Page 139 - Analysis, Synthesis and Design of Chemical Processes, Third Edition

withstanding the temperatures of reentry; the real need was to protect those inside the space vessel from
the high temperatures generated by friction with the edge of Earth’s atmosphere. This led to the
development of the sacrificial tiles used in the space shuttle. The energy generated by friction is
dissipated by vaporizing these sacrificial tiles, thereby protecting those inside the vessel from the heat.
Only after the correct need was identified was the problem solved.

Examples 4.1 through 4.4 [6–8] illustrate definition of needs.

Example 4.1

Zebra mussels are mollusks that have been known to infest the water intake pipes of water treatment and
electric power plants. Entire towns have been shut down because the infestation of zebra mussels has
halted the supply of water to purification plants. The initial solution to this problem was to remove the
infested zebra mussels manually. Identify the need(s) to alleviate the infestation problem.

The need is for a method to prevent the infestation, because it is undesirable to shut down water treatment
facilities for manual cleaning. If this method is to involve a chemical, it is important to specify the desired
features of this chemical. For example, it should be inexpensive, it must prevent infestation, it should not
harm other wildlife, and it should be removable in the water treatment facility.

Example 4.2

Maintaining a swimming pool, either at home or in a public facility, is both expensive and time
consuming. The water must be tested often, particularly for chlorine. The chlorine additive to a swimming
pool emits a characteristic odor, irritates the eyes, and can fade colors on swimsuits due to its bleaching
effect. Identify a product need.

There might be a need for a method to disinfect the pool water other than adding a chlorine-containing
compound. Suppose a continuous-flow device could be developed that disinfected the pool water as it
passed through the filter system. Is there a need for such a product? (This is one possible alternative to
chlorine. There are others.) Such a device would undoubtedly increase the capital cost of installing a
pool, even though it would save time and the cost of constantly adding chlorine. The unanswered question
is whether pool purchasers would be willing to pay the incremental capital cost. Even though a net
present value or an equivalent annual operating cost calculation, such as that illustrated in Chapter 10,
might prove that the incremental cost of such a device is justified by the savings, it is still unclear whether
people would purchase such a device. Most buyers will not sit down and do an incremental economic
analysis. It is difficult to put a dollar value on the savings in time created by such a device. Clearly, it
would be necessary to get feedback from potential customers before proceeding with development of such
a device.

Example 4.3

Research is under way to develop a magnetic refrigerator [9]. This refrigerator operates by using