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　　凍干機(ji)(ji)干燥箱和冷(leng)(leng)阱(jing)是(shi)需(xu)要專門提供制冷(leng)(leng)的(de)(de)(de)(de)場(chang)合(he)，在(zai)干燥箱場(chang)合(he)，不同(tong)物料的(de)(de)(de)(de)凍結溫(wen)(wen)度(du)需(xu)要在(zai)-20~-40℃之(zhi)間，在(zai)冷(leng)(leng)阱(jing)場(chang)合(he)，冷(leng)(leng)阱(jing)捕集(ji)器表面溫(wen)(wen)度(du)須低(di)(di)于物料凍結溫(wen)(wen)度(du)20℃以(yi)下(xia)，所以(yi)需(xu)要捕集(ji)器表面溫(wen)(wen)度(du)在(zai)-40~-60℃之(zhi)間，由于實(shi)(shi)(shi)際(ji)使(shi)用溫(wen)(wen)度(du)和制冷(leng)(leng)機(ji)(ji)提供的(de)(de)(de)(de)實(shi)(shi)(shi)際(ji)蒸發溫(wen)(wen)度(du)之(zhi)間存在(zai)傳熱溫(wen)(wen)差(cha)，所以(yi)制冷(leng)(leng)機(ji)(ji)提供的(de)(de)(de)(de)實(shi)(shi)(shi)際(ji)蒸發溫(wen)(wen)度(du)應(ying)比實(shi)(shi)(shi)際(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)統(tong)在(zai)凍干機(ji)(ji)應(ying)用實(shi)(shi)(shi)踐中(zhong)普遍得到令人滿(man)意的(de)(de)(de)(de)效(xiao)果，即節(jie)能(neng)環保，又縮短干燥時間，又增加(jia)了(le)制冷(leng)(leng)系(xi)統(tong)運行(xing)的(de)(de)(de)(de)穩(wen)定性，可實(shi)(shi)(shi)現(xian)無人工值守，其優點遠大(da)于普通低(di)(di)溫(wen)(wen)制冷(leng)(leng)系(xi)統(tong)。

　　首先在(zai)(zai)干(gan)(gan)燥(zao)倉場(chang)合，由(you)于(yu)制(zhi)(zhi)冷(leng)劑在(zai)(zai)制(zhi)(zhi)冷(leng)蒸發器(qi)中的(de)蒸發溫度(du)需(xu)要(yao)通(tong)(tong)過(guo)蒸發器(qi)管道壁傳(chuan)熱(re)(re)給(gei)導熱(re)(re)介質，然后通(tong)(tong)過(guo)循環泵將導熱(re)(re)介質導入干(gan)(gan)燥(zao)箱(xiang)擱板(ban)，再(zai)通(tong)(tong)過(guo)擱板(ban)金屬板(ban)層和(he)料盤(pan)傳(chuan)給(gei)被(bei)冷(leng)凍物料，在(zai)(zai)這(zhe)一過(guo)程(cheng)中存在(zai)(zai)著(zhu)復雜的(de)管道流體(ti)(ti)摩擦(ca)和(he)循環泵葉片摩擦(ca)造成的(de)熱(re)(re)損失(shi)和(he)流體(ti)(ti)與管道壁間(jian)(jian)的(de)傳(chuan)熱(re)(re)阻(zu)力(li)，此外(wai)在(zai)(zai)干(gan)(gan)燥(zao)箱(xiang)中的(de)真空(kong)條件下傳(chuan)熱(re)(re)比較(jiao)困難，也(ye)是造成傳(chuan)熱(re)(re)熱(re)(re)溫差較(jiao)大的(de)原因。一般在(zai)(zai)5~15之(zhi)(zhi)間(jian)(jian)，所以要(yao)求(qiu)制(zhi)(zhi)冷(leng)機提供的(de)實際蒸發溫度(du)在(zai)(zai)-30~-50℃之(zhi)(zhi)間(jian)(jian)。

