Energy density volumetric efficiency

Equation (5.7) indicates that etE is a figure of merit for dielectrics that are to be used at high fields. The various types of capacitor are compared on the bases of volumetric efficiencies and typical working energy densities in Table 5.1. 

Table 5.1 Typical values of volumetric efficiency and energy density for the various types of capacitor...

Capacitor type Volumetric efficiency (pF cm 3) Typical working energy density (mJ cm 3)... 

One of the obstacles to overcome is the largest volume occupied by DMFC (even when the volumetric energy density of methanol is higher than the Li-Ion batteries), due to the low efficiency with the current DMFC technology. 

High-performance electrodes for PEFCs are evaluated by (i) their Pt mass loading per unit electrode surface area, mpt (in mg cm ), (ii) voltage efficiency, = Eceii/Ef ji, (iii) (volumetric) energy density, Wceii = FEceii/lcL (in J L ), (iv) (volumetric) power density, Pceii = joEceii/lcL (in W L ), and (v) specific power, = joEceii/mpt (in W gp/). These parameters are related, as is obvious from their definitions. Yet, it is possible to adjust their values independently to specific requirements of energy-consuming appliances. 

Volumetric Efficiency versus Energy Density. The size and shape of the cell or battery and the ability to effectively use its internal volume infiuence the energy output of the cell. The volumetric energy density (watthours per liter) decreases with decreasing battery volume as the percentage of dead volume for containers, seals, and so on, increases for the smaller batteries. This relationship is illustrated for several button-type cells in Fig. 3.23. The shape of the cell (such as wide or narrow diameter) may also influence the volumetric efficiency as it relates to the amount of space lost for the seal and other cell construction materials. 

Thin flat prismatic sealed lead-acid cells have been designed for portable applications as they offer more flexibility in the design of the battery. They use space more efficiently than cylindrical cells, resulting in a higher volumetric energy density, and the slim design is adaptable to small-footprint equipment. " An exploded view of a typical flat cell is shown in Fig. 24.5. 

The slim or flat rectangular batteries are designed to meet the needs of lightweight and compact equipments. The rectangular shape permits more efficient battery assembly, eliminating the voids that occur with the assembly or cylindrical batteries. The volumetric energy density of batteries can be increased by a factor of about 20%. 

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