Nusselt number and friction factor correlations for solar air heater duct with broken V-down ribs combined with staggered rib roughness

Abstract

Experimental investigation of various designs of solar flat plate collectors: Application for the drying of green chili J. Renewable Sustainable Energy 4, 043116 (2012) Effect of solar intensity on efficiency of the convection solar air heater J. Renewable Sustainable Energy 4, 042901 (2012) Heat transfer and friction factor of solar air heater having duct roughened artificially with discrete multiple v-ribs J. Renewable Sustainable Energy 4, 033103 (2012) Spectrally selective ultra-high temperature ceramic absorbers for high-temperature solar plants J. Renewable Sustainable Energy 4, 033104 (2012) Additional information on J. Renewable Sustainable Energy Artificial roughening of a broad wall of solar air heater leads to significant enhancement in heat transfer besides comparable rise in friction losses. This paper presents the outcome of experimental study on heat transfer and fluid friction characteristics of solar air heater duct roughened with broken V-down rib combined with staggered rib piece. Experimental data were collected on a high aspect ratio rectangular duct by varying the Reynolds number from 3000 to 17 000, relative gap position (s 0 /s) 0.2-0.8, relative staggered rib position (p 0 /p) 0.2-0.8, relative staggered rib size (r/e) 1-2.5, for the fixed values of relative roughness pitch (p/e) of 10, relative roughness height (e/D h ) of 0.043, relative gap size (g/e) of 1, and angle of attack (a) of 60 . The effect of flow Reynolds number and roughness parameters on Nusselt number and friction factor has been explored and the results are compared with continuous V-down rib roughened duct and smooth duct under similar flow conditions. Correlations for the Nusselt number and friction factor as a function of Reynolds number and roughness parameters have been developed.

Effect of Alterations in V-down Rib on the Performance of an Artificially Roughened Solar Air Heater Duct

“…6. Better performance of these rib configurations is in agreement with the findings of Singh et al (2011) andPatil et al (2012) as reported in their studies with experimental investigations with similar geometries.…”

“…As shown in the figure, fixing of a small staggered rib piece in front of each gap at a distance of 2/3 rd of the pitch, further improves the rate of heat transfer. The observation is in agreement with the findings of Patil et al (2012), who performed extensive experiments with this type of geometry and stated that, fixation of a staggered rib piece in front of the gap in V-down rib increases the level of turbulence in the span between two adjacent V-ribs and causes enhancement of heat transfer from this region.…”

“…Roughness pattern was created by fixing V shaped circular Aluminum wires with an adhesive to the absorber plate followed by the cutting of gaps and fixing of staggered ribs. Values of P/e, e/D h and (α) were selected based upon their optimization in our previous study (Deo et al (2016)), whereas values of (w/e) and (p/P) were estimated based upon the data available in the literature (Mulluwork, 2000;Patil et al, 2012). …”

“…transverse ribs (Gupta et al (1993)), inclined ribs (Gupta et al (1997)), V-shaped ribs (Momin et al (2002)), staggered discrete V-shaped ribs (Mulluwork (2000)), V-up and V-down discrete ribs (Karwa (2003)), inclined rib with gap (Aharwal et al (2009)), V-rib with gap (Singh et al (2011)) and multi V-rib with gaps (Anil et al (2013)) resulted in enhancement of the performance of solar air heaters. Patil et al (2012) experimented with a variation of the V-rib with one gap geometry by fixing a staggered rib piece in front of each gap and reported improvement in heat transfer and thermohydraulic performance. Deo et al (2016) studied the effect of relative roughness pitch, angle of attack and relative roughness height on the performance of multigap Vdown rib combined with staggered ribs roughness and reported improvement in thermohydraulic performance as compared to the V-down rib with gap (Singh et al (2011)) and broken V-rib roughness combined with staggered ribs (Patil et al (2012)) geometries.…”

“…Patil et al (2012) experimented with a variation of the V-rib with one gap geometry by fixing a staggered rib piece in front of each gap and reported improvement in heat transfer and thermohydraulic performance. Deo et al (2016) studied the effect of relative roughness pitch, angle of attack and relative roughness height on the performance of multigap Vdown rib combined with staggered ribs roughness and reported improvement in thermohydraulic performance as compared to the V-down rib with gap (Singh et al (2011)) and broken V-rib roughness combined with staggered ribs (Patil et al (2012)) geometries.…”