　　在(zai)冷阱場合，冷阱是(shi)(shi)專(zhuan)門用于捕(bu)(bu)集(ji)(ji)水(shui)蒸(zheng)(zheng)氣的低(di)溫(wen)(wen)裝置，為(wei)有效捕(bu)(bu)集(ji)(ji)來自干燥箱(xiang)物料(liao)(liao)升(sheng)華出的水(shui)蒸(zheng)(zheng)氣，冷阱捕(bu)(bu)集(ji)(ji)器表(biao)面(mian)(mian)溫(wen)(wen)度(du)(du)須低(di)于物料(liao)(liao)凍(dong)(dong)結(jie)溫(wen)(wen)度(du)(du)，這(zhe)是(shi)(shi)因為(wei)干燥箱(xiang)和(he)冷阱間水(shui)蒸(zheng)(zheng)氣流(liu)動(dong)需要(yao)(yao)壓(ya)(ya)力(li)差(cha)作動(dong)力(li)，冷阱捕(bu)(bu)集(ji)(ji)器表(biao)面(mian)(mian)溫(wen)(wen)度(du)(du)越低(di)，壓(ya)(ya)力(li)差(cha)越大，水(shui)蒸(zheng)(zheng)氣流(liu)動(dong)速度(du)(du)越快(kuai)。反之(zhi)(zhi)，溫(wen)(wen)度(du)(du)越高甚至(zhi)接(jie)近物料(liao)(liao)的凍(dong)(dong)結(jie)溫(wen)(wen)度(du)(du)，水(shui)蒸(zheng)(zheng)氣流(liu)動(dong)速度(du)(du)越慢甚至(zhi)停止。因此冷阱器表(biao)面(mian)(mian)溫(wen)(wen)度(du)(du)須低(di)于物料(liao)(liao)凍(dong)(dong)結(jie)溫(wen)(wen)度(du)(du)15℃以(yi)下，需要(yao)(yao)在(zai)-40~-60℃之(zhi)(zhi)間。由(you)于實(shi)(shi)際(ji)使用溫(wen)(wen)度(du)(du)和(he)制冷機(ji)提供的實(shi)(shi)際(ji)蒸(zheng)(zheng)發(fa)溫(wen)(wen)度(du)(du)之(zhi)(zhi)間存在(zai)傳(chuan)(chuan)熱溫(wen)(wen)差(cha)，除捕(bu)(bu)集(ji)(ji)器管道壁及油膜產生的傳(chuan)(chuan)熱阻(zu)(zu)力(li)外，隨(sui)著捕(bu)(bu)集(ji)(ji)器表(biao)面(mian)(mian)結(jie)霜的不斷(duan)增(zeng)(zeng)厚，霜層傳(chuan)(chuan)熱阻(zu)(zu)力(li)也不斷(duan)增(zeng)(zeng)大，所(suo)以(yi)傳(chuan)(chuan)熱溫(wen)(wen)差(cha)平均在(zai)10℃左右，要(yao)(yao)求制冷機(ji)提供的實(shi)(shi)際(ji)蒸(zheng)(zheng)發(fa)溫(wen)(wen)度(du)(du)在(zai)-50 ~-70℃之(zhi)(zhi)間，尤其是(shi)(shi)冷阱捕(bu)(bu)集(ji)(ji)器表(biao)面(mian)(mian)在(zai)結(jie)霜過程中后(hou)期，實(shi)(shi)際(ji)需要(yao)(yao)的蒸(zheng)(zheng)發(fa)溫(wen)(wen)度(du)(du)應更低(di)。

　　總之，作為通用(yong)型凍(dong)干機，應(ying)能(neng)適應(ying)各種物(wu)料(liao)的(de)凍(dong)干工藝參數(shu)要(yao)求(qiu)，具有能(neng)將物(wu)料(liao)凍(dong)結到(dao)-40℃左右的(de)能(neng)力(li)，冷阱應(ying)能(neng)在-60℃溫度(du)以下長時間正常(chang)運轉。

