Exploration and application of thermal and moisture physical characteristics of porous building materials
In this paper, the heat transfer theory of porous media is analyzed, and the mass transfer coefficient of porous media materials is analyzed in combination with the building envelope, so that it is known that the thermal and moisture physical properties of porous building materials are closely related to the building materials themselves and the building envelope. Therefore, it provides an effective basis for further improving porous building materials and building envelope structure, thus providing certain guiding significance for the research and development of building materials.
Theoretical analysis of heat and mass transfer in 1. porous media
From the construction market, most materials belong to porous media, which is a composite medium composed of solid and fluid. But so far there is no clear definition, according to relevant research scholar J? Bear's simple definition shows that porous media means that there is at least one non-solid substance in some spaces, the solid part is called solid matrix, and the space outside the solid is called void space. At the same time, at least one void space in the porous medium is connected. In addition, in 1990 s? p？ W? Wong divides building materials into non-porous medium materials, porous medium materials with equal hygroscopicity and capillary porous medium materials. According to the phenomenon of porous media propagation, we can know that it has the following characteristics: first, porous media propagation involves more scientific theories, so it has interdisciplinary characteristics; Secondly, when porous media materials are used in different places, the emphasis is different. For example, when porous media materials are used in petroleum development, it is necessary to focus on the study of liquid phase flow law; Thirdly, porous media has the characteristics of heterogeneity, which is also an important reason for its complexity. Here, we need to understand its regularity through practice.
2. Analysis of mass transfer coefficient of porous media in building envelope.
Various transfer coefficients of porous media materials are difficult in the process of heat and mass transfer research. Through a series of studies, relevant researchers have made the following research results on mass transfer coefficient: water vapor diffusion coefficient, liquid water diffusion coefficient and conductivity coefficient.
(A) Research and analysis of water vapor diffusion coefficient
Water vapor diffusion coefficient refers to the amount of water vapor diffusing through a certain area in a certain time under a certain vapor pressure difference. At the same time, the diffusion coefficient of water vapor is different according to different materials. It is found that the diffusion coefficient of water vapor in materials has the following relationship with its coefficient in air: where is the diffusion resistance coefficient of water vapor, which is directly related to local atmospheric pressure and temperature. Through practical calculation, the water vapor diffusion coefficient has the following achievements: first, the water vapor diffusion coefficient is a certain value in the process of water transfer; Secondly, the water vapor diffusion coefficient will produce different values in different materials; Thirdly, the diffusion coefficient of water vapor has a certain relationship with material physics, showing a certain law.
(2) Research and analysis of liquid water diffusion coefficient.
With the increase of water content of water vapor, water vapor and liquid water will appear in porous materials. Different researchers put forward different equations to describe the changes of liquid water in the whole process of water transfer, such as: K? Nzel believes that the wet diffusion coefficient is formed by the joint action of moisture absorption stage and capillary moisture absorption stage; Roels gives two methods to calculate the moisture transfer and diffusion coefficient of water vapor, one is the comprehensive index method, the other is the superposition function method, and the water vapor curve can be obtained.
To sum up, the above are all researches on diffusion coefficient provided by foreign researchers, and a lot of research has been done on the diffusion of water in concrete in China. Taking the water flow in soil and rock stratum as an example, Tang Ren put forward the temperature correction formula of diffusion coefficient on the basis of analyzing the influence of rock diffusion system, thus establishing a set of methods for studying rock diffusion system. In addition, Liu Zhiyong and others put forward a formula for calculating the effective gas diffusion coefficient of concrete based on gas transmission of porous media materials, and thus put forward a test method for measuring the permeability of concrete by increasing the pressure gradient. Compared with building materials, there is little research on its diffusion coefficient, but some related researchers have put forward some research results. For example, Su Xianghui proposed that the mass diffusion coefficient and thermal mass diffusion coefficient should be taken as temperature and water content to observe the linear change of liquid water diffusion coefficient.
(3) Research and analysis of conductivity.
When the driving force is capillary pressure, the water transfer coefficient is equal to that of liquid water. Many domestic researchers use liquid water conductivity to calculate soil conductivity. Among ordinary building materials, foreign scholars put forward the following models: simplified model, network model and tube bundle model. The simplified model does not consider the porous structure and bending factor, while the network model uses the grid to simulate the actual porous structure, which is also verified by the resistance network model.
