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.

scholarly journals Novel Tubular Receiver Panel Configurations for Increased Efficiency of High-Temperature Solar Receivers

2015 ◽  
Author(s):  
Joshua M. Christian ◽  
Jesus D. Ortega ◽  
Clifford K. Ho
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Flat Plate ◽  
Heat Loss ◽  
Thermal Efficiency ◽  
Power Plants ◽  
Light Trapping ◽  
Heat Transfer Fluid ◽  
Base Case ◽  
Solar Absorptance

Typical Concentrated Solar Power (CSP) central receiver power plants require the use of either an external or cavity receiver. Previous and current external receivers consist of a series of tubes connected to manifolds that form a cylindrical or rectangular shape such as in the cases of Solar One, Solar Two, and most recently the Ivanpah solar plant. These receivers operate at high surface temperatures (>600°C) at which point thermal re-radiation is significant. However, the geometric arrangement of these heat transfer tubes results in heat losses directly to the environment. This work focused on how to fundamentally reduce this heat loss through the manipulation of heat transfer tube configurations. Four receiver configurations are studied: flat receiver (base case study), a radial receiver with finned structures (fins arranged in a circular pattern on a cylinder), a louvered finned structure (horizontal and angled fins on a flat plate), and a vertical finned structure (fins oriented vertically along a flat plate). The thermal efficiency, convective heat loss patterns, and air flow around each receiver design is found using the computational fluid dynamics (CFD) code ANSYS FLUENT. Results presented in this paper show that alternative tubular configurations increase thermal efficiency by increasing the effective solar absorptance of these high-temperature receivers by increasing the light trapping effects of the receiver, reducing thermal emittance to the environment, and reducing the overall size of the receiver. Each receiver configuration has finned structures that take advantage of the directional dependence of the heliostat field resulting in a light trapping effect on the receiver. The finned configurations tend to lead to “hot” regions on the receiver, but the new configurations can take advantage of high local view factors (each surface can “see” another receiver surface) in these regions through the use of heat transfer fluid (HTF) flow patterns. The HTF reduces the temperatures in these regions increasing the efficiency of heat transfer to the fluid. Finally, the new receiver configurations have a lower overall optical intercept region resulting in a higher geometric concentration ratio for the receiver. Compared to the base case analysis (flat plate receiver), the novel tubular geometries results showed an increase in thermal efficiency.

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 Coupled Optical-Thermal-Fluid Modeling of a Directly Heated Tubular Solar Receiver for Supercritical CO2 Brayton Cycle

2015 ◽  
Author(s):  
Jesus D. Ortega ◽  
Sagar D. Khivsara ◽  
Joshua M. Christian ◽  
Julius E. Yellowhair ◽  
Clifford K. Ho
Keyword(s):  
Solar Power ◽  
Fluid Model ◽  
Cfd Modeling ◽  
Radiation Absorption ◽  
Discrete Ordinates ◽  
Outlet Temperature ◽  
Brayton Cycle ◽  
Inlet Conditions ◽  
Solar Power Tower ◽  
Solar Receiver

Recent studies have evaluated closed-loop supercritical carbon dioxide (s-CO2) Brayton cycles to be a higher energy-density system in comparison to conventional superheated steam Rankine systems. At turbine inlet conditions of 923K and 25 MPa, high thermal efficiency (∼50%) can be achieved. Achieving these high efficiencies will make concentrating solar power (CSP) technologies a competitive alternative to current power generation methods. To incorporate a s-CO2 Brayton power cycle in a solar power tower system, the development of a solar receiver capable of providing an outlet temperature of 923 K (at 25 MPa) is necessary. The s-CO2 will need to increase in temperature by ∼200 K as it passes through the solar receiver to satisfy the temperature requirements of a s-CO2 Brayton cycle with recuperation and recompression. In this study, an optical-thermal-fluid model was developed to design and evaluate a tubular receiver that will receive a heat input ∼2 MWth from a heliostat field. The ray-tracing tool SolTrace was used to obtain the heat-flux distribution on the surfaces of the receiver. Computational fluid dynamics (CFD) modeling using the Discrete Ordinates (DO) radiation model was used to predict the temperature distribution and the resulting receiver efficiency. The effect of flow parameters, receiver geometry and radiation absorption by s-CO2 were studied. The receiver surface temperatures were found to be within the safe operational limit while exhibiting a receiver efficiency of ∼85%.

scholarly journals Performance Evaluation of Multiple Helical Tubes as a Receiver for Solar Parabolic Trough Collector

2019 ◽  
Vol 6 (2) ◽  
pp. 115-122
Author(s):  
Swapnil N. Lotake ◽  
M. M. Wagh
Keyword(s):  
Mass Flow ◽  
Thermal Efficiency ◽  
Power Plants ◽  
Focal Point ◽  
Thermal Power ◽  
Heat Transfer Fluid ◽  
Parabolic Trough ◽  
Black Paint ◽  
Parabolic Trough Collector ◽  
Helical Tubes

