日光温室热压-风压耦合通风机理及计算模型构建

Natural ventilation between the interior of a greenhouse and its environment is the main governing mechanism for the control of the greenhouse climate. It has its impact not only on the energy balance, but also on the concentration of water vapor, carbon dioxide and other gases. Ventilation is a dynamic physical process involves the wind pressure due to outside wind, and the stack effect due to buoyancy forces and temperature differences. The adjustment of ventilation and design of structure cannot be well arranged since lack of modelling and analyzing to the ventilation dynamic processes. The object of this research is to analyze the relationship between ventilation flux and temperature difference, wind velocity, wind direction. The coupling mechanisms between the stack and wind effects will be analyzed and models of air exchange in a solar greenhouse will be derived considering the two main driving forces of ventilation. The tracer gas technique using carbon dioxide will be used to analyze the variations of identified coefficients in relation to the wind and temperature characteristics for estimating the ventilation flux. The model parameters will be identified by fitting the experimental data to the models. Non-linear regressions using Marquardt’s algorithm will be used to identify thermal buoyancy coefficient and wind pressure coefficient. In this study a theoretical approach to design solar greenhouse ventilation flux will be developed and it is helpful for a proper design of vent construction therefore to control inside greenhouse climate.

自然通风是日光温室环境调节的重要手段，直接影响室内的热量平衡、水蒸气含量以及CO2浓度等环境因子。自然通风是一个动态的物理过程，受热压与风压等要素的驱动，但由于缺乏对这种动态过程的模拟与分析，日光温室自然通风的工程设计与调控仍无据可依。本项目拟在探明日光温室通风量与室外风速、风向以及室内外温差等多元定量关系的基础上，分析热压-风压耦合作用对通风量的影响机理，并以此为基础构建通风速率与热压-风压作用关系的数理模型，采用CO2气体示踪法测试室内气流动态变化规律和通风速率，通过Marquardt算法对模型与实验值进行非线性拟合，形成相关性最高的通风计算模型以及流量系数与风压系数计算方法。本项目研究为日光温室自然通风理论计算提供了新的方法，对温室自然通风的结构设计与调节控制具有重要的参考价值。

自然通风是日光温室环境调节的重要手段，直接影响室内的热量平衡以及、水蒸气含量以及CO2浓度等环境因子。自然通风是一个动态的物理过程，受热压与风压等要素的驱动，但由于缺乏对这种动态过程的模拟与分析，日光温室自然通风的工程设计与调控仍无据可依。本研究利用计算流体力学（CFD）软件，构建了日光温室自然通风环境模拟模型，并模拟分析了日光温室前覆盖上通风口单开、下通风口单开、上下通风口同时开启三种通风模式下温室内的温度与气流分布特征。模拟结果表明：当温室前覆盖上通风口单独开启时，室外冷空气从通风口下端进入并迅速下行，然后通过通风口上端流出，温室内气流主 要受热压的影响，空气流速小。当温室前覆盖下通风口单独开启时，温室内0.5m高度以下气流速度较大，室外 冷空气从通风口下端进入，与地面、后墙、后坡和覆盖层进行热交换后，从通风口上端流出，温室内温度分布与气流走向一致。当温室前覆盖上、下通风口同时开启时，冷空气从下通风口进入，从上通风口流出，在通风口处气流速度较大。为获得日光温室通风量与室外风速、风向以及室内外的温差等多元定量关系，根据温室内气流走向特点，分析了热压-风压耦合作用对通风量的影响机理，以此为基础构建通风速率与热压-风压作用关系的数理模型，采用CO2气体示踪法测试缩小比例温室内气流动态变化规律和通风速率，通过Marquardt算法对模型与实验值进行非线性拟合，结果表明：当通风口宽度为3、5和7cm时，流量系数分别为0.78、0.60和0.44, 风压体型系数分别为0.04、0.05和0.07。当室外风速大于2.5m·s-1时,可忽略温度即热压的影响。