Performance Of Solar Thermal Systems Research Articles

Thermal energy storage using phase change material for solar thermal technologies: A sustainable and efficient approach

Over-exploitation of fossil-based energy sources is majorly responsible for greenhouse gas emissions which causes global warming and climate change. To mitigate these challenges renewable energy sources, especially solar thermal technologies, can play a decisive role. United Nations also proposes steps to attenuate the adverse effects of fossil-based energy and climate change through Sustainable Development Goals (SDG7 and SDG8). Solar thermal technologies have seen a huge capacity expansion around the globe in previous decades because of their inherent advantages. However, solar energy faces crucial limitations of fluctuating intensity and time-dependent availability. This decreases solar thermal system performance and makes solar thermal technologies time-dependent. To overcome these challenges, integrating phase change material (PCM) in solar thermal technologies makes a sustainable approach to enhance the efficacy, productivity, and utilization rate of solar thermal technologies. In this manuscript, the sustainable approach of integrating PCM in solar thermal technologies was reviewed. This includes literature on PCMs which covers classification, properties, importance, and limitation. Comprehensive data on the integration of PCM with solar thermal technologies such as solar water heating, solar desalination, solar cooking, solar dryers, solar PV/T, solar ponds, solar chimneys, and solar power plants were reported explicitly in terms of the type of PCM, efficiency and their productivity. In addition, the effect of PCMs integration in solar thermal technologies was analyzed in terms of mitigation of CO2 emissions and economic analysis at different locations around the World.

Harnessing Nanomaterials for Enhanced Energy Efficiency in Transpired Solar Collectors: A Review of Their Integration in Phase-Change Materials

The building sector plays an important role in the global climate change mitigation objectives. The reduction of CO2 emissions and energy consumption in the building sector has been intensively investigated in the last decades, with solar thermal energy considered to be one of the most promising solutions due to its abundance and accessibility. However, the discontinuity of solar energy has led to the study of thermal energy storage to improve the thermal performance of solar thermal systems. In this review paper, the integration of various types of phase-change materials (PCMs) in transpired solar collectors (TSC) is reviewed and discussed, with an emphasis on heat transfer enhancements, including nanomaterials. Thermal energy storage applied to TSC is studied in terms of design criteria, materials technologies, and its impact on thermal conductivity. This review highlights the potential of nanomaterial technology integration in terms of thermal performance improvements. The utilization of nanomaterials in solar walls holds the potential to significantly enhance their performance. The integration of diverse materials such as graphene, graphite, metal oxides, and carbon nanoparticles can pave the way for improving thermal conductivity.

Enhanced performance of photovoltaic thermal module and solar thermal flat plate collector connected in series through integration with phase change materials: A comparative study

The decline in photovoltaic cell efficiency due to temperature elevation, coupled with solar energy's inherent intermittency, presents challenges for solar systems, including photovoltaic panels and solar thermal (ST) collectors. The integration of phase change materials (PCMs) emerges as a promising solution to enhance thermal energy storage and regulation, thereby improving system performance and sustainability. This study investigates the performance of series-connected photovoltaic thermal (PVT) and ST systems with integrated PCMs from energy and exergy viewpoints, utilizing a 3D transient numerical simulation. The proposed system's performance is compared with that lacking a PCM across various heat transfer fluid mass flow rates. Suitable PCM selection based on melting temperature is explored, along with PCM layer thickness and nanoparticle augmentation. The research highlights that PCM integration effectively regulates PV cell temperature, enhancing electrical power and exergy rate. While increasing the mass flow rate improves thermal and electrical power, it reduces the thermal exergy rate. Comparing different PCMs (RT28 HC, RT35 HC, and RT44 HC), the RT28 HC PCM provides the lowest temperature of PV cells and the best electrical performance during the day. Moreover, increasing PCM layer thickness results in lowering PV cell and outlet temperatures and storing more heat. Nanoparticles added to PCMs lead to a marginal improvement in energy and exergy, especially for the system with RT28 HC. This analysis emphasizes PCM integration's role in enhancing solar thermal system performance, highlighting the importance of considering the PCM's melting temperature for effective thermal energy management.

