ORIGINAL Natural convective heat transfer in water enclosed between pairs of differentially heated vertical plates Asish Mitra Æ Tapas Kumar Dutta Æ Dibyendu Narayan Ghosh Received: 9 October 2007 / Accepted: 25 June 2008 / Published online: 22 July 2008 Ó Springer-Verlag 2008 Abstract This paper presents the results of an experi- mental study of buoyancy-driven convective heat transfer between three parallel vertical plates, symmetrically spaced with water as the intervening medium. The centre plate was electrically heated, while the other side plates were water-cooled forming two successive parallel ver- tical channels of dimensions 20 cm 9 3.5 cm 9 35 cm (length W, gap L, height H) each. Top, bottom and sides of the channels were open to water in the chamber which is the novel aspect of this study. Plate surface tempera- ture and bath temperature at different levels of height from the bottom of channel were measured by K-type thermocouples. Experimental data have been correlated as under: Nu ¼ 0:62 Gr 0:29 ; 1:17 E6  Gr  1:48 E7; 2:9  Pr  4:7; A ¼ 10:3 Nu ¼ 0:14 Ra 0:35 ; 5:25 E6  Ra  4:36 E7, 2:9  Pr  4:7; A ¼ 10:3: List of symbols a, b, c, d experimentally evaluated constants, dimensionless A aspect ratio (height/gap) of the vertical rectangular channel, H/L, dimensionless A c cooler surface area (m 2 ) A h hot surface area (m 2 ) c p specific heat (J/Kg K) 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 , dimensionless 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 (A) 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, dimensionless Pr Prandtl number, c p l/k, dimensionless q c cold surface heat flow rate (W) q h hot surface heat flow rate (W) r correlation coefficient, dimensionless Ra Rayleigh number, (gb/ac)DT c L 3 or (gb/ac)DT h L 3 , dimensionless T c,m channel fluid arithmetic mean temperature cold plate/coil side, 1/2(T c,av + T cav,av )(°C) T h,m channel fluid arithmetic mean temperature hot plate side, 1/2(T h,av + T cav,av )(°C) T h,av hot surface average temperature (°C) T c,av cold surface average temperature (°C) T cav,av average temperature of the channel liquid (°C) t in cooling water inlet temperature (°C) t out cooling water outlet temperature (°C) A. Mitra (&) BSH Department, College of Engineering and Management, Kolaghat, KTPP Township, East Midnapur, West Bengal 721171, India e-mail: mitra_asish@yahoo.com T. K. Dutta  D. N. Ghosh Chemical Engineering Department, Jadavpur University, Calcutta 700032, India e-mail: proftapas_dutta@yahoo.com D. N. Ghosh Flat 3A, Dover Place, Calcutta 700019, India e-mail: drdn_ghosh@yahoo.com 123 Heat Mass Transfer (2008) 45:187–192 DOI 10.1007/s00231-008-0419-z