Results 1 - 10 of 43
Results 1 - 10 of 43. Search took: 0.016 seconds
|Sort by: date | relevance|
[en] Highlights: • A two-dimensional steady-state heat and mass transfer mathematical model is established. • A method of calculating the enthalpy of lithium chloride solution is proposed. • The fitted correlations for heat and mass transfer are obtained. • The diffusion coefficient is modified with the ΔPair to accord with the real situation in dehumidification. • Joint surface renewal rate is proposed for describing the relative motion of the fluids. - Abstract: A two-dimensional steady-state heat and mass transfer mathematical model is established to study the performances of air-to-liquid dehumidifier with PVDF ultrafiltration membrane in liquid desiccant dehumidification in this paper. Terms in this mathematical model are amended with experimental data and improved with the method of calculating enthalpy of lithium chloride solution. The mean Nusselt number in air channel and mean Sherwood number are calculated and the correlations are fitted with the relevant quantities for predicting the heat and mass transfer coefficients. Furthermore, the corresponding heat and mass transfer coefficients are obtained and substituted as initial conditions into the mathematical model. Meanwhile, according to the relationship between the moisture content difference and water vapor partial pressure difference between inlet and outlet on air side, the diffusion coefficient is modified to meet the actual situation of the experiment. Joint surface renewal rate is proposed and regarded as a comprehensive index describing the relative motion of the fluids on both sides in the membrane dehumidification process. After analyzing the influences of controlled variables on mass transfer coefficient divided by density, the conclusion is obtained that the variable solution temperature group is inferior to the variable solution concentration group. The importance of maintaining low solution temperature during the dehumidification process is emphasized.
[en] Highlights: • An energy-efficient refrigeration system with a novel subcooling method is proposed. • Thermodynamic analysis is conducted to discuss the effects of operation parameters. • Two different utilization ways of condensation heat are compared. • The system achieves much higher COP, even higher than reverse Carnot cycle. • Suggested mass concentration for LiCl–H2O is around 32% at a typical case. - Abstract: A new energy-efficient refrigeration system subcooled by liquid desiccant dehumidification and evaporation was proposed in this paper. In the system, liquid desiccant system could produce very dry air for an indirect evaporative cooler, which would subcool the vapor compression refrigeration system to get higher COP than conventional refrigeration system. The desiccant cooling system can use the condensation heat for the desiccant regeneration. Thermodynamic analysis is made to discuss the effects of operation parameters (condensing temperature, liquid desiccant concentration, ambient air temperature and relative humidity) on the system performance. Results show that the proposed hybrid vapor compression refrigeration system achieves significantly higher COP than conventional vapor compression refrigeration system, and even higher than the reverse Carnot cycle at the same operation conditions. The maximum COPs of the hybrid systems using hot air and ambient air are 18.8% and 16.3% higher than that of the conventional vapor compression refrigeration system under varied conditions, respectively
[en] Highlights: • A new system integrating CLC and the H2 and O2 combined cycle was proposed. • The new system has been investigated with the aid of the exergy principle. • The net efficiency of new system is 59.8% with CO2 capture when TIT is 1300 °C. • Efficiency are 8–12% higher than combined cycle with CO2 capture. - Abstract: In the current paper, new systems integrating chemical-looping hydrogen (CLH) generation and the hydrogen (H2) and oxygen (O2) combined cycle have been proposed. The new methane-fueled cycle using CLH has been investigated with the aid of the exergy principle (energy utilization diagram methodology). First, H2 is produced in the CLH, in which FeO and Fe3O4 are used as the looping material. The H2 and O2 combined cycle then uses H2 as fuel. Two types of these combined cycles have been analyzed. Waste heat from the H2–O2 combined cycle is utilized in the CLH to produce H2. The advantages of CLH and the H2 and O2 combined cycle have resulted in a breakthrough in performance. The new system can achieve 59.8% net efficiency with CO2 separation when the turbine inlet temperature is 1300 °C. Meanwhile, the cycle is environmentally superior because of the recovery of CO2 without an energy penalty
[en] Highlights: • A novel solar thermal collector using magnetic nano-particles to create a special array structure is put forward. • A set of experimental facility is set up to test the thermal efficiency of solar collectors. • A comparison among three different solar collectors is conducted under the stagnation experiment. • The normalized temperature difference instantaneous efficiency is separately calculated. - Abstract: A novel solar thermal collector using magnetic nano-particles to create a special array structure to capture solar light to enhance the thermal efficiency is put forward. The Gradient-Index Optics Theory is used to explain the physics of the proposed system. A set of experimental facility is set up to test the thermal collecting efficiency and a comparison between the coating vacuum tube and the conventional vacuum tube is conducted. 180 nm sphere iron nanoparticles were used under the stagnation experiment with water as the working medium. Results show that the magnetic tube performs as well as the coating tubes in lower temperatures and better than ordinary tubes all the time. Heat loss analysis shows the magnetic array structure has a larger ability to capture solar light while a lower ability to prevent heat loss due to the low emissivity layer in the coating. The normalized temperature difference instantaneous efficiency analysis shows that the magnetic tube has a higher top instantaneous efficiency as well as a higher heat loss coefficient, thus resulting a lower thermal efficiency as time passes and temperature rises. The temperature when the efficiency for the coating tube equals to that for the magnetic tube is about 53.8 °C and the temperature when the coating tube and the magnetic tube reach the same is about 73 °C. A comparison between the experimental results and what was available in literatures on the application of nanofluids to solar energy and a similar performance was observed.