Comparative thermal analysis of Nickel and Tantalum based hybrid nanofluid using constant proportional Caputo and Atangana–Baleanu operators with time-controlled condition

The main purpose of this research work is to examine how the immersion of nickel and tantalum nanoparticles in water affects the flow and thermal properties of water, with the aim of anticipating potential enhancements. The investigation pertains to the flow behavior of a hybrid nanofluid over an extensively elongated vertical surface under the influence of a condition that varies with time. The phenomenon of heat transfer transpires due to the combined effects of natural convection and thermal radiation. An in-depth comprehension of flow patterns and heat transfer over a vertical surface is essential for optimizing heat exchange processes, designing efficient cooling systems, and enhancing overall energy efficiency. It also helps in climate modeling, weather prediction, and the improvement of the performance of solar thermal systems. The basic model is generalized using Atangana–Baleanu (AB) and constant proportional Caputo (CPC) operators. This generalization leads to the development of two different fractional settings for which separate mathematical analyses are performed. With the help of some new unit-independent quantities, exact solutions for both fractional frameworks are computed using the Laplace transform. For the elucidation of changes in velocity and thermal fields due to different physical effects, several graphical and tabular representations are produced. The outcomes illustrate that the incorporation of uniform concentrations of nickel and tantalum nanoparticles in water leads to raising its thermal efficacy up to 40.39%. The nanoparticles consisting of lamina shapes are observed to produce the maximum amelioration in thermal features. The CPC model based profiles of flow and temperature fields are lower than those procured via the AB model. As a result of nanoparticles’ intrinsic characteristics, the insignificant heat transfer capability of water is greatly amplified, leading to a notable boost in its thermal performance. Thus, the examined hybrid nanofluid can be used as a viable alternative to water in various engineering applications.

Current density and thermal propagation of electromagnetic CoFe2O4 and TiO2/C2H6O2 + H2O hybridized Casson nanofluids: A concentrated solar power maximization

The limited availability of fossil fuel, ecosystem consideration and economic factor stimulates interest in alternative energy provision and thermal energy enhancement. Utilization of solar radiation and nanofluids with solid tiny particle provides a platform to optimize renewable solar thermal system performance. Owing to its usages, this study examines thermal transfer and current density of electromagnetic gravity driven Casson hybridized nanofluid flow through partially filled porous media with Ohmic heating. A mixture of cobalt ferrite (CoFe2O4) and titanium dioxide (TiO2) is considered for the nanoparticles thermal propagation in base solvent ethylene-glycol+water (C2H6O2+H2O). A parabolic concentrated solar collector is used for the solar radiation absorption with a continuous energy supply. An invariant transformation of the partial derivative model is obtained using similarity variables. A semi-analytical shifted Chebyshev method coupled with the integrated collocation scheme has been adopted to provide theoretical solutions to the model. The study revealed that concentrated solar power current density is raised as the electric field factor and medium porosity is increased. The fluid velocity is damped while the temperature distribution is enhanced as the nanoparticle volume fraction is boosted. Thus, this investigation will improve the efficiency of thermal engineering products and enhance industrial performance.

