Name: calibrating a smooth contraction flowmeter
Uploaded: 2023-04-30T07:02:48.000Z
Duration: 13 min 35 s
Channel: JoVE

1. 实验室设施的设置
<ol>
	<li>确保设施内无流体流动。</li>
	<li>确认数据采集系统符合图1B中的示意图。</li>
	<li>将压力传感器#1的正压端口（参见图1B）连接至可移动的皮托管（<img src="/files/ftp_upload/10445/10445eq018.jpg" alt="静力平衡方程 ΣFx=0 示意图，展示力与平衡概念" data-altupdatedat="1761830439000">）。</li>
	<li>将同一压力传感器的负压端口连接至进气通道的静压探头（<img src="/files/ftp_upload/10445/10445eq022.jpg" alt="静力平衡示意图，ΣFx=0。自由体分析，突出力的平衡与矢量分量。" data-altupdatedat="1761830439000">）。因此，该压力传感器的读数将直接表示（<img src="/files/ftp_upload/10445/10445eq023.jpg" alt="压力差方程，PT - P2；表示流体动力学图示中的静力平衡。" data-altupdatedat="1761830439000">）。</li>
	<li>记录该传感器从伏特到帕斯卡的转换系数（<img src="/files/ftp_upload/10445/10445eq024.jpg" alt="静力平衡，ΣFx=0，示意图，用于教学，展示力的平衡与矢量分量。" data-altupdatedat="1761830439000">）。将该值填入表1。</li>
	<li>使用三通接头将压力传感器#2的正压端口（参见图1B）连接至进气通道的静压探头（<img src="/files/ftp_upload/10445/10445eq022.jpg" alt="静力平衡示意图，ΣFx=0。自由体分析，突出力的平衡与矢量分量。" data-altupdatedat="1761830439000">）。</li>
	<li>将压力传感器#2的负压端口敞开，暴露于大气中（<img src="/files/ftp_upload/10445/10445eq025.jpg" alt="热力学图表中的大气压符号，P&lt;sub&gt;atm&lt;/sub&gt;。" data-altupdatedat="1761830439000">）。因此，该传感器的读数将直接表示（<img src="/files/ftp_upload/10445/10445eq026.jpg" alt='压力差方程，P-atm 减 P2，在流体动力学讨论中' data-altupdatedat="1761830439000">）。</li>
	<li>记录该传感器从伏特到帕斯卡的转换系数（<img src="/files/ftp_upload/10445/10445eq027.jpg" alt="静力平衡；ΣFx=0；示意图；物理概念；力分析；力学平衡" data-altupdatedat="1761830439000">）。将该值填入表1。</li>
	<li>设置数据采集系统以100 Hz的采样率采集共500个样本（即5秒的数据）。</li>
	<li>确保数据采集系统中的通道1对应压力传感器#1（<img src="/files/ftp_upload/10445/10445eq023.jpg" alt="压力差方程，PT - P2；表示流体动力学图示中的静力平衡。" data-altupdatedat="1761830439000">）。</li>
	<li>在数据采集系统中输入转换系数<img src="/files/ftp_upload/10445/10445eq024.jpg" alt="静力平衡，ΣFx=0，示意图，用于教学，展示力的平衡与矢量分量。" data-altupdatedat="1761830439000">，以确保压力测量值（<img src="/files/ftp_upload/10445/10445eq023.jpg" alt="压力差方程，PT - P2；表示流体动力学图示中的静力平衡。" data-altupdatedat="1761830439000">）直接转换为帕斯卡。</li>
	<li>将皮托管置于其行程末端，使其接触管壁。由于探头直径为2 mm，第一个速度测量点位于距管壁1 mm的径向坐标处。即，径向位置为<img src="/files/ftp_upload/10445/10445eq028.jpg" alt="半径减小计算方程：r = Ro - 1 = 81.25。" data-altupdatedat="1761830439000"> mm（此处，<img src="/files/ftp_upload/10445/10445eq029.jpg" alt="Ro=82.25，公式，静态测量，结果表示，物理计算，数学模型。" data-altupdatedat="1761830439000"> mm）。</li>
</ol>
<img alt="离心风机装置；使用皮托管和静压探针进行气流分析的空气动力学研究。" src="/files/ftp_upload/10445/10445fig2.jpg" data-altupdatedat="1761830439000" data-alt="图 2"> 
图 2．实验装置。（A）：被研究的流道。（B）：皮托管的手动扫描系统。 <a href="//cloudfront.jove.com/files/ftp_upload/10445/10445fig2large.jpg" target="_blank">请点击此处查看该图的放大版本。</a>
表1. 实验研究的基本参数。参数 数值
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>参数</td>
			<td>数值</td>
		</tr>
		<tr>
			<td>流道半径 (Ro)</td>
			<td>82.25 mm</td>
		</tr>
		<tr>
			<td>传感器#1校准常数 (m_p1)</td>
			<td>136.015944 Pa/V</td>
		</tr>
		<tr>
			<td>传感器#2校准常数 (m_p2)</td>
			<td>141.241584 N/V</td>
		</tr>
		<tr>
			<td>当地大气压</td>
			<td>100,474.15 Pa</td>
		</tr>
		<tr>
			<td>当地温度</td>
			<td>297.15 K</td>
		</tr>
		<tr>
			<td>P_atm-P_2</td>
			<td>311.01 Pa</td>