[en] Highlights: • A novel compressed air drying method using pressurized liquid desiccant was proposed. • Experiments verified the method and get compressed air with the humidity of 0.9 g/kg. • Energy efficiency was analyzed to show the energy saving potential of the new method. - Abstract: A novel compressed air drying method using pressurized liquid desiccant is proposed in this paper. The compressed air drying system is consisted of a compressed air module, a pressurized liquid desiccant dehumidifier, a liquid desiccant regenerator working in an atmospheric pressure, and other auxiliary components. An experimental apparatus of the pressurized liquid desiccant dehumidifier associated with a compressed air module is established to verify the proposed air drying method experimentally. The results show that, under the pressure of 0.5 MPa, the moisture content in the outlet air can reach 0.9 g/kg. The moisture content of the outlet air reaches 1.4 g/kg under the pressure of 0.3 MPa, and the power consumption of the drying system is 6.17 kJ/g, which is 0.69 kJ/g and 10.1% lower than the conventional compressed air cooling drying system. The dehumidification efficiency is around 0.90, indicating the sufficiently mass transfer between compressed air and solution in pressurized dehumidifier. Besides, the proposed compressed air drying system can use the low-grade heat from the air compressor to regenerate the diluted desiccant solution. The novel air drying method is verified to offer very dry air for industrial application, and shows significant energy saving potential compared with the conventional compressed air cooling drying system
[en] Highlights: • Present exergy analysis to three types of complicated polygeneration systems. • Compare the energy efficiencies of different chemical and power cogeneration plants. • System performance is optimized and energy saving mechanism is presented. • Effects of key parameters on exergy losses and system performance is investigated. • Main sources of exergy losses: coal gasification, SNG methanation, fuel combustion. - Abstract: The energy saving mechanism and the potential of efficiency improvement for coal to synthetic/substitute natural gas and power plant with different schemes and CO2 capture is disclosed through exergy analysis, and the effects of key parameters on exergy losses and system performance are investigated. Scheme A represents the system without CO2 capture but with a full syngas component adjustment and partial recycle of the chemical unconverted gas, Scheme B represents the system without CO2 capture and syngas component adjustment but with partial recycle of the chemical unconverted gas, and Scheme C represents the SNG and power cogeneration with CO2 capture and partial recycle of the chemical unconverted gas but without syngas component adjustment. Results show that the exergy efficiencies of Scheme A, B and C range from 56% to 62%, 57% to 67%, 52% to 62%, respectively. Coal gasification, water–gas-shift process, SNG methanation, and fuel combustion in combined cycle are identified as the main sources of exergy losses. Compared with Scheme A, the exergy efficiency of Scheme B is higher due to the avoidance of exergy losses from syngas adjustment. Scheme C is less energy efficient than Scheme B because of the CO2 capture. Compared with single product systems, the total exergy input of Scheme A, B and C can be reduced by 7.0–11.0%, 14.0–19.0%, 15.0–21.0%, respectively assuming the same product output. The chemical to power output ratio (CPOR) will impact the exergy losses of the whole plant greatly. For all schemes, with the increasing CPOR, the exergy losses for chemical synthesis island will increase whereas the exergy losses for power island will decrease. Especially high CPOR will cause sharp exergy losses of chemical synthesis island. The coupling between exergy losses for chemical synthesis and power islands leads to an optimal CPOR making the total exergy losses of the plant minimal and the system efficiency maximized. The results presented in this paper can help to confirm the potential of system integration and can be a guide for system integration
[en] Highlights: • A novel double-temperature chiller with zeotropic mixture R32/R236fa is proposed. • The chiller is applicable for temperature and humidity independent control system. • Effects of mass fraction, fluid flow rate and temperature on chiller are studied. • The suggested mass fraction of R32 is around 60%. • The maximum COP and refrigerating capacity are 4.17 and 4.49 kW, respectively. - Abstract: A novel double-temperature chiller with zeotropic mixture R32/R236fa is proposed in this paper, and chilled water with two different temperatures is produced, such as low temperature water (T_L_,_o_u_t = 7 °C) and high temperature water (T_H_,_o_u_t = 16 °C). An experimental setup is established to test the performance of the chiller. Effects of mass fraction of R32 in mixture R32/R236fa (M (R32)), T_L_,_o_u_t, T_H_,_o_u_t and the heat transfer media flow rate on the performance of the chiller are studied. When T_H_,_o_u_t is 18 °C, T_L_,_o_u_t is 8 °C and M (R32) is 0.6, COP and refrigerating capacity are 4.11 and 4.42 kW, respectively. COP and refrigerating capacity increase as M (R32) increases. Exhausting pressure of the chiller increases with the increase of M (R32). As M (R32) is 0.6, exhausting pressure is about 1.95 MPa. Compression ratio decreases with the increase of M (R32). When M (R32) increases from 0.3 to 0.6, the compression ratio decreases from 3.0 to 2.9.
