Heat transfer augmentation in 3D inner finned helical pipe
- Authors: Li, Longjian , Cui, Wenzhi , Liao, Quan , Mingdao, Xin , Jen, Tien-Chien , Chen, Qinghua
- Date: 2004
- Subjects: Heat transfer , Helical tubes
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/16052 , uj:15733 , Citation: • Li, L. et al. 2004, “Heat transfer augmentation in 3D inner finned helical pipe,” ASME Heat Transfer/Fluids Engineering Conference, July 11-15, 2004, Charlotte, North Carolina, Vol. 3, pp. 139-143. HT-FED2004-56430. ISSN: 0-7918-4692-X.
- Description: Abstract: Experiments were performed to investigate the performance enhancement of single-phase flow and boiling heat transfer in the 3D inner finned helical tubes. The tests for single-phase flow and heat transfer were carried out in the helical tubes with a curvature of 0.0663 and a length of 1.15m, the range of the Reynolds number examined varies from 1000 to 8500. In comparison to the smooth helical tube, the experimental results of two finned helical tubes with different inner fin geometry showed that the heat transfer and flow resistance in the 3D inner finned helical tube gains greater augmentation. Within the measured range of Reynolds number, the average augmentation ratio of heat transfer of the two finned tubes are 71% and 103%, compared with the smooth helical tube, and 90% and 140% for flow resistance, respectively. The tests for flow boiling heat transfer was carried out in the 3D inner finned helical tube with a curvature of 0.0605 and a length of 0.668m.Compared with that in the smooth helical tube, the boiling heat transfer coefficient in the 3D inner finned helical tube is increased by 40%~120% under varied mass flow rate and wall heat flux conditions, meanwhile, the flow resistance coefficient increased by 18%~119%.
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Improving three-phase induction machines power factor using single phase auxiliary winding fed by an active power filter
- Authors: Muteba, Mbika C. , Jimoh, Adisa A. , Nicolae, Dan-Valentin
- Date: 2007
- Subjects: Heat recovery , Heat transfer
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/20373 , uj:16089 , ISBN:078038606x , Citation: Muteba, M.C., Jimoh, A.A. & Nicolae, D.V. 2007. Improving three-phase induction machines power factor using single phase auxiliary winding fed by an active power filter, IEEE AFRICON’07, Windhoek, Namibia, 26-28 September 2007:1-7 , DOI:10.1109/AFRCON.2007.4401570
- Description: Abstract: This paper presents a three-phase induction machine that employs a single phase auxiliary winding, which is only magnetically coupled to the stator main winding, and controlled by an active power filter. The active filter consists mainly of a two leg PWM voltage source inverter, which together with the auxiliary winding serves to supply leading reactive power to the machine. With sufficient ampere-turn capability of the auxiliary winding and an adequate control algorithm, the computer simulation results show that it is possible to obtain nearly unity power factor operation at the terminals of the main winding over a range of load conditions including rated load. The simulated power factor of this scheme is compared with the measured result for a typical practical induction motor.
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Numerical analysis of the flow pathlines in thermo-acoustic couples
- Authors: Tartibu, L.K. , Kunene, T.
- Date: 2019
- Subjects: Thermo-acoustic , Heat transfer , Stack
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/401870 , uj:33606 , Citation: Tartibu, L.K. & Kunene, T. 2019. Numerical analysis of the flow pathlines in thermo-acoustic couples.
- Description: Abstract: Thermo-acoustic systems use a high amplitude sound-wave for refrigeration or electricity generation without the drawbacks of expensive construction, adverse environmental impact or high maintenance cost. The effective conversion of energy occurs within the “stack” considered as the heart of the system. The time-averaged rate of heat transfer across the edges of the stack is a good indicator of an effective performance. Hence, studying the effect of the geometry of the stack edges together with their locations is useful. Furthermore, current manufacturing practices make it possible to develop diverse stack edges, resulting in an improved efficiency of the heat transfer. For effective modelling of the heat transfer rate, a second-order, double-precision discretization of state variables and a laminar viscous model was used. A numerical model was developed using the commercial code FLUENT. The evolution of the flow vortices at different drive ratio was analyzed. Two edges shapes were considered namely rectangular and rounded edges. Using numerical analysis, this study has pointed out that stack edge profiles has a significant effect on the overall performance of thermo-acoustic systems. Rounding the stack edge profile appears to be beneficial for the system performance. This study point out the link between the non-linearity observed in thermo-acoustic systems, the flow streaming and the mean vorticity at the stack edges.
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