Thermal performance of a pipe in pipe heat exchanger with sinusoidal inner pipe

Heat and fluid flow characteristics for sinusoidal smooth pipes with different wavelength and amplitude have been investigated experimentally. The effects of the dimensionless wavelength (a/d(i)) and the amplitude (b/d(i)) on the thermal performance of a sinusoidal pipe inside a straight pipe heat exchanger are investigated. The experiments employed one straight smooth pipe, five sinusoidal smooth pipes at different a/d(i) and three sinusoidal smooth pipes at different b/d(i). The Reynolds number ranged from 8.8 x 10(3) to 2.8 x 10(4), and the Prandtl number ranged from 4.53 to 5.85. The range of the dimensionless wavelength (b/d(i)) is from 18.52 to 55.55, and the dimensionless amplitude (a/d(i)) range is from 4 to 13.6. The results showed that the heat transfers in sinusoidal pipes are increased in all cases of a/d(i) and b/d(i) above those of the straight pipe. Also, the friction factor(f) in the sinusoidal pipes is increased in all cases of a/d(i) and b/d(i) above that of the straight pipe. The dimensionless exergy loss (e) decreases with the increase of b/d(i), but in the case of a/d(i), the maximum of e is attained at a/d(i) = 6.22 and the minimum is attained at a/d(i) = 13.6. Correlations of Nu and f as a function of Re, b/d(i) and a/d(i) are presented. Also, a correlation of e as a function of Re, b/d(i) and a/d(i) is given. (c) 2007 Elsevier Ltd. All rights reserved.