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1、Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology真空物理与技术真空物理与技术第2章 真空技术的稀薄气体理论Vacuum Science and Technology Vac
2、uum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology第二章第二章 真空技术的稀薄气体理论真空技术的稀薄气体理论l气体定律l气体分子运动论l气体中的输运现象Vacuum Science and Technology Vacuum Science
3、 and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology气气 体体 定定 律律Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuu
4、m Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology物质的物理态物质的物理态l分子的聚合体u固态、液态或气态u取决于分子间相互作用力的强度和每个分子的平均动能l分子间毫无相互作用的物理态称为理想气体u分子都是微小的球体u它们的体积于气体实际所占的空间比非常小u分子间毫无作用力u它们完全无规则地沿直线运动u分子间碰撞完全是弹性碰撞Vacuum Science and
5、 Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology玻义耳玻义耳-马略特定律马略特定律lM一定，等温变化u一定质量的气体，当温度保持不变，它的压强和体积的乘积等于常量uPV = 常数uP1V1 = P2V2u真空
6、技术中PV表示气体量 实际真空系统： PV=CMVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology查理定律查理定律lM一定，等容变化u一定质量的气体,在恒定容积下,气体的压力
7、随温度线性变化uPt = P0(1+t)（摄氏温标）u= 1/273ut上升1，P上升1/273uPT = P0T（绝对温标）uP1/P2=T1/T2Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science a
8、nd Technology盖盖-吕莎克定律吕莎克定律lM一定，等压变化u一定质量的气体，压力保持不变时，它的体积随温度线性变化uVt = V0(1+ t)nV0：0时体积nVt：t 时体积n：等压膨胀系数1/273uVT=V0 TuV1/V2=T1/T2Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Techn
9、ology Vacuum Science and Technology Vacuum Science and Technology一般气体定律一般气体定律lP0V0T0-P2V2T2u先等压膨胀到P1V1T1n盖-吕莎克定律 P0=P1u然后等温膨胀到P2V2T2n玻义耳定律 T1 = T2uP0V0/T0=P2V2/T2uPV/T是恒定值Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Sci
10、ence and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology阿伏加德罗定律阿伏加德罗定律l克分子u以克为单位，数值上等于物质的分子量的重量u一克分子氧是32克，一克分子氢是2.016克l阿伏加德罗定律u不同种类的气体在同温同压下，等容积内含的分子数相同u一标准体积的气体质量正比于它的分子量u0，760Torr，1克分子任何气体的体积是22.4升l普适气体常数u1克分子气体 PV/T = R0lPV=(W/M)R0T（理想气体状态方程）Va
11、cuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology分子密度分子密度l阿伏加德罗常数NAu1克分子中的分子数u6.023x1023l单位体积分子数un=(W/M)(NA/V) =(
12、NA/R0)(P/T)uP=760Torr,T=273.16Kn=2.687x1019分子数/厘米3l波尔兹曼常数uk=R0/NAuP=n(R0/NA)T=nkTVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Sci
13、ence and Technology分子密度分子密度Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology道尔顿分压定律道尔顿分压定律l不起化学作用的混合气体不起化学作用的混合
14、气体总压强等于各种气体分等于各种气体分压强的的总和和li.e. If.uNt=N1+N2+N3.uPt=P1+P2+P3.lThen.uP1V=N1kTuP2V=N2kTlTotal Pressure = Sum of “Partial Pressures”lIdeal gas.Non-interactingVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technol
15、ogy Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyCO2的的PV曲线曲线lA，B：高温情况下，符合玻义耳定律的双曲线，符合理想气体假设lC出现拐点lDE完全不同于理想气体的双曲线uL M 气态u沿着平台N-O，系统体积变化而温度、压强不变。N点是气态，O点是液态，K点系统一部分是液态u每条曲线只有一个平台，即在给定温度下，只有一个使气体液化的压强l比曲线C温度更高时，没有能使气体液化的压强，P叫做临界点l压强越高，发生液化过程的温度也越高，气体液化的温度称为沸
16、点，取决于系统压强l分子施加于周围的气体和液体的压强称为蒸气压，蒸气压取决于物质的温度Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology气气-液相变化液相变化l液体的沸点u蒸
17、气压等于环境压强时的温度u标准沸点-对应于1个大气压时的蒸气压u曲线右侧为蒸汽，左侧为液体水的蒸气压曲线20C时，水的蒸汽压17.5Torr 水银的蒸汽压10-3TorrVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum
