这项工作得到了以色列科学基金会281/14 号赠款的支持。

1. 瞬时温度测量试验段
<ol><li>测试部分的制造过程 (图 2)
	<ol>
<li>切一根管子的一段至少70厘米长。 注意:试验段的直径和壁厚应与实验装置中所用的管材相同。</li>
		<li>使用铣削机在测试部分沿管道切割4相邻的窄窗, 每个窗口的宽度为6毫米, 长80毫米, 连续窗口之间有25毫米的间隙。</li>
		<li>从12µm 薄不锈钢箔, 削减 40-60 cmlong 和12毫米宽条。 注意:箔将被用来密封在测试管道的窗户。不锈钢应该涂上两条金条纹, 标有一个小的距离从箔的两端, 是用来焊接电源线加热箔, 请参阅图 2。</li>
		<li>使用欧姆计测量箔的电阻。</li>
		<li>按照下面描述的步骤将箔放在管道内。<ol>
<li>创建一个基础, 将箔插入到测试部分由刚性管, 外径等于测试管内径。为此, 切割20毫米宽, 约80厘米长的管壁的一部分</li>
			<li>在将箔放在上面之前, 用油脂涂上基础, 允许在以后的阶段断开基础与箔的连接。</li>
			<li>把箔放在基础上, 把它压扁。用酒精把布拿出来, 用多余的油脂清洗箔。</li>
			<li>将胶粘剂涂在箔片的外围和三段的箔上, 对应于连续窗口之间的桥梁位置。 注意:胶粘剂必须是强的以初期硬化期间至少20分钟为了保证充分的时间为箔附件过程;使用环氧树脂 DP 460。</li>
			<li>小心地插入的基础与箔到测试部分与箔朝向往窗口。 注意:这个过程应该由两个人来完成。</li>
			<li>确保箔与窗口对齐, 金条纹应位于两个外部窗口的边缘。一旦箔适当地被放置并且盖窗口, 连接依据到测试管子在每个末端用夹子。</li>
			<li>将折叠的自行车内轮胎小心地插入到管道中, 如果需要的话, 给轮胎上油。充气轮胎。在通货膨胀期间观察胶粘剂传播横跨箔并且到达依据。 注意:充气轮胎施加的压力, 应保证胶粘剂将管内壁和箔。这也将塑造箔到管子的曲率和减少任何可能的干扰对流动由于箔或胶粘剂。</li>
			<li>用布, 清除任何已达到窗口开口的多余粘合剂。</li>
			<li>让胶粘剂干燥 24 h. 使轮胎充气, 取出并打开夹具。</li>
			<li>在以下步骤中断开与箔和管道的基础:<ol>
<li>轻轻地触摸每一端的基础, 感觉哪一端更容易断开, 并开始断开与该端的连接。</li>
				<li>使用长辊或类似物体逐渐断开原有的基础, 慢慢进入管道, 直到整个基础断开, 箔在管道上保持安全无损。 注意:为了保护密封, 应仔细地进行此过程;如果密封损坏, 应进行新的传热试验管单元。</li>
				<li>通过关闭管道的一端并用水填充管道, 检查管道是否密封。</li>
			</ol>
</li>
		</ol>
</li>
		<li>用水和肥皂清洗管子内侧多余的油脂。</li>
		<li>通过焊接将电加热线连接到箔上的金色条纹上。 注意:为了保护箔在这些斑点, 建议先把一个小的库珀芯片链接到箔, 然后焊接电线。</li>
		<li>用热粘合剂将 T 型热电偶连接到每个窗口的底部。这些热电偶稍后将用于红外摄像机校准过程中。 注意:热电偶的温度读数由 PC 使用 a/d 转换器记录和记录。</li>
		<li>喷涂外层的箔与黑色的垫子喷雾, 以最大限度的发射率。</li>
