為什么冷卻塔(ta)(ta)(ta)(ta)要(yao)做成這種形(xing)狀呢(ni)？這要(yao)從塔(ta)(ta)(ta)(ta)內(nei)(nei)的空(kong)(kong)(kong)(kong)(kong)氣流(liu)動(dong)(dong)(dong)特性(xing)說(shuo)起。冷卻塔(ta)(ta)(ta)(ta)內(nei)(nei)的空(kong)(kong)(kong)(kong)(kong)氣溫度(du)較塔(ta)(ta)(ta)(ta)外(wai)高，密度(du)比塔(ta)(ta)(ta)(ta)外(wai)空(kong)(kong)(kong)(kong)(kong)氣小(xiao)(xiao)，塔(ta)(ta)(ta)(ta)內(nei)(nei)空(kong)(kong)(kong)(kong)(kong)氣受(shou)到(dao)浮力作(zuo)用(yong)，向上運(yun)動(dong)(dong)(dong)。對于不同(tong)的流(liu)體(ti)有不同(tong)的流(liu)動(dong)(dong)(dong)曲線，如(ru)圖示(shi)，若空(kong)(kong)(kong)(kong)(kong)氣是(shi)理想(xiang)流(liu)體(ti)，即，流(liu)體(ti)不會(hui)產生(sheng)能(neng)(neng)量(liang)損(sun)耗(hao)，塔(ta)(ta)(ta)(ta)內(nei)(nei)空(kong)(kong)(kong)(kong)(kong)氣持續受(shou)到(dao)浮力作(zuo)用(yong)，不斷(duan)加速(su)(su)，由于流(liu)體(ti)流(liu)量(liang)固定(ding)，加速(su)(su)時間越長，即隨高度(du)空(kong)(kong)(kong)(kong)(kong)氣流(liu)速(su)(su)增(zeng)加，過渡面(mian)積減(jian)(jian)小(xiao)(xiao)；而實(shi)際空(kong)(kong)(kong)(kong)(kong)氣是(shi)粘性(xing)流(liu)體(ti)，當(dang)空(kong)(kong)(kong)(kong)(kong)氣運(yun)動(dong)(dong)(dong)時會(hui)產生(sheng)能(neng)(neng)量(liang)損(sun)耗(hao)，損(sun)耗(hao)量(liang)與速(su)(su)度(du)平方呈正(zheng)比，塔(ta)(ta)(ta)(ta)內(nei)(nei)空(kong)(kong)(kong)(kong)(kong)氣同(tong)時受(shou)到(dao)浮力和空(kong)(kong)(kong)(kong)(kong)氣運(yun)動(dong)(dong)(dong)阻力作(zuo)用(yong)，當(dang)高度(du)低時，流(liu)速(su)(su)小(xiao)(xiao)空(kong)(kong)(kong)(kong)(kong)氣阻力小(xiao)(xiao)于浮力，空(kong)(kong)(kong)(kong)(kong)氣呈加速(su)(su)運(yun)動(dong)(dong)(dong)，流(liu)體(ti)的流(liu)動(dong)(dong)(dong)斷(duan)面(mian)漸(jian)減(jian)(jian)小(xiao)(xiao)，當(dang)阻力浮力相當(dang)后空(kong)(kong)(kong)(kong)(kong)氣將不加速(su)(su)，但能(neng)(neng)量(liang)仍(reng)有消(xiao)耗(hao)，這時，流(liu)體(ti)流(liu)動(dong)(dong)(dong)將以減(jian)(jian)速(su)(su)補償能(neng)(neng)耗(hao)，流(liu)動(dong)(dong)(dong)斷(duan)面(mian)將漸(jian)變大。冷卻塔(ta)(ta)(ta)(ta)的外(wai)殼(ke)就是(shi)符合(he)了(le)塔(ta)(ta)(ta)(ta)內(nei)(nei)空(kong)(kong)(kong)(kong)(kong)氣流(liu)動(dong)(dong)(dong)的特性(xing)，設(she)計成下大，腰收細，上擴(kuo)口的形(xing)狀。