		</tr>
	</tbody>
</table>
2. 测量
<ol>
	<li>启动流动装置。</li>
	<li>从数字万用表上记录压力传感器#2的电压读数（单位：伏特）。</li>
	<li>将该数值作为 <img src="/files/ftp_upload/10445/10445eq026.jpg" alt='alt="流体力学讨论中的压力差方程，P-atm 减 P2"' data-altupdatedat="1761830439000"> 填入表1，并使用转换因子 <img src="/files/ftp_upload/10445/10445eq027.jpg" alt="静力平衡；ΣFx=0；示意图；物理概念；受力分析；力学平衡" data-altupdatedat="1761830439000"> 将读数从伏特转换为帕斯卡。</li>
	<li>使用数据采集系统记录 (<img src="/files/ftp_upload/10445/10445eq023.jpg" alt="压力差方程，PT - P2；表示流体力学示意图中的静力平衡" data-altupdatedat="1761830439000">) 的读数。</li>
	<li>将 <img src="/files/ftp_upload/10445/10445eq023.jpg" alt="压力差方程，PT - P2；表示流体力学示意图中的静力平衡" data-altupdatedat="1761830439000"> 的数值填入表2。</li>
	<li>使用调节旋钮根据表2中建议的数值改变皮托管的径向位置。</li>
	<li>重复步骤2.4和2.6，直至表2填满。</li>
	<li>通过调节系统的出流来改变流量。</li>
	<li>对至少十个不同的流量重复步骤2.4至2.8。</li>
	<li>关闭流动装置。</li>
</ol>
<img alt="用于气流分析的空气动力学实验装置，包括进气口、孔板、狭缝和堆栈。" src="/files/ftp_upload/10445/10445fig5.jpg" data-altupdatedat="1761830439000" data-alt="图 "> 
图 5．实验装置。在流体系统出口处使用穿孔板以限制气流。 <a href="//cloudfront.jove.com/files/ftp_upload/10445/10445fig5large.jpg" target="_blank">请点击此处查看该图的放大版本。</a>
表2. 代表性结果。速度测量。r (mm) PT - P2 (Pa) u (r) (m/s
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>r (mm)</td>
			<td>PT - P2 (Pa)</td>
			<td>u(r) (m/s)</td>
		</tr>
		<tr>
			<td>2.25</td>
			<td>300.35</td>
			<td>22.34</td>
		</tr>
		<tr>
			<td>12.25</td>
			<td>302.84</td>
			<td>22.43</td>
		</tr>
		<tr>
			<td>22.25</td>
			<td>305.82</td>
			<td>22.54</td>
		</tr>
		<tr>
			<td>32.25</td>
			<td>302.34</td>
			<td>22.41</td>
		</tr>
		<tr>
			<td>42.25</td>
			<td>294.88</td>
			<td>22.13</td>
		</tr>
		<tr>
			<td>52.25</td>
			<td>295.37</td>
			<td>22.15</td>
		</tr>
		<tr>
			<td>62.25</td>
			<td>292.88</td>
			<td>22.06</td>
		</tr>
		<tr>
			<td>68.25</td>
			<td>293.63</td>
			<td>22.09</td>
		</tr>
		<tr>
			<td>72.25</td>
			<td>294.13</td>
			<td>22.10</td>
		</tr>
		<tr>
			<td>75.25</td>
			<td>299.60</td>
			<td>22.31</td>
		</tr>
		<tr>
			<td>77.25</td>
			<td>293.13</td>
			<td>22.07</td>
		</tr>
		<tr>
			<td>79.25</td>
			<td>284.67</td>
			<td>21.75</td>
		</tr>
		<tr>
			<td>80.25</td>
			<td>256.31</td>
			<td>20.63</td>
		</tr>
		<tr>
			<td>81.25</td>
			<td>198.33</td>
			<td>18.15</td>
		</tr>
	</tbody>
</table>
3. 数据分析。
<ol>
	<li>利用表2中的压差值 PT - P2, 确定速度分布。将结果填入表2。</li>
	<li>以半径 <img src="/files/ftp_upload/10445/10445eq030.jpg" alt="色谱图，显示纸上蛋白质分离，方法：保留因子（Rf）。" data-altupdatedat="1761830439000"> 为横坐标，绘制表2中的压力值和速度值（图3）。</li>
	<li>根据表2中的速度和半径值，计算公式（8）中的积分。</li>
	<li>利用公式（8）计算每个流量下的流出系数。</li>
	<li>以 <img src="/files/ftp_upload/10445/10445eq031.jpg" alt="1 减去 P2 与大气压比值的平方根；压力比方程；科学分析公式。" data-altupdatedat="1761830439000"> 为横坐标，绘制流出系数。</li>
	<li>对流出系数拟合函数，幂函数是一个合适的选择。</li>
</ol>
<img alt="流体动力学稳定性图；压力和速度随半径的变化；实验数据分析。" src="/files/ftp_upload/10445/10445fig3.jpg" data-altupdatedat="1761830439000" data-alt="图 3"> 
图 3．典型结果。（A）：沿流动通道径向坐标测量静压的示例。（B）：根据静压测量结果确定的速度分布。 <a href="//cloudfront.jove.com/files/ftp_upload/10445/10445fig3large.jpg" target="_blank">请点击此处查看该图的放大版本。</a>

