Shell Film Coefficient

Equation 44 is used to find the shell film coefficient for oil, /i, Btu/hr./sq. ft. °F, where  

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In large computers, where memory space is not a problem, it is possible to choose a pitch and cut combination which gives the highest heat transfer. To arrive at the optimum heat transfer coefficient, use is made of the fact that the shell film coefficient is directly proportional to the product of Gx and Gj. There is one combination of pitch... 

Figure 2-56 is the block diagram for the subroutine of the shell film coefficient. Equation 43 is used to determine the geometric mean velocity, Gm, Ib./sq. ft. sec. where G and Gi are found by equations 33 and 34. 

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. 

Typical film coefficients can be used to build rough overall heat transfer coefficients. This should suffice in most cases to establish that the design is within ballpark accuracy. Later, for final design, certain critical services will be checked in detail. Typical film resistances for shell and tube heat exchangers and overall heat transfer coefficients for air cooled heat exchangers are shown in Chapter 2, Heat Exchangers. 

Outside Film Coefficient (Shell-and-Tube Exchangers)... 

For sheU-aiKl-l-ube heat exchangers with shell-side balile. die shell-side fluid flow is perpendicular to the tubes. In this arrangement, the outside film coefficient can be calculated from the following equation ... 

The required heat duty, film coefficients, conductivity, etc. for a shell-and lube licat exchanger can be calculated using the procedures in Chapter 2 Approximate U-values are given in Table 2-8. 

The heat transfer area, A ft, in an exchanger is usually estahlished as the outside surface of all the plain or hare tubes or the total finned surface on the outside of all the finned tubes in the tube bundle. As will be illustrated later, factors that inherendy are a part of the inside of the tube (such as the inside scale, transfer film coefficient, etc.) are often corrected for convenience to equivalent outside conditions to be consistent. When not stated, transfer area in conventional shell and tube heat exchangers is considered as outside tube area. 

For example, a hot flue gas flows outside a tube and shell exchanger at 900°F (C) while a hot liquid is flowing into the tubes at 325°F (k). The film coefficients have been estimated to be hj = 225°F and h = 16 Btu/(hr) (fti) (°F). Estimate the tube wall temperature using hj as hj corrected to the outside surface for the inside coefficient ... 

Figure 10-45. Chart for determining U-clean from tube-side and shell-side fluid film coefficients no fouling included. Note s = shell side, t = tube-side. (Used by permission (q...

Figure 10-45 can be used to solve the overall coefficient, U, equation for the clean coefficient, composed of the tube-side and shell-side film coefficients only. Correction for tube-side and shell-side scaling and tube-wall resistance can... 

Film coefficients for turbulent flow that exist on the outside or shell side of the conventional baffled shell and tube exchanger are correlated for hydrocarbons, organic compounds, water, aqueous solutions, and gases by... 

Shell-side film coefficients can be conveniendy obtained from the charts of Chen, Figures 10-60, 10-61, and 10-62. These are based on Donohue s equation... 

Figure 10-62. Shell-side film coefficient. (Used with permission Ning Hsing Chen, Chemical Engineering, V. 65, Oct. 1958. McGraw-Hill, Inc. All rights reserved.)...

Determine the shell-side film coefficient for an assumed bafHe spacing. 

Shell-side film coefficient based on 2-in. baffle spacing. 

Calculate the shell-side dry-gas film coefficient, hg or h, for outside tube conditions. Assume a baffle spacing or about equal to one shell diameter. Use the shell-side method described in Equation 10-48 and Figure 10-54. This is necessary for inlet conditions and then must be checked and recalculated if sufficient change occurs in the mass flow rate, G, to yield a change in hg. 

A, Film coefficient outside bundle, Btu/ft -hr-°F 0 Inside diameter of shell,in. 

From Figure 10-150, read an expected film coefficient, hb, at the value of Atj,. The shell-side boiling temperature should be within 15-20°F of the values given on the graph in order to be reasonably close. Calculate 1 /hb from the chart. 

Figure 10-153A. For determination of h , shell-side (finned side) film coefficient h K for longitudinal fins, flow laminar. h must be...

Figure 10-153B. Shell-side film coefficient for longitudinal fins, transition flow. See Figure 10-153A for applicable details. (Used by permission Brown Fintube Company, A Koch Engineering Company, Houston, Texas.)...

Duplex tubes 1-in. O.D. X 16 ft, 0 in. long, 16 BWG steel outside, 16 BWG cupro-nickel inside No. = 578,1 V4 -in. triangular pitch Shell 36-in. O.D., 4 tube pass Film coefficients ... 

TWo tubular heat exchangers are available each with a 0.44 m i.d. shell fitted with 166 tubes, 19.0 mm o.d. and 15.0 mm i.d., each 5.0 m long. The tubes are arranged in two passes on 25 mm square pitch with a baffle spacing of 150 mm. There are two passes on the shell side and operation is to be countercurrent. With benzene passing through the tubes, the anticipated film coefficient on the tube side is 1000 W/m2K. 

Figure 12.1, which is adapted from a similar nomograph given by Frank (1974), can be used to estimate the overall coefficient for tubular exchangers (shell and tube). The film coefficients given in Figure 12.1 include an allowance for fouling. 

Shell-side film coefficient. The heat transfer through the resistance created by the fluid on the outside (shell-side) of the tubes is given by ... 

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