　　常(chang)用制(zhi)(zhi)(zhi)冷(leng)(leng)(leng)設備(bei)多(duo)使用單級壓(ya)(ya)縮(suo)制(zhi)(zhi)(zhi)冷(leng)(leng)(leng)循(xun)環(huan)系(xi)統，既一(yi)(yi)(yi)種(zhong)制(zhi)(zhi)(zhi)冷(leng)(leng)(leng)工(gong)(gong)(gong)質通過(guo)在壓(ya)(ya)縮(suo)機(ji)循(xun)環(huan)系(xi)統中排出高壓(ya)(ya)氣(qi)體(ti)并吸(xi)入(ru)(ru)(ru)制(zhi)(zhi)(zhi)冷(leng)(leng)(leng)蒸(zheng)發后的(de)(de)(de)低(di)(di)(di)壓(ya)(ya)氣(qi)體(ti)進行一(yi)(yi)(yi)次循(xun)環(huan)制(zhi)(zhi)(zhi)冷(leng)(leng)(leng)。常(chang)用單一(yi)(yi)(yi)制(zhi)(zhi)(zhi)冷(leng)(leng)(leng)劑(ji)(ji)冷(leng)(leng)(leng)凝(ning)溫度(du)(30℃)和(he)蒸(zheng)發溫度(du)(-40℃)是在一(yi)(yi)(yi)個大氣(qi)壓(ya)(ya)以上工(gong)(gong)(gong)作的(de)(de)(de)，這是由制(zhi)(zhi)(zhi)冷(leng)(leng)(leng)劑(ji)(ji)性質決(jue)定。如(ru)蒸(zheng)發溫度(du)低(di)(di)(di)于(yu)(yu)-40℃時(shi)，對應(ying)吸(xi)入(ru)(ru)(ru)蒸(zheng)發氣(qi)體(ti)壓(ya)(ya)力則低(di)(di)(di)于(yu)(yu)一(yi)(yi)(yi)個大氣(qi)壓(ya)(ya)。蒸(zheng)發溫度(du)越低(di)(di)(di)，吸(xi)入(ru)(ru)(ru)氣(qi)體(ti)密(mi)度(du)、吸(xi)氣(qi)壓(ya)(ya)力及吸(xi)氣(qi)效率(lv)越低(di)(di)(di)，制(zhi)(zhi)(zhi)冷(leng)(leng)(leng)量(liang)大幅度(du)下降(jiang)(jiang)(如(ru)制(zhi)(zhi)(zhi)冷(leng)(leng)(leng)工(gong)(gong)(gong)質F22在-25℃時(shi)的(de)(de)(de)密(mi)度(du)為(wei)(wei)9Kg/m3，吸(xi)氣(qi)壓(ya)(ya)力為(wei)(wei)0.2Mpa，在-55℃時(shi)密(mi)度(du)僅(jin)為(wei)(wei)2Kg/m3，吸(xi)氣(qi)壓(ya)(ya)力僅(jin)為(wei)(wei)0.05Mpa，制(zhi)(zhi)(zhi)冷(leng)(leng)(leng)量(liang)是-25℃時(shi)的(de)(de)(de)五(wu)分之一(yi)(yi)(yi))。由于(yu)(yu)壓(ya)(ya)縮(suo)機(ji)吸(xi)氣(qi)壓(ya)(ya)力過(guo)低(di)(di)(di)，吸(xi)入(ru)(ru)(ru)制(zhi)(zhi)(zhi)冷(leng)(leng)(leng)劑(ji)(ji)不順(shun)暢，導致制(zhi)(zhi)(zhi)冷(leng)(leng)(leng)劑(ji)(ji)攜帶潤(run)滑油的(de)(de)(de)能力下降(jiang)(jiang)，經長時(shi)間運(yun)(yun)轉，壓(ya)(ya)縮(suo)機(ji)壽命大大降(jiang)(jiang)低(di)(di)(di)，導致提(ti)前報廢。由于(yu)(yu)制(zhi)(zhi)(zhi)冷(leng)(leng)(leng)系(xi)統處(chu)于(yu)(yu)負壓(ya)(ya)狀態(tai)運(yun)(yun)行，還伴隨著系(xi)統吸(xi)入(ru)(ru)(ru)外界空氣(qi)等(deng)一(yi)(yi)(yi)系(xi)列問題。常(chang)見(jian)的(de)(de)(de)制(zhi)(zhi)(zhi)冷(leng)(leng)(leng)系(xi)統壓(ya)(ya)縮(suo)機(ji)不回油、冰(bing)堵(du)、溫度(du)突然升高、完(wan)全靠人工(gong)(gong)(gong)值守和(he)不斷調整維護等(deng)現象均系(xi)運(yun)(yun)行溫度(du)過(guo)低(di)(di)(di)造(zao)成(cheng)。

　　采用(yong)雙級壓(ya)縮(suo)(suo)制(zhi)冷(leng)循環系(xi)統(tong)也是(shi)使(shi)用(yong)同(tong)一(yi)種制(zhi)冷(leng)工(gong)質，并未改(gai)變(bian)單一(yi)制(zhi)冷(leng)劑的性(xing)質，不(bu)同(tong)的是(shi)制(zhi)冷(leng)工(gong)質在系(xi)統(tong)中進行(xing)二次壓(ya)縮(suo)(suo)循環，強行(xing)在-50℃以下(xia)(xia)蒸發溫度運行(xing)。因此雙級壓(ya)縮(suo)(suo)制(zhi)冷(leng)系(xi)統(tong)無論是(shi)采用(yong)活塞式或螺桿式壓(ya)縮(suo)(suo)機仍未解決壓(ya)縮(suo)(suo)機吸入氣體密度和(he)吸氣壓(ya)力過低，回油困難，制(zhi)冷(leng)量大幅(fu)度下(xia)(xia)降，系(xi)統(tong)負壓(ya)狀態運行(xing)等問題。