我们演示了如何应用质量守恒的控制体分析来校准流道，使其作为流量计使用。为此，我们展示了利用皮托管-静压系统，通过对速度分布进行积分，确定流道中流量的方法。随后，引入了流量系数的概念，以考虑流道壁面附近边界层增长的影响。基于不同流量下的一系列速度测量数据，我们建立了一个回归关系，将流量系数表示为流道内静压与当地大气压之比的函数，<img src="/files/ftp_upload/10445/10445eq036.jpg" alt="压力比变量，公式表示，物理或化学教育概念。" data-altupdatedat="1761830439000">。最后，将该回归关系代入流道流量方程中，使其成为<img src="/files/ftp_upload/10445/10445eq036.jpg" alt="压力比变量，公式表示，物理或化学教育概念。" data-altupdatedat="1761830439000">的函数。该方程的构建确保了其在不同当地大气条件、流道尺寸和单位制下均保持有效性。
通过控制体积分析实现质量守恒，可为标定作为流量计的流道提供多种替代方法。例如，在受限流动中...

质量守恒与流量测量

Mass Conservation and Flow Rate Measurements

来源：Ricardo Mejia-Alvarez 和 Hussam Hikmat Jabbar，密歇根州立大学机械工程系，美国密歇根州东兰辛市
本实验的目的是通过控制体（CV）公式法[1, 2]，演示将流道校准为流量计的过程。控制体分析关注的是流动对工程系统的宏观影响，而非通过详细的微分分析所能获得的精细描述。这两种技术应被视为互补的方法，因为控制体分析可为工程师在设计流动系统时选择后续研究路径提供初步依据。总体而言，控制体分析能够使工程师了解系统中主导的质量交换情况，因此在采用微分公式进行任何详细设计或分析之前，理想情况下应首先完成控制体分析。
质量守恒的控制体（CV）公式方法的基本原理是用一个被称作控制面（CS）所包围的简化体积来替代流动系统的细节。这一概念是假想的，可根据需要灵活定义，以巧妙地简化分析过程。例如，控制面应在垂直于主流速度的方向上“截断”进口和出口通道。随后，分析工作将集中于求解通过控制面的净质量通量与控制体内质量变化率之间的平衡关系。本技术将通过光滑收缩段作为流量计的标定过程加以演示。

