HT-Peer Discussion - Session-1

Heat Transfer Concepts and Applications

Karthikeyan discussed heat transfer concepts with other students, focusing on critical thickness, electrical wires, and fins. Arputhaselvi explained that critical thickness affects heat transfer rates in steam pipes and electrical wires, with larger radii needed for steam pipes and smaller radii for electrical wires to dissipate heat faster. Jeevitha clarified that fins increase heat transfer by providing a larger surface area for heat exchange. Karthikeyan acknowledged learning about the concept of using fins to increase heat dissipation rather than just reduce heat loss.

Karthikeyan led a discussion on heat transfer problems, explaining solutions to various questions involving thermal conductivity, resistance, and heat flux calculations. He demonstrated how to find thermal contact resistance between two materials and interface temperatures in a car's rear window using given data. Arputhaselvi contributed by suggesting the use of Newton's law of cooling for one problem, and Karthikeyan confirmed its applicability. They also discussed how to calculate the thickness of insulation needed to reduce the outer surface temperature of a spherical reactor to 40°C, with a final percentage reduction in heat loss after adding insulation.

Karthikeyan explained the relationship between thermal conductivity \(k\), temperature, and heat flux \(q\) in a one-dimensional steady-state heat conduction problem. He showed that \(k\) increases with temperature and that, to maintain a constant heat flux \(q\) through a region of increasing cross-sectional area, the temperature gradient \(dT/dx\) must decrease. Arputhaselvi clarified that thermal conductivity \(k\) decreases with increasing temperature, which Karthikeyan confirmed was due to the negative coefficient in the relationship. The discussion concluded with Karthikeyan emphasizing the importance of understanding the coordinate system and the relationship between area, temperature gradient, and heat flux for solving such problems.

Karthikeyan explained a problem involving heat transfer through a wall composed of multiple layers, including fiberglass and steel plates. He guided the participants through calculating the overall resistance of the system, which involves parallel and series resistances, and then determined the heat transferred. Karthikeyan concluded that the steel plates contribute significantly to heat transfer, accounting for 81.2%, and therefore cannot be removed without a substantial impact on the system's performance.

Karthikeyan and Arputhaselvi discussed the concepts of fin efficiency and fin effectiveness. Arputhaselvi explained that fin efficiency represents the actual heat transfer rate by the fin divided by the ideal heat transfer rate, while fin effectiveness is the heat transfer by the fin divided by heat transfer without the fin. They clarified that fin efficiency will be less than 100%, but fin effectiveness should be greater than 1. Karthikeyan understood that fin efficiency focuses on the fin alone, while fin effectiveness considers the overall heat transfer improvement by adding the fin to a surface.

Karthikeyan explained the concepts of heat transfer in cylindrical fins, including the calculation of fin efficiency and effectiveness. He described how to determine the heat transfer rate with and without a fin, considering both the curved surface area and cross-sectional area of the fin. Karthikeyan also explained the Biot number and characteristic length, and how to use these concepts to find the fin efficiency for an insulated tip fin.