Numerical Simulation Of Thermal-Hydraulic Performance On Convective Heat Transfer Through A Helical Coiled Passage

Helical coiled passage are widely employed in many industrial applications, such as piping systems, heat exchangers, chemical reactors and many other engineering systems, because of their compact size and high heat transfer performance. The heat transfer and flow characteristics in a helical coiled passage have been dealt with for quite some time based on the first /second thermodynamics. It is found that most of the previous studies are restricted to the heat transfer and flow developments for fully developed laminar forced convection in a helical coiled passage. While the research of the three-dimensional turbulent flow and heat transfer in a helical coiled passage and the research of the flow and heat transfer in the entrance region of helical coiled passage, both have become one of the urgent problems in engineering and one of challenging research fields in fluid mechanics. Consequently, this study is significant in theory and has a broad application future.The detailed review of the research on the flow and heat transfer in the curved pipes from the last century is firstly made in this dissertation. Based on the review, three-dimensional turbulent forced convective heat transfer, three-dimensional laminar forced convective heat transfer and non-dimensional entropy generation number in a helical coiled passage (entrance included) with circular cross section under uniform wall temperature condition and uniform heat flux condition have been researched by numerical simulation. Furthermore, the numerical computations reveal the laminar forced convective heat transfer in the helical coiled passage (entrance included) with annular cross section when the inner annular wall is heated and the outer annular wall is insulated, and the outer annular wall is heated and the inner annular wall is insulated, and the inner annular and outer annular are heated respectively. The results presented in this paper cover a Reynolds number range of 200-1000(laminar flow) and 2×104-6×104(turbulent flow), a pitch range of 0.1-0.2 and a curvature ratio range of 0.1-0.3. The variations of the distribution of velocity, the distribution of temperature, the average friction factor, the average Nusselt number at different axial cross–sections and the total entropy generation number with different dimensionless parameters have been examined. The results show that:①The secondary flow is weak and can be neglected at the entrance region, but the effect of the secondary flow is enhanced, the maximum velocity perpendicular to axial cross section shifts toward the outer side of helical coiled passage; two dean roll cells appear with the increase of axial angle when flow is laminar flow, but there no dean roll cell appear when flow is turbulent flow.②The average Nusselt number (Num) and friction factor (fm) at every different axial location and the total entropy generation number present different characteristics when the Reynolds Number, curvature ratio and pitch change. Compared with the curvature ratio, the pitch has relatively little influence on heat transfer and flow performance can be neglected.③In the fully developed region, the helical coiled passage with circular cross section in this paper for laminar flow show 2.622-7.1 times (uniform wall temperature) and 2.64-7.3 times (uniform heat flux)of Num in the heat transfer as compared to the straight tube, while the friction factor are 1.5-3 times (uniform wall temperature) and 1.62-3.23 times (uniform heat flux). Compared with a straight tube for turbulent, the Num are 1.35-2.2 times (uniform wall temperature) and 1.7-2.7 times (uniform heat flux) and fm are 1.4-2.25 times (uniform wall temperature) and 1.57-2.52 times (uniform heat flux).④The thermodynamic characteristics in a helical coiled passage with annular cross section are the same as the helical coiled passage with circular cross section. Compared with the helical coiled passage with circular cross section, the Num is reduced by 21.4%, fm is reduced by 20.6% when outer annular wall is heated; the Num is reduced by 11.6%, fm is reduced by 15.6% when inner annular wall is heated; when two annular wall are heated, the fm have no change with one annular wall is heated, the Num have a little increase with one annular wall is heated. The order of the total entropy generation number in the helical coiled passage from largest to smallest is the two annular walls are heated, the circular helical coiled passage, the outer annular wall is heated and the inner annular wall is heated.