Heat capacities, specific

To measure qp, which is equal to A//, we construct surroundings that retain the heat, and we observe the temperature change. Then, we relate the quantity of heat released (or absorbed) to that temperature change through a physical property called the specific heat capacity. 

You know from everyday experience that the more you heat an object, the higher its temperature that is, the quantity of heat (q) absorbed by an object is proportional to its temperature change  

Every object has its own heat capacity, the quantity of heat required to change its temperature by 1 K. Heat capacity is the proportionality constant in the preceding equation  

If we know c of the substance being heated (or cooled), we can measure its mass and temperature change and calculate the heat absorbed or released  

In general, the thermal conductivities of liquid mixtures and gas mixtures are not simple functions of composition and the thermal conductivity of the components. Bretsznajder (1971) discusses the methods that are available for estimating the thermal conductivities of mixtures from a knowledge of the thermal conductivity of the components. 

If the components are all nonpolar, a simple weighted average is usually sufficiently accurate for design purposes  

The specific heats of the most common organic and inorganic materials can usually be found in the handbooks. 

Approximate values can be calculated for solids and liquids by using a modified form of Kopp s law, which is given by Werner (1941). The heat capacity of a compound is taken as the sum of the heat capacities of the individual elements of which it is composed. The values attributed to each element for liquids and solids, at room temperature, are given in Table 8.2 the method is illustrated in Example 8.6. 

Kopp s rule does not take into account the arrangement of the atoms in the molecule and, at best, gives only very approximate, ballpark values. 

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Reactor heat carrier. Also as pointed out in Sec. 2.6, if adiabatic operation is not possible and it is not possible to control temperature by direct heat transfer, then an inert material can be introduced to the reactor to increase its heat capacity flow rate (i.e., product of mass flow rate and specific heat capacity) and to reduce... 

Example 9.1 A process involves the use of benzene as a liquid under pressure. The temperature can be varied over a range. Compare the fire and explosion hazards of operating with a liquid process inventory of 1000 kmol at 100 and 150°C based on the theoretical combustion energy resulting from catastrophic failure of the equipment. The normal boiling point of benzene is 80°C, the latent heat of vaporization is 31,000 kJ kmol the specific heat capacity is 150 kJkmoh °C , and the heat of combustion is 3.2 x 10 kJkmok. ... 

The most direct effect of defects on tire properties of a material usually derive from altered ionic conductivity and diffusion properties. So-called superionic conductors materials which have an ionic conductivity comparable to that of molten salts. This h conductivity is due to the presence of defects, which can be introduced thermally or the presence of impurities. Diffusion affects important processes such as corrosion z catalysis. The specific heat capacity is also affected near the melting temperature the h capacity of a defective material is higher than for the equivalent ideal crystal. This refle the fact that the creation of defects is enthalpically unfavourable but is more than comp sated for by the increase in entropy, so leading to an overall decrease in the free energy... 

Here, erfcjc is the eiTor function complement of jc and ierfc is its inverse. The physical properties are represented by a, the thermal dijfusivity, which is equal to lejpCp, where k is the drermal conductivity, p is the density and Cp, the specific heat capacity at constant pressure. The surface temperature during this iiTadiation, Tg, at jc = 0, is therefore... 

LATENT HEAT OF VAPORIZATION, kJ/kg. SPECIFIC HEAT CAPACITY OF LIQUID, kJ/kg.K SET TEMPERATURE, OC ... 

The dimensionless number Le is called the Lewis number (m Russian literature it is called the Luikov number). The Lewis number incorporates the specific heat capacity of humid air pCp (J/m C), the diffusion factor of water vapor in... 

The specific heat capacity of humid air calculated per kilogram of dry air is... 

Hence, Sensible heat = Air-mass flow rate (q , kg s ) x Specific heat capacity of humid air at constant volume (c ), which is 1.012 kj kg K. ... 

Because the specific heat capacity of the water vapor is different from that of the dry air, the true dry-bulb mixed-stream air temperature can be determined only by means of a heat balance. 

Heat storage, body The amount of heat that can be stored in a body due to its temperature, mass, and specific heat capacity. 

The heat capacity of a subshince is defined as the quantity of heat required to raise tlie temperature of tliat substance by 1° the specific heat capacity is the heat capacity on a unit mass basis. The term specific heat is frequently used in place of specific heat capacity. This is not strictly correct because traditionally, specific heal luis been defined as tlie ratio of the heat capacity of a substance to the heat capacity of water. However, since the specific heat of water is approxinuitely 1 cal/g-°C or 1 Btiiyib-°F, the term specific heal luis come to imply heat capacity per unit mass. For gases, tlie addition of heat to cause tlie 1° tempcniture rise m iy be accomplished either at constant pressure or at constant volume. Since the mnounts of heat necessary are different for tlie two cases, subscripts are used to identify which heat capacity is being used - Cp for constant pressure or Cv for constant volume. Tliis distinction does not have to be made for liquids and solids since tliere is little difference between tlie two. Values of heat capacity arc available in the literature. ... 

Cp = Specific heat capacity (tube or cold side), Btu/(lb)(°F)... 

Convective heat transmission occurs within a fluid, and between a fluid and a surface, by virtue of relative movement of the fluid particles (that is, by mass transfer). Heat exchange between fluid particles in mixing and between fluid particles and a surface is by conduction. The overall rate of heat transfer in convection is, however, also dependent on the capacity of the fluid for energy storage and on its resistance to flow in mixing. The fluid properties which characterize convective heat transfer are thus thermal conductivity, specific heat capacity and dynamic viscosity. 

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