	</ol></li>
	<li>热通量在铝箔上的应用
	<ol>
<li>将电加热线从箔片边缘连接到直流电源。</li>
		<li>设置电流, 这样箔就达到了理想的温度。 注意:不要达到可能损害管道的温度。为有机玻璃的极限是大约45°c。但是, 一定要加热箔足够, 以确保箔的温度保持至少几度在入口水温, 即使在冷却状态, 由于预期的瞬态变化的流量。</li>
		<li>计算热流量应用的Q = I2r , 其中I是当前应用的, R是箔的电阻。 注意:与管道内的热传递相比, 从箔的外侧向空气开放的传热是微不足道的, 这与管子内的水的传热为2。</li>
		<li>将 PC 可控电气开关连接到热流线之一, 以控制热流脉冲的启动和关断。</li>
	</ol></li>
	<li>红外摄像机 注意:实验室中使用的红外摄像机的详细细节可以在 Ferhstman34中看到。摄像机连接到 PC 并由计算机控制。<ol>
<li>如果可能, 将红外摄像机连接到一组导轨, 使相机的三维移动能够轻松地将其放置在测试部分的不同位置。</li>
		<li>在进行任何测量前几分钟打开红外摄像机, 内部传感器需要时间冷却到所需的温度。</li>
		<li>将红外摄像机从表面上的几厘米处放置在摄像机的焦距内以使焦点。 注意:根据相机分辨率, 确保测量的面积不小于单个像素。最好将测量的表面积由若干像素组成。</li>
		<li>设置红外摄像机的焦点。</li>
		<li>红外摄像机校准过程:<ol>
<li>应用1.2 中所述的热流, 等到达到热稳定状态, 即一旦热电偶放在箔上记录恒定温度。用热电偶测量实验装置附近的环境温度。 注意:这种温度将被用作表面的反射温度。对于表面发射率高的值, 这个参数几乎可以忽略不计。</li>
			<li>输入环境温度作为红外摄像机的反射温度参数。</li>
			<li>对于箔中的每个窗口, 将红外摄像机记录的温度与该窗口的热电偶记录进行比较。调整红外摄像机的发射率特性, 直到红外摄像机的温度记录等于热电偶记录的温度。 注意:这可以做几个热流值;然而, 在这个相对较低的温度范围内, 发射率是不敏感的。在实验记录中, 发射率的平均值为0.98。</li>
		</ol>
</li>
	</ol></li>
</ol>2. 泰勒气泡平移速度及其长度的测量
<ol><li>
光学探头 注:光学探头包括激光光源和光电二极管。当管道的整个截面包含水时, 激光束指向光电二极管, 导致电路关闭。当激光束撞击气泡时, 它会从光电二极管上轻轻地打开电路。因此, 得到了一个二进制信号, 指示光学探针是在气泡前还是液体蛞蝓的前面。<ol>
<li>为了将传感器连接到 a/d 卡, 请生成以下电路 (图 3)。</li>
		<li>打开激光, 指向二极管。检查电路 a/d 软件的数字输入。如果激光击中二极管, 则电路关闭, 并出现一个正信号。 注意:请确保二极管对激光器的波长输出敏感。光学传感器的数据以1赫的速率记录。</li>
	</ol>
</li>
</ol>3. 实验程序
<ol><li>通过法兰或管道记录将测试部分连接到实验设备。</li>
	<li>将加热电线与电源和热电偶连接到任何电脑温度记录仪。</li>
	<li>将红外摄像机置于所需位置的测试部分前面。</li>
	<li>确保摄像机聚焦在箔上;这是更容易做的热流。</li>