Solar parabolic trough collector consists of a parabolic reflector with a central receiver at a focal point through which heat transfer fluid is passed. Parabolic trough collector is used mostly in solar thermal power plants for generating electricity. This paper describes the experimental results of two straight tubes wrapped over each other to form a helically shaped receiver. The receiver was tested with aluminium material with and without black paint over it. Also, the helical tube receiver was tested with a glass cover over it, at two different mass flow rates and, with and without manual tracking. The tested instantaneous thermal efficiency ranges from 31.26% to 45.28% and the overall thermal efficiency ranges from 14.9% to 31.41% during the experimental period. The instantaneous thermal efficiency increased by an average of 1.32 times for unpainted receiver and 1.36 times for black painted receiver with the increase in mass flow rate. By tracking the parabolic collector according to sun’s position, there is an average increase in instantaneous thermal efficiency by 1.1 times for unpainted receiver and 1.04 times for black painted receiver. The paper further reveals that the use of multiple helical tubes as a receiver for parabolic trough collector increases the overall efficiency of the collector in a substantial manner.

Analytical assessment of a concentrated solar sub-critical thermal power plant using low temperature heat transfer fluid

2020 ◽  
pp. 0958305X2092159
Author(s):  
Umish Srivastva ◽  
K Ravi Kumar ◽  
RK Malhotra ◽  
SC Kaushik
Keyword(s):  
Heat Transfer ◽  
Power Plant ◽  
Thermal Efficiency ◽  
Thermal Power Plant ◽  
Solar Power ◽  
Thermal Power ◽  
Capital Cost ◽  
Shared Responsibility ◽  
Heat Transfer Fluid ◽  
Concentrated Solar Power

The paper presents energy–exergy–economic–environment–ethics analysis of a concentrated solar thermal power plant. Design basis of a concentrated solar power for 24 h operation on parabolic trough collector technology in best suited direct normal irradiation location and least capital cost analysis has been presented. An unconventional approach of reducing the capital cost is analyzed by intentionally designing the power plant for sub-critical conditions using a low-cost mineral oil with permissible operating temperature of 320°C in place of the conventional synthetic solar grade oil of 400°C. Using low pressure and temperature steam in the plant, it has been shown that while there is a reduction of 0.1% in energetic efficiency, there is a gain of 0.28% in the exergetic efficiency of the solar power plant conditions, gross thermal efficiency decreases by 1.18% and the net thermal efficiency decreases by 2.91%. However, the energetic and exergetic utilization factor for heat transfer fluid is increased by 0.84 and 5.58%, respectively. By suitably adjusting the solar field configuration and inlet oil temperature, energy savings to the tune of 45% is possible apart from 2.5 times of cost saving. An attempt has been made to quantifiably assess the ethics of switching to renewable electricity through shared responsibility as a novelty in the study. The payback period for the investment has also been shown to reduce from 20 years to 5 years assuming that the carbon price increases, concentrated solar power cost comes down by 25%, and cost at which electricity can be sold increases to US $0.14 (Rs. 10) per unit.

Experimental and Numerical Heat Transfer Analysis of an Air-Based Cavity-Receiver for Solar Trough Concentrators

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
R. Bader ◽  
A. Pedretti ◽  
A. Steinfeld
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Solar Power ◽  
Power Input ◽  
Heat Transfer Analysis ◽  
Heat Transfer Fluid ◽  
Inlet Temperature ◽  
Transfer Model ◽  
Outlet Temperature ◽  
Solar Receiver

We report on the field testing of a 42 m-long full-scale solar receiver prototype installed on a 9 m-aperture solar trough concentrator. The solar receiver consists of a cylindrical cavity containing a tubular absorber with air as the heat transfer fluid (HTF). Experimental results are used to validate a heat transfer model based on Monte Carlo ray-tracing and finite-volume techniques. Performance predictions obtained with the validated model yield the following results for the receiver. At summer solstice solar noon, with HTF inlet temperature of 120 °C and HTF outlet temperature in the range 250–450 °C, the receiver efficiency ranges from 45% to 29% for a solar power input of 280 kW. One third of the solar radiation incident on the receiver is lost by spillage at the aperture and reflection inside the cavity. Other heat losses are due to natural convection (9.9–9.7% of solar power input) and re-radiation (6.1–17.6%) through the cavity aperture and by natural convection from the cavity insulation (5.6–9.1%). The energy penalty associated with the HTF pumping work represents 0.6–24.4% of the power generated.

scholarly journals Performance Evaluation of Multiple Helical Tubes as a Receiver for Solar Parabolic Trough Collector

2020 ◽  
Vol 7 (1) ◽  
pp. 39-46
Author(s):  
Swapnil N. Lotake ◽  
M. M. Wagh
Keyword(s):  
Mass Flow ◽  
Thermal Efficiency ◽  
Power Plants ◽  
Focal Point ◽  
Thermal Power ◽  
Heat Transfer Fluid ◽  
Parabolic Trough ◽  
Black Paint ◽  
Parabolic Trough Collector ◽  
Helical Tubes

