Heat-transfer coefficients for

Correlations for Convective Heat Transfer. In the design or sizing of a heat exchanger, the heat-transfer coefficients on the inner and outer walls of the tube and the friction coefficient in the tube must be calculated. Summaries of the various correlations for convective heat-transfer coefficients for internal and external flows are given in Tables 3 and 4, respectively, in terms of the Nusselt number. In addition, the friction coefficient is given for the deterrnination of the pumping requirement. 

The effective thermal conductivity of a Hquid—soHd suspension has been reported to be (46) larger than that of a pure Hquid. The phenomenon was attributed to the microconvection around soHd particles, resulting in an increased convective heat-transfer coefficient. For example, a 30-fold increase in the effective thermal conductivity and a 10-fold increase in the heat-transfer coefficient were predicted for a 30% suspension of 1-mm particles in a 10-mm diameter pipe at an average velocity of 10 m/s (45). 

For the purpose of network synthesis, the overall heat-transfer coefficient is usually idealized as a constant value. This iadependence of the heat-transfer coefficient makes possible the iterations necessary to solve the network problem. Usually, the overall heat-transfer coefficient for each exchanger (match) is defined as... 

Fig. 35. Correlations for calculating heat-transfer coefficients for (a) turbine external jackets, internal cods, and baffle cods, and (b) for close-clearance...

Annuli Approximate heat-transfer coefficients for laminar flow in annuh may be predicted by the equation of Chen, Hawkins, and Sol-berg [Tron.s. Am. Soc. Mech. Eng., 68, 99 (1946)] ... 

Vertical Tubes For the following cases Reynolds number < 2100 and is calculated by using F = Wp/ KD. The Nusselt equation for the heat-transfer coefficient for condensate films may be written in the following ways (using liquid physical properties and where L is the cooled lengm and At is — t,) ... 

FIG. 11-23 Heat-transfer coefficients for water in short-tube evaporators. °C = (°F — 32)/1.8 to convert British thermal units per hour-square foot-degrees Fahrenheit to joules per square meter-second-kelvins, multiply hy 5.6783. 

TABLE 11-2 Overall Heat-Transfer Coefficients for Coils Immersed in Liquids... 

High Fins To calculate heat-transfer coefficients for cross-flow to a transversely finned surface, it is best to use a correlation based on experimental data for that surface. Such data are not often available, and a more general correlation must be used, making allowance for the possible error. Probably the best general correlation for bundles of finned tubes is given by Schmidt [Knltetechnik, 15, 98-102, 370-378 (1963)] ... 

One device uses four baffles in a baffle set. Only half of either the vertical or the horizontal tube lanes in a baffle have rods. The new design apparently provides a maximum shell-side heat-transfer coefficient for a given pressure drop. 

In order to estimate diying rates from Eq. (12-42) values of the empirical constants are required for the particular geometry under consideration. For flow parallel to plane plates, exponent n has been reported to range from 0.35 to 0.8 [Chu, Lane, and Conklin, Ind. E/ig. Chem., 45, 1856 (1953) Wenzel and White, Ind. Eng. Chem., 51, 275 (1958)]. The differences in exponent have been attributed to differences in flow pattern in the space above the evaporating surface. In the absence of apphcable specific data, the heat-transfer coefficient for the parallel-flow case can be taken, for estimating purposes, as... 

To do this one must sum all the resistances to heat transfer. The reciprocal of this sum is the heat transfer coefficient. For a heat exchanger the resistances are... 

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. 

Estimation of the heat transfer coefficients for forced convection of a fluid in pipes is usually based on empirical expressions. The most well known expression for this purpose is ... 

In water-cooled tube-and-shell condensers with shell side condensation, overall heat transfer coefficients for essentially pure steam range from 200 to 800 Btu per hour per square foot per °F. 

U = Heat transfer coefficient for transfer between the pipeline and surrounding ground, Btu/hr-ft -°F X = Distance from origin, ft Z = Distance above datum, ft = Joule-Thompson coefficient 6 = Incremental amount of a variable... 

A software package (MIXER) was developed to determine the heat transfer coefficient for any type of agitator and surface using the value in Table 7-16, fluid physical properties, agitator speed, and diameter. 

The cost of condensers/heat exchangers ( ) is taken as l,500 (heat transfer area in m ). The overall heat-transfer coefficients for the dehumidification, the... 

FIGURE 9.12 Diagram for determining the heat transfer coefficient for a straight fin plate. 

The heat transfer coefficient for a herringbone plate is calculated from ... 

This approach is much easier to use than the first, but may give less accurate results since it assumes an average or typical value for the heat transfer coefficient for all heated source geometries. 

Therefore, the following equation is used to determine the oxerall heat transfer coefficient for use in Equation 2- F... 

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