Heat transfer to vessels

The simplest way to transfer heat to a process or storage vessel is to fit an external jacket, or an internal coil. 

The pitch of the coils and the area covered can be selected to provide the heat transfer area required. Standard pipe sizes are used, ranging from 60 to 120 mm outside diameter. The half-pipe construction makes a strong jacket capable of withstanding pressure better than the conventional jacket design. 

Factors to consider when selecting the type of jacket to use are as follows  

Cost In terms of cost, the designs can be ranked, from cheapest to most expensive, as 

Heat transfer rate required Select a spirally baffled or half-pipe jacket if high rates are required. 

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Nagata, S., M. Nishikawa, and T. Kayama (1972). Heat transfer to vessel wall by helical ribbon impeUo- in highly viscous liquids, J. Chem. Eng. Jpn., 5, 83-85. 

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 ... 

The heat transfer to the liquid from an engulfment fire has been estimated at around lOOkW/m, and the above formula equates this to the vapor produced from this input as latent heat. The exponential is an area exposure factor, which recognizes that large vessels are less likely to be completely exposed to flames. 

A flat-bottomed cylindrical vessel, 2 m in diameter, containing boiling water at 373 K, is mounted on a cylindrical section of insulating material, l m deep and 2 m ID at the base of which is a radiant heater, also 2 m in diameter, with a surface temperature of 1500 K. If the vessel base and the heater surfaces may be regarded as black bodies and conduction though the insulation is negligible, what is the rate of radiant heat transfer to the vessel How would this be affected if the insulation were removed so that the system was open to the surroundings at 290 K ... 

A vessel contains 1 tonm (I Mg) of a liquid of specific heat capacity 4.0 kj/kg K. The vessel is heated by steam at 393 K which is fed to a cod immersed in the agitated liquid and heat is lost to the surroundings at 293 K from the outside o." the vessel. How long dots it take to heat the liquid from 293 to 353 K and what is the maximum temperature to which the liquid can be heated When the liquid temperature has reached 353 K, the steam supply is tinned off for 2 hours (7.2 ks and the vessel cools. How long will it take to reheat the material to 353 K The surface area of the coil is 0 5 m2 and the overall coefficient of heat transfer to the liquid may be taken as 600 W/m2 K. The outside area of Lie vessel is 6 m2 and the coefficient of heat transfer to the surroundings may be taken as 10 W/m2 K. 

Values for the various parameters in these equations can be estimated from published correlations. See Suggestions for Further Reading. It turns out, however, that bubbling fluidized beds do not perform particularly well as chemical reactors. At or near incipient fluidization, the reactor approximates piston flow. The small catalyst particles give effectiveness factors near 1, and the pressure drop—equal to the weight of the catalyst—is moderate. However, the catalyst particles are essentially quiescent so that heat transfer to the vessel walls is poor. At higher flow rates, the bubbles promote mixing in the emulsion phase and enhance heat transfer, but at the cost of increased axial dispersion. 

The most damaging BLEVE occurs when a vessel contains a flammable liquid stored at a temperature above its normal boiling point. The vessel walls below the liquid level are maintained at a low temperature due to the rapid heat transfer to the liquid. However, the vessel walls exposed to the fire above the liquid level will heat rapidly due to the much lower heat transfer to the vapor. The vessel wall temperature... 

GLS fluidized with a stable level of catalyst. Only the fluid mixture leaves the vessel. Gas and liquid enter at the bottom. Liquid is continuous, gas is dispersed. Particles are larger than in bubble columns, 0.2-1.0 mm. Bed expansion is small. Bed temperatures are uniform within 2 C in medium size beds, and heat transfer to embedded surfaces is excellent. Catalyst may be bled off and replenished continuously, or reactivated continuously. 

Fireproofing is a fire resistant material or system that is applied to a surface to delay heat transfer to that surface. Fireproofing, a form of passive fire protection, protects against intense and prolonged heat exposure that can cause the weakening of steel and eventual collapse of unprotected equipment, vessels, and supports and lead to the spread of burning liquids and substantial loss of property. The primary purpose is to improve the capability of equipment/struc-... 

A//, the change in enthalpy, equals q, the heat transferred to or from a system at constant pressure A// = q. Since most organic reactions are performed at atmospheric pressure in open vessels. A// is used more often than is A . For reactions involving only liquids or solids A = A//. A// of a chemical reaction is the difference in the enthalpies of the products, Hp, and the reactants, // ... 

If the rate of heat transfer to or from the broth is important, then the heat transfer area per unit volume of broth should be considered. As the surface area and the liquid volume will vary in proportion to the square and cube of the representative length of vessels, respectively, the heat transfer area of jacketed vessels may become insufficient with larger vessels. Thus, the use of internal coils, or perhaps an external heat exchanger, may become necessary with larger fermentors. 

More recently, Sole391 studied the system to determine the extent, if any, of heterogeneous reaction. By means of differential calorimetry, he compared the heat transferred to the vessel walls with that transferred to a probe in the center of the vessel. He found that heterogeneous effects could be completely disregarded. 

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