18、 Science and Technology液液-固相变化固相变化l大气压下对应于液-固变化的温度称为凝固点或熔点凝固时膨胀凝固时收缩液-固转变曲线Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science a
19、nd Technology三相点三相点l蒸气压曲线上各点液体和蒸气共存l凝固点曲线上各点固体和液体共存l两条曲线交叉点称为三相点l三相点以下，不经液态直接升华沸腾、凝固和升华曲线Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Va
20、cuum Science and Technology气体分子运动论气体分子运动论Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology气体的压强气体的压强l压强u大量气体分子对
21、器壁不断碰撞的结果首先考虑单个分子在一次碰撞中对dA的作用然后考虑一段时间dt内所有分子施加与dA的总冲量分子施加于dA的冲量是2mvix宏观压力dAVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science a
22、nd Technology气体压强气体压强数值上等于单位体积气体分子总动能的2/3统计平均量，统计规律，不是力学规律Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology温度的微
23、观解释温度的微观解释u气体分子的平均动能只于温度有关u与热力学温度成正比u温度标志着物体内部分子无规则运动的剧烈程度l能量均分定理u u粒子在每一自由度上的能量为P=nkTVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuu
24、m Science and Technology气体分子的速率分布气体分子的速率分布l气体分子速率分布的定性说明u分子处于无规则的运动和不断的碰撞，速率不断变化n能量守恒、动量守恒u平衡状态时，密度分布均匀，有确定的P,Tn说明服从大小一定的分布u分布：将粒子按某一物理量的大小进行分类，然后统计其相应的数目u分子速率分布就是要知道各速率间隔内分子的百分比以及大部分分子分布在哪个速率区间Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science a
25、nd TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology速率分布函数速率分布函数lf(v)的物理意义：表示速率在v附近单位速率间隔内的分子数占总分子数的百分比u平衡条件下粒子数守恒u气体分子各向同性，同种气体分子u分子间引力忽略N表示一定量气体分子总数dN表示速率分布在某一区间v-v+dv内的分子数dN/N表示分布在这一区间内的分子数百分比不同速率附近取相等间隔，dN/N一定不同，即比率与
26、速率相关，与v的函数正比如果所取间隔越大，则分子数越多，即dN/N越大，dv足够小时dN/N与dv成正比Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyMaxwell-Bo
27、ltzmann分布分布速度为0的分子几乎没有速率很大的分子数很少对大量分子体系才成立速率严格等于某一具体数值的分子数没有意义Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology
28、最可几速率最可几速率lf(v)极大值对应的速率叫做最可几速率vm(vp)u分布在vm所在的区间分子比率最大nH2=1572m/secnN2=421m/secnH2O=525m/secVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology
29、Vacuum Science and Technologyl温度升高时，气体中速率较小的分子减少，而速率较大的分子增加，最可几速率变大，曲线峰值移向速率大的一方，单总面积等于1，所以温度升高曲线变平坦Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Te
30、chnology Vacuum Science and Technology平均速率平均速率l平均速率：大量分子速率的算术平均值val方均根速率 l当分子用速度直接影响研究过程（如气流）时用算术平均值，而当分子动能影响过程时用方均根速率Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vac
31、uum Science and Technology Vacuum Science and Technology分子迁移分子迁移l描述碰撞过程的两个重要的物理量u平均自由程（Mean Free Path MFP）nHow far does a molecule go before it strikes another?u碰撞频率（Impingement rate） Surface FluxnHow many molecule strike the surface in a given period of time？u大气中， MFP很短，Surface Flux 很大u高真空中，MFP很长，S
32、urface Flux很小Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology平均自由程平均自由程l自由程u一个分子连续两次碰撞间经过的距离l平均自由程u所有分子彼此碰撞间经过
33、的平均距离u一个分子在给定时间内连续碰撞间经过的平均距离25C空气温度恒定时，平均自由程和压强成反比Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology平均自由程平均自由程50
34、 meters 10-6 torr5*10-5 m1 torr 50 micrometers5*10-8 m 1000 torr 50 nanometersVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Scienc
35、e and Technology离子和电子的平均自由程离子和电子的平均自由程l离子（或电子）从一个分子碰撞到另一个分子经过的距离，它们本身的碰撞不考虑u离子n速度很快，可认为分子静止n u电子n速度更快，电子直径忽略不计Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Scie
