16 research outputs found
A method for assessing measurement precision and stability of optical probes
The current strategy for measuring non-specular metre-scale surfaces â for instance segmented freeform optics post-grinding â in the mid- frequency bandwidths (S-filter), involves the use of contact probe based systems where measurement precision is a limiting factor. Equivalent non-contact optical probes claim accuracies up to an order of magnitude higher and could therefore improve current measurement systems. Chromatic confocal probes measure the distance to a surface using the principle of axial chromatic dispersion. The stability of a CHRocodile SE 300 ÎŒm probe was shown to be 200 ± 20 nm over an eight hour measurement period. A probe holder should be designed with a low thermal expansion material in order to thermally insulate the probe measurement for further investigation. The accuracy of the probe was assessed at the extremes of its measurement range. The maximum deviation over a 5 ÎŒm displacement was measured to be 85 nm. The entire measuring range should be investigated
Towards the development of the supply chain of concentrated solar power
This work focuses on the investigation into the planning of renewable energy power plants in Brazil using the Concentrated Solar Power (CSP) technology. The main aim of the paper is to present an analysis of the planning process that can be used as a basis of the development of a method to assess the Brazilianâs local manufacturing and supply chain capabilities in supporting the deployment of the CSP technology. The paper identifies areas in which the concerted efforts should be emphasized. For this, the paper will first discuss the key components of the chosen CSP technology (in this case the parabolic through). The manufacturing processes of these components will subsequently be analyzed and the key enabling technologies will be determined. The demands of electricity will be estimated using the System Advisory ModelÂź, a modelling tool developed by the National Renewable Energy Laboratory (NREL). An assessment method will finally be proposed to identify the potentials of the local Brazilian supply chain, through the readiness evaluation of the key enabling technologies and manufacturing processes
Commercial development of bio-combustible fuels from hydrothermal liquefaction of waste using solar collectors
Current methods to improve the viability of microalgae based biofuel production depend on improved microalgae strains, biorefinery concepts and identification of higher value applications such as cosmetics and nutraceuticals. Despite such efforts, the energy inputs into the microalgae conversion process remain high. The technical approach presented is to design, deploy and field test an integrated set-up of Concentrated Solar Power and Hydrothermal Liquefaction systems to produce bio-oil and evaluate the production and conversion processes. Phycofeedsâ approach is to integrate CSP and HTL technologies into the conversion process to improve the energy efficiency and the economic case for scaling microalgae based biofuel production. Further sustainability enhancements are achieved by integrating wastewater feedstock and market integration of output by-products for the aquaculture feed industry. This paper presents the microalgae harvesting and HTL bio-oil formation analysis procedures on a pre-pilot field scale. Solar concentrating captors are described and theoretical values obtained prior to experimental work that will be carried out in India
Theoretical and experimental analysis of an innovative dual-axis tracking linear Fresnel lenses concentrated solar thermal collector
Linear concentrating solar thermal systems offer a promising method for harvesting solar energy. In this paper, a model for a novel linear Fresnel lens collector with dual-axis tracking capability is presented. The main objective is to determine the performance curve of this technology by means of both experiment and theoretical analysis. A mathematical model including the optical model of the concentrator and the heat transfer model of the receiver pipe was developed. This tool was validated with experimental data collected using a proof of concept prototype installed in Bourne, UK. The performance curve of the collector was derived for temperatures between 40 °C and 90 °C. The results show that the global efficiency of the collector is limited to less than 20%. The energy losses have been analysed. The optical losses in the lens system accounts for 47% of the total energy dissipated. These are due to absorption, reflection and diffraction in the Fresnel lenses. Furthermore manufacturing error in the lens fabrication has to be considered. One third of the solar radiation collected is lost due to the low solar absorptance of the receiver pipe. Thermal radiation and convection accounts for 6% of the total as relatively low temperatures (up to 90 °C) are involved. In order to increase the performance of the system, it is recommended to install an evacuated receiver and to insulate the recirculation system. Considering data from manufacturers, these improvements could increase the global efficiency up to 55%. Utilising the results from this work, there is the intention of building an improved version of this prototype and to conduct further tests
