LAMINAR AIR FLOW FREE CONVECTIVE HEAT TRANSFER INSIDE A VERTICAL CIRCULAR PIPE WITH DIFFERENT INLET CONFIGURATIONS

Free con vec tion heat trans fer has been ex per i men tally in ves ti gated for lam-i nar air flow in a ver ti cal cir cu lar pipe by us ing the bound ary con di tion of con stant wall heat flux in the ranges of lo cal Rayleight num ber (RaL) from 1.1·10 9 to 4.7·10 9. The ex per i men tal setup was de signed for de ter min ing the ef fect of dif fer ent con fig u ra tions placed at the in let of a ver ti cal heated pipe, on the sur face tem per a ture, the lo cal and av er age heat trans fer co ef fi cients. The ap pa ra tus was made with an elec tri cally heated alu mi num pipe with length of 900 mm and in side di am e ter 30 mm. The in let con fig u ra tions in-cluded two cir cu lar pipes hav ing the same di am e ter as the heated pipe but with lengths of 600 and 1200 mm, sharp-edge and bell-mouth. It was found that the sur face tem per a ture along the pipe sur face for same heat flux would be higher val ues for in let con di tion with length of 1200 mm and would be lower val ues for bell-mouth in let con di tion. The re sults show that the lo cal Nusselt num ber Nux and av er age Nusselt num ber ( NuL) val ues would be higher for bell-mouth in let con di tion and lower val ues for 1200 mm in let con di tion. For all in let con fig u ra tions, the re sults re veal that the Nu in-creases as the heat flux in creases. Em pir i cal cor re la tions have been pro-posed in a form of log NuL vs. log RaL for each case in ves ti gated and a gen-eral cor re la tion for all cases has been ob tained which re veals the ef fect of in let con di tions ex is tence on the free con vec tion heat trans fer pro cess in a ver ti cal cir cu lar pipe. Key word: laminar flow, free convective heat transfer, vertical pipe, sharp-edge, bell-mouth, different inlet configuration