Effect of various configurations of swirl generator system on the hydrothermal performance of the flat-plate solar collector

This is a numerical study that analysis the heat extraction potential of solar collector tubes by assembling a couple of nozzles at the sealed end of the pipe to make swirl flow. Swirl flow intensifies the turbulence rate which augments heat transfer by ruffling the boundary layer. To this end, several decisive factors including nozzle angle (A: 30�, 45�, 60�, 90�), tube diameter (D: 20 mm, 50 mm), nozzle edge size (N: 6.25, 12.5, 25 mm (for D50) and N: 2.5, 5, 10 mm (for D20)), and mass flow rate (M: 0.1, 0.5, 1 kg/s (for D50) and M: 0.04, 0.2, 0.4 kg/s (for D20)) were considered. Results demonstrated that all of the models of class ’’A.../D20/N.../M...‘‘ had higher heat extraction potential but lower friction factor compared with ”A.../D50/N.../M...‘‘. Maximum and minimum values of heat flux extractions are 2113390 W/m2 and 59239 W/m2 that were obtained by ”A60/ D20/N2.5/M0.400 and ‘‘A30/D50/N25/M0.100. The created friction factor by class ”A.../D50/N .../M...‘‘ is higher than class ’’A.../D20/N.../M...”. The highest friction factor is 3.51 (’’A90/D 20/N2.5/M0.0400) and the lowest friction factor is 0.019 (‘‘A30/D20/N2.5/M0.200). Overall, for all cases, class ”A.../D50/N.../M...‘‘ bear the higher TPF compared with class ”A.../D50/N.../M ...‘‘ so that the greatest and lowest values of TPF are 5.09 and 0.49 achieved by ”A30/D50/N6.2 5/M100 and ‘‘A90/D20/N5/M0.400, respectively

A simplified economic model and case study for recovery ventilation based on SPECO method

Covid-19 further revealed the significance of ventilation by air conditioning systems. Most common split heaters and resistance heaters recirculate the indoor air without ventilation process. Ventilation wastes energy consumption by the building. However, adding an air-to-air heat recovery unit seems a quick solution to reduce the wasted heat of the ventilation process. Nonetheless, recovery unit means further pumping power (pressure drop through the air-to-air heat exchanger), capital cost, additional fans and their electricity consumption, exergy costs and so on. Hence, the profitability of the recovery unit depends on outdoor temperature, desired indoor temperature, electricity price of the region, exergy loss and also the aforementioned factors. In this research the general standard Specific Exergy Costing theory is employed and simplified as an economic strategy for recovery ventilation. The model not only is able to predict the profitability of the ventilation process using air-to-air heat exchanger, but also it is an optimization tool for air-to-air heat recovery units as provided as a case study in this paper

Study and multi-objective optimization of integrating an energetic solar thermal application, a supercritical process, and a high-temperature electrolyser

Supercritical processes using carbon dioxide reached suitable sustainability in previous research. Hence, the current paper proposes and examines a recompression supercritical carbon dioxide Brayton cycle integrated with a solar power tower. To improve the stability of the solar subsystem for continuous daily operation, two energy storage stages are employed innovatively. In addition, the whole scheme embraces a solid oxide electrolyzer. Therefore, a novel combined electricity and hydrogen cogeneration model based on solar energy is evaluated here. To this end, the energy-, exergy-, sustainability-, and economic-based parametric sensitivity study is implemented comprehensively. Net present value is another performance metric investigated in this paper. Besides, a novel multi-objective approach utilizing an artificial neural network combined with a multi-objective grey wolf optimization is performed. Considering four different decision parameters, optimum objectives include exergy efficiency, hydrogen production rate, and products’ unit cost. From the parametric sensitivity study, it is inferred that the outlet pressure of the low-pressure turbine significantly affects performance metrics. Also, from the optimization, the optimum values of mentioned objectives equal 2587 kg/day, 20.89%, and 17.25 $/GJ, respectively. Moreover, the net present value indicates that the payback period can be reduced up to 8.1 years corresponding to optimum operational conditions

A novel heat recovery for a marine diesel engine with power and cooling outputs; exergetic, economic, and net present value investigation and multi-criteria NSGA-II optimization

Owing to the marine environmental pollution affected by cruises, the use of techniques to mitigate carbon dioxide emission (CO2) is vital. Since a quarter of the fuel energy input to the engine is lost, waste management for marine diesel engines can provide some valuable outputs by which the need for other energy conversion-based methods disappears. Hence, the current work proposes a novel model of waste heat recovery for a 1 MW marine diesel engine in a low-temperature framework by which outstanding results are predictable. The defined auxiliary model consists of an absorption power cycle and an ejector refrigeration cycle to produce useful electricity and cooling for air conditioning. This model is designed for the first time and comprehensively analyzed and optimized to set the most suitable state of operation. The potential of the model is measured through the exergy, environmental, economic, and net present value standpoints. Moreover, an advanced evolutionary algorithm based on the non-dominated sorting genetic algorithm-II is applied to reach the optimum cost and exergetic performance. The optimum state showed an exergy efficiency of 35.19 % and products’ specific cost of 53.01 $/GJ. Moreover, the optimum payback period and CO2 emission reduction equal 6.79 years and 21.5 kg/MWh, respectively

