Why do we still feel hot while sweating on a humid beach

Why do we still feel hot while sweating on a humid beach  

Sometimes we feel hot even when sweating, particularly in a humid environment like a beach by the sea on a hot day. Two processes occur in tandem on the skin evaporation (liquid water - gaseous water) and condensation (gaseous water liquid water). It is quite possible that the same water condenses on our face as evaporated earlier. In effect, then, a cycle of liquid gas - liquid occurs. The two halves of this cycle operate in opposite senses, since both exo- and endo-thermic processes occur simultaneously. The net change in energy is, therefore, negligible, and we feel no cooler. 

Conversely, if we were to vaporize exactly 1 mol of water from the skin of a sweaty body, the change in internal energy would be +40 700 J. In other words, the magnitude of the change is identical, but the sign is different. 

The value of AU when condensing exactly 1 mol of water is termed the molar change in internal energy. We will call it AUm (condensation), where the small m indicates that a mole is involved in the thermodynamic process. Similarly, the molar 

We often omit the small m so, from now on, we assume that changes in internal energy are molar quantities. 

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