Fusion, specific latent heat

The heat energy that is required for a material to undergo a change of phase (J). Specific latent heat of fusion... 

The curve crosses the y axis at a negative value of your choosing. Between the plateaus, the slope is approximately linear. The plateaus are crucial as they are the visual representation of the definition of latent heat. The first plateau is at 0°C and is short in duration as only 334kJ.kg 1 is absorbed in this time (specific latent heat of fusion). The next plateau is at 100 °C and is longer in duration as 2260kJ.kg-1 is absorbed (specific latent heat of vaporization). 

Polymer compounds vary considerably in the amount of heat required to bring them up to processing temperatures. These differences arise not so much as a result of differing processing temperatures but because of different specific heats. Crystalline polymers additionally have a latent heat of fusion of the crystalline structure which has to be taken into account. 

Extrusion blow moulding of bottles has been successfully accomplished in reeent years by attention to the points mentioned above. It is to be noted here that UP VC has a much lower average specific heat between the proeessing temperature and room temperature than polyethylene and, being essentially amorphous, no latent heat of fusion. This leads to much less heat needing to be removed on cooling of mouldings and very short cycle times are possible. 

Example 1.—If the specific heats of the solid and liquid forms are linear functions of temperature, show that the melting-point is determined by dividing the latent heat of fusion by the difference between the specific heats of the solid and liquid forms at the melting-point (cf. Taramann, Kryst. and Schmelz., p. 42). 

Qf298° is —111540cal/mole specific heat, 0.262cal/g at 25° latent heat of fusion is -5355cal/mole at 310° (Ref 6)... 

Latent heat of sublimation at -84°C Latent heat of fusion at triple point Flammable limits in air Auto-ignition temperature Gross heat of combustion at 15.6°C, 1 atm Specific heat, gas at 25°C, 1 atm Cp Cv... 

One would expect the enthalpy of sublimation (d) to be the largest of the four quantities cited. Molar heat capacities are quite small, on the order of fractions of a kilojoule per mole-degree. (Remember that specific heats have values of joules per gram-degree.) All of the heats of transition (or latent heats) are positive numbers and on the order of kilojoules per mole. Since the heat of sublimation is the sum of the heat of fusion and the heat of vaporization, AHsubl must be the largest of the three. 

Specific heat at 25°C Latent heat of fusion Latent heat of vaporization Coefficient of linear expansion at 25°C Thermal conductivity at 25°C... 

Scottish chemist, physicist, and physician. Professor of chemistry at Glasgow. He clearly characterized carbon dioxide ( fixed air ) as the gas which makes caustic alkalies mild, and distinguished between magnesia and lime. He discovered the latent heats of fusion and vaporization, measured the specific heats of many substances, and invented an ice calorimeter. 

Next, the thermal properties of the dye must be such that absorption of the laser energy will result in dye diffusion but not in decomposition. The melting temperature Tm, the latent heat of fusion, AH, and the specific heat for these dyes were determined by differential scanning calorimetry using a DuPont 990 Thermal Analyzer. The data are given in Table II. No thermal decomposition products for these dyes were detected upon heating to 600 °C for 20 msec. 

Baxter (B3) uses an enthalpy-flow temperature method, due originally to Dusinberre (D5, D6) and Eyres et al. (E4), whereby the movingboundary effect is reduced to a property variation. To begin with, the melting of a slab of finite thickness initially at the fusion temperature is considered. At the surface of the melt, which is of the same density as the solid, a heat transfer boundary condition is applied. The technique takes into account latent heat effects by allowing the specific heat to become infinite at the fusion temperature in such a way that... 

This concept presumes that the calorific input of the fire may be partly absorbed by the endothermic changes of the mineral substances employed in the formulation of the mastic. Thus, for example, such latent heat as the heat of fusion, heat of vaporization, heat of sublimation, and heat of transition (the heat required to change a unit mass of a given substance from one crystalline structure to another) all can absorb considerable energy which would otherwise be used to raise the combustible substrate to an ignition point. The efficiency of these fire-resistant minerals can also be adjudged by their specific heat values. 

For latent heat, we look up the corresponding entry in the tables for either the latent heat of vapourisation (or simply the heat of vapourisation) or the heat of fusion, depending on the type of phase change encountered (liquid to vapour and solid to liquid, respectively). These quantities are in units of energy per unit mass and are given for a specific reference state (often the 1 atm boiling point or melting point of the substance). 

Some of the unique properties of water that stem from it s dipolar character are as follows (1) an excellent solvent (2) thermal expansion (3) high surface tension and viscosity (4) high dielectric constant (5) high specific heat and (6) high latent heats of fusion and evaporation. 

Referring to Table XVI-1, let us first, consider the latent heat of fusion. We observe that in practically every case it is but a small fraction of the heat of vaporization. That is, the atoms or molecules are pulled apart only slightly in the liquid state compared with the solid, while in the vapor they are completely separated. Of course, this holds only for pressures low compared to the critical pressure near the critical point, the heat of vaporization reduces to zero. To be more specific, we notice that in the metals the heat of fusion is generally three or four per cent of... 

Very pure liquid water can be supercooled at atmospheric pressure to temperatures well below 0°C. Assume that 1 kg has been cooled as a liquid to -6 C. A small ice crystal (of negligible mass) is added to seed" the supercooled liquid. If the subsequent change occurs adiabatically at atmospheric pressure, what fraction of the system freezes and what is the final temperature What is 5,ou] for the process, and what is its irreversible feature The latent heat of fusion of water at 0°C = 333.4 J g l, and the specific heat of supercooled liquid water = 4.226 J g-1 °C I. 

Solid Water—Influence of Prcssuro on Melting-point—Different Kinds of leo— Density—Vapour Pressure—Expansion-—Compressibility —Specific Heat— Latent Heat of Fusion—Colloidal Ice... 

The following properties belong to the calorimetric category (1) specific and molar heat capacities, (2) latent heats of crystallization or fusion. It will be shown that both groups of properties can be calculated as additive molar quantities. Furthermore, starting from these properties the molar entropy and enthalpy of polymers can be estimated. 

The above formula for the solubility, in which also the corrections for the temperature dependence of the latent heat of fusion AH were taken into account, has been very extensively tested by Hildebrand on the solubility of iodine in a very large number of solvents (violet solution, p. 342). Since the specific cohesion (p. 359) of iodine is very high (y/UjV — 14.1), the solubility line only approaches the ideal line for solvents with similarly large specific cohesion, such as Snl4 (11.7) and Sg (12.7), molten sulphur (Table 33). 

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