在给定风机出口流动受限的条件下，图3A展示了使用皮托管在管道内不同径向位置测得的动压（<img src="/files/ftp_upload/10445/10445eq023.jpg" alt="压差方程，PT - P2；表示流体动力学图示中的静力平衡。" data-altupdatedat="1761830439000">）。这些数值用于确定相应径向位置的局部流速，结果如图3B所示。对上述数据应用梯形法则求解方程（4）以计算平均流速，得到结果为<img src="/files/ftp_upload/10445/10445eq032.jpg" alt="电压测量公式，V=21.54；理论计算，物理方程。" data-altupdatedat="1761830439000"> m/s。另一方面，利用表1中的<img src="/files/ftp_upload/10445/10445eq026.jpg" alt='压差方程，P-atm 减 P2，在流体动力...

来源：密歇根州立大学机械工程系，Ricardo Mejia-Alvarez 和 Hussam Hikmat Jabbar，美国密歇根州东兰辛市  
本研究的目的是……

质量守恒是众所周知的物理原理，常与控制体方法结合使用，用于设计多种机械系统。采用控制体分析质量守恒特别适用于估算大尺度水力结构（如大坝、水处理厂或配水系统）的流量。该方法通常作为初步步骤，使工程师能够了解系统中主要的质量交换情况。例如，贯穿坝体设置的出口阀门常用于控制水流。由于质量守恒，通过控制面的净质量通量必须与封闭体积内质量变化率保持平衡。本视频将演示如何应用控制体法进行质量守恒分析，以标定光滑收缩段作为流量计。在之前的视频中，我们讨论了动量守恒的控制体方法的基本原理。本文中，我们将展示该方法在质量守恒中的应用。考虑示意图中的流动通道，其由一台带有平滑收缩段的离心风机组成。质量守恒的控制体分析如何应用于我们的系统？首先，我们取一个假想的封闭表面，称为控制面，用以定义包含一定流动区域的控制体。接下来，写出质量守恒的一般方程。该方程的第一项表示控制体内质量随时间的变化率。在本例中，该项为零，因为流经控制体的流动是稳定的。由于控制体固定于收缩段，方程的第二项得以简化。该项表示通过控制面的净质量通量。对于我们的系统，质量通过端口一进入控制体，并通过端口二离开控制体。假设沿收缩段流体密度恒定，并计算流体速度与单位面积矢量之间的点积后，方程进一步简化。由于质量守恒，两个端口处的质量通量相同。接下来，已知某一端口的质量通量和体积流量，即可求得该端口的平均流速。对于无黏性流体，端口二处的流速在端口截面上是均匀的。该流速可通过沿中心流线应用伯努利方程计算得出。如果您需要回顾伯努利方程，可观看我们之前的视频。端口一处的流体压力为大气压。我们还假设端口一处的流体速度为零，因为其足够接近外部静止环境。因此，无黏性流体在端口二处的速度由以下公式给出。然而，实际速度分布并不均匀。实际上，由于边界层的发展，当流体流经固体壁面附近时，与壁面接触的流体层将具有与壁面相同的速度。随着与壁面距离的增加，流动速度逐渐恢复，直至达到主流速度。这种靠近壁面的速度变化区域称为边界层，其产生是由于黏性作用。为了考虑这一效应，将理想估算结果与实验测量值通过流量系数进行比较。对于一个圆形端口（如本例中所用），若已知流道内径向速度分布，则可计算该系数。速度分布可通过皮托管-静压探针测量获得。如果您需要回顾皮托管-静压探针的工作原理，可观看我们之前的视频。皮托管使流动停滞，从而感应总压，而流体中任意点的总压包含两个部分：静态分量和动态分量。壁面上的静压探针仅感应静态压力。在端口二处应用伯努利方程，可确定管道内任意位置 r 处的流速。通过沿管道径向移动皮托管，并利用压力传感器测量压差，即可获得速度分布。最后，可通过流量系数、通道横截面积以及第二个传感器测得的压差共同确定端口二处的流量。现在您已了解如何使用控制体方法结合质量守恒分析流动系统，接下来我们将应用该方法对流动通道进行校准，并确定其流量系数。实验开始前，请熟悉实验室的布局及内部设备。首先，通过检查主开关确认设备内部无流体流动。然后检查射流装置的盖子是否已盖好。接下来，按照“原理”部分所述的示意图开始设置数据采集系统。