Fault detective: Automatic fault-detection for solar thermal systems based on artificial intelligence

Fault-Detection (FD) is essential to ensure the performance of solar thermal systems. However, manually analyzing the system can be time-consuming, error-prone, and requires extensive domain knowledge. On the other hand, existing FD algorithms are often too complicated to set up, limited to specific system layouts, or have only limited fault coverage. Hence, a new FD algorithm called Fault-Detective is presented in this paper, which is purely data-driven and can be applied to a wide range of system layouts with minimal configuration effort. It automatically identifies correlated sensors and models their behavior using Random-Forest-Regression. Faults are then detected by comparing predicted and measured values.The algorithm is tested using data from three large-scale solar thermal systems to evaluate its applicability and performance. The results are compared to manual fault detection performed by a domain expert. The evaluation shows that Fault-Detective can successfully identify correlated sensors and model their behavior well, resulting in coefficient-of-determination scores between R²=0.91 and R²=1.00. In addition, all faults detected by the domain experts were correctly spotted by Fault-Detective. The algorithm even identified some faults that the experts missed. However, the use of Fault-Detective is limited by the low precision score of 30% when monitoring temperature sensors. The reason for this is a high number of false alarms raised due to anomalies (e.g., consecutive days with bad weather) instead of faults. Nevertheless, the algorithm shows promising results for monitoring the thermal power of the systems, with an average precision score of 91%.

Implementation of artificial intelligence for prediction performance of solar thermal system

A related input parameter is used in this case study to forecast solar thermal systems (STS) capabilities and to compare which artificial neural network (ANN) algorithms and other artificial intelligence (AI) methods have the most reliable predictor for STS performance. In order to gauge the performance of the STS, this research aims to implement AI for predicting STS performance by comparing the ANN technique with other methods. Three different training algorithms which are Levenberg-Marquardt (LM), scaled conjugate gradient (SCG) and Bayesian regularization (BR) are considered in this research. This research will identify acceptable parameters and the best AI technique to use in predicting the STS performance. Previous research on STS demonstrates that the efficiency of STS has been estimated using different input parameters. The results show that the prediction of the LM training algorithm is the best for STS performance.

Numerical simulation of the transient turbulent natural convection in an inclined rectangular shaped solar air heater

Due to high energy demand and adverse effect of global warming, improving the performance of solar thermal systems is of great importance. In this respect, the transient flow and thermal behavior of turbulent naturally ventilated airflow in a flat plate solar air heater (SAH) are investigated numerically. To achieve this aim, conservation of mass, momentum, and energy equations are solved for the turbulent airflow concurrently with the conduction equation inside the solid element using finite element method (FEM). The low Reynolds turbulence model is applied in the calculation of turbulent stress and heat flux, and the Boussinesq approximation is applied for computing buoyancy forces associated with the density gradient. The surface radiation is also considered explicitly in the calculations to obtain more accurate and reliable results. It is found that although based on the considered location the maximum incident radiation occurs at the optimum angle of 30°, the maximum flow rate reach to its peak when the inclination angle is 60°, in which the total increase of incident radiation is nearly 17%. It is also found that the rate of heat transfer is a decreasing function of the inclination angle (30⩽θ⩽90), such that the overall rate of heat transfer reduction is around 50%. Further, investigation of the impacts of solar radiation and air duct width on thermal performance showed that by increasing both parameter the rate of heat transfer and air flow increase by about 35% and 100% respectively. The exclusive analysis of the effects of sudden climate change on the SAH’s behavior revealed that a short time climate change leads to zero incident radiation, and considerable fluctuations in outlet temperature and flow rate.

Experimental and modelled performance of a building-scale solar thermal system with seasonal storage water tank

Building energy loads in cold climates may be largely offset with solar energy if seasonal thermal energy storage is employed. This article describes a full-scale experimental solar thermal system equipped with a 36 m3 buried water tank for seasonal storage. The solar thermal system provides space heating and domestic hot water to an energy-efficient two-storey research house in Ottawa, Canada. Long-term experiments on the system are described, which revealed key performance parameters for the system. Under-performing solar collectors were found to have the most detrimental effect on the system’s performance. Losses from the seasonal storage tank were found to exceed those predicted based on the nominally-rated insulation properties. Piping losses are shown to be non-negligible. A detailed simulation model of the building and solar thermal system was developed and validated with experimental data, and is used to demonstrate the potential performance of the solar thermal system with simple improvements to the experimental system. Results indicate the system can achieve a solar fraction of 100% for space heating loads (total load = 15 GJ) and 86% for domestic hot water loads (total load = 13 GJ). The seasonal storage tank achieves an annual energy storage efficiency of 42%. The performance results obtained in this article may serve as a benchmark for future research into the design, economics, optimization, and control of systems employing seasonal storage at the building scale.

