Exploring the potential of nanofluids to enhance the productivity of solar stills

Desalination technologies are being used to augment access to safe drinking water around the world. Nonetheless, most of these technologies are energy-intensive and driven by fossil fuels which emit greenhouse gases into the atmosphere, thereby contributing to climate change. Additionally, fossil fuels are non-renewable sources of energy and the exhaustion of such reserves can cause a threat to energy security. Consequently, exploitation of sustainable sources of energy for the desalination process has attracted a lot of attention. One such strategy is the use of a solar still which utilises solar energy to produce fresh water from saline or brackish water. However, the major drawback of a solar still lies in its low productivity. Many studies have investigated means of increasing the productivity of a solar still. One such technique which has recently been studied is to disperse nanoparticles into the impure water inside the basin of a solar still in order to obtain a nanofluid with enhanced optical and heat transfer characteristics. Since this is a relatively new topic, very few numerical studies on solar stills with nanofluids are available. Moreover, based on a literature review, no study examining the effect of nanoparticle size on the productivity of solar stills, and on the economic and environmental performance of solar stills was found. Additionally, the few available numerical studies on solar stills with nanofluids have not taken into account the view factor in the computation of the internal radiative heat transfer coefficient. Therefore, the aim of this study was to investigate both numerically and experimentally the effect of nanoparticle size on the performance of solar stills. Mathematical models with the view factor (Model 1) and without the view factor (Model 2) were developed for single slope solar stills, and a code was written in MATLAB software to solve a system of equations iteratively. Calculations were performed using climatic data from Stellenbosch (latitude 33.93°S, longitude 18.86°E) and University of Cape Town (latitude 33.96°S, longitude 18.46°E), South Africa, in order to evaluate the performance of solar stills with varying nanoparticle sizes. For the experimental phase, four identical solar stills were designed and built, and they were first tested with water only (base fluid) in all of them to test their performance and for calibration purposes. An Analysis of Variance (ANOVA) test was conducted on the experimental data collected from this first test. Subsequently, nanofluids containing aluminium oxide (Al2O3) nanoparticles of size 10 nm, 50 nm and 100 nm were used in three of the solar stills, with the other solar still containing the base fluid only. All the experiments were conducted at the University of Cape Town. The mathematical models were then validated using experimental data. Simulations in MATLAB based on Stellenbosch climatic data showed that for the month of January, which is a summer month in South Africa, the productivity of the solar still with the 10 nm, 50 nm and 100 nm Al2O3 nanoparticles was 9.01%, 8.94% and 8.89%, respectively higher than the productivity of the solar still with the base fluid only. On the other hand, for the month of July, which is a winter month in South Africa, the average productivity of the solar still with the 10 nm, 50 nm and 100 nm Al2O3 nanoparticles was 1.31%, 1.23% and 1.19%, respectively higher than the productivity of the solar still with base fluid only. In terms of the economic analysis, the simulations in MATLAB based on annual climatic data from Stellenbosch revealed that the cost of distilled water obtained from the solar still with the 10 nm, 50 nm and 100 nm Al2O3 nanoparticles was 10.42%, 6.21% and 3.51%, respectively higher than the cost of water obtained from the solar still with the base fluid only. Additionally, the payback period for the solar still with the 10 nm, 50 nm and 100 nm Al2O3 nanoparticles was 13.32%, 7.86% and 4.37%, respectively higher than the payback period for the solar still with the base fluid only. In terms of the environmental performance, the amount of carbon dioxide equivalent (CO2 equivalent) mitigated by the solar still with the 10 nm, 50 nm and 100 nm Al2O3 nanoparticles was 6.18%, 6.11% and 6.06%, respectively higher than the amount of CO2 equivalent mitigated by the solar still with the base fluid only. For the experimental phase, the ANOVA test based on the first set of experimental data (with base fluid only in all four solar stills) gave a probability-value (P-value) of 1.00. Moreover, experimental data collected from solar stills with base fluid and nanofluids revealed that the productivity of the solar still with nanoparticles of size 10 nm and 50 nm was 26.46% and 1.46%, respectively higher than the productivity of the solar still with base fluid only. On the other hand, the productivity of the solar still with nanoparticles of size 100 nm was 9.38% lower than that of the solar still with base fluid only. Furthermore, the root mean square error (RMSE) for the solar stills with nanofluids for Model 1 and Model 2 was 22.02% and 36.03%, respectively. It was confirmed that the performance of the calibrated solar stills was not significantly different. Moreover, the enhancement in the productivity of a solar still with nanofluids is much more distinct in summer than in winter. It was also demonstrated that the productivity of a solar still decreases with increasing nanoparticle size. Additionally, it was established that the cost of distilled water, the payback period and the amount of mitigated CO2 equivalent decrease with increasing nanoparticle size. Theoretically, the distillate yield and environmental performance of a solar still with nanofluids were marginally sensitive to the nanoparticle size while the cost of distilled water and payback period were significantly affected by the nanoparticle size. The effect of nanoparticle size on distillate yield was experimentally significant. Finally, it was demonstrated that the inclusion of the view factor improves the accuracy of modelling of solar stills with nanofluids

