Annulus heat transfer

J Ordinate, Colburn j factor, equals f/2 for heat transfer for inner wall of annulus /h2 for outer wall of annulus jy for heat transfer for ideal tube bank Dimensionless Dimensionless... 

Example 2 Calculation of j Factors in an Annulus Calculate the heat-transfer / factors for both walls of an annulus for the following condi-... 

Double-Pipe Scrapea-Surface Crystallizer This type of equipment consists of a double-pipe heat exchanger with an internal agitator fitted with spring-loaded scrapers that wipe the wall of the inner pipe. The cooling hquid passes between the pipes, this annulus being dimensioned to permit reasonable shell-side velocities. The scrapers prevent the buildup of solids and maintain a good film coefficient of heat transfer. The equipment can be operated in a continuous or in a recirculating batch manner. 

This unit consists of two pipes or tubes, the smaller centered inside the larger as shown in Figure 10-92. One fluid flows in the annulus between the tubes the other flows inside the smaller tube. The heat transfer surface is considered as the outside surface of the inner pipe. The fluid film coefficient for the fluid inside the inner tube is determined the same as for any straight tube using Figures 10-46-10-52 or by the applicable relations correcting to the O.D. of the inner tube. For the fluid in the annulus, the same relations apply (Equation 10-47), except that the diameter, D, must be the equivalent diameter, D,.. The value of h obtained is applicable directly to the point desired — that is, the outer surface of the inner tube. ... 

Dz = Inside Diameter of the Outer Tube (A). Annulus Area for Flow is Between Tubes (A) and Heat Transfer Coefficients used are hj at Inside Surface of Tube (B) ho at Outside Surface of Tube (B)... 

The outer and inner tubes extend from separate stationary tube sheets. The process fluid is heated or cooled by heat transfer to/from the outer tube s outside surface. The overall heat transfer coefficient for the O.D. of the inner tube is found in the same manner as for the double-pipe exchanger. The equivalent diameter of the annulus uses the perimeter of the O.D. of the inner tube and the I.D. of the inner tube. Kem presents calculation details. 

The heat transfer from annulus space through insulation to air ... 

Op = heat transfer from annulus space to pipe, Btu/hr/ft pipe... 

Obtain, by dimensional analysis, a functional relationship for the heat transfer coeflicien for forced convection at the inner wall of an annulus through which a cooling liquid is flowing. 

Internal-loop airlift reactors (ALRs) are widely used for their self-induced circulation, improved mixing, and excellent heat transfer [1], This work reports on the design of an ALR with a novel gas-liquid separator and novel gas distributor. In this ALR, the gas was sparged into the annulus. The special designed gas-liquid separator, at the head of the reactor, can almost completely separate the gas and liquid even at high gas velocities. 

The correlation for forced convective heat transfer in conduits (equation 12.10) can be used to predict the heat transfer coefficient in the annulus, using the appropriate equivalent diameter ... 

The mean temperature difference should be less than 35 to 55°C. This will avoid excessive fouling and excessive vaporization per pass (i.e. low recirculation ratio), leading to poor heat transfer in the upper parts of the tubes as heat transfer to a liquid annulus is replaced by heat transfer to a mist. 

Bennett, A. W., J. G. Collier, and P. M. C. Lacey, 1963, Heat Transfer to Mixtures of High Pressure Steam and Water in an Annulus, Part 111. The Effect of System Pressure on the Burnout Heat Flux for an Internally Heated Unit, UK Rep. AERE-R-3934, Harwell, England. (5)... 

Collier, J. G., and D. J. Pulling, 1962, Heat Transfer to Two-Phase Gas-Liquid System, Part II, Further Data on Steam-Water Mixtures in the Liquid Dispersed Region in an Annulus, UK Rep. AERE-R-3809, Harwell, England. (4)... 

Schraub, F. A., R. L. Simpson, and E. Janssen, 1969, Two-Phase Flow and Heat Transfer in Multirod Geometries Air-Water Flow Structure Data for a Round Tube, Concentric Eccentric Annulus, and Nine-Rod Bundle, GEAP-5739, General Electric Co., San Jose, CA. (5)... 

The heat transfer behavior in a spouted bed (see 9.8) is different from that in dense-phase and circulating fluidized bed systems as a result of the inherent differences in their flow structures. The spouted bed is represented by a flow structure that can be characterized by two regions the annulus and the central spouting region (see Chapter 9). The heat transfers in these two regions are usually modeled separately. For the central spouting region, the correlation of Rowe and Claxton (1965) can be used for Repf > 1,000... 

Compared to the fluidized bed, a spouted bed with immersed heat exchangers is less frequently encountered. Thus, the bed-to-surface heat transfer in a spouted bed mainly is related to bed-to-wall heat transfer. The bed-to-immersed-object heat transfer coefficient reaches a maximum at the spout-annulus interface and increases with the particle diameter [Epstein and Grace, 1997]. 

Since the solid particles in the spouted bed are well mixed, their average temperature in different parts of the annulus can be considered to be the same, just as in the case of a fluidized bed. The maximum value of the heat transfer coefficient in the h-U plot is also similar to that in a dense-phase fluidized bed [Mathur and Epstein, 1974]. 

The scraped surface, or close-clearance exchanger, illustrated in Fig. 10 is required for a few very difficult situations. An example is purification by fractional crystallization, in which a refrigerant boiling in the annulus cools a solution of various substances and certain species selectively crystallize out on the surface of the inner pipe. The crystalline deposit must be continuously scraped off of the surface in order that the heat transfer rate be maintained. The crystals are eventually removed from the remaining liquid by filtration. 

Taking the heat transfer coefficient, h, as a function of the fluid velocity, density, viscosity, specific heat and thermal conductivity, u, p, p, Cp and k, respectively, and of the inside and outside diameters of the annulus, di and do respectively, then ... 

Maitra, D. and Sabba Raju, K., Combined Free and Forced Convection Laminar Heat Transfer in a Vertical Annulus". J. Heat Transfer Vol. 97. pp. 135-137. 1975. 

Aung, W., Moghadam, H.E., and Tsou, F.K., Simultaneous Hydrodynamic and Thermal Development in Mixed Convection in a Vertical Annulus with Ruid Property Variations , J. Heat Transfer, Vol. 113, pp. 926-931, 1991. 

Nieckele, A.O. and Patankar, S.V., Laminar Mixed Convection in a Concentric Annulus with Horizontal Axis , J. Heat Transfer, Vol. 107, pp. 902-909, 1985. 

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