XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX''"> 1.3 Thermal Material Properties
MD Nastran thermal material properties include thermal conductivity, constant pressure specific heat, density, dynamic viscosity, internal heat generation, and temperature range and latent heat quantities associated with phase change phenomena.
Conductivity
Thermal conductivity is an intrinsic property of all materials and in the absence of any other mode of heat transfer, provides the proportionality constant between the flow of heat through a region and the temperature gradient maintained across the region (Fourier’s Law). Thermal conductivity is generally a mild function of temperature, decreasing with increasing temperature for solids and generally increasing with increasing temperature for liquids and gases. Additionally, within a solid, thermal conductivity can vary due to material orientation (anisotropy). Preferential paths for heat flow can result. MD Nastran allows for temperature-dependent and directionally dependent thermal conductivity.
Specific Heat and Heat Capacitance
Specific heat is another intrinsic material property. When multiplied by the volume and density of material, the quantity of interest is referred to as heat capacitance. Given a closed thermodynamic system, heat capacitance provides the proportionality constant between heat added or subtracted from the system and the resultant temperature rise or fall of the system (dq = C * dT). Since heat capacitance only multiplies the time derivative of temperature in the heat conduction equation, specific heat is usually only relevant in the solution of transient thermal phenomenon. We will note later that advection introduces a pseudo-transient flavor even in steady-state analysis and therefore the specific heat and density of the advecting fluid are needed in these calculations.
Specific heat is also slightly temperature dependent. However, in typical heat transfer problems, the largest variations in specific heat are generally attributed to materials changing phase.
Density
For the purpose of conserving mass, the density cannot be allowed to vary with temperature. Since grid points are fixed in space in MD Nastran thermal analysis, if the density were to change with temperature, Density*Volume would also be changing, thus altering the system mass.
Table 1‑1 provides several sets of consistent units which may be used by MD Nastran for the various material properties.
Table 1‑1 Table 1‑2 Thermal Conductivity | Table 1‑3 W/m-oC | Table 1‑4 Btu/hr-ft-oF |
Table 1‑5 Specific Heat | Table 1‑6 J/kg-oC | Table 1‑7 Btu/lbm-oF |
Table 1‑8 Density | Table 1‑9 kg/m3 | Table 1‑10 lbm/ft3 |
Table 1‑11 Dynamic Viscosity | Table 1‑12 kg/m-sec | Table 1‑13 lbm/ft-hr |
Table 1‑14 Enthalpy | Table 1‑15 J/kg | Table 1‑16 Btu/lbm |
Table 1‑17 Latent Heat | Table 1‑18 J/kg | Table 1‑19 Btu/lbm |