Shell-side heat transfer coefficient

Hms Ht Film heat transfer coefficient from the wall to the shell Film heat transfer coefficient, tube-side kj/m2 K s kj/m2 K s... 

Shell-Side Heat-Transfer Coefficient Calculation... 

For subcooling, a liquid inventory may be maintained in the bottom end of the shell by means of a weir or a hquid-level-controUer. The subcoohng heat-transfer coefficient is given by the correlations for natural convection on a vertical surface [Eqs. (5-33 ), (5-33Z )], with the pool assumed to be well mixed (isothermal) at the subcooled condensate exit temperature. Pressure drop may be estimated by the shell-side procedure. 

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. 

Coolant flow is set by the designed temperature increase of the fluid and needed mass velocity or Reynolds number to maintain a high heat transfer coefficient on the shell side. Smaller flows combined with more baffles results in higher temperature increase on the shell side. Reacting fluid flows upwards in the tubes. This is usually the best plan to even out temperature bumps in the tube side and to minimize temperature feedback to avoid thermal runaway of exothermic reactions. 

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. 

Some processes have large heat transfer requirements. This may result in large inventories of material within the heat transfer equipment. If the material is thermally unstable it would be inherently safer to reduce the residence time in the heat exchanger. Options to minimize heat exchanger inventory include the use of different types of heat exchangers. Inventories in shell and tube heat exchangers can be reduced by the use of turbulators in the tubes to enhance heat transfer coefficients, and by placing the more hazardous material on the tube side. 

Figure 10-154. Finned transfer efficiency is never as great per unit area as the bare pipe therefore, fin efficiency must be calculated to arrive at correct h , shell-side heat transfer coefficient. (Used by permission Technical paper. Brown Fintube Co., A Koch Engineering Company, Houston, Texas.)...

Ganapathy, V, Shell-Side Heat Transfer Coefficients Found Fast for Liquids, Oil and Gas Journal, Oct. 30, (1978) p. 114. 

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. 

In a shell and lube heat exchanger with horizontal tubes 25 mm external diameter and 22 rnm internal diameter, benzene is condensed on the outside by means of water flowing through the tubes at the rate of 0.03 m Vs. If the water enters at 290 K and leaves at 300 K and the heat transfer coefficient on the water side is 850 W/in2 K, what total length of tubing will be required ... 

Will the distribution of flow on the shell side be uniform enough to give the same heat transfer coefficient for aU the tubes ... 

Pressure drop. For the same pressure drop, higher heat-transfer coefficients will be obtained on the tube-side than the shell-side, and fluid with the lowest allowable pressure drop should be allocated to the tube-side. 

Viscosity. Generally, a higher heat-transfer coefficient will be obtained by allocating the more viscous material to the shell-side, providing the flow is turbulent. The critical Reynolds number for turbulent flow in the shell is in the region of 200. If turbulent flow cannot be achieved in the shell it is better to place the fluid in the tubes, as the tube-side heat-transfer coefficient can be predicted with more certainty. 

The complex flow pattern on the shell-side, and the great number of variables involved, make it difficult to predict the shell-side coefficient and pressure drop with complete assurance. In methods used for the design of exchangers prior to about 1960 no attempt was made to account for the leakage and bypass streams. Correlations were based on the total stream flow, and empirical methods were used to account for the performance of real exchangers compared with that for cross flow over ideal tube banks. Typical of these bulk-flow methods are those of Kern (1950) and Donohue (1955). Reliable predictions can only be achieved by comprehensive analysis of the contribution to heat transfer and pressure drop made by the individual streams shown in Figure 12.26. Tinker (1951, 1958) published the first detailed stream-analysis method for predicting shell-side heat-transfer coefficients and pressure drop, and the methods subsequently developed... 

The Engineering Sciences Data Unit has also published a method for estimating shell-side the pressure drop and heat transfer coefficient, EDSU Design Guide 83038 (1984). The method is based on a simplification of Tinker s work. It can be used for hand calculations, but as iterative procedures are involved it is best programmed for use with personal computers. 

The procedure for calculating the shell-side heat-transfer coefficient and pressure drop for a single shell pass exchanger is given below ... 

This will reduce the shell-side heat-transfer coefficient by a factor of (l/2)0 H(ho oc Re0 8 oc u°s-8)... 

Step 10 Shell-side heat transfer coefficient... 

The shell-side heat transfer coefficient is given by ... 

In partial condensation it is usually better to put the condensing stream on the shell-side, and to select a baffle spacing that will maintain high vapour velocities, and therefore high sensible-heat-transfer coefficients. 

Emerson, W. H. (1973) Conference on Advances in Thermal and Mechanical Design of Shell and Tube Exchangers, NEL Report No. 590. (National Engineering Laboratory, East Kilbride, Glasgow, UK). Effective tube-side temperature in multi-pass heat exchangers with non-uniform heat-transfer coefficients and specific heats. 

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