Heat transfer coefficient, correlations

Published correlations for the process-side heat transfer coefficient are all of the form 

For heat transfer to or from the vessel wall or bottom head in a jacketed vessel 

The characteristic length of Wpc/4 is recommended for a plate coil because Petree and Small (1978) used the width of the plate coil divided by the number of utility fluid passes within the utility side of the plate coil as the characteristic length in the Nusselt number. It is unlikely that the number of passes on the utility side have any significant effect on the heat transfer coefficient. Thus, the only reason to use Wpc/4 as the characteristic length in the Nusselt number is that Petree and Small (1978) used a plate coil with fom passes in their experimental apparatus. 

Geometrical Corrections (i.e., Gc). In some cases the exact forms of the geometric corrections have been changed from the original references, and in several 

Impeller Surface Re Range K a B c Geometry Correction Reference 

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The differential equation describing the temperature distribution as a function of time and space is subject to several constraints that control the final temperature function. Heat loss from the exterior of the barrel was by natural convection, so a heat transfer coefficient correlation (2) was used for convection from horizontal cylinders. The ends of the cylinder were assumed to be insulated. The equations describing these conditions are ... 

A second generalized form for the heat-transfer coefficient correlations is... 

Note the similarity between Equations (c) and (a), where x = ht and y = U. From a standard heat transfer coefficient correlation (Gebhart, 1971), you can find that ht also varies according to Ktwt°, where Kt is a coefficient that depends on the fluid physical properties and the exchanger geometry. If we lump 1 /hs and 1 /hf together into one constant l/hsf, the semiempirical model becomes... 

TABLE 8.10. Recommended Individual Heat Transfer Coefficient Correlations ... 

Individual heat transfer coefficient correlations are summarized in Table 10.2. Penney (1983) has given the recommended geometry for anchors and helical ribbons ... 

TABLE 10.2. Summary of Heat Transfer Coefficient Correlations for Agitated Vessels... 

Heat-transfer-coefficient correlations are usually presented in terms of dimensionless numbers, which are groups of variables that have no net dimensions when evaluated in any consistent system of units. The most important dimensionless numbers for heat transfer are defined next. 

Chun and Kim [24] recommend the following semiempirical average heat transfer coefficient correlation that is valid over a wide range of film Reynolds numbers. For 10 < Re, < 3.1 x 104,... 

C. Zhang and Y. Zhang, Sensitivity Analysis of Heat Transfer Coefficient Correlations on the Predictions of Steam Surface Condensers, Heat Transfer Eng., 15, pp. 54-63,1994. 

Ansioer by Author A problem on which a considerable amount of work remains to be done is that of establishing a satisfactory heat transfer coefficient correlation between heated surfaces such as are obtained in a rocket nozzle and a cryogenic fluid such as hydrogen. Another problem is that of describing correctly two-phase flow of hydrogen in channels of variable geometry under conditions of high pressure and heat input. 

In the current literature on heat transfer in microchannels in homogeneous systems, large deviations between the different correlations and measurements can be seen. So far, no general conclusion can be drawn and the available heat transfer coefficient correlations are often restricted to the experimental setup and device used in a particular study. Therefore, there is still a need for precise experimental and numerical work in heat transfer analysis in microchannels to gain a better understanding. 

Select the appropriate heat transfer coefficient correlation. From Table 14-3 (for the standard helix pitch/impeller diameter ratio P/D = 5, the appropriate heat transfer correlation is... 

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