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　　凍干(gan)(gan)機(ji)(ji)干(gan)(gan)燥(zao)箱和(he)冷(leng)(leng)阱(jing)是需(xu)要專門提供制冷(leng)(leng)的場合(he)(he)，在干(gan)(gan)燥(zao)箱場合(he)(he)，不同物料(liao)的凍結(jie)溫(wen)(wen)度(du)需(xu)要在-20~-40℃之間(jian)，在冷(leng)(leng)阱(jing)場合(he)(he)，冷(leng)(leng)阱(jing)捕(bu)(bu)集器表面(mian)溫(wen)(wen)度(du)須低(di)(di)于物料(liao)凍結(jie)溫(wen)(wen)度(du)20℃以下(xia)，所以需(xu)要捕(bu)(bu)集器表面(mian)溫(wen)(wen)度(du)在-40~-60℃之間(jian)，由于實(shi)際(ji)(ji)使(shi)用溫(wen)(wen)度(du)和(he)制冷(leng)(leng)機(ji)(ji)提供的實(shi)際(ji)(ji)蒸(zheng)發溫(wen)(wen)度(du)之間(jian)存在傳熱溫(wen)(wen)差，所以制冷(leng)(leng)機(ji)(ji)提供的實(shi)際(ji)(ji)蒸(zheng)發溫(wen)(wen)度(du)應(ying)比實(shi)際(ji)(ji)使(shi)用溫(wen)(wen)度(du)更低(di)(di)。使(shi)用超低(di)(di)溫(wen)(wen)制冷(leng)(leng)系(xi)(xi)統(tong)在凍干(gan)(gan)機(ji)(ji)應(ying)用實(shi)踐中(zhong)普遍得到令人滿(man)意的效果(guo)，即節能環保，又縮短干(gan)(gan)燥(zao)時間(jian)，又增加了制冷(leng)(leng)系(xi)(xi)統(tong)運行的穩(wen)定性(xing)，可實(shi)現無人工(gong)值守，其優點(dian)遠大于普通(tong)低(di)(di)溫(wen)(wen)制冷(leng)(leng)系(xi)(xi)統(tong)。

　　首先在(zai)干燥倉場合(he)，由于(yu)制(zhi)冷(leng)劑在(zai)制(zhi)冷(leng)蒸(zheng)發器(qi)中的蒸(zheng)發溫度需要(yao)通(tong)過蒸(zheng)發器(qi)管(guan)道壁(bi)傳(chuan)熱(re)給導(dao)熱(re)介質，然(ran)后通(tong)過循(xun)環泵將導(dao)熱(re)介質導(dao)入干燥箱(xiang)擱板(ban)，再通(tong)過擱板(ban)金屬(shu)板(ban)層和料盤傳(chuan)給被冷(leng)凍(dong)物料，在(zai)這一過程中存在(zai)著復雜的管(guan)道流(liu)體(ti)摩擦(ca)和循(xun)環泵葉片(pian)摩擦(ca)造成的熱(re)損(sun)失和流(liu)體(ti)與管(guan)道壁(bi)間的傳(chuan)熱(re)阻力，此外在(zai)干燥箱(xiang)中的真(zhen)空條件下(xia)傳(chuan)熱(re)比(bi)較困難，也是(shi)造成傳(chuan)熱(re)熱(re)溫差較大的原因。一般在(zai)5~15之間，所以要(yao)求制(zhi)冷(leng)機提供的實際蒸(zheng)發溫度在(zai)-30~-50℃之間。

