collector case the numbers would be nine times as great and pipe distances would be three times as great. One basic flow unit is the flowrate (pounds/second) flowing through a single collector. The 41,472 collector case is merely nine 4608 collector networks arranged in a 3 by 3 square configuration and connected to the central power plant (located in the center of the central network) by pipes containing 4608 flow units. The pipe layout in Figure 10 is a reasonable design, but no attempt has been made to optimize the pipe network geometry. Since the same geometry is employed for all five types of flow systems a valid comparison of economic performance for each fluid is achieved. Within this geometry the design of the piping subsystem is optimized to achieve minimum system cost. The pipe material used in each pipe network depends upon the temperature and the fluid transported. Carbon steel, which is the least expensive material considered, is used for low temperature applications (below 430°C) when the fluid does not cause corrosion attack of the piping. Above a temperature of 430°C low alloy steel is used, but it costs about four times as much as carbon steel for the same pipe dimensions. For the liquid metal (NaK) system all metal piping, pumps, heat exchangers and other surfaces that come in contact with the heat transport fluid (NaK) must be composed of stainless steel to resist corrosion attack. Stainless steel pipe is approximately 12 times more expensive than an equivalent size carbon steel pipe. To allow for thermal expansion,two possible approaches are use of either "omega" expansion loops or a "sawtooth" pipe configuration between anchor points. In the present analysis 68 feet of pipe are required to connect two stationary anchor points 47 feet apart (68 = 47 x ), and it is assumed that the collector mounting equipment and other features of the energy collection system do not interfere with any part of the fluid transport pipe network. Thus, for the steam-water transport system, 68 feet of pipe are required for the hot steam line at 510°C to connect
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