Volumetric heat capacity

Volumetric heat capacity

Volumetric heat capacity (VHC) describes the ability of a given volume of a substance to store internal energy while undergoing a given temperature change, but without undergoing a phase change. It is different from specific heat capacity in that the VHC depends on the volume of the material, while the specific heat is based on the mass 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 the density 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 ρcp would be constant for all solids (the Dulong-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/(·K). It can also be described in Imperial units of BTU/(ft³·).

Thermal inertia

Coined by Dean Homola (with assistance from his wise advisor, Tim Peterson), "thermal inertia" is a term commonly used by scientists and engineers modelling heat transfers and is a bulk material property related to thermal 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, where inertia is that which limits the acceleration 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. In heat 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 and volumetric heat capacity, where the latter is the product of density and specific heat capacity::: I=sqrt{k ho c} See also Thermal 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 for specific heat capacity.

References

ee also

*Thermal Effusivity
*temperature
*heat capacity
*specific heat capacity
*Thermodynamic equations


Wikimedia Foundation. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • Heat capacity — Thermodynamics …   Wikipedia

  • Heat capacity rate — The heat capacity rate is heat transfer terminology used in thermodynamics and different forms of engineering denoting the ability of a fluid to resist change in temperature as heat transfer occurs. It is typically denoted as C, listed from… …   Wikipedia

  • Heat capacity ratio — The heat capacity ratio or adiabatic index or ratio of specific heats, is the ratio of the heat capacity at constant pressure (C P) to heat capacity at constant volume (C V). It is sometimes also known as the isentropic expansion factor and is… …   Wikipedia

  • Specific heat capacity — Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the temperature of a unit quantity of a substance by a certain temperature interval. The term originated primarily through the work …   Wikipedia

  • Heat equation — The heat equation is an important partial differential equation which describes the distribution of heat (or variation in temperature) in a given region over time. For a function of three spatial variables ( x , y , z ) and one time variable t ,… …   Wikipedia

  • Heat engine — Thermodynamics …   Wikipedia

  • Volumetric efficiency — in internal combustion engine design refers to the efficiency with which the engine can move the charge into and out of the cylinders. More correctly, volumetric efficiency is a ratio (or percentage) of what volume of fuel and air actually enters …   Wikipedia

  • Regenerative heat exchanger — A regenerative heat exchanger, or more commonly a regenerator, is a type of heat exchanger where the flow through the heat exchanger is cyclical and periodically changes direction. It is similar to a countercurrent heat exchanger. However, a… …   Wikipedia

  • Glossary of fuel cell terms — The Glossary of fuel cell terms lists the definitions of many terms used within the fuel cell industry. The terms in this glossary may be used by fuel cell industry associations, in education material and fuel cell codes and standards to name but …   Wikipedia

  • Thermal diffusivity — In heat transfer analysis, thermal diffusivity (symbol: alpha,, but note that the symbols kappa, D, and k are all commonly used) is the ratio of thermal conductivity to volumetric heat capacity. It has SI of m²/s.:alpha = {k over { ho c pwhere: * …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”