Master of Engineering Science
Mechanical and Materials Engineering
Environment and Sustainability
Microalgae has been identified as a potential source for the production of biofuels and other bio-products. The growth of microalgae is sensitive to the temperature variations inside the photobioreactor. The present research investigated an innovative approach to thermally regulate photobioreactors by introducing passive thermal energy storage using phase change material (PCM). The research was specifically focused on a novel design to integrate thermal storage in the reactor channel in the form of offset columns containing PCM. Two column shapes were considered: circular and square. The first part of the study was focused on characterizing the influence of offset column shapes on flow dynamics in the channel over a range of Reynolds numbers 20-90. Experiments with microalgae Chlamydomonas reinhardtii were also conducted in a similar setup to determine if the presence of obstacles would impact the algae growth. The second part of the study was focused on the thermo-fluid characterization in a similar configuration using PCM-filled offset columns. Experiments were conducted over a Reynolds number range 40 to 120 at three inlet fluid temperatures 28 °C, 33 °C and 38 °C. The results show that the modification of the flow field in the channel due to the column shapes influenced the heat transfer into the PCM thermal storage.
Summary for Lay Audience
This thesis project was inspired by the need for temperature control inside a microalgae incubator (photobioreactor). Microalgae are a photosynthesizing organism that can be used to produce an array of valuable oil products. They are sensitive to temperature changes, so an innovative approach is proposed in this research to regulate the temperature of photobioreactors passively by use of thermal storage using a phase change material (PCM). This thermal storage would store excess heat throughout the day and release it into the incubator during the cooler nights. A novel design of thermal storage in the form of offset columns inside the channel was considered.
The research was focused on three main aspects: (1) how does the shape and position of columns influence the flow behavior through the channel; (2) does this flow behavior has any negative effects on the growth of microalgae; and (3) how the fluid thermally interacts with the columns that are filled with the PCM energy storage.
First, experiments were conducted to measure the flow velocity fields inside the channel in the presence of offset columns at low flow rates. Two column shapes circular and square were considered. An imaging technique called particle image velocimetry was used to measure flow velocities. The results show that the presence of columns significantly influenced the flow velocity behavior in the channel.
Second, investigations were conducted to study how the growth of microalgae, Chlamydomonas reinhardtii, is affected by the flow conditions in this set up. The microalgae are exposed to a subset of flow conditions from previous tests, and their growth was determined through daily measurements of their swimming speed, size and concentration in the flow.
The final part of this study used a similar setup up to the first, but also considered PCM-filled columns as thermal energy storage. Experiments were conducted at different inlet fluid temperatures at three flow rates to investigate the flow and thermal behaviors in the channel. The results show that presence of offset columns altered the flow, which in turn, influenced the transfer of heat in the thermal energy storage columns.
Toxopeus, Kira, "Experimental investigation of flow and thermal behavior in channels with PCM-filled thermal energy storage columns for potential application in photobioreactors" (2020). Electronic Thesis and Dissertation Repository. 7133.
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