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Chapter 3: Problem 120

Consider two finned surfaces that are identical except that the fins on the first surface are formed by casting or extrusion, whereas they are attached to the second surface afterwards by welding or tight fitting. For which case do you think the fins will provide greater enhancement in heat transfer? Explain.

Short Answer

Expert verified
Answer: The casting/extrusion manufacturing process is expected to provide greater enhancement in heat transfer for identical finned surfaces. This is mainly due to better thermal contact between the fins and the base surface, resulting in less thermal contact resistance and better heat transfer performance.

Step by step solution

01

Recognize the main factors affecting heat transfer in finned surfaces

The main factors affecting heat transfer in finned surfaces are the geometry of the fins (length, thickness, and spacing), the material used for the fins (thermal conductivity and properties), and the contact between the fins and the base surface (thermal contact resistance). Since the geometry and materials are exactly the same in both cases, the difference in heat transfer enhancement lies in the contact between the fins and the base surface.
02

Understand the implications of each manufacturing process

In the casting/extrusion process, the fins are formed by shaping molten material into a desired geometry. Consequently, the fins and the base surface are an integral part of the same object. There is no additional interface or gap between the fins and the base surface, meaning that there is less thermal contact resistance. On the other hand, welding/tight fitting involves attaching the fins to the base surface after they have been formed separately. In this case, there can be small gaps or imperfections at the interface, leading to increased thermal contact resistance. Moreover, high temperatures used for welding could have an impact on the material properties, altering their thermal conductivity, and hence, the overall heat transfer performance.
03

Compare the two cases in terms of heat transfer enhancement

Considering the differences in thermal contact resistance between the two cases, it is expected that the fins will provide greater enhancement in heat transfer when they are formed by casting or extrusion. This is because of the absence of an additional interface and gaps between the fins and the base surface, leading to less thermal contact resistance and better heat transfer performance. In conclusion, the fins formed through casting or extrusion are expected to provide greater heat transfer enhancement than those attached through welding or tight fitting, mainly due to better thermal contact between the fins and the base surface.

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Most popular questions from this chapter

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