Sub-surface damage issues for effective fabrication of large optics
A new ultra precision large optics grinding machine, BoXÂźhas been developed at
Cranfield University. BoXÂźislocated at the UK's Ultra Precision Surfaces
laboratory at the OpTIC Technium. This machine offers a rapidand economic
solution for grinding large off-axis aspherical and free-form optical
components.This paper presents an analysis of subsurface damage assessments of
optical ground materials produced usingdiamond resin bonded grinding wheels. The
specific materials used, ZerodurÂźand ULEÂźare currently understudy for making
extremely large telescope (ELT) segmented mirrors such as in the E-ELT
project.The grinding experiments have been conducted on the BoXÂźgrinding machine
using wheels with grits sizes of76 ÎŒm, 46 ÎŒm and 25 ÎŒm. Grinding process data
was collected using a Kistler dynamometer platform. Thehighest material removal
rate (187.5 mm3/s) used ensures that a 1 metre diameter optic can be ground in
lessthan 10 hours. The surface roughness and surface profile were measured using
a Form Talysurf. The subsurfacedamage was revealed using a sub aperture
polishing process in combination with an etching technique.These results are
compared with the targeted form accuracy of 1 ÎŒm p-v over a 1 metre part,
surface roughnessof 50-150 nm RMS and subsurface damage in the range of 2-5 ÎŒm.
This process stage was validated on a 400mm ULEÂźblank and a 1 metre hexagonal Z
Thermal effects compensation and associated uncertainty for large magnet assembly precision alignment
Big science and ambitious industrial projects continually push technical requirements forward beyond the grasp of conventional engineering techniques. An example of these are the extremely tight micrometric assembly and alignment tolerances required in the field of celestial telescopes, particle accelerators, and the aerospace industry. Achieving such extreme requirements for large assemblies is limited, largely by the capability of the metrology used, namely, its uncertainty in relation to the alignment tolerance required. The current work described here was done as part of Maria Curie European research project held at CERN, Geneva. This related to future accelerators requiring the spatial alignment of several thousand, metre-plus large assemblies to a common datum within a targeted combined standard uncertainty (uctg(y)) of 12âŻÎŒm. The current work has found several gaps in knowledge limiting such a capability. Among these was the lack of uncertainty statements for the thermal error compensation applied to correct for the assembly's dimensional instability, post metrology and during assembly and alignment. A novel methodology was developed by which a mixture of probabilistic modelling and high precision traceable reference measurements were used to quantify the uncertainty of the various thermal expansion models used namely: Empirical, Finite Element Method (FEM) models and FEM metamodels. Results have shown that the suggested methodology can accurately predict the uncertainty of the thermal deformation predictions made and thus compensations. The analysis of the results further showed how using this method a âdigital twinâ of the engineering structure can be calibrated with known uncertainty of the thermal deformation behaviour predictions in the micrometric range. Namely, the Empirical, FEM and FEM metamodels combined standard uncertainties ( uc(y) ) of prediction were validated to be of maximum: 8.7âŻÎŒm, 11.28âŻÎŒm and 12.24âŻÎŒm for the studied magnet assemblies
Precision grinding for rapid manufacturing of large optics
