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.

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.

scholarly journals Generation of a Parabolic Trough Collector Efficiency Curve From Separate Measurements of Outdoor Optical Efficiency and Indoor Receiver Heat Loss

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Charles Kutscher ◽  
Frank Burkholder ◽  
J. Kathleen Stynes
Keyword(s):  
Ambient Temperature ◽  
Heat Loss ◽  
Thermal Efficiency ◽  
Operating Temperature ◽  
Efficiency Curve ◽  
Parabolic Trough ◽  
Optical Efficiency ◽  
Parabolic Trough Collector ◽  
Collector Efficiency ◽  
The Difference

The thermal efficiency of a parabolic trough collector is a function of both the fraction of direct normal radiation absorbed by the receiver (the optical efficiency) and the heat lost to the environment when the receiver is at operating temperature. The thermal efficiency can be determined by testing the collector under actual operating conditions or by separately measuring these two components. This paper describes how outdoor measurement of the optical efficiency is combined with laboratory measurements of receiver heat loss to obtain the thermal efficiency curve. This paper describes this approach and also makes the case that there are advantages to plotting collector efficiency versus the difference between the operating temperature and the ambient temperature at which the receiver heat loss was measured divided by radiation to a fractional power (on the order of 1/3 but obtained via data regression)—as opposed to the difference between operating and ambient temperatures divided by the radiation. The results are shown to be robust over wide ranges of ambient temperature, sky temperature, and wind speed.

Thermoelectric Power of the Liquid Sn—Te Alloy

1982 ◽  
Vol 37 (10) ◽  
pp. 1127-1131 ◽  
Author(s):  
D. H. Kurlat ◽  
M. Rosen
Keyword(s):  
Thermoelectric Power ◽  
Hard Sphere ◽  
Stoichiometric Composition ◽  
Band Model ◽  
Liquid Alloys ◽  
Sphere Approximation ◽  
The Difference ◽  
Predicted Values ◽  
Experimental Values ◽  
Two Band Model

The Seebeck coefficient (S) of Sni1-x- Tex liquid alloys was measured as a function of concentration and temperature. For 0 ≦ x <0.45 the behaviour is metallic; S values are small and negative, rising linearly with temperature. The predicted values of Ziman's theory when using the hard sphere approximation disagree with the experimental ones. The change in sign occurs for 0.45. For x = 0.5 (stoichiometric composition) the thermoelectric power decreases linearly with temperature. This fact is explained assuming a two-band model. For x ≧ 0.6 the liquid alloy becomes more semiconducting and presents a maximum in the isotherms of S for x = 0.65. For the excess tellurium concentration range we have calculated the difference EF - EV and γ/kB, assuming a S(1/T) law. The experimental values are compared with those of Dancy and Glazov.

scholarly journals Composite Distribution Solution for Minimizing Heat Loss in a Pyrolysis Reactor

2011 ◽  
Vol 9 (1) ◽  
Author(s):  
Werner O. Filtvedt ◽  
Morten Melaaen ◽  
Arve Holt ◽  
Massoud Javidi ◽  
Birger Retterstøl Olaisen
Keyword(s):  
Heat Loss ◽  
Reaction Chamber ◽  
Inlet Temperature ◽  
Chemical Reactors ◽  
Normal Procedure ◽  
Pyrolysis Reactor ◽  
The Difference ◽  
Distribution Plate ◽  
Composite Distribution ◽  
Novel Design

The article presents a novel design for a distribution plate. The solution is suitable for a reactor vessel where a reactant gas needs to be maintained at a different temperature from the reaction chamber in order to avoid unwanted occurrences, such as clogging of the distribution plate. A normal procedure involves cooling of the distribution plate which is reported to either increase heat loss substantially or yield insufficient temperature in parts of the reaction chamber. The problem is especially important for reactors where the difference in reactant inlet temperature and desired reaction temperature is large. The investigated design utilized materials of very different thermal conductivity to only cool specific parts of the distribution arrangement and thereby minimize heat loss. Our system is a distribution plate for use in a fluidized bed reactor for silane pyrolysis. However, the solution is general and may be utilized in many types of vessels and chemical reactors.

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 Evaluation of the Vertical Producing Degree of Commingled Production via Waterflooding for Multilayer Offshore Heavy Oil Reservoirs

Energies ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 2428 ◽  
Author(s):  
Fei Shen ◽  
Linsong Cheng ◽  
Qiang Sun ◽  
Shijun Huang
Keyword(s):  
Heavy Oil ◽  
Flow Model ◽  
Dynamic Method ◽  
Theoretical Models ◽  
Oil Reservoirs ◽  
Sweep Efficiency ◽  
One Dimensional ◽  
Heavy Oil Reservoirs ◽  
The Difference ◽  
Important Form

Recently, commingling production has been widely used for the development of offshore heavy oil reservoirs with multilayers. However, the differences between layers in terms of reservoir physical properties, oil properties and pressure have always resulted in interlayer interference, which makes it more difficult to evaluate the producing degree of commingled production. Based on the Buckley–Leverett theory, this paper presents two theoretical models, a one-dimensional linear flow model and a planar radial flow model, for water-flooded multilayer reservoirs. Through the models, this paper establishes a dynamic method to evaluate seepage resistance, sweep efficiency and recovery percent and then conducts an analysis with field data. The result indicates the following: (1) the dynamic difference in seepage resistance is an important form of interlayer interference during the commingled production of an offshore multilayer reservoir; (2) the difference between commingled production and separated production is small within a certain range of permeability ratio or viscosity ratio, but separated production should be adopted when the ratio exceeds a certain value.

TRUE AND APPARENT METABOLIZABLE ENERGY VALUES FOR POULTRY OF CANADIAN WHEATS AND OATS MEASURED BY BIOASSAY AND PREDICTED FROM PHYSICAL AND CHEMICAL DATA

1977 ◽  
Vol 57 (2) ◽  
pp. 365-374 ◽  
Author(s):  
I. R. SIBBALD ◽  
K. PRICE
Keyword(s):  
Metabolizable Energy ◽  
Chemical Data ◽  
Accuracy And Precision ◽  
Apparent Metabolizable Energy ◽  
The Difference ◽  
Variation Explained ◽  
Predicted Values ◽  
Naked Oats ◽  
Physical And Chemical ◽  
Better Than

Thirty samples of wheat and 28 samples of oats were assayed for true and apparent metabolizable energy (TME, AME). Within grains, the difference TME−AME increased with decreasing AME values; there is evidence that this trend is associated with reduced voluntary consumption of AME assay diets containing low energy grains. The TME and AME data were compared with ME values predicted from physical and chemical data describing the grains. Previously published prediction equations were tested and new equations were derived. Comparisons between predicted and observed data suggested that both the TME and AME values of wheat were predicted with insufficient accuracy and precision for practical use. Similar comparisons using the oat data showed high correlations between observed and predicted values, although the predictions were no more accurate than for wheat; however, when data describing four samples of naked oats were removed, the correlations were reduced substantially. Comparisons involving data for the hulled oats indicated that most equations were able to predict AME better than TME. Multiple regression analysis was used to identify those combinations of variables best able to predict TME data. No combination of variables was best for both wheat and oats. The combinations of variables used in published equations performed quite well. With four variables, the percentage of the TME variation explained was as high as 52 for wheat, 82 for oats and 64 for hulled oats. Predictions based on air-dry data are associated with higher correlations than those based on dry matter data, but the air-dry predictions are the less useful in practice. The reason for this is discussed.

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