International Journal of Thermal Sciences 46 (2007) 637–648 www.elsevier.com/locate/ijts Numerical simulation of double diffusive laminar mixed convection in a horizontal annulus with hot, solutal and rotating inner cylinder Mohamed A. Teamah Mechanical Engineering Department, Alexandria University, Alexandria, Egypt Received 6 July 2006; received in revised form 12 August 2006; accepted 10 September 2006 Available online 9 October 2006 Abstract A numerical investigation of double-diffusive laminar mixed convection within a two-dimensional, horizontal annulus has been carried out. The inner cylinder was considered to rotate in an anti-clockwise direction to introduce the forced convection effect. In addition, the solutal and thermal buoyancy forces are sustained by maintaining the inner and outer cylinders at uniform temperatures and concentrations, but their values for the inner are higher than the outer. The laminar flow regime is considered under steady state conditions. Moreover, the transport equations for continuity, momentum, energy and mass transfer are solved using the Patankar–Spalding technique. The streamlines, isotherms and isoconcentrations as well as both local and average Nusselt and Sherwood numbers were studied. The study covers a wide range for 10 2  Ra T  10 6 ,0.1  Le  10 and −20  N  20. Through this investigation, the following parameters are kept constant: Prandtl number at 0.7, the rotational Reynolds number at 100 and the radius ratio at 0.5. The predicted results for both average Nusselt and Sherwood numbers were correlated in terms of Lewis number, thermal Rayleigh number and buoyancy ratio. A comparison was made with the published results and a good agreement was found.  2006 Elsevier Masson SAS. All rights reserved. Keywords: Double-diffusive flow; Heat and mass transfer; Rotating annulus; Mixed convection; Two-dimensional; Numerical simulation 1. Introduction Double-diffusive convection is referred to the problems where the fluid flow is induced by the simultaneous presence of two diffusive components. These are the difference in tem- peratures and concentrations. A substantial amount of research has been reported on double-diffusive convection in confined spaces due to its many engineering and technology applica- tions. Such as, the technologies involved in the chemical vapor deposition processes for the semiconductor device fabrications. Also, the migration of impurities in non-isothermal material processing applications has motivated many researchers in ex- ploring the characteristics of the associated species and energy transport processes. The effect of forced flow in a double- diffusive convection has been considered in natural phenomena as atmospheric and oceanic flows. Also, these phenomena ap- pear in many engineering applications. The migration of the E-mail address: mteamah@yahoo.com. species is known to be sensitive to the magnitude of rotational speed, which is a crucial parameter in drying technologies, printing and crystal growth applications. Other technologies including melting and solidification processes in rotating fur- nace are likely candidates for such applications. In addition, the flow and heat transfer characteristics under the simultaneous ef- fect of temperature and concentration gradients as well as the centrifugal forces are defined by the mixed convection. In gen- eral, both thermal and solutal Grashof numbers as well as the rotational Reynolds number represent these effects. Early studies of the combined heat and mass transfer in rec- tangular enclosures were reported by Hu and EL-Wakil [1], Os- trach [2–4] has pointed out that various convection modes can emerge based on the orientations of the temperature and con- centration gradients. For a vertical annulus, Ship et al. [5] con- ducted a numerical study for steady laminar double-diffusive natural convection within a vertically mounted closed annulus with constant temperature and mass species differences im- posed across the vertical walls. Their results showed that the buoyancy ratio was the primary parameter that defined the flow 1290-0729/$ – see front matter  2006 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.ijthermalsci.2006.09.002