Heat exchangers sizing problem

To actually build a commercial-sized side entry reactor is another problem. Chem. Eng. News (1997) reports on how this was cleverly done by using a reactor somewhat like a shell-and-tube heat exchanger which used porous walled tubes. 

Internal flows of the type here being considered occur in heat exchangers, for example, where the fluid may flow through pipes or between closely spaced plates that effectively form a duct Although laminar duct flows do not occur as extensively as turbulent duct flows, they do occur in a number of important situations in which the size of the duct involved is small or in which the fluid involved has a relatively high viscosity. For example, in an oil cooler the flow is usually laminar. Conventionally, it is usual to assume that a higher heat transfer rate is achieved with turbulent flow than with laminar flow. However, when the restraints on possible solutions to a particular problem are carefully considered, it often turns out that a design that involves laminar flow is the most efficient from a heat transfer viewpoint. 

Pyrolysis vessels can range from 3 to 20 m in volume. Towards the upper end of the size range, heat transfer limitations occur and it is necessary to use heat exchanging pipes internally to assist with heat transfer. The problem with an array of heat exchanging pipes internally however is that they are susceptible to fouling and coking by a carbonaceous residue. 

A second kind of problem encountered in heat exchanger analysis is the determination of the heal transfer rale and the outlet temperatures of the hot and cold fluids for prescribed fluid mass flow rales and inlet temperatures when the type and size of Ihe heat exchanger are specified. The heat transfer surface area of the heat exchanger in this case is known, but Ihe outlet temperatures are not. Here the task is to determine the heat transfer performance of a specified heat exchanger or to determine if a heat exchanger available in storage will do the job. 

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