Efficiency thennal

Pollution control such as the reduction of nitrogen oxides, halocarbons and hydrocarbons from flue gases [37] is another important field of plasma-assisted chemistry using non-thennal plasmas. The efficiency of plasma chemical reactions can be enhanced by introducing catalysts into the plasma [38, 39]. 

The photo-thennal detoxification unit uses photo-thennal reactions conducted at temperatures higher than those used in conventional photochemical processes (200 to 500°C, rather than 20°C) but lower than combustion temperatures (typically greater than 1000°C). At these temperatures the developer claims that photochemical reactions are energetic enough to destroy wastes quickly and efficiently without producing complex and potentially hazardous by-products. 

Power Generation Station. The turbine-generator is raled at 12.5 megawatts and is sized to handle the full plant system output plus all internal plantloads. The dual-admission turbine has a high-pressure steam inlet for steam produced by the receiver and a low -pressure inlet for steam produced from thermal storage. The rated turbine thennal-to-electric efficiency from receiver to steam is 35%. The efficiency is 25% from the lower quality thermal storage system. 

Show that the thennal efficiency of this cycle is given by... 

Equations (5.7) and (5.8) are known as Carnot s equations. In Eq. (5.7) the smallest possible value of I (2cl is zero the corresponding value of Tc is the absolute zero of temperature on the kelvinscale. As mentionedin Sec. 1.5, this occurs at (—273.15°C). Equation (5.8) shows tliat the thennal efficiency of a Carnot engine can approach miity only when Tu approaches infinity or Tc approaches zero. Neither of these conditions is attainable all heat engines therefore operate witli thennal efficiencies less than unity. The cold reservoirs naturally available on eartli are die atmosphere, lakes and rivers, and the oceans, for which Tc — 300 K. Hot reservoirs are objects such as furnaces where the temperature is maintainedby combustionof fossil fuels and nuclear reactors where the temperature is maintainedby fission of radioactive elements. For these practical heat sources, T 600 K. Witii these values,... 

Tills is a rough practical limit for the thennal efficiency of a Carnot engine actual heat engines are irreversible, and their thermal efficiencies rarely exceed 0.35. 

Steam enters die turbine of a power plant operating on the Rankine cycle (Fig. 8.3) at 873.15 K (600°C) and exhausts at 30 kPa. To show die effect of boiler pressure on die perfoniianceof die cycle, calculate the thennal efficiency of the cycle and die quality of die exhaust steam from the turbine for boiler pressures of 5000,7500, and 10 000 kPa. 

S. Kasahara, S. Kubo, K. Onuki, M. Nomura, Thennal efficiency evaluation of HI synthesis/concentration procedures in thennochemical water splitting IS process . International Journal of Hydrogen Eneigy, 29, 579-587 (2004). 

Although the surface of a fabric can be significantly enhanced by physical/thennal means, such as singeing and calendering, the development of chanical coatings such as Madison Filter s (formerly Scapa Filtration s) Primapor (Fig. 3.30) has led to the production of still more efficient filter media. The use of stretched PTFE m branes in liquid filtration has also been reported although it is suspected that the rather delicate nature of this material will restrict its use to niche applications. 

The auto thennal operation of these plants (self-sustaining the reactions involving oxidation of SO2 to SO3) depends on the gas composition. Auxiliary gas cleaning and reheating equipment is provided in these plants for efficient and smooth working. 

Finally, there are several obvious computational facilities such as heat balances and thennal efficiency calculations which could be of value in optimizing station efficiency under rapidly changing operating conditions. 

In ceramics, the heat flow is primarily due to phonon generation, and the thermal conductivity is generally lower than that of metals. Crystalline structures, such as alumina and beryllia, are more efficient heat conductors than amorphous structures such as glass. Organic materials used to fabricate printed circuit boards or epoxy attachment materials are electrical insulators and highly amorphous, and tend to be very poor thennal conductors. 

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