The Effects of Prandtl Numbers on Local and Average Convective Heat Transfer Characteristics in Helical Pipes

Abstract

To investigate the effects of the Prandtl number and geometric parameters on the local and average convective heat transfer characteristics in helical pipes, experiments with three different fluids—air, water, and ethylene glycol—were carried out on five uniformly heated helical pipes. The test sections were made from 22.9 mm I.D. and 10.2 mm I.D. 304 stainless steel pipes. The ratios of the pipe diameter and pitch to coil diameter (d/D and b/D) ranged from 0.0267 to 0.0884 and 0.20 to 2.56, respectively. The peripheral and average, fully developed Nusselt numbers were evaluated in the experiments. Experimental findings indicate that after two turns (X > 2) the temperature distributions along the wall are almost parallel to the linear fluid bulk temperatures, and all dimensionless peripheral wall temperatures are nearly identical, implying that both the flow and temperature distribution within the helical pipes are fully developed. These results reveal that the peripheral Nusselt number varies significantly for higher Prandtl numbers and Dean numbers in the laminar flow region. A new set of empirical expressions for the average fully developed Nusselt number has therefore been regressed based on the present data and some data from previous investigations. No obvious effects of the coil pitch or torsion were observed in the scope of this investigation.

Numerical Study of Turbulent Flow and Convective Heat Transfer Characteristics in Helical Rectangular Ducts

“…The results indicated that the presence of torsion has large effects on flow field and heat transfer if the ratio of curvature to torsion is of order unity. Xin and Ebadian [3] tested five helical pipes with different torsions and curvature ratios to investigate local and averaged heat transfer characteristics. They found that the temperature distribution becomes fully developed after two turns from the inlet.…”

Heat Transfer Characteristics and Performance of a Spirally Coiled Heat Exchanger under Sensible Cooling Conditions

“…The effects of the Reynolds number and pitch of the coiled tube on the heat transfer coefficient were investigated. Xin et al (5) studied the effects of the Prandtl numbers and geometric parameters on the local and average convective heat transfer characteristics in helical-pipes. The experiments were performed with three different working fluids: air, water, and ethylene-glycol.…”

Performance of Dish-Stirling CSP system with dislocated engine

“…Roger and Mayhev's correlation [14] has greater error than Xin and Ebadian's correlation [15]. These correlations, as already said, are the only ones that directly take into account the curvature of the heat exchanger.…”

“…Xin and Ebadian [15] presented an experimental study on heat transfer for helical tubes. The correlation proposed by them, which is valid for both air and water, with 0.7 \ Pr \ 5 and Reynolds between 5.5 9 10 3 and 1.1 9 10 5 and cooled fluid, is:…”