**1. Introduction**

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119, 265-271, 1997.

When you read a standard textbook on thermodynamics (like [1-3]) as one of the most fundamental formulae you will find

$$
\delta Q = TdS\tag{1}
$$

indicating that the (process) quantity heat (*δQ*) is obviously closely linked to the (state) quantity entropy (d*S*), here both written as infinitesimal quantities.

If, however, you do the same with a standard textbook on heat transfer (like [4] with 1024 pages or [5] with 1107 pages), you will find entropy neither in the index of these books, nor in the text.

There may be two reasons for that: Either entropy has turned out to be irrelevant for a heat transfer analysis or entropy is ignored deliberately in the heat transfer community in spite of its relevance. What is true is a yet open question and can only be answered when thermody‐ namic considerations are taken into account.

In thermodynamics the relevance of entropy with respect to heat transfer is beyond any controversy, it is the heat transfer community that has to be persuaded of its relevance. This can best be done by showing the advantages of including entropy in a heat transfer analysis as well as showing the disadvantages one has to face when entropy is ignored.
