ORIGINAL Augmentation of heat transfer in a bubble agitated vertical rectangular channel Asish Mitra • Tapas Kumar Dutta • Dibyendu Narayan Ghosh Received: 17 May 2010 / Accepted: 5 October 2011 / Published online: 19 October 2011 Ó Springer-Verlag 2011 Abstract This paper presents the results of an experi- mental study of convective heat transfer between three par- allel vertical plates symmetrically spaced with and without bubble agitation to ascertain the degree of augmentation of the heat transfer coefficients due to agitation. The centre plate was electrically heated, while the other side plates were water-cooled forming two successive parallel vertical rect- angular channels of dimensions 20 cm 9 3.5 cm 9 35 cm (length W, gap L, height H) each. At the bottom of the hot and cold plates air spargers were fitted. Water/ethylene glycol (100%) was used to fill the channels. The superficial gas velocity ranged from 0.0016 to 0.01 m/s. Top, bottom and sides of the channels were open to the water/ethylene glycol in the chamber which is the novel aspect of this study. Experimental data have been correlated as under: Natural convective heat transfer: Nu = 0.60 Gr 0.29 , r = 0.96, r = 0.186, 1.17 E6 \ Gr \ 1.48 E7; Bubble agitated heat transfer: St = 0.11(ReFrPr 2 ) -0.23 , r = 0.82, r = 0.002, 1.20 E-2 \ (ReFrPr 2 ) \ 1.36 E2. List of symbols a 1 , a 2 , a 3 , b 1 , b 2 , c 1 , c 2 , d 1 , d 2 , d 3 Experimentally evaluated constants A Aspect ratio (height/gap) of the vertical rectangular channel, H/L A c Cold surface area, m 2 A h Hot surface area, m 2 A cav Cross-sectional area of the channel, W 9 L,m 2 c p Specific heat, J/Kg K D h Hydraulic diameter, 4A cav /C,m Fr Froude number, u G 2 /(gD h ) g Acceleration due to gravity, 9.81 m/s 2 Gr Grashof number, gbDT c L 3 /c 2 , or gbDT h L 3 /c 2 H Height of the channel, m h c Cold surface heat transfer coefficient, W/m 2 K h h Hot surface heat transfer coefficient, W/m 2 K I Electric current to the heater, ampere k Thermal conductivity, W/m K L Gap of the channel, m m c Total coolant mass rate, kg/h Nu Nusselt number, hL/k n Number of data points Pr Prandtl number, c p l/k q c Cold surface heat flow rate, W q h Hot surface heat flow rate, W r Correlation coefficient Ra Rayleigh number (gb/ac)DT c L 3 or (gb/ac)DT h L 3 Re Reynolds number, D h u G q/l St Stanton number, h/u G qc p A. Mitra (&) BSH Department, College of Engineering and Management, Kolaghat, KTPP Township, Kolaghat, West Bengal, India e-mail: mitra_asish@yahoo.com URL: www.cemkolaghat.org T. K. Dutta  D. N. Ghosh Chemical Engineering Department, Jadavpur University, Calcutta, India e-mail: proftapas_dutta@yahoo.com D. N. Ghosh e-mail: dnghosh@yahoo.com 123 Heat Mass Transfer (2012) 48:695–704 DOI 10.1007/s00231-011-0918-1