Large scale nuclear fusion and astronomy scientific programmes have increased the demand for large freeform mirrors and lenses. Thousands of one metre class, high quality aspherical optical components are required within the next five to ten years. Current manufacturing process chains production time need to be reduced from hundred hours to ten hours. As part of a new process chain for making large optics, an efficient low damage precision grinding process has been proposed. This grinding process aims to shorten the subsequent manufacturing operations. The BoX R grinding machine, built by Cranfield University, provides a rapid and economic solution for grinding large off-axis aspherical and free-form optical components. This thesis reports the development of a precision grinding process for rapid manufacturing of large optics using this grinding mode. Grinding process targets were; form accuracy of 1 m over 1 metre, surface roughness 150 nm (Ra) and subsurface damage below 5 m. Process time target aims to remove 1 mm thickness of material over a metre in ten hours. Grinding experiments were conducted on a 5 axes Edgetek high speed grinding machine and BoX R grinding machine. The surface characteristics obtained on optical materials (ULE, SiC and Zerodur) are investigated. Grinding machine influence on surface roughness, surface profile, subsurface damage, grinding forces and grinding power are discussed. This precision grinding process was validated on large spherical parts, 400 mm ULE and SiC parts and a 1 m Zerodur hexagonal part. A process time of ten hours was achieved using maximum removal rate of 187.5 mm 3 /s on ULE and Zerodur and 112.5 mm 3 /s on SiC. The subsurface damage distribution is shown to be "process" related and "machine dynamics" related. The research proves that a stiffer grinding machine, BoX, induces low subsurface damage depth in glass and glass ceramic.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
The design and modification of a parabolic trough system for the hydrothermal liquefaction of waste
We describe the design of a small-scale parabolic trough with a high-pressure absorber bundle to convert microalgae into bio-oil. The âproof-of-conceptâ system uses an existing Global CSP solar captor, with its reflectance enhanced by the addition of SkyfuelÂź ReflecTech Plus polymer film and has its original receiver tube replaced by a novel high-pressure multi-tube absorber and reactor. Initial results obtained at Kota University in Rajasthan, India demonstrated that temperatures up to 320°C are possible, and a bio-oil, similar to palm oil, was extracted from the reactor
Precision Grinding for Rapid Manufacturing of Large Optics
Large scale nuclear fusion and astronomy scientific programmes have increased the demand
for large freeform mirrors and lenses. Thousands of one metre class, high quality
aspherical optical components are required within the next five to ten years. Current manufacturing
process chains production time need to be reduced from hundred hours to ten
hours.
As part of a new process chain for making large optics, an efficient low damage precision
grinding process has been proposed. This grinding process aims to shorten the
subsequent manufacturing operations. The BoX
R
grinding machine, built by Cranfield
University, provides a rapid and economic solution for grinding large off-axis aspherical
and free-form optical components.
This thesis reports the development of a precision grinding process for rapid manufacturing
of large optics using this grinding mode. Grinding process targets were; form
accuracy of 1 m over 1 metre, surface roughness 150 nm (Ra) and subsurface damage
below 5 m. Process time target aims to remove 1 mm thickness of material over a metre
in ten hours.
Grinding experiments were conducted on a 5 axes Edgetek high speed grinding machine
and BoX
R
grinding machine. The surface characteristics obtained on optical materials
(ULE, SiC and Zerodur) are investigated. Grinding machine influence on surface
roughness, surface profile, subsurface damage, grinding forces and grinding power are
discussed.
This precision grinding process was validated on large spherical parts, 400 mm ULE and
SiC parts and a 1 m Zerodur hexagonal part. A process time of ten hours was achieved using
maximum removal rate of 187.5 mm
3
/s on ULE and Zerodur and 112.5 mm
3
/s on SiC.
The subsurface damage distribution is shown to be "process" related and "machine dynamics"
related. The research proves that a stiffer grinding machine, BoX, induces low
subsurface damage depth in glass and glass ceramic
Limiting travel speed in additive layer manufacturing
Wire and Arc Additive Manufacture (WAAM) is new approache to modern manufacturing. This technology has been gaining the interest of the research community due to its high deposition rate and efficiency. In Wire and Arc Additive Manufacture an increase in productivity can be achieved through the use of high weld travel speeds. However, this can be overshadowed by the so called humping effect. Humping is a defect in welding which expresses itself by the formation of humps and valleys that prevent further welding deposition operation. The generation of these defects is studied by critically examining the various weld travel speeds from different weld parameters. From the study the actual weld travel speed in which humping formation starts to appear is 0.6m/min. The effects of wire feed speed and travel speed on bead geometries are also been discussed