Management of heat transfer and hydraulic characteristics of a micro-channel heat sink with various arrangements of rectangular vortex generators utilizing artificial neural network and response surface methodology

It is common to use micro-channel heat sinks (MCHSs) in equipment such as; ICs, transistors, LEDs, and high-power lasers, which generate heat due to the passage of electric current. This heat is often a menace to harm these devices and their internal parts. For this reason, heat rejection in the MCHSs is an endless challenge for researchers. Placing vortex generators (VGs) within the MCHS improves the cooling capacity but incurs a considerable pressure drop. Meanwhile, the shape, geometric dimensions, and arrangement of the VGs significantly affect this heat transfer. In the current study, the placement angle (θ), the longitudinal distance (dl), and the transverse distance (dt) of the VGs were chosen to be altered. The Artificial Neural Networks (ANN) and Response Surface Methodology (RSM) were exerted to study their variation's effect on the Nusselt number (Nu) and pressure drop (ΔP) of an MCHS. The presented data illustrated that the results of the ANN model were closer to the data provided by the numerical simulation. With the coefficient of determination of 0.995 and 0.992 in forecasting the Nu and ΔP, the ANN exhibited better performance than the RSM model. Besides, the ANN model recommended that to acquire the highest relative efficiency index, the optimum values of placement angle, the longitudinal and transverse distances of the VGs should be 60, 0.151 mm, and 0.166 mm, respectively

Flow and heat transfer in a plain fin-and-hexagonal tube heat exchanger with different side ratios

Improving the thermo-hydraulic performance of heat exchangers (HEs) can considerably manage the energy requirements in various engineering processes. The fin-and-tube heat exchangers (FTHEs) are extensively utilized in recent decades, and they provide substantial benefits over the typical HEs such as high heat transfer surface. The shape and geometry of the tubes remarkably affect the thermal efficiency and pressure drop of these devices. There are many experimental and numerical investigations relating to improving the thermo-hydraulic performance of FTHEs with circular and elliptical tubes in the literature. In the current research, five various hexagonal tubes with different side ratios were utilized to enhance the performance of an FTHE. The impact of various hexagon side ratios on heat transfer capacity and fluid flow characteristic of the FTHE at different Reynolds numbers has studied numerically. According to the obtained results, the plain-fin-and hexagonal tube HE with the side ratio of 0.25 had the best performance. Although the lowest values of the Colburn factor and the weakest heat transfer belong to the FTHE with the side ratio of 0.25, it is preferred to circular tube HEs due to the lower pressure drop they caus

Response Surface Methodology and Artificial Neural Network modellings on hydraulic and thermal performances of a disk-shaped heat sink with tree-like microchannels

To cope with the increasing heat generation resulting from increased power in micro-scale devices, an optimum design of a tree-like microchannel heat sink is suggested utilizing Artificial Neural Networks (ANN) and Response Surface Methodology (RSM). Based on the numerical finite volume model, both ANN and RSM models were trained, and their performances were assessed using four distinct performance criteria. The results showed that both of the models are reliable for the purpose of this study, showing a significantly high adjusted R2 for both performance control variables pressure drop (ΔP) and Nusselt number (Nu). The adjusted R2 values observed for the RSM were 0.987 and 0.997, respectively, for the Nu and ΔP. These values were calculated as high as 0.997 for Nu prediction and 0.997 for ΔP prediction using the ANN. Finally, utilizing the calibrated RSM and ANN models, three optimum design configurations for three different purposes given the priority requirements of the heat sink implementations were suggested. The minimum ΔP configuration is suitable for the longevity of the heat sink, and the maximum Nu configuration is suitable for applications where heat transfer performance is more critical. For a balanced optimum design, the efficiency index was maximized

Heat transfer analysis on ferrofluid natural convection system with magnetic field

Free convection of Fe3O4-water inside the porous enclosure was investigated in the presence of magnetic fields. The SIMPLE algorithm was employed to solve the equations based on FVM. The inner wall of enclosure was considered in the constant flux and that of outer wall were at a constant temperature, respectively. Also, two other walls are thermal insulation and the radiation reflects to inner semi-annulus. An electric current coil for producing a magnetic field is wrapped around the semi-annulus. The effects of Rap=10and1000, the concentration (φAve=0,0.01and0.03), porosities (ε=0.4and0.7) and magnetic numbers (0≤Mn≤8×107) are investigated considering first laws of thermodynamics. The findings revealed that the mean Nusselt number has direct relation with the magnetic number, porosity, Rap and concentration, respectively. Moreover, increasing volume fraction from 0.01 to 0.03 in high magnetic number enhanced the Nusselt number by 32 %