Tubes film condensation

Temp. Gas Water at Interface Out. °F Tube Ciun. Film Condensed, No. Gas Area Tube, Length of... 

Corrosion of. power-station condenser tubes by polluted, waters has been particularly troubles ome in Japan anil efforts have been made to,study the problem by, electrochemical methods and by exposing model condensers at a variety of bower station sites ., Improved results have been reported, using tin. brasses , or special, tin bronzes. . Pretreatment with sodium dimethyldithiOcarbamate is reported to give protective films that will withstand the action of polluted waters , though the method would be economic only in special circurtistapcies., , , . ... 

Campbell points out that in evaluating condenser tube materials a test apparatus is required that will include all the principal hazards likely to be encountered in service and should thus cater for the following conditions impingement, slow moving water, heat transfer and shielded areas. Furthermore, the internal surfaces should not be abraded, as in the jet impingement test, but should be tested in the as-manufactured condition, particularly in view of the deleterious effect of carbon films produced during manufacture (see Sections 1.6 and 4.2). LaQue has pointed out the importance of specimen area in impingement tests... 

Parker, J. G. and Roscow J. A., Method for the Assessment of the Quality of Surface Films Formed on the Cooling Water Side of Copper-Based Alloy Condenser Tubes , Br. Corros. J., 16, 2, 107-110(1981)... 

Protective films on metals also can be destroyed and corrosion accelerated by the impingement of a high-velocity stream of sea water onto the metallic surface. The inlet ends of condenser tubes, are frequently attacked (Figure 3,a). Jet tests have been devised for ranking the susceptibility of metals to such impingement attack. A corrosion cell is formed between the bare surface directly under the jet (anode) and the adjacent filmed surface (cathode). These jet tests give more dependable information, if natural sea water is continuously supplied to the equipment. 

In brackish waters, the same general corrosion principles may apply as for sea water. Experience has also shown that there may be considerable variation from plant to plant in the performance of metals, even where the cooling water comes out of the same general source such as a deep bay or estuary. There are coastal sites where the salinity may show very marked seasonal fluctuation. Protective film formation is essential for long lifetime in condenser tubing. Tubes installed at the season of the year when conditions are most favorable to form protective films tend to give longer service. 

This program is also used for condensing steam. A given Q fixes heat transfer. A 1500 Btu/h ft2 °F steam-condensing tube-side film coefficient is assumed. This condensing film coefficient is set by inputting a specific heat value of 0. 

AirCIri). This is an executable program for any air-cooler condenser. The inputted Q will be the heat duty transferred. Data inputs for condenser tube-side transport property values of viscosity, thermal conductivity, and specific heat should be determined as for two-phase flow values calculated in Chap. 6. Use the average tube-side temperature for these condensing film transport property values. Weighted average values between gas and liquid should also be determined and applied like that used in the two-phase flow equations in Chap. 6. 

Theft are a number of very important practical situations in which film condensation occurs on the outside of horizontal tubes. An obvious example is a shell-and-tube... 

Stagnant saturated steam at 100°C condenses on the outside of a horizontal copper tube with outside diameter 5.0 cm. The copper tube has a wall thickness of 1.5 mm and a thermal conductivity of 390 W/m-K. At the axial location being considered, the bulk temperature of the vater flowing inside the copper tube is 80°C and the inside heat transfer coefficient is 3500 W/m2. Assuming film condensation, calculate the heat transfer and condensation rate per unit length of pipe. 

Chen. M.M., An Analytical Study of Laminar Film Condensation. Part 1. Flat Plates Part 2. Single and Multiple Horizontal Tubes." J. Heat Transfer, Vol. 83. pp. 48-60,1961. 

Labuntsov, D.A., Heat Transfer in Film Condensation of Pure Steam on Vertical Surfaces and Horizontal Tubes, Teploenergetika, Vol. 4, p. 72, 1957. 

High velocities of aqueous solutions impinging on copper and brass tubes produce impingement on the metal or alloy. The aluminum brass and cupronickel alloys have great resistance to flow-induced attack up to a well-defined maximum for the flow rate, beyond which the film on the metal surface will be disrupted. Admiralty brass and aluminum brass have lower values for maximum velocity of flow than cupronickels. Admiralty brass and aluminum brass are preferred to cupronickels for use in media containing sulfide species. Coatings have been developed for cupronickel and aluminum brass condenser tubes for land-based and marine systems. 

For laminar film condensation on horizontal tubes Nusselt obtained the relation... 

Our discussion of film condensation so far has been limited to exterior surfaces, where the vapor and liquid condensate flows are not restricted by some overall flow-channel dimensions. Condensation inside tubes is of considerable practical interest because of applications to condensers in refrigeration and air-conditioning systems, but unfortunately these phenomena are quite complicated and not amenable to a simple analytical treatment. The overall flow rate of vapor strongly influences the heat-transfer rate in the forced convection-condensation system, and this in turn is influenced by the rate of liquid accumulation on the walls. Because of the complicated flow phenomena involved we shall present only two empirical relations for heat transfer and refer the reader t.o Rohsenow [37] for more complete information. 

Select the calculation method to be used. Condensation inside horizontal tubes can be predicted assuming two mechanisms. The first assumes stratified flow, with laminar film condensation. The... 

Select the calculation method to be used. Condensation on the outside of banks of horizontal tubes can be predicted assuming two mechanisms. The first assumes laminar condensate flow the second assumes that vapor shear dominates the heat transfer. The following equations can be used to predict heat-transfer coefficients for condensation on banks of horizontal tubes For laminar-film condensation,... 

For low-fin tubes, the laminar condensing coefficient can be calculated by applying an appropriate correction factor F to the value calculated using the preceding equation for laminar-film condensation. The factor F is defined thus ... 

Heat Transfer Correlations for Film Condensation 581 10-6 Film Condensation Inside Horizontal Tubes 591 10-7 Dropwise Condensation 591... 

Equation 10 22 for vertical plates can also be used to calculate the average heat transfer coefficient for laminar film condensation on the outer surfaces of vertical lubes provided that the tube diameter is large relative to the thickness of the liquid film. 

Film condensation on a vertical tier of horizontal tubes. 

So far we have discussed film condensation on the outer surfaces of tubes and other geometries, which is characterized by negligible vapor velocity and the unrestricted flow of the condensate. Most condensation processes encountered in refrigeration and air-conditioning applications, however, involve condensation on the inner surfaces of horizontal or vertical tubes. Heat transfer analysis of condensation inside tubes is complicated by the fact that it is strongly influenced by the vapor velocity and the rate of liquid accumulation on the walls of the tubes Q ig. 10-34). 

The average heat transfer coefficient for film condensation on the outer surfaces of a horizontal tube is determined to be... 

For low vapor velocities, film condensation heat transfer inside horizontal tubes can be determined from... 

C Consider film condensation on the outer surfaces of four long tubes. For which orieiitalion of the tubes will ihc condensation heat transfer coefficient be the highest (a) vertical, (b) horizontal side by side, (c) horizontal but in a vertical tier (directly on lop of each other), or ([Pg.619]

Consider film condensation on the outer surfaces of W horizontal tubes arranged in a vertical tier. For what value of N will the average heat transfer coefficieni for the entire slack of tubes be equal to half of what it is for a single horizontal tube ... 

---