　　采用(yong)兩種以上(shang)制(zhi)冷工質運(yun)(yun)行(xing)(xing)的(de)制(zhi)冷循環(huan)系統(tong)(tong)可(ke)有效地解決上(shang)述問題(ti)。兩種以上(shang)制(zhi)冷工質由于(yu)各工質的(de)性(xing)質不同(tong)，工作(zuo)溫(wen)度范圍(wei)不同(tong)，如(ru)R22冷凝(ning)溫(wen)度和(he)蒸(zheng)發溫(wen)度在(zai)(zai)(zai)(zai)30℃~-40℃范圍(wei)內(nei)(nei)，R13(或R23)在(zai)(zai)(zai)(zai)-10℃~-80℃范圍(wei)內(nei)(nei)，R14在(zai)(zai)(zai)(zai)-60℃~-130℃范圍(wei)內(nei)(nei)，可(ke)以組成各自獨(du)立的(de)運(yun)(yun)行(xing)(xing)系統(tong)(tong)，并取(qu)各工質氣(qi)(qi)(qi)(qi)體(ti)(ti)密度及(ji)吸(xi)氣(qi)(qi)(qi)(qi)效率(lv)最(zui)高的(de)工況段運(yun)(yun)行(xing)(xing)，如(ru)一級(ji)(ji)壓(ya)縮(suo)循環(huan)蒸(zheng)發溫(wen)度-15℃左(zuo)(zuo)右(you)(you)，吸(xi)氣(qi)(qi)(qi)(qi)壓(ya)力(li)0.29Mpa，二(er)級(ji)(ji)壓(ya)縮(suo)循環(huan)蒸(zheng)發溫(wen)度-65℃左(zuo)(zuo)右(you)(you)，吸(xi)氣(qi)(qi)(qi)(qi)壓(ya)力(li)為0.22Mpa，三級(ji)(ji)壓(ya)縮(suo)循環(huan)蒸(zheng)發溫(wen)度-115℃左(zuo)(zuo)右(you)(you)，吸(xi)氣(qi)(qi)(qi)(qi)壓(ya)力(li)為0.25Mpa，各系統(tong)(tong)吸(xi)氣(qi)(qi)(qi)(qi)壓(ya)力(li)均在(zai)(zai)(zai)(zai)一個大(da)氣(qi)(qi)(qi)(qi)壓(ya)(0.1Mpa)以上(shang)，從根本上(shang)避免了壓(ya)縮(suo)機(ji)因吸(xi)氣(qi)(qi)(qi)(qi)壓(ya)力(li)過(guo)(guo)低(di)(di)而導(dao)致的(de)回油困難、吸(xi)入氣(qi)(qi)(qi)(qi)體(ti)(ti)密度和(he)運(yun)(yun)行(xing)(xing)效率(lv)過(guo)(guo)低(di)(di)、制(zhi)冷量低(di)(di)下、溫(wen)度突然升高、負壓(ya)狀態運(yun)(yun)行(xing)(xing)、系統(tong)(tong)吸(xi)入空氣(qi)(qi)(qi)(qi)等諸多問題(ti)的(de)產生(sheng)。用(yong)較小功率(lv)的(de)壓(ya)縮(suo)機(ji)就能(neng)(neng)滿足制(zhi)冷量要求(qiu)，能(neng)(neng)源利(li)用(yong)率(lv)大(da)大(da)提高。由于(yu)壓(ya)縮(suo)機(ji)在(zai)(zai)(zai)(zai)正常工況下運(yun)(yun)行(xing)(xing)，回油正常，所以無需靠人工值守，經(jing)常維護和(he)調整(zheng)，更有利(li)于(yu)延長壓(ya)縮(suo)機(ji)的(de)使用(yong)壽命。

　　由(you)此可以得出結論(lun)，凍干機制(zhi)(zhi)冷系(xi)統(tong)(tong)在蒸發(fa)溫度-55℃以下使用時(shi)，多(duo)工(gong)質(zhi)壓(ya)縮制(zhi)(zhi)冷循環(huan)系(xi)統(tong)(tong)較單一(yi)工(gong)質(zhi)制(zhi)(zhi)冷循環(huan)系(xi)統(tong)(tong)無(wu)論(lun)是(shi)單級或是(shi)雙級壓(ya)縮制(zhi)(zhi)冷循環(huan)系(xi)統(tong)(tong)有(you)明顯優勢(shi)。強行采用單一(yi)制(zhi)(zhi)冷工(gong)質(zhi)在-55℃以下蒸發(fa)溫度運行要(yao)以增加能源消耗、人力成本和縮短壓(ya)縮機使用壽(shou)命為代價。