Influence of concave and convex shaped sample surfaces on heat transfer and development of stress during immersion cooling in synthetic hardening oil

摘要

Heat transfer coefficientsα were determined during submerging of hollow cylinders with a temperature of 850℃ in fast hardening synthetic oils with a temperature of 60℃ and exactly defined convection velocities of 0.0, 0.3 and 0.6 m/s. Theserings were fitted with 6 cover thermocouples under the inner (concave) and outer (convex) surfaces at different heights to measure the temperature slope. Additionally the course of the wetting behavior at the outer surface was recorded by photographs.Temperature distribution, distribution of the heat flux and development of the thermal stresses were calculated by FEM.The local change of the "Leidenfrost"-temperatures on the concave and convex surfaces and the wetting behavior show no influence of the flow velocities but a clear decrease from the lower to the upper surfaces' end. The maxima of the α-values in themantel-line of the concave surface is about 20 to 50 % higher than the values of the convex surface. According to these results the region beneath the surfaces with compressive stresses at the inner side is about 50 % of the outer side (concave).