Heat efficiency

A special coil configuration is used to heat thin strips of metal that caimot be heated efficiently with a coil that encircles the load, as the strip thickness is small compared to the depth of penetration. The transverse flux induction coil is positioned on either side of a strip to produce a uniformly heated strip with good efficiency in a much smaller space than conventional radiant or convective strip heating furnaces (6). 

Rapid cool-down by helium heat transfer is made possible at an interior of ca 100 Pa (0.1 atm). A convective fan transfers heat efficiently from the interior hot surfaces of the furnace to water-cooled base and wall parts. 

The reaction between carbon monoxide and hydrogen is exothermic (Ai/gQQp. = —100.5 kJ or 24.0 kcal) and plants must be designed to remove heat efficiently. In order to control the exotherm, CO conversions are typically maintained well below the equiUbrium conversion, 45% at 523 K. This necessitates a substantial recycle of carbon monoxide and hydrogen. 

Furnaces and boilers sold today must by law have annual fuel utilization efficiency of at least 78 to 80 percent. Gas water heaters operating this way as space heaters are equivalent to the efficiency of pre-1992 furnaces and boilers which had space heating efficiencies typically in the mid-60 percent range. However, the combined efficiency for space and... 

To act as an efficient sterilizing agent, steam should be able to provide moisture and heat efficiently to the article to be sterilized. This is most effectively done using saturated steam, which is steam in thermal equilibrium with the water from which it is derived, i.e. steam on the phase boundary (Fig. 20.5). Under these circumstances, contact with a cooler surface causes condensation and contraction drawing in fresh steam and leading to the immediate release ofthe latent heat, which represents approximately 80% ofthe heat energy. In this way heat and moisture are imparted rapidly to articles being sterilized and dry porous loads are quickly penetrated by the steam. 

Water has a high heat of vaporization, ie, the amount of heat needed to convert from liquid to gas phase. In conjunction with its high heat capacity, this property allows water to carry away heat efficiently as it evaporates, which accounts for the cooling effects of perspiration. 

Automatic operation linked to process outlet temperature while on the bad side of absolute combustion is potentially hazardous because the heater outlet temperature will drop as a result of the reduced heating efficiency of the fuel. The automatic control will then call for more... 

Several workers have employed monomodal cavities for microwave chemistry on the sub-gram scale. In some cases in which monomodal cavities have been used7, special benefits of so-called focussed microwaves have been claimed. As mentioned earlier, the dielectric properties of a sample can alter substantially with temperature and/or with changing chemical composition. Hence, regardless of whether multi-modal or unimodal cavities are employed, frequent tuning may be necessary if heating efficiency is to be retained. This aspect has often been overlooked by proponents of focussed microwaves. The nett result is that transfer of microwave conditions between monomodal to multi-modal cavities is usually facile. With the MBR (which had a tunable multimodal cavity), Cablewski et al. performed five reactions that had been conducted earlier on the gram scale or below with focussed microwaves (T. Cablewski, B. Heilman, P. Pilotti, J. Thorn, and C.R. Strauss, personal communication see also Ref. 117 for conference poster). These were scaled-up between 40- and 60-fold and reaction conditions... 

Typically, viscous materials transfer energy poorly. With conventional con-ductively heated vessels, thermal decomposition on the walls can occur at the same time as incomplete reaction towards the center of the sample. Such substantial thermal gradients can afford sub-optimal conversions. That in turn leads to loss of product and renders product isolation difficult. Furthermore, at high temperatures, heat losses with conductive heating increase and the efficiency declines. With microwave systems, these problems are not as pronounced and in some cases, even the heating efficiency can increase with temperature. 

To investigate these findings further the authors determined heating rates of the employed multimode instruments and the Discover unit, once again using toluene as solvent. After 10 min irradiation at a constant maximum power output for each microwave reactor, different final temperatures were measured (Fig. 17). Furthermore, it could be shown that the observed differences in temperature are not only related to the different heating efficiencies of the instruments but also to the specific vessel material [27]. Usually the vessel material itself is not completely microwave-transparent and therefore it is at least partially responsible for heating of the irradiated solvent via conventional thermal conduction [42]. 

In general terms, capillary electrophoresis is the electrophoretic separation of a substance from (usually) a complex mixture within a narrow tube filled with an electrolyte solution which is normally an aqueous buffer solution. Although one example of separation performed in a totally non-aqueous solution has been reported (50), neutral and slightly basic buffer solutions are generally used. Small tubes dissipate heat efficiently and prevent disruption of separations by thermally driven convection currents. Therefore, capillary electrophoresis can use... 

Still another multi-reactor approach is to divide the MTG reaction into two steps as shown in Figure 7. In the first step, methanol is partially dehydrated to form an equilibrium mixture of methanol, dimethyl ether and water over a dehydration catalyst. About 15% of the reaction heat is released in this first step. In the second step, this equilibrium mixture is converted to hydrocarbons and water over ZSM-5 catalyst with the concomitant release of about 85% of the reaction heat. Though this two step approach does not have any of the inherent complications of the previously mentioned multibed reaction systems, it leaves one with a substantial amount of the reaction heat (85%) still to be taken over one catalyst bed. This requires a fairly high recycle stream to moderate the temperature rise over the second reactor. Such a high recycle design would require careful engineering in order to transfer heat efficiently from the reactor effluent to the recycle gas and reactor feed. However, this two stage reactor system is the simplest of the fixed-bed systems to develop. 

J. H. Omstead and P. S. Grimes, "Heat Efficiency Improvements Through Chemical Recovery of Waste Heat", IECEC 729046 (1972). 

For a given f and e, the heating efficiency is directly proportional to E and tan 6. The product of these two parameters is called the loss index, e". Loss index of 0.2 or more results in good heatability 0.08-0.2, fairly good heatability 0.01-0.08, poor heatability and under 0.01 there is little or no response (2). 

Summary. Microwaves have been employed successfully to heat and subsequently cure silicone compositions to give elastomers and foams. Microwaves were found to be responsible for heating the silicone polymers and the heat, thus generated, was responsible for the curing. In order for a silicone polymer to be heated efficiently, it should contain some substituents [e.g.,... 

The residual carbon contents at different axial locations of the combustor were measured in the pilot plant tests (Li et al., 1991), as shown in Fig. 18. These data show that axial variations in carbon content with temperature (from 810 °C-923 °C) are as a whole rather slight, but mean carbon content increases with decreasing excess air ratio. Besides, for excess air ratios greater than 1.2, the carbon content at the top of the combustor is somewhat less than that at the bottom, while for excess air ratio less than 1.2, the opposite tendency is evident. In conclusion, for this improved combustor, an excess air ratio of 1.2 is considered enough for carbon burn-out, leading to reduced flue gas and increased heat efficiency as compared to bubbling fluidized bed combustion. That is probably attributable to bubbleless gas-solid contacting for increased mass transfer between gas and solids in the fast fluidized bed, as explained by combustion kinetics. 

High excess air ratio will result in increasing sensible heat loss in the flue gas, while insufficient air supply means low combustion efficiency. To gain high heat efficiency, a rational excess air ratio needs to be specified. Figure... 

SOFCs also produce high-quality heat with their working temperature of 850°C. This makes combined heat and power production possible with SOFC systems. The total efficiency can then reach 85%. Advanced conventional cogeneration of heat and power can reach total efficiencies up to 94% with electrical efficiencies over 50%. This occurs only at full load. A high electrical efficiency is preferred over heat efficiency, since this results in a higher energy with the initial energy source better utilized, in terms of practical end-use. 

In spite of these reported successes, the Madelung cyclization offers the following disadvantages (i) the drastic conditions necessary limit its application to the synthesis of unsubstituted or alkyl- and aryl-substituted azaindoles (ii) the reaction is often, if not always, intractable and Hi) yields are erratic, often unreproducible, and subject to such variables as stirring and heating efficiency, purity of starting materials, quality (or manufacturer ) of reagents, and operator. 

This heat must be dissipated by cooling, which can be done but only to a limited extent The ability to dissipate heat efficiently is usually the factor that limits the speed of electrophoresis, since excess heat leads to non-uniform electrophoresis and a decrease in resolution. The main reason for this is convection in matrix-free electrophoresis in solution, and the effect of temperature on viscosity and diffusion. High temperatures can also lead to denaturation of proteins and nucleic acids. The thinner the layer used for electrophoresis, the more readily is the heat dissipated, and the higher the voltages that can be used. The thickness of the layer will be a compromise between a desire to have a thin layer to minimise heat problems whilst maintaining sufficient capacity to ran samples that can be detected easily. Consis-... 

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