Size effects Specific heat

Any characteristic of a system is called a property. The essential feature of a property is that it has a unique value when a system is in a particular state. Properties are considered to be either intensive or extensive. Intensive properties are those that are independent of the size of a system, such as temperature T and pressure p. Extensive properties are those that are dependent on the size of a system, such as volume V, internal energy U, and entropy S. Extensive properties per unit mass are called specific properties such as specific volume v, specific internal energy u, and specific entropy. s. Properties can be either measurable such as temperature T, volume V, pressure p, specific heat at constant pressure process Cp, and specific heat at constant volume process c, or non-measurable such as internal energy U and entropy S. A relatively small number of independent properties suffice to fix all other properties and thus the state of the system. If the system is composed of a single phase, free from magnetic, electrical, chemical, and surface effects, the state is fixed when any two independent intensive properties are fixed. 

Effect of Uncertainties in Thermal Design Parameters, The parameters that are used in the basic sizing calculations of a heat exchanger include heat-transfer coefficients tube dimensions, eg, tube diameter and wall thickness and physical properties, eg, thermal conductivity, density, viscosity, and specific heat. Nominal or mean values of these parameters are used in the basic sizing calculations. In reality, there are uncertainties in these nominal values. For example, heat-transfer correlations from which one computes convective heat-transfer coefficients have data spreads around the mean values. Because heat-transfer tubes cannot be produced in precise dimensions, tube wall thickness varies over a range of the mean value. In addition, the thermal conductivity of tube wall material cannot be measured exacdy, adding to the uncertainty in the design and performance calculations. 

Particle Mesh Form Size Effective Diameter Dp- ft- External Bulk Void Density Fraction pb, Lb/cu.ft. Fg External Surface a , sq.ft. Specific Heat Cx, Btu/lb 0 Reactivation Temperature F °F Examples ... 

Specific Heat Release Rate. To utilize many combustion systems most effectively, the maximum power output is to be obtained for the smallest possible size and weight. As a result, the physical size of the combustion chamber as well as all other components should be held to a minimum. This requirement specifies that the specific heat release should be as high as possible. This quantity, usually expressed in energy units per unit volume, unit time, and unit pressure squared, is a measure of the ability to heat the gases used in the thermodynamic cycle. Some idea of the orders of magnitude of prevailing heat releases in combustion equipment can be obtained from the values in Table II. 

Specific heats of metals and hydrides are easily determined and typically fall in the range of 0.1-0.2 cal/g°C. Thermal conductivity is a little more difficult to determine. The conductivity of the metal or hydride phase is not sufficient the effective conductivity of the bed must be determined. This depends on alloy, particle size, packing, void space, etc. Relatively little data of an engineering nature is now available and must be generated for container optimization. Techniques to improve thermal conductivity of hydride beds are needed. As pointed out earlier, good heat exchange is the most important factor in rapid cycling. 

The effects of bubble size and specific areas of heat exchangers on the transient average carbon concentration and bed temperature are presented in Figure 9. It can be seen that the critical bubble size is about 5 cm, which is much smaller than that for the type A combustor. This is because of the relatively small excess air rate used and the large carbon concentration gradient... 

Figure 8. Effect of bubble size and specific area of heat exchangers on the ( )...

Giant molecules zeolites de-ionized" water., Temporary hardness and permanent hardness methods of softening water. Heat capacity (specific heat). Van der Waals attraction, boiling point, melting point-dependence on molecular size. Electric dipole moments of molecules—effect on boiling point. Ionic dissocia-... 

Here a = kp m cp, with kp the Boltzmann constant, m the mass of the atoms and cp their specific heat, T denotes the temperature, 3 l = kpT and To is the optical lattice potential. The influence of evaporation becomes the dominant effect for T 25 // K. Around T 300 /iK these fluctuations become comparable in size to the square of the optical lattice potential ((IF2) Vq 100(neV)2) and atoms then largely escape from the lattice. 

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