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Simultaneously Developing Flows Under Conjugated Conditions in a Mini-Channel Array: Liquid Crystal Thermography and Computational Simulations

This work presents experimental and computational calculations concerning thermo-hydrodynamics of simultaneously developing single-phase liquid flow in a semicircular mini-channel array subjected to conjugate thermal boundary conditions. Inherently, such developing flow conditions give higher species transfer coefficients. The understanding of transport processes in such systems is important because of its potential widespread use in many engineering systems. An array of seven parallel semicircular channels (internal diameter = 3.0 mm, hydraulic diameter = 1.83 mm, and length = 200 mm) was milled on a copper substrate (200 × 85 × 5 mm3). The interchannel pitch was 6.0 mm. Liquid crystal thermography was employed to measure spatial steady-state distribution of wall/fluid temperatures over the array. This technique was chosen to (i) obtain spatial field information needed for analyzing developing flows and (ii) overcome the limitations posed by conventional techniques when employed on small geometries. A differential transducer measured the pressure drop across the array. The flow experimental Reynolds number varied from 300 to 3200. The working fluid employed was distilled, deionized, and degassed water. A three-dimensional (3D) computational grid, representing the physical domain of the experiment, was generated and conservation equations were solved on a commercial platform. The results of the study show that: (a) Conventional theory, which predicts thermo-hydrodynamics of internal flows, is well applicable for the channels used in this study. The experimental Poiseuille number and Nusselt number under laminar as well as turbulent flow conditions closely matched with those generated by the computation model. Experimental data suggests that transitional flows existed between Reynolds number 800 and 1500. (b) Although with some limitations, liquid crystal thermography is well suited for mini-/micro-scale applications, especially for studying developing flows. (c) Wall conduction effects cannot be neglected under certain boundary/experimental conditions (d) A realizable k–ϵ model was found to be more suitable for turbulent flow modeling in mini-channels.