	<li>应用热流 (1.2) 和执行红外摄像机校准过程 (1.3.5)。</li>
	<li>将两个光学探头沿试验管放置 注意:如果可能, 在红外摄像机的位置放置一个光学探头;这将允许在温度测量和气泡位置之间进行同步, 因为红外摄像机无法看到气泡。如果不可能, 一定要相应地将结果及时地转移到气泡速度和红外摄像机与光学探头之间的距离。<ol>
<li>检查激光光束确实击中二极管并产生一个正读。</li>
	</ol>
</li>
	<li>打开水泵并设置所需的流量。通过调整电源电流来应用热流。</li>
	<li>等到稳定的状态温度达到。执行计算机程序记录单相管流的壁温。 注意:为了分离泰勒气泡对对流换热系数的影响, 必须首先测量两相流中同流速和热流的对流换热系数, 并在两相实验中进行。建议在每个单独的事件之前执行此操作。</li>
	<li>运行控制气泡注入的计算机程序。 注意:该程序应首先注入一个泰勒气泡, 然后用红外摄像机同时测量壁面温度, 并记录两个光学探针的二进制信号。应同步这两种测量, 以避免录制之间的额外时间偏移。</li>
	<li>在运行之间, 设置足够的延时以确保系统恢复到初始状态, 即壁温返回初始单相稳态值。 注意:在高热流持续的情况下, 单相稳态流动的壁温可能会增加。通过关闭热通量并在实验中休息, 可以避免这种情况发生。</li>
</ol>4. 数据处理
<ol><li>基于情商 1, 计算单相稳态条件的传热系数。 注意:这个系数与时间无关。它将被用作一个正常化的因素在续集。<ol>
<li>对于在给定条件下记录的每个事件, 计算泰勒气泡的长度和平移速度, 方法是将光学探针的距离 ( L) 除以尖端到达时间的时间间隔到每个光学传感器: , 其中tL1和<img alt="Equation 2" src="/files/ftp_upload/57437/57437eq2.jpg"> </img> tL2分别是气泡尖端到达底部和上部光学传感器的时间。</li>
		<li>利用泰勒气泡的平移速度计算气泡长度, 将其乘以其中一个光学探针的开路周期。</li>
	</ol>
</li>
	<li>计算两相流的瞬时局部传热系数应如下所示: 注意:虽然整个实验过程是计算机化的, 泰勒气泡的长度和平移速度在每次实验运行时都不会保持不变。因此, 气泡到达测量点的瞬间就会变化。光学探头和红外摄像机分别具有不同的帧速率、1000和30赫兹。<ol>
<li>使用位于红外摄像机附近的光学探头, 记录气泡尖端到达的瞬间。</li>
		<li>此触发器信号为红外摄像机录制提供时间参考。 注意:为了获得对流换热系数为从气泡底部到测量点 ( z) 的距离函数, 需要使用合奏平均过程, 其中z= 0 对应于气泡底部。此参数应由管道直径D进行规范化。</li>
		<li>设置z/D的分辨率。每个事件 (对应于相同条件) 的所有记录数据值都位于指定的空间分辨率范围内, 并且应平均获得在该距离气泡处的壁面温度的唯一代表值。底部。 注意:该空间分辨率应根据红外摄像机的记录频率和泰勒气泡的平移速度来决定。在这项研究中, 它被采取了在 0.15-0. 3 之间。</li>
		<li>计算传热系数作为一个函数的距离从气泡尖端/底部使用 eq. 1。</li>
		<li>用单相恒定系数规范两相局部瞬时传热系数。 注意:与单相流动相比, 这一比值代表了气泡通道对流换热速率的提高。</li>
	</ol>
</li>
</ol>

