Solar air collectors (SAC) convert the available solar energy into useful thermal energy for different heating applications such as drying, space heating, hot water etc. The study aims to enhance the ...thermal performance of a flat plate SAC by modifying the absorber surface. The experimental performance of two variant SACs (a sand coated absorber to increase surface roughness and a conventional plain absorber) was compared under controlled laboratory conditions The experimental tests were performed under a solar simulator for radiation levels of 400, 600, and 800 W/m2 and variable air mass flow rate ranging from 0.01 to 0.02 kg/s/m2. Results indicated that increasing the air flow rate by 90% enhanced the thermal efficiency on a plain absorber SAC by almost 68%, and the rate of increase was higher for the sand coated absorber. SAC with the sand coated absorber provided additional surface area resulting in an increase in the effective heat transfer. The thermal efficiency of the collector was improved by up to 17% for the sand coated absorber compared to the plain absorber. The absolute thermal efficiency of the SAC varied from 19% to 41% under the different tests conditions.
•Performance of solar air collector (SAC) with sand coated absorber is presented.•Increase in air flow rate by 90% enhance efficiency by 68% for plain absorber.•SAC with sand coated absorber provides 17% higher efficiency than plain absorber.•The absolute thermal efficiency of the SAC varied from 19% to 41%.•Low cost addition of a layer of sand coating improves thermal performance of SAC.
To enhance the thermal treatment of Linear Fresnel Reflector (LFR) unit, multi-way twisted tape (MWTT) was applied in current research. Twelve mirrors and one tube with trapezoidal cavity around it, ...generates new LFR unit. The operating fluid is Al2O3-water and for predicting the properties, temperature dependent formulas were employed. Finite volume simulations results in finding the distribution of velocity, temperature, entropy generation. Also, thermal performance was measured. The geometrical factors are number of wings (nw), revolution (TR) and width (ER) of tapes. To evaluate the modeling procedure, various examinations with numerical and experimental publications were verified. To extract the distribution of absorb flux, SolTrace and ANSYS FLUET have been utilized and they are in good agreement. The output of SolTrace demonstrates the path of rays and selecting higher number of rays results in higher accuracy. Highest absorb flux occurs in bottom of pipe. As mixing of fluid improves with rise of revolution and width of tapes, Nu increases and augmentation in interaction of fluid with wall enhances the friction factor. Increasing number of wings can enhance the secondary flow. So, stronger impingement with wall can augment the friction factor. Nu enhances with rise of nw about 4.384% when TR = 2, ER = 0.34,V˙ = 19. Augmenting TR makes Nu to increase about 7.135% when nw = 4, ER = 0.1, V˙ = 19. Besides, with selecting higher ER, friction factor augments about 20.019% at TR = 2, nw = 2, V˙ = 6.3. To evaluate the amount of available work of this solar unit, components of entropy generation (Sgen,f, Sgen,h) have been measured. Thermal irreversibility declines with increase of turbulent intensity while friction component increases. Thermal efficiency (ηth) augments with growth of TR, ER and nw while it decreases with enhance of inlet temperature. As Tin rises, ηthreduces about 31.51% when TR = 2, nw = 2, ER = 0.1, V˙ = 19. Inclusion of nano-powders can enhance the useful heat and ηthaugments about 0.153%.
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•Multi way Twisted tape (TT) has been employed in LFR solar system.•Optical performance of suggested design is 73.5%.•The operating fluid is Al2O3-water and temperature dependent formulation was utilized.•Thermal efficiency augments with growth of twisted ration.•As inlet temperature augments, thermal efficiency decreases about 31.51%.
•The still performance was enhanced by using reflectors and woven wire mesh.•Many factors were tested such as water depth, water salinity and using wire mesh.•The percentage increase in daily thermal ...efficiency for the MSS raised to 45.04%.•The percentage increase in water productivity raised to 46.8 % at 1 cm water depth.•The cost per liter for the MSS decreased by 37.5% compared with the CSS.
In recent years, the urgency for harnessing solar energy for water desalination has grown significantly, driven by the escalating costs and the increasing scarcity of clean water sources. Numerous research efforts were dedicated to enhance the productivity of solar still, including the thermal energy storage materials, solar concentrators, nanofluid, and more. The main objective of this research is to improve the solar still performance by using wastes of workshops and factories so, their actual cost can be assumed to be zero. The experimental setup placed at faculty of Engineering Suez Canal University. Two solar still were included: one representing the conventional and the second one is modified with internal reflectors and woven wire mesh. The performance of the stills was assessed under identical climate conditions, considering water depths of 1, 2, 3 and 4 cm using both fresh and saline water with Total dissolved Solids of 18,562 and 35643 ppm. The obtained results indicated that the incorporation of internal reflectors and woven wire mesh led to a notable percentage increase in daily thermal efficiency and accumulative productivity ranged from 42.49 % to 45.04 % and from 43.0 % to 46.8 % respectively. The economic analysis demonstrated that the cost per liter for conventional and modified solar still was about 0.0018 and 0.0011$ per liter per m2 respectively. This study’s findings suggested that the integration of internal reflectors and woven wire mesh into solar stills to obtain high productivity potable water with low cost. These results align with and reinforce previous publications in this field, highlighting the potential of this approach for addressing the pressing challenges of affordable and efficient water desalination.
