熱質(zhì)交換課第04講-瞬態(tài)傳質(zhì)

1、2.7.7 瞬態(tài)質(zhì)量擴(kuò)散以建材有機(jī)化學(xué)污染散發(fā)規(guī)律為例，說(shuō)明瞬態(tài)質(zhì)量擴(kuò)散在其間的應(yīng)用：大有用武之地。常見的有害氣體：有機(jī)揮發(fā)物，Volatile organic compounds, 簡(jiǎn)稱VOCs。常見的VOCs有：甲醛、甲苯等。參見文獻(xiàn) 1, 2。散發(fā)問(wèn)題1: 建材板單面散發(fā)問(wèn)題 (參見圖115、圖116, 兩者實(shí)質(zhì)上是同一問(wèn)題。)要了解：建材和裝修材料有害氣體散發(fā)速率。空氣 界面C(L,t)Cs(t)LC¥(t)xC0 建材 (a) 平板建材散發(fā)示意圖Cout(t)C(x,t) solid C(L,t)Cs(t)C¥(t) airVxLCin(t)QQ(b) 小室VOC

2、濃度平衡示意圖圖115 建材在小室內(nèi)散發(fā)情況示意圖 2 L C C0 C圖1-16 平板VOCs雙面散發(fā)示意圖(對(duì)稱問(wèn)題)數(shù)學(xué)模型假設(shè): 一維傳質(zhì)，底部與不滲透表面接觸（絕質(zhì)），常物性， 室內(nèi)空氣充分混合、濃度均勻，如圖1所示。無(wú)窮長(zhǎng)平板內(nèi)VOCs的質(zhì)量擴(kuò)散方程為： （1）其中，C(x,t)為平板內(nèi)VOC的瞬時(shí)濃度,mol/m3；x為離底面的距離，m；t為時(shí)間,s；D為擴(kuò)散傳質(zhì)系數(shù)，m2/s，假設(shè)其為常數(shù)。方程(1)的初始條件為： （2）方程(1)的邊界條件為： (3) (4)其中，hm為對(duì)流傳質(zhì)系數(shù)，m/s；Cs(t)為x=L邊界處氣體側(cè)VOCs濃度（見圖1），C¥(t)為室內(nèi)空氣

3、中VOCs濃度，mol/m3。在x=L邊界處，氣體側(cè)VOCs濃度和固體側(cè)VOCs濃度存在以下平衡關(guān)系式2： (5)其中，K稱為分離常數(shù)(partition coefficient)。小室內(nèi)VOC平衡方程為： (6)上述問(wèn)題的幾種簡(jiǎn)化特例：(1) Little 模型3假設(shè)： hm, i.e., const。 方程及邊界條件和初始條件為： (7-1) (7-2) (7-3) (7-4)采用分離變量法，可得： (8-1) (8-2) (8-3)問(wèn)題2：空氣加濕問(wèn)題。Moist air<-dry air補(bǔ)充解。體會(huì)擴(kuò)散傳熱和熱傳導(dǎo)的異同點(diǎn)。寫一篇小論文，闡述自己的觀點(diǎn)和心得。 Bridge 傳熱

4、 傳質(zhì)作業(yè)：1-24, 1-25*, 1-28*,131*。下節(jié)課：習(xí)題課。參考文獻(xiàn)1 周中平，趙壽堂，周立，室內(nèi)空氣污染檢測(cè)與控制，化學(xué)工業(yè)出版社，2001。2 J. D. Spengler, J. M. Samet, J.F.McCarthy, Indoor Air Quality Handbook, New York: McGraw-Hill, Inc., 2001. 3 John C. Little et al. Modeling emissions of volatile organic compounds from new carpets. Atmospheric Environm

5、ent,1994, Vol.28, No.2,227-234.4 美 M.N.奧齊西克著，俞昌銘主譯，熱傳導(dǎo)，北京：高等教育出版社，·1983年7月第1版。5 成通寶，室內(nèi)空氣品質(zhì)控制研究，2003年清華大學(xué)博士論文。6 Hongyu, Huang, Fariborz and Haghighat, (2002) “Modeling of VOC emission from dry building materials”, Building and Environment, 37, 1349 13607 Ying Xu, Yinping Zhang, An improved mass

6、transfer based model for analyzing VOC emissions from building materials, Atmospheric Environment, Vol.37, No. 18, June, 2003, pp.2497-2505. 8 Yinping Zhang, Ying Xu, Characteristics and formulae of VOC emissions from building materials, Inter. J. of Heat and Mass Transfer, 2003, Vol.46, No.25, pp.4

7、877-4883. 9 Baoqing Deng; Kim,Chang Nyung 2004. An analytical model for VOC emission from dry building materials. Atmospheric Environment, 2004, Vol.38 , pp. 1173-1180.10 Ying Xu, Yinping Zhang, A general model for analyzing VOC emission characteristics from building materials and its application, A

8、tmospheric Environment，Vol.38, No.1, 2004, pp.113-119.11 Xudong Yang, Study of building material emissions and Indoor Air Quality, Thesis submitted to the department of architecture on August 6,1999 in partial fulfillment of the requirements for the degree of doctor of philosophy in the field of arc

9、hitecture: building technology at the Massachusetts Institute of Technology, September, 1999, 124-12612 Xinke Wang, Yinping Zhang, Ying Xu, Modeling of double surface VOC emissions fromFaces flat-plate building materials under asymmetric convective conditions, Proc. of the 4th Inter. Conference of H

10、eating, Ventilating and Air-conditioning, pp.439-446, Oct.9-11, 2003, Beijing, China.13 Yinping Zhang, Hanping Hu, Xinke Wang, A general model of VOC emissions from a multi-layer building material with double emission surfaces, accepted by Prof. of the 4th International Conference of Heating, Ventil

11、ating and Air-conditioning, pp.375-383, Beijing, Oct.9-11, 2003.14 Kumar D., and Little J.C. (2003a), Characterizing of the source/sink behavior of double-layer building materials, Atmospheric Environment, 2003, 37 (39-40): 5529-5537.15 Kumar D., and Little J. C., (2003b), Single-layer model to predict the source/sink behavior of diffusion-control building materials, Environment Science Technology, 2003, 27, 3821-3827. 16 T