查看更多>>摘要：The importance of considering the water price in the analysis of the impact of dry versus hybrid condensing systems in the thermo economical performance of solar tower plants was demonstrated in this work. The dry condensing system consists of several induced-draft air-cooled condenser cells (ACCs) and the hybrid system consists of a parallel system where the condensing steam is split between the ACCs and a surface steam condenser where circulating water is cooled in a wet mechanical-draft cooling tower. The influence of the operating parameters of either the dry or wet cooling systems on the cooling load and fan power consumption were studied. Then, for a given condensing system (a system with a defined number of installed ACCs units and cooling tower units) and given the dry-air and wet-bulb air temperatures, the operating parameters were optimized to maximize the revenues of the power plant. This optimization depends on the water-to-electricity price ratio R, showing that at low ambient temperature when this ratio increases it is not profitable to turn on the cooling towers since the water cost is not counterbalanced by the higher cycle efficiency obtained with the lower condensation temperature. Finally, the annual operation and the LCOE and NPV of the CSP plant located in Dunhuang were analyzed for both dry and hybrid condensing systems with different number of ACCs and wet towers, showing that the most cost-effective configuration is the 16 ACCs with 3 wet cooling towers for water-to-electricity price ratio R = 4 ($/m(3))/($/kWh(e)) and R = 5 ($/m(3))/($/kWh(e)), but for R = 10 ($/m(3))/($/kWh(e)), the best option is with only 2 wet towers.
查看更多>>摘要：Organic Rankine cycle (ORC) has been widely used to utilize low-grade waste heat from low, medium, and hightemperature heat sources. Meanwhile, the research of the ORC operates in the cryogenic temperature has also attracted much attention due to the increasing requirement of liquid natural gas (LNG). However, there is still a lack of experimental research on the cryogenic ORC. In this paper, the experimental study of a cryogenic ORC using a semi-hermetic scroll expander and propane (R290) has been investigated. Liquid nitrogen is used as the cryogenic cold source in this system while the circulation water is used to simulate the low-grade waste heat. The system performance of utilizing the cold energy of the liquid nitrogen and thermal energy of the circulation water has been investigated. First, the effects of the evaporation pressure and pressure drop on system performance are examined. Moreover, the system performance between the regenerative organic Rankine cycle (RORC) and basic organic Rankine cycle (BORC) has been compared. The experimental results indicate that evaporation pressure has a significant effect on system performance, and different optimum evaporation pressure will be obtained under different liquid nitrogen mass flow rates. The maximum electrical power 673.59 W, system thermal efficiency 6.78%, and cold energy utilization efficiency 12.32% can be obtained, while the evaporation pressure and liquid nitrogen mass flow rate are 1.36 MPa and 120 kg/h, respectively. What's more, the results also indicate that the pressure drop exhibits a high sensitivity on system performance, and there is a clear linear proportional relationship between pressure drop and electrical power. Furthermore, the comparison results show that RORC has a better system performance than BORC. The experimental results provide design and optimal operation strategy for the cryogenic organic Rankine cycle.
El-Said, Emad M. S.Gohar, Mohammed A.Abdelaziz, Gamal B.Ali, Aml...
14页
查看更多>>摘要：In this research, a double pass solar air heater with a corrugated absorber plate and built-in external reflector is adopted to improve its thermo-hydraulic performance. The proposed solar air heater is tested with five tilt angles: 0 degrees, 5 degrees, 10 degrees, 15 degrees and 20 degrees. Data obtained from the proposed heater are compared with the conventional design without reflector under a typical seven air flow rates 11, 13, 15, 17, 20 and 25 l/s. The measured results are reported based on some parameters such as thermal, exergy, thermo-hydraulic efficiencies, cost heat unit and temperature differences. The heater with external reflector improves the performance parameters when compared with the conventional heater. Also, the air flow rate has a strong effect on enhancement of the thermal and thermo-hydraulic efficiencies and production cost. The energy input configuration has been shown to be the superior effect on the enhancement of heater performance than the others effects. The maximum effectiveness and achieved average temperature differences for proposed heater were 0.74 and 26.5 degrees C, respectively. The maximum improvements in average thermal and thermo-hydraulic efficiencies for proposed heater were 19.33% and 19.84% respectively. The maximum value and enhancement ratio of average exergy efficiency for proposed heater was 1.14% and 27.01% respectively. The minimum cost heat unit is achieved using proposed heater estimated by about 0.0047 $ and maximum 93.11% reduction. The optimum values of the performance parameters of the proposed heater under study are obtained when the mass flow rate of flowing air and tilt angle are 25 l/s and 20 degrees respectively. The current study is considered as an attempt to open the research way to new design depends on maximize utilization of the available solar energy.
