Thermal engine cycles

The thermal efficiency of a power cycle is a function of the source and sink temperatures, as well as the enthalpy characteristics of the working fluid. The total efficiency of waste heat recovery is a function of the thermal efficiency of the cycle and the mechanical efficiencies of the turbine, pump, and generator. In typical systems only 10 to 20% of the available heat is recovered. 

The economic justification for this method of heat recovery depends on the source and sink temperatures, the heat load, and the site location. Other 

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Thermal efficiencies of heat exchangers are high 90 to 95%. Thermal efficiencies of thermal engine cycles are low 10 to 20%. Heat pumps permit external energy to be reduced by a factor of 4 to 25 however, the energy required in a heat pump is in the work form, the most expensive energy form. 

Such a thermal engine cycle is shown in Figure l3-9. Evaporation, expansion, condensation, and pressure rise are repeated in a simple Rankine cycle. In the simplest form, "waste heat" is applied to a boiler which provides saturated or superheated vapor to the expander, and the fluid passes on to a condenser, which provides liquid to the pump. The pump raises the pressure and resupplies fluid to the boiler, thereby completing the cycle. The working fluid condenser heat is rejected to a cooling fluid in the condenser, either cooling water or air. The expander shaft work is ultimately used as shaft power to drive compressors or pumps, or to drive a generator to produce electrical power. 

Critoph, R.E., Evaluation of alternative refrigerant - adsorbent pairs for refrigeration cycles. Applied Thermal Engineering, 1996,16(11), 891 900. 

The operative concept is essentially based on the relationship between work and energy, and accounts for the reversibility of processes in thermodynamic cycles (in relation to the development of thermal engines in the 19th century, or steam age cf Kittel, 1989). 

Considering the concepts of reversible processes, a reversible cycle can be carried out for given thermal reservoirs at temperatures and Tl. The Carnot heat engine cycle on a p-V diagram and a T-S diagram, as shown in Fig. 1.4 is composed of the following four reversible processes ... 

Thu K, Chakraborty A, Saha BB, Ng KC. Thermo-physical properties of silica gel for adsorption desalination cycle. Applied Thermal Engineering (in pres). 

Kanniche, M. and Bouallou, C. (2007) C02 capture study in advanced integrated gasification combined cycle. Applied Thermal Engineering, 27, 2693—2702. 

To illustrate the calculation of thermal efficiencies, we analyze in this chapt several common heat-engine cycles. 

In each cycle of its operation, a thermal engine absorbs 1000 J of heat from a large heat reservoir at 400 K and discharges heat to another large heat sink at 300 K. Calculate ... 

Suppose a thermal engine working like a Curzon and Ahlborn cycle, in which an internal heat by internal processes of working fluid appears, assuming ideal gas as working fluid. The Clausius inequality with the parameter of non-endoreversibility becomes... 

The cycle consists in converting potential thermal energy of organic wastes into a combustible gas for heavy duty thermal engines. The efficiency of the gasification process is generally about 70 to 80 % (Figure 1). ... 

While the chemical kinetics of the thermal autoignition process are relatively well understood, means of controlling the ignition timing in the engine cycle when operating in the HCCI mode are still elusive. Chemists and chemical engineers will need to help overcome this obstacle if HCCI is to be executable in automotive practice. 

Sanjay, Y., Singh, O., Prasad BN, 2007, Energy and exergy analysis of steam cooled reheat gas- steam combined cycle. Applied Thermal Engineering 27 2779-2790. 

Solid Sorption Heat Powered Cycles for Cooling and Heat Pumping Applications, Applied Thermal Engineering, 18 (1998), p. 715-729. 

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