Atmospheric_Thermodynamics _II

Atmospheric_Thermodynamics _II - Atmospheric Thermodynamics...

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Unformatted text preview: Atmospheric Thermodynamics –II The first Law of Thermodynamics and applications Prof. Leila M. V. Carvalho Dept. Geography, UCSB The first Law of Thermodynamics • Is the law that describes the relationships between heat, work and internal energy. • It establishes the physical and mathematical framework to understand heating processes in our atmosphere, the formation of clouds, the thermodynamical modifications in parcels in movement, etc… • Let’s explore these relationships and applications… Motivation: Ex: formation of clouds Pressure q Volume expands and the parcel’s temperature decreases. q As it cools the air becomes saturated q When that begins : Lifting Condensation Level (clouds are formed) LCL: Cloud base : Releases Latent heat: The first Law of Thermodynamics provides the physical concepts to understand cloud formation: Heat • Internal Energy u : measure of the total kinetic and potential energy of a gas Kinetic energy: depend on molecular motions -> relationship with temperature Potential energy: changes in the relative position of the molecules due to internal forces that act between molecules (small Closed System definition: • Is the one in which the total amount of matter, which may be in the form of gas, liquid, solid or a mixture of these phases, is kept constant Suppose a closed system with one unity of mass Ø Suppose that this volume receives certain quantity of thermal energy q (joules) by ‘conduction’ and/or radiation. Ø This system may do a certain amount of external work w (also measured in Joules) . 1 2 u u w q- =- Differences will cause changes in the internal energy Where 1 is before and 2 after the change This is the First Law of Thermodynamic s In the differential form Ø dq is the differential increment of heat added to the system, Ø dw is the differential element of work done by the system Ø du is the differential increase in internal energy of the system Changes in du depend only on the final and initial state: functions of du dw dq =- (34) Visualization Volume is proportional to the distance Frictionless Every state of the substance, corresponding to a given position of the piston, can be represented in this diagram below AREA A If the Piston moves outward with the same pressure p, then the work done by the substance in pushing the external force F through a distance dx is: F = pA Fdx dW = pA F = pdV pAdx dW = = If pressure is constant then: (35) p V dV pd V If the substance passes from state A...
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This note was uploaded on 12/28/2011 for the course GEOG 226 taught by Professor Leila during the Fall '09 term at UCSB.

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Atmospheric_Thermodynamics _II - Atmospheric Thermodynamics...

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