Transient determination of water vapor diffusion coefficient of porous building materials
YI Si yang1,JIN Hong qing1,FAN Li wu1,XU Xu2,YU Zi tao1,GE Jian3
1. Institute of Thermal Science and Power Systems,Zhejiang University,Hangzhou 310027,China；2. College of Metrological and Measurement Engineering,China Jiliang University,Hangzhou 310018,China；3. Institute of Architectural Technology,Zhejiang University,Hangzhou 310058,China
A transient method was proposed based on solving an inverse problem of transient one dimensional mass diffusion in order to shorten the measurement time for determination of the water vapor diffusion coefficient of porous building materials. A typical porous building material was taken as an example by choosing the type B04 autoclaved aerated concrete. The proposed transient method was implemented by dynamically monitoring the relative humidity distribution inside the sample with a set of capacitor based hygrometers. The water vapor diffusion coefficient was finally acquired via the solution of the inverse problem of transient one dimensional mass diffusion. Results showed that the transient results accorded with those measured by the steady state method with a maximum relative deviation being less than 30%. The proposed transient method only took several days to accomplish compared to the steady state method that lasted for more than 2 months. The significantly improved measurement efficiency was due to the fact that the variation of water vapor diffusion coefficient as a function of relative humidity can be determined by a single experiment．
YI Si yang,JIN Hong qing,FAN Li wu,XU Xu,YU Zi tao,GE Jian. Transient determination of water vapor diffusion coefficient of porous building materials. JOURNAL OF ZHEJIANG UNIVERSITY (ENGINEERING SCIENCE), 2016, 50(1): 16-20.
［1］ 张华玲,刘朝,付祥钊. 多孔墙体湿分传递与室内热湿环境研究［J］. 暖通空调,2006,36(10)：29-34．
ZHANG Hua ling, LIU Chao, FU Xiang zhao. Study on moisture transfer in porous building components and indoor environment ［J］. Journal of Heating, Ventilating and Air Conditioning, 2006, 36(10): 29-34．
［2］ ROELS S, TALUKDAR P, JAMES C, et al. Reliability of material data measurements for hygroscopic buffering ［J］. International Journal of Heat and Mass Transfer, 2010, 53(23): 5355-5363．
［3］ 周晓燕,彭秋云. 定向结构板内水蒸汽稳态扩散系数的研究［J］. 林产工业,2001,28(6)：13-14．
ZHOU Xiao yan, PENG Qiu yun. Study on steady state diffusion coefficient of vapour in OSB ［J］. China Forest Products Industry, 2001, 28(6): 13-14．
［4］ ISO 12572: 2001. Hygrothermal performance of building materials and products: determinations of water vapor transmission properties ［S］. Switzerland:ISO, 2001．
［5］ ISO 12571: 2000. Hygrothermal performance of building materials and products:determination of hygroscopic sorption properties ［S］. Switzerland:ISO, 2000．
［6］ COLLET F, ACHCHAQ F, DJELLAB K, et al. Water vapor properties of two hemp wools manufactured with different treatments ［J］. Construction and Building Materials, 2011, 25(2): 1079-1085．
［7］ ARFVIDSSON J, CUNNINGHAM M J. A transient technique for determining diffusion coefficients in hygroscopic materials ［J］. Building and Environment, 2000, 35(3): 239-249．
［8］ DELGADO J, RAMOS N M M, DE FREITAS V P. Application of hybrid and moment methods to the measurement of moisture diffusion coefficients of building materials ［J］. Heat and Mass Transfer, 2011, 47(11): 1491-1498．
［9］ PAVLK Z, UMR J, PAVLKOV M, et al. A Boltzmann transformation method for investigation of water vapor transport in building materials ［J］. Journal of Building Physics, 2012, 35(3): 213-223．
［10］ CARMELIET J, HENS H, ROELS S, et al. Determination of the liquid water diffusivity from transient moisture transfer experiments ［J］. Journal of Thermal Envelope and Building Science, 2004, 27(4): 277-305．
［11］ KUISHAN L, XU Z, JUN G. Experimental investigation of hygrothermal parameters of building materials under isothermal conditions ［J］. Journal of Building Physics, 2009, 32(4): 355-370.
［12］ COLLET F, CHAMOIN J, PRETOT S, et al. Comparison of the hygric behaviour of three hemp concretes ［J］. Energy and Buildings, 2013, 62: 294-303.
［13］ 姚晓莉,易思阳,范利武,等. 不同孔隙率下含湿加气混凝土的有效导热系数［J］. 浙江大学学报：工学版, 2015, 49(6)：1101-1107．
YAO Xiao li, YI Si yang, FAN Li wu, et al. Effective thermal conductivity of moist aerated concrete with various porosities ［J］. Journal of Zhejiang University: Engineering Science, 2015, 49(6): 1101-1107．
［14］ LACKEY J C, MARCHAND R G, KUMARAN M K. A logical extension of the ASTM standard E96 to determine the dependence of water vapour transmission on relative humidity ［J］. ASTM Special Technical Publication, 1997, 1320: 456-470．
［15］ JERMAN M, KEPPERT M, VY′BORNY′ J, et al. Hygric, thermal and durability properties of autoclaved aerated concrete ［J］. Construction and Building Materials, 2013, 41: 352-359．
［16］ 冯驰,吴晨晨,冯雅,等. 干燥方法和试件尺寸对加气混凝土等温吸湿曲线的影响［J］. 建筑材料学报,2014,17(1)：132-137.
FENG Chi, WU Chen chen, FENG Ya, et al. Effect of drying methods and sample sizes on moisture absorption isotherms of aerated concrete ［J］. Journal of Building Materials, 2014, 17(1): 132-137．
［17］ GALBRAITH G H, MCLEAN R C, TAO Z. Vapour permeability: suitability and consistency of current test procedures ［J］. Building Services Engineering Research and Technology, 1993, 14(2): 67-70．