查看更多>>摘要：This work investigates the effects of an additively manufactured (AM) evaporator on two-phase loop thermosyphon performance. The thermosyphon employs a radially finned, air-cooled condenser connected to an aluminum side-heated evaporator by nylon tubing. Two evaporator surfaces were examined: one with smooth conventionally machined aluminum channels and the other with channels additively manufactured by selective laser melting (SLM). The loop thermal performance and the operational instabilities were characterized for different working fluid charge volumes using water and ethanol. The instabilities were quantified using the maximum fluctuation amplitude of the evaporator wall temperature. Results show that increasing the input power decreases the total resistance and lessens the corresponding instabilities. Low fluid charges result in better thermal performance and lower evaporator temperature instabilities, but they reduce the loop's maximum heat transport capacity. The peak in condenser resistance was found to serve as a good indicator for the end of geysering. Finally, the AM evaporator resulted in slightly higher thermal resistances compared with the conventionally machined version; however, it decreased temperature fluctuations at the heat source.
查看更多>>摘要：Heliostat field aiming strategy significantly affects the safety and operational efficiency of the Solar Power Tower (SPT) system. Heliostats installed in fields are likely to show deviations of optical properties from design specification to some extent. Such deviations generally reflect in the surface curvatures and normal directions of heliostat facets. These differences can give rise to the inevitable degradation of optical performance, impacting the execution effect of the pre-designed aiming strategy. Focusing spot distortion with an inappropriate aiming strategy possibly leads to overheated local areas or component damages. To cope with this error and to improve the light concentration performance, an aiming strategy optimization approach with post installation calibration was proposed in this paper. An equivalent parameter model was developed based on heliostat parameters, producing a more accurate description of optical performance. The adopted heliostat parameters were obtained by the parameter identification method. The parameter identification was formulated by photographed solar flux images and simulated flux distributions. The aiming strategy optimization model of heliostat field was built with obtained identification parameters, and the optimization goal considers utilized solar power absorbed by the heat transfer fluid and flux distribution uniformity. The simulation results showed substantial improvement from the proposed aiming strategy.
查看更多>>摘要：The China VI natural gas engine is based on the theory of the air-fuel ratio method, leading to a high exhaust temperature, large heat load and difficult cooling. The paper carried out a thermal balance experiment of the China VI natural gas engine under different working conditions. A dual-loop organic Rankine cycle system is designed to reduce the difficulty of cooling system and improve the thermal efficiency. The high-temperature loop uses water as working fluid to recover the heat of engine exhaust gas and recirculation exhaust gas. The low-temperature loop recovers the heat from cooling water and waste heat of the high-temperature loop. The high-temperature and low-temperature loops are coupled through a shared heat exchanger. The results show that the China VI natural gas engine has a higher and more stable waste heat temperature than traditional engines and is more adaptable to waste heat recovery under variable operating conditions. For fixed evaporation temperature, with the increase of inlet temperature of the expander, the net output power of high-temperature loop increases first and then decreases, reaching the maximum value at about 800 K. In the low-temperature loop working fluids R601a, R601b, R600, R600a and R12333zd, The maximum net output power of the waste heat recovery system based on the combination of water and R12333zd is approximately 75.4 kW under the rated condition, which is 22.24% of the rated power of the engine.
查看更多>>摘要：Day-and-night radiative sky cooling has emerged as a potential alternative to conventional cooling technologies such as refrigeration-based air conditioning and evaporative wet cooling. Both radiative cooling and evaporative cooling can passively achieve sub-ambient cooling without consuming electricity. Although both cooling techniques are subject to impacts from various weather conditions, the extents of the impacts under the same conditions are not well understood. In this work, we experimentally and theoretically study the thermal performances of a passive radiative cooler and a passive evaporative cooler when exposed to a clear night sky. We show that evaporative cooling is better suited for high-temperature and low-humidity weather conditions, with the measured sub-ambient temperatures of the radiative and evaporative coolers being-13.5 degrees C and-15.0 degrees C, respectively, at a low relative humidity of 13% and a high ambient temperature of 26.0 degrees C. On the other hand, radiative cooling is relatively more resilient than evaporative cooling under high-humidity and/or low temperature weather conditions, with the measured sub-ambient temperatures of the coolers being-11.5 degrees C and-10.5 degrees C, respectively, at a slightly higher relative humidity of 32.0% and a slightly lower ambient temperature of 17.0 degrees C. Depending on water availability and weather conditions, both evaporative cooling and radiative cooling can be adopted as mutually supplemental cooling technologies.