Thirdly, the research and analysis of diffusion coefficient of porous building materials.
(A) analysis of porous pore structure of building materials
For building materials, porous pores affect their physical properties, such as strength, capital and elasticity. Therefore, it is necessary to study and understand the influence of pore structure on the properties of materials, so as to effectively solve the coupling calculation problem of porous materials. The physical properties of heat and moisture inside the material are directly related to the structural characteristics of the material itself. The complexity and diversity of porous materials make it difficult to establish the pore structure model of porous materials, but a breakthrough has been made. For example, in the study of structural characterization of porous materials, image analysis technology and other related equipment have been explored. Pore structure can be divided into the following two categories, namely isotropic and anisotropic, in which anisotropic materials bring some difficulties to the study of heat and moisture transfer performance, so this paper focuses on the analysis of heat and moisture transfer performance of isotropic building materials with porous pore structure.
(2) Derivation and analysis of mass diffusion coefficient.
In order to explain the transfer process of moisture in isotropic building materials with porous structure, it is necessary to further subdivide the pore volume of the materials. In thermodynamic equilibrium, the humidity of porous materials will increase with the humidity of nearby air, and once it reaches a certain humidity level, it will condense liquid water. At this time, liquid water will live in the pores, and with the further increase of humidity, it will form the form of liquid water to transfer humidity. In this process, there are three moisture content processes, namely dry moisture content, transitional moisture content and effective moisture content. Because of the different transmission mechanisms of water vapor and liquid water, there are series mode and parallel mode, so the moisture and heat transfer in porous media are not the same.
Conclusion:
In this paper, the theory of heat and mass transfer in porous media is analyzed, and the physical properties of heat and moisture are analyzed combined with the theory of mass diffusion coefficient of porous building materials. The physical properties of heat and humidity produced by porous building materials are directly related to the overall energy consumption of the building and the indoor heat and humidity environment. Improving the physical properties of heat and moisture of cross-hole structure building materials plays a very important role in realizing low-carbon and low-energy construction projects, thus bringing economic and social benefits to construction enterprises.
Building materials paper 3000 words 4
Problems and Countermeasures in the Teaching of Building Materials
Building materials is an important basic course for architecture majors in engineering colleges. For a long time, building materials have troubled many teachers and students with its messy system and complicated content. Facing the challenge of the curriculum system in the new period, how to complete the teaching task well and quickly should be a subject that professional teachers constantly explore.
1 Problems in course teaching
1. 1 has many contents, wide coverage and poor systematicness.
Building materials mainly introduce commonly used building materials, such as lime, gypsum, wood, concrete, sound-absorbing materials, building mortar, cement, lightweight materials, building decoration materials, building steel, lime, waterproof materials, thermal insulation materials, building colloid, pipeline materials, etc. , the content is complex and varied. Although all kinds of data are self-contained, there is a lack of logical relationship between the systems and the system is poor. Students are easy to learn boring, and have no interest and energy in class, not to mention how much they can learn.
1.2 is boring, poor in logic and practical.
This course is rich in empirical content, with many conceptual terms, pure text narration and less logical reasoning. It seems easy to learn, but it is not. If you really want to learn this course well, it is still difficult to master. In the daily teaching process, if the teaching method is wrong and the learning method is meaningless, the teacher will be tired of teaching, and the students will learn hard and can't master much practical knowledge.
1.3 There are few class hours, so students can't be guaranteed to finish it.
Generally speaking, students majoring in architecture in technical colleges are usually arranged to practice in the first line of the construction site in the last semester or two, which leads to the reduction of students' actual study time at school. In order to ensure the smooth completion of the teaching content, many teachers naturally appeared? Cramming at the last minute? Teaching, regardless of students' learning effect, teachers only pursue? Quick? Ignore? Okay？ In the end, students are boring to learn and teachers are nervous and helpless to teach.
1.4 The content of the textbook is lagging behind and lacks innovation.
At present, traditional materials such as lime, cement, ordinary concrete, steel, wood and so on. They are all talked too much and too detailed in the relevant teaching materials of building materials, which takes up more class hours. However, many new materials are not mentioned in the textbooks, such as high-performance concrete, various new glasses, double steel bars, new waterproof materials, new pipes, etc. These materials have been widely used in construction projects.
1.5 teaching methods and means are relatively backward.
