Mahdi's Professional Experiences
Particle Image Velocimetry (PIV), Planar Laser Induced Fluorescence (PLIF)
Particle Image Velocimetry (PIV) and Planar Laser Induced Florescence (PLIF) are practically non intrusive methods for quantitative measurements of fluid flow. In PIV, movement of tracer particles being carried by a fluid is used as a means to observe velocity field. Another similar method incorporates different types of dyes instead of the tracer particles and that gives a measurement of an scalar field. This method is called PLIF and can be used to measure different fluid phases, varying temperature, or different species in reaction.
The above image is really cool and probably is the best way of describing PIV, but you need red/blue 3D goggles to see what it shows. Open the actual image and there, the red dots are the particles in the first frame and blue dots are the particles in the second frame. That movement of particles you can see alternating between red and blue. The white arrows then show the velocity calculated based on that movement of particles. Scan through the image to see different directions and magnitudes of velocity in different regions. It is worth mentioning that it is a real image I took for the case of a single sphere in flow.
Prof. Olsen has worked with founders of these methods and throughout past years, his research group have developed the knowledge and expertise to carry out a broad range of experiments using methods related to PIV.
Fluidized bed reactors have application in catalytic reactions for different types of plants in a variety of industries. We are trying to use simultaneous PIV/PlIF to quantitatively measure flow and temperature fields in such an environment. My experiment involves liquid-solid two phase flow that incorporates the technique of matching index of refraction of fluid and particles. This enables us to visually access the inside of the reactor without interrupting its behavior.
I designed a larger column with fixed solid particles that can be arranged in different geometries. We currently have preliminary velocity and passive scalar data from this apparatus and I am working on preparing publications based on our recent results. The next step would be to install heated solid spheres and start with simultaneous velocity and temperature field measurements.
This is the main project I have been working on. I started with designing this facility based on the proposal and then manufacturing and assembly of it as the next step. The last step was to get the instrumentation for data collection and process to work. I finally started collecting data for the regular 2C velocity field, 3C velocity field, and finally the exciting simultaneous SPIV/PLIF. Based on the preliminary results, we could identify a fundamental problem with our method. It was quite discouraging to find out that the type of data resulting from the experimental method is in its nature different from the simulation results. We will be relying on the instantaneous data from this apparatus rather than the statistics of it.
The upside of the current situation is that now, I am building the concept of experiment by myself rather than just performing some tests. The new design will allow me to collect data in a real fluidized bed rather than the current fixed particle scheme. I am focusing on sedimentation as a starting point and I will be working to get 3D particle tracking data in the new facility. This is a much smaller reactor incorporating much smaller particles and that would make it more difficult for performing PIV. We are planning to do some particle tracking and then lunch Tomographic PIV in this setup.
Flow of a fluid between rotating cylinders is called a Taylor-Couette flow if the inner cylinder velocity is beyond a known threshold. This type of reactor is being used in algae growth application in our labs in which air as a second fluid phase is injected from the bottom of the reactor containing water and algae. We are setting out to gather precise data of bubble shape and transport in such a flow regime. As a first step, we have experimented the oxygen mass transfer in our apparatus in order to have a measure of that parameter in algae growth improvement.
The next idea is to use two immiscible fluids with the similar index of refraction inside a reactor so that we can prevent distortion of laser sheet and image due to the bubble shape. That would allow us to collect velocity field data in a bubble column and verify our numerical models against it. A fluorescence dye in the bubbling phase would enable us to use PLIF for distinguishing the two phases. Another possibility would be to use tracer particles in only one of the phases.
Free and Forced Convection Heat Transfer
My BSc project was in collaboration with Mohammad Mazaheri who is one of my best friends. Most of the credit of it goes to him, but our project turned to be chosen as the best in Iranian Society for Mechanical Engineers (ISME). We experimentally investigated convection Heat transfer of air in eccentric annulus. That was quite an experience in my undergraduate level and motivated me to get involved in graduate studies.