昆明冷庫為獲取低溫采用兩級壓縮復疊制冷循環的原因
發布時間:2015-08-10點擊數:1778
昆明冷庫為獲取低(di)溫采用(yong)兩級壓縮復疊制冷循環的原因
現在制(zhi)(zhi)冷(leng)(leng)(leng)行業中不乏少數制(zhi)(zhi)冷(leng)(leng)(leng)設備(bei)、冷(leng)(leng)(leng)凍干燥機、冷(leng)(leng)(leng)水機等(deng)設備(bei)都在改進(jin)提升制(zhi)(zhi)冷(leng)(leng)(leng)系統(tong),如壓縮復疊制(zhi)(zhi)冷(leng)(leng)(leng)循環系統(tong)。關(guan)于恒(heng)溫(wen)恒(heng)濕箱制(zhi)(zhi)冷(leng)(leng)(leng)系統(tong)介紹。
三(san)元(yuan)復疊制冷循(xun)環(huan)
兩個單級制(zhi)冷(leng)系統復疊的(de)制(zhi)冷(leng)循環
兩級壓縮系統復疊的制冷循環
針(zhen)對獲取-20℃以下的低溫時均采用復疊(die)式制冷循(xun)環系統。獲取低溫而采用兩級壓縮復疊(die)制冷循(xun)環的原因:
1.壓(ya)縮(suo)機線圈散熱的限制(zhi)
單級(ji)壓(ya)(ya)縮(suo)(suo)機(ji)工作時,在(zai)做-35℃左右,因為壓(ya)(ya)縮(suo)(suo)機(ji)的線圈(quan)是(shi)(shi)(shi)旋(xuan)空在(zai)壓(ya)(ya)縮(suo)(suo)機(ji)中間的,這就產生一(yi)個問題,-35℃時,壓(ya)(ya)縮(suo)(suo)機(ji)的低壓(ya)(ya)是(shi)(shi)(shi)為負數值,也就是(shi)(shi)(shi)產生了(le)一(yi)個真(zhen)空度,這樣線圈(quan)的頂端熱(re)量就沒有辦(ban)法(fa)散去,這樣就壓(ya)(ya)縮(suo)(suo)機(ji)表面是(shi)(shi)(shi)十分涼,可(ke)是(shi)(shi)(shi)實際上內部,他的溫度是(shi)(shi)(shi)很(hen)高(gao)的,(因為真(zhen)空是(shi)(shi)(shi)最好的隔熱(re)介(jie)質)!
2.單級(ji)壓(ya)縮蒸氣制(zhi)冷循環壓(ya)比(bi)的限(xian)制(zhi)
單級(ji)蒸(zheng)氣壓(ya)(ya)(ya)(ya)(ya)縮(suo)式制冷(leng)機(ji)(ji)的(de)(de)最(zui)低蒸(zheng)發(fa)溫度(du),主要取(qu)決于它的(de)(de)冷(leng)凝(ning)(ning)壓(ya)(ya)(ya)(ya)(ya)力(li)及壓(ya)(ya)(ya)(ya)(ya)縮(suo)比(bi)(bi)。制冷(leng)劑的(de)(de)冷(leng)凝(ning)(ning)壓(ya)(ya)(ya)(ya)(ya)力(li)由制冷(leng)劑的(de)(de)類別(bie)和(he)(he)環(huan)境介質(zhi)(如空氣或水(shui))的(de)(de)溫度(du)決定,在通常情況(kuang)下,它處(chu)于0.7~1.8Mpa范圍內。壓(ya)(ya)(ya)(ya)(ya)縮(suo)比(bi)(bi)與冷(leng)凝(ning)(ning)壓(ya)(ya)(ya)(ya)(ya)力(li)和(he)(he)蒸(zheng)發(fa)壓(ya)(ya)(ya)(ya)(ya)力(li)有(you)關,當冷(leng)凝(ning)(ning)壓(ya)(ya)(ya)(ya)(ya)力(li)一定時,隨(sui)著(zhu)蒸(zheng)發(fa)溫度(du)的(de)(de)降(jiang)(jiang)低,蒸(zheng)發(fa)壓(ya)(ya)(ya)(ya)(ya)力(li)也相(xiang)應下降(jiang)(jiang),因而(er)使壓(ya)(ya)(ya)(ya)(ya)縮(suo)比(bi)(bi)上升,它將(jiang)引(yin)起壓(ya)(ya)(ya)(ya)(ya)縮(suo)機(ji)(ji)排氣溫度(du)的(de)(de)升高,潤滑油(you)變(bian)稀,使潤滑條件(jian)變(bian)壞,嚴重(zhong)時甚至(zhi)會出現結炭和(he)(he)拉缸(gang)現象;另(ling)一方面,壓(ya)(ya)(ya)(ya)(ya)縮(suo)比(bi)(bi)的(de)(de)增大將(jiang)導致壓(ya)(ya)(ya)(ya)(ya)縮(suo)機(ji)(ji)的(de)(de)輸氣系(xi)數降(jiang)(jiang)低,制冷(leng)量減少,實際壓(ya)(ya)(ya)(ya)(ya)縮(suo)過(guo)程(cheng)偏離等熵過(guo)程(cheng)越遠,壓(ya)(ya)(ya)(ya)(ya)縮(suo)機(ji)(ji)功耗增加,制冷(leng)系(xi)數下降(jiang)(jiang),經濟性降(jiang)(jiang)低。將(jiang)出現以下一些影響。
a.任何制冷劑,蒸(zheng)發(fa)溫(wen)度越低,則(ze)蒸(zheng)發(fa)壓(ya)力(li)也就越低。過(guo)低的(de)蒸(zheng)發(fa)壓(ya)力(li),有時可(ke)能造(zao)成壓(ya)縮(suo)機難以吸(xi)氣(qi),或者使(shi)外界的(de)空(kong)氣(qi)進(jin)入制冷系(xi)統。
