Development of a linear compressor for two-stage pulse tube cryocoolers

A valveless linear compressor was built up to drive a self-made two-stage pulse tube cryocooler. With a designed maximum swept volume of 60 cm^3, the compressor can provide the cryocooler with a pressure volume （PV） power of 400 W. Preliminary measurements of the compressor indicated that both an efficiency of 35%-55% and a pressure ratio of 1.3-1.4 could be obtained. The two-stage pulse tube cryocooler driven by this compressor achieved the lowest temperature of 14.2 K.     

Design and preliminary experimental investigation of a 4 K Stirling-type pulse tube cryocooler with precooling

A Stirling-type pulse tube cryocooler （PTC） with precooling was designed and manufactured to investigate its performance at 4 K. Numerical simulation was carried out based on the well-known regenerator model REGEN with an emphasis on the performance of a 4 K stage regenerator of the Stifling-type PTC as influenced by the warm end temperature, pressure ratio, frequency and average pressure with helium-4 and helium-3 as the working fluid respectively. This study demonstrates that the use of a cold inertance tube can significantly improve the efficiency of a 4 K Stirling-type PTC. A preliminary experimental investigation was carried out with helium-4 as the working fluid and a refrigeration temperature of 4.23 K was achieved. The experimental results show that the operating frequency has a significant influence on the performance of the Stirling-type PTC and a relatively low average pressure is favorable for decreasing the loss associated with the real gas effects of a 4 K Stirling-type PTC.     

北极昆虫的绝技

<正>在北极地区,由于环境严酷,气候恶劣,昆虫的种类要少得多,总共也不过几千种,主要是苍蝇、蚊子、螨、蜢、蜘蛛和蜈蚣等。其中,苍蝇和蚊子的数量最多,占昆虫总数的60%-70%。大的昆虫和鸟类,可以靠身上的长绒毛抵御严寒,但昆虫却永远只能赤身裸     

一个人的群山

北纬四十八度落日还会照耀这里:遥远的汤旺河,寒冷的铁皮屋顶在冬天反射着夕阳的余光。照耀街道上羁留的雪,还有在日出与日落之间我们变幻的脸。落日还会照耀:生死交织的瞬间父亲绝望的眼神。一百个冬天的雪也不能掩盖内心的愧疚。越冷它就越坚硬,一百次的重生也不能把它消融。那黄昏里幽暗的森林,冰冷的树桩     

田野上的歌者

暖风习习的夜晚,乡村三月的田野是蛙们最活跃的舞台。沉寂了一个漫长的寒冬,惊蛰的一声响雷把蛙从冬眠的酣梦中唤醒。蛙们宛如埋入土壤里的一粒粒种子,纷纷从泥土中冒出敏捷的身影。是抑制不住的激情迸发,还是积攒了一冬的力量需要释放,蛙啊!你这乡村田野上最质朴的歌手,在这静谧的春天的夜晚,演绎出一曲雄浑亢奋、激动人心的乐章,令人心潮起伏。这是一曲对新春的礼赞。绿油油的麦苗,金灿灿的菜花,勤劳的农民用双手描绘出了一幅绚丽多彩的画卷,装饰着锦绣河山。