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瞬态管流局部传热的实验研究是一项复杂的任务, 需要高端测量仪器和方法, 以及一个定制的实验设备, 特别是一个专门设计的测试部分。本协议显示了一种热成像技术, 它能够忠实地测量由于流动流体力学的变化而在壁温和传热速率上的快速时间变化。
详细介绍了测试部分的制造过程。该设施的关键步骤是用薄薄的不锈钢箔代替管道壁的一部分。箔由电流加热;它的内部边是?...

在过去的几十年中, 大量的对流换热实验研究, 使用不同的技术来测量墙体和/或流体温度的各种流动结构。影响非恒定过程温度测量精度的因素之一是传感器的响应速度慢。为了记录局部瞬时壁温, 测量设备的响应速度足够快, 而记录温度的表面必须与随时间变化的流量处于热平衡状态。因此, 表面的热惯性必须足够小。相关的时间尺度是由引起对流换热变化的水动力现象决定的。因此, 快速响应对于记录瞬态流中的时间依赖性温度至关重要。
为了满足这些要求, 红外摄像机用于记录一个特殊的自制造测试部分, 它允许对流程中的任何变化进行快速的温度响应。管子壁的一部分被切断, 用薄的不锈钢箔代替。Hetsroni et使用了类似的方法。1但是, 它们使用的箔太厚, 无法精确测量瞬时温度的变化, 只显示了时间平均温度。降低箔厚度大大提高了时间响应。2在实验室中应用此方法测量两相流3、4和单相管道流5中的瞬态现象的对流换热系数。
在图 1中给出了两相流设备的示意图布局, 在 Babin et . 中可以找到关于独特进气装置的附加信息。3
由于瞬态流动行为和孔隙率对管内截面的影响, 两相流中对流换热的研究非常复杂。因此, 许多研究只提出了一个给定流的平均对流换热系数作为特定流条件的函数6,7,8,9,10,11. 然而, 文件由唐纳利et 。12和刘et 。13表示两阶段局部对流换热研究的实例。
本研究讨论了在管道中注入停滞或流动液体的单个拉长 (泰勒) 气泡的传热测量。泰勒气泡以恒定的平移速度传播14,15,16。气泡传播速度的确定使用光学探针方法, 由激光光源和光电二极管3,4。
红外摄像机和光学探头的结合允许测量局部瞬时对流换热, 作为从泰勒气泡顶部或底部的距离的函数。
瞬时壁温可用于计算对流换热系数、 h和努塞尔数:
<img alt="Equation 1" src="/files/ftp_upload/57437/57437eq1.jpg">, (1)
其中q为箔的热流, tw 和T∞分别为壁温和入口水温, k为液体电导率, D为管径。通常用于确定传热系数的体积温度没有测量, 以避免对流量产生任何干扰。

<table><tbody><tr><td>Infra red camera</td><td>Optris</td><td>PI-1450</td><td></td></tr><tr><td>Thermocouples A/D card&amp;nbsp;</td><td>National Instruments</td><td>NI cDAQ-9714.</td><td></td></tr><tr><td>Labview program</td><td>National Instruments</td><td></td><td></td></tr><tr><td>Epoxy DP-460</td><td>3M Scotch-weld</td><td></td><td></td></tr></tbody></table>

measurements of local instantaneous convective heat transfer in a pipe - single and two-phase flow

本手稿提供一步一步的描述的制造过程的测试部分设计, 以测量局部瞬时传热系数作为一个函数的液体流速在透明管道。通过某些修正, 该方法扩展到气液流动, 特别强调单拉长 (泰勒) 气泡对传热增强的影响。采用无创热成像技术测量了电加热金属箔的瞬时温度。箔被胶合在管子的一个狭窄的槽切开的盖子。箔的热惯量小到足以检测瞬时箔温度的变化。测试部分可以沿着管道移动, 足够长的时间覆盖不断增长的热边界层的相当一部分。
在每一个实验运行的开始, 得到一个恒定的水流速率和热通量到箔的稳定状态, 并作为参考。然后将泰勒气泡注入管道中。泰勒气泡通过垂直管内传播时的传热系数变化是测量点距离从运动泰勒气泡底部的函数。因此, 结果代表了局部传热系数。在相同条件下预制的多个独立运行允许积累足够的数据, 以计算在瞬态对流换热过程中可靠的集合平均结果。为了在与气泡一起移动的参考框架中执行此操作, 必须在任何时候都知道气泡沿管道的位置。本文详细描述了用光学探针测量泰勒气泡的长度和平移速度的方法。

在图 4中显示了一个光学传感器输出记录的示例, 其中一个泰勒气泡在充满积水的垂直管道中上升。最初的大下落代表电路的开头由于泰勒气泡尖, 而以后更短的下落跟随上升到最初的价值由于延长的气泡尾巴的通过, 代表在液体苏醒的分散的气泡在泰勒的泡沫后面。两个光学探针的输出之间的时间漂移是明显的, 这是由于两个探头沿管道之间的距离。...

