Shell-side calculations

This looks satisfactory, but check the pressure drop before doing the shell-side calculation. jf = 5.5 x 10 3... 

Shell-Side Calculations. In the shell, kerosene flows between the baffles over the tubes. The area for cross-flow between the tubes is given by the length of tube between baffles, Z.T/(/VB + 1), multiplied by the shell internal diameter, DiS, adjusted by the fractional available area for flow between the tubes, (Ft — DoT)/PT. Thus, the shell-side cross-flow area is... 

A shell-and-tube heat exchanger with one shell pass and two tube passes is used to heat 5.0 kg/s of water from 30°C to 80°C. The water flows in the tubes. Condensing steam at 1 atm is used in the shell side. Calculate the area of the heat exchanger, if the overall heat-transfer coefficient is 900 W/m2 - °C. Suppose this same exchanger is used with entering water at 30°C, U = 900, but with a water flow rate of 1.3 kg/s. What would be the exit water temperature under these conditions ... 

Shell-Side Heat-Transfer Coefficient Calculation... 

Calculate the shell-side heat-tran.sfer coefficient for an ideal tube bank hi. 

Calculate the pre.s.sure drop acro.ss the. shell side (excluding nozzles). Units for pressure drop are Ibf/ft. ... 

Calculate the average shell-side concentration according to Eq. (11.6) ... 

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 simplest type of shell-and-tube heat exchanger is shown in Eigure 3-1. The essential parts are a shell (1), equipped with two nozzles and having tube sheets (2) at both ends, which also serve as flanges for the attachment of the two channels or beads ( 3) and their respective channel covers (4). The tubes are expanded into both tube sheets and are equipped w nil transverse baffles (5) on the shell side for support. The calculation of the effective heat transfer surface is based on the distance between the inside faces of the tube sheets instead of the overall tube length. 

An alternate and possibly less accurate calculation (but not requiring the calculation of caloric temperature) using reasonably assumed or calculated film coefiicients and bulk rather than caloric temperature is For hot fluid on shell side ... 

Equivalent tube diameter for shell-side heat transfer calculations is used by permission from Kem and Kraus. ... 

Calculate the shell-side pressure drop. (Refer to the later section on Pressure Drop Relations and Figure 10-140. If AP is too high, reassume unit (step 3). 

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. 

Shell-side fluid properties. From previous process calculations, the following properties were determined for the dry gas stream ... 

If the tube bundle is to be large in diameter, it is possible that the liquid head will suppress the boiling in the lower portion of the horizontal bundle thereby actually creating a liquid heating in this region, with boiling above this. Under such situations, the boiling in the unit cannot be considered for the full volume hence, there should be two shell-side coefficients calculated and the resultant areas added for the total. 

Now, the hb coefficient can be used with the overall U equation, including shell-side fouling, to calculate a final overall coefficient for boiling. 

The friction factor, f, is determined using Figure 10-140 for shell-side pressure drop with D, used in determining R,. For bundles with hare tubes (plain tubes), f, = f/1.2 (see Figure 10-140), calculate pressure drop ... 

This equation gives values that are half of those calculated as total gas flow for the shell side by using friction factors from Figure 10-140. (Note that f for plain or bare tubes = f/1.2 (with f from Figure 10-140)). 

Assume fouling resistances for shell side and tube side. Calculate the overall resistance, less shell-side film resistance ... 

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 10-154. Finned transfer efficiency is never as great per unit area as the bare pipe therefore, fin efficiency must be calculated to arrive at correct h , shell-side heat transfer coefficient. (Used by permission Technical paper. Brown Fintube Co., A Koch Engineering Company, Houston, Texas.)...

B = overall resistance to heat transfer less shell-side resistance (for finned tube calculations), 1/Btu (hr) (ft ) (°F). 

Heat load on the shell side of the exchanger can also be calculated by ... 

Wills, M.J.N. and JOHNSTON, D. 22nd Nat. Heat Transfer Conf, HTD., 36. (ASME, New York, 1984) A new and accurate hand calculation method for shell side pressure drop and flow distribution. 

The Engineering Sciences Data Unit has also published a method for estimating shell-side the pressure drop and heat transfer coefficient, EDSU Design Guide 83038 (1984). The method is based on a simplification of Tinker s work. It can be used for hand calculations, but as iterative procedures are involved it is best programmed for use with personal computers. 

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