　　在(zai)(zai)冷阱(jing)場合，冷阱(jing)是(shi)專門用(yong)于捕集(ji)水(shui)蒸(zheng)氣的(de)(de)低(di)溫(wen)(wen)(wen)裝置，為有效捕集(ji)來自干(gan)(gan)燥箱(xiang)(xiang)物(wu)料(liao)(liao)升華出的(de)(de)水(shui)蒸(zheng)氣，冷阱(jing)捕集(ji)器(qi)(qi)表(biao)面(mian)溫(wen)(wen)(wen)度(du)(du)(du)須低(di)于物(wu)料(liao)(liao)凍(dong)(dong)結(jie)(jie)(jie)溫(wen)(wen)(wen)度(du)(du)(du)，這是(shi)因為干(gan)(gan)燥箱(xiang)(xiang)和冷阱(jing)間(jian)水(shui)蒸(zheng)氣流(liu)(liu)動需要(yao)(yao)壓力(li)(li)差作(zuo)動力(li)(li)，冷阱(jing)捕集(ji)器(qi)(qi)表(biao)面(mian)溫(wen)(wen)(wen)度(du)(du)(du)越低(di)，壓力(li)(li)差越大(da)，水(shui)蒸(zheng)氣流(liu)(liu)動速(su)度(du)(du)(du)越快。反(fan)之，溫(wen)(wen)(wen)度(du)(du)(du)越高甚至接近物(wu)料(liao)(liao)的(de)(de)凍(dong)(dong)結(jie)(jie)(jie)溫(wen)(wen)(wen)度(du)(du)(du)，水(shui)蒸(zheng)氣流(liu)(liu)動速(su)度(du)(du)(du)越慢甚至停止。因此冷阱(jing)器(qi)(qi)表(biao)面(mian)溫(wen)(wen)(wen)度(du)(du)(du)須低(di)于物(wu)料(liao)(liao)凍(dong)(dong)結(jie)(jie)(jie)溫(wen)(wen)(wen)度(du)(du)(du)15℃以(yi)下，需要(yao)(yao)在(zai)(zai)-40~-60℃之間(jian)。由于實(shi)際使(shi)用(yong)溫(wen)(wen)(wen)度(du)(du)(du)和制冷機(ji)提供的(de)(de)實(shi)際蒸(zheng)發溫(wen)(wen)(wen)度(du)(du)(du)之間(jian)存(cun)在(zai)(zai)傳熱(re)溫(wen)(wen)(wen)差，除捕集(ji)器(qi)(qi)管道壁及油膜產生(sheng)的(de)(de)傳熱(re)阻力(li)(li)外(wai)，隨(sui)著捕集(ji)器(qi)(qi)表(biao)面(mian)結(jie)(jie)(jie)霜(shuang)(shuang)(shuang)的(de)(de)不(bu)斷增厚(hou)，霜(shuang)(shuang)(shuang)層傳熱(re)阻力(li)(li)也不(bu)斷增大(da)，所(suo)以(yi)傳熱(re)溫(wen)(wen)(wen)差平均在(zai)(zai)10℃左右，要(yao)(yao)求制冷機(ji)提供的(de)(de)實(shi)際蒸(zheng)發溫(wen)(wen)(wen)度(du)(du)(du)在(zai)(zai)-50 ~-70℃之間(jian)，尤(you)其是(shi)冷阱(jing)捕集(ji)器(qi)(qi)表(biao)面(mian)在(zai)(zai)結(jie)(jie)(jie)霜(shuang)(shuang)(shuang)過(guo)程中(zhong)后期，實(shi)際需要(yao)(yao)的(de)(de)蒸(zheng)發溫(wen)(wen)(wen)度(du)(du)(du)應更低(di)。

　　總之，作為通(tong)用型凍干機，應(ying)能適應(ying)各種物料的(de)凍干工藝參數(shu)要求，具有能將物料凍結(jie)到-40℃左(zuo)右的(de)能力(li)，冷阱(jing)應(ying)能在-60℃溫度以下長(chang)時間正(zheng)常運轉。