Watch this Scientific Journal Video about Measurements of Local Instantaneous Convective Heat Transfer in a Pipe - Single and Two-phase Flow at JoVE.com

Measurements of Local Instantaneous Convective Heat Transfer in a Pipe - Single and Two-phase Flow

本文介绍了在单或两相管流中测量局部瞬时对流换热系数的方法。本文还提出了一种简单的光学方法来确定长 (泰勒) 气泡在恒定速度下运动的长度和传播速度。

管道单、两相流局部瞬时对流换热的测量

This manuscript provides step by step description of the manufacturing process of a test section designed to measure the local instantaneous heat transfer ...

measurements-local-instantaneous-convective-heat-transfer-pipe-single

Universidad de Cartagena UDEC

Research

JoVE Journal

Engineering

7.1K 次观看.  Tel-Aviv University. 本文介绍了在单或两相管流中测量局部瞬时对流换热系数的方法。本文还提出了一种简单的光学方法来确定长 (泰勒) 气泡在恒定速度下运动的长度和传播速度。

视频: Measurements of Local Instantaneous Convective Heat Transfer in a Pipe - Single and Two-phase Flow

Echo Particle Image Velocimetry

The transport of mass, momentum, and energy in fluid flows is ultimately determined by spatiotemporal distributions of the fluid velocity field.1 Consequently, a prerequisite for understanding, predicting, and controlling fluid flows is the capability to measure the velocity field with adequate spatial and temporal resolution.2 For velocity measurements in optically opaque fluids or through optically opaque geometries, echo particle image velocimetry (EPIV) is an attractive diagnostic technique to generate "instantaneous" two-dimensional fields of velocity.3,4,5,6 In this paper, the operating protocol for an EPIV system built by integrating a commercial medical ultrasound machine7 with a PC running commercial particle image velocimetry (PIV) software8 is described, and validation measurements in Hagen-Poiseuille (i.e., laminar pipe) flow are reported.
For the EPIV measurements, a phased array probe connected to the medical ultrasound machine is used to generate a two-dimensional ultrasound image by pulsing the piezoelectric probe elements at different times. Each probe element transmits an ultrasound pulse into the fluid, and tracer particles in the fluid (either naturally occurring or seeded) reflect ultrasound echoes back to the probe where they are recorded. The amplitude of the reflected ultrasound waves and their time delay relative to transmission are used to create what is known as B-mode (brightness mode) two-dimensional ultrasound images. Specifically, the time delay is used to determine the position of the scatterer in the fluid and the amplitude is used to assign intensity to the scatterer. The time required to obtain a single B-mode image, t, is determined by the time it take to pulse all the elements of the phased array probe. For acquiring multiple B-mode images, the frame rate of the system in frames per second (fps) = 1/&delta;t. (See 9 for a review of ultrasound imaging.)
For a typical EPIV experiment, the frame rate is between 20-60 fps, depending on flow conditions, and 100-1000 B-mode images of the spatial distribution of the tracer particles in the flow are acquired. Once acquired, the B-mode ultrasound images are transmitted via an ethernet connection to the PC running the PIV commercial software. Using the PIV software, tracer particle displacement fields, D(x,y)[pixels], (where x and y denote horizontal and vertical spatial position in the ultrasound image, respectively) are acquired by applying cross correlation algorithms to successive ultrasound B-mode images.10 The velocity fields, u(x,y)[m/s], are determined from the displacements fields, knowing the time step between image pairs, &Delta;T[s], and the image magnification, M[meter/pixel], i.e., u(x,y) = MD(x,y)/&Delta;T. The time step between images &Delta;T = 1/fps + D(x,y)/B, where B[pixels/s] is the time it takes for the ultrasound probe to sweep across the image width. In the present study, M = 77[&mu;m/pixel], fps = 49.5[1/s], and B = 25,047[pixels/s]. Once acquired, the velocity fields can be analyzed to compute flow quantities of interest.

