Studies on Influence of Chromium Layer on Inner Surface of Steel Tube on Heat Transfer

Abstract

This paper presents the results of numerical calculations of heat transfer in the steel wall of a tube with different chromium layer thicknesses on the inner surface for a single and a sequence of heat impulses. In modeling the thermal phenomenon, the tube material was assumed to be homogeneous, and the inner surface of the tube had a protective chromium layer. The calculations were performed for temperature-dependent parameters of the 30HN2MFA steel and chromium. The tube was divided into 30 zones. The time varying the heat transfer coefficient and the heat flux density on the inner surface of the tube in each zone were calculated. The numerical simulations of heat transfer in the tube wall were performed using the FEM implemented in COMSOL Multiphysics software. On account of the high thermal conductivity of chromium, after the first and subsequent heat impulses, as the thickness of the chrome layer increases, the highest peak temperature drops, while the temperature inside the steel wall of the tube increases. After the first heat impulse, the temperature of the wall at a depth 0.5 mm below the inner surface is twice as high for a tube with a 200 µm thick chrome coating compared to a tube without this coating. This paper showed that, after seven heat impulses, the temperature of the steel tube substrate does not exceed 750 °C, at which the shrinkage of the material occurs, causing cracks in the chrome coating.

Influence of the Shrinkage of the Inner Layer of Steel Tubes on Permissible Thermal Load

“…870 • C. The model of the tube with an overall length of 3150 mm and 35 mm inner channel is presented in Figure 1. The gas temperature, T g (t), and the heat transfer coefficient, h i (t), were determined for 30 cross-sections (P1 to P30-see Table 1), using the method described in [17,18]. The results of the calculations for cross-section P i are applicable to the entire length of the S i zone.…”

“…Sufficiently breaks can prevent the steel from reaching the shrinkage temperature. However, in w [16][17][18], the length of the series of thermal impulses that causes the shrinkage tempera to be reached was determined. The analyzes were performed for various steel grades.…”

“…Geometrical parameters of the tube zones: PS i -zone boundaries; R out,PS i -outer radius in zone boundary i; z i -distance from the bottom of the tube to the cross-section P i in the middle of zone Si. Data from [18]. In devices of this type, heat is transferred mainly through convection from the gas of the heat impulse.…”

“…Due to the very short impulse duration, we ignore the heat transfer through radiation between the gas and the inner surface of the tube [17]. The h i (t) and T g (t) data are taken from [18]. An example of the calculation results of h i (t) and T g (t) in the selected cross-sections PS 4 , PS 10 , PS 16 , PS 21 , PS 25 , and PS 30 is presented in Figure 2.…”

“…An example of the calculation results of h i (t) and T g (t) in the selected cross-sections PS 4 , PS 10 , PS 16 , PS 21 , PS 25 , and PS 30 is presented in Figure 2. A detailed method of calculating h i (t) and T g (t) is presented in [18]. In devices of this type, heat is transferred mainly through convection from the gas of the heat impulse.…”