　　常用(yong)制(zhi)(zhi)(zhi)(zhi)冷(leng)設備多使用(yong)單級(ji)壓(ya)(ya)(ya)(ya)縮(suo)(suo)制(zhi)(zhi)(zhi)(zhi)冷(leng)循環(huan)系(xi)統，既一(yi)(yi)種制(zhi)(zhi)(zhi)(zhi)冷(leng)工(gong)質(zhi)通過在壓(ya)(ya)(ya)(ya)縮(suo)(suo)機(ji)循環(huan)系(xi)統中(zhong)排(pai)出(chu)高壓(ya)(ya)(ya)(ya)氣(qi)(qi)(qi)體(ti)并吸(xi)(xi)入(ru)制(zhi)(zhi)(zhi)(zhi)冷(leng)蒸發(fa)后的(de)(de)低(di)(di)(di)壓(ya)(ya)(ya)(ya)氣(qi)(qi)(qi)體(ti)進行(xing)一(yi)(yi)次循環(huan)制(zhi)(zhi)(zhi)(zhi)冷(leng)。常用(yong)單一(yi)(yi)制(zhi)(zhi)(zhi)(zhi)冷(leng)劑(ji)冷(leng)凝(ning)溫(wen)(wen)度(du)(du)(30℃)和蒸發(fa)溫(wen)(wen)度(du)(du)(-40℃)是(shi)在一(yi)(yi)個(ge)大(da)氣(qi)(qi)(qi)壓(ya)(ya)(ya)(ya)以上工(gong)作的(de)(de)，這是(shi)由制(zhi)(zhi)(zhi)(zhi)冷(leng)劑(ji)性(xing)質(zhi)決定。如蒸發(fa)溫(wen)(wen)度(du)(du)低(di)(di)(di)于(yu)-40℃時(shi)(shi)，對應吸(xi)(xi)入(ru)蒸發(fa)氣(qi)(qi)(qi)體(ti)壓(ya)(ya)(ya)(ya)力(li)則(ze)低(di)(di)(di)于(yu)一(yi)(yi)個(ge)大(da)氣(qi)(qi)(qi)壓(ya)(ya)(ya)(ya)。蒸發(fa)溫(wen)(wen)度(du)(du)越低(di)(di)(di)，吸(xi)(xi)入(ru)氣(qi)(qi)(qi)體(ti)密(mi)度(du)(du)、吸(xi)(xi)氣(qi)(qi)(qi)壓(ya)(ya)(ya)(ya)力(li)及吸(xi)(xi)氣(qi)(qi)(qi)效率越低(di)(di)(di)，制(zhi)(zhi)(zhi)(zhi)冷(leng)量大(da)幅度(du)(du)下降(如制(zhi)(zhi)(zhi)(zhi)冷(leng)工(gong)質(zhi)F22在-25℃時(shi)(shi)的(de)(de)密(mi)度(du)(du)為(wei)(wei)9Kg/m3，吸(xi)(xi)氣(qi)(qi)(qi)壓(ya)(ya)(ya)(ya)力(li)為(wei)(wei)0.2Mpa，在-55℃時(shi)(shi)密(mi)度(du)(du)僅為(wei)(wei)2Kg/m3，吸(xi)(xi)氣(qi)(qi)(qi)壓(ya)(ya)(ya)(ya)力(li)僅為(wei)(wei)0.05Mpa，制(zhi)(zhi)(zhi)(zhi)冷(leng)量是(shi)-25℃時(shi)(shi)的(de)(de)五分之(zhi)一(yi)(yi))。由于(yu)壓(ya)(ya)(ya)(ya)縮(suo)(suo)機(ji)吸(xi)(xi)氣(qi)(qi)(qi)壓(ya)(ya)(ya)(ya)力(li)過低(di)(di)(di)，吸(xi)(xi)入(ru)制(zhi)(zhi)(zhi)(zhi)冷(leng)劑(ji)不(bu)(bu)順(shun)暢，導致(zhi)制(zhi)(zhi)(zhi)(zhi)冷(leng)劑(ji)攜帶潤滑油(you)的(de)(de)能力(li)下降，經長時(shi)(shi)間運(yun)轉，壓(ya)(ya)(ya)(ya)縮(suo)(suo)機(ji)壽命大(da)大(da)降低(di)(di)(di)，導致(zhi)提前報(bao)廢。由于(yu)制(zhi)(zhi)(zhi)(zhi)冷(leng)系(xi)統處于(yu)負壓(ya)(ya)(ya)(ya)狀態運(yun)行(xing)，還伴(ban)隨著(zhu)系(xi)統吸(xi)(xi)入(ru)外界空氣(qi)(qi)(qi)等(deng)一(yi)(yi)系(xi)列問題。常見的(de)(de)制(zhi)(zhi)(zhi)(zhi)冷(leng)系(xi)統壓(ya)(ya)(ya)(ya)縮(suo)(suo)機(ji)不(bu)(bu)回油(you)、冰堵(du)、溫(wen)(wen)度(du)(du)突然(ran)升高、完全靠人(ren)工(gong)值守和不(bu)(bu)斷調整維(wei)護等(deng)現(xian)象均系(xi)運(yun)行(xing)溫(wen)(wen)度(du)(du)過低(di)(di)(di)造成。

　　采(cai)用雙級壓(ya)(ya)縮(suo)制(zhi)(zhi)冷(leng)(leng)循(xun)環系統(tong)(tong)也(ye)是使用同一種(zhong)制(zhi)(zhi)冷(leng)(leng)工質(zhi)，并未改變(bian)單(dan)一制(zhi)(zhi)冷(leng)(leng)劑的性質(zhi)，不同的是制(zhi)(zhi)冷(leng)(leng)工質(zhi)在(zai)系統(tong)(tong)中進(jin)行(xing)二次壓(ya)(ya)縮(suo)循(xun)環，強行(xing)在(zai)-50℃以(yi)下(xia)蒸(zheng)發溫度運行(xing)。因此雙級壓(ya)(ya)縮(suo)制(zhi)(zhi)冷(leng)(leng)系統(tong)(tong)無(wu)論是采(cai)用活塞式或螺桿式壓(ya)(ya)縮(suo)機仍(reng)未解決壓(ya)(ya)縮(suo)機吸(xi)入氣體(ti)密度和(he)吸(xi)氣壓(ya)(ya)力(li)過低(di)，回油困難，制(zhi)(zhi)冷(leng)(leng)量(liang)大幅度下(xia)降，系統(tong)(tong)負壓(ya)(ya)狀(zhuang)態運行(xing)等問題(ti)。