[en] Highlights: • Exergy analysis of a process with supercritical water gasification of coal is conducted. • The exergy conversion mechanism of the process is obtained. • The exergy destruction and distribution of the process is analyzed. • A maximum exergy efficiency of 89.18% is obtained. - Abstract: Supercritical water gasification (SCWG) is a promising technology for clean and efficient coal utilization. The exergy analyses on the processes with integrated SCWG of coal and syngas separation are conducted for clear understanding about the exergy distributions in the processes. The energy level of the heat provided for the gasifier is upgraded to the energy level of the syngas, which is driven by the decrease of energy levels from the coal to the syngas. The minimum temperatures of the heat provided for the gasifier are obtained in different coal-water-slurry concentrations (CWSCs). The total exergy destruction firstly increases, and then decreases with increasing CWSC. The maximum total exergy destruction of the process is obtained when the CWSC is approximately 10%. The exergy efficiency of the process has a converse trend with the total exergy destruction. When the CWSC is in the range of 6% and 20%, the maximum exergy efficiency is 89.18%. The origins for the production of the exergy destruction are also studied.
[en] Highlights: • Present techno-economic analysis of SNG and power cogeneration from coal. • Predict cost reduction potential for SNG and power cogeneration. • Current localization level of key technologies in China is investigated. • Investigate role of efficiency upgrade and further localization in cost reduction. - Abstract: The cogeneration of substitute/synthetic natural gas (SNG) and power from coal based plants with CO2 capture is an effective way to improve energy efficiency and to reduce CO2 emissions. In this paper, we evaluate the techno-economic performance of a SNG and power cogeneration technology with CO2 capture. Current localization level (the cost difference of a technology in different nations and districts) of each subunit of this technology is analyzed. The cost reduction potential of this technology is also predicted, and the role of technology localization and efficiency upgrade in cost reduction is investigated based on a range of learning rates and different coal prices from 90$/t to 150$/t. Results show that the unit investment of this cogeneration technology presented in our previous paper is around 1700$/kW currently and the investment of SNG synthesis, coal gasification and combined cycle unit comprises over 60% of the total investment. The equivalent SNG production cost is quite sensitive to coal prices and ranges from 0.15 to 0.50$/Nm3. Through localization, the unit investment of this technology can be decreased by 30% currently. The key technologies including coal gasification, SNG synthesis and high performance gas turbine need further localization because of their relatively low current localization levels and big localization potential. Through cost learning, the future investment of the technology can be decreased to 700–1100$/kW, which may be competitive with the unit investment of IGCC technology with CO2 capture and even may be lower than that of the pulverized coal power plant with CO2 capture. Technology localization and efficiency upgrade will play important roles in cost reduction, which can contribute 300–500$/kW and 125–225$/kW to cost reduction, respectively. The results presented in this paper indicate that the coal to SNG and power technology with CO2 capture is a promising and competitive option for energy saving and CO2 abatement, and can be a support for policy making, technology options etc
[en] Trap-rich CdS nanocrystals were synthesized by employing CdSt2 and sulfur as precursors via thermal decomposition. Furthermore, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), absorption and photoluminescence (PL) spectra were used to characterize structure, morphology and luminescence properties of CdS nanocrystals (NCs). CdS NCs have a broad emission across 500–700 nm under the excitation of blue light with 460 nm, consequently, white light can be produced by mixing broad emission from CdS NCs excited by blue light, with the remaining blue light. In addition, the broad emission generation is closely and inseparably related to surface defects. Moreover, LaMer model was used to explain the phenomenon that the intensity of the trap emission gradually decreases as the reaction time increases in contrast with that of the band-edge emission. - Graphical abstract: Trap-rich CdS nanocrystals were synthesized. Furthermore, white light is produced by mixing broad emission across 500–700 nm from CdS NCs excited by blue light, in combination with the remaining blue light. - Highlights: • Trap-rich CdS nanocrystals were synthesized. • CdS NCs have a broad emission across 500–700 nm under the excitation of blue light. • White light can be produced by mixing broad emission with the remaining blue light