将第一个压力传感器的正端口连接到可移动的皮托管上，将该传感器的负端口连接到进气通道的静压探头。因此，该压力传感器的读数将直接给出压力差 PT - P2。记录该传感器从伏特到帕斯卡的转换系数。接着，使用三通接头将第二个压力传感器的正端口连接到皮托管上，将该传感器的负端口暴露于大气中。该压力传感器的读数将给出大气压差。记录该传感器从伏特到帕斯卡的转换系数。使用直尺测量流道半径。同时，从美国国家气象局网站获取实验地点的大气压和温度数据。将这些数值与两个压力传感器的转换系数一起记录在参数表中。现在，将数据采集系统设置为以100赫兹的采样率采集总共500个样本，以获得五秒的数据。确保数据采集系统中的0号通道对应第一个压力传感器，然后在系统中输入其转换系数，使压力读数直接以帕斯卡为单位显示。接着输入第二个压力传感器的转换系数，并确保该传感器对应数据采集系统中的1号通道。将皮托管调节至其移动行程的末端，使其接触管道壁。由于探头直径为2毫米，第一次测量将在距管壁1毫米的径向位置进行。在设置好数据采集系统后，启动流动装置。现在可以开始进行数据采集。使用数字万用表记录第二个压力传感器的读数。利用转换系数将该电压值转换为压力单位，并将其记录在参数表中。对于当前皮托管的位置，使用数据采集系统记录第一个传感器提供的压差值，并将该值记录在结果表中。通过调节移动旋钮改变皮托管的径向位置，使用数据采集系统测量流道内该位置的压差。对流道内不同径向位置重复此步骤，并将读数记录在结果表中。接下来，通过调节系统的出口流量来改变流道内的流速。为此，可在系统出口处安装具有不同孔径的穿孔板，以不同程度地限制流动。测量流道内不同径向位置下的压差，并对至少十个不同的流速值重复此步骤。实验结束后，记得关闭流动装置。在皮托管穿过流道直径的每个位置 r 处，您都获得了总压与静压之间差值的测量结果。针对每个数据点，计算流速并将其数值填入结果表格中。对表格中的所有数据点重复此操作，然后绘制管道横截面上的速度分布曲线。接下来，计算流量系数。为此，首先需要绘制速度与半径的乘积随半径变化的曲线图。由于速度测量是在离散位置进行的，因此流量系数公式中的积分必须通过数值方法求解，例如使用梯形法则。接着，利用该积分值以及参数表中记录的流体密度、流道半径和测点2处大气压与静压之差的测量值，计算流量系数。对流道内每个实验流量值对应的数据组重复上述计算。现在，查看您的结果。绘制不同流量下流量系数与静压比平方根（即1减去压力比的平方根）的散点图。对散点图拟合幂律函数，确定流量系数与流道内静压和当地大气压之比之间的通用关系。接着，将此关系代入流量计算公式中。此处为方便起见，可利用理想气体定律将密度表示为大气压力和绝对温度的函数。由此得到的流量表达式能够在当地大气条件、流道尺寸和单位制发生变化时仍保持有效性。综上所述，将流道校准为流量计的关键在于建立流量与易于测量的变量（如压差）之间的关系。质量守恒的控制体方法在机械工程领域具有广泛的应用。文丘里管是一种用于受限流动的装置，通过测量通道内两个不同截面之间的压力变化来确定流速。本视频中介绍的方法可用于修正文丘里管内的边界层效应，并确定该装置的流量系数。通过比较流动受限前后液流深度的变化，采用质量守恒的控制体分析方法还可用于评估大型液压系统的流量。您刚刚观看了 JoVE 关于质量守恒控制体分析的简介视频。您现在应该理解如何应用此方法来测量流道中的流量，并确定系统的流量系数。感谢观看。

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质量守恒和流速测量

calibrating a smooth contraction flowmeter

Mass conservation can be used to calibrate a smooth contraction as a flowmeter. The experiment uses a control volume, or CV, formulation. A control volume is a simplified region used to study the macroscopic effect of flow on an engineering system.

