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JoVE Science Education

A video library dedicated to teaching the practice and theory of scientific experiments through engaging and easy-to-understand visual demonstrations.

Education

Buoyancy and Drag on Immersed Bodies

Source: Alexander S Rattner and Sanjay Adhikari; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
Objects, vehicles, and organisms immersed in fluid mediums experience forces from the surrounding fluid in the form of buoyancy- a vertical upward force due to fluid weight, drag- a resistive force opposite the direction of motion, and lift- a force perpendicular to the direction of motion. Prediction and characterization of these forces is critical to engineering vehicles and understanding the motion of swimming and flying organisms.
In this experiment, the balance of buoyancy, weight, and drag forces on submerged bodies will be investigated by tracking the rise velocity of air bubbles and oil droplets in a glycerin medium. The resulting drag coefficients at terminal rise velocities will be compared with theoretical values.

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

Stability of Floating Vessels

Source: Alexander S Rattner and Kevin Rao Li Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
 The objective of this experiment is to demonstrate the phenomenon of stability of floating vessels - the ability to self-right when rolled over to the side by some external force. Careful design of hull shapes and internal mass distribution enables seagoing vessels to be stable with low drafts (submerged depth of hull), improving vessel maneuverability and reducing drag. 
In this experiment, a model boat will first be modified to enable adjustment of its center of mass (representing different cargo loadings) and automated tracking of its roll angle. The boat will be placed in a container of water, and tipped to different angles with varying heights of its center of mass. Once released, the capsizing (tipping over) or oscillating motion of the boat will be tracked with a digital camera and video analysis software. Results for the maximum stable roll angle and frequency of oscillation will be compared with theoretical values. Stability calculations will be performed using geometric and structural properties of the boat determined in a computer aided design environment.

The Buoyant Force and Stability of Floating Vessels

Source: Alexander S Rattner and Kevin Rao Li Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
 The ...

Propulsion and Thrust

Source: Alexander S Rattner; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
Aircraft, rockets, and ships produce propulsion by accelerating surrounding fluid or high temperature combustion products to high velocity. Because of the principle of conservation of momentum, the increased fluid velocity results in an effective thrust force on the vehicle. The thrust capabilities of propulsion systems are often measured with static thrust tests. In these tests, propulsion systems are mounted and operated on fixed, instrumented platforms, and the holding force on the mounts is measured as the thrust
In this experiment, a small-scale static thrust measurement facility will be constructed and modeled. The thrust curves for two model aircraft motors and propeller systems and a computer cooling fan will be measured. Thrust efficiencies will also be evaluated (thrust force / electrical power input). Measured thrust values will be compared with theoretical predictions based on measured air velocities.

Aircraft/Rocket/Ship Propulsion; Static Thrust Measurement

Source: Alexander S Rattner; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
Aircraft, rockets, ...

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

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

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

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

Hydraulic Jumps

Source: Alexander S Rattner and Mahdi Nabil; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
When liquid flows along an open channel at high velocity, the flow can become unstable, and slight disturbances can cause the liquid upper surface to transition abruptly to a higher level (Fig. 1a). This sharp increase in the liquid level is called a hydraulic jump. The increase in the liquid level causes a reduction in the average flow velocity. As a result, potentially destructive fluid kinetic energy is dissipated as heat. Hydraulic jumps are purposely engineered into large water works, such as dam spillways, to prevent damage and reduce erosion that could be caused by fast moving streams. Hydraulic jumps also occur naturally in rivers and streams, and can be observed in household conditions, such as the radial outflow of water from a faucet onto a sink (Fig. 1b).
In this project, an open-channel flow experimental facility will be constructed. A sluice gate will be installed, which is a vertical gate that can be raised or lowered to control the discharge rate of water from an upstream reservoir to a downstream spillway. The flow rate required to produce hydraulic jumps at the gate outlet will be measured. These findings will be compared with theoretical values based on mass and momentum analyses.
<img alt="Figure 1" src="/files/ftp_upload/10405/10405fig1.jpg" /> 
Figure 1: a. Hydraulic jump occurring downstream from a spillway due to a slight perturbation to an unstable high-velocity flow. b. Example of hydraulic jump in radial outflow of water from a household faucet.

Hydraulic Jumps in Radial Outflow of Water

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

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

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

Introduction to Refrigeration

Source: Alexander S Rattner and Christopher J Greer; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
This experiment demonstrates the principles of vapor compression refrigeration. The vapor compression cycle is the dominant refrigeration technology, found in most refrigerators, freezers, air-conditioning systems, and heat pumps. In this cycle, cooling (heat acquisition) is achieved with low-pressure evaporation of refrigerant. Thermal energy absorbed in evaporation is rejected to the surroundings through high-pressure refrigerant condensation. Mechanical work is applied in the compressor to raise the working fluid from low to high pressure. 
While refrigeration technology is ubiquitous, the concealing packaging and autonomous operation of most refrigerators makes it difficult to appreciate the operating principles and function of key components. In this experiment, a rudimentary vapor compression refrigerator is constructed. The compressor is manually actuated with a bicycle pump, allowing intuitive appreciation of cycle operation as the experimenter becomes part of the system. Resulting component pressures and temperatures can be interpreted in terms of the thermodynamic T-s and P-h diagrams, which capture the variation of fluid properties from the liquid-to-vapor states (during evaporation and condensation).

