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Архивы рубрики: Stirling Engines for Low-Temperature Solar-Thermal Electric Power Generation

Gas Spring Hysteresis

The Stirling thermodynamic cycle undergoes both pressure and volume variations. Since it is a closed cycle, the Stirling engine chamber functions as a gas spring to the power piston (Beta-type and Gamma-type engines) or both displacer and power pistons (Alpha-type engine). Since the thermodynamic process that occurs in a gas spring is not perfectly reversible,

Regenerator Effectiveness

The regenerator is a counterflow heat exchanger. However, unlike conventional heat exchangers, it does not involve two distinct working fluids as “hot stream” and “cold stream.” In addition, heat transfer from the hot stream to the regenerator material and then to the cold stream does not happen simultaneously. During the first half of the cycle,

Heat Transfer

In addition to low viscous dissipation, a good heat exchanger should provide enough surface area to transfer the required heat to the working fluid with the least possible temperature drop. The difference between heat exchanger wall temperature, Tw and the temperature of the working fluid that passes through the heat exchanger, T, is expressed in

Fluid Flow Dissipation

Unidirectional Flow The unidirectional flow regime is the classical approach for studying the pressure drop across heat exchangers and corresponding flow dissipation as discussed in [39, 40]. In this approach, the pressure drop, Ap, is computed as, AP=2 u2= 4 V 2 ^ Aau —- ► Figure 3.1: Nonlinear resistor model for fluid flow through

Heat Exchangers

“Heat exchanger” is a broad name for the heater, cooler, or regenerator in Stirling engine. The heater is responsible for transferring heat from outside of the engine chamber to the working fluid, whereas the cooler transfers the thermal power in the opposite direction. The regenerator, however, absorbs heat from the working fluid when the fluid

Stirling Cycle and Non-Idealities

A Stirling engine cycles through four main processes: cooling, compression, heating and expansion. Ideally, the thermodynamic cycle will be equivalent to a Carnot cycle and will achieve the highest possible thermodynamic efficiency. However, the actual cycle diverts from its ideal model and exhibits lower output power and lower efficiency due to non­idealities in engine components

Conclusions

A promising case was outlined for the use of distributed solar-thermal-electric genera­tion, based on low temperature-differential Stirling engine technology in conjunction with state-of-the-art solar thermal collectors. Although the predicted efficiencies are modest, the estimated cost in $/W for large scale manufacturing of these systems is quite attractive in relation to conventional photovoltaic technology. Nonimaging CPC

System Cost Analysis

The system cost per watt (CPW) of peak electricity output is an important figure of merit for judging cost effectiveness of investment in an electrical generation system. Since investors (system owners) prefer a short period after which the revenue from energy sold offsets the initial investment, the output power of the system should be maximized

System Efficiency

The efficiency of a solar-thermal collector, nsTC, as measured experimentally, is given By, (2.1) Where n0 is the maximum collector efficiency, Ui and U2 are the thermal loss coefficients, G is the power density of incident sunlight, Tm is the mean temperature of the collector in the Kelvin scale (K), and Tamb is the ambient

Stirling Engines

The Stirling Engine has been in existence for many years, spread over two centuries. The research and development on Stirling cycle machines has been documented in open literature such as references [33, 34, 35]. The Stirling engine converts heat to mechanical Table 2.1: Comparison of market available STCs. Assumptions: G=1000 W/m2, tCarnot = 66%, Tamb