Modeling of a High-Temperature-Serpentine External Tubular Receiver Using Supercritical CO2

2014 ◽  
Author(s):  
Samia Afrin ◽  
Jesus D. Ortega ◽  
Clifford K. Ho ◽  
Vinod Kumar
Keyword(s):  
Thermal Efficiency ◽  
Supercritical Co2 ◽  
Incidence Angle ◽  
Normal Incidence ◽  
Incident Radiation ◽  
Heat Transfer Fluid ◽  
Discrete Ordinates ◽  
Outlet Temperature ◽  
Dynamics Model ◽  
Ansys Fluent

This paper describes the modelling and design of an external receiver using supercritical CO2 as the heat transfer fluid that can reach up to 700 °C outlet temperature with ∼85% thermal efficiency. The internal pressure of the tubes is 20 MPa. The receiver tubes are arranged in a serpentine fashion and are coated with Pyromark 2500. Analyses were performed to evaluate the thermal efficiency of the receiver as a function of incidence angle of the incident radiation. Two different radiation models, discrete ordinates and surface-to-surface ray tracing, were used in the computational fluid dynamics model (ANSYS FLUENT). The receiver thermal efficiency ranged from 75% for incidence angles of 80 degrees to 88% for near-normal incidence angles of 10 degrees.

scholarly journals Calorimetric Evaluation of Novel Concentrating Solar Receiver Geometries With Enhanced Effective Solar Absorptance

2016 ◽  
Author(s):  
Jesus D. Ortega ◽  
Julius E. Yellowhair ◽  
Clifford K. Ho ◽  
Joshua M. Christian ◽  
Charles E. Andraka
Keyword(s):  
Thermal Efficiency ◽  
Solar Power ◽  
Solar Furnace ◽  
Heat Transfer Fluid ◽  
Discrete Ordinates ◽  
Base Case ◽  
Outlet Temperature ◽  
Black Paint ◽  
Solar Absorptance ◽  
Flow Rates

Direct solar power receivers consist of tubular arrays, or panels, which are typically tubes arranged side by side and connected to an inlet and outlet manifold. The tubes absorb the heat incident on the surface and transfer it to the fluid contained inside them. To increase the solar absorptance, high temperature black paint or a solar selective coating is applied to the surface of the tubes. However, current solar selective coatings degrade over the lifetime of the receiver and must be reapplied, which reduces the receiver thermal efficiency and increases the maintenance costs. This work presents an evaluation of several novel receiver shapes which have been denominated as fractal like geometries (FLGs). The FLGs are geometries that create a light-trapping effect, thus, increasing the effective solar absorptance and potentially increasing the thermal efficiency of the receiver. Five FLG prototypes were fabricated out of Inconel 718 and tested in Sandia’s solar furnace at two irradiance levels of ∼15 and 30 W/cm2 and two fluid flow rates. Photographic methods were used to capture the irradiance distribution on the receiver surfaces and compared to results from ray-tracing models. This methods provided the irradiance distribution and the thermal input on the FLGs. Air at nearly atmospheric pressure was used as heat transfer fluid. The air inlet and outlet temperatures were recorded, using a data acquisition system, until steady state was achieved. Computational fluid dynamics (CFD) models, using the Discrete Ordinates (DO) radiation and the k-ω Shear Stress Transport (SST) equations, were developed and calibrated, using the test data, to predict the performance of the five FLGs at different air flow rates and irradiance levels. The results showed that relative to a flat plate (base case), the new FLGs exhibited an increase in the effective solar absorptance from 0.86 to 0.92 for an intrinsic material absorptance of 0.86. Peak surface temperatures of ∼1000°C and maximum air temperature increases of ∼200°C were observed. Compared to the base case, the new FLGs showed a clear air outlet temperature increase. Thermal efficiency increases of ∼15%, with respect to the base case, were observed. Several tests, in different days, were performed to assess the repeatability of the results. The results obtained, so far, are very encouraging and display a very strong potential for incorporation in future solar power receivers.

