Analysis of the operation and performance of a solar cooling system

In recent years, renewable sources of energy have been increasingly sought after to shift the consumption of energy from conventional sources to clean energy sources. A myriad of applications exist to exploit solar, wind, geothermal and any other means to provide the required process. Solar energy systems can either produce electricity or hot water. Solar cooling systems are being installed to provide space cooling or process cooling in locations where sufficient thermal energy is present to operate the vapour absorption chiller to replace vapour compression systems. Thus since sufficient solar energy was incident on the building of the Oenology and Viticulture Research Centre at Buskett, it was used to generate hot water to operate a solar cooling system to supply chilled water to control the temperature of fermenting wine. Prior to the installation, process cooling was provided through a vapour compression system. Initially a control system was designed to operate the solar cooling system. The system could not operate during high solar radiation scenarios and thus significant number of experimentats were carried out to improve the operation and performance of the solar cooling system.peer-reviewe

Solar cooling at the oenology and viticulture research centre, Buskett, Rabat

This paper describes the design, installation and testing of two solar cooling systems at the Oenology and Viticulture Research Centre, Buskett, Rabat, Malta. One system consisted of a bank of photovoltaic panels converting solar energy into electricity which was fed into the national grid and a conventional vapour compression chiller powered by electricity from the grid. The second system was based on an ammonia-water vapour absorption chiller which was driven by hot water from a bank of vacuum-tube solar collectors. Dry re-cooling was chosen as the method of heat rejection.peer-reviewe

Temperature measurement in solar thermal applications

While measuring the temperature of a fluid such as air or water which is exposed to solar radiation, the temperature measuring device, such as a thermocouple, should be shielded from incident irradiance. The probe should be well ventilated in order to increase heat transfer by convection and thus get a reading closer to the true temperature. The popular Stevenson screen which is used for meteorological air temperature measurement consists of a cage with horizontal louvers. This makes it too bulky to use in enclosures such as solar collectors. In this study, various shields have been analysed under laboratory conditions using a halogen lamp as a source of infrared radiation. The standard on Guidance for Solar Radiation Testing (60068-2-9:2000) suggests to use a thermocouple freely mounted in a radiation shield comprising a cupro-nickel tube. However experimental results show that the thermocouple reading resulted in 9°C higher than the true air temperature. Other radiation shields consisting of white vertical PVC tubes, varying in length and diameter, resulted in a temperature increase of 3-5°C. The closest temperature reading was achieved by using a longitudinally slit tube as the radiation screen. This resulted in a discrepancy of around 1-3°C higher than the true temperature. It was observed that the difference between the true temperature and the reading from the shielded thermocouple decreases with increasing both length and diameter of the slit tube.peer-reviewe

Decarbonising the shipping sector : a critical analysis on the application of waste heat for refrigeration in fishing vessels

The integration of sorption systems on-board fishing vessels has been explored in the last decade, but the limitations in power density and temperature levels achievable have hindered their application. In the present paper, the integration of hybrid sorption–compression systems was evaluated. Different shipping vessels and routes in seas and oceans were considered in the analysis, with engine powers from 190 kW to 500 kW. The feasibility of series and cascade configurations was studied and the possible benefits, in terms of fuel and CO2 savings, were evaluated. The analysis, which also considered the payload due to the extra fuel needed to transport the equipment for refrigeration, showed that up to 75% savings can be obtained, with CO2 emissions avoided up to 20 t/y.peer-reviewe

Simulation and experimentation of heat transfer in a solar distillation still

This paper deals with a simple and inexpensive solar desalination configuration. The performance of a simple solar still operating under Maltese climatic conditions is analysed both theoretically and experimentally. The internal and external heat transfer modes of the distillation unit are examined. This paper concludes that the distillation rate in a simple solar distiller increases with ambient temperature and solar radiation, even though the condensation capacity of the glass is reduced. A higher wind speed decreases the evaporation and condensation processes. The energy fractions within the solar still have also been analysed. The simulations and the experiments conclude that the glass components handle the bulk of the heat transferred in a solar still namely radiation, evaporation and condensation and thus the distillation efficiency is enhanced by improving the thermal and optical properties of the glass.peer-reviewe

The use of a solar chimney to enhance the productivity of a solar still

Solar distillation is one of the possible solutions to mitigate both the energy and water scarcity issues in remote areas especially those in hot and arid countries. The main advantages of solar stills include the facts that they are passive, inexpensive to construct and maintain, require very low technical expertise and are reliable. However since the productivity is relatively low when compared to other technologies, solar stills are mostly applicable for decentralised water production to provide water to families or small villages which have access to brackish or seawater. This paper analyses the use of a solar chimney which was used to enhance the convective currents within a solar still. Moreover, a condenser was also installed to improve the condensation process. Condensers in solar stills typically consist of fresh seawater flowing through a bank of tubes. However in the configuration presented in this paper, water vapour was forced through a number of ducts immersed in seawater. This solar still was constructed and tested under natural weather conditions using a typical simple solar still as a benchmark. The paper describes how the solar chimney and condensers improved the efficiency of the solar still.peer-reviewe

A Multilaboratory Comparison of Calibration Accuracy and the Performance of External References in Analytical Ultracentrifugation

