Films bundle

A routine inspection of the tube bundle during a plant outage revealed fine cracks of the type shown in Fig. 9.11. Scattered longitudinal cracks were observed along the lengths of most tubes. The external surface was covered with a thin film of black copper oxide and deposits. The bundle had been exposed to ammonia levels that produced 14 ppm of ammonia in the accumulated condensate. 

Fig. 2a. Bundles and individual single-layer carbon nanotubes bridge across a gap in a carbon film.

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. 

Vj = superficial vapor velocity, ft/sec N = number of tubes in center vertical row of bundle hj( = h = theoretical boiling film coefficient for a single tube, Btu/(hr) (ft ) (°F)... 

Palen and Taborek proposed as the best choice for circular tube bundles (as compared to square) the following film boiling coefficient after analyzing available data (their... 

Calculate the correction to the nucleate boiling film coefficient for the tube bundle number of tubes in vertical row, hi,. See previous discussion. 

Due to the development of the data, the method requires the use of a single tube boiling film coefficient. Using this to reach the overall bundle transfer The overall U value is determined for a theoretical boiling coefficient of an unfouled tube (single) (this is an iterative procedure). See reference 90 also. 

For the entire bundle, the film boiling coefficient (assumes all tubes boiling, no liquid head effect so that some tubes are not boiling) ... 

A, Film coefficient outside bundle, Btu/ft -hr-°F 0 Inside diameter of shell,in. 

For purposes of standardisation, 19 mm outer diameter tubes of 1.65 mm wall thickness will be used, and these may be 2.5, 3-6, or 5 m in length. The film coefficient for condensing pentane on the outside of a horizontal tube bundle may be taken as 1.1 kW/m2 K, The condensation is effected by pumping water through the tubes, the initial water temperature being 288 K. 

Two methods for modification of polymer surfaces by photoinitiated graft copolymerization have been developed a discontinuous method (1) with vapor phase transfer of initiator and monomer and a continuous method (2) with presoaking of a film strip or a fiber bundle in a solution of initiator and monomer. Both methods have been applied to polyelefins and linear polyester. 

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