Heat Transfer Characteristics with Single and Multi-stage Flat Spray Nozzles on a Hot Vertical Surface Cooling

Abstract

In order to improve water cooling technique for flanges in rolled H-shapes for the prevention of cooling buckling on thin web, an experimental study on a hot vertical surface cooling with single and multi-stage spray nozzles was carried out.
First, the effects of nozzle pressure, nozzle angle and nozzle-plate distance on heat transfer coefficient of a hot vertical surface were investigated with a single spray nozzle. Next, with multi-stage spray nozzles the effect of flowing water from the upper area on heat transfer coefficients of the lower water strike zone and flowing water zone was investigated.
The results obtained are summarized as follows.
(1) The heat transfer coefficient of water strike zone with a single spray nozzle was described by water flux which is functions of nozzle pressure, nozzle angle and nozzle-plate distance.
(2) In the case of high temperature with a single spray nozzle, the heat transfer coefficient ratio between flowing water zone and water strike zone is not affected by the cooling conditions, such as nozzle pressure, nozzle angle and nozzleplate distance.
(3) However, in the case of low temperature, the ratio between flowing water zone and water strike zone on heat transfer coefficient strongly depends on the nozzle operating conditions.
(4) On the other hand, in the case of multi-stage spray cooling, the existance of flowing water from the upper area enhances heat transfer coefficient of lower flowing zone. The maximum ratio of heat transfer coefficient between flowing water zone with water flowing down from above and without is from about 1.3 to 1.7.