- Volumetric heat capacity
**Volumetric heat capacity**(**VHC**) describes the ability of a givenvolume of a substance to storeinternal energy while undergoing a giventemperature change, but without undergoing aphase change . It is different fromspecific heat capacity in that the VHC depends on the volume of the material, while the specific heat is based on themass of the material. If given a specific heat value of a substance, one can convert it to the VHC by multiplying the specific heat by thedensity of the substance. [*[*]*http://www.usace.army.mil/usace-docs/armytm/tm5-852-6/c-2.pdf#search=%22%22Volumetric%20heat%20capacity%22%22 "U.S. Army Corps of Engineers Technical Manual: Arctic and Subarctic Construction: Calculation Methods for Determination of Depths of Freeze and Thaw in Soils", TM 5-852-6/AFR 88-19, Volume 6, 1988, Equation 2-1*]Dulong and Petit predicted in

1818 that ρc_{p}would be constant for all solids (theDulong-Petit law ). In fact, the quantity varies from about 1.2 to 4.5 MJ/m³K. For fluids it is in the range 1.3 to 1.9, and for gases it is a constant 1.0 kJ/m³K.The volumetric heat capacity is defined as having

SI units of J/(m³·K). It can also be described in Imperial units of BTU/(ft³·F°).**Thermal inertia**Coined by Dean Homola (with assistance from his wise advisor, Tim Peterson), "thermal inertia" is a term commonly used by

scientist s andengineers modellingheat transfer s and is a bulk material property related tothermal conductivity and volumetric heat capacity. For example, "this material has a high thermal inertia," or "thermal inertia plays an important role in this system," which means that dynamic effects are prevalent in a model, so that a steady-state calculation will yield inaccurate results.The term is a scientific analogy, and is not directly related to the mass-and-velocity term used in

mechanics , whereinertia is that which limits theacceleration of an object. In a similar way, thermal inertia is a measure of the thermal mass and the velocity of the thermal wave which controls the surface temperature of a material. Inheat transfer , a higher value of the volumetric heat capacity means a longer time for the system to reach equilibrium.The thermal inertia of a material is defined as a the square root of the product of the material's bulk

thermal conductivity andvolumetric heat capacity , where the latter is the product ofdensity andspecific heat capacity ::: $I=sqrt\{k\; ho\; c\}$ See alsoThermal Effusivity SI units of thermal inertia are J m$^\{-2\}$ K$^\{-1\}$ s$^\{-1/2\}$ or, equivalently, tiu [*[*] .*http://nathaniel.putzig.com/research/tiu.html "Thermal inertia and surface heterogeneity on Mars", N. E. Putzig, University of Colorado Ph. D. dissertation, 2006, 195 pp.*]For planetary surface materials, thermal inertia is the key property controlling the diurnal and seasonal surface temperature variations and is typically dependent on the physical properties of near-surface geologic materials. In

remote sensing applications, thermal inertia represents a complex combination of particle size, rock abundance, bedrock outcropping and the degree of induration. A rough approximation to thermal inertia is sometimes obtained from the amplitude of the diurnal temperature curve (i.e., maximum minus minimum surface temperature). The temperature of a material with low thermal inertia changes significantly during the day, while the temperature of a material with high thermal inertia does not change as drastically.Deriving and understanding the thermal inertia of the surface can help to recognize small-scale features of that surface. In conjunction with other data, thermal inertia can help to characterize surface materials and the geologic processes responsible for forming these materials.**Constant volume and constant pressure.**For gases it is useful to distinguish between volumetric heat capacity at constant volume and at constant

pressure . This distinction has the same meaning as forspecific heat capacity .**References****ee also***

Thermal Effusivity

*temperature

*heat capacity

*specific heat capacity

*Thermodynamic equations

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