Amphiphilic Janus nanofibers film composed of microscopically assembled hydrophilic and hydrophobic nanofibers is fabricated as a base film for the solar steam generator possessing functions of solar ...steam generation and photodegradation. The amphiphilic Janus nanofibers film integrates many advantageous properties including water pumping, thermal resisting, self floating, salt resisting, and high stability, which make it an excellent base film for solar steam generators. The mixture comprising carbon nanotubes, black TiO2 nanoparticles and poly(dopamine) is synthesized as a dual-functional photothermal layer on the solar steam generator for realizing photothermal conversion and photocatalysis. The fabricated solar steam generator can achieve a superior water evaporation rate (2.491 kg m−2 h−1, 1 sun) and synchronously degrade organic pollutants. Furthermore, it is delighted to find that the water evaporation rate can be boosted while treating organic-contaminated water. The synergistic property of solar steam generation and photodegradation offers an inspiration in the fields of wastewater elimination and clean water generation.
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•Hydrophilic and hydrophobic nanofibers are microscopically assembled.•Synergistic solar steam generation and photodegradation are realized.•Photodegradation process can boost water evaporation rate.•The solar steam generator exhibits superior salt resistance in desalination process.•High evaporation rate of 2.491 kg m−2 h−1 is achieved under 1 sun.
•SMR performance in flexible operation depends on the steam generator (SG) behavior.•U-tube and helical coil steam generators are characteristically very different.•Comparative analysis of SMRs with ...these SGs reveals interesting results.
A steam generator (SG) is one of the most important subsystems in a pressurized water reactor (PWR). As the interface between the reactor and the turbine for power/energy transform, its behavior dictates the response of the entire plant, especially when maneuvering the power output under dynamic operation. Generally, two types of SGs are most commonly employed in PWR designs: a recirculation-type U-tube steam generator (UTSG) and a once-through steam generator (OTSG). Among the PWR-type SMR concepts, some designs use a UTSG while several others rely on the helical coil steam generator (HCSG), which is a type of OTSG. These two designs differ in a variety of ways, namely construction, physical size for a given capability, thermodynamic characteristics, and control techniques – leading to a very different dynamic behavior under flexible operation. This paper examines the dynamic characteristics of a UTSG and a HCSG in the context of SMR flexible operation and highlights the key implications of choosing one against the other. Detailed moving boundary models are developed for both SGs. Simulation studies have been carried out in MATLAB/Simulink environment to compare their characteristics quantitatively under different loading conditions. The results have indicated that there are significant differences in dynamic behaviors between these two SGs during transient operations. Relatively larger pressure excursions in the UTSG during power maneuvers suggest more stringent considerations in equipment design and selection for safe operation.
•PFBR has eight units of steam generators to transfer 1250MWt power.•A model steam generator was tested for its heat transfer performance.•The model steam generator transferred 6.05MWt power at ...nominal conditions.•To produce steam at nominal conditions 91.7% of area is sufficient.•The steam generator design for PFBR is validated by experiments.
Steam generator is a crucial component in a nuclear power plant because its availability is directly linked to the availability of heat transport system and thus the plant availability. In Prototype Fast Breeder Reactor (PFBR) which is in advanced stage of construction in India, eight number of steam generators each with a heat transfer capacity of 156MWt transfers 1250MW of heat from secondary sodium to the conventional steam/water system. The sodium heated once through steam generator with 23m long seamless straight tubes produces super heated steam at 17.2MPa pressure and 493°C temperature. A model steam generator of 5.5MWt power was tested in steam generator test facility of Indira Gandhi Center for Atomic research for validating the thermal hydraulic and mechanical design of the steam generator. The testing revealed the adequacy of heat transfer capability of the steam generator to transfer the intended power. From the experimental data it is estimated that the steam generator has 8.3% more tube surface area than the required to produce steam at nominal conditions. This paper gives the details of the model steam generator, heat transfer experiments conducted to validate the thermal design and the method for estimating the additional heat transfer area in once through type steam generator.
Steam Generator (SG) is a prime component in Indian Pressurized Heavy Water Reactors (PHWRs). The Steam Generator consists of an inverted vertical U-tube bundle in shell for primary flow (Heavy ...water). The shell side is designed for recirculation. Steam Generator is a Safety Class-1 component and designed & fabricated as per the requirements of ASME Section III, Subsection-NB.
