冷卻塔水傳導散熱和流散熱

傳(chuan)(chuan)(chuan)(chuan)(chuan)導(dao)(dao)散(san)熱(re)(re)(re)(re)也稱(cheng)接(jie)(jie)觸(chu)(chu)散(san)熱(re)(re)(re)(re)，有時(shi)(shi)也稱(cheng)接(jie)(jie)觸(chu)(chu)傳(chuan)(chuan)(chuan)(chuan)(chuan)導(dao)(dao)散(san)熱(re)(re)(re)(re)。這種(zhong)散(san)熱(re)(re)(re)(re)是(shi)(shi)(shi)指(zhi)熱(re)(re)(re)(re)水水面(mian)(mian)(mian)與(yu)空(kong)(kong)(kong)(kong)(kong)(kong)氣(qi)(qi)(qi)(qi)(qi)直接(jie)(jie)接(jie)(jie)觸(chu)(chu)時(shi)(shi)的傳(chuan)(chuan)(chuan)(chuan)(chuan)熱(re)(re)(re)(re)過(guo)程，包括傳(chuan)(chuan)(chuan)(chuan)(chuan)導(dao)(dao)和對(dui)(dui)流(liu)兩(liang)種(zhong)傳(chuan)(chuan)(chuan)(chuan)(chuan)熱(re)(re)(re)(re)形式。如水的溫(wen)(wen)度(du)(du)與(yu)空(kong)(kong)(kong)(kong)(kong)(kong)氣(qi)(qi)(qi)(qi)(qi)溫(wen)(wen)度(du)(du)不一(yi)樣，將(jiang)會產生(sheng)傳(chuan)(chuan)(chuan)(chuan)(chuan)熱(re)(re)(re)(re)過(guo)程，當(dang)水溫(wen)(wen)高于空(kong)(kong)(kong)(kong)(kong)(kong)氣(qi)(qi)(qi)(qi)(qi)溫(wen)(wen)度(du)(du)時(shi)(shi)，水就(jiu)(jiu)把(ba)熱(re)(re)(re)(re)量傳(chuan)(chuan)(chuan)(chuan)(chuan)給空(kong)(kong)(kong)(kong)(kong)(kong)氣(qi)(qi)(qi)(qi)(qi)，空(kong)(kong)(kong)(kong)(kong)(kong)氣(qi)(qi)(qi)(qi)(qi)自身的溫(wen)(wen)度(du)(du)就(jiu)(jiu)逐漸升高，使水面(mian)(mian)(mian)以上周圍空(kong)(kong)(kong)(kong)(kong)(kong)氣(qi)(qi)(qi)(qi)(qi)內(nei)部的溫(wen)(wen)度(du)(du)不均勻，這樣冷空(kong)(kong)(kong)(kong)(kong)(kong)氣(qi)(qi)(qi)(qi)(qi)與(yu)熱(re)(re)(re)(re)空(kong)(kong)(kong)(kong)(kong)(kong)氣(qi)(qi)(qi)(qi)(qi)之(zhi)間就(jiu)(jiu)產生(sheng)對(dui)(dui)流(liu)作(zuo)用注：對(dui)(dui)流(liu)只(zhi)發(fa)生(sheng)在(zai)流(liu)體中(zhong)，而傳(chuan)(chuan)(chuan)(chuan)(chuan)導(dao)(dao)是(shi)(shi)(shi)指(zhi)傳(chuan)(chuan)(chuan)(chuan)(chuan)熱(re)(re)(re)(re)的分子之(zhi)間無(wu)混合現象(xiang)，對(dui)(dui)流(liu)的結果是(shi)(shi)(shi)使空(kong)(kong)(kong)(kong)(kong)(kong)氣(qi)(qi)(qi)(qi)(qi)本(ben)身各(ge)點的溫(wen)(wen)度(du)(du)達到一(yi)致，最后到水面(mian)(mian)(mian)溫(wen)(wen)度(du)(du)與(yu)空(kong)(kong)(kong)(kong)(kong)(kong)氣(qi)(qi)(qi)(qi)(qi)溫(wen)(wen)度(du)(du)一(yi)致時(shi)(shi)傳(chuan)(chuan)(chuan)(chuan)(chuan)導(dao)(dao)散(san)熱(re)(re)(re)(re)停止。上述(shu)(shu)可見：傳(chuan)(chuan)(chuan)(chuan)(chuan)導(dao)(dao)和對(dui)(dui)流(liu)是(shi)(shi)(shi)同時(shi)(shi)發(fa)生(sheng)的，總稱(cheng)為接(jie)(jie)觸(chu)(chu)散(san)熱(re)(re)(re)(re)。從(cong)上述(shu)(shu)討論(lun)可見：傳(chuan)(chuan)(chuan)(chuan)(chuan)導(dao)(dao)散(san)熱(re)(re)(re)(re)的推(tui)動力(li)為溫(wen)(wen)度(du)(du)差(cha)Δt=tf-θ水面(mian)(mian)(mian)溫(wen)(wen)度(du)(du)與(yu)空(kong)(kong)(kong)(kong)(kong)(kong)氣(qi)(qi)(qi)(qi)(qi)溫(wen)(wen)度(du)(du)差(cha)，溫(wen)(wen)差(cha)越大，傳(chuan)(chuan)(chuan)(chuan)(chuan)熱(re)(re)(re)(re)效果越好，傳(chuan)(chuan)(chuan)(chuan)(chuan)熱(re)(re)(re)(re)量可用下(xia)式表示：式中(zhong)Hα——單位面(mian)(mian)(mian)積(ji)上的接(jie)(jie)觸(chu)(chu)傳(chuan)(chuan)(chuan)(chuan)(chuan)遞(di)熱(re)(re)(re)(re)量kcalm2·h；tf——水面(mian)(mian)(mian)溫(wen)(wen)度(du)(du)℃水氣(qi)(qi)(qi)(qi)(qi)交界(jie)面(mian)(mian)(mian)溫(wen)(wen)度(du)(du)；θ——空(kong)(kong)(kong)(kong)(kong)(kong)氣(qi)(qi)(qi)(qi)(qi)溫(wen)(wen)度(du)(du)℃；α——傳(chuan)(chuan)(chuan)(chuan)(chuan)熱(re)(re)(re)(re)系數kcalm2·h。只(zhi)要tfθ，Hα始終從(cong)水面(mian)(mian)(mian)傳(chuan)(chuan)(chuan)(chuan)(chuan)導(dao)(dao)給空(kong)(kong)(kong)(kong)(kong)(kong)氣(qi)(qi)(qi)(qi)(qi)；反(fan)過(guo)來，當(dang)tf＜θ時(shi)(shi)，Hα就(jiu)(jiu)從(cong)空(kong)(kong)(kong)(kong)(kong)(kong)氣(qi)(qi)(qi)(qi)(qi)傳(chuan)(chuan)(chuan)(chuan)(chuan)導(dao)(dao)給水。

橫流式冷卻塔熱力計算基本方程求解

這里主要介紹(shao)采用較普遍的(de)平均焓(han)差法。將式6-58中(zhong)的(de)dx改(gai)為(wei)填(tian)料深度(du)(du)L，dy改(gai)為(wei)填(tian)料高度(du)(du)H，則式6-58的(de)左邊(bian)的(de)積分式為(wei)：