The effect of oxide layer in case of novel coolant spray at very high initial surface temperature

ABSTRACT

The significant reduction of Leidenfrost effect during the cooling of high carbon steel plate by different potential cooling methodologies does not assure their successful implementation in the fast quenching of high carbon steel plate due to the formation of oxide layer of comparatively low thermal conductivity on the quenching surface. Therefore, the role of oxide layer in case of different potential cooling methodologies needs to be addressed. In the present study, the effect of oxide layer on heat transfer rate in case of upward, downward, and both upward and downward facing spray with additives has been investigated by conducting and comparing the heat transfer cooling data of an AISI 1020 plate with the AISI 304 plate. The comparison clearly depicts that the formation of oxide layer during cooling significantly hinders the heat transfer rate in nucleate boiling regime; however, the reverse phenomenon is observed in transition boiling regime. Among all the coolants, the least effect of oxide layer on enhancement is obtained in case of NaCl (0.4 M)-added water spray due to the deposition of salt on the evaporating surface. The X-ray diffraction analysis and the thickness of the formed oxide layer clearly assert that the coolant depicting minimum oxidation characteristic is preferred.

Abbreviations: AISI: American iron and steel institute; OES: Optical emission spectrophotometer; CHF: Critical heat flux, MW/m²; IHF: Initial heat flux, MW/m²; T_CHF: Temperature at which CHF is achieved, °C; Fps: Frames per second; XRD: X-Ray diffraction; k₁: Thermal conductivity of steel plate, W/m °C; k₂: Thermal conductivity of oxide layer, W/m °C; k₃: Thermal conductivity of coolant, W/m °C; X: x-axis, mm; Y: y-axis, mm; Z: z-axis, mm

KEYWORDS:

• oxide layer
• transition boiling
• nucleate boiling
• fast quenching