Numerical Investigation of the Thermal Performance of an Axially Rotating Internally Finned Receiver Tube of Parabolic Trough Concentrator

Enhancement of the thermal performance of the parabolic trough receiver tube is one of the approaches to energy sustainability. In the present work, the thermal performance of an axially rotating receiver tube equipped with internal flat longitudinal fins is studied. The effects of both the fin height and the rate of axial rotation are investigated at low values of axial Reynold’s number. The numerical analysis is held at various rotation rates using ANSYS Fluent. The numerical findings showed that the effect of the axial rotation on the internally finned receiver tube is not significant yet negative where a maximum reduction of 6% in the outlet temperature is reached in the 2mm height internally finned tube at rotation rate of N=21. However, the analysis showed that as the rotation rate increases, the temperature homogeneity between the fluid layers also increases and thus the liquid stratification phenomenon between the fluid layers is eliminated. The percentage of temperature difference between the fluid layers near the pipe center and the layers near the pipe wall reaches an optimum value of 58.4% at N=21 which is confirmed by an optimum increase of 110% in Nusselt number at the same rotation rate. However, a maximum loss of 81.6% in pressure coefficient is found in the case of the 2mm internally finned tube due to the increased turbulence. Thus, the integration of pipe axial rotation and internal fins can yield an enhancement in the heat transfer to the parabolic trough concentrator receiver tube and thus its thermal performance.

Effect of fin and tube configuration on heat transfer of an internally finned tube

Purpose – The purpose of this paper is to determine the heat transfer and fluid flow characteristics of an internally finned tube for different flow conditions. Design/methodology/approach – Numerical investigation have been performed by solving the conservation equations of mass, momentum, energy with two equation-based k-eps model to determine the wall temperature, outlet temperature and Nusselt number of an internally finned tube. Findings – It has been found from the numerically investigation that there exists an optimum fin height and fin number for maximum heat transfer. It was also found that the heat transfer in T-shaped fin was highest compared to other shape. The saw type fins had a higher heat transfer rate compared to the plane rectangular fins having same surface area and the heat transfer rate was increasing with teeth number. Keeping the surface area constant, the shape of the duct was changed from cylindrical to other shape and it was found that the heat transfer was highest for frustum shape compared to other shape. Practical implications – The present computations could be used to predict the heat transfer and fluid flow characteristics of an internal finned tube specifically used in chemical and power plants. Originality/value – The original contribution of the paper was in the use of the two equation-based k-eps turbulent model to predict the maximum heat transfer through optimum design of fins and duct.

Augmentation of Convective Heat Transfer of Highly Viscous Fluid within Three-Dimensional Internally Finned Tube

Investigation on the heat transfer and friction characters for fresh oil flowing inside three-dimensional internally finned tube (3-DIFT) was carried out with orthogonal experimental design method. Reynolds numbers varied from 30 to 800，Prandtl numbers 550 to 1000. The experimental results showed that low critical Reynolds numbers at the range of 100 to 200 were attained within all the experimental tubes, which indicated that 3-DIFT could obvious accelerate the transformation of high viscous fluid from laminar flow to turbulent flow. It offered a particular advantage to enhance the convective heat transfer of highly viscous fluid. Empirical equations on flow resistance and heat transfer were obtained using a least-squares regression. Compared with empty smooth tube, the maximal thermal performance factor for the turbulent flow within 3-DIFT could be enhanced up to 3.61. The optimization on shape of 3-DIFT for further augmentation heat transfer was also obtained.