Combined Forced and Free Convective Heat Transfer Characteristics in Narrow Vertical Rectangular Channel Heated from Both Sides

Abstract

Combined forced and free convective heat transfer characteristics were experimentally investigated for water flowing under about 1 atm in a narrow vertical rectangular (750 mm long, 50 mm wide and 18 mm in gap) channel heated from both sides. Experiments were carried out for both downward and upward forced convective flows for Reynolds number Re of 4 × 101 ∼5 × 105 and Grashof number Gr of 5 × 104 ∼4 × 1011, where the distance x from the inlet of the channel is adopted as the characteristic length in Re and Gr. As the results, the following were revealed 1. (1) Heat transfer coefficients for the combined convective flow region can be expressed in simple forms with a dimensionless parameter Gr/Re 21/8 Pr 1/2 which is constituted by Gr, Re and Prandtl number Pr. 2. (2) From the above-mentioned simple expressions it can be identified that the combined convective heat transfer is significant for the condition of 2.5 × 10−4<Gr/(Re 21/8 Pr 2/1)< 1.8 × 10−3.3. (3) In the present experiment, little significant differences were observed in heat transfer characteristics between the combined convective flow region with upward forced convective flow and that with downward forced convective flow.