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Four heat transfer enhancing tubes (tubes A – D) with transverse studs are fabricated and tested. The studs are regularly welded in the tubes at a pitch of 53.2 mm. The inner and outer diameters of the tubes are 13.3 and 17.3 mm, respectively. Tubes A, B and C use the same threaded studs (M4) as flow disturbing device, but the arrangements of the studs on the tube walls are different. Tube D adopts the same stud arrangement as tube A, but its studs are smooth instead of threaded. Air is the working fluid in the tubes. For the Reynolds number (Re) in the range of 4000 to 23000, fluid friction and heat transfer data of the four heat transfer enhancing tubes are measured and the results are compared with those of a smooth tube. The transverse studs are quite effective for enhancing the heat transfer in the tubes. Regardless of the Re value and stud arrangement, a twofold increase in the convection heat transfer coefficient can be achieved. It is also found that the stud arrangement and the stud surface roughness are insignificant to the heat transfer. A frequent variation in stud direction or a rough stud surface would result in an increase in pressure drop, instead of an increase in heat transfer.References
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