5,116 research outputs found
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Effect factors of part-load performance for various Organic Rankine cycles using in engine waste heat recovery
The Organic Rankine Cycle (ORC) is regarded as one of the most promising waste heat recovery technologies for electricity generation engines. Since the engine usually operates under different working conditions, it is important to research the part-load performance of the ORC. In order to reveal the effect factors of part-load performance, four different forms of ORCs are compared in the study with dynamic math models established in SIMULINK. They are the ORC applying low temperature working fluid R245fa with a medium heat transfer cycle, the ORCs with high temperature working fluid toluene heated directly by exhaust condensing at low pressure and high pressure, and the double-stage ORC. It is regarded that the more slowly the system output power decreases, the better part-load performance it has. Based on a comparison among the four systems, the effects of evaporating pressure, condensing condition, working fluid, and system structure on part-load performance are revealed in the work. Further, it is found that the system which best matches with the heat source not only performs well under the design conditions, but also has excellent part-load performance
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Experimental study on transcritical Rankine cycle (TRC) using CO2/R134a mixtures with various composition ratios for waste heat recovery from diesel engines
A carbon dioxide (CO2) based mixture was investigated as a promising solution to improve system performance and expand the condensation temperature range of a CO2 transcritical Rankine cycle (C-TRC). An experimental study of TRC using CO2/R134a mixtures was performed to recover waste heat of engine coolant and exhaust gas from a heavy-duty diesel engine. The main purpose of this study was to investigate experimentally the effect of the composition ratio of CO2/R134a mixtures on system performance. Four CO2/R134a mixtures with mass composition ratios of 0.85/0.15, 0.7/0.3, 0.6/0.4 and 0.4/0.6 were selected. The high temperature working fluid was expanded through an expansion valve and then no power was produced. Thus, current research focused on the analysis of measured operating parameters and heat exchanger performance. Heat transfer coefficients of various heat exchangers using supercritical CO2/R134a mixtures were provided and discussed. These data may provide useful reference for cycle optimization and heat exchanger design in application of CO2 mixtures. Finally, the potential of power output was estimated numerically. Assuming an expander efficiency of 0.7, the maximum estimations of net power output using CO2/R134a (0.85/0.15), CO2/R134a (0.7/0.3), CO2/R134a (0.6/0.4) and CO2/R134a (0.4/0.6) are 5.07 kW, 5.45 kW, 5.30 kW, and 4.41 kW, respectively. Along with the increase of R134a composition, the estimation of net power output, thermal efficiency and exergy efficiency increased at first and then decreased. CO2/R134a (0.7/0.3) achieved the maximum net power output at a high expansion inlet pressure, while CO2/R134a (0.6/0.4) behaves better at low pressure
A unique distant submillimeter galaxy with an X-ray-obscured radio-luminous active galactic nucleus
We present a multiwavelength study of an atypical submillimeter galaxy in the
GOODS-North field, with the aim to understand its physical properties of
stellar and dust emission, as well as the central AGN activity. Although it is
shown that the source is likely an extremely dusty galaxy at high redshift, its
exact position of submillimeter emission is unknown. With the new NOEMA
interferometric imaging, we confirm that the source is a unique dusty galaxy.
It has no obvious counterpart in the optical and even NIR images observed with
HST at lambda~<1.4um. Photometric-redshift analyses from both stellar and dust
SED suggest it to likely be at z~>4, though a lower redshift at z~>3.1 cannot
be fully ruled out (at 90% confidence interval). Explaining its unusual
optical-to-NIR properties requires an old stellar population (~0.67 Gyr),
coexisting with a very dusty ongoing starburst component. The latter is
contributing to the FIR emission, with its rest-frame UV and optical light
being largely obscured along our line of sight. If the observed fluxes at the
rest-frame optical/NIR wavelengths were mainly contributed by old stars, a
total stellar mass of ~3.5x10^11Msun would be obtained. An X-ray spectral
analysis suggests that this galaxy harbors a heavily obscured AGN with
N_H=3.3x10^23 cm^-2 and an intrinsic 2-10 keV luminosity of L_X~2.6x10^44
erg/s, which places this object among distant type 2 quasars. The radio
emission of the source is extremely bright, which is an order of magnitude
higher than the star-formation-powered emission, making it one of the most
distant radio-luminous dusty galaxies. The combined characteristics of the
galaxy suggest that the source appears to have been caught in a rare but
critical transition stage in the evolution of submillimeter galaxies, where we
are witnessing the birth of a young AGN and possibly the earliest stage of its
jet formation and feedback.Comment: 13 pages in printer format, 10 figures, 1 table, accepted for
publication in the A&
Effect of solid solution treatment on microstructure and mechanical properties of extruded MgY12Zn2,5 magnesium alloys
The microstructural evolution of MgY12Zn2,5 magnesium alloys was observed, and the strengthening and toughening mechanism of the alloys were studied. The results showed that the MgY12Zn2,5 alloy after solution treatment with higher content of 14H - LPSO (long - period stacking - ordered structures) could more effectively inhibit the recrystallization and growth of recrystallized grains, and the microstructure was more fine and uniform. And its tensile strength (Rm), yield strength (Rv) were 395 MPa, 308 MPa and elongation (A) 17,5 %, respectively. In contrast, the MgY12Zn2,5 alloy treated at 470 °C for 24 h, whose Rm, Rv, were only 376 MPa, 282 MPa and A 15,5 %, respectively
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