查看更多>>摘要：Elastocaloric cooling represents a potentially higher efficiency cooling technique that is also potentially more environmentally friendly than conventional technologies. Elastocaloric devices have now been investigated for some time for this purpose, with materials that are Cu-based, Fe-based or Ni-based. These devices are highly promising, but their main drawback is the lifetime of the devices. A solution could be to activate the devices by compression instead of tension. An active elastocaloric regenerator operating under compression composed of eight NiTi tubes was built and tested in a flow system to evaluate its performance and lifetime. Two regenerator configurations were tested, one with only the NiTi tubes in the regenerator and one with the addition of a flow distributor to improve the thermal exchange between the tubes and the heat transfer fluid. The flow system used was also optimized and modified to reach the best operating conditions. A maximum temperature span of 5 K could be reached by this regenerator and a temperature span of 0.4 K for a cooling power of 1071 W kg- 1. Moreover, under compressive cycling, the regenerator could withstand more than 100 000 cycles without failure.
查看更多>>摘要：Additive manufacturing technology with metal powder has facilitated the production of innovative and even more complex heat sinks. The layer-additive process offers a wide range of geometries that may be exploited for advanced cooling purposes and the final identification of the best heat sink configuration has to deal with other constraints imposed by the specific application. This contribution focuses on the thermal and fluid dynamic characterization of water cooling annular channels for applications in internal combustion engine components, where also the load-bearing capacity is requested together with the cooling performances. The heat transfer inside the annular channel was enhanced by pin fins arrays that were manufactured by selective laser melting technology in AISI 316L stainless steel. Four pin fins arrays that differ in dimensions and geometries were experimentally tested over a range of mass flow rates to compare their pressure losses and heat transfer performances against those of the smooth annular channel. Furthermore, the test coupons were analysed through optical non-destructive techniques to characterize their geometrical morphology in terms of conformity with the designed model, surface roughness and waviness. In the investigated channel Reynolds number range (from 2000 to 12,000), the pin fins arrays with the largest height-to-pin diameter ratio show better thermal performances (Nu/Nu(0) always greater than 2), however their heat sink efficiencies are above unity only for Re < 3000. In addition, the 45 degrees oriented pin arrangement seems the most promising geometry due to high thermal efficiency, lighter weight and slightly lower manufacturing cost.
查看更多>>摘要：There is increasing interest in decision support software tools that evaluate the techno-economic potential of distributed energy system technologies for deployment in combined heat and power (CHP) applications, such as commercial buildings, microgrids, and connected communities. This trend is particularly evident among end-users looking to integrate renewable resources with more traditional CHP technologies for on-site generation and enhanced resiliency. However, many of these software tools do not account for part-load and off-design characteristics of prime mover and heat recovery equipment, resulting in lower accuracy for both the optimal selection and sizing and the economic value proposition of integrated hybrid renewable energy-CHP systems. Microturbine technology is an attractive distributed energy resource whose performance is sensitive to both part-load and off-design (i.e., excursions of ambient conditions away from the design point temperature and pressure) operating conditions but is widely unreported. In the present work, we address this deficiency by developing a detailed, thermodynamic model of a commercial 200 kW microturbine CHP system and paramaterizing results for incorporation into the Renewable Energy Optimization (REopt) tool developed by the National Renewable Energy Laboratory. The details of the microturbine model, including model benchmarking and validation, are presented. Microturbine off-design modeling includes part-load analysis, assessment of ambient sensitivities, and mapping heat recovery heat exchanger response to hot water grade requirements. The model is then exercised in several illustrative examples to depict the numerous factors which alter electric power, electric efficiency, and hot water recovery. Model results show, for example, predictions of a 4 percentage point electric efficiency range occurring between intake air temperatures of -18 to 50 degrees C. Likewise, the model closely predicts the 25 % loss in heat recovery while at -18 degrees C and the 8 % gain in heat recovery while at 35 degrees C. An additional case shows how heat recovery may increase or decrease by 9.5 % of the design value when changing the return water temperature plus-or-minus 22 degrees C. In particular, the impact of ambient conditions on best-possible microturbine performance is conveyed through hourly simulations of the system subjected to the weather of different geographic locations within the United States.
NSTL
Elsevier