At present, traditional teaching methods still have a great market in many technical colleges. Although the traditional teaching methods have a certain influence on students' basic knowledge of some disciplines, it is impossible for students to really grasp the essence of the course of building materials, which is very practical, only by using teachers' lectures and students' passive learning methods. This traditional teaching method makes students' knowledge only stay at the theoretical level, and they know little about the application knowledge of various materials and the application of practical engineering materials. After entering the construction site, they can't deal with the problems on the site in time, let alone comprehensively use the material knowledge they have learned to solve practical problems in the project.
2. The improvement of course teaching
According to the curriculum standards of building materials in technical colleges, their own characteristics and the problems often existing in the teaching process of building materials, the teaching methods can start from the following aspects.
2. 1 Improve teaching methods
2. 1. 1 Adopt modern teaching methods.
Adopting modern teaching methods and enhancing teaching intuition can cultivate and stimulate students' interest in learning. Building materials is a fast-growing industry, and new materials emerge one after another, but the content of teaching materials widely used at present is far behind the reality. Due to the different conditions of teachers in different places, teachers can present the characteristics and applications of various building materials to students in the form of multimedia display to increase their perceptual knowledge. Multimedia teaching, in the form of dynamic and static, excellent audio-visual and illustrated pictures, intuitively and vividly combines knowledge points, presents abstract theories to students in an image and acceptable form, provides students with learning experiences of watching, listening, doing and thinking, stimulates students' learning initiative and improves teaching quality.
2. 1.2 A large number of cases were introduced into teaching.
Practice has proved that the case teaching method is a very effective teaching method for students in technical colleges, which is well received by teachers and students. According to the needs of teaching objectives, the course of Building Materials can make use of common building materials in building engineering, from introducing problems, analyzing problems to solving problems, so as to present knowledge in cases, enhance students' intuitive feelings and increase their intuitive understanding.
2. 1.3 Strengthening practical teaching
Practice teaching is an effective and necessary way to consolidate theoretical knowledge and deepen theoretical understanding, an important link to cultivate high-quality engineering and technical personnel with innovative consciousness, and an important platform to integrate theory with practice, train students to master scientific methods and improve their practical ability. It is conducive to the improvement of students' literacy and the formation of correct values. There are a lot of building materials that students need to know about in the discipline of building materials. Through the building materials experiment, we can not only verify the theoretical knowledge we have learned, but also exercise our hands-on ability and cultivate our ability to analyze and solve problems.
2.2 Strengthen the cultivation of students' autonomous learning ability
A large number of teaching practices have proved that the potential of students' active development is strong, students' desire for autonomous learning is huge, and students have the desire to control the classroom. Teachers' teaching should focus on improving students' intelligence, treat students as the masters of classroom and learning, and let students have enough time to discuss, observe, think, ask questions and evaluate, thus enhancing students' learning ability.
2.3 Make full use of Internet resources
At present, most technical colleges are covered with high-speed internet, and students can easily obtain relevant information online, keep learning and increase their knowledge. Teachers can guide students to make full use of network resources, such as various professional building materials websites, research institutes websites, and even building materials market trends. These stones from other mountains are very conducive to expanding students' knowledge and contacting technology and market.
2.4 Choose simple, practical and novel teaching materials.
It is very important to choose the right teaching materials, so as a professional teacher, we should take good care of the students' teaching materials. How to choose teaching materials? Level three? First, grasp? Shallow? Word, two grasping? Use? Word, three grasp? New? Words. Simplicity means that we should try to understand and solve a problem? Shallow? Words, on the basis of necessity, sufficiency and usefulness, reduce the difficulty as much as possible; ? Use? The word "practical" refers to the basic knowledge, basic theory and basic analysis methods that are useful for cultivating students' professional ability and re-learning ability. ? New? The word "novelty" means that the teaching content conforms to and reflects the new situation of scientific and technological progress and the development of the times, which is advanced and prominent. New? Words. In recent years, new information such as new materials and new technologies in the field of architecture should be reflected in the teaching content.
3 Conclusion
In the teaching process of building materials, it is necessary to combine the actual learning situation of students in technical colleges, select appropriate teaching materials according to the course characteristics of technical colleges, carefully study the teaching contents, and adopt the best teaching methods and means, so as to effectively improve the teaching quality of building materials in technical colleges and cultivate more and better building talents widely welcomed by the society.
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