Secondary side of the steam generator consists of a shell, Feed Water Nozzle (FWN), Steam Outlet Nozzle, moisture separator, drier, tubes and shroud. The principal material of construction for secondary side pressure boundary is of low alloy carbon steel. Secondary side of steam generator is subjected various loadings (Dead weight, pressure, pipe reactions & thermal) during normal plant condition as well as transient conditions including severe transient like crash cool down where in the thermal gradients are much higher. To take care of these thermal transient loadings a special thermal sleeve type of design has been incorporated in the FWN.
As mentioned above, FWN is subjected to thermal transients throughout its life and susceptible to high thermal gradient which makes it important to evaluate for structural integrity and fatigue failure. This paper covers the approach & results for structural integrity assessment (stress evaluation) and fatigue evaluation (cumulative fatigue damage factor) of Feed Water Nozzle of 700MWe PHWR SG for various Service levels A, B, D & Design. These service conditions comprise of thermal & pressure transients during operating and accidental conditions. Detailed integrity check performed for all conditions by stress categorization at critical locations and qualify primary & secondary stresses against ASME Section III allowable.
Solar steam generation can be a practical and sustainable technology for wastewater purification and seawater desalination. However, both the inefficient utilization of solar energy and high ...complicity/cost of current solar steam generators hinder the scalable application of this technique. Herein, we demonstrate a facile, scalable and low-cost approach to produce highly-efficient solar steam generator via a one-step calcination of commercial melamine sponges (MS) in air. The in-air calcinated MS (AMS) with thermal insulator achieves an ultrafast solar evaporation rate (1.98 kg m−2 h−1) and a high photothermal efficiency (~92%) under one sun illumination (1 kW m−2), superior to most reported values. This high solar evaporation rate is attributed to the effective heat localization and adequate water supply in AMS, caused by the low bulk thermal conductivity, high porosity and hydrophilicity of AMS, as well as the set-up of a thermal insulator. The AMS is found to be highly efficient and stable, and it can be used to purify various types of waste water, including river water, seawater, and strong acid/alkaline water. Performance analysis of a large-scale prototype device based on the AMS design for field tests promises significant opportunities for highly-efficient, reusable, portable and low-cost water purification systems.
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•Scalable production of solar evaporator by calcinating melamine sponge in air (AMS).•AMS yields a solar evaporation rate of 1.98 kg m−2 h−1 with a photothermal efficiency of ~92% under 1 sun.•AMS achieves high efficiency, stability and cycling capability on river water and seawater.•AMS demonstrates remarkable anti-fouling performance when purifying strong acid/alkaline water.
•An inhouse STH code named SACLER is modified developed with LBE and pure lead thermal properties and heat transfer models.•The liquid metal Helical Coiled Once Through Steam Generator model is ...applied in SACLER code.•Model separation validation and system integrity validation are carried out for the code.
LFRs are one of six advanced Generation IV reactor concepts using lead-based coolant with high thermal conductivity, and HCOTSGs are generally adopted to highlight LFR miniaturization characteristics. An inhouse STH code SACLER with the HCOTSG model and the cover gas model was developed specifically for LFRs. NACIE facility was used to demonstrate SACLER accuracy. The HCOTSG model was verified using the RELAP code, experimental data, and ELSY design parameters. The validation results are consistent with the experimental data of NACIE. The HCOTSG model calculation results are in good agreement with the experimental data and the RELAP code. The error between the ELSY simulation result and the design value is within 1.0%. Liquid level simulation of ELSY shows that liquid levels are mainly determined by the pump head and flow resistance. SACLER can accurately simulate the LFR system with HCOTSG, including transient and steady-state conditions.
•Critical assessment of 25 existing correlations with large databank (980 points).•New prediction method proposed (mean absolute error 7.3% and 9/10 points within ±15%).•Curvature effects on pressure ...gradient proportional to flow velocity and coil curvature.