This approach focuses on the main mass exchange in the system rather than the detailed flow pattern. It is a complementary method to differential analysis, which looks at the flow in more detail. In design work, the CV method can give an engineer an initial basis for choosing a path forward.

The key idea is to replace the full flow passage with a control surface, or CS, that surrounds the region of interest. The control surface is imaginary and can be placed to simplify the analysis. For this setup, the CS should cut the inlet and outlet ports perpendicular to the dominant velocity.

The analysis then compares the net mass flux through the control surface with the rate of change of mass inside the control volume. This balance is the main principle of mass conservation in the CV form. It provides a practical way to calibrate the flow passage as a flowmeter before moving on to more detailed analysis.

Calibrating a Smooth Contraction Flowmeter

calibrating-a-smooth-contraction-flowmeter

buoyancy and drag on immersed bodies

Measuring Drag on Rising Bubbles

Objects, vehicles, and organisms in fluids experience buoyancy, drag, and lift. Buoyancy is the upward force from the fluid’s weight. Drag is the resistive force that acts opposite motion. Lift is the force perpendicular to the direction of motion. These forces matter in engineering and in the study of swimming and flying organisms. Predicting and measuring them helps explain how bodies move through a fluid medium. It also supports the design of vehicles that travel through liquids or gases. <br...

stability of floating vessels

How Cargo Changes Boat Stability

Boat stability depends on hull shape and internal mass distribution. A stable vessel can self-right after it is rolled to one side by an outside force. Careful hull design helps seagoing vessels stay stable with a low draft, which is the submerged depth of the hull. That can improve maneuverability and reduce drag. This experiment uses a model boat with an adjustable center of mass, which represents different cargo loadings. The boat is also modified for automated tracking of its roll angle.

propulsion and thrust

Static Thrust Testing in Propulsion Systems

Propulsion systems create thrust by speeding up a surrounding fluid or high-temperature combustion products. Aircraft, rockets, and ships all use this basic idea. When the fluid leaves at high velocity, conservation of momentum produces an effective force on the vehicle. Thrust is often checked with static thrust tests. In these tests, the propulsion system is fixed to an instrumented mount, and the holding force on the mount is measured as thrust. This setup lets the system run while the...

piping networks and pressure losses

Measuring Pressure Drop in Pipe Components

This experiment measures pressure drop in pipe components used in internal flow systems. Friction from channel walls, fittings, and obstructions can turn fluid pressure into heat, which reduces the pressure available for flow. A piping network is built with straight tubing, helical tube coils, and elbow fittings with sharp 90° bends. Pressure loss is measured across each component set with manometers, which show fluid pressure by the height of liquid in an open vertical column. The measured...

quenching and boiling

Heat Transfer During Metal Quenching

Controlled heating followed by rapid cooling is a key step in many materials processing applications. This heat-treating process can make a material harder. That matters for cutting tools and for surfaces that must resist wear. The rapid cooling stage is called quenching. It is often done by placing the material in a fluid bath, such as water or oil. Quenching heat transfer can happen by forced convection, when fast movement through the coolant drives heat transfer, or by free convection, when...

hydraulic jumps

Water Flow Slowing in a Hydraulic Jump

Hydraulic jumps show how fast open-channel water can suddenly slow down and rise. When water moves at high velocity along an open channel, the flow can become unstable. Small disturbances can make the upper surface jump to a higher level. This abrupt rise is called a hydraulic jump. As the water level increases, the average flow velocity drops. The fast-moving water also loses kinetic energy, and that energy is dissipated as heat. Engineers often build hydraulic jumps into large water works,...

heat exchanger analysis

Measuring Heat Transfer in a Tube Exchanger

Heat exchangers move thermal energy between two fluid streams and are common in energy systems. They appear in car radiators, refrigerator evaporators, and cooling towers in power plants. In each case, heat moves from one fluid to another, either directly or through a surface. This experiment focuses on a water-to-water tube-in-tube heat exchanger. The setup is built and then tested with temperature and flow rate measurements. These measurements are used to find the heat transfer rate, or Q,...

