HEAT TRANSFER ENHANCEMENT FOR CONDENSATION ON A HORIZONTAL TUBE BY COILING WIRES: (THEORETICAL CONSIDERATION FOR VAPOR VELOCITY EFFECT).

Numerical solutions are presented for combined shear-and gravity-controlled condensation on a horizontal tube, around which a fine wire is coiled, by using a simplified physical model. The local Nusselt number distribution shows that the effect of surface tension upon heat transfer decreases with the increase of vapor velocity. The average Nusselt number can be expressed by a rule of fourth-power combination of the equations for shear-controlled condensation and gravity-controlled condensation. The heat transfer enhancement ratio against a smooth tube decreases with the increase of vapour velocity, because the decrease of effective heat transfer surface becomes more significant than the heat transfer enhancement due to surface tension. The Nu-equation for gravity-controlled condensation can be applicable in the velocity range where the heat transfer enhancement is achieved.