Tube-side calculations

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

Tube-Side Calculations. The tube-side velocity is given by G 1 G 4 IVpT... 

Reactant on the Tube Side Tube-Side Calculations... 

Tube-side water velocities should be kept within reasonable limits, even though calculations would indicate that improved tube-side film coefficients can be obtained if the water velocity is increased. Table 10-24 suggests guidelines that recognize the possible effects of erosion and corrosion on the system. 

Calculate the tube-side flow rate based upon the assumed number of tubes per pass and the heat balance. 

Calculate the tube-side pressure drop. (Use Figure 10-139 for the end return losses. For water in tubes, use Figure 10-138 for tube losses. For other liquids and gases in tubes, use Figure 10-137. 

Calculate the tube-side film coefficient, hj, and reference it to the outside of the tube, hj. Calculate the condensing film coefficient ... 

Tube side Determine heat transfer coefficient from Figure 10-46 (using tube-side curve) at Reynold s number calculated for pressure drop evaluation. If the hj calculated exceeds 300 for organics (Figure 10-103), use a value of 300 and correct to outside coefficient, hj. ... 

Calculate the tube-side film coefficient for finned tube, hj. If water, use Figure 10-50A or 10-50B if other fluid, use Equation 10-44 or 10-47. Use an assumed or process determined tube-side velocity or other film fixing characteristic. 

Assume tube-side passes and calculate hj, hj in the usual manner. 

Calculate tube-side pressure drop in usual manner, including loss in headers. 

In operation the tube sheets are subjected to the differential pressure between shell and tube sides. The design of tube sheets as pressure-vessel components is covered by BS 5500 and is discussed in Chapter 13. Design formulae for calculating tube sheet thicknesses are also given in the TEMA standards. 

Given the uncertainties associated with the calculations, especially those on the shell-side, a sensible design basis for the heat transfer area specification would be the shell-side flow characterized by the clean condition. Of course, the fouling coefficients for the shell-side and tube-side should be included to account for the surface fouling resistance. 

While it is possible to calculate the existing overall heat transfer coefficient from the operating data, it is not possible to calculate the individual film transfer coefficients. The individual film transfer coefficients can be combined in any number of ways to add up to an overall value of 285 W-m 2-K 1. However, the film transfer coefficients can be estimated from the correlations in Appendix C. Given that the tube-side correlations are much more reliable than the shell-side correlations, the best way to determine the individual coefficients is to calculate the coefficient for the tube-side and allocate the shell-side coefficient to add up to U = 285 W-m 2-K 1. Thus, to calculate the tube-side film transfer coefficient, KhT must first be determined. 

Rather than specify the tube-side velocity, the tube-side pressure drop could have been specified (e.g. A Pt = 30,000 N-nf 2). Had this been the case, then the calculation would have required Equation 15.16 to be solved simultaneously with the above equations by varying A and hr simultaneously, similar to the solution of Example 15.1c. 

The tube-side heat transfer coefficient can be calculated from3 ... 

Suppose the overall heat transfer coefficient of a shell-and-tube heat exchanger is calculated daily as a function of the flow rates in both the shell and tube sides (ws and wt, respectively). U has the units of Btu/(h)(°F)(ft2), and ws and wt are in lb/h. Figures E2.3a and E2.3b illustrate the measured data. Determine the form of a semiempirical model of U versus ws and wt based on physical analysis. 

Porous alumina tube externally coated with a MgO/PbO dense film (in double pipe configuration), tube thickness 2.5 mm, outer diameter 4 mm, mean pore diameter 50 nm, active film-coated length 30 mm. Feed enters the reactor at shell side, oxygen at tube side. Oxidative methane coupling, PbO/MgO catalyst in thin film form (see previous column). r-750X,Pr ed 1 bar. Conversion of methane <2%. Selectivity to Cj products > 97%. Omata et al. (1989). The methane conversion is not given. Reported results are calculated from permeability data. 

The requirement to leave one end of the tubes free to float creates a rather unpleasant process problem. The most efficient way to transfer heat between two fluids is to have true countercurrent flow. For a shell-and-tube exchanger, this means that the shell-side fluid and the tube-side fluid must flow through the exchanger in opposite directions. When calculating the log-mean temperature driving force (LMTD), an engineer assumes true countercurrent flow between the hot fluid and the cold fluid. 

But suppose we are operating a heat exchanger subject to rapid rates of initial fouling. The start-of-run heat-transfer coefficient U is 120 Btu/[(h)(ft2(°F)]. Four months later, the U value has lined out at 38. The calculated clean tube-side velocity is lV2 ft/s. This is too low, but what can be done ... 

Calculation of tube-side pressure drop is straightforward, even of vapor-liquid mixtures when their proportions can be estimated. Example 8.7 employs the methods of Chapter 6 for pressure drop in a thermosiphon reboiler. 

Find the needed tube surface area from the heat absorbed and the radiant flux. When a process-side calculation has been made, the required number of tubes will be known and will not be recalculated as stated here... 

The tube-side heat-transfer coefficient may be calculated in two ways. The first uses the Dittus-Boelter equation for heat-transfer in a turbulent environment. This equation is given below. 

The tube-side presure drop is calculated using the equation in Ref. E2 (p. 542). 

Some difference is noticed if you calculate the shell-side Q. This difference is mainly due to variations in the accuracies of the specific heat values obtained. For our purpose and for accuracy within 3%, however, the calculated tube-side heat is sufficient. 

Choose the number of passes NP next and calculate the tube-side mass flow rate GT in lb/(s ft2) ... 

Step 14. Calculate the tube-side pressure drop in this step, applying the Fflw program discussed in Chap. 6, where this step will be reviewed and worked. 

AirCIri). This is an executable program for any air-cooler condenser. The inputted Q will be the heat duty transferred. Data inputs for condenser tube-side transport property values of viscosity, thermal conductivity, and specific heat should be determined as for two-phase flow values calculated in Chap. 6. Use the average tube-side temperature for these condensing film transport property values. Weighted average values between gas and liquid should also be determined and applied like that used in the two-phase flow equations in Chap. 6. 

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