Bianco, VincenzoScarpa, FedericoTagliafico, Luca A.Abd Alla, Sara...
9页
查看更多>>摘要：The share of renewables in the electric power generation is rapidly increasing and shifting the buildings heating demand to electricity represents a sustainable solution to decrease the fossil fuel dependency. In this paper, the maximum share of heating demand that can be switched to electricity by using heat pumps, according to the power market capacity, is estimated. By determining market price, plants generation and fuel consumption, the optimal share is calculated in terms of carbon emissions minimization. The methodology is developed with the support of a bid stack model (BISM) that performs an hourly simulation of the electricity market. Firstly, the analysis is led considering values of the heat pumps coefficient of performance, COP, in the range between 2 and 4. Then a focus is made on the COP dependence on local climatic conditions. In addition, three different time schedules of heat pumps activity are modelled to simulate the final users' habits. Italy is considered as a case study to test the model. Italian market conditions are particularly favourable for the heat pumps utilization. The analysis is developed ex-post for the year 2019 as well as an outlook for the 2030 is provided. For the 2019 results show that the Italian electricity market allows a penetration of heat pumps in the range of 10%-56% for COP values between 2 and 4. In 2030 switching rates in the order of 5%-10% are estimated due to tighter market conditions.
查看更多>>摘要：Efficient management of energy in buildings necessitates the accurate evaluation of the air conditioning (AC) system performance. Ideally, the system must be operated with its cooling capacity matching the cooling load demand, and with maximum possible performance. This paper presents a simplified method that can predict cooling capacity in operative AC installations with limited input information. It is developed using an artificial neural network (ANN) with Bayesian regularization. The training data are generated by numerical simulations of operating scenarios representing the real system operation. The refrigerant temperatures at the inlet and outlet of the evaporator and the condenser are selected as inputs for the proposed method to predict the cooling capacity in relevant operating scenarios, thereby eliminating the need for a flow meter and facilitating implementation on operative systems. The ANN model is developed to capture the performance of different systems by using a data normalization method. The ANN prediction is tested on both simulation scenarios and experimental data with different nominal capacities. The results show that the ANN model can successfully predict cooling capacity variations using limited input parameters with RMSE and Delta Qe,rel 0.09 kW and 3.99%, respectively.
Benaissa, SabrinaAdouane, BelkacemAli, S. M.Aouachria, Z....
18页
查看更多>>摘要：In the present work, numerical investigations are performed to study the combustion characteristics of biogas fuel blended with hydrogen at various compositions for a non-premixed swirling flame in a can-type gas turbine combustor. The amount of hydrogen enrichment varies from 0 to 50% by volume. A numerical approach using the non-premixed flamelet model, turbulent standard (k-epsilon) model, and P-1 radiation model was adopted for simulating the can-type combustor power at a fixed operating power of 60 kW. The steady laminar flamelet model was used to analyze the effect of hydrogen enrichment, global equivalence ratio with different swirl numbers on a stable flame operation, temperature distribution and contours, velocity streamline contours, NO emissions, and species concentrations. The results indicate that hydrogen enrichment and the variation of the equivalence ratio and the swirl numbers significantly impacted the flame macrostructure. Hydrogen enrichment in the fuel intensifi combustion, leading to higher flame temperature and wider flammability than bure biogas. Maximum NO emissions in the outlet chamber have been dropped by 43 and 78 (ppm @15 % by volume of O-2) for the biogas and biogas-50% H-2, respectively, due to the reduced flame temperature leading to reduction in thermal NOx formation with reduction equivalence ratio from 0.5 to 0.2. The flame temperature and NO emissions at phi = 0.2 with a high rate of hydrogen (50% H-2) are close to the results of pure biogas (0% H-2) at the same equivalence ratio. The results show that CO and CO2 emissions decrease with increasing hydrogen addition and decreasing the equivalence ratio; due to a decrease in the amount of carbon, the cooling effect, and an increase in the OH concentration.
查看更多>>摘要：Models' accuracy and reliability are important factors for designers of the humidification-dehumidification (HDH) desalination systems. A model used for designing the system must consider all important parameters in order to maintain high accuracy over the wide range of fluctuating conditions. The empirical models for HDH systems which are mostly available in literature are simple and easy to develop but also have limited predictive accuracy for extreme conditions because of consideration of only a few of many influential parameters. Usage of these models may lead to an expensive redesign at latter stages in development of the real system. Therefore, the aim of this paper is to propose the mechanistic model of the HDH desalination process with an improved prediction accuracy as an alternative to conventional models. This model is developed by coupling the heat and mass transfer equations at the water-air interface into enthalpy equations. Performances of the proposed model and an empirical model from literature are compared against experimental data obtained from the HDH system, which is also designed in this work. Results show the proposed model has relatively low mean square error (0.4) hence more accurate than the empirical model with mean square error of 7. It was also found that, the recovery ratio attained by the system increases substantially with an increase of the feed water temperature, but decreases with an increase of water-to-air flow ratio. Freshwater productivity increases with an increasing packing's specific area while doubling of dehumidifiers' surface area improves the recovery ratio by 16%.
Abdelaziz, Gamal B.Dahab, Mohamed A.Omara, M. A.Sharshir, Swellam W....