An echo particle image velocimetry (EPIV) system capable of acquiring two-dimensional fields of velocity in optically opaque fluids or through optically opaque geometries is described, and validation measurements in pipe flow are reported.

回声粒子图像测速技术

The transport of mass, momentum, and energy in fluid flows is ultimately determined by spatiotemporal distributions of the fluid velocity field.1 ...

科研

工程学

Experimental Methodology for Estimation of Local Heat Fluxes and Burning Rates in Steady Laminar Boundary Layer Diffusion Flames

Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex interactions occurring at the interface between gas-phase flames and condensed-phase fuels. The current research provides a technique to explore the dynamic relationship between a combustible condensed fuel surface and gas-phase flames in laminar boundary layers. Experiments have previously been conducted in both forced and free convective environments over both solid and liquid fuels. A unique methodology, based on the Reynolds Analogy, was used to estimate local mass burning rates and flame heat fluxes for these laminar boundary layer diffusion flames utilizing local temperature gradients at the fuel surface. Local mass burning rates and convective and radiative heat feedback from the flames were measured in both the pyrolysis and plume regions by using temperature gradients mapped near the wall by a two-axis traverse system. These experiments are time-consuming and can be challenging to design as the condensed fuel surface burns steadily for only a limited period of time following ignition. The temperature profiles near the fuel surface need to be mapped during steady burning of a condensed fuel surface at a very high spatial resolution in order to capture reasonable estimates of local temperature gradients. Careful corrections for radiative heat losses from the thermocouples are also essential for accurate measurements. For these reasons, the whole experimental setup needs to be automated with a computer-controlled traverse mechanism, eliminating most errors due to positioning of a micro-thermocouple. An outline of steps to reproducibly capture near-wall temperature gradients and use them to assess local burning rates and heat fluxes is provided.

We describe the use of micro-thermocouples to estimate local temperature gradients in steady laminar boundary layer diffusion flames. By extension of the Reynolds Analogy, local temperature gradients can be further used to estimate the local mass burning rates and heat fluxes in such flames with high accuracy.

在稳定层流边界层扩散火焰本地热通量和燃烧率的估计实验方法

Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex ...

Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the hybrid wettable pattern. Hybrid wettable patterns were produced by coating superhydrophilic SiO2 on a masked, hydrophobic, cylindrical copper surface. Using de-ionized (DI) water as the working fluid, pool-boiling heat-transfer studies were conducted on the different surface-treated copper cylinders of a 25-mm diameter and a 40-mm length. The experimental results showed that the number of interlines and the orientation of the hybrid wettable pattern influenced the wall superheat and the HTC. By increasing the number of interlines, the HTC was enhanced when compared to the plain surface. Images obtained from the charge-coupled device (CCD) camera indicated that more bubbles formed on the interlines as compared to other parts. The hybrid wettable pattern with the lowermost section being hydrophobic gave the best heat-transfer coefficient (HTC). The experimental results indicated that the bubble dynamics of the surface is an important factor that determines the nucleate boiling.

Pool-boiling heat-transfer experiments were carried out to observe the effects of hybrid wettable patterns on the heat-transfer coefficient (HTC). The parameters of investigation are the number of interlines and the pattern orientation of the modified wettable surface.

在圆柱面池沸腾传热强化与混合可湿性模式

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the ...