Transition to carbon-neutral energy generation is a reality, and great efforts are being made in this direction in the last years. Ammonia is a promising carbon-free fuel, and it can be used as a gas ...turbine fuel in existing power generation cycles without significant modification. This paper considers various aspects of the use of ammonia as a gas turbine fuel: it provides a review of existing ammonia-fired gas turbines and conducts a study of the prospective technology of using ammonia via thermochemical transformation into hydrogen-rich gas. Moreover, this paper considers on-board hydrogen production technology via thermochemical ammonia transformation. The ammonia fired chemically recuperated gas turbine is analyzed for which the thermal efficiency can be increased up to 5%–7% comparing to traditional gas turbines. Moreover, hydrogen-rich fuel with a hydrogen mole fraction up to 75% is used as a fuel, leading to more stable combustion with lower NOx emission up to 6–10 ppm. Additionally, an approach to on-board hydrogen production from ammonia via the utilization of solar energy is investigated. It is shown that solar energy can replace up to 25% of heat obtained via ammonia combustion. The paper discusses future perspectives in investigations for ammonia-fired gas turbines with on-board ammonia transformation.
•Ammonia as a gas turbine fuel with zero CO2 emission.•NH3 containing blends show the better combustion and emission performances when pure NH3.•Thermochemical ammonia transformation as an on-board hydrogen production system is considered.•Use of exhaust gas for ammonia decomposition leads to an increase in efficiency up to 7%.•Use of solar energy for ammonia decomposition can decrease the ammonia consumption up to 25%.
Low temperature combustion (LTC) is a recent engine technology that can reduce the oxides of nitrogen (NOx) and soot emissions simultaneously while maintaining higher thermal efficiency. The present ...review work investigates the performance, emission and combustion characteristics of LTC mode engines. Partially premixed LTC (PPLTC), homogeneous charge compression ignition (HCCI), premixed charge compression ignition (PCCI) and reactivity controlled compression ignition (RCCI) modes are researched under LTC mode. In recent decades, different engine strategies have been employed to reduce exhaust emissions and to enhance thermal efficiency. Exhaust gas recirculation, variable valve timing (VVT), advanced fuel injection technologies are adapted to achieve LTC mode in internal combustion (IC) engines to get improved outcomes. This review highlights the properties of fuels, fuel supply systems, valve actuation mechanisms, engine operating conditions and its effects on the engine characteristics. This review provides a perspective plan to the researchers for enhancing the performance, emission and combustion behavior of an engine by using LTC mode with lower NOx and soot emissions. Among LTC mode engines, RCCI mode engine operates well in 60% load, 60% premixed ratio, 35:1 air-fuel ratio and 56% brake thermal efficiency within the combustion phasing control.
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•LTC mode reduces NOx (85%), soot emissions (95%) and fuel consumption (15%).•High ON and CN fuels supplied in PFI and DFI mode for combustion phasing control.•RCCI mode is an advanced LTC mode engine which gives better outputs than other LTCs.•About 55% thermal efficiency achieved in RCCI within Euro VI emission limits.•LTC mode engines have more cycle-to-cycle variations above 60% engines loads.
Photovoltaic/Thermal (PV/T) systems are getting attention due to limitations in rooftop space, especially in apartment buildings. Those buildings must improve electricity generation from photovoltaic ...(PV) systems and hot water for domestic use. PV/T systems were investigated experimentally for Jordanian weather in this paper. Thermal and exergy efficiency was evaluated for commercially available PV/T panels under different connection configurations, open-loop, and closed-loop connections. Results showed a significant effect for the PV/T panel for Jordanian weather. Closed-loop performance can be improved if the heat collected by PV/T is extracted from the tank. Finally, the total efficiency of the PV/T system in an open-loop configuration is significantly higher, 76 %, than in a closed-loop one, 58 %, due to the improvement in thermal efficiency.
Schematic of the problem.