36、nce and Technology Vacuum Science and Technologyeg空气分子在标准状态下的平均自由程、平均速率和碰撞频率d=3.5x10-10m 平均分子量29 T=273K P=1.01x105Pa标准状态下，分子平均自由程约为其直径的200倍每秒碰撞6.5亿次Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vac
37、uum Science and Technology Vacuum Science and Technology Vacuum Science and Technology分子入射率分子入射率l单位时间内与表面碰撞的分子数25C 空气Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacu
38、um Science and Technology Vacuum Science and Technology分子入射率分子入射率Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technol
39、ogy单分子层单分子层25C 空气吸附剂量：1Langmuir=10-6Torr.s，数量级上与1个单分子层相当Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology气体中的输运
40、现象气体中的输运现象Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology粘滞态和分子态粘滞态和分子态l两种重要的气体流动形式u粘滞态u分子态l平均自由程和容器尺度的比值u平均自
41、由程的数量级和容器的线度u分子间碰撞与分子和器壁间的碰撞Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology粘滞态和分子态粘滞态和分子态lMFPd “sparse”/ “ va
42、cant” u气体分子密度非常小u气体分子只和器壁发生碰撞u单个分子u分子间没有动量和能量传递l对单个分子行为研究l一种新的形态l中、高、超高真空Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and
43、 Technology粘滞态和分子态粘滞态和分子态Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology输运输运l输运现象u由于气体分子热运动，使存在于气体中不均匀性逐渐消除，并
44、引起某一物理量从一处迁移至另一处的现象u本质上输运发生在气体从不平衡态到平衡态的过程中u尽管分子热运动速度相当大，但输运完成有时需要很长时间u输运现象和分子自由程密切相关l输运方程Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology V
45、acuum Science and Technology输运种类输运种类粘滞态分子态粘滞性（动量）由于气体各部分流动速度差异内摩擦粘滞性分子拽力热传导（能量）由于气体各部分温度差异热传导热传导扩散（质量）由于气体各部分密度不同扩散热扩散由于容器的温度梯度热扩散热流逸Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and
46、 Technology Vacuum Science and Technology Vacuum Science and Technology粘滞现象粘滞现象现象：象：A 盘自由，自由，B 盘由由电机机 带动而而转动，慢慢，慢慢 A 盘 也跟着也跟着转动起来。起来。解解释：B 盘转动因摩擦作用力因摩擦作用力带 动周周围的空气的空气层，这层又又 带动邻近近层，直到，直到带动A 盘。 这种相种相邻的流体之的流体之间因速度不同，引起的因速度不同，引起的相互作用力称相互作用力称为内摩擦力内摩擦力，或，或粘滞力粘滞力。BAVacuum Science and Technology Vacuum Scie
47、nce and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology实验证明：明：流速不均匀，沿流速不均匀，沿 z 变化（或有梯度）化（或有梯度）, ,流速梯度流速梯度不同流不同流层之之间有有粘滞力粘滞力f流速大的流层带动流速小的流层，流速大的流层带动流速小的流层，流速小的
48、流层后拖流速大的流层。流速小的流层后拖流速大的流层。 dS 的上层面上流体对下层面上流体的上层面上流体对下层面上流体的粘滞力为的粘滞力为 df，反作用为，反作用为 df ，这一，这一对力满足牛顿第三定律。对力满足牛顿第三定律。Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum S
49、cience and Technology Vacuum Science and Technology测定测定 实验实验 A,B 为两筒，两筒，C 为悬丝，M 为镜面；面；A 保持恒定保持恒定转速，速，B 会会跟着跟着转一定角度，大小可通一定角度，大小可通过 M 来来测定，从而知道粘性力大小，定，从而知道粘性力大小，流速梯度及面流速梯度及面积可可测定，故粘度定，故粘度可可测。Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Te
50、chnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology热传导现象热传导现象现象：物体内各部分温度不均匀象：物体内各部分温度不均匀时，将有，将有热量由温度量由温度较高高处传递到温度到温度较低低处，这种种现象叫做象叫做热传导现象象假假设沿沿 z 方向温度梯度最大，方向温度梯度最大，实验证明，明，单位位时间内，通内，通过垂直于垂直于z 轴的的某指定面某指定面传递的的热量与量与该处的温度梯的温度梯度成正比
51、，与度成正比，与该面的面面的面积成正比，成正比，负号号“- -”表示表示热从温度高从温度高处向温度低向温度低处传递， 为导热系数。系数。Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Tech
52、nology扩散现象扩散现象现象：两种物象：两种物质混合混合时，如果其中一种物，如果其中一种物质在在各各处的密度不均匀，的密度不均匀，这种物种物质将从密度大的地将从密度大的地方向密度小的地方散布，方向密度小的地方散布，这种种现象叫象叫扩散散现象象设沿沿z方向有密度梯度，方向有密度梯度，实验证明，明，单位位时间内通内通过垂直垂直于于z轴的某面的某面传递的的质量与量与该出的密度梯度成正比，与出的密度梯度成正比，与该面面面面积成正比成正比负号号“- -”表示表示质量从密度高量从密度高处向密度低向密度低处传递，与密度梯度方向相反，与密度梯度方向相反，D 为扩散散系数。系数。zn（z）dSdMVacuu