Development of a Ceramic Pressurized Volumetric Solar Receiver for Supercritical CO2 Brayton Cycle

2014 ◽  
Author(s):  
S. D. Khivsara ◽  
Rathindra Nath Das ◽  
T. L. Thyagaraj ◽  
Shriya Dhar ◽  
V. Srinivasan ◽  
...  
Keyword(s):  
Thermal Efficiency ◽  
Supercritical Co2 ◽  
Material Selection ◽  
Radiation Heat Transfer ◽  
Small Scale ◽  
Attractive Alternative ◽  
Transfer Model ◽  
Outlet Temperature ◽  
Brayton Cycle ◽  
Solar Thermal Energy

Recently, the supercritical CO2 (s-CO2) Brayton cycle has been identified as a promising candidate for solar-thermal energy conversion due to its potentially high thermal efficiency (50%, for turbine inlet temperatures of ∼ 1000K). Realization of such a system requires development of solar receivers which can raise the temperature of s-CO2 by over 200K, to a receiver outlet temperature of 1000K. Volumetric receivers are an attractive alternative to tubular receivers due to their geometry, functionality and reduced thermal losses. A concept of a ceramic pressurized volumetric receiver for s-CO2 has been developed in this work. Computational Fluid Dynamics (CFD) analysis along with a Discrete Ordinate Method (DOM) radiation heat transfer model has been carried out, and the results for temperature distribution in the receiver and the resulting thermal efficiency are presented. We address issues regarding material selection for the absorber structure, window, coating, receiver body and insulation. A modular small scale prototype with 0.5 kWth solar heat input has been designed. The design of a s-CO2 loop for testing this receiver module is also presented in this work.

Experimental Study to Characterize the Performance of Combined Photovoltaic/Thermal Air Collectors

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Véronique Delisle ◽  
Michaël Kummert
Keyword(s):  
Thermal Efficiency ◽  
Closed Loop ◽  
Multiple Linear Regression Model ◽  
Open Loop ◽  
Electrical Performance ◽  
Back Surface ◽  
Inlet Temperature ◽  
Outlet Temperature ◽  
Cell Temperature ◽  
Average Temperature

Combined photovoltaic/thermal (PV/T) collectors show great potential for reaching the objective of net-zero energy consumption in buildings, but the number of products on the market is still very limited. One of the reasons for the slow market uptake of PV/T collectors is the absence of standardized methods to characterize their performance. Performance characterization is a challenge for PV/T collectors because of the interaction between the thermal and electrical yield. This study addresses this particular issue for PV/T air collectors used in either closed-loop or open-loop configurations. In particular, it presents the potential of the equivalent cell temperature method to determine the temperature of the PV cells in a PV/T air collector and validates models to predict the thermal performance and cell temperature for this particular type of solar collector. Indoor and outdoor experimental tests were performed on two c-Si unglazed PV/T modules. The indoor part of this procedure provided the thermal diode voltage factor and the open-circuit voltage temperature coefficient, two parameters that are essential in the calculation of the equivalent cell temperature. The outdoor procedure consisted of acquiring simultaneous electrical and thermal measurements at various inlet temperatures and flowrates. For the collector used in a closed-loop configuration, thermal efficiency models using the fluid inlet, outlet, or average temperature in the calculation of the reduced temperature provided similar results. For an open-loop configuration, a thermal efficiency model as a function of the fluid outlet flowrate was found to be more appropriate. Using selection of variable methods, it was found that a multiple linear regression model using the fluid inlet temperature, the irradiance, and the fluid outlet temperature as predictive variables could be used to estimate both the PV module back surface average temperature and the equivalent cell temperature. When using the PV temperature predicted by these models in the electrical efficiency model, both PV temperatures showed similar performance. In collectors where the PV back surface temperature is not accessible for temperature sensors mounting, the equivalent cell temperature provides a valuable alternative to be used as the PV temperature. The PV/T collector thermal and electrical performance in either closed-loop or open-loop configurations was found to be encapsulated with a series of five-plots.

A Comparison Between ORC and Supercritical CO2 Bottoming Cycles For Energy Recovery From Industrial Gas Turbines Exhaust Gas

2021 ◽  
Author(s):  
M. A. Ancona ◽  
M. Bianchi ◽  
L. Branchini ◽  
A. De Pascale ◽  
F. Melino ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Thermal Efficiency ◽  
Gas Turbines ◽  
Supercritical Co2 ◽  
Energy Demand ◽  
Oil And Gas ◽  
Gas Production ◽  
Medium Size ◽  
Oil And Gas Production ◽  
Industrial Gas Turbines