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•Forced convection of nanofluids through a double pipe heat exchanger was studied.•Effects of flow direction, nanoparticle concentration and Re were ...investigated.•More nanoparticles volume fraction, higher outlet or wall temperature.•Increasing Re, thermal efficiency gradually tends to a constant amount.
In present study, heat transfer and turbulent flow of water/alumina nanofluid in a parallel as well as counter flow double pipe heat exchanger have been investigated. The governing equations have been solved using an in-house FORTRAN code, based on finite volume method. Single-phase and standard k-ε models have been used for nanofluid and turbulent modeling, respectively. The internal fluid has been considered as hot fluid (nanofluid) and the external fluid, cold fluid (base fluid). The effects of nanoparticles volume fraction, flow direction and Reynolds number on base fluid, nanofluid and wall temperatures, thermal efficiency, Nusselt number and convection heat transfer coefficient have been studied. The results indicated that increasing the nanoparticles volume fraction or Reynolds number causes enhancement of Nusselt number and convection heat transfer coefficient. Maximum rate of average Nusselt number and thermal efficiency enhancement are 32.7% and 30%, respectively. Also, by nanoparticles volume fraction increment, the outlet temperature of fluid and wall temperature increase. Study the minimum temperature in the solid wall of heat exchangers, it can be observed that the minimum temperature in counter flow has significantly reduced, compared to parallel flow. However, by increasing Reynolds number, the slope of thermal efficiency enhancement of heat exchanger gradually tends to a constant amount. This behavior is more obvious in parallel flow heat exchangers. Therefore, using of counter flow heat exchangers is recommended in higher Reynolds numbers.
•Neat approximations for temperature and solar collector efficiency are presented.•The non-adiabatic and isothermal base mechanisms optimize the surface absorption.•Heat transferring material at the ...bottom panel enhances the thermal efficiency.•Isothermal base panel leads to maximum thermal efficiency of the solar receiver.
The enhancement of performance by increasing the thermal efficiency of a direct absorption solar collector based on an alumina–water nanofluid is the prime target of the present research. The base panel of the collector channel is subject to either a non adiabatic or an isothermal wall condition both of which introduce two new physical parameters. Analytical solutions for the temperature field are worked out in both cases for a two dimensional steady-state model recently outlined in the literature. The desired increase in the temperature of the heat transferring nanofluid is achieved either by slightly rising the heat transfer coefficient of the bottom panel coating or by prescribing a bottom surface temperature. As a consequence of the increase in the final outlet mean temperature, the solar collector thermal efficiency is found to be enhanced via increasing the new physical parameters as compared to the traditional adiabatic wall case. For instance, 85.63% thermal efficiency of solar collector is achievable for non adiabatic bottom panel by adding suspended aluminum nanoparticles into the pure water. Even better than this, considering isothermal base panels, 100% efficiency is attained more rapidly with lesser base temperatures in the presence of higher nanoparticle volume fractions.
•A comprehensive review of recent advances in nanofluid-based solar energy harvesting devices.•Incorporating nanofluid with receiver tube modification is the best option for improving collector ...performance.•This review identifies a grey area for further research to advance the field.•Future trends and challenges of using nanofluids in solar energy harvesting devices were discussed.
The increase in energy demand due to population explosion and the recent global pandemic stressed the need to maximize solar energy harvesting. Nanofluids are used to enhance the performance of solar collectors due to the desirable inherent thermal properties of the fluid. One of the major research trends in solar energy utilization is improving the efficiency of the harvesting devices. Hence, investigating the performance of nanofluid-based solar energy harvesting devices is of great importance. The review presents an overview of the recent advancement in nanofluid-based solar energy harvesting devices and how various parameters such as nanoparticle size, concentration, shapes, and nanofluid flow rates can be manipulated to efficiently harness solar energy from the sun. The type of working fluid used in the collectors significantly influences its performance, and nanofluid performed excellently compared to the conventional fluid. This study investigates the role of nanofluids in various solar-powered desalination systems, parabolic trough solar collectors, flat plate solar collectors, solar dishes, direct absorption solar collectors, evacuated tube solar collectors, solar cookers, and the photovoltaic thermal system. The collector performance was compared for the system with nanofluid and convectional fluid as working fluid based on the heat transfer performance, exergy and energy efficiency improvement, and thermal efficiency enhancement. It is found that maximum collector performance enhancement is obtained using nanofluid. More freshwater was produced with low energy input into a nanofluid-based solar-powered desalination system. The review will update readers on the recent progress made in the field, identify the current challenges and proffer suggestions on how the practical problems can be solved. It is hoped that the review will help young researchers, funding agencies, investors, government, and journal outlets understand the recent advances in this area and what needs to be done for the commercialization of nanofluid as a working fluid in solar collectors.
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