Effect of light penetration depth during laminar mixed convection in a discretely, asymmetrically and volumetrically laser-heated vertical channel of finite length

Particle image velocimetry (PIV) measurements are carried out in an experimental investigation of laminar opposing mixed convection in a vertical flow cell of finite length with a square cross-section. The bulk downward flow is driven by gravity while a portion of a lateral side is heated with laser irradiation. The working fluid is a copper nitrate aqueous solution, and the experiments are performed for three values of the Reynolds number of Re = 20, 40 and 60 and three values of the nondimensional absorption coefficient of a∗ = 0.5, 4.2 and 6.7. These parameters correspond to modified Richardson number range from 67 to 8084. A parametric study has been carried out to assess the effect of light penetration depth (i.e. absorption coefficient or solution concentration) on the final flow configuration; shear stress distributions have been calculated from the velocity field. Numerical simulations are also carried out to determine the thermal distributions, local and overall nondimensional heat transfer rates (Nusselt numbers) along the irradiated cell wall, and the complex flow features are presented in the form of contours of velocity, vorticity and temperature. The results reported herein demonstrate the modulation effect of Re and a∗ on the flow and temperature distributions, and explore the convenience of laser irradiation heating for the purpose of selectively localizing energy deposition during thermal therapies by modeling biological tissues as light-absorbing media.