Energy The First Law of Thermodynamics

When applied to closed (constant-mass) systems for which the only form of energy that changes is the internal energy, the first law of thermodynamics is expressed mathematically as... 

The engineering science of transport phenomena as formulated by Bird, Stewart, and Lightfoot (1) deals with the transfer of momentum, energy, and mass, and provides the tools for solving problems involving fluid flow, heat transfer, and diffusion. It is founded on the great principles of conservation of mass, momentum (Newton s second law), and energy (the first law of thermodynamics).1 These conservation principles can be expressed in mathematical equations in either macroscopic form or microscopic form. 

It will be instructive to look now a little more closely at internal energy. The first law of thermodynamics is formulated in differential form as... 

The law of conservation of energy (the first law of thermodynamics) states that energy cannot be created or destroyed but only changed from one form to another. We will apply this principle to the energy balance of a leaf, which occurs in an environment with many energy fluxes. We can summarize the various contributors to the energy balance of a leaf as follows ... 

Once the continuum hypothesis has been adopted, the usual macroscopic laws of classical continuum physics are invoked to provide a mathematical description of fluid motion and/or heat transfer in nonisothermal systems - namely, conservation of mass, conservation of linear and angular momentum (the basic principles of Newtonian mechanics), and conservation of energy (the first law of thermodynamics). Although the second law of thermodynamics does not contribute directly to the derivation of the governing equations, we shall see that it does provide constraints on the allowable forms for the so-called constitutive models that relate the velocity gradients in the fluid to the short-range forces that act across surfaces within the fluid. 

The conservation of energy can be stated and utilized entirely in terms of macroscopic variables. A transformation of state may occur due to exchange of heat, performance of work and change in chemical composition. Each of them is associated with a change in energy. The First Law of thermodynamics states that ... 

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