Uncoupling Coriolis Force and Rotating Buoyancy Effects on Full-Field Heat Transfer Properties of a Rotating Channel

An experimental method for exploring the heat transfer characteristics of an axially rotating channel is proposed. The governing flow parameters that characterize the transport phenomena in a rotating channel are identified via the parametric analysis of the momentum and energy equations referring to a rotating frame of reference. Based on these dimensionless flow equations, an experimental strategy that links the design of the test module, the experimental program and the data analysis is formulated with the attempt to reveal the isolated Coriolis-force and buoyancy effects on heat transfer performances. The effects of Coriolis force and rotating buoyancy are illustrated using the selective results measured from rotating channels with various geometries. While the Coriolis-force and rotating-buoyancy impacts share several common features among the various rotating channels, the unique heat transfer signatures are found in association with the flow direction, the channel shape and the arrangement of heat transfer enhancement devices. Regardless of the flow configurations of the rotating channels, the presented experimental method enables the development of physically consistent heat transfer correlations that permit the evaluation of isolated and interdependent Coriolis-force and rotating-buoyancy effects on the heat transfer properties of rotating channels.

Here, we present an experimental method for decoupling the interdependent Coriolis-force and rotating-buoyancy effects on full-field heat transfer distributions of a rotating channel.

解耦科里奥利力和旋转浮力对旋转通道全场传热性能的影响

An experimental method for exploring the heat transfer characteristics of an axially rotating channel is proposed. The governing flow parameters that ...

Testing the Heat Transfer Efficiency of a Finned-tube Heat Exchanger

Source: Michael G. Benton and Kerry M. Dooley, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA
Heat exchangers transfer heat from one fluid to another fluid. Multiple classes of heat exchangers exist to fill different needs. Some of the most common types are shell and tube exchangers and plate exchangers1. Shell and tube heat exchangers use a system of tubes through which fluid flows1. One set of tubes contains the liquid to be cooled or heated, while the second set contains the liquid that will either absorb heat or transmit it1. Plate heat exchangers use a similar concept, in which plates are closely joined together with a small gap between each for liquid to flow1. The fluid flowing between the plates alternates between hot and cold so that heat will move into or out of the necessary streams1. These exchangers have large surface areas, so they are usually more efficient1.
The goal for this experiment is to test the heat transfer efficiency of a finned-tube heat exchanger (Figure 1) and compare it to the theoretical efficiency of a heat exchanger without fins. The experimental data will be measured for three different flow rates of monoethylene glycol (MEG). Two different water flow rates for each MEG flow rate will be used. Using the Wilson plot method the heat transfer coefficients will be determined from the experimental data. Additionally, the Reynold&#39;s number and the amount of heat transferred will be compared for flow with and without the fins to evaluate heat transfer efficiency.
<img alt="Figure 1" src="/files/ftp_upload/10437/10437fig1.jpg" /> 
Figure 1: Finned-tube Heat Exchanger. 1) MEG outlet temperature 2) water inlet temperature 3) MEG inlet temperature 4) water outlet temperature 5) water meter 6) MEG accumulation sight glass/cylinder.

Heat Transfer Efficiency Test of a Finned-tube Heat Exchanger

测试芬管热交换器的传热效率

Source: Michael G. Benton and Kerry M. Dooley, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA
Heat exchangers transfer ...

教育

JoVE Science Education

化学工程

Piping Networks and Pressure Losses

Source: Alexander S Rattner, Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
This experiment introduces the measurement and modeling of pressure losses in piping networks and internal flow systems. In such systems, frictional flow resistance from channel walls, fittings, and obstructions causes mechanical energy in the form of fluid pressure to be converted to heat. Engineering analyses are needed to size flow hardware to ensure acceptable frictional pressure losses and select pumps that meet pressure drop requirements.
In this experiment, a piping network is constructed with common flow features: straight lengths of tubing, helical tube coils, and elbow fittings (sharp 90&#176; bends). Pressure loss measurements are collected across each set of components using manometers - simple devices that measure fluid pressure by the liquid level in an open vertical column. Resulting pressure loss curves are compared with predictions from internal flow models.

Pressure Losses in Piping Networks and Internal Flow Systems

管道网络和压力损失

Source: Alexander S Rattner, Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
This experiment ...

