[{"data":1,"prerenderedAt":86},["ShallowReactive",2],{"$fhvhqpi52opqx":3},{"slug":4,"publishedAt":5,"category":6,"title":7,"summary":8,"image":9,"imageAlt":14,"readingMinutes":15,"serviceId":16,"keywords":17,"imageCaption":22,"sections":23,"sources":76},"drop-shaped-tubes-heat-transfer","2026-10-12","guides","Drop-Shaped Tubes vs Circular Tubes: Heat Transfer Compared","Drop-shaped tubes keep the flow attached longer than circular ones. See what that does to heat transfer, pressure drop and pumping power, and its limits.",{"src":10,"thumbnail":11,"width":12,"height":13},"\u002Fassets\u002Fcfd-cases\u002Fexternal\u002Fimages\u002F06.webp","\u002Fbrand\u002Fstudies\u002Fexternal.svg",1448,1086,"DEEB-FLOW illustration of streamlines around circular, cam-shaped and drop-shaped tubes",5,"thermal",[18,19,20,21],"drop-shaped tube heat transfer","non-circular tubes cross-flow","drop-shaped tube bundle","tube bundle pressure drop","Concept illustration from the DEEB-FLOW case library. It is not a result from this article.",[24,30,39,48,54,61,71],{"id":25,"title":26,"paragraphs":27},"circular-tube","A circular tube is a poor shape for the flow outside it",[28,29],"A circular tube is easy to make, easy to clean and holds pressure well. For the fluid flowing across it, it is a poor shape. The flow follows the front half of the cylinder, separates just past the widest point and leaves a broad, slow wake. That wake is drag you pay for at the fan or pump, and the surface underneath it transfers heat badly. In a tube bundle you repeat that loss on every row.","A drop-shaped tube asks the obvious question: keep a round nose, taper the back, and see how much of that loss comes back. A good part of my research has gone into that question. This article summarises what the work shows and where the idea runs out.",{"id":31,"title":32,"paragraphs":33},"what-changes","What changes when the tube is streamlined?",[34],{"list":35},[36,37,38],"**Separation moves back.** On the tapered tail the pressure recovers more gently, so the boundary layer stays attached over more of the surface.","**The wake narrows.** A smaller region of slow, recirculating fluid behind each tube means less form drag, and in cross-flow form drag is most of the pressure drop.","**More of the surface works.** The back of a circular tube sits in its own wake. The tail of a drop-shaped tube is still in contact with moving fluid.",{"id":40,"title":41,"paragraphs":42},"fair-comparison","How do you compare two tube shapes fairly?",[43,44,47],"Higher heat transfer is easy to get by pushing the fluid faster, so comparing Nusselt numbers alone is not enough. The comparison that matters to someone paying for a fan is heat transferred for a given pumping power. A common measure sets the gain in Nusselt number against the gain in friction factor, with the friction ratio raised to the power one third.",{"formula":45},[46],"ε = (Nu \u002F Nu₀) \u002F (f \u002F f₀)^(1\u002F3)","By that measure a shape wins if it gives up a little heat transfer and saves a lot of pressure drop, which is what streamlining tends to do.",{"id":49,"title":50,"paragraphs":51},"single-tubes","What we found for single tubes",[52,53],"With D. V. Sidenkov I studied single tubes in cross-flow numerically, at Reynolds numbers from 1.5 × 10³ to 26.5 × 10³. The axis ratio L\u002FD went from 1, which is a circular tube, to 4 in steps of 0.5. We reported local heat transfer, pressure and friction coefficients over the surface and checked the results against published data.","The drop-shaped tubes needed less pumping power than the circular tube to deliver the same heat transfer under the same operating conditions. The most elongated shape, with L\u002FD = 4, had the best thermo-hydrodynamic characteristics of those studied. The work also gave correlations for the average Nusselt number and the friction factor in terms of Reynolds number and axis ratio.",{"id":55,"title":56,"paragraphs":57},"bundles","A bundle is more than a set of single tubes",[58,59,60],"In a bundle every row sits in the wake of the one in front, so the best single tube is not automatically the best bundle. In a later study I compared six-row staggered bundles at Reynolds numbers from 1.78 × 10³ to 18.72 × 10³: one of circular tubes, one of drop-shaped tubes, and six mixed arrangements.","The pure drop-shaped bundle has low resistance, and it also gives up heat transfer. Mixing the shapes recovers it. Alternating rows, with circular tubes in rows 1, 3 and 5 and drop-shaped tubes in rows 2, 4 and 6, raised the average Nusselt number by about 1 to 8% over the circular bundle and by about 48 to 49% over the drop-shaped one.","On thermal-hydraulic performance, the best mixed arrangements beat the pure drop-shaped bundle by about 14.5% at the lowest Reynolds number and by 2 to 4.5% at higher ones. Where each shape sits in the bundle matters as much as the shape itself. The same idea, a bundle that combines circular and drop-shaped tubes, is the subject of patent RU-2848594.",{"id":62,"title":63,"paragraphs":64},"limits","Where the idea has limits",[65,70],{"list":66},[67,68,69],"**Angle of attack.** A circular tube does not care which way the flow arrives. A drop-shaped tube does: turn it sideways and it becomes a bluff body with a large wake. The benefit measured in an ideal cross-flow is an upper bound, so check the real approach flow across the bundle.","**Pressure containment.** A circle is the natural shape for internal pressure. A non-circular tube under pressure tries to become round, which puts bending stress in the wall and changes the outside shape you were counting on. The structural check is part of the design.","**Manufacturing and cleaning.** Tubesheets, expansion tools and cleaning equipment are built around round tubes.","None of these rules the idea out. They decide where it makes sense: gas-side heat recovery with low internal pressure and a high cost of fan power is a more natural home than a high-pressure liquid service.",{"id":72,"title":73,"paragraphs":74},"for-designers","What this means if you design heat exchangers",[75],"If your constraint is fan or pump power and the service allows a non-circular tube, the published results show a real saving. Three questions decide whether it survives in your unit: what is the real approach flow angle across the bundle, what does the tube arrangement do row by row, and does the tube hold its shape under pressure. All three can be answered by simulation before a prototype is built, and the last should be confirmed by a test.",[77,80,83],{"href":78,"label":79},"https:\u002F\u002Fdoi.org\u002F10.17586\u002F1606-4313-2020-19-3-91-99","Deeb and Sidenkov (2020), Vestnik Mezhdunarodnoi akademii kholoda: numerical investigation of heat transfer and aerodynamics of single drop-shaped tubes",{"href":81,"label":82},"https:\u002F\u002Fdoi.org\u002F10.33257\u002FPhChGD.23.2.987","Deeb (2022), Physical-Chemical Kinetics in Gas Dynamics: thermal-aerodynamic characteristics of a staggered mixed bundle of circular and drop-shaped tubes",{"href":84,"label":85},"https:\u002F\u002Fdoi.org\u002F10.18698\u002F1812-3368-2021-2-102-117","Deeb, Sidenkov and Salokhin (2021), Herald of the Bauman Moscow State Technical University: circular, cam-shaped and drop-shaped tubes in cross-flow",1791759706766]