A Review on Solar Thermal Utilization for Industrial Heating and Cooling Processes: Global and Ethiopian Perspective

A substantial share of the total energy in various countries is consumed by industries and manufacturing sectors. Most of the energy is used for low and medium temperature process heating (up to 3000C) as well as low and medium cooling capacity (up to 350kW). To meet the demand, the industrial sector consumes most of its energy in either thermal (heat) or electrical energy forms. The use of fossil fuels accounts for about half of the overall share. This resulted in a necessity to commercialize local and clean renewable energy sources efficiently considering the reduction of economic dependence on fossil fuels and greenhouse gases emission. As such, solar energy has proven potential and resulted in considerable development and deployment of solar heating industrial processes (SHIP) and solar cooling systems in recent times. Thus, an attempt to present a review of the available literature on overall energy intensiveness, process temperature levels, solar technology match, and solar thermal system performance and cost have been made in this paper. The review also includes identifying the potential and relevance of involving solar thermal for industrial heating and cooling demand. As a result, at least 624 SHIP including promising large-scale plants and 1350 solar cooling systems most of them in small and medium capacities in operation are identified. Though limited data is available for solar cooling potential and installation, investigations projected the global SHIP potential to 5.6 EJ for 2050. Consequently, given the presence of many low and medium temperature heating processes and cooling capacities in industries with immense solar energy potential, developing counties such as Ethiopia can take experience and pay attention to the development of sustainable industrial systems.

Heat transfer and energy storage performances of phase change materials encapsulated in honeycomb cells

Thermal energy storage devices are vital for reducing the inconsistency between energy supply and demand as well as for enhancing the performance of solar thermal systems. The present study investigates the melting process in metallic honeycombed heat exchangers filled with n-octadacane as phase change material (PCM). Further, a parametric study is conducted for four different honeycomb cell sizes, fin thicknesses, and angles of inclinations of the computational domain. The findings are described in the form of heated surface average temperature variation, melt fraction of the PCM, and thermal energy stored. Results show that the honeycomb fin structure considerably improves the heat transfer in the PCM. Further, it was observed that the honeycomb cell size and fin thickness greatly influence the variation of the average front surface temperature, melt fraction, and energy storage rate, whereas the inclination angle doesn't have a significant effect when cell size is less than 0.01 m. From the study, it was also observed that when the computational domain is horizontal without honeycomb cells, the pure conduction in the PCM results in much higher front surface temperature, which is greatly reduced in presence of the honeycomb cells.

Experimental study and analysis of single slope solar still integrated with Phase Change Material

Solar thermal systems are playing important role to encounter environmental issues like global warming, in the last two decades they replace conventional systems to create an eco-friendly environment. Lot of research have been undergone on solar thermal systems to improve their performance and efficiency, but still the area is wide open for improvement because of demand on renewable sources increase. As their is need for increasing the performance of solar thermal systems, phase change materials could serve as energy storing device during abundant available of energy. For solar thermal systems the major challenge is energy availability will not be round the clock, in order to clear this hurdle phase change materials backing served as a better support. The biggest challenge of developing countries today is to provide clean drinking water, as there are many conventional systems to convert saline water into drinking water their main disadvantage is pollution of environment due to harmful emissions. Hence, solar thermal systems with phase change materials are considered as best option in production of clean drinking water due to their operation by renewable energy, compactness and zero emissions. Phase change materials are coupled with solar system experimentally, and their behaviour and performance were characterized with results and observation, here the phase change material paraffin wax is embedded in copper tubes coupled with solar system is employed in production of clean drinking water; their performance and efficiency are compared with single slope solar still without phase change material. The thermal stability, corrosive resistance and impressive properties of paraffin wax and thermal conductivity of copper were tied together to single slope solar still for improving performance and efficiency of clean drinking water production. It is observed solar still without phase change material could generate drinking water from saline water only during day time, but the solar still coupled with phase change material embedded in copper tubes showed better results with 11 percent increase in production of drinking water even during dark hours.

