Improving heat transfer in stirred tanks cooled by helical coils

Pedrosa, S.M.C.P.; Nunhez, José Roberto

doi:10.1590/s0104-66322003000200004

Cited by 10 publications

(3 citation statements)

References 4 publications

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“…This approach overcomes the assumption of perfect mixing, which is a major flaw of lumped‐parameter models. In previous CFD based modelling studies of heat transfer, for example, in baffled STRs and unbaffled STRs, the simulation of temperature distributions in the vessel was carried out using a prescribed uniform thermal boundary condition at the inner surface of the vessel wall such as the wall temperature and heat transfer coefficient. Yapici and Basturk carried out semi‐conjugate (coupled process and wall) heat transfer simulations in an unbaffled hemispherical agitated vessel, not representative of industrial STRs, using the temperature and heat transfer coefficient as boundary conditions at the outer surface of the vessel wall.…”

Section: Introductionmentioning

confidence: 99%

CFD modelling of conjugate heat transfer in a pilot‐scale unbaffled stirred tank reactor with a plain jacket

2018

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Semi‐conjugate and fully‐conjugate computational fluid dynamic investigations of the flow and heat transfer in a 25 L pilot‐scale unbaffled stirred tank reactor with a plain jacket are reported. A hot heat transfer fluid (DW‐Therm) flows through the plain jacket and heats water in the vessel, which is agitated by a pitched three‐blade impeller. The shape of the free‐surface of the vortex formed in the unbaffled vessel is captured by the use of a homogeneous multiphase and free‐surface flow model. The simulations of flow and heat transfer are carried out using the ANSYS CFX (V.15) code. The semi‐conjugate simulation considers the vessel wall and the vessel contents, and the fully‐conjugate simulation also includes the flow in the jacket. The upward flow in the jacket is uneven and this dominates the distributions of heat transfer coefficients and shear stresses on the inner and outer surfaces of the vessel wall. The downward motion created by the impeller generates very high heat transfer on the base surface of the vessel, but this is nullified by a stagnation zone in the base region of the jacket. Overall heat transfer coefficients evaluated from average film heat transfer coefficients values from the simulations are around 15 % higher than those evaluated from correlations in the literature. In this pilot plant facility, the combined thermal resistances for the convection in the jacket and across the glass wall dominate the overall heat transfer coefficient.

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Section: Introductionmentioning

confidence: 99%

CFD modelling of conjugate heat transfer in a pilot‐scale unbaffled stirred tank reactor with a plain jacket

2018

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“…One can design the new equipment and also carry out the trouble shooting of any chemical process using CFD. There were several studies reported on CFD modeling agitated vessel to find out flow modeling and mixing performance. Several studies also reported on modeling of heat transfer studies using nanofluids in agitated vessel .…”

Section: Introductionmentioning

confidence: 99%

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

Sivashanmugam

2018

Heat Trans. Asian Res.

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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 )

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“…Their study also includes the effects of the types of the agitators and their configuration on heat transfer process. Pedrosa and Nunhez (2003) showed that the design of vessels cooled by helical coils can be further improved by introducing some minor modifications in the coil arrangements. Triveni et al (2008) studied heat transfer of few industrially important systems namely castor oil and its methyl esters, soap solution, CMC and chalk slurries in a stirred vessel fitted with anchor/turbine impeller and a coil for heating or cooling.…”

Section: Introductionmentioning

confidence: 99%

Heat Transfer Studies in Coiled Agitated Vessel with Varying Heat Input

Perarasu¹,

Arivazhagan²,

Sivashanmugam³

2011

International Journal of Food Engineering

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Recommended Citation: Perarasu, V T; Arivazhagan, M; and Sivashanmugam, P (2011) "Heat Transfer Studies in Coiled AbstractHeat transfer studies in a coiled agitated vessel with varying heat input is presented using two agitators namely propeller and disk turbine. Heat transfer rate increases with agitator speed for both the agitators for a given heat input. The heat transfer coefficient also increases with heat input for a given agitator speed for turbine agitator for all the heat inputs, whereas for propeller it is increasing up to a certain value and then decreases. The heat transfer coefficient (heat transfer rate) for turbine agitator is higher than that for propeller for all heat inputs. Empirical correlations separately were formed for each agitator and found to fit the experimental values within range of ±15% for both the agitators.

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Improving heat transfer in stirred tanks cooled by helical coils

Cited by 10 publications

References 4 publications

CFD modelling of conjugate heat transfer in a pilot‐scale unbaffled stirred tank reactor with a plain jacket

CFD modelling of conjugate heat transfer in a pilot‐scale unbaffled stirred tank reactor with a plain jacket

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

Heat Transfer Studies in Coiled Agitated Vessel with Varying Heat Input

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