Heat Transfer Measurement on a Rotating Surface With Eccentric Jet Impingement Using Liquid Crystal Thermography and Stroboscopic Photography

Abstract

Abstract. This study investigates the convective heat transfer from an eccentric air jet impinging on a high-speed rotating disk using thermochromic liquid crystal thermography. The stroboscopic photography method was used to capture clear, blur-free images of liquid crystals on a rotating surface. A detailed calibration procedure was conducted to address the stroboscopic effect on liquid crystal measurement, covering various rotational speeds (0–3600 RPM), exposure times (50–550 μs), viewing angles, lighting conditions, and image gain settings. The effects of rotational Reynolds number (40,000–120,000), jet Reynolds number (7000–30,000), and jet-to-disk spacing ratios (1–5) on Nusselt number distributions were investigated. A stroboscopic imaging system converted liquid crystal images to temperature data during calibration, maintaining hue standard deviation below 5%. Eccentric jet impingement displayed an annular-ring heat transfer pattern with radially increasing Nusselt numbers influenced by Reynolds numbers. Decreasing jet-to-disk spacing ratios under fixed flow conditions improved heat transfer by around 5–10%. An empirical correlation was established using jet-to-disk spacing, jet Reynolds number, and rotational Reynolds number. This study showed that stroboscopic liquid crystal thermography can be used to measure heat transfer on high-speed rotating surfaces and for real-time thermal monitoring of rotating machinery.