transfer coefficients increased from 0.666×10^(-2) m/s to 1.711×10^(-2) m/s,and 6.555 W/(m^(2)·K)to 16.834 W/(m^(2)·K),respectively,as the air velocity increased from 0.207 m/s to 1.567 m/s at 60°C.The drying simulation model using the heat and mass transfer model made accurate predictions.The thermal properties of colored potato,such as the thermal conductivity and specific heat,decreased significantly from 0.440 W/(m·K)to 0.034 W/(m·K)and 3906.45 J/(kg·K)to 2198.52 J/(kg·K),respectively,as the moisture content decreased from 78% to 5%.With the variable thermal and physical properties,the heat transfer simulation model made accurate predictions of the hot-air drying characteristics for the colored potatoes,and the RMSE values for all cases were(1.85±0.27)℃.

关键词： colored potato hot air drying drying characteristics computational fluid dynamics thickness air velocity

New and innovative wind catcher designs to improve indoor air quality in buildings

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能源与人工环境(英文)

能源与人工环境(英文) 2021年第4期2卷 337-344页

作者： Mamdooh Alwetaishi Mohamed Gadi Department of Civil Engineering College of EngineeringTaif UniversityTaif 21974Saudi Arabia Department of Architecture and Built Environment Faculty of EngineeringUniversity of NottinghamNottingham NG72RDUnited Kingdom

Wind catchers used in various countries in Middle East and North Africa in order to improve indoor air environ-ment and to reduce reliance on cooling load.However,nowadays they are used across the globe with modern shapes and advanced techniques.The study focuses on investigating new and innovative shapes of wind catch-ers to improve air speed indoors which will elevate indoor comfort and air quality in buildings.The study used computer modeling CFD and a real model experiment to conduct the study.The study highlighted that curved shapes have highest pattern of wind speed driven,especially curved shape with double inlets.In addition,the study showed that octagon shape has the lowest pattern of wind speed driven because of its various sides which prevent air to flow easily inside the tunnel.

关键词： Wind catcher shape Indoor air quality air velocity CFD Energy saving

air flow characteristics of an air-assisted sprayer through horizontal crop canopy

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International Journal of Agricultural and Biological Engineering 2012年第1期5卷 1-6页

作者： Pankaj Gupta N.P.S.Sirohi I.M.Mishra Department of Farm Machinery and Power Engineering College of Agricultural Engineering and TechnologyAnand Agricultural UniversityGodhraGujaratIndia ADG Engineering Indian Council of Agricultural ResearchNew DelhiIndia Division of Agricultural Engineering Indian Agricultural Research InstituteNew DelhiIndia

Artificially induced air currents or air-assistance to droplet spectrum produced by hydraulic nozzles not only facilitate in transporting and depositing the droplets in different parts of canopy but also reduce the application rate of chemicals.The air streams increase the velocity of smaller droplets so that extra momentum would increase impaction and improve penetration into the crop as well as mitigating the influence of wind on drift.It is necessary to quantify the airflow characteristics.But,control of climatic and other conditions in the field is very difficult.Thus,airflow characteristics study was done under controlled conditions on a horizontal simulated crop canopy.Based on this study,an airflow distribution model was developed and airflow characteristics for vegetable crops,namely,eggplant,chilli and bittergourd were predicted.The differences between predicted and actual field study values were not statistically significant.Kinetic energy of air stream dissipated with its movement from top to bottom of the canopy.The rate of kinetic energy dissipation was higher in denser canopies.Higher air velocity 15 m/s was the best as it produced maximum turbulence throughout the canopy.

关键词： air assisted sprayer simulated crop canopy air velocity