High mass flux spray quenching on an inclined surface: A novel methodology for the attainment of enhanced uniform cooling with unaltered surface morphology in transition boiling regime Lily a , A.R. Pati a , A. Panda a , B. Munshi a , S.S. Mohapatra a,⇑ , A. Behera b , B. Saha c a Department of Chemical Engineering, National Institute of Technology, Rourkela 769008, India b Department of Metallurgical and Materials Engineering, National Institute of Technology, Rourkela 769008, India c Department of Mechanical Aerospace Engineering, Seoul National University, South Korea article info Article history: Received 22 February 2018 Received in revised form 9 September 2018 Accepted 26 October 2018 Keywords: Spray cooling Plate orientation Transition boiling regime Morphology Hardness abstract The main obligation in the successful implementation of ultra-fast cooling in a manufacturing process are: (1) significant minimization of film boiling effect, (2) achievement of unaltered surface morphology and (3) uniform cooling on the surface of the plate. The literature does not reveal any methodology, which depicts simultaneously enhancement, unaltered surface morphology and uniform cooling. Therefore, in the current work, an attempt has been made to develop an appropriate cooling process depicting all the aforesaid requirements. The cooling on an inclined condition of the plate mitigates the aforesaid requirements. The result reveals that the heat removal rate enhances (CHF from 1.21 MW/m 2 to 1.46 MW/m 2 ) due to augmentation of sweeping rate of vapor film from the hot surface as inclination angle increases from 0° to 30°. Further increase of the inclination from 30° to 60° decreases the cooling rate due to reduction of droplet velocity, residence time and the replacement rate of the vapor and liquid layers. The optimum inclination of the plate to achieve the maximum average surface heat flux is 30°. In addition, the temperature distribution on the surface and across the thickness of the heat treated plate confirms uniform cooling. The SEM image and the EDS of the current heat treated metal is compared with the SEM images and EDS data of the metals cooled by potential coolants such as surfactant added water, NaCl added water and MgSO 4 added water and the comparison clearly asserts unaltered surface morphology for the current case. The variation of the hardness on the surface and across the thickness clearly asserts the excellent shock absorbing characteristics. Ó 2018 Elsevier Ltd. All rights reserved. 1. Introduction A very high cooling rate of metal is essential for very high tem- perature (>900 °C) metal bodies in metal industries to achieve a desirable property [1,2]. The formation of vapor layer at this condi- tion over the hot plate inhibits the direct contact of coolant liquid and hot surface, and reduces heat transfer rate drastically [3–5]. This phenomenon becomes stronger with the increasing stability of the vapor film, which is directly controlled by the amount of vapor produced and the residence time of the vapor on the hot plate. The literature does not reveal any methodology to com- pletely eliminate the vapor film effect and reduce the stability of vapor film. Thus, the fast quenching of metal with very high initial temperature is still a challenging task to the process engineers. In the conventional cooling system of the run-out table (ROT), jet cooling or laminar cooling is used and these methodologies are not appropriate for the fast quenching operation due to the film boiling effect [6,7]. Because of the favorable characteristics like higher heat transfer due to minimum film boiling effect and unifor- mity in cooling in case of high mass flux spray, further reduction in film boiling effect and significant cooling enhancement can be expected. The open literature reveals that there are various factors that influence the formation and the growth of the vapor film which include type of nozzle, nozzle to plate surface distance, surface character, liquid flow rate, droplet velocity, spray type, orientation of the plate and the cooling medium [8–10]. The heat transfer rate is also dependent on the droplet momentum and the spray area along with the formation, growth and stability of the vapor film. Too small orifice-to-surface distances would result in only a small fraction of the test surface impacted by the spray, while too large https://doi.org/10.1016/j.ijheatmasstransfer.2018.10.116 0017-9310/Ó 2018 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Spray Boiling Heat Transfer Laboratory, Room No-114, Department of Chemical Engineering, NIT Rourkela 769008, India. E-mail address: mohapatras@nitrkl.ac.in (S.S. Mohapatra). International Journal of Heat and Mass Transfer 131 (2019) 11–30 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt