The energy conversion performance of commercial photovoltaic (PV) systems is only 15–20 percent; moreover, a rise in working temperature mitigates this low efficiency. To enhance their performance and prevent damage, researchers test new technologies and integrate heat recovery devices with PV systems. Concentrated photovoltaic systems (CPVs) are especially vulnerable to high radiation levels. This paper explores novel cooling techniques for PV systems, an area that has not been extensively investigated before. The cooling methods are categorized into front-surface and back-surface cooling methods, offering a unique perspective on how to keep PV systems cool. Moreover, the paper delves into the advancements made in PV cooling systems and CPVs, shedding light on the cutting-edge developments in this field. The results demonstrate the profound impact of various operational factors, such as radiation and wind speed, on the selection of suitable cooling systems or heat recovery methods. These findings unveil the crucial importance of considering these factors when choosing cooling techniques, adding a compelling dimension to the research. For example, it was depicted that optical cooling techniques can enhance the performance of PV systems by up to 4.2

This work delves into the efficiency of the disturber device on the productivity of a Concentrated PhotovoltaicThermal (CPV/T) unit. For this purpose, numerical techniques were employed to model the three-dimensional CPV/T system along with a TT (twisted tape) device. Initially, the influence of tube cross-section patterns was investigated. This involves designing three distinct tubes with plain, three-lobed, and five-lobed patterns. The simulation considers PV/T systems with various tubes, both with and without the inclusion of twisted tapes, utilizing H2O as the testing fluid. The research assesses the influence of concentration ratio through varying incident irradiations at 1, 2, and 3 suns. The investigation of the temperature over the silicon layer reveals a substantial decrease in the temperature gradient with the incorporation of a twisted tape insert. The three-lobed tube demonstrated optimal performance for the PV/T module. Consequently, an examination was conducted to assess the efficacy of utilizing Al2O3-H2O nanofluid on the productivity of the system. Using the optimal insert pattern under 3 suns has been determined to improve thermal and electrical performances by 5.1 % and 4.2 %. A thermohydraulic analysis is implemented to measure the thermal improvement brought about by various configurations. The results demonstrated that the inserts have the potential to elevate this factor above unity. Additionally, an environmental evaluation of the presented configurations includes an analysis of two key parameters: emission reduction and saved carbon credits. The findings demonstrated that employing the CPV/T system under 3 suns with the optimal design leads to a reduction of approximately 5541 kg of carbon emissions over 10 years, resulting in a savings of about $80.3 in carbon credits.

This investigation emphases on the performance of a solar cell with a 1 m2 area, using a micro-channel heat sink as a cooling unit. The goal is to explore the optimal design of the sinusoidal geometry of the cooling heat sink to intensify output power, enhance cooling, and minimize the negative impact of heat on solar cells under high radiation, thus extending their lifespan. The study employs simulation and modeling in ANSYS FLUENT software v2021 to analyze the impact of different factors on solar cell treatment. Fourteen designs are tested, varying in the number, frequency, and wavelength of fin sine waves used in the thermal heat sinks. Furthermore, the investigation evaluates the influence of operational factors like the velocity of fluid and the intensity of applied radiation on efficiency and exergy. The outputs demonstrated that augmenting the sinusoidal fins in the cooling fluid (from 5 to 21) leads to a maximum electrical perfomance of 38.52 % for the solar cell. Expanding the sine wave's amplitude can improve efficiency from 38.41 % to 38.69 %. Similarly, decreasing the wavelength leads to efficiency gains from 38.43 % to 38.56 %. In the best-case scenario, efficiency is meaningfully improved when the flow rate is augmented from 20 to 100 g/min. The efficiency increases exponentially from 37.16 % to 38.97 %.

Due to the needs of industries for clean and environmentally friendly fuels today, new energy sources such as fuel cells are at the center of attention. Polymer fuel cells, meanwhile, require a short start-up time due to low operating temperature, high power density, no emission and very low noise, making them the best option for vehicles as an alternative to internal combustion engines. One of the most important reasons for fuel cell loss is the uneven distribution of reactants on the active area, which causes non-uniform reactions. Therefore, the use of an optimal flow field to improve the durability and performance of PEM fuel cells seems necessary. Although different studies introduced novel designs, a study comparing different patterns comprehensively to introduce the best ones is not performed yet. In this study, first, a numerical validation was performed with an experimental test that showed good accuracy. Then, to achieve efficient patterns, several flow field designs were inspired by previous effective designs and others were selected as superior designs from the literature. The effects of presented geometries on the performance of a PEMFC were investigated to improve its performance. In addition, efficient evaluation criteria from the literature were employed to better analyze the performance of such systems, and the ones consistent with the I-V performance were introduced. By surveying the criteria, a novel performance factor was introduced that showed the best agreement with the I-V performance. The results were obtained in single-phase and two-phase approaches, which lead to remarkable findings. The two-phase study revealed that the waved serpentine case has the highest electrical performance with the highest mass fraction of oxygen.