b.當蒸發溫度過低時,某些(xie)常用制冷(leng)劑已達凝固(gu)溫度,無法實(shi)現制冷(leng)劑的(de)流動(dong),循環。
c.蒸(zheng)發壓(ya)(ya)力降(jiang)低,制(zhi)冷劑的比(bi)體(ti)積(ji)增大(da)(da),制(zhi)冷劑的質量(liang)(liang)流量(liang)(liang)減少,制(zhi)冷量(liang)(liang)大(da)(da)大(da)(da)下降(jiang)。為了獲得所需制(zhi)冷量(liang)(liang),必(bi)須增大(da)(da)吸氣容積(ji),使壓(ya)(ya)縮機體(ti)積(ji)過于龐大(da)(da)。
3.制冷劑熱物理(li)特性的(de)限制
現在(zai)(zai)恒溫(wen)(wen)(wen)(wen)恒濕試驗機(ji)中單(dan)級制(zhi)(zhi)(zhi)(zhi)冷(leng)(leng)(leng)循(xun)環(huan)基本上采用(yong)的(de)(de)中溫(wen)(wen)(wen)(wen)制(zhi)(zhi)(zhi)(zhi)冷(leng)(leng)(leng)劑是(shi)R404A,在(zai)(zai)一個大氣壓(ya)下其蒸發溫(wen)(wen)(wen)(wen)度(du)是(shi)-46.5℃(R22/-40.7℃),但空氣冷(leng)(leng)(leng)卻式冷(leng)(leng)(leng)凝器(qi)傳熱(re)溫(wen)(wen)(wen)(wen)差(cha)通常取10℃左(zuo)右(在(zai)(zai)強制(zhi)(zhi)(zhi)(zhi)送(song)風(feng)散熱(re)循(xun)環(huan)下,蒸發器(qi)和內箱的(de)(de)溫(wen)(wen)(wen)(wen)差(cha)),就是(shi)說箱內只能制(zhi)(zhi)(zhi)(zhi)取-36.5℃的(de)(de)低(di)(di)(di)(di)溫(wen)(wen)(wen)(wen),當然,通過調低(di)(di)(di)(di)壓(ya)縮機(ji)的(de)(de)蒸發壓(ya)力,可(ke)以將R404A制(zhi)(zhi)(zhi)(zhi)冷(leng)(leng)(leng)劑的(de)(de)最低(di)(di)(di)(di)蒸發溫(wen)(wen)(wen)(wen)度(du)降低(di)(di)(di)(di)到-50℃;所以要獲(huo)取-50℃及以下的(de)(de)低(di)(di)(di)(di)溫(wen)(wen)(wen)(wen)時必須采用(yong)中溫(wen)(wen)(wen)(wen)制(zhi)(zhi)(zhi)(zhi)冷(leng)(leng)(leng)劑與低(di)(di)(di)(di)溫(wen)(wen)(wen)(wen)制(zhi)(zhi)(zhi)(zhi)冷(leng)(leng)(leng)劑復(fu)疊式的(de)(de)制(zhi)(zhi)(zhi)(zhi)冷(leng)(leng)(leng)循(xun)環(huan),制(zhi)(zhi)(zhi)(zhi)取-50℃~-80℃的(de)(de)低(di)(di)(di)(di)溫(wen)(wen)(wen)(wen),低(di)(di)(di)(di)溫(wen)(wen)(wen)(wen)制(zhi)(zhi)(zhi)(zhi)冷(leng)(leng)(leng)劑一般選用(yong)R23它在(zai)(zai)一個大氣壓(ya)下的(de)(de)蒸發溫(wen)(wen)(wen)(wen)度(du)是(shi)-81.7℃。
由上可見:恒(heng)溫恒(heng)濕試(shi)驗(yan)針對(dui)-40℃機(ji)型可以(yi)采(cai)用(yong)(yong)單(dan)級制(zhi)(zhi)冷(leng)(leng)(leng)(leng)循環,也可以(yi)采(cai)用(yong)(yong)復疊(die)式制(zhi)(zhi)冷(leng)(leng)(leng)(leng)循環系(xi)(xi)統,但單(dan)級制(zhi)(zhi)冷(leng)(leng)(leng)(leng)循環是靠調(diao)小壓縮(suo)機(ji)的(de)膨脹閥開(kai)啟(qi)度,減小制(zhi)(zhi)冷(leng)(leng)(leng)(leng)劑流(liu)量限(xian)流(liu)來調(diao)低蒸發壓力(約(yue)0.7個大(da)氣(qi)壓),從而獲(huo)得更低的(de)蒸發溫度的(de),這樣的(de)設計(ji)是以(yi)犧牲(sheng)系(xi)(xi)統的(de)制(zhi)(zhi)冷(leng)(leng)(leng)(leng)量來達到的(de)(制(zhi)(zhi)冷(leng)(leng)(leng)(leng)量約(yue)只有標準(zhun)的(de)0.7~0.8),導致制(zhi)(zhi)冷(leng)(leng)(leng)(leng)效率低并加大(da)了壓縮(suo)機(ji)的(de)負載,而且易引起(qi)壓縮(suo)機(ji)線圈過(guo)熱(re),影響了壓縮(suo)機(ji)的(de)壽命。
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