Comparison of Thermal Design Methods

Thermal design methods that address engineering uncertainties can be divided into two types the first uses the random values of the parameters directly and the second uses dimensionless factors, which are known as engineering hot spot factors. 

The thermal design methods can also be divided into deterministic, semistatistical, and statistical methods according to the different ways they combine various uncertainties. The direct deterministic method uses values of random parameters directly to account for engineering imcertainties. It is usually employed during the preliminary stage of the core design. All the parameters are taken at their worst values and are assumed to occur at the same time and at the same location. Such a cumulative approach is highly conservative. 

Therefore, it is reasonable to introduce a statistical method to deal with engineering uncertainties. An intermediate approach, so-called semistatistical methods, is also widely used as a compromise between the deterministic and statistical methods. In the semistatistical method, the subfactors are divided into two groups of cumulative contributors and statistical contributors and then two different approaches can be taken the semistatistical vertical approach and the semistatistical horizontal approach, based on different combination schemes [30], 

Hot spot factors consider the effects of the uncertainties separately. This means that each subfactor is evaluated in an independent manner, relative only to a specific uncertainty and without respect to other uncertainties. However, different types of 

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