Abstract Gas turbines are often employed in the industrial field, especially for remote generation, typically required by oil and gas production and transport facilities. The huge amount of discharged heat could be profitably recovered in bottoming cycles, producing electric power to help satisfying the onerous on-site energy demand. The present work aims at systematically evaluating thermodynamic performance of ORC and supercritical CO2 energy systems as bottomer cycles of different small/medium size industrial gas turbine models, with different power rating. The Thermoflex software, providing the GT PRO gas turbine library, has been used to model the machines performance. ORC and CO2 systems specifics have been chosen in line with industrial products, experience and technological limits. In the case of pure electric production, the results highlight that the ORC configuration shows the highest plant net electric efficiency. The average increment in the overall net electric efficiency is promising for both the configurations (7 and 11 percentage points, respectively if considering supercritical CO2 or ORC as bottoming solution). Concerning the cogenerative performance, the CO2 system exhibits at the same time higher electric efficiency and thermal efficiency, if compared to ORC system, being equal the installed topper gas turbine model. The ORC scarce performance is due to the high condensing pressure, imposed by the temperature required by the thermal user. CO2 configuration presents instead very good cogenerative performance with thermal efficiency comprehended between 35 % and 46 % and the PES value range between 10 % and 22 %. Finally, analyzing the relationship between capital cost and components size, it is estimated that the ORC configuration could introduce an economical saving with respect to the CO2 configuration.

Thermal Aspects of Using Uranium Mononitride Fuel in a SuperCritical Water-Cooled Reactor at Maximum Heat Flux Conditions

2010 ◽  
Author(s):  
Ashley Milner ◽  
Caleb Pascoe ◽  
Hemal Patel ◽  
Wargha Peiman ◽  
Graham Richards ◽  
...  
Keyword(s):  
Heat Flux ◽  
Supercritical Water ◽  
Thermal Efficiency ◽  
Inlet Temperature ◽  
Outlet Temperature ◽  
Maximum Heat ◽  
Light Water ◽  
Maximum Heat Flux ◽  
Centerline Temperature ◽  
Uranium Mononitride

Generation IV nuclear reactor technology is increasing in popularity worldwide. One of the six Generation-IV-reactor types are SuperCritical Water-cooled Reactors (SCWRs). The main objective of SCWRs is to increase substantially thermal efficiency of Nuclear Power Plants (NPPs) and thus, to reduce electricity costs. This reactor type is developed from concepts of both Light Water Reactors (LWRs) and supercritical fossil-fired steam generators. The SCWR is similar to a LWR, but operates at a higher pressure and temperature. The coolant used in a SCWR is light water, which has supercritical pressures and temperatures during operation. Typical light water operating parameters for SCWRs are a pressure of 25 MPa, an inlet temperature of 280–350°C, and an outlet temperature up to 625°C. Currently, NPPs have thermal efficiency about of 30–35%, whereas SCW NPPs will operate with thermal efficiencies of 45–50%. Furthermore, since SCWRs have significantly higher water parameters than current water-cooled reactors, they are able to support co-generation of hydrogen. Studies conducted on fuel-channel options for SCWRs have shown that using uranium dioxide (UO2) as a fuel at supercritical-water conditions might be questionable. The industry accepted limit for the fuel centerline temperature is 1850°C and using UO2 would exceed this limit at certain conditions. Because of this problem, there have been other fuel options considered with a higher thermal conductivity. A generic 43-element bundle for an SCWR, using uranium mononitride (UN) as the fuel, is discussed in this paper. The material for the sheath is Inconel-600, because it has a high resistance to corrosion and can adhere to the maximum sheath-temperature design limit of 850°C. For the purpose of this paper, the bundle will be analyzed at its maximum heat flux. This will verify if the fuel centerline temperature does not exceed 1850°C and that the sheath temperature remains below the limit of 850°C.

A 3-D Model Simulation of High Temperature Solar Cavity Receiver

2017 ◽  
Author(s):  
Huayi Feng ◽  
Yanping Zhang ◽  
Chongzhe Zou
Keyword(s):  
Heat Transfer ◽  
Radiation Intensity ◽  
Large Scale ◽  
Model Simulation ◽  
Heat Transfer Fluid ◽  
Working Fluid ◽  
Outlet Temperature ◽  
Fluid Temperature ◽  
Heat Transfer Efficiency ◽  
Direct Normal Irradiance

In this paper, a 3-D numerical model is proposed to investigate the capability of generating high operating temperature for a modified solar cavity receiver in large-scale dish Stirling system. The proposed model aims to evaluate the influence of radiation intensity on the cavity receiver performance. The properties of the heat transfer fluid in the pipe and heat transfer losses of the receiver are investigated by varying the direct normal irradiance from 400W/m2 to 1000W/m2. The temperature of heat transfer fluid, as well as the effect of radiation intensity on the heat transfer losses have been critically presented and discussed. The simulation results reveal that the heat transfer fluid temperature and thermal efficiency of the receiver are significantly influenced by different radiation flux. With the increase of radiation intensity, the efficiency of the receiver will firstly increase, then drops after reaching the highest point. The outlet working fluid temperature of the pipe will be increased consistently. The results of the simulations show that the designed cylindrical receiver used in dish Stirling system is capable to achieve the targeted outlet temperature and heat transfer efficiency, with an acceptable pressure drop.

