Abstract 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 × 10 3 to 2.8 × 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.