Experimental and Mathematical Research of Convection Heat Transfer for a High Integral Finned Tube Heat Exchanger

This research exhibits an experimental and numerical investigation for the characteristics of heat transfer by utilizing an integral and smooth high finned tube and shows how the integral high fins affect in improving the transfer of heat. In the experimental work, the experimental rig consists of a cold water loop, a hot air loop and the trial part which is a concentric parallel flow double pipe heat exchanger. The first test smooth tube made of brass has external and internal diameter (32 mm) and (22 mm), respectively, the second test section made of the same material has external fins, the third test section possesses internal fins, and the fourth test section has internal and external fins. The dimensions of the fin are (2 mm) in thickness, (2 mm) in height and pitch (2.5 mm) center to center. And, the water flow rates are (6, 8, 10, 12 and 14 L/min). The inlet water to the trial tube was at temperatures (15, 25, 35, and 45oC). The investigational results manifested that the air side heat transfer coefficient of the smooth tube was lesser than the integral high finned tube. The ratio of improvement when using the integral high finned tube was (47.5%, 60.5% and 67.5 %). Numerical simulation was applied on the current heat exchanger to study both the transfer of heat and the field of flow by using ANSYS, FLUENT15 package. Steady state, Newtonian flow, incompressible and three dimensional analyses were assumed. The comparison between experimental work and numerical results elucidated a good agreement.

Mechanical Properties and Heat Transfer Performance of Conically Corrugated Tube

Conically corrugated tube is a new type of high-efficiency heat exchange tube. In this paper, the mechanical and heat transfer properties of conically corrugated tubes formed by the cold rolling of smooth tubes are studied through experimental measurement and numerical simulation to lay the foundations for applying the tubes in heat exchangers. The results show that while conically corrugated tube has a lower axial elastic stiffness compared with smooth tube, conically corrugated tube has a higher yield strength and ultimate strength. Unlike smooth tubes, conically corrugated tubes develop three-dimensional stresses when an axial tensile load is applied to them. In addition, the heat transfer coefficient of conically corrugated tube is 15%, 17%, and 115% higher than that of spiral grooved tube, convergent divergent tube, and smooth tube, respectively. Finally, the correlation equations of the axial stress concentration factor, stiffness equivalent coefficient, Nusselt number, and flow resistance coefficient of conically corrugated tubes are obtained for engineering application.

Visualization of Heat Transfer Characteristics of 1EHT and Smooth Surface Tubes

High efficiency heat transfer tubes play a major role in industrial applications due to its benefits in recovering more energy, smaller footprint and lower operational costs. Given the importance of enhanced heat transfer tubes, an experimental investigation was carried out to compare the performance of the Vipertex 1EHT tube with an equivalent smooth tube using Particle Image Velocimetry (PIV). For the experimental setup a Dantec Dynamics PIV system was considered, and both tubes used had an outer diameter of 19.05 mm and inner diameter of 17.09 mm. Heat transfer experiments were conducted at 100% of the heater power capacity, i.e. 750 W, and observations were made in terms of boiling visualization, particle velocity vector field, and seeding particle velocity. The results obtained from the visualization showed higher density of bubble formation on the surface of 1EHT tube compared to the smooth tube, as well as a more frequent formation of bubbles. Moreover, the high-speed camera films recorded for comparison between smooth and enhanced tubes, showed that the dimples provided nucleation sites. Additionally, the average particle velocity for the 1EHT tube was 0.300 m.s−1 and for the smooth tube it was only 0.230 m.s−1, as a result of the higher heat transfer of the enhanced tube. These results suggest that the 1EHT tube performs better in boiling heat transfer application, which can be attributed to the enhanced heat transfer area produced by the series of dimples/protrusions and petals distributed over its surface.