Solar parabolic trough collector consists of a parabolic reflector with a central receiver at a focal point through which heat transfer fluid is passed. Parabolic trough collector is used mostly in solar thermal power plants for generating electricity. This paper describes the experimental results of two straight tubes wrapped over each other to form a helically shaped receiver. The receiver was tested with aluminium material with and without black paint over it. Also, the helical tube receiver was tested with a glass cover over it, at two different mass flow rates and, with and without manual tracking. The tested instantaneous thermal efficiency ranges from 31.26% to 45.28% and the overall thermal efficiency ranges from 14.9% to 31.41% during the experimental period. The instantaneous thermal efficiency increased by an average of 1.32 times for unpainted receiver and 1.36 times for black painted receiver with the increase in mass flow rate. By tracking the parabolic collector according to sun’s position, there is an average increase in instantaneous thermal efficiency by 1.1 times for unpainted receiver and 1.04 times for black painted receiver. The paper further reveals that the use of multiple helical tubes as a receiver for parabolic trough collector increases the overall efficiency of the collector in a substantial manner.

scholarly journals Study on Outlet Temperature Control of External Receiver for Solar Power Tower

Energies ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 340
Author(s):  
Qiang Zhang ◽  
Kaijun Jiang ◽  
Yanqiang Kong ◽  
Jiangbo Wu ◽  
Xiaoze Du
Keyword(s):  
Temperature Control ◽  
Control Strategy ◽  
Solar Power ◽  
Heat Transfer Fluid ◽  
Weather Data ◽  
Unstable State ◽  
Inlet Temperature ◽  
Outlet Temperature ◽  
Power Load ◽  
Solar Power Tower

Due to the change of direct normal irradiance (DNI) and the change of output power load, the receiver of the solar tower is in an unstable state in the actual operation. In this paper, a 100 MW external cylindric receiver is designed and modelled. The dynamic and comprehensive model is established for the receiver, including the thermal and mechanical equations. The temperature control strategy is applied to the receiver model. The validity of the control strategy is verified by disturbance experiments, including DNI, the inlet temperature of the heat transfer fluid (HTF), and the weather data on a cloudy day. The response characteristics of the receiver are demonstrated. Its thermal lag characteristics and restraining effect on the fluctuating environment are revealed. The dangerous occasion of the receiver during operation are detected, including the overheat of the local panel, and the dissociation point of the molten salt. Both the robustness and the deficiency of the control strategy of the receiver are pointed out. The research results will contribute to the control strategy formulation of the SPT (solar power tower) station.

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.

scholarly journals Comparative Modeling of a Parabolic Trough Collectors Solar Power Plant with MARS Models

Energies ◽  
2017 ◽  
Vol 11 (1) ◽  
pp. 37 ◽  
Author(s):  
Jose Rogada ◽  
Lourdes Barcia ◽  
Juan Martinez ◽  
Mario Menendez ◽  
Francisco de Cos Juez
Keyword(s):  
Heat Transfer ◽  
Water Vapor ◽  
Power Plant ◽  
Solar Radiation ◽  
Thermal Energy ◽  
Power Plants ◽  
Solar Power ◽  
Rankine Cycle ◽  
Heat Transfer Fluid ◽  
Solar Field

Power plants producing energy through solar fields use a heat transfer fluid that lends itself to be influenced and changed by different variables. In solar power plants, a heat transfer fluid (HTF) is used to transfer the thermal energy of solar radiation through parabolic collectors to a water vapor Rankine cycle. In this way, a turbine is driven that produces electricity when coupled to an electric generator. These plants have a heat transfer system that converts the solar radiation into heat through a HTF, and transfers that thermal energy to the water vapor heat exchangers. The best possible performance in the Rankine cycle, and therefore in the thermal plant, is obtained when the HTF reaches its maximum temperature when leaving the solar field (SF). In addition, it is necessary that the HTF does not exceed its own maximum operating temperature, above which it degrades. The optimum temperature of the HTF is difficult to obtain, since the working conditions of the plant can change abruptly from moment to moment. Guaranteeing that this HTF operates at its optimal temperature to produce electricity through a Rankine cycle is a priority. The oil flowing through the solar field has the disadvantage of having a thermal limit. Therefore, this research focuses on trying to make sure that this fluid comes out of the solar field with the highest possible temperature. Modeling using data mining is revealed as an important tool for forecasting the performance of this kind of power plant. The purpose of this document is to provide a model that can be used to optimize the temperature control of the fluid without interfering with the normal operation of the plant. The results obtained with this model should be necessarily contrasted with those obtained in a real plant. Initially, we compare the PID (proportional–integral–derivative) models used in previous studies for the optimization of this type of plant with modeling using the multivariate adaptive regression splines (MARS) model.

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