TABLE OF CONTENTS One of the tasks of a designer is to select the size of the various pipe runs in the systems and to specify the pipe materials, the placement, slope, and support of this pipe. The usual concern is to be sure to make the pipe large enough, but there are several situations where a minimum refrigerant velocity must be maintained in the pipe which specifies a maximum pipe size.
This chapter explains how to compute the pressure drop, both by the use of equations from fluid mechanics as well as by special-purpose charts. Most often the pipe carries either liquid or vapor in horizontal or vertical runs. Some exceptions are when a mixture of liquid and vapor flow in the pipe. Sometimes the vapor is responsible for lifting liquid in a vertical riser, and in other cases the pipe must be inclined so that open-channel flow results.
Somewhat different requirements apply to the various section of pipe, depending on the location and purpose served in the system. Table 9.1 lists the various categories of piping in an industrial system, the state of the refrigerant, the importance of pressure drop, and whether pitching or trapping is required. The pipes listed in Table 9.1 carry either liquid or vapor, except for several lines in liquid recirculation systems that convey a mixture of liquid and vapor. The almost universal criterion for selecting the pipe size is the pressure drop, and this calculation...
