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超导磁共振制冷系统的工作原理及日常维护

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发表于 2020-10-21 12:22:11 | 显示全部楼层 |阅读模式

                    

                    

                    
                    
                    <p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);"><span style="box-sizing: border-box;font-weight: 700;">1工作原理</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">众所周知,维持超导磁体超导状态所用的制冷剂是价格昂贵的液氦。一个良好的、稳定的冷却系统,不仅是超导环境存在的重要保证,而且能大大降低液氦的挥发,减轻磁共振运行成本。</p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);"><span style="box-sizing: border-box;font-weight: 700;">1.1磁场的建立</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">超导型磁体的磁场建立是在超导环境中为超导线圈通电流而产生强磁场的。<span style="box-sizing: border-box;font-weight: 700;">在理想状态下,磁场一旦建立,只要维持超导线圈的超低温环境,强磁场就长期存在。</span><span style="box-sizing: border-box;font-weight: 700;">超导材料主要是铌,钛与铜的多丝复合线,它的工作温度为4.2K(-268.8℃)。因此我们必须建立超导环境,将超导材料置于工作温度4.2K下。</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">建立超导环境的过程是首先将超导型磁体的真空绝热层抽真空,将内部压力抽至约0.001Pa,然后将磁体预冷,把液氦容器腔内温度降到接近4.2K,最后在磁体液氦容器中灌满液氦,使超导线圈浸泡在液氦中。因此,<span style="box-sizing: border-box;font-weight: 700;">磁共振的超导线圈用浸泡在低温液氦中的方法以获得其正常工作的超低温环境,虽然磁体采用了真空绝热结构,但由于结构支撑等多种因素,不可能完全阻止热传导,所以液氦会以蒸发的形式带出导入的热量,以维持4.2K的温度。为减少液氦的蒸发,磁共振配备了制冷系统,提供降温减少液氦蒸发。</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);"><span style="box-sizing: border-box;font-weight: 700;">1.2冷却系统</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">磁共振冷却系统是由<span style="box-sizing: border-box;font-weight: 700;">液氦冷屏、冷头、氦压缩机和水冷机组</span>四部分组成。液氦冷屏是磁体的组成部分之一,设有20K、70K两级冷屏,二者的作用都是直接减少辐射传导。</p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);"><span style="box-sizing: border-box;font-weight: 700;">冷头是制冷部件,通过两级缸套端面的铟线圈将低温高压氦气传输到磁共振的两级冷屏上,为低温容器中的液氦降温,保持液氦中超导线圈的环境温度,以隔绝结构导热,降低液氦消耗。</span>它又是一个膨胀机,经过氦压缩机压缩的低温高压氦气在这里膨胀带走周围的热量。冷头的材料主要是丝绸胶木,两级缸套分别以铜丸和铅丸为蓄冷填料。</p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);"><span style="box-sizing: border-box;font-weight: 700;">氦压缩机主要为冷头提供低温高压氦气。氦压缩机中充以高纯度的氦气,并通过软管与冷头相连,工作时,由冷头循环来的热氦气,经过压缩提升压力,在热交换器中与压缩机油交换热量,使温度迅速下降,成为低温高压氦气,经油水分离器滤油,再经吸附器进一步过滤,方送冷头制冷用,此过程即为氦气循环过程。</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);"><span style="box-sizing: border-box;font-weight: 700;">水冷机组类似于一个空调系统,经过热交换给氦压机提供冷却水。氦压缩机产生的热量最终由循环水带走。通过水冷机组、压缩机和冷头不停地工作,就可以源源不断地为磁共振提供冷量,以达到减少液氦蒸发的目的。</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);"><span style="box-sizing: border-box;font-weight: 700;">2维护</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);"><span style="box-sizing: border-box;font-weight: 700;">2.1维护重点</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">磁共振的水冷机组、压缩机和冷头就好像人的心脏一样,需要一刻不停地运行。<span style="box-sizing: border-box;font-weight: 700;">冷头的额定工作寿命一般在(1.5~2)年,冷头中的活塞、旋转阀都是运动部件,随时间不断磨损,造成气密不严、制冷效率下降。</span>另外超期使用会使填料松漏,严重的会将活塞卡死在缸套中造成彻底报废,以致引起氦压升高,液氦气化泄漏,从而导致磁体失超。冷头损坏的情况有两种可能:一是渐进式的逐步扩大。如液氦在一段时间内损失速度明显加快;二是突然间完全不起作用了。<span style="box-sizing: border-box;font-weight: 700;">压缩机组的吸附器只有10000h的寿命。</span><span style="box-sizing: border-box;font-weight: 700;">吸附器是过滤氦气中油雾的重要部件,它的好坏与否关系到冷头的使用寿命,这是因为氦气经过压缩机压缩后,气里面带有的油雾(压缩需油滑),经过油滤器过滤掉大部分,剩下的完全依靠吸附器吸附掉,而吸附器的主要成分是活性炭,一定时间后就会饱和,失去吸附作用,这样油就会跟随氦气污染管道,进入冷头冷凝在冷头里,造成活塞急剧磨损,因此吸附器应定期更换,有利于延长冷头的使用寿命。