Heat transfer in forced vibrated pipe with water laminar flow

Vertical tube was exposed to vibrations with frequency 30 ≤ f ≤ 150 Hz and amplitudes 0,3 ≤ A ≤ 3,0 (mm). Water of initial temperature 80-86 degrees C was flowing through the tube which was cooled by air streaming with average velocity 29,8 (m/s) and temperature 20-23 degrees C. In the test tube laminar flow in range of 120 ≤ Re ≤ 1500 and 3,18 · 109 ≤ Gr ≤ 6,70 · 109 was maintained. The copper tube of inside diameter d = 6,8 mm and length of the test section L 30 d was used. To create a possibility of defining the proportion Nup/nu for the same test pipe but without vibrations the dependence Nu=f(Gz) was defined separately. Only a little negative influence of vibration frequency on the heat transfer was observed, because of a small and minus value of the exponent for the (Ka) number. In the range of amplitudes 1,0 ≤ A ≤ 3,0 mm increase of heat transfer by the simultaneous growth of the (Gz) number was observed, whereas amplitudes 0,3 ≤ A ≤ 0,5 mm and increase of value of the (Gz) number resulted in deterioration of heat transfer