Session: 17-01-01: Research Posters

Paper Number: 150428

150428 - Heat Transfer Enhancement in Solar Air Heaters Using Vortex Generators as Passive Flow Controls 

Energy production has perpetually posed a global challenge due to the severe environmental impacts of conventional fossil fuel-based methods, compounded by their non-renewable nature and inevitable depletion. Presently, numerous countries are embracing renewable sources in a concerted effort to accelerate the transition towards greener energy production. Among these, solar energy stands out as the most abundant renewable resource, offering versatility in both electricity and thermal energy production. Various thermal utilization methods exist, including flat plate collectors, evacuated tube collectors, and air collectors. However, harnessing heat from solar energy often encounters issues with low efficiency, particularly when employing air as the working fluid, because of its inherently low heat transfer coefficient. Consequently, increasing the efficiency of renewable energy systems remains a focal point of extensive ongoing research efforts.

A widely employed technique for systems utilizing solar energy heat with air as the working fluid involves inducing vortex turbulent flow. This approach enhances mixing between the flow and the heated surface, effectively delaying boundary layer separation. This mixing can be accomplished through the use of either active or passive devices, with the latter considered more efficient as it does not consume power. Various passive flow control methods, including fins, ribs, grooves, baffles, and vortex generators (VG), have been subjects of studies and research. However, the literature reveals a notable lack of experimental validation for different configurations and arrangements of VGs. To address this research gap and gain insights into the performance of passive flow controls for enhancing heat transfer, an experimental setup was constructed at the Guimarães Instrumentation, Measurements, and Aerodynamic Sensing Laboratory (GIMAS Lab) at the Pennsylvania State University. This setup will facilitate heat transfer enhancement experiments utilizing arrays of VGs.

The experimental setup consists of three main sections – entrance, test, and exit – that have lengths of 35”, 36”, and 18”, respectively. Throughout the sections, the channel height is 2” and width is 20”. Before entering the channel, the airflow undergoes pre-conditioning in a settling chamber, concluding with a contraction featuring a ratio of 1:6.5. To ensure flow uniformity, a honeycomb flow straightener is positioned at the outlet of the settling chamber.

Electric heating elements are positioned on the top surface of the test section, serving as the heat source for the experiment. The test section is made of clear acrylic sheets allowing for optical flow measurements, such as particle image velocimetry (PIV). This will allow for the visualization of flow structures in the future, which will then be directly compared with previous computational results in the literature. Moreover, the bottom surface of the test section is modular, facilitating easy replacement for experiments involving different designs of VGs. For precise temperature measurements while minimizing ambient losses, the test section is encased in insulation. This insulation is strategically placed between the acrylic wall and plywood boards on all sides to maintain structural integrity. The upper part of this insulation is designed to be detachable, facilitating access for instrumentation and packaging purposes.

Thermocouples are positioned throughout the test section to measure local temperatures. In addition, two thermocouples are placed in the inlet and another two in the exit section to measure the inlet and exit flow temperature. Static and total pressures will also be measured by pressure probes.

The expected outcome from this research is to increase the Nusselt number with minimal pressure drop by experimentally testing different geometries, distributions, combinations, and positioning of VGs, and studying the physical properties of the flow and thermal conduction to find an optimal solution.

Presenting Author: Mohannad Khair The Pennsylvania State University

Presenting Author Biography: Mohannad Khair joined the Department of Mechanical Engineering at Penn State in the Spring of 2023 as a Ph.D. student. He earned his B.Sc. in Mechanical Engineering from Hashemite University, Jordan, and his M.Sc. in Mechanical Engineering with a specialization in Renewable Energy from the University of Jordan. Currently, he is working in the GIMAS lab on heat transfer enhancement experiments for solar air heaters using vortex generators.

Authors:

Mohannad Khair The Pennsylvania State University
Tamy Guimaraes The Pennsylvania State University