Dynamic simulation and energy analysis of forced circulation solar thermal system in two various climate cities in Iraq

This study aimed towards an essential subject in the field of solar energy. The sun is a free clean energy source. This research presents the modeling and simulating of forced circulation solar thermal system for domestic hot water production in Iraq. The TRNSYS dynamic simulation program was chosen as the primary research tool. The TRNSYS model comprises component (collectors, controls, storage tanks, circulation pump, solar radiation processor, printer, equations, and integrators). The study was conducted in two different regions in Iraq (Baghdad and Basrah). The model investigated in many aspects, such as provide the demand of hot water for a family (ten persons) by using 10 m2 of flat plate collector, stratification effect in a storage tank on the collector's thermal efficiency, and effect of hot domestic water different consumption on solar thermal system performance. Results present that the system could provide hot water demand in Baghdad (67–81% and 39–62%) and Basrah (69–82% and 49–66%) in summer and winter, respectively, by using solar energy. The maximum auxiliary energy was used during the cold months are (2980 MJ/month) in Baghdad and (2607 MJ/month) in Basrah. There was an increase in the isothermal layers in the storage tank due to a rise in collector efficiency. There was a higher performance of forced circulation solar thermal systems (SDHW) when the domestic hot water consumption is lower.

Solar medium-low temperature thermal utilization and effect analysis of boundary condition: A tutorial

Solar thermal utilization is an important part of renewable energy applications, and its development and application have received extensive attention. Based on the development status of medium and low temperature solar thermal utilization systems, this paper first introduces the application and performance research on subsystems of the solar system including heat collection, heat storage and heat utilization units. It then introduces the theoretical and experimental development of matching relationships and dynamic performance of the medium and low temperature thermal utilization systems. Lastly, a case study analysis of a solar thermal system performance was carried out under different thermal boundary conditions. The influence of the boundary conditions of the heat storage system and the actual weather conditions on its performance is explored. The results showed that the boundary conditions of constant temperature and the boundary conditions of constant heat flow density have their own advantages. The heat source conditions provided by heat transfer medium are similar to the constant heat flux boundary condition. The work of this paper provided a theoretical basis for the subsequent application and performance study of solar medium and low temperature thermal utilization systems.

Implementation of ANN technique for performance prediction of solar thermal systems: A Comprehensive Review

Solar thermal systems (STS) are efficient and environmentally safe devices to meet the rapid increasing energy demand now a days. But it is very important to optimize their performance under required operating condition for efficient usage. Hence intelligent system-based techniques like artificial neural network (ANN) play an important role for system performance prediction in accurate and speedy way. In present paper, it is attempted to scrutinize the approach of ANN as an intelligent system-based method to accurately optimize the performance prediction of different solar thermal systems. Here, 25 research works related to various solar thermal systems have been reviewed and summarized to understand the impact of different ANN models and learning algorithms on performance prediction of STS. Using ANN, a brief stepwise summary of researchers’ work on various STS like solar air heaters, solar stills, solar cookers, solar dryers and solar hybrid systems, their predictions (results) and architectures (network and learning algorithms) in the literature till now, are also discussed here. This paper will genuinely help future researchers overview the work concisely related to solar thermal system performance prediction using various types of ANN models and learning algorithm and compare it with other global methods of machine learning. Citation: Ahmad, A., Ghritlahre, H. K., and Chandrakar, P. (2020). Implementation of ANN technique for performance prediction of solar thermal systems: A Comprehensive Review. Trends in Renewable Energy, 6, 12-36. DOI: 10.17737/tre.2020.6.1.00110

