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Abstract
This paper presents experimental and analytical results of an investigation of heat transfer and pressure loss in a new type of convection heat exchanger tube bank with triple-finned tubes (TFTs). An initial evaluation of the optimal geometry of TFT banks using the Lusas code is presented. The heat transfer between the external environment and the medium inside the TFTs was modeled. Fins were arranged on a tube in the following three configurations: three fins with the same geometry with 45° between two symmetric fins and a vertical line of symmetry, denoted by T90, three fins with the same geometry with 30° between two symmetric fins and a vertical line of symmetry, denoted by T60, and one fin and angle steel plate placed parallel to the line of symmetry of the triple-finned tube, denoted by TAS90. The naphthalene sublimation technique is used as a heat/mass transfer analogy to evaluate the Sherwood (Nusselt) number ratios in the tube banks. The heat transfer performance of staggered S1T90 tube banks and the basic plain tube bank SP was compared. The second possibility for using TFTs is in a tube bank with all tubes finned was studied using the naphthalene analogy technique. The results are then compared with those computed using the computational fluid dynamics code. A comparison of the numerical and experimental heat transfer results shows that the trends in the heat transfer increase are very similar. The results show that triple-finned tubes can be used to increase the performance of cross-flow tube banks.
NOMENCLATURE
| A | = | ratio of C numbers, Ci/Cib |
| C, n | = | constants |
| d | = | equivalent diameter, m |
| D | = | external diameter of the tube, m |
| Eu | = | Euler number, Δp/ρw2 |
| g | = | fin thickness, m |
| h | = | fin height, m |
| m | = | ratio of Re exponents, ni-nib |
| Nu | = | Nusselt number, αd/λ |
| Q | = | convective heat transfer rate, W |
| q | = | specific heat fluxes, W/m2 |
| Re | = | Reynolds number, wd/v |
| s1 | = | transverse pitch, m |
| s2 | = | longitudinal pitch, m |
| Sh | = | Sherwood number, βD/δ |
| SP | = | staggered plain tube bank (basic arrangement) |
| S1T90 | = | combination staggered tube bank with TFTs in the first two rows and plain tubes (angle 90°) |
| S1T60 | = | combination staggered tube bank with TFTs in the first two rows and plain tubes (angle 60°) |
| ST90 | = | staggered tube bank with triple-finned tubes (angle 90°) |
| t | = | temperature, °C |
| TFT | = | triple-finned tube |
| w | = | mean velocity in the cross section of the tube bank, m/s |
Greek Symbols
| α | = | heat transfer coefficient, W/m2-K |
| β | = | mass transfer coefficient, kg/m2-s |
| Δp | = | pressure loss, Pa |
| δ | = | dynamic mass diffusion coefficient, kg/m-s |
| λ | = | thermal conductivity of the medium, W/m-K |
| v | = | kinematic viscosity of the medium, m2/s |
| ρ | = | density of the medium, kg/m3 |
Subscripts
| i | = | tube row number for the new tube bank configurations |
| ib | = | tube row number for the basic tube bank configurations |
| in | = | internal |
| out | = | external |
Additional information
Notes on contributors
Robert Wejkowski
Robert Wejkowski is a researcher at the Silesian University of Technology (SUT) in Poland. He graduated from the Faculty of Energy and Environmental Engineering at SUT in 1998, and from the Faculty of Economics at the University of Economics in Katowice, Poland, in 1997. After completing doctoral studies he received his Ph.D. from SUT in 2004. He began working in the Department of Boilers and Steam Generators of the Institute of Power Engineering and Turbomachinery. Basic research problems lying in his interest include issues of physical and numerical studies on solutions to increase heat transfer in boilers, and processes of erosion and deposition. His main areas of expertise are primary and secondary methods of NOx reduction (SCR and SNCR).