流体流动

管内中心处速度最大，欲靠近管壁速度愈小；管壁处水的速度为零

液体的粘度随温度升高而减小，气体的粘度随温度升高而增大

粘度为零的流体称为理想流体

压力的单位:<span class="equation-text" data-index="0" data-equation="Pa" contenteditable="false"><span></span><span></span></span>、<span class="equation-text" data-index="1" data-equation="atm" contenteditable="false"><span></span><span></span></span>（标准大气压)、某流体柱高度、<span class="equation-text" data-index="2" data-equation="bar" contenteditable="false"><span></span><span></span></span>（巴）或<span class="equation-text" contenteditable="false" data-index="3" data-equation="kgf/cm^2"><span></span><span></span></span>

表压力=绝对压力-大气压力

<span class="equation-text" contenteditable="false" data-index="0" data-equation="\omega_s=V_s\rho=uA\rho"><span></span><span></span></span>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span class="equation-text" contenteditable="false" data-index="1" data-equation="\omega_s"><span></span><span></span></span>，质量流量，单位<span class="equation-text" contenteditable="false" data-index="2" data-equation="kg/s"><span></span><span></span></span>；<span class="equation-text" contenteditable="false" data-index="3" data-equation="V_s"><span></span><span></span></span>,体积流量，单位<span class="equation-text" contenteditable="false" data-index="4" data-equation="m^3/s"><span></span><span></span></span>

稳态流动系统：各截面上流体的流速、压力、密度等有关物理量仅随着位置变化&nbsp;<br><span class="equation-text" data-index="0" data-equation="\omega_{s1}=\omega_{s2}" contenteditable="false"><span></span><span>，</span></span>即：<span class="equation-text" contenteditable="false" data-index="1" data-equation="\mu_1A_1\rho_1=\mu_2A_2\rho_2=……=\mu A\rho"><span></span><span></span></span>=常数&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;圆管：<span class="equation-text" contenteditable="false" data-index="2" data-equation="\mu_1d_1^2=\mu_nd_n^2"><span></span><span></span></span>=常数

位能、动能及静压能又称为机械能，三者之和称为总机械能或总能量

能量衡算式：<span class="equation-text" contenteditable="false" data-index="0" data-equation="U_1+gZ_1+{u_1^2 \over 2}+p_1v_1+Q_1+W_e=U_2+gZ_2+{u_2^2 \over 2}+p_2v_2"><span></span><span></span></span>

伯努利方程式：<span class="equation-text" contenteditable="false" data-index="0" data-equation="gZ_1+{u_1^2 \over 2}+{p_1 \over \rho}=gZ_2+{u_2^2 \over 2}+{p_2 \over \rho}"><span></span><span></span></span>（理想气体，没有外功加入）<br>阀门减小时，速度减小；局部阻力的变化比速度的变化大

<span class="equation-text" contenteditable="false" data-index="0" data-equation="Z_1+{u_1^2 \over 2g}+{p_1 \over g\rho}+H_e=Z_2+{u_2^2 \over 2g}+{p_2 \over g\rho}+H_f"><span></span><span></span></span>&nbsp; &nbsp; &nbsp; &nbsp;<br>常把Z、<span class="equation-text" contenteditable="false" data-index="1" data-equation="u^2/2g"><span></span><span></span></span>、<span class="equation-text" contenteditable="false" data-index="2" data-equation="{p \over \rho g}"><span></span><span></span></span>与<span class="equation-text" contenteditable="false" data-index="3" data-equation="H_f"><span></span><span></span></span>分别称为位压头、动压头或速度头、静压头与压头损失，<span class="equation-text" contenteditable="false" data-index="4" data-equation="H_e"><span></span><span></span></span>称为有效压头

<span class="equation-text" contenteditable="false" data-index="0" data-equation="\pi"><span></span><span></span></span>取3.14，g取9.81，水的密度为1000<span class="equation-text" contenteditable="false" data-index="1" data-equation="kg/m^3"><span></span><span></span></span>

有效功率&nbsp;&nbsp;<span class="equation-text" contenteditable="false" data-index="0" data-equation="N_e=W_e\omega_s"><span></span><span></span></span>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 轴功率&nbsp; &nbsp;<span class="equation-text" contenteditable="false" data-index="1" data-equation="N=N_e/\eta"><span></span><span></span></span>

