Heat transfer shell losses

The shape of the coohng and warming curves in coiled-tube heat exchangers is affected by the pressure drop in both the tube and shell-sides of the heat exchanger. This is particularly important for two-phase flows of multicomponent systems. For example, an increase in pressure drop on the shellside causes boiling to occur at a higher temperature, while an increase in pressure drop on the tubeside will cause condensation to occur at a lower temperature. The net result is both a decrease in the effective temperature difference between the two streams and a requirement for additional heat transfer area to compensate for these losses. 

Multi-stage preheating, pre-calciners, kiln combustion system improvements, enhancement of internal heat transfer in kiln, kiln shell loss reduction, optimize heat transfer in clinker cooler, use of waste fuels Blended cements, cogeneration... 

Figure 10-73. Shell-side pressure loss for 3 shell-side baffle configurations—RODbaffles . (Used by permission Small, W. M., and Young, R. K. Heat Transfer Engineering, V. 2, 1979. Taylor and Francis, Inc., Philadelphia, PA. All rights reserved.)...

Higher overall heat transfer coefficients are obtained with the plate heat exchanger compared with a tubular for a similar loss of pressure because the shell side of a tubular exchanger is basically a poor design from a thermal point of view. Considerable pressure drop is used without much benefit in heat transfer efficiency. This is due to the turbulence in the separated region at the rear of the tube. Additionally, large areas of tubes even in a well-designed tubular unit are partially bypassed by liquid and low heat transfer areas are thus created. 

This is the same result as derived by McAdams (1942), having the interpretation that the friction losses in the shell and tube sides, and the heat transfer resistances must be balanced economically. The value of h( can be obtained by solving... 

The best way to diminish the effect of laminar flow is to place the higher-viscosity fluid on the shell side. The shell side of an exchanger is far more resistant to heat transfer loss due to film resistance than is the tube side because of... 

The design calculations highlighted the shortcomings of the Kern method of exchanger design. The Kern method fails to account for shell-side inefficiencies such as bypassing, leakage, crossflow losses, and window losses. This leads to a marked overestimate of the shell-side heat-transfer coefficient and shell-side pressure drop. The Bell method is recommended to correct these deficiencies. 

Dc = clearance between tubes to give smallest free area across shell axis, ft De = equivalent diameter = 4 x hydraulic radius, ft E = power loss per unit of outside-tube heat-transfer area, ft lbf/(hXft2) subscript i designates inside tubes, and subscript o designates outside tubes... 

Steam a T i = 320°C flows in a cast iron pipe (k = 80 W/m °C) whose inner and outer diameters are D, = 5 cm and Dj 5.5 cm, respectively. The pipe is covered with 3-cm-thick glass wool insulation with k = 0.05 W/m C. Heat is lost to the surroundings at - 5°C by natural convection and radiation, with a cyimblned heat transfer coefficient of hj = 18 W/m °C. Taking the heat transfer coefficient inside the pipe to be hi = 60 W/m °C, determine the rate of heat loss from the steam per unit length of the pipe. Also determine the temperature drops across the pipe shell and the insulation. 

Here P indicates the effectiveness of the heat exchanger (to be elaborated in Section 7.4) and R (from its definition) is the ratio of the heat-capacity flow rates Note the change in nomenclature from subscripts h and c to t and s, the latter two referring to tube and shell, respectively. An important fact is that whether the hot (or cold) fluid is flowing in the shell side or in the tubes has no effect on F as long as the heat transfer to the ambient is negligible. Otherwise, the cold fluid should be in the shell side to reduce heat losses Combination of Eqs (7.28) and (7.29) gives... 

The shell temperatures were monitored on the rotary kiln, preheater, and clinker cooler with an optical pyrometer. Shell thermal losses are given by a radiation and either natural or forced convection heat transfer, which are evaluated as follows (see Table 31.37 and Figure 31.23). 

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