A Study on Performance of Solar Thermal System for Domestic Hot Water According to the Weather Conditions and Feedwater Temperatures at Different Locations in Korea

A Study on Performance of Solar Thermal System for Domestic Hot Water According to the Weather Conditions and Feedwater Temperatures at Different Locations in Korea

Thermo-physical properties of solar thermic fluids dispersed with carbon nanotubes

The paper examines the influence of dispersion of multi-walled carbon nanotubes on the thermo-physical properties of working fluids used in solar thermal engineering systems. Thermo-physical property evaluation is very vital to evaluate the performance of solar thermal systems. Ethylene glycol and a commercially reachable thermic fluid therminol 62 are preferred as based fluids. Nanofluids are prepared by dispersing 0.1 %, 0.25 %, 0.5 % and 0.1 % weight fraction of surface modified Multi-walled carbon nanotubes. The nanomaterials are surface modified before dispersion in the thermic fluids and extreme care is taken to prevent property deterioration during surface modification. Thermal conductivity of test fluids is evaluated in the temperature range of 100 to 300°C while viscosity is evaluated in the range of 50 to 150°C s. A 15 to 20 % increase in the thermal conductivity is observed with the dispersion of carbon nanotubes. The viscosity is significantly increased in the low-temperature ranges while the change is minimal above 70. The data could be predicted successfully using artificial neural networks.

Scoping Low-Cost Measures to Nowcast Sub-Hourly Solar Radiations for Buildings

Solar energy, as a clear, renewable and promising resource, has brought tremendous value for carbon emission reduction in the last three decades. However, the uncertainty of solar radiation brings significant challenges to the renewable heat and electrical system for buildings. Thus, many different solar radiation forecasting methods, such as Numerical Weather Prediction Methods (NWP), Statistical Methods, Top-Down Methods, Bottom-Up Methods and Hybrid Methods have been developed to make the best guess on future solar radiations. Based on the meteorology definition, nowcasting refers to the forecast of the temporal horizon from the next few seconds up to six hours. Predicting solar radiation within this range are extremely challenging, but crucial for solar energy system operation. This paper firstly reviewed the state of art of solar radiation forecasting methods and compared the key features of each method. According to the advantage and costs of each method, this paper then proposed a methodology to generate high accuracy low-cost solar radiation nowcast data for optimising building solar thermal system performance and related control strategies. Note that this paper focused on the scoping study of methodology rather than field experiments, and further research with experiments data will be reported in a journal publication.

Special Issue: Advances in Nanofluids: Modeling and Applications (ANMA)

