Overall heat transfer coefficients table

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

Typical overall heat-transfer coefficients are given in Tables 11-3 through 11-8. Values from these tables may be used for preliminaiy estimating purposes. They should not be used in place of the design methods described elsewhere in this section, although they may serve as a useful check on the results obtained by those design methods. 

TABLE 11-3 Typical Overall Heat-Transfer Coefficients in Tubular Heat Exchangers... 

The calculation of overall heat transfer coefficient U using the equations jireviously presented can be rather tedious. Fleat transfer specialists have computer programs to calculate this value. There are some quick approximation techniques. Table 2-8 comes from the Gas Processors Suppliers Association s Engineering Data Book and gives an approximate value of U for shell and tube heat exchangers. 

A fire tube contains a flame burning inside a piece of pipe which is in turn surrounded by the process fluid. In this situation, there is radiant and convective heat transfer from the flame to the inside surface of the fire tube, conductive heat transfer through the wall thickness of the tube, and convective heat transfer from the outside surface of that tube to the oil being treated. It would be difficult in such a simation to solve for the heat transfer in terms of an overall heat transfer coefficient. Rather, what is most often done is to size the fire tube by using a heat flux rate. The heat flux rate represents the amount of heat that can be transferred from the fire tube to the process per unit area of outside surface of the fire tube. Common heat flux rates are given in Table 2-11. 

The procedure for calculating the number of tubes required for an aerial cooler is similar to that for a shell- and-tube exchanger. Table 3-6 shows approximate overall heat transfer coefficients. Ub should be used when the outside surface area of the bare tube (neglecting fins) is used in the heat... 

A few typical overall heat transfer coefficients, U, are presented in Table 5-9 [27] [29]. 

Table 10-40 provides a suggested range of overall heat transfer coefficients, Uq, for actual finned heat exchangers. 

Typical values of thermal resistances and individual and overall heat transfer coefficients are given in Tables 9.15-9.18. 

Table 9.17. Approximate overall heat transfer coefficients U for shell and tube equipment...

Figure 12.8 Temperature profile along the reactor at steady state for different 1. Table 12.7 Overall heat transfer coefficient for all experiments (with reaction).

The desired product is P, while S is an unwanted by-product. The reaction is carried out in a solution for which the physical properties are independent of temperature and composition. Both reactions are of first-order kinetics with the parameters given in Table 5.3-2 the specific heat of the reaction mixture, c, is 4 kJ kg K , and the density, p, is 1000 kg m . The initial concentration of /I is cao = 1 mol litre and the initial temperature is To = 295 K. The coolant temperature is 345 K for the first period of 1 h, and then it is decreased to 295 K for the subsequent period of 0.5 h. Figs. 5.3-13 and 5.3-14 show temperature and conversion curves for the 63 and 6,300 litres batch reactors, which are typical sizes of pilot and full-scale plants. The overall heat-transfer coefficient was assumed to be 500 W m K. The two reactors behaved very different. The yield of P in a large-scale reactor is significantly lower than that in a pilot scale 1.2 mol % and 38.5 mol %, respectively. Because conversions were commensurate in both reactors, the selectivity of the process in the large reactor was also much lower. 

Typical values of the overall heat-transfer coefficient for various types of heat exchanger are given in Table 12.1. More extensive data can be found in the books by Perry et al. (1997), TEMA (1999), and Ludwig (2001). 

Estimate the overall heat transfer coefficient see Table 12.1. 

From Table 15.4, the heat transfer coefficient for the tube wall in many cases is so high that its contribution to the overall heat transfer coefficient can be neglected. 

Calculation of the overall heat transfer coefficient from Equation 15.13 requires knowledge of the film transfer coefficients. Although Table 15.1 presents typical values,... 

Table 3.4-2 summarizes typical values of the overall heat-transfer coefficient for heat exchangers and high-pressure gases. 

TABLE 8.4. Overall Heat Transfer Coefficients in Some Petrochemical Applications, LI Btu/(hr)(sqft)(°F)... 

TABLE 17.11. Jacketed Vessels Overall Heat Transfer Coefficients... 

TABLE 17.12. Overall Heat Transfer Coefficients with immersed Coils [U expressed in Btu/(h -ftz-eF)]... 

TABLE 17.16. Data for the Overall Heat Transfer Coefficient, u (kcal/mzh°C), in Packed Beds... 

Finally, fouling factors typical of the two fluid media are taken from Table 12 in Ref. El (p. 645) and converted into their metric equivalents. All factors are then combined into the final equation for determination of the overall heat-transfer coefficient ... 

For a numerical base case, the kinetic and process parameters given in Table 2.1 are selected. Reactors with several design values of conversion and over a range of temperatures are sized. The purpose is to see the effect of these parameters on the size of the reactor and its heat transfer area. The effects of changes in the base case parameters, such as feed flowrate, heat of reaction, and overall heat transfer coefficient, will also be explored. Densities and heat capacities are assumed to be constant. 

Apart from the important effect of mass velocity, summarised in Table II, the particle size and, to a greater extent, the particle shape were also found to be important. The salt bath temperature gave an effect on U which could not be explained by the induced changes in the conductivity and viscosity of air alone. Particle conductivity and tube diameter, within their range of variation, have only marginal effects on the overall heat transfer coefficient. 

In discussing particle shape effects it seems sensible to compare overall heat transfer coefficients for different shapes relative to a common base,i.e. with regard to pressure drop/extem-al surface area for non-porous supports or pressure drop/solid volume for porous supports. Thus, Fig. 4 is constructed from the heat transfer correlations in Table II, together with pressure drop data collected over the packings at NTP in a 24 an diameter tube. 

Table B.3 gives values of thermal resistance due to fouling. Thicker walls of stainless steel should also be included in the overall heat-transfer coefficient. The...

Table B.4 Overall heat-transfer coefficients for shell-and-tubes heat exchangers.

Table B.5 Overall heat-transfer coefficients for air-cooled heat (bare tube basis).

Table B.6 Overall heat-transfer coefficients for jacketed vessels. ...

Calculations of the convection heat-transfer coefficients for use in the overall heat-transfer coefficient are made in accordance with the methods described in later chapters. Some typical values of the overall heat-transfer coefficient are given in Table 10-1. 

Although final heat-exchanger designs will be made on the basis of careful calculations of U, it is helpful to have a tabulation of values of the overall heat-transfer coefficient for various situations which may be encountered in practice. Comprehensive information of this sort is available in Refs. 5 and 6, and an abbreviated list of values of U is given in Table 10-1. We should remark that the value of U is governed in many cases by only one of the convection heat-transfer coefficients. In most practical problems the conduction resistance is small compared with the convection resistances. Then, if one value of h is markedly lower than the other value, it will tend to dominate the equation for U. Examples 10-1 and 10-2 illustrate this concept. 

A shell-and-tube heat exchanger is used as an ammonia condenser with ammonia vapor entering the shell at 50°C as a saturated vapor. Water enters the single-pass tube arrangement at 20°C and the total heat transfer required is 200 kW. The overall heat-transfer coefficient is estimated from Table I0-I as 1000 W/m2 °C. Determine the area to achieve a heat exchanger effectiveness of 60 percent with an exit water temperature of 40°C. What percent reduction in heal transfer would result if the water flow is reduced in half while keeping the heat exchanger area and V the same ... 

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