Analysis of the exergy balance of green leaves
In this paper we analyse the exergy balance of green leaves. The exergy source comes from the direct and diffuse solar radiation absorbed in the leaves, while exergy destruction occurs as the consequence of evapotranspiration, of internal flows and of leaf metabolism. Exergy storage occurs namely in the form of glucose which is a result of photosynthesis and oxygen release into the environment. Based on the exergy balance equation we show how to evaluate the leaf metabolic rate and the survival threshold conditions. In the absence of the exergy source (solar radiation) we can also understand how the trees use the exergy stored for their metabolic needs. This process is similar to the discharge of a capacitor through a resistance, which is a characteristic found in every living structure.
Keywords: exergy storage, exergy destruction, exergy balance, green leaves, solar radiation, glucose, evapotranspiration, internal flows, leaf metabolism, photosynthesis, oxygen release, metabolic rate, survival threshold, trees