机械工程

Quenching and Boiling

Source: Alexander S Rattner, Sanjay Adhikari, and Mahdi Nabil; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
Controlled heating followed by rapid cooling is an important element of many materials processing applications. This heat-treating procedure can increase material hardness, which is important for cutting tools or surfaces in high wear environments. The rapid cooling stage is called quenching, and is often performed by immersing materials in a fluid bath (often water or oil). Quenching heat transfer can occur due to forced convection - when the action of rapidly moving material through coolant drives the heat transfer process, and due to free convection - when the reduced density of hot fluid near the material surface causes buoyancy-driven circulation and heat transfer. At high material temperatures, the coolant can boil, leading to increased heat transfer effectiveness. However, when extremely hot materials are quenched, they can be blanketed in relatively low thermal conductivity coolant vapor, leading to poor heat transfer.
In this experiment, quenching heat transfer will be measured for a heated copper cylinder, which is representative of small heat-treated parts. The transient sample temperature profile will be measured during quenching and compared with theoretical results for free convection heat transfer. Boiling phenomena will also be investigated qualitatively.

Quenching, Boiling, Convection and Nusselt Number

淬火和沸腾

Source: Alexander S Rattner, Sanjay Adhikari, and Mahdi Nabil; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, ...

Heat Exchanger Analysis

Source: Alexander S Rattner and Christopher J Greer; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
Heat exchangers transfer thermal energy between two fluid streams, and are ubiquitous in energy systems. Common applications include car radiators (heat transfer from hot engine coolant to surrounding air), refrigerator evaporators (air inside refrigerator compartment to evaporating refrigerant), and cooling towers in power plants (condensing steam to evaporating water and ambient air). The objective of this experiment is to introduce experimental measurement (rating) and modeling procedures for heat exchangers.
In this experiment, a water-to-water tube-in-tube heat exchanger will be constructed, and evaluated. Temperature and flow rate measurements will be employed to determine the heat transfer rate (Q) and overall conductance (UA). The measured heat exchanger UA will be compared with predicted values for the geometry and operating conditions.

Rating and Modeling Procedures for Heat Exchangers

换热器分析

Source: Alexander S Rattner and Christopher J Greer; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, ...

Measuring Turbulent Flows

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
Turbulent flows exhibit very high frequency fluctuations that require instruments with high time-resolution for their appropriate characterization. Hot-wire anemometers have a short enough time-response to fulfill this requirement. The purpose of this experiment is to demonstrate the use of hot-wire anemometry to characterize a turbulent jet.
In this experiment, a previously calibrated hot-wire probe will be used to obtain velocity measurements at different positions within the jet. Finally, we will demonstrate a basic statistical analysis of the data to characterize the turbulent field.

Measuring Turbulent Flows Using Hot-Wire Anemometers

测量紊流

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
Turbulent flows ...

Mass Conservation and Flow Rate Measurements

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
The purpose of this experiment is to demonstrate the calibration of a flow passage as a flowmeter using a control volume (CV) formulation [1, 2]. The CV analysis focuses on the macroscopic effect of flow on engineering systems, rather than the detailed description that could be achieved with a detailed differential analysis. These two techniques should be considered complementary approaches, as the CV analysis will give the engineer an initial basis on which route to pursue when designing a flow system. Broadly speaking, a CV analysis will give the engineer an idea of the dominant mass exchange in a system, and should ideally be the initial step to take before pursuing any detailed design or analysis via differential formulation.
The main principle behind the CV formulation for mass conservation is to replace the details of a flow system by a simplified volume enclosed in what is known as the control surface (CS). This concept is imaginary and can be defined freely to cleverly simplify the analysis. For instance, the CS should &#39;cut&#39; inlet and outlet ports in a direction perpendicular to the dominant velocity. Then, the analysis would consist of finding the balance between the net mass flux through the CS and the rate of change of mass inside the CV. This technique will be demonstrated with the calibration of a smooth contraction as a flowmeter.

Control Volume Analysis for Mass Conservation and Calibration of a Flow Passage

质量守恒和流速测量

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
The purpose of ...