Experimental Analysis of Subcooled Flow Boiling Heat Flux on Gray Cast Iron Block in Heavy-duty Diesel Engine-like Conditions: Optimization using Central Composite Design

The two-phase fluid flow in the Heavy-duty diesel (HDD) engine water jacket coolant can greatly reduce the thermal load of the cylinder head. In this experimental work, the characteristic of two-phase fluid flow in a transparent Plexiglas channel using C2H6O2- H2O (50%–50%) is investigated. Gray cast iron surfaces were selected as the heated surfaces to simulate the material of the HDD-cylinder head. Operating conditions of the HDD- engine (i.e. Vinlet from 0.46 to 2.0 m/s, Psystem from 1 to 2 bar and Tinlet from 70 to 110°C) are optimized using Response Surface Method (RSM) within the framework of the Central Composite Design (CCD) model. The outputs indicate: the onset of nucleate boiling (ONB) temperature increases by about ≈ 11.92% when the pressure changes from 1 to 2bar. By reducing the inlet temperature (from 70 to 110℃), the effect of superheating disappears around the bubble, so to reach the non-linear (i.e. two-phase region) area, the heat flux must be increased between 10 to 15 kW/m2 to observe the ONB point. The cooling system pressure at low velocities (i.e. < 1m/s) should be considered in such a way that the saturation temperature of the fluid is about 35 to 50℃ lower than the HDD-engine wall temperature. Instead, at high velocities (i.e  1m/s) this temperature difference between the fluid saturation temperature and the wall temperature is about 55 to 85℃.