This study considers the prediction of the pressure gradient with water–steam two-phase flows through helically coiled steam generator tubes, focusing in particular on the operating conditions of low-medium pressure, low mass flux and low heat flux typical of once-through steam generators with in-tube boiling adopted in small modular nuclear reactor systems. Twenty-five widely used empirical correlations have been tested against an experimental pressure drop databank drawn together in this study containing 980 data points. Since no existing correlation is capable of collapsing and satisfactorily fitting the collected databank, a new pressure drop prediction method for helically coiled tubes is proposed. This new prediction method is very simple to implement, as it is based on the homogeneous flow model, is asymptotically consistent with straight tube two-phase flows and is largely superior in accuracy to existing prediction methods (mean absolute error of 7.3%, and 9 points out of 10 captured to within ±15%). The new prediction method is applicable for operating pressures in the range of 0.75–9.0MPa, mass fluxes from 400kg/m2s to 1191kg/m2s, heat fluxes up to 750kW/m2, tube diameters within 5–20mm and coil to tube diameter ratio above 32.4. Curvature effects on the pressure gradient in helical coil two-phase flows can be significant, particularly with high velocity flows in tight curvature coils where the centrifugal force is intense.
•A robust carbonized hierarchical flax fabric modified by PPy is prepared as solar steam generation.•An evaporation rate of 1.4 kg−1 m−2 h with an efficiency of 91.5 % are realized.•The evaporator ...with micro- and macro-capillary channels enables the long-term salt rejection for continuous application in high-salinity desalination.
Solar steam generation is considered to be a perspective technology to address water scarcity issues globally. However, its further application is limited by the complicated preparation strategy, poor salt rejection, and durability. In this study, a novel solar steam generation system based on a three-dimensional (3D) hierarchical flax fabric (HFF) is fabricated by carbonizing and coating with polypyrrole (PPy) on the fibers surface. The HFF fabric fabricated by an ordinary loom has a 3D hierarchical structure composed of float layer (FL), basket weave layer (BWL) and plain weave layer (PWL) by an ordinary loom. The hydrophilic carbonized hierarchical flax fabric modified by PPy (CHFF-PPy) shows highly efficient water supply by the continuous water transport channels for water transportation. The formed double-scale capillary water on the surface of CHFF-PPy is composed of micro-capillary water in the yarns for high interfacial water evaporation and macro-capillary water between the yarns for salt-rejection. Therefore, these functions cooperatively to endow the CHFF-PPy with all-in-one function including superior solar-driven water evaporation (1.4 kg m−2 h−1, 91.5 % efficiency for saline), efficient solar desalination, and long-term salt-rejecting property without any post-cleaning treatment. The design principle of the 3D fabric structures is provided for extending the application of salt rejection and the investigation of structure-design-induced double-scale capillaries control in the solar desalination field.
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•Efficient solar evaporator was developed from solid wastes and graphite.•Solar evaporation rate as high as 1.61 kg/m2 h was achieved under 1 sun.•Quantitative studies suggest the ...design of highly-efficient solar steam generator.•High efficiency and cycling stability were proved for purifying various water.•Prototype can produce 8–13 L of clean water daily with 1 m2 of material.
Utilizing the clean and renewable solar energy to generate steam for wastewater purification or seawater desalination is a promising solution to the worldwide scarcity of fresh water. Herein, we report a highly-efficient, eco-friendly and cost-effective solar steam generator based on ball-milling graphite and cellulose fiber from waste paper. Ball-milling graphite/cellulose fiber composite aerogels are facilely developed via a freeze casting-drying method, endowing a featured vertically aligned porous structure. The fabrication of composite aerogels and the construction of evaporation systems take full advantages of recycled materials, contributing to the low cost and solid waste reclamation. High porosity, strong solar absorption, hydrophilicity and low thermal conductivity of the composite aerogels collectively contribute to a splendid solar evaporation rate of water as high as 1.61 kg m−2 h−1, with photothermal efficiency of ~90% under one sun illumination (1 kW m−2). Quantitative studies reveal the effects of ball-milling graphite/cellulose fiber ratio, ball-milling graphite concentration and thickness of composite aerogels on the solar evaporation rates, suggesting the optimal design of composite aerogels. Furthermore, the cycling stability and the capability for seawater desalination as well as polluted water purification manifest the potential of the composite aerogels to purify diverse water. Outdoor tests show 8–13 L of fresh water could be produced daily by 1 m2 of composite aerogel.
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