Commercial photovoltaic (PV) systems have a relatively low energy conversion efficiency (15∼20%) and this low efficiency reduces by an increase in the working temperature. A higher operating temperature can also reduce the working life of PVs. Therefore, researchers are trying new technologies and also combining them with heat recovery units to elevate the overall productivity of such systems and prevent performance loss and possible damages. The performance loss problem is more considerable in concentrated photovoltaic systems (CPV) and extra consideration is required for them under a higher level of radiation. The present review remarks on the advances obtained in cooling techniques for PVs and especially for CPVs. The current findings showed that various operation and environmental factors could be important in the selection of suitable heat recovery or cooling systems. In this regard, the applied passive and active cooling methods on the front and back surfaces of PVs under different working conditions are categorized here with a broad discussion concerning the advantages, disadvantages, and advances. It is expected that based on the findings, relying on the needs and conditions, the appropriate cooling unit is selected.

A numerical technique is applied to study the efficacy of integrating twisted tapes to the collector of Photovoltaic/Thermal (PV/T) units on the system performance when the tubes with different cross-sections are used. Hence, computational fluid dynamics is employed to evaluate PV/T systems with and without twisted tapes when using cylindrical, rectangular, and triangular patterns for the tube cross-section. The effect of employing twisted tapes with various pitch-to-width ratios (YD) of 3, 4 and 5 is evaluated. The impact of the total inlet mass flow rate ranging from 25 to 150 Lhr is also studied. To analyze the system performance the evaluation of energy and exergy is performed. The results demonstrated that the triangular pattern is the optimum pattern for the tube cross-section without twisted tapes. However, inserting a twisted tape makes the cylindrical tube superior to other designs from electrical and thermal aspects. A collector employing a cylindrical tube with and without a twisted tape could increase the module's electrical efficiency by 7.2 and 9%, respectively. Also, it was observed that integrating twisted tape with the lowest value of pitch-to-width ratio could decrease the surface temperature by 3.2 and 17.55 K compared to the systems with cylindrical tubes and PV alone.

Boiling jet impingements (normally water) are being widely used in various industries such as cooling power electronic components, due to the high heat transfer rate and low cost. Also, oils and molten salts are used in single-phase quenching processes. Many studies have been carried out into this field, but most of them were experimental. A quenching jet impingement process is simulated numerically in this research. For a comprehensive solution, a solver code based on the Volume of Fluid (VOF) method was modified to analyze the effects of conjugation and mass transfer. To validate the solution, an experimental quenching process of an impinging jet was simulated in 3D, and the results showed a good agreement. In addition to the temperature uniformity of the block, the cooling rate is also important during the process. Thus, Optimized Cooling Factor (OCF) was defined to involve both features simultaneously. Subsequently, the quenching of a hot steel cubic block by four simultaneous liquid jets was simulated in 3D. Studies were conducted on the effects of parameters such as the sinusoidal inlet velocity, jets width and spaces between the jets on the Standard Temperature Uniformity Index (STUI) and OCF, for water, molten salt and non-Newtonian molten salt quenchants. Some remarkable results are achieved by the proposed configurations. The results indicated that in all cases with pulsative jets, improvements in STUI and OCF relative to constant-velocity ones were observed and optimal STUI and OCF factors were accessible in lower values of the jet-flow frequency. Furthermore, by changing the quenchant from molten salt to non-Newtonian molten salt, the STUI and OCF plot averages enhanced from 0.1 to 0.085 and 4.8 to 6.5, respectively. Comparing the water and non-Newtonian molten salt from required input energy and pumping power points of view revealed that the input heat for non-Newtonian molten salt in all cases changes in the range of 2600-8200 J, while the input heat for water jet equals to zero, and the power needed to pump the water is almost 40-45% less than the needed pumping power of the non-Newtonian molten salt, on average.