introduction to refrigeration

Hand-Pump Vapor Compression Refrigeration

Vapor compression refrigeration shows how refrigerators, freezers, air-conditioning systems, and heat pumps remove heat. It is the dominant refrigeration technology used in many everyday devices. In this cycle, cooling happens when refrigerant evaporates at low pressure. The absorbed thermal energy is then released to the surroundings when the refrigerant condenses at high pressure. The compressor is the part that raises the working fluid from low pressure to high pressure. Mechanical work is...

hot wire anemometry

Measuring Turbulent Flow with Hot Wires

Hot-wire anemometry measures fast changes in fluid flow with a thin heated wire. Its very short time response makes it useful for rapidly fluctuating motion, especially turbulent flows. This experiment demonstrates how hot-wire anemometry is used in practice. It shows a method for tracking flow conditions when quick changes matter. The setup highlights why a hot-wire anemometer can capture details that slower sensors may miss.

measuring turbulent flows

Hot-Wire Analysis of a Turbulent Jet

Hot-wire anemometry is used to measure a turbulent jet and study its fast changes in speed. Turbulent flows have very high-frequency fluctuations, so they require instruments with a fast time response for proper measurement. A hot-wire anemometer has that short response time and can capture these rapid velocity changes. A previously calibrated hot-wire probe is used to collect velocity data at different positions within the jet. These measurements show how the flow varies across the turbulent...

visualization of flow past a bluff body

Hydrogen Bubble Flow Around a Cylinder

Hydrogen bubble flow around a circular cylinder shows how fluid moves past a bluff body. A bluff body is an object with a shape that causes separated flow over most of its surface. This is different from a streamlined body, such as an airfoil, which stays aligned with the stream and causes less flow separation. Fluid motion can form complex patterns because its governing laws are non-linear. Scientists have studied these patterns for centuries. Computers and supercomputers can help predict...

jet impinging on an inclined plate

Measuring Jet Force on an Inclined Plate

A plane jet striking an inclined plate shows how fluid flow can exert force on a surface. The experiment focuses on how dynamic pressure changes into static pressure at the plate and how that change affects the load on the structure. Pressure is measured along the plate to build a pressure distribution. The plate has small perforations called pressure taps, and these taps connect through hoses to a scanning valve. The scanning valve sends pressure from one tap at a time to a diaphragm pressure...

conservation of energy approach to system analysis

conservation-of-energy-approach-to-system-analysis

Fan-Pipe Flow and Valve Pressure Loss

This experiment examines steady, incompressible flow in a short pipe with a gate valve. It uses the energy conservation equation to track how pressure and flow change through the system. The gate valve is gradually closed, and its effect on the flow conditions is measured. The setup shows how energy dissipation helps a valve restrict flow. It also links the pipe system to the fan that drives the flow by comparing the system curve with the fan’s characteristic curve. The same pressure-based...

mass conservation and flow rate measurements

Mass conservation can be used to calibrate a smooth contraction as a flowmeter. The experiment uses a control volume, or CV, formulation. A control volume is a simplified region used to study the macroscopic effect of flow on an engineering system. This approach focuses on the main mass exchange in the system rather than the detailed flow pattern. It is a complementary method to differential analysis, which looks at the flow in more detail. In design work, the CV method can give an engineer an...

determination of impingement forces on a flat plate with the control volume method

determination-impingement-forces-on-flat-plate-with-control-volume

Jet Impact and Plate Force Measurement

A plane jet striking a flat plate creates a force that can be estimated from changes in linear momentum. This experiment uses a control volume formulation to study that force at different angles. A control volume is an imaginary closed surface that surrounds the flow region and helps simplify the analysis. The control volume approach focuses on the macroscopic effect of flow on an engineering system. It does not try to describe every detail of the fluid motion. Instead, it identifies the main...

mechanical engineering

该系列介绍了一系列的概念, 是理解和设计机械系统的关键。每个视频检查一个特定的主题, 并描述基本的分析方法, 通常用于了解物理行为。

Learn how mass conservation and control volume analysis are used to calibrate a smooth contraction as a flowmeter by comparing mass flux and mass change.

Calibrating a Smooth Contraction Flowmeter

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