# Thermo Lecture 4

 Energy boundary crossing closed system - form of heat or workopen system - (control surface) heat, work, and mass transfer 1st Law of Thermo / conservation of energy principle (total energy entinering the system) - (total energy leaving the system) = (change in total energy of the system)or delta (E = U + KE + PE) Esystem E = U + KE + PEinternal + kinetic + potential Internal Energy U - dependent on the state and mass of the system stationary system System not moving with velocity/changing elevationdelta E = delta U Heat Transfer Q - caused by temperature difference between system and surroundings. Heat transfer into system is energy increase, out of system is decrease. Adiabatic system, Q = 0. Work W - energy transfer at a system boundary, the force acting through a distance or energy to lift a weight. Transfered into system energy increases, out of system energy decreases. Mass flow m - mass flowing into system, energy increases by the amount of energy carried with the mass. m = 0 for closed systems. Heat and Work similarities 1. Boundary phenomena2. systems posses energy, not heat/work3. Associated with process, not state4. path function Total heat transfer/work Calculated by following the process path and adding differential amounts along the wayδQ = Q12 or δW = W12 classical sign convention positive - heat transfer to a system/work done by a systemnegative - heat transfer from a system/done done on a system conduction heat transfer in progressive exchange of energy btwn the molecules of a substance Fourier's law of heat conduction k - thermal conductivity [W/mK]dT/dx - temp gradient, direction of heat flow Convection heat transfer of the energy transfer btwn a solid surface and adj liquid or gas in motion, and involves combined effects of conduction and fluid motion. Newton's law of cooling h - convection heat transfer coe [W/m2K]Ts - surface temp, Tf - bulk fluid temp Radiative Heat Transfer energy in transition from the surface of one body to the surface of another due to electromagnetic radiation. Radiative Heat Transfer Eq. sigma - Stefan-Boltzmann constant, 5.57x10-8 W/m2K4 epsilon - emissivity Electrical Power rate of electrical work done by electrons crossing a system boundaryP = VI Mechanical vs. thermo work force of a distance vs. energy to lift weight angle bten force and displacement vectordelta means it is path dependent Types of Mechanical Work shaft, spring, elastic solid bars, stretching liquid film, raise/accelerate a body AuthorAnonymous ID5774 Card SetThermo Lecture 4 DescriptionThermo Updated2010-02-01T00:12:19Z Show Answers