Analytical ultracentrifugation (AUC) is a first principles based method to determine absolute sedimentation coefficients and buoyant molar masses of macromolecules and their complexes, reporting on their size and shape in free solution. The purpose of this multi-laboratory study was to establish the precision and accuracy of basic data dimensions in AUC and validate previously proposed calibration techniques. Three kits of AUC cell assemblies containing radial and temperature calibration tools and a bovine serum albumin (BSA) reference sample were shared among 67 laboratories, generating 129 comprehensive data sets. These allowed for an assessment of many parameters of instrument performance, including accuracy of the reported scan time after the start of centrifugation, the accuracy of the temperature calibration, and the accuracy of the radial magnification. The range of sedimentation coefficients obtained for BSA monomer in different instruments and using different optical systems was from 3.655 S to 4.949 S, with a mean and standard deviation of (4.304 ± 0.188) S (4.4%). After the combined application of correction factors derived from the external calibration references for elapsed time, scan velocity, temperature, and radial magnification, the range of s-values was reduced 7-fold with a mean of 4.325 S and a 6-fold reduced standard deviation of ± 0.030 S (0.7%). In addition, the large data set provided an opportunity to determine the instrument-to-instrument variation of the absolute radial positions reported in the scan files, the precision of photometric or refractometric signal magnitudes, and the precision of the calculated apparent molar mass of BSA monomer and the fraction of BSA dimers. These results highlight the necessity and effectiveness of independent calibration of basic AUC data dimensions for reliable quantitative studies

A multilaboratory comparison of calibration accuracy and the performance of external references in analytical ultracentrifugation.

Analytical ultracentrifugation (AUC) is a first principles based method to determine absolute sedimentation coefficients and buoyant molar masses of macromolecules and their complexes, reporting on their size and shape in free solution. The purpose of this multi-laboratory study was to establish the precision and accuracy of basic data dimensions in AUC and validate previously proposed calibration techniques. Three kits of AUC cell assemblies containing radial and temperature calibration tools and a bovine serum albumin (BSA) reference sample were shared among 67 laboratories, generating 129 comprehensive data sets. These allowed for an assessment of many parameters of instrument performance, including accuracy of the reported scan time after the start of centrifugation, the accuracy of the temperature calibration, and the accuracy of the radial magnification. The range of sedimentation coefficients obtained for BSA monomer in different instruments and using different optical systems was from 3.655 S to 4.949 S, with a mean and standard deviation of (4.304 ± 0.188) S (4.4%). After the combined application of correction factors derived from the external calibration references for elapsed time, scan velocity, temperature, and radial magnification, the range of s-values was reduced 7-fold with a mean of 4.325 S and a 6-fold reduced standard deviation of ± 0.030 S (0.7%). In addition, the large data set provided an opportunity to determine the instrument-to-instrument variation of the absolute radial positions reported in the scan files, the precision of photometric or refractometric signal magnitudes, and the precision of the calculated apparent molar mass of BSA monomer and the fraction of BSA dimers. These results highlight the necessity and effectiveness of independent calibration of basic AUC data dimensions for reliable quantitative studies

Approaches to industrial heritage: what works?

Malta has a rich industrial heritage. The Dockyard Boiler Shop is full of artefacts of industrial heritage, from buses to machinery salvaged from the Dockyard. There are then the engines and steam plant at Kordin, engines in water pumping stations, the beautifully preserved 1907 machine-shop at the Conservatorio Vincenzo Bugeja, the underground mills, and lots more, besides private collections, some of which are quite interesting and extensive. One problem is how to conserve all this material, and another problem is deciding what to keep. One positive aspect that has helped safeguard some industrial heritage items is that it sometimes costs more money to scrap them than to leave them where they are.peer-reviewe

Successive stages of amyloid-? self-assembly characterized by solid-state nuclear magnetic resonance with dynamic nuclear polarization

Self-assembly of amyloid-β (Aβ) peptides in human brain tissue leads to neurodegeneration in Alzheimer’s disease (AD). Amyloid fibrils, whose structures have been extensively characterized by solid state nuclear magnetic resonance (ssNMR) and other methods, are the thermodynamic end point of Aβ self-assembly. Oligomeric and protofibrillar assemblies, whose structures are less well-understood, are also observed as intermediates in the assembly process in vitro and have been implicated as important neurotoxic species in AD. We report experiments in which the structural evolution of 40-residue Aβ (Aβ40) is monitored by ssNMR measurements on frozen solutions prepared at four successive stages of the self-assembly process. Measurements on transient intermediates are enabled by ssNMR signal enhancements from dynamic nuclear polarization (DNP) at temperatures below 30 K. DNP-enhanced ssNMR data reveal a monotonic increase in conformational order from an initial state comprised primarily of monomers and small oligomers in solution at high pH, to larger oligomers near neutral pH, to metastable protofibrils, and finally to fibrils. Surprisingly, the predominant molecular conformation, indicated by ¹³C NMR chemical shifts and by side chain contacts between F19 and L34 residues, is qualitatively similar at all stages. However, the in-register parallel β-sheet supramolecular structure, indicated by intermolecular ¹³C spin polarization transfers, does not develop before the fibril stage. This work represents the first application of DNP-enhanced ssNMR to the characterization of peptide or protein self-assembly intermediates