Experimental investigation of spray cooling performance with enhanced heating surface structures

An open loop spray cooling experimental system with ten enhanced groove surfaces was established. The results show that maintaining an unchanged groove width and changing the groove depth from 0.2 mm to 1.6 mm, the surface with a groove depth of 0.8 mm, the largest heat flux enhancement appears when volume flow rate is 0.45 L/min and 0.75 L/min. However, the heat transfer performance increased with an increasing groove depth under the flow rate of 1.25 L/min. Then based on the analysis of the forces acting on the falling droplet, the residual velocity of the droplet is calculated to explain why the optimal heat transfer of enhanced surfaces is different at different volume flow rates. Maintaining a groove depth of 0.8 mm, as the groove bottom width was reduced from 4 mm to 1 mm, the heat transfer coefficient increased by 41%. With the spray flow rate of 1.25 L/min, the heat transfer coefficient increased by only 8.5% and the reason for this phenomenon is explained by the variation of Bond number which reflects the capillary force. Finally, a relevant correlation of the non-dimensional Nusselt number Nu for the grooved surface is proposed in the non-boiling area with water coolant.