Heat transfer Agitated vessels

Consider a vessel containing an agitated liquid. Heat transfer occurs mainly through forced convection in the liquid, conduction through the vessel wall, and forced convection in the jacket media. The heat flow may be based on the basic film theory equation and can be expressed by... 

Baker, C. K and G. H. Waller, Application of Dynamic Modeling Technique to the Analysis and Prediction of Heat Transfer with Particular Reference to Agitated Vessels, Heat Trans. Eng.,Y. 2, p. 28, Oct.-Dec. (1979). 

Most of the correlations for heat transfer from the agitated hquid contents of vessels to jacketed walls have been of the form ... 

A wide variety of configurations exists for coils in agitated vessels. Correlations of data for heat transfer to helical coils have been of two forms, of which the following are representative ... 

Topics that acquire special importance on the industrial scale are the quality of mixing in tanks and the residence time distribution in vessels where plug flow may be the goal. The information about agitation in tanks described for gas/liquid and slurry reactions is largely apphcable here. The relation between heat transfer and agitation also is discussed elsewhere in this Handbook. Residence time distribution is covered at length under Reactor Efficiency. A special case is that of laminar and related flow distributions characteristic of non-Newtonian fluids, which often occiu s in polymerization reactors. 

Stirred Vessels Gases may be dispersed in hquids by spargers or nozzles and redispersed by packing or trays. More intensive dispersion and redispersion is obtained by mechanical agitation. At the same time, the agitation will improve heat transfer and will keep catalyst particles in suspension if necessaiy. Power inputs of 0.6 to 2.0 kW/m (3.05 to 10.15 np/1,000 gal) are suitable. 

Slurry Reactors with Mechanical Agitation The catalyst may be retained in the vessel or it may flow out with the fluid and be separated from the fluid downstream. In comparison with trickle beds, high heat transfer is feasible, and the residence time can be made veiy great. Pressure drop is due to sparger friction and hydrostatic head. Filtering cost is a major item. 

A common process task involves heating a slurry by pumping it through a well-stirred tank. It is useful to know the temperature profile of the slurry in the agitated vessel. This information can be used to optimize the heat transfer process by performing simple sensitivity studies with the formulas presented below. Defining the inlet temperature of the slurry as T, and the temperature of the outer surface of the steam coil as U then by a macroscopic mass and energy balance for the system, a simplified calculation method is developed. 

This chapter reviews the various types of impellers, die flow patterns generated by diese agitators, correlation of die dimensionless parameters (i.e., Reynolds number, Froude number, and Power number), scale-up of mixers, heat transfer coefficients of jacketed agitated vessels, and die time required for heating or cooling diese vessels. 

Determine the heat transfer eoeffieient from a eoil immersed in an agitated vessel with a diameter of 10 ft (3.048 m). The agitator is a paddle measuring 3.5 ft (1.01 m) in diameter and revolving at 200 rev/min. The fluid properties are ... 

Heat transfer coefficient to fluids in a vessel using mechanical agitated coils or jacket... 

Heating or cooling of process fluids in a batch-operated vessel is common in the chemical process industries. The process is unsteady state in nature because the heat flow and/or the temperature vary with time at a fixed point. The time required for the heat transfer can be modified, by increasing the agitation of the batch fluid, the rate of circulation of the heat transfer medium in a jacket and/or coil, or the heat transfer area. Bondy and Lippa [45] and Dream [46] have compiled a collection of correlations of heat transfer coefficients in agitated vessels. Batch processes are sometimes disadvantageous because ... 

A vertical cylindrical, and mechanical agitated pressure vessel, equipped with baffles to prevent vortex formation is the most widely used fermenter configuration. The baffles are typically one-tenth of the fermenter diameter in widtli, and are welded to supports tliat extend from the sidewall. A small space between the sidewall and the baffle enables cleaning. Internal heat transfer tube bundles can also be used as baffles. The vessels must withstand a 45 psig internal pressure and full vacuum of -14.7 psig, and comply with the ASME code. 

Empirieal dimensionless group eorrelations have been used in the seale-up proeess. In partieular, the eorrelation for the inside film heat transfer eoeffieient for agitated, jaeketed vessels has been employed for the seale-up to a larger vessel. Reaetion ealorimeters are often used to give some indieation of heat transfer eoeffieients eompared to water in the same unit. Conelation for plant heat transfer is of the general form... 

Figure 5-38. Heat transfer surfaces in agitated teinks may be the actual wall of the vessel or immersed tubes. By permission, Dickey, D. S. and Hicks, R. W., Chem. Engn, Feb. 2,1976, p. 93 [35].

Heat Transfer in Jacketed, Agitated Vessels/Ketdes... 

Figure 10-93B. Process vessel with internal coil and agitation to improve heat transfer. (Used by permission Engineering Manual Dowtherm Heat Transfer Fluids, 1971. The Dow Chemical Co.)...

Heat transfer in agitated vessels with internal coils containing the heat transfer fluid (process on outside of coil) is expressed by the outside coefficient on coils ... 

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