The effects of V-nozzle inserts on

The effects of V-nozzle inserts on heat transfer and friction characteristics in a uniform heat flux tube are experimentally studied. Three different pitch ratios (PR) of V-nozzle arrangements in the test tube are introduced with PR=2.0, 4.0, and 7.0, in each run. The results of experimental investigations of heat transfer, friction characteristic and enhancement efficiency are presented. It is found that using the V-nozzle can help to increase considerably the heat transfer rate at about 270% over the plain tube. A maximum gain of 1.19 on enhancement efficiency is obtained for the smallest pitch ratio used, PR=2.0. This indicates that the effect of the reverse/re-circulation flows can improve the heat transfer rate in the tube. In addition, correlations from the results are presented.

Experimental investigations have been carried out to study the effects of the V-nozzle turbulators on heat transfer, friction and enhancement efficiency, in a circular tube. Major findings can be summarized as follows:
1. The heat transfer in the circular tube could be promoted by fitting with V-nozzles while it brings about the energy
loss of the fluid flow. heat transfer rates obtained from using the V-nozzles with PR=2.0, 4.0, and 7.0 are found to be 270%, 236%, and 216%, respectively, over the plain tube. However, the increase in friction factor is much higher than the increase in Nusselt number at the same Reynolds number.
2. The enhancement efficiency decreases with increasing Reynolds number. The maximum value of enhancement efficiency obtained from using the PR=2.0, 4.0, and 7.0, are found to be 1.19, 1.14, and 1.09, respectively. In addition, the enhancement efficiency increases as the pitch decreases and, generally, it lowers at high Reynolds number for all pitches.