Microencapsulated phase change material (mPCM) slurry has the advantages of excellent flow and heat transfer performance as traditional single-phase fluids and high heat storage density as phase change materials (PCM). In this paper, a three-dimensional numerical model of an immersed heat storage tank containing a vertical helical coiled tube was established. Combined with the physical properties of the prepared mPCM slurry, the coupling relationship between temperature and velocity field and the mPCM slurry’s natural convective heat transfer process were simulated. The influence of particle concentrations on its heat transfer and storage performances was discussed. Results show that the heat transfer process of mPCM slurry can be divided into three stages: heat conduction dominated stage-convection development stage-convection attenuation stage. Although the increase in particle concentrations reduces the heat transfer coefficient, the heat storage capacity of mPCM slurry with 30% particle concentrations increases by 38.6% compared with base fluid (water).
To reduce heavy reliance on greenhouse gas-emitting power plants, various countries have focused on the development of renewable energy technology with the appropriate energy storage installed. Pumped hydropower energy storage (PHES) technology has been utilized for several decades for electrical ancillary benefits (e.g. spinning reserve) or linked to renewable energy sources to store excessive power and exploit it, if needed. However, several factors in hybrid renewable energy systems have been given less attention, such as hydraulic loss influences and evaporation rate, which are extremely essential parameters where a noncontinuous water sources (closed loop power plants) is used. Consequently, this study aims to investigate the impact of those factors against integration systems comprising of a photovoltaic energy system and pumped storage connected to the grid. A mathematical model is developed taking into account various monitoring variables: loss of renewable energy, amount of electricity supplied by grid, and load covered by renewable sources. It is clearly observed that hourly evaporation rate and hydraulic losses may affect the whole hybrid system performance if they are neglected. The results show that more than 10 mm of water evaporated on the first of August in Bisha, located in Saudi Arabia, which is adapted as a case study .Based on the obtained results, it is recommended that considering both essential parameters increases the accuracy of such system and raises reliability of hybrid renewable energy sources.
Diffusion coefficient study gains an interest to know the mass transfer properties of molecules especially in the study of the absorption process. The main objective of the present study is to investigate the effect of temperature on the diffusivity of the MEA absorption process for CO2 capture and to explore the effect of solvent concentration on intermolecular interactions of 2EAE (2-ethylamino ethanol) and 2DMAE (2-dimethylamino ethanol). The molecular dynamic simulation study is conducted for the calculation of diffusivity and intermolecular interaction of amines. Three different values of process temperature are chosen for calculation of diffusivity i.e. 298 K, 313 K and 318 K. Mean Square Displacement (MSD) analysis was done to compute the diffusion coefficient of molecules in secondary and tertiary amine system. Radial distribution function analysis was carried out for the calculation of intermolecular interactions. The results show that the rate of the diffusion coefficient is increased as temperature is increased and the CO2 diffusivity on MEA is higher as compared to 2DMAE but lower than 2EAE. The diffusivity results obtained from the present work are in good agreement with theoretical results. The results of the main solvent concentration on intermolecular interaction show that by increasing the concentration of the solvent, the intermolecular interaction strength increases in both cases of secondary and tertiary amines. The 30% of 2EAE shows highest intermolecular interactions in CO2 and 40%
The flow and heat transfer characteristics of contact condensation in rectangular microchannels were studied experimentally. All tests were performed with water and steam. At a certain gas-liquid ratio, three flow patterns were found in the microchannel of 600 Î¼m: slug flow, annular flow and mist flow. The experimental results show that the contact condensation heat transfer process in the microchannel is affected by the channel structure and gas-liquid flow. In the experimental conditions with higher Reynolds number, due to the influence of inertia force, the Nusselt number decreases with the increase of hydraulic diameter, and increases with the increase of flow rate. However, in the same microchannel, the Nux of the fluid reaches the maximum at the entrance, and then decreases gradually along the flow direction.
