| The construction field has always been the dominant field of energy consumption in the world.Building energy conservation has become one of the key tasks of the Chinese government,which is of great significance to promote energy conservation and emission reduction and to realize the transformation,upgrading and healthy development of the construction industry.The composite block wall is a new type of wall material developed with the continuous improvement of national energy-saving design standards,which has significant advantages such as fire prevention,good thermal performance and meeting self-heating requirements.The composite block is composed of the host material and the filling material,whose internal heat and moisture transfer has obvious bidimensionality.However,most of the current researches on the heat and moisture coupling transfer model of the wall applies the one-dimensional model,which is inconsistent with the actual situation inside the composite block wall.This brings certain difficulties to the energy-saving analysis and heat-moisture characteristic study of composite block walls.Therefore,it is urgent to 0.tudy the two-dimensional heat-moisture coupling transfer characteristics of composite block walls,provide a basis for the optimization design and moisture-proof design of energy-saving structures,and promote the popularization and application of composite block walls.In this thesis,based on the water vapor,temperature and air pressure as the driving force,the volume-average theory was used to establish the theoretical model of heat-moisture coupling transfer of composite block wall.The highest mass mix ratio of coal gangue composite block and fly ash composite block materials was independently developed,and the heat-moisture transfer properties of the host materials and filling materials of the two composite blocks are tested.The heat-moisture coupling transfer law inside the composite block wall was discussed by physical model test and numerical simulation.The characteristics of heat-moisture coupling transfer were revealed,and the effects of heat-moisture coupling effect on the heat-moisture characteristics and energy consumption of composite block walls were studied.The main research conclusions are as follows:(1)A heat-moisture coupling model of composite block wall with water vapor partial pressure,temperature and air pressure as driving force was established.The model includes three equations of water transfer,air transfer,and heat transfer.The equation coefficients have clear physical meanings and are easy to determine.The total water transfer equation uses Kelvin's law to convert the water vapor and liquid water transfer in the building material into a uniform function of the water vapor partial pressure as the driving force and the built-in equation in the COMSOL MULTIPHYSICS~?multiphysics simulation software,which is more concise.This function solved the problem that the transmission performance parameter test needs to distinguish between two modes of water vapor diffusion and liquid water penetration,and simplified the parameter setting in the numerical simulation calculation process.(2)The optimal mix ratio(mass ratio)of coal gangue composite block and fly ash composite block materials was obtained.The optimal mix ratio of the host material of coal gangue composite block is:shale content 10%,rice husk content 5%,coal gangue content85%;that of the host material of fly ash composite block is:fly ash 50%,Portland cement20%,fly ash ceramsite 30%;that of the filling material of fly ash composite block:37.5%Portland cement,25%rice husk,37.5%901 glue.(3)The heat-humidity coupling transfer performance parameter database of the composite block wall was constructed,and the relational expression between the water permeability coefficient and the equilibrium relative humidity and that between the effective thermal conductivity and the equilibrium moisture content were obtained.The experimental research scheme of the heat-moisture coupling transfer theoretical model to solve the required heat-humidity performance parameters such as porosity,moisture characteristic curve,moisture permeability coefficient and effective thermal conductivity was proposed.The host material and the filling material EPS of self-developed coal gangue composite block,as well as the host material and the filling material rice hull slurry of fly ash composite block were tested.The parameters of heat-moisture coupling performance of composite block wall required for numerical simulation were obtained.(4)The heat-moisture coupling transfer law inside the composite block wall was revealed.6 test walls under three working conditions:the internal environment condition of above 0°C,the outdoor environment and the indoor environmental condition of below 0°C were constructed.The heat-moisture coupling transfer law inside the wall of coal gangue and fly ash composite blocks was tested,and the numerical simulation calculation of the heat-humid coupling transfer law of 6 walls under test conditions using COMSOL MULTIPHYSICS~?multiphysics simulation software was conducted,which showed good consistency,and suggested that the relative error of the temperature and water vapor pressure is within the allowable scope of the project.The temperature and humidity inside the wall showed certain bidimensionality.The nodes near the boundary of the wall were more affected by the external environment and their changed waveforms were similar to the external environment.The temperature and humidity fluctuations of the internal nodes have different degrees of attenuation delay.(5)The heat-humidity coupling law inside coal gangue and fly ash composite block walls in two typical urban areas:Guangzhou(hot summer and warm winter)and Shanghai(hot summer and cold winter).The COMSOL MULTIPHYSICS~?multiphysics simulation software was used to simulate the two composite blocks for 10 years.The results showed that after being put into use,under the action of cyclical temperature and humidity changes in the natural environment,after a certain period of time,they gradually reached normal phase under periodic boundary conditions.The period until the humidity reached the normal condition is significantly longer than that until the temperature reached.The temperature and humidity inside the wall changed irregularly,and the inner and outer surfaces were greatly affected by indoor and outdoor conditions,showing a certain attenuation delay.The relative humidity of the surface was less than 1.0 and there was no condensation both in the first year when the coal gangue and fly ash composite block walls in the two climatic areas were used and under the normal conditions,but the relative humidity was sometimes higher than 0.8 in the initial phase and normal conditions,which showed the risk of mold breeding,so it is necessary to take necessary measures to prevent moisture.(6)The influence laws of factors such as heat-moisture transfer performance parameters,initial moisture content and wall orientation on the heat-humidity characteristics of the wall was ascertained.The higher the initial moisture content,the longer the period required for the block to reach the normal condition under periodic boundary conditions,and the greater the effect of initial moisture content on the wall performance.When the wall type is different,the degree of influence of the initial value change showed obvious difference;the periods of the walls with different orientations to reach to the normal conditions were different,where that of the wall towards south was the shortest,that of the walls towards east and west was the second,and that of the wall towards north was the longest.(7)The heat-moisture coupling transfer characteristics inside the wall were revealed.Study method system of heat and moisture characteristics were established which consists of boundary parameter calculation method for heat and mass transfer,Heat and moisture transfer performance parameter,numerical simulation parameters setting method of COMSOL MULTIPHYSICS~?.By comparing the magnitude of relative error about the results of the two-dimensional and a one-dimensional coupled heat and moisture model and physical model test of 6 test walls under three kinds of working condition,and the temperature and humidity distribution of different sections at the same height of the test wall,test and the experimental test of the same height in the cross section of the different distribution of temperature and humidity,the two-dimensional coupled heat and moisture transfer characteristics inside the composite block wall was illuminated.(8)The influence law of heat-moisture coupling transfer on the building energy consumption of walls was given.Compared with the normal condition,affected by the initial temperature and moisture content,the energy consumption year by year calculated by the heat-humidity coupling model of the two types of composite block walls in two typical areas:Guangzhou(hot summer and warm winter)and Shanghai(hot summer and warm winter)showed that heating and cooling load presented change trends year by year in the first several years before being put into use,and the degree and direction of the influence are related to the climatic conditions and seasons.The calculation method of simply considering heat transfer but ignoring the influence of moisture content on the heat and moisture transfer performance of the wall was inconsistent with the actual situation of heat-humidity transfer inside the wall,which led to the deviations in the calculation of building energy consumption.The paper has 198 figures,62 tables,and 172 references. |
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