An experimental investigation of heat transfer characteristics for steam cooling and air cooling in a rectangular channel roughened with parallel ribs

Abstract A comparative experimental study on the heat transfer characteristics of steam and air flow in rectangular channels roughened with parallel ribs was conducted with the use of an infrared camera. The effects of Reynolds numbers ( Re ), rib spacing ratio ( P / e ) and rib angles ( α ) on steam and air convective heat transfer were obtained and compared. The blockage ratio ( e / D h ) of the tested channel is 0.078 and the aspect ratio ( W / H ) is fixed at 3.0. In the paper, the Reynolds number for both coolants ranges from 3000 to 15,000, the rib spacing ratios were 8, 10 and 12, and rib angles were 90°, 75°, 60°, and 45°, respectively. For a square channel with 90° ribs with wider rib spacing ratio ( P / e  = 10 and 12) respectively give a area-averaged heat transfer about 8.4% and 11.4% more than P / e  = 8 model. The heat transfer enhancement of both steam and air increased with decreasing the rib angle from 90° to 45°. Although the heat transfer distributions of steam and air flow in the rib roughness channels were similar to each other in all the investigated channels, the steam flow can obtain a high convective heat transfer enhancement capability. The area-averaged Nusselt numbers of steam flow at a Reynolds number of 12,000 were approximately 13.9%, 14.2%, 19.9%, and 23.9% higher than those of air flow for rib angles of 90°, 75°, 60°, and 45°, respectively.

[1]  Je-Chin Han,et al.  LOCAL HEAT TRANSFER DISTRIBUTIONS NEAR A SHARP 180° TURN OF A TWO-PASS SMOOTH SQUARE CHANNEL USING A TRANSIENT LIQUID CRYSTAL IMAGE TECHNIQUE , 1995 .

[2]  R. J. Goldstein,et al.  Heat transfer and friction in tubes with repeated-rib roughness , 1971 .

[3]  Jie Han,et al.  Heat transfer and friction characteristics in rectangular channels with rib turbulators , 1988 .

[4]  Dieter Bohn,et al.  Experimental and Numerical Investigation of a Steam-Cooled Vane , 2002 .

[5]  Je-Chin Han,et al.  Augmented heat transfer in rectangular channels of narrow aspect ratios with rib turbulators , 1989 .

[6]  Karsten Kusterer,et al.  Cooling Performance of the Steam-Cooled Vane in a Steam Turbine Cascade , 2005 .

[7]  Jianmin Gao,et al.  Numerical Investigation of Heat Transfer and Flow Characteristics in a Steam-Cooled Square Ribbed Duct , 2010 .

[8]  Je-Chin Han,et al.  Heat transfer enhancement in channels with turbulence promoters , 1984 .

[9]  Bruno Facchini,et al.  Evaluation and Comparison of Different Blade Cooling Solutions to Improve Cooling Efficiency and Gas Turbine Performances , 2001 .

[10]  Je-Chin Han,et al.  Heat Transfer and Friction in Channels With Two Opposite Rib-Roughened Walls , 1984 .

[11]  Je-Chin Han,et al.  Heat Transfer in Two-Pass Rotating Rectangular Channels (AR=1:2 and AR=1:4) With 45° Angled Rib Turbulators , 2004 .

[12]  Je-Chin Han,et al.  An investigation of heat transfer and friction for rib-roughened surfaces , 1978 .

[13]  Xiaojun Shi,et al.  Heat transfer characteristics in steam-cooled rectangular channels with two opposite rib-roughened walls , 2013 .

[14]  Y. Rao,et al.  An Experimental Study of Transitional Flow Friction and Heat Transfer Performance of a Channel With Staggered Arrays of Mini-Scale Short Pin Fins , 2009 .

[15]  C. P. Lee,et al.  Augmented Heat Transfer in Square Channels With Parallel, Crossed, and V-Shaped Angled Ribs , 1991 .

[16]  Giovanni Ferrara,et al.  Blade cooling improvement for heavy duty gas turbine: the air coolant temperature reduction and the introduction of steam and mixed steam/air cooling , 2000 .

[17]  Xiaojun Shi,et al.  Effect of duct aspect ratio on heat transfer and friction in steam-cooled ducts with 60° angled rib turbulators , 2013 .

[18]  Yousef S.H. Najjar,et al.  Comparative performance of combined gas turbine systems under three different blade cooling schemes , 2004 .

[19]  Weiqi Wang,et al.  Flow and Heat Transfer Characteristics in Rotating Two-pass Channels Cooled by Superheated Steam , 2012 .

[20]  S. J. Kline,et al.  Describing Uncertainties in Single-Sample Experiments , 1953 .

[21]  Xiangyu Wu,et al.  A Simplified Approach to Design Transverse Ribs Which Array Alternately in Rectangular Channel , 2010 .