Heat energy, value

The heat energy values of the oils (Table 3) were estimated using the approach outlined in the literature (Livesey, 1984 Peters et al., 1991), and calculated using the equation ... 

Polystyrene has a high heating value, 46,000 kj/kg compared to heating oil, 44,000 kj/kg (46). Thus, incineration for its energy value is another possible appHcation for recovered polystyrene. 

Waste-Heat Boiler. In a waste-heat boder (Fig. 6), the approach AT sets both the amount of the unrecovered energy and the amount of heat-exchange surface. When terms are added for energy value, and surface cost, the optimum occurs when... 

A given value for Aec enables a cost in, say, dollars per gigajoule, to be assigned to the heat energy made available by a heat pump. 

Equation 2-5 gives a value for U based on the outside surface area of the tube, and therefore the area used in Equation 2-3 must also be the tube outside surface area. Note that Equation 2-5 is based on two fluids exchanging heat energy through a solid divider. If additional heat exchange steps are involved, such as for finned tubes or insulation, then additional terms must be added to the right side of Equation 2-5. Tables 2-1 and 2-2 have basic tube and coil properties for use in Equation 2-5 and Table 2-3 lists the conductivity of different metals. 

Frcc-energy values at lOOO C approximately equal to the heats of decomposition, assuming that A5 0. 

The correctness of this statement is to be inferred from the exact agreement between the values of the mechanical equivalent of heat obtained by different methods. Thus, in Joule s second series of experiments, mechanical work is directly converted into heat in the first and third series, it is indirectly transformed through the medium of electro-magnetic energy in the fourth series, the energy of an electric current is converted into heat the identity of the values of J so obtained implies a complete conversion of the initial forms of energy into heat energy. 

A pipeline of 100 mm outside diameter, carrying steam at 420 K, is to be insulated with a lagging material which costs 10/m3 and which has a thermal conductivity of 0.1 W/m K. The ambient temperature may be taken as 285 K, and the coefficient of heat transfer from the outside of the lagging to the surroundings as 10 W/m2 K. If the value of heat energy is 7.5 x 10 4 /MJ and the capital cost of the lagging is to be depreciated over 5 years with an effective simple interest rate of 10 per cent per annum based on the initial investment, what is the economic thickness of the lagging ... 

In formulating a set of bond-energy values we first calculated the energies of formation of molecules from experimental values of the heats of combustion of the compounds6 and thermochemical data pertaining to the products of combustion—carbon dioxide, water, nitrogen, etc. The same values for the latter quantities were used as previously.4... 

We can estimate the effect of energy dissipation on liquid heating and values of flow parameters corresponding to arising oscillations in the flow. We assume that the density of the fluid and its thermal conductivity are constant. Then, the energy equation attains the form... 

Heat energy must be supplied continuously to keep the temperature from falling while the endothermic reaction proceeds. Otherwise, the temperature would quickly fall below the minimum value at which H2 synthesis is spontaneous. For this reason, the production of H2 (and ultimately of fertilizer) requires considerable amounts of... 

It is thus seen that heat capacity at constant volume is the rate of change of internal energy with temperature, while heat capacity at constant pressure is the rate of change of enthalpy with temperature. Like internal energy, enthalpy and heat capacity are also extensive properties. The heat capacity values of substances are usually expressed per unit mass or mole. For instance, the specific heat which is the heat capacity per gram of the substance or the molar heat, which is the heat capacity per mole of the substance, are generally considered. The heat capacity of a substance increases with increase in temperature. This variation is usually represented by an empirical relationship such as... 

So far we have not touched on the fact that the important topic of solvation energy is not yet taken into account. The extent to which solvation influences gas-phase energy values can be considerable. As an example, gas-phase data for fundamental enolisation reactions are included in Table 1. Related aqueous solution phase data can be derived from equilibrium constants 31). The gas-phase heats of enolisation for acetone and propionaldehyde are 19.5 and 13 keal/mol, respectively. The corresponding free energies of enolisation in solution are 9.9 and 5.4 kcal/mol. (Whether the difference between gas and solution derives from enthalpy or entropy effects is irrelevant at this stage.) Despite this, our experience with gas-phase enthalpies calculated by the methods described in this chapter leads us to believe that even the current approach is most valuable for evaluation of reactivity. 

The enthalpy change of a reaction, AH, is the heat energy change when the reaction is carried out at constant pressure. It is necessary to express these values under standard conditions. For enthalpy changes measured under standard conditions, the symbol AH is used. Thermodynamic standard conditions are ... 

Nutritional energy values are usually measured in kilocalories (kcal or simply calories). One kilocalorie represents the amount of heat required to raise the temperature of 1 kg of water by 1°C at room temperature. In the metric system, the energy value is expressed in joules (J), with 1 kcal being equal to 4.184 kilojoules (kJ). 

The total amount of heat energy will be the sum of these values (AHcalorimeter + AHwater). However, before we can sum these values, we must make sure the units match. We can either convert the kilojoules to joules or the joules to kilojoules. In this case we will convert the joules to kilojoules and then add the values. 

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