Numerical studies on heat transfer characteristics of graphite–water microfluid in a coiled agitated vessel

Abstract

Agitation is one of the widely used chemical engineering operations involving both simultaneous heat transfers and reaction. In this study, an effort has been made to simulate experimentally studied heat transfer behavior of microfluid in an agitated vessel. Simulated Nusselt numbers were compared with experimental values and found to be in good agreement with experimental values within ±10% deviation. Simulated temperature contours clearly depicted the temperature of cooling water increases gradually along the length of helical coil from the inlet to outlet. Radial mixing was found to be more in disk turbine agitator than the propeller agitator which lead to higher heat transfer rate in disk turbine agitator confirming the experimental observation. K E Y W O R D S CFD, coiled agitated vessel, graphite microfluids, heat transfer enhancement, impeller, Nusselt number Nomenclature: A o , Outside surface area of helical coil (m 2 ); C p , Specific heat capacity of water at given temperature (J/kg K); D a , Diameter of the agitator (m); D c , Average diameter of the helix tubing (m); d i , Inside diameter of the coiled tube (m); d o , Outside diameter of the coiled tube (m) For inside heat transfer coefficienth i d i /k For outside heat transfer coefficienth o d o /k; h i , Inside heat transfer coefficient (W/m 2 K); h o , Outside heat transfer coefficient (W/m 2 K); k, Thermal conductivity of fluid at given temperature (W/mK); k c , Thermal conductivity of coil material (W/m 2 K); l, Length of the helical coil (m); M, Mass flow rate of water (kg/s); N, Rotating speed of agitator (revolutions/s); Nu, Nusselt number (dimensionless); Pr, Prandtl number (c p /k) (dimensionless); Q, Heat transfer rate (W); Q 1 , Heat supplied to the agitated medium by immersion heaters (W); Q 2 , Heat rate gained by cooling medium (W); Re, Agitator Reynolds number (dimensionless) -ND a 2 / ; Re c , Coolant Reynolds number (dimensionless)vd i / ; T, Temperature (K); T B , Average bath temperature of agitated liquid medium (K); T i , Inlet temperature of cooling water (K); T o , Outside temperature of cooling water (K); T w , Wall temperature of cooling coil (K); x w , Helical coil wall thickness (m)Greek symbol: , Volume fraction of nanoparticles (no unit); ΔT ln , Logarithmic mean temperature difference (K); , Viscosity at given temperature (kg/ms); w , Viscosity at wall temperature (kg/ms); , Density at given temperature (kg/m 3 )

Heat Transfer and Hydrodynamics in Stirred Tanks with Liquid-Solid Flow Studied by CFD–DEM Method

“…Early research works mainly involved the simulation of heat transfers in mixers with different configurations such as the rounded-bottom vessel with an atypical helical ribbon impeller [9] and the stirred tanks with improved Intermig impellers [10]. Other researchers have focused on the heat transfer characteristics of different fluids in stirred tanks and in a jacketed stirred heat exchanger [3,[11][12][13][14][15]. Johnson et al [15] derived a non-adiabatic heat-transfer model for the study of heat transfers in laboratory to pilot-scale reactors, which could be used to predict the temperature distribution within the uncertainty of the experimental measurements.…”