</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);"><span style="box-sizing: border-box;font-weight: 700;">水冷机组的循环水管时间久了由于腐蚀等原因会产生杂质,使水流不畅,影响热交换的效率;或者由于循环管道的渗漏、冷冻液的蒸发等因素引起冷冻液流失,都会导致水冷系统发生故障,此时氦压缩机会因温度报警而立即停机,冷头自然就不制冷,冷屏温度逐渐上升,辐射漏热增多,液氦蒸发率将成倍提高。</span>此外由于近年来梯度功率增大,梯度系统也采用水冷散热方式来提高冷却效率、降低噪音。因此水冷系统是MRI正常工作的最重要的保障。</p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);"><span style="box-sizing: border-box;font-weight: 700;">2.2日常维护</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">我院自2004年12月安装GEsignatwins1.5TMRI以来,鉴于以上种种原因,总结水冷系统的日常维护经验:</p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">2.2.1<span style="box-sizing: border-box;font-weight: 700;">每日坚持记录水冷系统的各种技术参数,包括液氦压力、液氦容量、氦压机压力、氦压机水冷温度、梯度水冷温度。</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);"><span style="box-sizing: border-box;font-weight: 700;">液氦压力设定为4psi(1psi=6.89476kpa),记录时若压力超出(3.8-4.2psi)范围则表明故障。</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);"><span style="box-sizing: border-box;font-weight: 700;">液氦容量应大于60%,50%是极限值,正常情况下每季度消耗液氦0.2%左右,当遇停电及水冷机、氦压机、冷头故障时液氦挥发加剧,此时要及时维修,否则有失超危险。</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">水冷机温度可监测水冷机工作状态,本系统采用“阿尔西”室外水冷系统,监测温度在18℃~23℃范围之内。</p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">2.2.2<span style="box-sizing: border-box;font-weight: 700;">定期更换吸附器,氦压机上记录有吸附器的使用时间,需一年更换一次。</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">2.2.3<span style="box-sizing: border-box;font-weight: 700;">即使冷头工作正常,三年更换一次。</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">2.2.4需<span style="box-sizing: border-box;font-weight: 700;">定期用水冲洗水冷机组内的过滤网</span><span style="box-sizing: border-box;font-weight: 700;">,尤其在初春杨花时节以及风沙天气时,极易造成因过滤网堵塞而导致水冷停机。</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">2.3故障处理现象一:水冷机状态面板上没有温度显示而是错误码,液氦压力上升,液氦浓度下降。</p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">解决一:室外机组过滤网堵塞,清洗后恢复。</p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">解决二:冷冻液泄漏,更换配件,添加冷冻液后恢复。此种故障在等待配件期间,可临时打开应急自来水通道,可不影响病人,但要注意在上冻季节不适宜用。</p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">现象二:液氦压力超过4.5psi并继续上升,液氦浓度不变,冷头仍然工作。</p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">解决一:更换冷头后排除。更换冷头与系统存化大约在3h左右,另外冷头并不与液氦层相连而是与冷屏相连,不会造成液氦大量流失</p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">解决二:冷头与冷屏之间有结冰,清除结冰后排除。</p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);"><span style="box-sizing: border-box;font-weight: 700;">3维护体会</span></p><p style="box-sizing: border-box;margin-bottom: 18px;overflow-wrap: break-word;text-indent: 30px;color: rgb(85, 85, 85);text-align: start;white-space: normal;background-color: rgb(255, 255, 255);">MRI设备的维护不同于一般小型医疗设备,它严格要求定期检查和保养,同时必须坚持做好每日运行记录,才能保证制冷系统发生故障后能及时发现和处理。</p><p style="max-width: 100%;min-height: 1em;font-family: -apple-system-font, BlinkMacSystemFont, &quot;Helvetica Neue&quot;, &quotingFang SC&quot;, &quot;Hiragino Sans GB&quot;, &quot;Microsoft YaHei UI&quot;, &quot;Microsoft YaHei&quot;, Arial, sans-serif;letter-spacing: 0.544px;white-space: normal;background-color: rgb(255, 255, 255);box-sizing: border-box !important;overflow-wrap: break-word !important;"><span style="max-width: 100%;font-size: 15px;box-sizing: border-box !important;overflow-wrap: break-word !important;"><img