Boiling jet impingements are being widely used in various industries. Hence, a quenching jet impingement is simulated numerically. A solver code based on volume of fluid method was modified to analyze the effects of conjugation and mass transfer, and validated against an experimental study. Then, optimized cooling factor (OCF) was defined to involve temperature uniformity of the block and the cooling rate simultaneously. Subsequently, in laminar two-jet configurations, the effects of velocity inlet function, jet-to-surface and jet-to-jet spacing on standard temperature uniformity index (STUI) and OCF in a highly heated block were investigated. Heaviside function of time for the inlet velocity and periods of pulse between 0 and 0.2 were considered. Some remarkable results are achieved by the proposed configurations. In all cases with pulsating jets, improvements in STUI and OCF relative to pulse-free ones were observed; when V = 0.4 m s−1, OCF peaked at 2 in P = 0.06, which was almost eight times greater than OCF of pulse-free configuration (OCF = 0.24). As velocity decreased, the temperature uniformity improved; however, OCF showed the highest value at higher velocities occurring for lower periods of pulses. This happens because of more uniform temperature distribution in both plate sides and continual destroying film boiling layers generated on the surface. Also, in a jet-to-jet spacing of about one-third of the block length, for all plate lengths, optimal temperature uniformity with maximum OCF was obtained, due to formation of two stagnation points having the highest heat transfer rate by positioning in an ideal distance from each other.

In this paper, a numerical simulation of jet impingement quenching is provided. The VOF method in the basic solver of the OpenFOAM CFD package is developed to simulate boiling and condensation phenomena. In simulations, surface tension and mass transfer between two phases were modeled with continuous surface force (CSF) model and Lee mass transfer model, respectively, and energy equation was solved in the solid region. Numerical simulation of jet impingement quenching process is validated by experimental data and a good agreement is observed. The effects of pulsating jet velocity and step jet velocity on quenching process are studied, and parameters such as temporal and spatial variation of solid part temperature and standard temperature uniformity index (STUI) are investigated. The effects of frequency and amplitude of sinusoidal single jet and also the period of two jets with step pulse are investigated. The results revealed that using two jets with step velocity profile leads to the best performance or least uniformity index (best temperature distribution) among the considered cases. Studying the maximum temperature difference inside the solid region indicated that for pulse flows this parameter is considerably lower than the continuous flows. Also, at a constant flow rate, 43% reduction in STUI is achieved by sinusoidal pulsating jet compared to the single continuous jet, while 66% STUI reduction was reached for two-jet cases. These substantial reductions in uniformity index present these methods as promising approaches for the quenching process in various industrial applications.

Present study analyzes the issue of entropy generation of water with Al2O3 nanoparticles in a horizontal porous microchannel heated symmetrically. 2D distribution of temperature in both phases are derived using two-energy-equation model. An analytic investigation is carried out and the parameters of magnetohydrodynamic (MHD) field, solid heat generation and symmetric thermal condition are explored thoroughly. The results revealed that the MHD field noticeably affects the distribution of temperature and velocity and as an output the heat transfer irreversibilities during the process. The solid and fluid heat transfer irreversibilities for the case under MHD field are lower than those of the case without it, which proves the advantages to MHD field in declining the heat transfer irreversibility. Then, it was obtained that when Ha number is constant and Reynolds number has the optimum value of 6.5, total entropy generation is minimum and it decreases when MHD is intensified at Reop. Also MHD was effective merely when the value of Reynolds number was lower than the critical value. By applying heat generation to the solid, for the MHD cases, no significant changes were observed in MHD irreversibility, however, entropy generation of the solid was achieved to be the most effective parameter and the value of total irreversibility increased noticeably. The analysis of thermal equilibrium and non-equilibrium models and the differences in irreversibilites showed that the increments in suspension of nanoparticles reduced the deviation between the two models, and intensification of Ha number at low biot numbers further reduces it.

The present study investigates heat transfer of nanofluid flow in micro channel heat sink (MCHS) in the presence of a magnetic field. Al2O3-water nanofluid is chosen the best among other nanolfluid and is used as a coolant fluid in solution. The KKL correlation is utilized for calculation of the effective thermal conductivity and viscosity of nanofluid. Modified Darcy equation is applied for porous medium and the two-equation model with thermal dispersion is employed for heat transfer between fluid and solid sections. Since the coupled heat transfer equations of nanofluid and solid phase are nonlinear, the analytical Collocation method (CM) is employed to solve this problem. Effects of the Hartmann number, nanoparticles volume fraction, nanoparticle diameter, porosity, channel aspect ratio on temperature distribution, velocity and Nusselt number are investigated deliberately. Results show that Nusselt number has direct relationship with applying a magnetic field on MCHS.