Pressure drop shell and tube

This pressure drop is composed of several parts which are calculated as shown in Tables 1 and 2. 

Calculation of Tubeside Pressure Drop in Shell and Tube Exchangers 

Part Pressure Drop in Number of Velocity Heads Equation 

Straight tube loss See Chapter 1, Fluid Flow, Piping Pressure Drop  

Up = Velocity in the pipe leading to and from the exchanger, ft/sec Ut = Veiocity in the tubes N = Number of tube passes 

Entering plus exiting the exchanger 1.6 Ah = 1.6 -2g (This term is small and often neglected) 

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APm.AP,., Pressure drop for ideal-tube-bank cross-flow and ideal window respectively AP for shell side of baffled exchanger kPa Itf ft ... 

There are many text books that describe the fundamental heat transfer relationships, but few discuss the complicated shell side characteristics. On the shell side of a shell and tube heat exchanger, the fluid flows across the outside of the tubes in complex patterns. Baffles are utilized to direct the fluid through the tube bundle and are designed and strategically placed to optimize heat transfer and minimize pressure drop. 

Figure 10-57. Effect of velocity on heat transfer rates and pressure drop shell-side and tube-side. (Used by permission Shroff, P. D. Chemical Processing, No.4, 1960. Putnam Publishing Co., Itasca, III. All rights reserved.)...

When a fluid flows over a stationary or moving surface, the pressure of the fluid decreases along the length of the surface due to friction. This is commonly called the pressure drop of the system. Of particular interest are the pressure drops in pipes (tubes) and in heat exchanger shells. 

These curves provide a comparison of heat transfer rotes for plate heat exchangers and shell and tube equipment. The values given ore typical for pressure drops shown and ore based upon the thermal characteristics of the fluids. 

At a 12.5 psi pressure drop in water to water applications, the surtoce heat transfer rote achieved in a Graham plate exchanger exceeds that of a shell and tube unit by a factor of 3.4. Similar or higher improvement toctors are obtained with other fluids. 

Pressure drop on the tube-side of a shell and tube exchanger is made up of the friction loss in the tubes and losses due to sudden contractions and expansions and flow reversals experienced by the tube-side fluid. The friction loss may be estimated by the methods outlined in Section 3.4.3 from which the basic equation for isothermal flow is given by equation 3.18 which can be written as ... 

A note of caution on the use of photo-etched channels has been offered by RAMSHAWfl3 ) who points out that the system is attractive in principle provided that severe practical problems such as fouling are not encountered. With laminar flow in matrices with a mean plate spacing of 0.3-1 mm, volumetric heat transfer coefficients of 7 MW/m3 K have been obtained with modest pressure drops. Such values compare with 0.2 MW/m3 K for shell and tube exchangers and 1.2 MW/m3 K for plate heat exchangers. 

ESDU Engineering Sciences Data Unit Report 83038 Baffled shell and tube heat exchangers flow distribution, pressure drop and heat transfer on the shell side. (ESDU International, London 1983)... 

ESDU 84023 (1985) Shell-and-tube exchangers pressure drop and heat transfer in shellside downflow condensation. 

Design a shell and tube exchanger to heat 50,000 kg/h of liquid ethanol from 20°C to 80°C. Steam at 1.5 bar is available for heating. Assign the ethanol to the tube-side. The total pressure drop must not exceed 0.7 bar for the alcohol stream. Plant practice requires the use of carbon steel tubes, 25 mm inside diameter, 29 mm outside diameter, 4 m long. 

A condenser is required to condense n-propanol vapour leaving the top of a distillation column. The n-propanol is essentially pure, and is a saturated vapour at a pressure of 2.1 bara. The condensate needs to be sub-cooled to 45°C. Design a horizontal shell and tube condenser capable of handling a vapour rate of 30,000 kg/h. Cooling water is available at 30°C and the temperature rise is to be limited to 30° C. The pressure drop on the vapour stream is to be less than 50 kN/m2, and on the water stream less than 70 kN/m2. The preferred tube size is 16 mm inside diameter, 19 mm outside diameter, and 2.5 m long. 

Heat Transfer Coefficients and Pressure Drops for Shell-and-Tube Heat Exchangers 319... 

HEAT TRANSFER COEFFICIENTS AND PRESSURE DROPS FOR SHELL-AND-TUBE HEAT EXCHANGERS... 

Pressure drop during condensation results essentially from the vapor flow. As condensation proceeds, the vapor flowrate decreases. The equations described previously for pressure drop in shell-and-tube heat exchangers are only applicable under constant flow conditions. Again the exchanger can be divided into zones. However, in preliminary design, a reasonable estimate of the pressure drop can usually be obtained by basing the calculation on the mean of the inlet and outlet vapor flowrates. 

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