In building HVAC systems, chilled water flowmeter is an important sensor whose reading could be used to measure the real time cooling load, a critical variable for automated control of building HVAC systems. To maintain the reading data accurate, the fault detection and diagnosis (FDD) of flowmeters is necessary. Existing FD/FDD methods for chilled water flowmeters have several common shortcomings: (1) High requirements on sensor integrity: multiple sensors are usually involved to build energy balance models; (2) Complex methodology, the fault of any monitored sensor could trigger the detection hit, thus diagnosis procedure is unavoidable to isolate the faulty sensor; (3) the more sensors involved, the harder to collect fault-free historical data to build a fault-free benchmark. To tackle these existing problems, a user-friendly fault detection (FD) method for building chilled water flowmeters is proposed in this study. The proposed method requires three types of variables to function: pump frequency, pump power, and measured chilled water flowrate on the header pipe. The field data of a real HVAC system is used in the case study to validate the performance of the proposed method. Results of the validation case study suggest that the proposed method could reach high hit rates confronting different faults (bias, noise and drift) at different levels. Compared to existing FD methods, the simple workflow and low sensor requirements make the proposed method more feasible and user-friendly for engineering practice.
A method of mutual humidification strategy is explored in this study making the best use of water production characteristics of proton exchange membrane fuel cell (PEMFC) and anion exchange membrane fuel cell (AEMFC). And the results show that in the relatively dry outside humidification condition, the performance of PEMFC can be elevated in various extends. Technically, in the various extents of load, the performance changes show stable and consistent trend. With the electrochemical test measures, the principles of mutual humidification are investigated.
Replacing steam methane reforming with electrolysis using renewable electricity for hydrogen production can reduce CO2 emissions with a trade-off of larger energy use, water use and cost. A linear programming optimization model that accounts for energy use, water use, CO2 emissions and cost was developed to optimize the configuration of a hydrogen production system; considering Japan in 2030 as a case of study. Four scenarios were considered, prioritizing 1) cost, 2) energy use, 3) Water-Energy-Carbon nexus and 4) Water-Energy-Carbon nexus and cost; under maximum CO2 intensities for hydrogen production between 0 and 18 kg-CO2/kg-H2. Hydrogen production routes include steam methane reforming; and electrolysis using grid electricity, wind electricity, solar photovoltaic electricity, geothermal electricity and hydroelectricity. For CO2 intensities higher than 8 kg-CO2/kg-H2, steam methane reforming accounts for more than 50% of hydrogen production in all scenarios. For a CO2 intensity of 0 kg-CO2/kg-H2, hydroelectricity represents more than 76% of hydrogen production when energy use or cost are prioritized. Including water use in the priorities drives the share of wind electricity in hydrogen production to 37.6%. The remaining hydrogen is produced using solar electricity if cost is not prioritized; or 23.7% geothermal electricity and 38.7% hydroelectricity if cost is prioritized simultaneously.
Twin-screw compressors with an adaptable built-in volume ratio can significantly increase the overall process efficiency for applications with fluctuating operating conditions. Detailed component models, necessary to assess their full potential, are rare in literature. Therefore, this work develops and validates a novel semi-empiric compressor model taking into account the mechanical adaptation of the built-in volume ratio. The model shows good agreement with operating data provided by the manufacturer.
In order toÂ enhance heat and mass exchange, the internal heat exchanger is introduced into the adsorption chamber based on the temperature swing adsorption (TSA) process. Heating is carried out by condensing steam, and cooling by water circulation. The influence of the number of internal heat exchangers, inlet speed and porosity on the CO2 purity, recovery rate, energy consumption and COPCO2 are discussed numerically to improve the energy efficiency performance of TSA process. The results show that under the same operating conditions, the CO2 purity, recovery rate and COPCO2 of the three-tube heat exchanger in adsorption chamber are higher than that of the one-tube heat exchanger, with lower energy consumption of three-tube heat exchanger. The temperature distribution of the adsorption chamber is greatly influenced by the inlet speed and porosity. By increasing inlet speed or porosity, the CO2 purity, recovery rate and COPCO2 can be improved and energy consumption can be reduced. The obtained simulation results can provide further guidance for engineering design.
With high penetration of distributed generations (DGs), distribution networks are becoming more and more â ‘active’. Active distribution networks (ADNs) provide the opportunity of providing flexibility for the transmission system operator (TSO) through a flexibility trading platform. To provide such a trading platform, a TSO-DSO coordinated flexibility market is proposed in this paper. To clear the market while protecting the privacy of TSO and DSO, an ADMM-based market clearing solution is proposed. Case studies are conducted on the testing system of the IEEE 30-bus transmission network with two 33-node ADNs. Numerical studies demonstrate the proposed flexibility market framework can reduce the total flexibility cost of the TSO. Besides, the economic benefits of ADNs can also be improved.