data-type="png" class="" data-ratio="0.6100178890876565" data-w="559" src="http://mmbiz.qpic.cn/mmbiz_png/A1DicCH9Vl6MK5Q8sxibcIbgTPECicmaSpkdc8Z9sZ08Rp4HCzAicktdjPgic7Q7trLRwDf6Z3zz8icJhxWHoCn4iaN0w/640?wx_fmt=png" style="box-sizing: border-box !important;overflow-wrap: break-word !important;visibility: visible !important;width: 559px !important;"  /></span></p><p style="margin-top: 10px;max-width: 100%;min-height: 1em;font-family: -apple-system-font, BlinkMacSystemFont, &quot;Helvetica Neue&quot;, &quotingFang SC&quot;, &quot;Hiragino Sans GB&quot;, &quot;Microsoft YaHei UI&quot;, &quot;Microsoft YaHei&quot;, Arial, sans-serif;letter-spacing: 0.544px;white-space: normal;background-color: rgb(255, 255, 255);text-align: center;box-sizing: border-box !important;overflow-wrap: break-word !important;"><strong style="max-width: 100%;font-size: 14px;line-height: 21px;color: rgb(255, 255, 255);font-family: arial, helvetica, sans-serif;box-sizing: border-box !important;overflow-wrap: break-word !important;"><span class="" style="margin-right: 8px;padding: 4px 10px;max-width: 100%;border-radius: 5px;background-color: rgb(191, 0, 0);box-sizing: border-box !important;overflow-wrap: break-word !important;"></span></strong><br data-filtered="filtered" style="max-width: 100%;box-sizing: border-box !important;overflow-wrap: break-word !important;"  /></p><p style="max-width: 100%;min-height: 1em;font-family: -apple-system-font, BlinkMacSystemFont, &quot;Helvetica Neue&quot;, &quotingFang SC&quot;, &quot;Hiragino Sans GB&quot;, &quot;Microsoft YaHei UI&quot;, &quot;Microsoft YaHei&quot;, Arial, sans-serif;letter-spacing: 0.544px;white-space: normal;background-color: rgb(255, 255, 255);text-align: center;box-sizing: border-box !important;overflow-wrap: break-word !important;"><strong style="max-width: 100%;box-sizing: border-box !important;overflow-wrap: break-word !important;"><span style="max-width: 100%;line-height: 2em;color: rgb(255, 0, 0);box-sizing: border-box !important;overflow-wrap: break-word !important;">ID: </span></strong></p><p style="max-width: 100%;min-height: 1em;font-family: -apple-system-font, BlinkMacSystemFont, &quot;Helvetica Neue&quot;, &quotingFang SC&quot;, &quot;Hiragino Sans GB&quot;, &quot;Microsoft YaHei UI&quot;, &quot;Microsoft YaHei&quot;, Arial, 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&quot;Helvetica Neue&quot;, &quotingFang SC&quot;, &quot;Hiragino Sans GB&quot;, &quot;Microsoft YaHei UI&quot;, &quot;Microsoft YaHei&quot;, Arial, sans-serif;letter-spacing: 0.544px;white-space: normal;background-color: rgb(255, 255, 255);text-align: center;box-sizing: border-box !important;overflow-wrap: break-word !important;"><strong style="max-width: 100%;box-sizing: border-box !important;overflow-wrap: break-word !important;"><span style="max-width: 100%;color: rgb(127, 127, 127);font-size: 11px;box-sizing: border-box !important;overflow-wrap: break-word !important;">加群主微信&nbsp;</span></strong><strong style="max-width: 100%;box-sizing: border-box !important;overflow-wrap: break-word !important;"><span style="max-width: 100%;color: rgb(149, 55, 52);font-size: 11px;box-sizing: border-box !important;overflow-wrap: break-word !important;">shanying916</span></strong><strong style="max-width: 100%;box-sizing: border-box !important;overflow-wrap: break-word !important;"><span 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