Thermal efficiency, indicated

Performance data on some typical tray and compartment diyers are tabulated in Table 12-10. These indicate that an overall rate of evaporation of 0.0025 to 0.025 kg water/(s m") of tray area may be expected from tray and tray-truck diyers. The thermal efficiency of this type of diyer will vary from 20 to 50 percent, depending on the diying temperature used and the humidity of the exhaust air. In diying to very low moisture contents under temperature restrictions, the thermal efficiency may be in the order of 10 percent. The major operating cost for a tray diyer is the labor involved in loading and unloading the trays. About two labor-hours are required to load and unload a standard two-truck tray diyer. In addition, about one-third to one-fifth of a... 

Employing wood chips, Cowan s drying studies indicated that the volumetric heat-transfer coefficient obtainable in a spouted bed is at least twice that in a direct-heat rotaiy diyer. By using 20- to 30-mesh Ottawa sand, fluidized and spouted beds were compared. The volumetric coefficients in the fluid bed were 4 times those obtained in a spouted bed. Mathur dried wheat continuously in a 12-in-diameter spouted bed, followed by a 9-in-diameter spouted-bed cooler. A diy-ing rate of roughly 100 Ib/h of water was obtained by using 450 K inlet air. Six hundred pounds per hour of wheat was reduced from 16 to 26 percent to 4 percent moisture. Evaporation occurred also in the cooler by using sensible heat present in the wheat. The maximum diy-ing-bed temperature was 118°F, and the overall thermal efficiency of the system was roughly 65 percent. Some aspec ts of the spouted-bed technique are covered by patent (U.S. Patent 2,786,280). 

The Intercooled Regenerative Reheat Cycle The Carnot cycle is the optimum cycle between two temperatures, and all cycles try to approach this optimum. Maximum thermal efficiency is achieved by approaching the isothermal compression and expansion of the Carnot cycle or by intercoohng in compression and reheating in the expansion process. The intercooled regenerative reheat cycle approaches this optimum cycle in a practical fashion. This cycle achieves the maximum efficiency and work output of any of the cycles described to this point. With the insertion of an intercooler in the compressor, the pressure ratio for maximum efficiency moves to a much higher ratio, as indicated in Fig. 29-36. 

The thermal efficiency of the process (QE) should be compared with a thermodynamically ideal Carnot cycle, which can be done by comparing the respective indicator diagrams. These show the variation of temperamre, volume and pressure in the combustion chamber during the operating cycle. In the Carnot cycle one mole of gas is subjected to alternate isothermal and adiabatic compression or expansion at two temperatures. By die first law of thermodynamics the isothermal work done on (compression) or by the gas (expansion) is accompanied by the absorption or evolution of heat (Figure 2.2). 

This cycle produces an increase of 30% in work output, but the overall efficiency is slightly decreased as seen in Figure 2-15. An intercooling regenerative cycle can increase the power output and the thermal efficiency. This combination provides an increase in efficiency of about 12% and an increase in power output of about 30%, as indicated in Figure 2-16. Maximum efficiency, however, occurs at lower pressure ratios, as compared with the simple or reheat cycles. 

The [CBT]ig efficiency is replotted in Fig. 3.14, against (Tt,ITx) with pressure ratio as a parameter. There is an indication in Fig. 3.14 that there may be a limiting maximum temperature for the highest thermal efficiency, and this was observed earlier by Horlock et al. [8] and Guha [9]. It is argued by the latter and by Wilcock et al. [10] that this is a real gas effect not apparent in the a/s calculations such as those shown in Fig. 3.9. This point will be dealt with later in Chapter 4 while discussing the turbine cooling effects. 

The thermal efficiency of the gas turbine cycle is not high. It is observed that the exhaust temperature of the turbine is quite high, indicating that... 

Published performance data [38-42] indicate the high development status already reached Volume-specific productivity values up to 750 iNHi/lit./h = 2,3 kWiHv.mf lit. and overall thermal efficiency values from 80 to 90 % have been reported for gas generation processes including feed preheating, gas generation and purification. Unfortunately, no further details are available about reactor design and the process conditions except for very few of them. 

Figure 11. Indicated thermal efficiency, Indolene base fuel, 600 rpm...

Figure 11 displays the energy consumption characteristics of the clear and blended fuels on a thermal efficiency basis. From this information it is apparent that, at equivalent operating conditions, there is essentially no difference in engine efficiency caused by the addition of methanol. The figures also indicate that if the engine can be operated at greater (leaner) equivalence ratios, some increases in thermal efficiency can be expected. 

A small value of thermal resistance indicates a small temperature drop across the heat sink, and thus a high fin efficiency. 

Thermal efficiency. Typical values are usually around 60 % at pilot scale. Pilot plant data and modelling indicate that the carbon conversion is the most important parameter in thermal efficiency optimisation for the ECN gasifier ... 

As indicated in the results, thermal efficiencies are in the range of 27-31% which are 20-30% higher than for those of current biomass power plants. COj emissions and electricity costs by biomass power plants are low compared to those by PV systems as shown in the previous section (6.1). Technology barriers to realize a new biomass power plant seem not so high, however, a high barrier is to find a plantation site. 

Thermal efficiency referred to indicated horsepower [(2546.5 -i-Item 36) X 100]. 

Fig. 13 illustrates the quantity of heat that must be added to the indirectly heated system as a function of PSU to achieve heat equilibrium. Once this system reaches approximately 40% PSU the quantity of heat that must be added reaches an almost constant value indicating that high thermal efficiency is reached as soon as the system approaches this value. 

These preliminary experiments indicate that pyrolysis of agricultural biomass appears to have a good potential for small scale production of fuels for farm operations. The kiln was easily started and operated and would require little supervision for continuous operation. Thermal efficiencies for a self-sustaining process are expected to be about 65%. 

Pyrolysis of agricultural residue was experimentally assessed as a fuel production process for farm applications. A rotary kiln (3.4 m by 0.165 m I.D.) was used due to its ease of operation, commercial availability, low operating costs and ease of start-up and shutdown. Ground oat straw and corn stover at less than 10% moisture were pyrolysed in an indirectly fired continuous-flow rotary kiln located at the University of Sherbrooke. The principle products were char and gas, less than 1% of the feed mass was converted to tar. Calorific values were about 17 MJ/kg for the feed, 26 MJ/kg for the char, and 12 MJ/m3 for the gas. Calculations indicate that the thermal efficiency of a self-sustaining process would be around 65%. 

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