scholarly journals Method for fast determination of the angle of ionizing radiation incidence from data measured by a Timepix3 detector

2021 ◽  
Vol 10 (1) ◽  
pp. 63-70
Author(s):  
Felix Lehner ◽  
Jürgen Roth ◽  
Oliver Hupe ◽  
Marc Kassubeck ◽  
Benedikt Bergmann ◽  
...  
Keyword(s):  
Ionizing Radiation ◽  
Incidence Angle ◽  
Computation Time ◽  
Incident Radiation ◽  
Angle Of Incidence ◽  
Time Behavior ◽  
Calculation Algorithm ◽  
3D Geometry ◽  
Photon Event ◽  
Radiation Incidence

Abstract. This paper presents a method of how to determine spatial angles of ionizing radiation incidence quickly, using a Timepix3 detector. This work focuses on the dosimetric applications where detectors and measured quantities show significant angle dependencies. A determined angle of incidence can be used to correct for the angle dependence of a planar Timepix3 detector. Up until now, only passive dosemeters have been able to provide a correct dose and preserve the corresponding incidence angle of the radiation. Unfortunately, passive dosemeters cannot provide this information in “real” time. In our special setup we were able to retrieve the spatial angles with a runtime of less than 600 ms. Employing the new Timepix3 detector enables the use of effective data analysis where the direction of incident radiation is computed from a simple photon event map. In order to obtain this angle, we combine the information extracted from the map with known 3D geometry surrounding the detector. Moreover, we analyze the computation time behavior, conditions and optimizations of the developed spatial angle calculation algorithm.

Construction and Experimental Study of an Elevation Linear Fresnel Reflector

2016 ◽  
Vol 138 (3) ◽  
Author(s):  
J. D. Nixon ◽  
P. A. Davies
Keyword(s):  
Heat Loss ◽  
Thermal Efficiency ◽  
Theoretical Models ◽  
Loss Coefficient ◽  
Heat Transfer Fluid ◽  
Stagnation Temperature ◽  
Model Predictions ◽  
The Difference ◽  
Predicted Values ◽  
Linear Fresnel Reflector

This paper outlines a novel elevation linear Fresnel reflector (ELFR) and presents and validates theoretical models defining its thermal performance. To validate the models, a series of experiments were carried out for receiver temperatures in the range of 30–100 °C to measure the heat loss coefficient, gain in heat transfer fluid (HTF) temperature, thermal efficiency, and stagnation temperature. The heat loss coefficient was underestimated due to the model exclusion of collector end heat losses. The measured HTF temperature gains were found to have a good correlation to the model predictions—less than a 5% difference. In comparison to model predictions for the thermal efficiency and stagnation temperature, measured values had a difference of −39% to +31% and 22–38%, respectively. The difference between the measured and predicted values was attributed to the low-temperature region for the experiments. It was concluded that the theoretical models are suitable for examining linear Fresnel reflector (LFR) systems and can be adopted by other researchers.

Wells Turbine With Variable Blade Profile for Wave Energy Conversion

2018 ◽  
Author(s):  
Celia Miguel González ◽  
Ginés Rodríguez Fuertes ◽  
Manuel García Díaz ◽  
Bruno Pereiras García ◽  
Francisco Castro ◽  
...  
Keyword(s):  
Rotation Speed ◽  
Incidence Angle ◽  
Main Flow ◽  
Performance Curve ◽  
Oscillating Water Column ◽  
Blade Profile ◽  
Wave Energy Conversion ◽  
Wells Turbine ◽  
Sharp Drop ◽  
Ansys Fluent

It is well known among the researchers involved in the field of turbines for Oscillating Water Column systems (OWC) that the main problem for Wells turbines is the stall, which appears when the main flow incidence angle exceeds certain value and leads to a sharp drop in the efficiency. It also causes problems during the starting, driving the turbine to not reach the designing rotation speed. Delaying the stall apparition is the key to improve the performance of the Wells turbine. is necessary to delay the flow separation at the trailing edge because it is the reason which leads to the sharp efficiency drop at the stall point. One of the solutions proposed by researchers in this field is using a variable blade profile instead of the traditional ones, built using constant chord and profile from hub to tip. This work tries to dig deeper in this line by analysing a blade with variable chord and shape among the blade span. The work has been developed numerically by using commercial software ANSYS FLUENT®. A CFD code was created in order to obtain the performance curve of the turbine proposed to be compared with those assumed as reference, which were taken from the bibliography and also used to validate the numerical model. The results have shown that an improvement has been achieved. It confirms that using a variable blade profile is a suitable solution to delay the stall apparition.

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