Lateral conduction effect study using 2-D transient liquid crystal measurement

Abstract

In most liquid crystal thermography (LCT) based heat transfer investigations, one-dimensional (1-D) conduction solution for semi-infinite wall is widely used to determine surface heat transfer coefficients (HTCs). The conventional 1-D solution ignores the transverse and longitudinal variation of surface temperature values, which makes HTCs prone to lateral conduction errors. Accounting the lateral conduction effect demands full-scale multidimensional boundary conditions, which is seldom possible in Liquid Crystal (LC) experiments. Present investigation is a forward step in that direction and performs comprehensive analysis to evaluate the lateral conduction effect with the help of actual LC measurements. Investigations have been performed at different Reynolds number for the duct carrying smooth surface and surface mounted with different types of turbulence promoters, i.e., round-edged perforated rib (2-D rib) and truncated prismatic rib (3-D rib), which are supposed to produce two/three-dimensionality in flow field and hence the lateral conduction effects. Eventually, 2-D and 3-D conduction results are compared against 1-D results. Accuracy and reliability of transient conduction scheme is also reviewed by varying several inherent parameters. For undisturbed flow (smooth duct), 1-D solution (wall normal, y-direction) under predicts HTC as against the transverse spanwise (2-D), longitudinal streamwise (2-D), and full scale multidimensional (3-D) conduction results by ∼ 7–9 %, 2–4 %, and 8–12 %, respectively. 2-D conduction-based (transverse or longitudinal) solution fails to predict the actual HTC distribution in vortex induced flow condition (ribbed duct). 3-D conduction-based analysis accurately capture the small-scale HTC distribution pattern, and yields 10–13 % higher HTC values as against conventional 1-D semi-infinite conduction-based solution.