雷诺数或雷诺准数：<span class="equation-text" contenteditable="false" data-index="0" data-equation="Re={du \rho \over \mu}"><span></span><span></span></span>

层流和湍流的区分不仅在于各有不同的Re值,两种流型的质点运动方式有本质区别，湍流运动质点径向脉动

层流时速度分布：<br><span class="equation-text" contenteditable="false" data-index="0" data-equation="u_{max}=2u(平均速度)"><span></span><span></span></span>&nbsp; &nbsp;&nbsp;<span class="equation-text" contenteditable="false" data-index="1" data-equation="u_r=u_{max}[1-({r \over R})^2]"><span></span><span></span></span><br>层流时速度沿管径的分布为一抛物线

流体在管路中流动时的阻力可分为直管阻力和局部阻力

<span class="equation-text" contenteditable="false" data-index="0" data-equation="\sum h_f=h_f+h_f\prime"><span></span><span></span></span>&nbsp; &nbsp; &nbsp; &nbsp;<span class="equation-text" contenteditable="false" data-index="1" data-equation="h_f"><span></span><span></span></span>:直管损失，<span class="equation-text" contenteditable="false" data-index="2" data-equation="h_f \prime"><span></span><span></span></span>:局部阻力损失

<span class="equation-text" contenteditable="false" data-index="0" data-equation="h_f=\lambda {l \over d}{u^2 \over 2}={64 \over Re} {l \over d}{u^2 \over 2}={ 64\mu\over du\rho}{l \over d}{u^2 \over 2}={ 32\mu \over d^2\rho}u"><span></span><span></span></span><br><span class="equation-text" contenteditable="false" data-index="1" data-equation="\triangle p_f=\rho h_f=\lambda {l \over d}{\rho u^2 \over 2}"><span></span><span></span></span><br><span class="equation-text" contenteditable="false" data-index="2" data-equation="\rho \sum h_f"><span></span><span></span></span>是指单位体积流体流动时所损失的机械能，以<span class="equation-text" contenteditable="false" data-index="3" data-equation="\triangle p_f"><span></span><span></span></span>表示，又称压力降，即<span class="equation-text" contenteditable="false" data-index="4" data-equation="\triangle p_f=\rho \sum h_f"><span></span><span></span></span>,<span class="equation-text" contenteditable="false" data-index="5" data-equation="\triangle p_f"><span></span><span></span></span>的单位为<span class="equation-text" contenteditable="false" data-index="6" data-equation="Pa"><span></span><span></span></span>

光滑管包括玻璃管、黄铜管、塑料管，粗糙管包括钢管和铸铁管

层流时的摩擦系数&nbsp; &nbsp;&nbsp;<span class="equation-text" contenteditable="false" data-index="0" data-equation="\lambda={64 \over Re} "><span></span><span></span></span>&nbsp; &nbsp; &nbsp;&nbsp;

完全湍流区：摩擦系数<span class="equation-text" contenteditable="false" data-index="0" data-equation="\lambda"><span></span><span></span></span>只与<span class="equation-text" contenteditable="false" data-index="1" data-equation="\epsilon /d"><span></span><span></span></span>有关，与<span class="equation-text" contenteditable="false" data-index="2" data-equation="Re"><span></span><span></span></span>准数无关。若<span class="equation-text" contenteditable="false" data-index="3" data-equation="l/d"><span></span><span></span></span>为一定值时，此区又称为阻力平方区

大截面到小截面，局部阻力系数<span class="equation-text" contenteditable="false" data-index="0" data-equation="\zeta_c=0.5"><span></span><span></span></span>;小截面到大截面，<span class="equation-text" contenteditable="false" data-index="1" data-equation="\zeta_e=1"><span></span><span></span></span>

管路上的配件如弯头、三通、活接头等总称为管件

总能量损失，是管路上直管阻力与局部阻力之和<br><span class="equation-text" contenteditable="false" data-index="0" data-equation="\sum h_f=(\lambda{\sum l_i+\sum l_e \over d}+\sum \zeta_i){u^2 \over 2}"><span></span><span></span></span><br>

管路

测速管

孔板流量计

孔板流量计、文氏流量计节流口面积不变，压力差随流量的不同而变化，统称为差压流量计；转子流量计压力差恒定，截面积反应流量大小，又称为截面流量计