BOILING HEAT-TRANSFER IN SMALL HORIZONTAL TUBE BUNDLES AT LOW CROSS-FLOW VELOCITIES

An experimental investigation has been carried out to determine the local forced convective boiling heat transfer coefficient in small tube bundles consisting of horizontal tubes in a vertical column arranged in a large channel under low cross-flow velocities in saturated distilled water at atmospheric pressure. The effects of the impressed heal flux, cross-flow velocity and tube geometry on the heat transfer characteristics have been investigated. While no significant effect of the bundle geometry was observed on the heat transfer coefficient of the bottom tube compared to that of the single tube, vapour bubbles rising from the lower tubes and agitating the liquid around the upper tubes were found to yield higher values for heat transfer coefficients on the upper tubes. A Chen-type relation has been used to correlate the data on local forced convective heat transfer coefficients of upper tubes with reasonably accuracy.