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Digital Simulation of Temperature in Modern Greenhouse

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Tutor: WangXiao
School: Nanjing Agricultural College
Course: Detection Technology and Automation
Keywords: Greenhouse,CFD simulation,Tomato,Temperature distribution,Radiation model
CLC: S625.51
Type: Master's thesis
Year:  2011
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Abstract:
The modern greenhouse is a good direction for protected agriculture of china with radid development, because has characteristics of high yield and high quality. But the greenhouse production in home and abroad differs a lot in yield and quality for the complexity of greenhouse environment control technology. With the fast development of the computer technology, CFD software has been an effective means and method for greenhouse environmental study and effect evaluation of environmental control technology, but in china it is still in the initial stage. The urgency is to apply CFD in greenhouse microclimate simulation.This paper took the WSBRZ glasshouse in Zhangjiagang as the research object, simulated and analyzed the greenhouse thermal environment, and verified its feasibility experimentally.The main contents and conclusions of this paper include follows:(1) Because of the barriers to a traditional wired greenhouse monitoring system included high cost and complex wiring, a wireless monitoring system based on ZigBee wireless sensing network is designed. The system was composed of the management center and wireless collection node network, which is made up of gateway node, router nodes and end device nodes. All nodes could be awakened up to acquire data sent to gateway node directly or by routers. The management center received data from gateway node by RS232, which could save humiture to databases and illustrate data in real-time. Experiments show that this system operates stably, and the energy consumption is 22.4 mA at work,4.7 mA in sleep. Its success rate of data packets reception is 97.1%. The designed system was applied to collect environmental parameters of test greenhouse.(2) The greenhouse heat and quality discharge mechanism is studied together with the CFD numerical method of greenhouse. Based on this, the heat balance of greenhouse cover, inside air, plant surface and soil surface is analyzed.Through these, a crop layer temperature calculation model is established., which is applied to crop porous medium area of greenhouse CFD model.The simulated crop layer temperature agrees well with the measured data with the correlation determination coefficient R2 of 0.9301.(3) Three-dimensional CFD model for test greenhouse was established with the computational domain included the modelled greenhouse and the surroundings. The turbulence transfer was described by the standard k-¦Åturbulence model, and dealt with the near-wall region. DO radiation model was selected and the tomato crop was described as porous medium. The simulation boundary conditions were given by the test data. The CFD numerical model were validated with respect to experimental measurement performed for steady-state outside conditions. The difference between the simulated and measured air temperature ranges between 0.2 and 2.2¡æ, with an average difference of 0.91¡æ.The biggest relative error is 7.7%, with an average relative error of 3.1%. The average relative error of the simulated and measured relative humidity is 6.4%, with a biggest relative error of 16.6%. The result shows the CFD model is feasible and effective.The model is used for further study of the air temperature and relative humidity distribution inside the greenhouse. The air temperature of crop is lower, but the relative humidity is higher. It is the opposite in the upper of the greenhouse. The maximum temperature difference along north-south are 5.3¡æand the temperature of west is a little higher than the east.
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