Correction factors for heat

FIG. 11-4 (Continued) LMTD correction factors for heat exchangers. In all charts, fi = (Ti — T<>y(U — t ) and S = (to — ti)/(Ti — ti). ( ) Cross-flow (drip type), two horizontal passes with U-hend connections (trombone type). (/) Cross-flow (drip type), helical coils with two turns. 

Bypassing will affect the pressure drop only in the cross-flow zones. The correction factor is calculated from the equation used to calculate the bypass correction factor for heat transfer, equation 12.30, but with the following values for the constant a. 

FIG. 11-4 Continued) LMTD correction factors for heat exchangers. In all charts, R = (Ti — — and S = — — i) Cross-flow (drip type), two hor-... 

Table 1. Calibration matrix for the correction factors for heating rate,...

Mechanical equivalent of heat Correction factors for baffle by )assing, baffle configuration, baffle 1.0(N-m)/J 778(ft-lkf)/Btii... 

The price of air-cooled exchangers should be obtained from vendors if possible. If not, then by coirelating in-house historical data on a basis of /ft of bare surface vs. total bare surface. Correction factors for materials of construction. pressure, numbers of tube rows, and tube length must be used. Literature data on air coolers is available (Reference 15). but it should be the last resort. In any event, at least one air-cooled heat exchanger in each project should be priced by a vendor to calibrate the historical data to reflect the supply and demand situation at the expected time of procurement. 

Heated Length Correction Factors, Streamline Flow Tube Size Correction Factors for Streamline Flow ... 

The equations for estimating nucleate boiling coefficients given in Section 12.11.1 can be used for close boiling mixtures, say less than 5°C, but will overestimate the coefficient if used for mixtures with a wide boiling range. Palen and Small (1964) give an empirical correction factor for mixtures which can be used to estimate the heat-transfer coefficient in the absence of experimental data ... 

Figure 12.62. Log mean temperature correction factor for plate heat exchangers (adapted from Raju and Chand (1980))...

The relative bond enthalpies from the photoacoustic calorimetry studies can be placed on an absolute scale by assuming that the value for D//(Et3Si—H) is similar to D/f(Me3Si—H). In Table 2.2 we have converted the D/frei values to absolute T>H values (third column). On the basis of thermodynamic data, an approximate value of D//(Me3SiSiMc2—H) = 378 kJ/mol can be calculated that it is identical to that in Table 2.2 [1]. A recent advancement of photoacoustic calorimetry provides the solvent correction factor for a particular solvent and allows the revision of bond dissociation enthalpies and conversion to an absolute scale, by taking into consideration reaction volume effects and heat of solvation [8]. In the last colunm of Table 2.2 these values are reported and it is gratifying to see the similarities of the two sets of data. 

Exclusively for shell and tube heat exchangers, the Purohit Method has been used (Purohit, 1983). This method takes into account a large number of technical characteristics according to TEMA standard and allows the use of correction factors for different materials. Material factors compared with carbon steel have been updated in 2008 (Gilardi, 2008). 

Fc = friction due to sudden contraction, ft 1 lbf/lbm Fe = friction due to sudden enlargement, ft lbf/lbm Fe = correction factor for radiant heat transfer based on emissivities and absorptivities of surfaces, dimensionless defined by Eqs. (6) and (7)... 

Use the correction factor for a 1-1 cross flow. The mean temperature difference for a 1 -1 cross-flow heat exchanger can be calculated by using the correction factor determined from Fig. 7.12. The mean temperature difference will be the product of this factor and the log mean temperature difference for countercurrent flow. To obtain the correction factor F, calculate the value of two parameters P and R ... 

Related Calculations. Mean temperature differences for multipass heat exchangers may also be calculated by using appropriate correction factors for the log mean temperature difference for countercurrent flow... 

For shell-and-tube heat exchangers with cross-flow baffles, the preceding methods assume that an adequate number of baffles has been provided. If the shell-side fluid makes less than eight passes across the tube bundle, the mean temperature difference may need to be corrected for this cross-flow condition. Appropriate curves are presented in Caglayan and Buthod [20]. The curves in this reference may also be used to determine correction factors for cross-flow exchangers with one shell pass and more than two tube passes. 

Table 2.11 Cost Correction Factors for Shell-and-Tube Heat Exchangers —Design, Materials, and Pressure (Source Reference 13.)... 

The correction factor for a one-shell-pass and a two-tube-pass heat exchanger (a 1-2 heat exchanger), which is derived by Kern [1], is... 

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