Heat transfer enhancement in heat-exchange devices is one of the key factors affecting energy savings and compact designs in wide variety of engineering applications. Pioneering heat transfer research has been carried out leading to the development of a new innovative energy enhancement technique through the addition of nanoparticles (usually less than 100 nm) to low thermal conductivity conventional fluids. Fluids with suspended nanoparticles are called “nanofluids.” The suspended metallic or nonmetallic nanoparticles change the transport properties and heat transfer characteristics of the base fluid by a significant extent. Metallic nanofluids often refer to those containing metallic nanoparticles (such as Cu, Al, Zn, Ni, Si, Fe, Ti, Au, and Ag), while nanofluids containing nonmetallic nanoparticles such as aluminum oxide (Al2O3), copper oxide (CuO), and silicon carbide (SiC, ZnO, TiO2) are often considered as nonmetallic nanofluids. Nanofluids exhibit superior heat transfer properties compared to conventional heat transfer fluids. Recently, the idea of using hybrid nanofluids by suspending dissimilar nanoparticles has been investigated for further improvement of the heat transfer and pressure drop characteristics by employing a trade-off between the advantages and disadvantages of individual suspension (attributed to good aspect ratios), better thermal networks, and the synergistic effects of nanomaterials.The conventional direct absorption solar collector system uses a well-established technology that has been employed in a variety of applications. However, the efficiency of this type of collector is limited by the absorption properties of the working fluid. The solar collector technology in combination with the technology associated with emerging nanofluids is considered as a promising combined technology. Reviews on the topic suggest significant potential enhancements in the efficiency and performance of solar thermal systems, solar water heaters, thermal energy storage systems, solar cells, and solar stills. Despite the touted importance of this concept, a very limited number of research papers in the area of solar collectors augmented with nanofluids has been published in the literature. In general, research on nanofluids is still considered in its early-to-moderate stages and much more is needed in terms of developing new models for experimentally verified nanofluids and in demonstrating the viability of these fluids in key areas such as biomedicine and cancer treatment, renewable and nuclear energy, automotive lubrication, electronics cooling, heat exchangers, energy conversion and storage, and many other areas.This special issue was initiated to focus on the latest advances in nanofluids research and to address their utilization and application in various engineering and technological systems. Many papers were submitted, but only 22 were accepted. The contributions to this special issue addressed various pertinent aspects of nanofluids in terms of their models and applications. The accepted papers ranged from reporting on theoretical and numerical investigations to reporting on experimental investigations. The topical coverage included heat transfer enhancement using nanofluids; nanofluid mixed convection in cavities and porous media; magnetohydrodynamic flows of nanofluids; double spirally coiled tube heat exchangers employing nanofluids; application of hybrid nanofluids in TPCT and cubical cavities with active walls; synthesis of WO3/liquid paraffin nanofluids; melting of nanophase-change materials inside an open cell metal foam; solidification of phase-change material nanocomposites; application of ferrofluids in solar photovoltaic systems; application of pseudo-plastic nanofluids and/or olive leaf synthesized nanofluids in solar collectors; use of nanofluid coolants in radiators; use of bearing nanofluids in axial piston pumps; stability analysis of cross diffusion of Waters B fluids in saturated permeable nanofluids and nanofluid flows; and heat transfer in the presence of various effects such as homogenous–heterogeneous chemical reactions, gyrotactic microorganisms, and magnetohydrodynamics.The Guest Editors of this issue would like to express their deep appreciation and thanks to the Editor-in-Chief, Professor S.A. Sherif for his diligent efforts and unique editorial skills and to the staff of the ASME Journal of Thermal Science and Engineering Applications, and in particular Jennifer L. Smith who was instrumental in ensuring that this issue is published on time and Beth Darchi who has been unfailing in helping with issues pertaining to the Journal Tool throughout the whole process. Special thanks are also due to the various talented authors for their excellent original contributions and to the anonymous professional reviewers for their valuable time, comments, and suggestions which significantly improved the quality of the accepted papers.It is important to note here that while this special issue could not possibly cover all aspects and areas of nanofluids research and applications, it is hoped that it succeeded in providing a review of recent advances in specific fields and problems in nanofluids. It is also hoped that this issue succeeded in providing motivation to researchers to fully engage in this important and emerging research area.

Development of an analytical model for the daily performance of solar thermal systems with experimental validation

Flat plate collectors are the most widespread solar thermal collectors for low-temperature level applications as domestic hot water production and space heating. The objective of this study is to present a simple and analytical model for the prediction of the daily performance of an integrated system with flat plate collector. The developed model is tested with experimental results from a laboratory integrated system. This experimental set-up is investigated with details in order to determine its thermal performance and its dynamic response. After the validation of the developed model, the model is extended to realistic weather data for the climate conditions of Athens (Greece). The integrated system is evaluated energetically and financially by examining twelve typical days, one for every month. It is found that the investigated system can produce 2171 kW h thermal energy during the year with a mean thermal efficiency equal to 54.24%. The payback period is calculated at 5.03 years, an acceptable value which indicates sustainability. The present analysis clearly indicates that the developed model can be used for quick and accurate calculations on solar thermal systems in order to evaluate and optimize them on a daily basis.