　　采(cai)用(yong)兩(liang)種以(yi)(yi)上制(zhi)冷(leng)(leng)工質(zhi)運(yun)(yun)行的(de)(de)(de)制(zhi)冷(leng)(leng)循(xun)(xun)環(huan)系統(tong)(tong)可有效地解決上述(shu)問題。兩(liang)種以(yi)(yi)上制(zhi)冷(leng)(leng)工質(zhi)由于(yu)各工質(zhi)的(de)(de)(de)性質(zhi)不(bu)同，工作溫(wen)(wen)度(du)范圍(wei)不(bu)同，如R22冷(leng)(leng)凝溫(wen)(wen)度(du)和(he)(he)蒸(zheng)(zheng)發溫(wen)(wen)度(du)在(zai)30℃~-40℃范圍(wei)內(nei)，R13(或(huo)R23)在(zai)-10℃~-80℃范圍(wei)內(nei)，R14在(zai)-60℃~-130℃范圍(wei)內(nei)，可以(yi)(yi)組成各自獨立的(de)(de)(de)運(yun)(yun)行系統(tong)(tong)，并取各工質(zhi)氣(qi)體密度(du)及吸(xi)(xi)氣(qi)效率最高的(de)(de)(de)工況段運(yun)(yun)行，如一級壓(ya)(ya)(ya)(ya)縮(suo)循(xun)(xun)環(huan)蒸(zheng)(zheng)發溫(wen)(wen)度(du)-15℃左(zuo)右(you)，吸(xi)(xi)氣(qi)壓(ya)(ya)(ya)(ya)力(li)0.29Mpa，二級壓(ya)(ya)(ya)(ya)縮(suo)循(xun)(xun)環(huan)蒸(zheng)(zheng)發溫(wen)(wen)度(du)-65℃左(zuo)右(you)，吸(xi)(xi)氣(qi)壓(ya)(ya)(ya)(ya)力(li)為(wei)0.22Mpa，三級壓(ya)(ya)(ya)(ya)縮(suo)循(xun)(xun)環(huan)蒸(zheng)(zheng)發溫(wen)(wen)度(du)-115℃左(zuo)右(you)，吸(xi)(xi)氣(qi)壓(ya)(ya)(ya)(ya)力(li)為(wei)0.25Mpa，各系統(tong)(tong)吸(xi)(xi)氣(qi)壓(ya)(ya)(ya)(ya)力(li)均在(zai)一個大(da)(da)氣(qi)壓(ya)(ya)(ya)(ya)(0.1Mpa)以(yi)(yi)上，從根本(ben)上避免(mian)了壓(ya)(ya)(ya)(ya)縮(suo)機因吸(xi)(xi)氣(qi)壓(ya)(ya)(ya)(ya)力(li)過低(di)而導致的(de)(de)(de)回油(you)困難、吸(xi)(xi)入(ru)氣(qi)體密度(du)和(he)(he)運(yun)(yun)行效率過低(di)、制(zhi)冷(leng)(leng)量(liang)低(di)下(xia)、溫(wen)(wen)度(du)突然升(sheng)高、負壓(ya)(ya)(ya)(ya)狀態運(yun)(yun)行、系統(tong)(tong)吸(xi)(xi)入(ru)空氣(qi)等諸多問題的(de)(de)(de)產(chan)生(sheng)。用(yong)較小功率的(de)(de)(de)壓(ya)(ya)(ya)(ya)縮(suo)機就能滿足制(zhi)冷(leng)(leng)量(liang)要求，能源(yuan)利(li)用(yong)率大(da)(da)大(da)(da)提(ti)高。由于(yu)壓(ya)(ya)(ya)(ya)縮(suo)機在(zai)正常(chang)工況下(xia)運(yun)(yun)行，回油(you)正常(chang)，所以(yi)(yi)無需靠人工值守(shou)，經常(chang)維護(hu)和(he)(he)調整，更有利(li)于(yu)延長(chang)壓(ya)(ya)(ya)(ya)縮(suo)機的(de)(de)(de)使(shi)用(yong)壽(shou)命。

　　由此可以(yi)得出結(jie)論(lun)，凍干(gan)機制(zhi)(zhi)(zhi)冷(leng)系(xi)統(tong)在(zai)蒸(zheng)發溫度-55℃以(yi)下使用(yong)時(shi)，多(duo)工(gong)質壓縮(suo)制(zhi)(zhi)(zhi)冷(leng)循(xun)環系(xi)統(tong)較(jiao)單一工(gong)質制(zhi)(zhi)(zhi)冷(leng)循(xun)環系(xi)統(tong)無論(lun)是(shi)單級或是(shi)雙級壓縮(suo)制(zhi)(zhi)(zhi)冷(leng)循(xun)環系(xi)統(tong)有明顯(xian)優勢。強行(xing)采(cai)用(yong)單一制(zhi)(zhi)(zhi)冷(leng)工(gong)質在(zai)-55℃以(yi)下蒸(zheng)發溫度運行(xing)要以(yi)增加能源消耗、人力成本和縮(suo)短壓縮(suo)機使用(yong)壽命為代價。