Heat exchanger general discussion

It is a general principle of heat exchange that low flows tend to promote fouling and fouling promotes corrosion. The corroded, fouled heat-exchanger surface retards flow and creates a vicious cycle. We will see this problem again in shell-and-tube heat exchangers, as discussed in Chap. 21. 

In direct contact condensers, a physical contact of the working fluids (a saturated or superheated vapor and a liquid) occurs, allowing for the condensation to be accomplished simultaneously with the mixing process. The fluids can be subsequently separated only if they are immiscible. Direct contact is generally characterized with a very high heat transfer rate per unit volume. The classification of indirect and direct contact heat exchangers is discussed in more detail in Ref. 2. 

Shell and Tube Heat Exchangers for General Piefineiy Seivices, API Standard 660, 4th ed., 1982, is published by the American Petroleum Institute to supplement both the TEMA Standards and the ASME Code. Many companies in the chemical and petroleum processing fields have their own standards to supplement these various requirements. The Jnterrelation.ships between Codes, Standards, and Customer Specifications for Proce.ss Heat Tran.sfer Equipment is a symposium volume which was edited by F. L. Rubin and pubhshed by ASME in December 1979. (See discussion of pressure-vessel codes in Sec. 6.)... 

Shell Sizes Heat-exchanger shells are generally made from standard-wall steel pipe in sizes up to 305-mm (12-in) diameter from 9.5-mm (ys-in) wall pipe in sizes from 356 to 610 mm (14 to 24 in) and from steel plate rolled at discrete intervals in larger sizes. Clearances between the outer tube limit and the shell are discussed elsewhere in connection with the different types of construc tion. 

Tinker, T. Proceedings of the General Discussion onHeat Transfer, September, 1951, p. 89. Analysis of the fluid flow pattern in shell and tube exchangers and the effect of flow distribution on the heat exchanger performance, (Inst, of Mech. Eng. and Am, Soc. Mech. Eng.). 

In the following section, we will discuss the approach proposed by Ciric and Floudas (1991) for the synthesis of heat exchanger networks without decomposition. Note that we will present the approach for the pseudo-pinch case (which is the most general). The approach for the strict-pinch case (which is a constrained scenario of the pseudo-pinch and as such features more structure) can be found in Ciric and Floudas (1991). 

Radiation is frequently associated with that bad nuclear stuff. However, the general scientific meaning of this word is much broader. Back in chapter 4 we discussed the concept of heat, or the process by which energy is transferred from a hotter body to a colder one. What wasn t discussed was how energy gets exchanged between objects. Heat exchange can occur via conduction, convection, and radiation. 

In addition, the heat transport at the boundary between the fixed bed and the heat exchange surface is also decisive for the heat exchange. The latter heat transport is generally described by a wall heat-transfer coefficient otB.. It lumps the complex interplay between convective flow at the tube wall and conduction transport by contact between the fixed bed and the heat exchange surface. Heat transport in packed tubes has been investigated and discussed in detail [8, 21]. How-... 

There are a number of other configurations called compact heat exchangers which are primarily used in gas-flow systems where the overall heat-transfer coefficients are low and it is desirable to achieve a large surface area in a small volume. These exchangers generally have surface areas of greater than 650 m2 per cubic meter of volume and will be given a fuller discussion in Sec. 10-7. 

---