53、m Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology输运过程的微观解释输运过程的微观解释l分子的热运动虽然是气体内输运过程的一个重要因素，但却不是唯一的主要因素。l在研究输运过程时，我们
54、还必须注意到另一个因素，即分子间的碰撞。分子间的碰撞越频繁，分子运动所循的路线就越曲折，分子由一处转移到另一处所需的时间就越长。l所以，分子间相互碰撞的频繁程度直接决定着输运过程的强弱。Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technolog
55、y Vacuum Science and Technology粘滞现象的微观解释粘滞现象的微观解释气体气体动理理论的的观点（微点（微观上）上）认为，这种种粘滞力是粘滞力是动量量传递的的结果果。气体既做整体运气体既做整体运动, ,又做分子又做分子热运运动同一同一时间，平均来看，有等量的气，平均来看，有等量的气体分子从上、下两个方向穿体分子从上、下两个方向穿过 P 面，面，这些分子既些分子既带有有热运运动的能量和的能量和动量，量，还带有定向运有定向运动动量。量。定向定向动量量在垂直于流速的方向上在垂直于流速的方向上净迁移迁移由于上由于上层分子分子动量大于下量大于下层，故上，故上层定向定向动量减少，
56、下量减少，下层定向定向动量增加，量增加，类似摩擦力。似摩擦力。Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology气体的粘滞系数气体的粘滞系数 气体的粘滞性随温度增加而增加液体
57、的粘滞性随温度增加而减小与气体密度无关？极高压强和低压强时与预测不符分子间力起作用分子间无碰撞，无动量交换动量迁移只发生在分子与器壁之间Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Tech
58、nology热传导现象的微观解释热传导现象的微观解释49气体气体动理理论认为：a.a.温度温度较高的高的热层分子平均分子平均动能大，能大，温度温度较低的冷低的冷层分子平均分子平均动能小；能小；b.b.由于两由于两层分子碰撞和分子碰撞和掺和，从和，从热层到冷到冷层出出现热运运动能量的能量的净迁移迁移。在时间在时间dt内，沿内，沿z轴正方向输运的总热运动能量轴正方向输运的总热运动能量dQ等于等于A、B两部分在此时间内两部分在此时间内交换的分子数乘以每交换一对分子所引起的交换的分子数乘以每交换一对分子所引起的能量改变能量改变。Vacuum Science and Technology Vacuum
59、Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology热传导系数热传导系数Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology
60、 Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology扩散现象的微观解释扩散现象的微观解释l扩散u各部分气体密度不同时，气体由密度大处向密度较小处渗透l自扩散uP和n到处一致的情况下一种气体扩散于同类气体中单位时间通过单位面积的迁移质量和该处密度梯度成正比反比与P，压强越高，扩散越困难正比与va 温度越高，质量越小，扩散越容易，不同气体扩散速率不同Vac
61、uum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology气体的互扩散气体的互扩散l性质互异的气体间的扩散u气体的扩散过程比压强平衡过程慢得多un处处一致u在气体混合过程中，空间气体成分不
62、断变化，趋向均匀，任何时刻p及n不变Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology ， 和和D之间的关系之间的关系53根据实验结果，/cv介于1.3到2.5之间，D/介于
63、1.3到1.5之间，具体的数值因气体的不同而异。理论值与实验值出现了较大的偏差在于理论中未考虑分子按速率分布。Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology气体分子与器壁
64、碰撞气体分子与器壁碰撞l粘滞态弹性碰撞l分子态余弦定律(克努曾定律)u分子态情况下，分子与器壁的作用分为“凝结、停留、蒸发”三步u分子离开表面时，在与表面法线成角的一定立体角内分子数与cos成正比u物理意义n固体表面对气体分子的作用：分子忘掉原有运动，漫反射n分子在固体表面停留一段时间，分子与表面能量、动量交换的前提Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Tec
65、hnology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology外摩擦力（分子拽力）外摩擦力（分子拽力）l分子拽力u气体分子在空间没有碰撞，直线飞行u分子在表面停留的时间足够将能量迁移至分子u如果表面在运动，它就能将速度分量迁移至分子正比于p，和板A的u与两板间距无关随温度升高而降低，与气体种类相关（分子量减小而减小）Vacuum Science and Technology Vacuum Science and Technology Vacuum Science
66、and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology分子态气体热传导分子态气体热传导l自由分子传导 平均能量2kT分子态气体热导正比与压强P适应系数 Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technolog
67、y Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology分子泻流分子泻流Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and TechnologyVacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology Vacuum Science and Technology热流逸热流逸当测量压强的量具温度与真空容器不同时，测量值和实际值不符平衡时压强与温度平方根成正比