Refrigeration; Vapor Dome; Hand-pump Refrigerator

Hot Wire Anemometry

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
Hot-wire anemometers have a very short time-response, which makes them ideal to measure rapidly fluctuating phenomena such as turbulent flows. The purpose of this experiment is to demonstrate the use of hot-wire anemometry.

Hot-Wire Anemometer; Flow Velocity Based on Heat Dissipation

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

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

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

Visualization of Flow Past a Bluff Body

Source: Ricardo Mejia-Alvarez, Hussam Hikmat Jabbar and Mahmoud N. Abdullatif, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
Owing to the non-linear nature of its governing laws, fluid motion induces complicated flow patterns. Understanding the nature of these patterns has been the subject of intense scrutiny for centuries. Although personal computers and supercomputers are extensively used to deduce fluid flow patterns, their capabilities are still insufficient to determine the exact flow behavior for complex geometries or highly inertial flows (e.g. when momentum dominates over viscous resistance). With this in mind, a multitude of experimental techniques to make flow patterns evident have been developed that can reach flow regimes and geometries inaccessible to theoretical and computational tools.
This demonstration will investigate fluid flow around a bluff body. A bluff body is an object that, due to its shape, causes separated flow over most of its surface. This is in contrast to a streamlined body, like an airfoil, which is aligned in the stream and causes less flow separation. The purpose of this study is to use hydrogen bubbles as a method of visualizing flow patterns. The hydrogen bubbles are produced via electrolysis using a DC power source by submerging its electrodes in the water. Hydrogen bubbles are formed in the negative electrode, which needs to be a very fine wire to ensure that the bubbles remain small and track fluid motion more effectively. This method is suitable for steady and unsteady laminar flows, and is based on the basic flow lines that describe the nature of the flow around objects. [1-3]
This paper focuses on describing the implementation of the technique, including details about the equipment and its installation. Then, the technique is used to demonstrate the use of two of the basics flow lines to characterize the flow around a circular cylinder. These flow lines are used to estimate some important flow parameters like flow velocity and the Reynolds number, and to determine flow patterns.

Flow Around a Bluff Body, Bubbles and Von Karman Vortex Street

Source: Ricardo Mejia-Alvarez, Hussam Hikmat Jabbar and Mahmoud N. Abdullatif, Department of Mechanical Engineering, Michigan State University, East ...

Jet Impinging on an Inclined Plate

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
The goal of this experiment is to demonstrate how a fluid flow exerts forces on structures by conversion of dynamic pressure into static pressure. To this end, we will make a plane jet impinge on a flat plate and will measure the resulting pressure distribution along the plate. The resultant force will be estimated by integrating the product between the pressure distribution and appropriately defined area differentials along the surface of the plate. This experiment will be repeated for two angles of inclination of the plate with respect to the direction of the jet and two flow rates. Each configuration produces a different pressure distribution along the plate, which is the result of different levels of conversion of dynamic pressure into static pressure at the plate's surface.
For this experiment, pressure will be measured with a diaphragm pressure transducer connected to a scanning valve. The plate itself has small perforations called pressure taps that connect to the scanning valve through hoses. The scanning valve sends the pressure from these taps to the pressure transducer one at a time. The pressure induces mechanical deflection on the diaphragm that the pressure transducer converts into voltage. This voltage is proportional to the pressure difference between the two sides of the diaphragm.

Jet Impinging and Conversion of Dynamic Pressure into Static Pressure

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

Conservation of Energy Approach to System Analysis

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 application of the energy conservation equation to determine the performance of a flow system. To this end, the energy equation for steady, incompressible flow is applied to a short pipe with a gate valve. The gate valve is then gradually closed and its influence on flow conditions is characterized. In addition, the interplay between this flow system and the fan that drives the flow is studied by comparing the system curve with the characteristic curve of the fan.
This experiment helps understanding how energy dissipation is used by valves to restrict the flow. Also, under the same principle, this experiment offers a simple method to measure flow rate using the pressure change across a sharp entrance.

Energy Conservation Equation to Analyze a Flow System

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

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

Determination of Impingement Forces on a Flat Plate with the Control Volume Method

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 forces on bodies as the result of changes in the linear momentum of the flow around them using a control volume formulation [1, 2]. The control volume analysis focuses on the macroscopic effect of flow on engineering systems, rather than the detailed description that could be achieved with a differential analysis. Each one of these two techniques have a place in the toolbox of an engineering analyst, and they should be considered complementary rather than competing approaches. Broadly speaking, control volume analysis will give the engineer an idea of the dominant loads in a system. This will give her/him an initial feeling about what route to pursue when designing devices or structures, and should ideally be the initial step to take before pursuing any detailed design or analysis via differential formulation.
The main principle behind the control volume formulation is to replace the details of a system exposed to a fluid flow by a simplified free body diagram defined by an imaginary closed surface dubbed the control volume. This diagram should contain all surface and body forces, the net flux of linear momentum through the boundaries of the control volume, and the rate of change of linear momentum inside the control volume. This approach implies cleverly defining the control volume in ways that simplify the analysis at the same time that capture the dominant effects on the system. This technique will be demonstrated with a plane jet impinging on a flat plate at different angles. We will use control volume analysis to estimate the aerodynamic load on the plate, and will compare our results with actual measurements of the resulting force obtained with an aerodynamic balance.

Impingement Forces on a Flat Plate with Control Volume Method

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