Biosystems Engineering Lecture 2: Thermal Coefficients and Convection - Prof. Glenn Brown, Study notes of Heat and Mass Transfer

Download Biosystems Engineering Lecture 2: Thermal Coefficients and Convection - Prof. Glenn Brown and more Study notes Heat and Mass Transfer in PDF only on Docsity! Oklahoma State University Biosystems Engineering BAE 3013 Lecture 2 - 1 BAE 3013 Lecture 2 Today • Thermal coefficients • Convection Oklahoma State University Biosystems Engineering BAE 3013 Lecture 2 - 2 Question: What is the conductive heat transfer into the cab of an air conditioned tractor on the hottest day of the summer? (www.deere.com) Oklahoma State University Biosystems Engineering BAE 3013 Lecture 2 - 3 Thermal Coefficients thermal conductivity: k (W/m oK) density: ρ (kg/m3) specific heat: cp (J/kg oK) volumetric heat capacity: ρcp (J/m3 oK) thermal diffusivity: α = k/ρcp (m2/s) thermal energy per unit volume, (heat storage) U = ρcpT (J/m3) Question: What are the fundamental units for a Watt (W)? Oklahoma State University Biosystems Engineering BAE 3013 Lecture 2 - 4 Return to Fourier’s Law qx”=-k x T ∂ ∂ factor in ρcp into RHS x Tc c kq p p x ∂ ∂ −= ρ ρ " x Uqx ∂ ∂ −= α" This has “transformed” the gradient from temperature to the heat storage. Oklahoma State University Biosystems Engineering BAE 3013 Lecture 2 - 5 An alternative Convection Equation Earlier we had Newton’s Law qx”= h(Ts - T∞) This relation is used to quantify heat transfer from a discreet solid body to a fluid flow. Oklahoma State University Biosystems Engineering BAE 3013 Lecture 2 - 6 To quantify the heat energy that is carried by a fluid flow TQcTcmE pp ρ== && where: Ė = heat energy flow rate (W) m&=mass flow of fluid (kg/s) m&=ρ Q Q = fluid volumetric flow rate (m3/s)