Friction factors heat exchanger tubes

Figure 10-137. Heating and cooling in tube bundles—tube-side friction factor. (Used by permission Kern, D. Q. Process Heat Transfer, 1 Ed., p. 836, 1950. McGraw-Hill, Inc. All rights reserved. Using nomenclature of Standards of Tubular Exchanger Manufacturers Association.)...

Since plate-and-frame exchangers are made by comparatively few concerns, most process design information about them is proprietary but may be made available to serious enquirers. Friction factors and heat transfer coefficients vary with the plate spacing and the kinds of corrugations a few data are cited in HEDH (1983, 3.7.4-3.7.5). Pumping costs per unit of heat transfer are said to be lower than for shell-and-tube equipment. In stainless steel... 

Fig. 10-19 Heat transfer and friction factor for finned flat-tube heat exchanger according to Ref 3...

Heat-transfer coefficient for cross flow over an ideal tube bank Fouling coefficient on outside of tube Heat-transfer coefficient in a plate heat exchanger Shell-side heat-transfer coefficient Heat transfer coefficient to vessel wall or coil Heat transfer factor defined by equation 12.14 Heat-transfer factor defined by equation 12.15 Friction factor... 

Internally finned tubes are ducts with internal longitudinal fins. These tubes are widely used in compact heat exchangers. The friction factor-Reynolds number product and the Nusselt number for such internally finned tubes, designated as (/ Re), and Nu/,c> respectively, are computed from the following definitions ... 

Fig. 17.15 shows how the friction factor increased with time in a "sample" finned tube heat exchanger exposed to an air flowing through laden with calcium carbonate particles the apparatus shown in Fig. 17.14. It may be regarded as a typical curve obtained in the laboratory apparatus. During the experiments water at temperature in the range 10 - 90°C was passed through the tubes. The equipment allowed thermal performance and pressure drop to be measured. From Fig. 17.15 it can be seen that the friction factor rises asymptotically to a level 50%...

The basic design data consisted of the Fanning friction factor and Colburn modulus versus Reynolds number characteristics (/versus Re and i versus Re) for gas flow both normal to the tube bundle and inside the turbulated tubes. The data for flow normal to the tubes were taken from a geometrically similar surface described by Kays and London [1] in their Fig. 45 and may be expressed by the equations / = 0.285 Re and j = 0.320 Re" , where 300 < Re < 15,000. Data for the turbulated tube were obtained partly from steam-air tests on a small shell and turbulated tube heat exchanger, and partly from transient tests with nitrogen on a hollow copper cylinder which contained a turbulator. The turbulated tube is described in Fig. 4, and the basic data are shown in Fig. 6. The data may also be expressed by the equations / 0.05 and j =0.05 Re" , where Re > 6000. 

Since heat exchangers cannot be designed or constructed without considering pressure drop, the number of velocity heads, NVH, is a useful concept in conjunction with the NTU. The pressure drop equation for fluids flowing inside of tubes, based on the Fanning friction factor, may be written as... 

It is to be noted that the ratio of the friction factor / to the heat transfer factor J for compact ribbon-packed heat exchangers is approximately equal to the ratio of / to j reported in the present work. F rom this it may be concluded that more compact heat exchangers can be designed with helically finned and coiled tubing, which also represents a Collins type of heat exchanger, without any sacrifice in shell-side pressure drop. 

Flows are usually turbulent on both the tube and shell sides of coiled tube heat exchangers. To calculate pressure drops for single-phase tube side flows, it is simplest to use the normal Fanning friction factor correlation for... 

Determine the friction factor and pressure drop for the low-pressure side of a coiled-tube heat exchanger where the fluid flows past 100 tubes in a staggered-tube arrangement. An air flow rate of 0.5 kg/s enters the low-pressure side of the heat exchanger at 0.121 MPa and 183 K. The outside diameter of each tube is 10 mm while the minimum flow area between each tube is 0.0125 m. The transverse pitch is 0.0003 m. 

---