Conceptualisation and Early Implementation of an Academic Advising System at the University of Cape Town

AbstractAcademic advising is a High-Impact Practice that supports better outcomes for all students, particularly those encountering structural barriers to success. This paper presents a case study of processes followed in a three-year project (2018–20) at the University of Cape Town (UCT) to conceptualise, design, and start implementing an academic advising system. Three goals were formulated:1. to develop conceptual capacity and a theory of academic advising;2. to develop an academic advising model responsive to institutional context and student need; and3. to develop structures, relationships, tools, and resources to implement a coherent system.An informed grounded theory approach was used to analyse baseline data of existing support and advising at the institution. Data was collected through document and desktop research, interviews with stakeholders, and student focus groups. A monitoring and evaluation framework was developed to track and reflect on progress against the goals. Iterative cycles of data collection, analysis, and reflection took place as implementation started. A key finding was that UCT’s advising structures incline towards a decentralised faculty-based model, complemented by centralised support services that encompass advising functions. Low levels of integration were found, as well as inefficient duplication of services. To address these challenges, the conceptual and operational capacity of the academic advising team needed to be advanced. This was done by assembling a multidisciplinary team, undergoing professional training, and by running a journal club. A promising theoretical approach that emerged was a capability approach to academic advising. A shared model of academic advising was found to be best suited to the institutional context and a three-tiered model operationalised by faculty, professional, and peer advisers, as well as by automated advising tools, was designed. Implementation started through pilot projects. During Covid-19, innovative concept and centralised systems development that connected students to institutional resources, enabling them to practise agency and supporting their ability to achieve despite unprecedented structural barriers, demonstrated the viability of the capability approach adopted for steering further development of the system

Numerical study of the thermal performance of solar chimneys for ventilation in buildings

Building ventilation is crucial for improving the indoor air quality and thermal comfort. Nowadays, mechanical ventilation systems such as air conditioning and fans are most commonly used in buildings. However, these devices consume a lot of electricity which is mainly generated from the combustion of fossil fuels, resulting in the release of greenhouse gases and thereby contributing to climate change. Consequently, it is essential to switch to natural ventilation systems which are environmentally friendly as they are based on renewable sources of energy. One such type of natural ventilation system is the solar chimney which can either be roof-mounted or wall-mounted in buildings. The aim of this study was to develop a mathematical model for assessing the thermal performance of roof-mounted (inclined) and wall-mounted (vertical) solar chimneys. The model was validated using numerical simulations in MATLAB. Different configurations of solar chimneys were designed and modelled in MATLAB in order to compare their performances, in terms of the ventilation rate expressed as the number of air changes per hour, ACH. Raw climatic data, including the intensities of global and diffuse solar radiation on a horizontal plane, wind speed and ambient temperature were obtained for Stellenbosch, located in the Western Cape Province of South Africa. This was used for the MATLAB modelling of the solar chimneys. The effects of inclination angle, air gap, chimney height and view factor on the thermal performance of solar chimneys were explored in this study

Integration of waste heat in thermal desalination technologies: A review

Desalination is increasingly becoming a crucial method for providing fresh water globally. However, most of the desalination technologies are energy-intensive and driven by fossil fuels that are contributing to climate change and other environmental problems. In this vein, renewable energy and energy efficiency are promising pillars of sustainable energy production and consumption, and the recovery of waste heat helps to augment the energy efficiency of a system. Based on the temperature (T) of the heat source, waste heat can be classified into three categories: low temperature (T<100°C), medium temperature (100°C£T<300°C) and high temp-erature (T³300°C). There is scarcity of review work on the integration of waste heat in desalination technologies. In this study, the progress in the utilisation of waste heat to drive thermal desalination processes has been investigated. It is found that 63% of waste heat streams are of low grade, which is still satisfactory for thermal desalination technologies that run on low-temperature heat sources. As of 2018, there was only one known thermal desalination plant driven by waste heat. Lack of data on waste heat, especially in developing countries, has been identified as a major challenge to the advancement of desalination technologies driven by this source of thermal energy. Other constraints are presented and discussed in this paper