Internally finned tubes

Fabbri, G. Heat Transfer Optimization in Internally Finned Tubes Under Laminar Flow Conditions. Int J Heat Mass Transfer 41 (10) 1243-1253 (1998). 

A. Hydrodynamic Studies with an Internally Finned Tube... 

Figure 11 Internally finned tube cut off at an angle at the lower end. Left side view. Right front view.

Figure 12 shows some results of pressure drop measurements over a 1-m-long internally finned round tube (4-mm internal diameter, six fins, fm height 1 mm, fin thickness 0.5 mm) with a cutoff angle at the bottom end of 60 . With n-decane as the liquid and air at ambient temperature and pressure as the gas, the pressure drop increases steadily with increasing gas velocity until a certain critical gas velocity is reached. Below this critical velocity, the pressure drop is low, viz., orders of magnitude lower than in a fixed bed of catalyst under comparable conditions. It can also be seen that under these conditions the superficial velocity of the liquid in the internally finned tube has little effect on the pressure drop. 

Figure 13 also shows the range of liquid and gas velocities corresponding with the operation of industrial trickle-flow reactors. It follows that an internally finned tube of the present geometry with an outlet angle of 70 allows counterflow operation in the... 

Figure 12 Pressure drop over a 1-m-long internally finned tube with countercurrent flow of n decane and air at ambient conditions. Circular channel of 4-mm i.d. with six fins of I-mm height and 0.5-mm thickness. Tube end cut off at an angle of 60 ...

From the observable effect of the cutoff angle on the flow regime transition it can be deduced that notwithstanding the favorable results obtained at an angle of 70°, the transition is still determined by the outlet geometry to a large extent. This implies that the limits to counterflow operation in the internally finned tube proper have not yet been reached in the previously discussed experiments. 

Figure 14 Outlet of internally finned tube with gas introduction through an inserted capillary.

Figure 15 Map of flow regimes for n-decane/air and ethanol/air at ambient conditions for internally finned tube with gas introduction through inserted capillary. A = countercurrent annular flow B = slugging flow. The hatched area represents the range of velocities corresponding with the operation of large industrial trickle-bed reactors. Channel cross section is the same as in Fig. 12.

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 ... 

J. H. Masliyah, and K. Nandakumar, Heat Transfer in Internally Finned Tubes, J. Heat Transfer, (98) 257-261,1976. 

The extension of these PECs to two-phase heat transfer is complicated by the dependence of the local heat transfer coefficient on the local temperature difference and/or quality. Heat transfer and pressure drop have been considered in the evaluation of internally finned tubes for refrigerant evaporators [14] and for internally finned tubes, helically ribbed tubes, and spirally fluted tubes for refrigerant condensers [15]. Pumping power has been incorporated into the evaluation of inserts used to elevate subcooled boiling critical heat flux (CHF) [16, 17]. A discussion of the application of enhancement to two-phase systems is given by Webb [373],... 

Internally finned tubes can be stacked to provide multiple internal passages of small hydraulic diameter. Carnavos [119] demonstrated the large increases in heat transfer coeffi-... 

FIGURE 11.18 Heat transfer coefficients for evaporation in internally finned tubes... 

Internally finned tube with twisted-tape insert (Van Rooyen and Kroeger [356])... 

A. E. Bergles, G. S. Brown Jr., and W. D. Snider, Heat Transfer Performance of Internally Finned Tubes, ASME Paper 71-HT-31, ASME, New York, 1971. 

G. R. Kubanek and D. L. Miletti, Evaporative Heat Transfer and Pressure Drop Performance of Internally-Finned Tubes with Refrigerant 22, /. Heat Transfer (101) 447-452,1979. 

E. C, Brouillette, T. R. Mifflin, and J. E. Myers, Heat Transfer and Pressure Drop Characteristics of Internal Finned Tubes, ASME Paper 57-A-47, ASME, New York, 1957. 

A. P. Watkinson, D. C. Miletti, and G. R. Kubanek, Heat Transfer and Pressure Drop of Internally Finned Tubes in Laminar Oil Flow, ASME Paper 75-HT-41, ASME, New York, 1975. 

W. E. Hilding and C. H. Coogan Jr., Heat Transfer and Pressure Loss Measurements in Internally Finned Tubes, in Symp. Air-Cooled Heat Exchangers, pp. 57-85, ASME, New York, 1964. 

S. V. Patankar, M. Ivanovic, and E. M. Sparrow, Analysis of Turbulent Flow and Heat Transfer in Internally Finned Tube and Annuli, J. Heat Transfer (101) 29-37,1979. 

T. C. Carnavos, Cooling Air in Turbulent Flow With Internally Finned Tubes, Heat Transfer Eng. (1/2) 4W6,1979. 

W. J. Marner and A. E. Bergles, Augmentation of Tubeside Laminar Flow Heat Transfer by Means of Twisted-Tape Inserts, Static-Mixer Inserts and Internally Finned Tubes, Heat Transfer 1978, Proc. 6th Int. Heat Transfer Conf, Hemisphere, Washington, DC, vol. 2, pp. 583-588,1978. 

Various investigators have studied in-tube condensation in noncircular passages. Fieg and Roetzel [121] and Chen and Yang [160] analyzed condensation inside elliptical tubes. Kaushik and Azer [161] established an experimental correlation for internally finned tubes. Lee et al. [162] experimentally studied condensation of R-113 within an internally finned tube and a spirally twisted tube and compared performance to that of a smooth tube. Using a modified form of the correlation of Cavallini and Zecchin [148] (Eq. 14.138) ... 

N. Kaushik and N. Z. Azer, A General Heat Transfer Correlation for Condensation Inside Internally Finned Tubes, ASHRAE Trans., 94(2), pp. 261-279,1988. 

S. C. Lee, M. Chung, and H. S. Shin, Condensation Heat Transfer and Pressure Drop Performance of Horizontal Smooth and Internally-Finned Tubes with Refrigerant 113, Exp. Heat Transfer, Fluid Mech. and Thermodynamics, 2, pp. 1349-1356, Elsevier Science Publishers, 1993. 

---