11页
查看更多>>摘要：An experimental investigation on the solar desalination system was conducted according to humidification dehumidification methodology hybrid with hot air stream flow and vapor compression cycle as a condensation unit. A high-frequency ultrasonic atomizer (HFUA) was used as a humidifier which rapidly reaches 100% Relative Humidity. The tests were done during Aug. and Sept. 2020 under the climate of Suez city, Egypt 29.9668 degrees N, 32.5498 degrees E. The effect of high-frequency ultrasound atomizer situation, water height, and hot air stream flow rate on distillate yield were studied. The results illustrated that increasing atomizer number and decreasing water height increases the daily distillate production. The maximum daily freshwater productivity occurred at atomizer number N = 6, rising 38.6% and 115% compared with N = 4 and N = 2, respectively. Furthermore, water height at H = 1 cm is the most efficient with 16% and 28.6% increment compared with H = 2 cm and H = 3 cm, respectively. The optimum hot air stream flow rate m(a) = 0.01156 kg/s with an increment of 55.95%, 31%, 6.48%, 11.3%, and 38.5% compared with 0.0086, 0.01011, 0.013006, 0.0144, and 0.0173 kg/s, flow rates, respectively. The daily production reaches 7.72 kg\day, the system efficiency 33.84 % and the estimated cost per unit liter is 0.03437 $/L.
查看更多>>摘要：The performance of H2O/EMISE (1-ethyl-3-methylimidazolium ethyl sulfate) absorption chiller driven by stationary solar collectors including the flat plate collector (FPC), evacuated tube collector (ETC), compound parabolic collector (CPC) in hot-humid climate is the focus of this study. As a case study, the cooling capacity of the absorption chiller is constant at 100 kW and used for air conditioning in Guangzhou, China with the inlet/outlet temperature of cooling water fixed at 32/37 degrees C and the inlet/outlet temperature of chilled water set at 17/12 degrees C. The effects of heat source temperature between 78 and 100 degrees C on the thermodynamic as well as economic performance of the solar absorption chiller system have been analyzed and meanwhile the application potentials of the three candidate solar collectors are compared also. The results show that there is an optimum heat source temperature makes the coefficient of performance (COP) and exergetic efficiency (ECOP) of solar absorption chiller system maximum, which is featured with a shifting to lower values compared to the optimum one that leads to the COP of absorption chiller machine maximum. Besides, while the CPC absorption chiller system has the best thermodynamic performance with the overall COP and ECOP about 0.351 and 0.027, respectively, the ETC system becomes the most economic one with the specific investment cost about 1194 USD/kW. Recommendations are given based on the findings as resources to help the design of solar driven H2O/EMISE absorption chiller systems in the hot-humid region.
查看更多>>摘要：A mathematical model of a solar chimney was developed considering moist air as a participatory media. This model coheres to the steady-state heat transfer equations derived for glass cover, moist-air between the glass cover and the absorber wall, and for the absorber wall separately. An in-house developed MATLAB code solves the equations via matrix method, utilizing the Gauss-Seidel iteration technique. A study was done on dry as well as moist air that flows between the glass and absorber plate of the solar chimney. Air absorbing heat by mode of convection, radiation, and both was considered. Performance of the system is characterized in terms of the mass flow rate of air. Variation of mass flow rate of air with the gap between the glass and the absorber plate is studied as a function of relative humidity. The effect of ambient temperature and radiation on solar chimney's performance was reported. The result shows an improvement of 10% in the performance of solar chimney driven by moist air as compared to dry air at 45 degrees inclination of chimney. Chimney inclination of 45 degrees was found to be optimum for Bhubaneswar (India), as it has higher mass flow rate compared to other inclination for most duration. It is also concluded that the mass-flow rate through the solar chimney directly depends on the gap between absorber plate and glass cover. Compared to 0.1 m air gap, there is about 62% and 114% increase in mass flow for the gap of 0.2 m and 0.3 m, respectively.
查看更多>>摘要：The purpose of this paper is to manufacture super-hydrophilic surface on stainless steel flat plates using nanoscale bilayer assembly surface modification. Visual and quantitative evaporation experiments were conducted on the most hydrophilic surface using water as working fluid, proposing a super-hydrophilic surface that could reduce the evaporation time by about one order of magnitude. In this study, super-hydrophilic surfaces were manufacture using environmentally friendly nanoscale bilayer assembly method. During evaporation experiments, different liquid film areas and mean thicknesses on the surfaces were observed; subsequent analysis of the evaporation enhancements were made and contributing factors discussed. The most hydrophilic surface manufactured in this study resulted in contact angle of <4 degrees during the experiments. Compared to a normal clean surface, this modified surface's evaporation effectiveness was enhanced by 850%; the evaporation time of the best super-hydrophilic surface was only one tenth that of the clean surface, showing an improvement in evaporation speed by almost one order of magnitude.
查看更多>>摘要：This paper establishes a 3-dimensional mathematical model to investigate the relationship between transpiration rate and environmental factors via a finite element and controlled variable method. The results show that an increase in photosynthetically active radiation (PAR), ambient temperature and air velocity promote transpi-ration, and an increase in relative humidity (RH) leads to a decrease in the transpiration rate. However, the transpiration rate decreases with increasing relative humidity. The reason for this phenomenon is that the vapour pressure deficit (VPD), the diffusion resistance of vapour through the boundary layer, and leaf stomatal conductance are strongly affected by these environmental factors. Stomatal conductance controls the diffusion of water vapour from the mesophyll interstitial spaces to the stomatal surface. The boundary layer resistance and VPD control the diffusion of water vapour from the pore surface to the environment. When the boundary layer resistance does not change, VPD determines the transpiration rate of the leaf. In contrast, the transpiration rate of the leaf is synergistically affected by the VPD, boundary layer resistance and stomatal conductance (gs). Due to the influence of the transpiration rate and energy exchange, the leaf temperature increases with increasing PAR, RH and ambient temperature and decreases with increasing air velocity. This research can provide some guid-ance for agricultural production and the development of bionic materials with thermal infrared properties similar to those of natural leaves.
NSTL
Elsevier