# ME 3304 - Ch. 1

 Heat Transfer (Heat) Thermal energy in transit due to a SPATIAL temperature difference. Heat Flux The rate of heat transfer in the x direction per unit area PERPENDICULAR to the direction of transfer q'' = q / A variable: k Conduction Heat Transfer Coefficient PROPERTY CONDUCTION Mechanism, Who?, Equation Diffusion of energy due to random molecular motion Fourier's LawHeat flux, q'' = CONVECTION Mechanism, Who?, Equation Same as conduction + energy transfer due to bulk motion Newton's Law of Cooling q'' = h ( Tsurface - Tfluid ) variable: h Convection Heat Transfer Coefficient W/(m2 * K) NOT A PROPERTY Advection energy transfer due to bulk motion Convection heat transfer is_______ if transferred TO the surface --( Tsurface < Tfluid ) NEGATIVE heat transfer TO the surface Convective heat transfer is________ if heat is transferred FROM the surface --( Tsurface > Tfluid ) POSITIVE heat transfer FROM the surface Forced Convection Flow is caused by external means, such as by a fan, pump, or atmospheric winds. Free (natural) Convection Flow is induced by buoyancy forces, which are due to density differences caused by temperature variations in the fluid. Sensible energy Internal thermal energy of the fluid Latent heat exchange associated with a phase change between the liquid and vapor states of the fluid RADIATION Mechanism, Equation **occurs most efficiently in a vacuum** Energy transfer by electromagnetic waves (or photons) qrad'' = q / A = qrad'' = variable: emissivity variable PROPERTY Ideal Radiator Blackbody: emits radiation at the maximum possible rate = 1 variable: Eb Emissive Power Stefan-Boltzmann Law = 5.67 x 10-8 W/(m2K4) Eb = Incident Radiation may originate from a special source, such as the sun, or from other surfaces to which the surface of interest is exposed. variable: G IRRADIATION = Irradiation energy = (reflected + transmitted + absorbed) energy variable: ABSORBTIVITY Gray surface condition? variable: hr radiation heat transfer coefficient Thermal and Mechanical Energy Equation Internal energy consists of a: 1. Sensible component 2. Latent component 3. Chemical component 4. Nuclear component 1. accounts for translational, rotational, and/or vibrational motion of the atoms composing the matter.2. relates intermolecular forces influencing phase change3. accounts for energy stored in the chemical bonds4. accounts for binding forces in the nucleus Simplify the TME Equation for STEADY STATE conditions. Edot stored = 0 Simplified STEADY-FLOW thermal energy equation Qdot = q = mdot x Cp x ( Tout - Tin ) 1. ideal gas with KE, PE, W = 02. incompressible liquid with KE, PE, W = 0ORideal gas/incompressible fluid with negligible viscous dissipation Surface Energy Balance Edot in - Edot out = 0 q''cond - q''conv - q''rad = 0 Authorkylecaro ID126944 Card SetME 3304 - Ch. 1 DescriptionStudy Material Updated2012-01-12T20:55:14Z Show Answers