Thermal losses

The efficiency of an induction furnace installation is determined by the ratio of the load usehil power, P, to the input power P, drawn from the utihty. Losses that must be considered include those in the power converter (transformer, capacitors, frequency converter, etc), transmission lines, cod electrical losses, and thermal loss from the furnace. Figure 1 illustrates the relationships for an induction furnace operating at a constant load temperature with variable input power. Thermal losses are constant, cod losses are a constant percentage of the cod input power, and the usehd out power varies linearly once the fixed losses are satisfied. 

P = power input P = electrical loss P = induced power and P = thermal loss. 

The term channel induction furnace is appHed to those in which the energy for the process is produced in a channel of molten metal that forms the secondary circuit of an iron core transformer. The primary circuit consists of a copper cod which also encircles the core. This arrangement is quite similar to that used in a utdity transformer. Metal is heated within the loop by the passage of electric current and circulates to the hearth above to overcome the thermal losses of the furnace and provide power to melt additional metal as it is added. Figure 9 illustrates the simplest configuration of a single-channel induction melting furnace. Multiple inductors are also used for appHcations where additional power is required or increased rehabdity is necessary for continuous operation (11). 

Pure talc is thermally stable up to 930°C, and loses its crystalline bound water (4.8%) between 930 and 970°C, leaving an enstatite (dehydrated magnesium siUcate) residue. Most commercial talc products have thermal loss below 930°C on account of the presence of carbonates, which lose carbon dioxide at 600°C, and chlorite, which loses water at 800°C. Talc is an insulator for both heat and electricity. 

It follows that the efficiency of the Carnot engine is entirely determined by the temperatures of the two isothermal processes. The Otto cycle, being a real process, does not have ideal isothermal or adiabatic expansion and contraction of the gas phase due to the finite thermal losses of the combustion chamber and resistance to the movement of the piston, and because the product gases are not at tlrermodynamic equilibrium. Furthermore the heat of combustion is mainly evolved during a short time, after the gas has been compressed by the piston. This gives rise to an additional increase in temperature which is not accompanied by a large change in volume due to the constraint applied by tire piston. The efficiency, QE, expressed as a function of the compression ratio (r) can only be assumed therefore to be an approximation to the ideal gas Carnot cycle. 

In some activities metabolic energy may be converted to useful work (force distance). At steady state the rate of doing work P = force distance/ time and the thermal losses must balance with metabolism ... 

Ventilation thermal load The heating or cooling load required to compensate for thermal losses resulting from natural or mechanical ventilation. 

Corresponding to the charge in the potential of single electrodes which is related to their different overpotentials, a shift in the overall cell voltage is observed. Moreover, an increasing cell temperature can be noticed. Besides Joule-effect heat losses Wj, caused by voltage drops due to the internal resistance Rt (electrolyte, contact to the electrodes, etc.) of the cell, thermal losses WK (related to overpotentials) are the reason for this phenomenon. 

G. A. White I think I would take exception to the premise that methanation is a low thermal efficiency operation. If you look in some of the publications on methanation as a part of the total project, you will find that the majority of processes turn around and produce steam by burning coal or product gas or something else. So, if you define thermal efficiency by reduction in heating value, I would certainly agree with that. But if you then have to utilize, or you can utilize, this energy in the form of steam, I don t see that methanation represents a thermal loss. If in fact you don t produce steam in excess of what is required in the process, then it should be incorporated in the calculation of thermal efficiency. 

These data indicate that thermal losses during unsteady flame-wall interactions constitute an intense source of combustion noise. This is exemplified in other cases where extinctions result from large coherent structures impacting on solid boundaries, or when a turbulent flame is stabilized close to a wall and impinges on the boundary. However, in many cases, the flame is stabilized away from the boundaries and this mechanism may not be operational. 

TES can be achieved by separating the desorption step (charging mode) from the adsorption step (discharging mode). After desorption the adsorbent and the absorbent can theoretically remain in the charged state without any thermal losses due to the storage period until the adsorption process is activated. 

Qads depends on the actual application. For the heat pump is Qa(h = Qdes-For long-term TES, Qsens cannot be used due to thermal losses. For a desiccant cooling system only Qcond can be used during adsorption. 

Equations 12.7.28 and 12.7.29 provide a two-dimensional pseudo homogeneous model of a fixed bed reactor. The one-dimensional model is obtained by omitting the radial dispersion terms in the mass balance equation and replacing the radial heat transfer term by one that accounts for thermal losses through the tube wall. Thus the material balance becomes... 

ILLUSTRATION 12.9 PRODUCTION OF SULFUR TRIOXIDE IN A FIXED BED REACTOR WITH THERMAL LOSSES... 

However, the energy balance equation appropriate for use in this illustration differs from that employed in the previous case because thermal losses through the reactor walls must be accounted for. It will be of the same general form as equation 12.7.48, but with the wall heat transfer coefficient replaced by an overall heat... 

Flash vacuum pyrolysis (FVP) of the 3-(iV-(pyrimidin-2-yl)imino-l-morpholino)propanoate 179 led to pyrimido-pytimidines 182 and 184, as a result of competition between thermal loss of ethanol or morpholine. The ketenimine 181, being unable to undergo cyclization, underwent [l,3]-ethoxy migration to form 183, leading to 184 (Scheme 28). The ratio of the products was studied on variation of the temperature (400, 530, and 600 °C) and the nature of the amino substiuent (NR1R2 = morpholino, pyrrolidino, N(Me)Ph ) <2004AJC577>. 

Photothermal decomposition of palladium acetate by scanned cw Ar+ laser irradiation produces metal features that exhibit pronounced periodic structure as a function of laser power, scan speed, substrate and beam diameter, as shown in Figures 3 and 4. The periodic structure is a function of the rate at which the film is heated by absorption of the incident laser radiation coupled with the rate at which the heat of the decomposition reaction is liberated. This coupling generates a reaction front that outruns the scanning laser until quenched by thermal losses, the process to be repeated when the laser catches up and reaches unreacted material. Clearly, such a thermal process is also affected by the thermal conductivity of the substrate, the optical absorption of the substrate in those cases where the overlying film is not fully absorbing,... 

Consider the case of pure methanol for which the values of Cp and a are known. Using a specific volume of 0.00127 m3/kg, a temperature of 25°C (298 K), and a compression pressure of 1000 bar, Equation 13.2 predicts the eluent temperature will increase approximately 15°C assuming adiabatic conditions. In actual practice, the increase in eluent temperature entering the column will be lower than this upper limit due to thermal losses in the pump, connecting tubing, and injection system, as well as entropic changes (AS A 0). 

Although [ReH3(dppe)2] does not undergo thermal loss of... 

---