Finned tube heat exchangers film coefficients

The heat transfer area, A ft, in an exchanger is usually estahlished as the outside surface of all the plain or hare tubes or the total finned surface on the outside of all the finned tubes in the tube bundle. As will be illustrated later, factors that inherendy are a part of the inside of the tube (such as the inside scale, transfer film coefficient, etc.) are often corrected for convenience to equivalent outside conditions to be consistent. When not stated, transfer area in conventional shell and tube heat exchangers is considered as outside tube area. 

Extended surfaces created from integrally formed low transverse fins can be used in conventional shell-and-tube heat exchangers to enhance the outside film transfer coefficient. Low transverse fins can increase the surface area by a factor of around 2.5 relative to plain tubes. 

PROGRAM CALCULATES HEAT-TRANSFER FILM COEFFICIENT IN THE SHELL SIDE (FINNED-TUBE) AND THE OVERALL HEAT TRANSFER COEFFICIENT OF THE HEAT EXCHANGER. ... 

Sizing an Exchanger with Radial Finned Tubes A liquid is heated from 150 to 190°F with a gas that goes from 250 to 200°F. The duty is 1.25 MBtu/hr. The inside film coefficient is 200, the bare tube outside coefficient is hb = 20 Btu/(hr)(sqft)(°F). The tubes are 1 in. OD, the fins are in. high, 0.038 in. thick, and number 72/ft. The total tube length will be found with fins of steel, brass, or aluminum ... 

Heat Transfer Enhancements Heat transfer enhancements increase the film heat transfer coefficient, thus improving U and consequently heat tfansfer in the exchanger. In the case of the ubiquitous ST heat exchanger, heat transfer enhancement can be achieved on the shell and/or tube sides as required. Tube-side enhancements help in improving the film heat transfer coefficient on the tube side, and are useful if the exchanger involved has lower film heat transfer coefficient on the tube side. Tube-side enhancements include, but are not limited to, twisted-tape inserts, coiled-wire inserts and internal fins. Similarly, shell-side enhancements are used to improve the heat transfer coefficient on the shell side. They include helical baffles, external fins and Expanded Metal (EM) baffles. More details on heat transfer enhancements are available in Pan et al. (2013). 

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