Fuel utilization efficiency

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... 

Most new gas and oil-fueled furnaces and boilers have similar efficiencies. The range of efficiency has narrowed with the introduction of minimum efficiency standards for new products sold since 1992. New gas and oil heating equipment currently available in the marketplace have /knnual Fuel Utilization Efficiency (AFUE) ratings of at least 78 to 80 percent. /VFUE is a measure of how efficient a furnace operates on an annual basis and takes into account cycling losses of the furnace or boiler. It does not include the... 

In comparing the fuels, it is important to take into account the utilization efficiencies at the user end. For utilization by the user, fuels are converted to various energy forms, such as thermal, mechanical, and electrical. Studies show that in almost every instance of utilization, hydrogen can be converted to the desired energy form more efficiently than other fuels [6], Table 5 presents the utilization efficiency factors, defined as the fossil fuel utilization efficiency divided by the hydrogen utilization efficiency, for ... 

FIG. 19.9. Conversion ratios and fuel utilization efficiencies. (From Thermal Breeder Consultants Group, Saldiuig, 1977.)... 

Annual Fuel Utilization Efficiency (AFUE) - The measure of seasonal or annual efficiency of a residential heating furnace or boiler. It takes into account the cyclic on/off operation and associated energy losses of the heating unit as it responds to changes in the load, which in turn is affected by changes in weather and occupant controls. 

Ukrainian NPPs have been operating advanced fuel assemblies with Zr alloy-110 and Zr alloy-635 guide tubes (GT) and Zr alloy-110 spacer grids (SG) since 1995. According to the calculations the substitution of the steel by Zr alloy in materials of guide tubes and spacer grids increases the fuel utilization efficiency by 8.2%. Advanced fuel implementation allows to increase fuel burnup by 5-7%. 

Enhanced fuel utilization efficiency and the reduction of natural uranium consumption are affected by the following engineering solutions ... 

The catalytic (supported or unsupported) interface in the vast majority of direct liquid fuel cell studies is realized in practice either as a catalyst coated membrane (CCM) or catalyst coated diffusion layer (CCDL). Both configurations in essence are part of the electrode design category, which is referred to as a gas diffusion electrode, characterized by a macroporous gas diffusion and distribution zone (thickness 100-300 pm) and a mainly mesoporous, thin reaction layer (thickness 5-50 pm). The various layers are typically hot pressed, forming the gas diffusion electrode-membrane assembly. Extensive experimental and mathematical modeling research has been performed on the gas diffusion electrode-membrane assembly, especially with respect to the H2-O2 fuel cell. It has been established fliat the catalyst utilization efficiency (defined as the electrochemically available surface area vs. total catalyst surface area measured by BET) in a typieal gas diffusion electrode is only between 10-50%, hence, flie fuel utilization eflfieieney can be low in such electrodes. Furthermore, the low fuel utilization efficiency contributes to an increased crossover rate through the membrane, which deteriorates the cathode performance. 

Defects of this fuel cell variant are the relatively low fuel utilization efficiency and the high heat losses, just as in the case described above. Also, considerable mechanical stresses may arise in the fuel cell itself because of its considerable temperature gradients and because of the rapid changes in temperature. 

Mini-fuel cells and mobile fuel cells have some specific features. One of the most important jobs of ordinary (large-sized) fuel cells is the highly efficient conversion of chemical fuel energy to electrical energy. For higher fuel utilization efficiency, power plants involving such fuel cells include many peripherals to monitor and regulate the rate of the fuel supply, as weU as external parameters such as temperature and pressure that influence this efficiency. 

Substituting Equation 4.23b into Equation 4.62, the current or fuel utilization efficiency can be expressed as a function of the stoichiometric factor... 

Physically, a current or fuel utilization efficiency value represents the fraction of the fuel converted into current. The remaining fraction of the fuel leaves the cell without reacting or without being consumed for the production of the current. The excess fuel that exits the cell may be recycled back into the cell or may be burnt to produce heat for other system use. 

The overall efficiency of a fuel cell is then represented by a product of all three above-mentioned fuel cell efficiencies, that is, thermal efficiency, voltage efficiency, and current of fuel utilization efficiency, as... 

Faradic efficiency is often called the fuel utilization efficiency (Hf) when applied to the fuel in a galvanic redox reaction ... 

Example 2.4 Stoichiometry and Utilization Consider a portable 20 cm active area fuel cell operating steadily at 0.75 V, 0.6 A/cm. The fuel utilization efficiency is 50%, and the cathode stoichiometry is 2.3. The fuel ceU is expected to run for three days before being recharged. The cathode operates on ambient air, and the anode runs off of compressed hydrogen gas. 

Determine the single-pass fuel utilization efficiency for a 150-plate fuel cell stack with 120 A current output... 

We desire a fuel utilization efficiency of >95% on the anode of a 300-plate, 100-cm -active-area stack. Determine the hydrogen mass flow rate required in the stack as a function of current density. 

Fuel Eocv (V) Maximum Fuel utilization efficiency (%) factor at maximum efficiency (%) ... 

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