Report Task 5 Finite Elements

BDA 40303 Laboratory Task 5 MUHAMMAD HANIF BIN ABD RASHID Matrix No: CD120111 May 21, 2014

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MODEL/PROBLEM DESCRIPTION As a research engineer in a company you are requested to investigate two types of aluminum fins as illustrated in Figure 5.1 that will be implemented to remove heat from a surface whose temperature is 150 °C. The temperature of surrounding air is 25 °C. The natural heat transfer coefficient associated with the surrounding air is 30W/m2 °C. The thermal conductivity of aluminum is 168W/ m2 °C. Determine which one of the fin that you would suggest. Your report should be concise, attractive and very convincing.

Figure 1: New types of Fin

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FINITE ELEMENT MODEL

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Element Model The fins structure is modeled in LISA as three dimensional type analysis (2D) model thermal steady state with the nodes of structure in accordance to Figure 2 and Figure 3 below. Material used in the model is Aluminium with a thermal conductivity of 168 W/m2 C attached to a surface of temperature 150 C.

Figure 2: FEM model of first design and number of nodes

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Figure 3: FEM model of second design and number of nodes

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Constraints Constraints in the thermal evaluation refer to a set temperature value for the fins. In this case, a constant 150 C is supplied at the left end of the fins as shown in Figure 1. The constraint temperature is set with a command of temperature=150 at all appropriate nodes according to the Figure 2 and Figure 3. Both designs will have the same temperature constraint represented by tiny circle circling the involved nodes.

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Loadings Instead of an actual load, thermal evaluations consider the convection aspects of the design and how it reacted to surroundings. Both designs will undergo the same temperature surrounding of 25 C with natural heat transfer coefficient of 30W/m2 C. Conditions set in the FEM model are as follows.

Figure 4: Convection set for the first design

Figure 5: Convection set for the second design

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RESULTS AND SHORT DISCUSSION Due to the difference in shapes, the temperature results will differ. Selecting the best shapes depends on the final temperature value produced in each design. The next two

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figures shown will display the resultant temperature when all of the involved factors are taken into consideration

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First Design

Figure 6: Temperature estimation of first design

The tip of this fin’s design will have a 133.4 C of temperature value. The temperature drops are greater with distance because of the smaller area exposed. However because of this exact small area, it has a disadvantage in conducting heat to the tip efficiently. This only proves first design’s inefficient shape because the transfer of heat is not used to the most optimum.

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Second Design

Figure 7: Temperature estimation of second design

The tip of this fin’s design on the other hand produces 133.1 in temperature, slightly lower than previous design. The first part of the fin, rectangular in shape, could transfer a much larger heat to surrounding precisely because of the bigger area of the fin.

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CONCLUSION

In conclusion, by considering both design we found that the appropriate fin shape would be the second design as it has greater temperature drop and therefore greater heat transfer. This means that second design would be suitable for a higher temperature application than the other. Conversely for design 1, due to the shape 6/6

factor at the base attached to the hot surface, which is wide, this design would render useless. That is because firstly, the temperature difference is about 0.3. Secondly, when multiple fins are attached and considered; the second design could produce a greater contact area thus a huge heat removal rate than the first. For the sole logic, second design is undoubtedly the best shape in terms of practicality and heat transfer among the two and I would strongly recommend it.

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