Analyzing microchannel heat sinks (MCHS) in terms of the second thermodynamic law is useful, and it is necessary to examine MCHSs in terms of irreversible factors. In this research, the second ...thermodynamic law analysis is conducted for graphene–platinum/water hybrid nanofluid flow to assess how a new cylindrical microchannel heat sink has wavy-shaped fins performs. A variety of Reynolds numbers, nanoparticle concentrations as well as wave amplitudes are used to simulate the problem, while the heat flux is constant. Fluent software is employed to solve the governing equations employing the control-volume method. The distributions of velocity and temperature are derived, and the entropy generation rate (including the generation of thermal as well as frictional entropy), along with the Bejan number, is obtained. The minimum values corresponding to the pointed parameters are, respectively, obtained as 7.63 × 10
−2
, 1.24 × 10
−4
, and 7.78 × 10
−2
, while the maximum magnitudes are 1.09 × 10
−1
, 1.49 × 10
−3
, and 1.09 × 10
−1
, respectively. Increasing each factor, including wave amplitude, particle fraction, and Reynolds number, causes a decline in the thermal entropy generation rate, while frictional entropy rises significantly. The Bejan number was obtained greater than 0.98 in all cases, which means that irreversibility mainly results from the thermal entropy generation. This could be a desirable finding, noting that increasing input variables reduced the thermal entropy generation rate. Finally, by employing an artificial neural network, a model is obtained for the entropy generation of entropy based on distinct factors of wave amplitude, nanofluid concentration, and Reynolds number.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Nowadays, due to the energy and environmental crisis, using renewable energy is considered to reduce environmental pollution. In this paper, a comprehensive review of geothermal source heat pumps ...(GSHPs) and air source heat pumps (ASHPs) are studied from various aspects including refrigerant change, single-stage heat pump and heat pump with an economizer. This study is conducted to meet the heating needs of the central laboratory of Hakim Sabzevari University. These cycles are analyzed using energy, exergy, and environmental and economic equations (4E analysis). The results show that the coefficient of performance (COP) and exergy efficiency values for the GSHP cycle are higher than the ASHP cycle, and the best refrigerant for both is R134A. The economic and environmental analysis also reveals that using the GSHP cycle can save the electricity to 239 MWh/year (by cycle equipment), which reduces CO2 emissions to 140 tons/year and saves costs 27,280 $/year, compared to ASHP.
Moreover, by using an economizer in the heat pump cycle, the COP of the GSHP cycle improved by 9%. The exergy efficiency about 6.8% and the COP of the ASHP cycle grew about 7.5% and its exergy efficiency by 7.4%. It is concluded that the economizer has a more significant impact on the GSHP cycle.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this paper, the effect of the presence of radiation on the convection heat transfer rate and the nanofluid entropy generation within a diagonal rectangular chamber is investigated numerically in ...the presence of a magnetic field. The governing equations have been solved via finite volume method using the simple algorithm. In this paper, the effects of Rayleigh number, Hartmann number, magnetic field angle changes, chamber angle changes, entropy parameter, radiation parameter and volume percent of nanoparticles on the entropy generation and heat transfer have been investigated. The results show that with increasing Rayleigh number and decreasing the Hartmann number, the Nusselt number and entropy generation increase and the Bejan number decreases. By increasing the angle of the magnetic field, the heat transfer rate and the entropy generation are reduced and the Bejan number increases. By increasing the angle of the chamber at high Rayleigh numbers, the heat transfer rate increases, or by adding 6% of the nanoparticles to the base fluid, the heat transfer rate increases by 9.3% and the entropy generation increases by 15.5% in the absence of radiation. This increase in the Rd = 3 radiation parameter is 5.4% and 6.2%, respectively. It was also observed that the Nusselt number and the entropy generation increased, and with increasing the radiation parameter, the Bejan number decreased. Increasing the heat transfer rate is more significant at higher Rayleigh numbers by increasing the radiation parameter.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Nanofluids are broadly employed in heat transfer mediums to enhance their efficiency and heat transfer capacity. Thermophysical properties of nanofluids play a crucial role in their thermal behavior. ...Among various properties, the dynamic viscosity is one of the most crucial ones due to its impact on fluid motion and friction. Applying appropriate models can facilitate the design of nanofluidics thermal devices. In the present study, various machine learning methods including MPR, MARS, ANN-MLP, GMDH, and M5-tree are used for modeling the dynamic viscosity of CuO/water nanofluid based on the temperature, concentration, and size of nanostructures. The input data are extracted from various experimental studies to propose a comprehensive model, applicable in wide ranges of input variables. Moreover, the relative importance of each variable is evaluated to figure out the priority of the variables and their influences on the dynamic viscosity. Finally, the accuracy of the models is compared by employing the statistical criteria such as
R
-squared value. The models’ outputs disclosed that employing ANN-MLP approach leads to the most precise model.
R
-square value and average absolute percent relative error (AAPR) value of the model by using ANN-MLP model are 0.9997 and 1.312%, respectively. According to these values, ANN-MLP is a reliable approach for predicting the dynamic viscosity of the studied nanofluid. Additionally, based on the relative importance of the input variables, it is concluded that concentration has the highest relative importance; while the influence of size is the lowest one.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This work is a three-dimensional numerical study of a U-shaped evacuated tube solar collector employing different types of oxide nanofluids including water–Al
2
O
3
, water–CuO and water–TiO
2
under ...the steady-state condition. The simulation is performed using the single-phase method for nanofluid modeling, the DO method for radiation modeling, incompressible and fluid flow laminar regime. The thermo-physical properties of the water are considered as a function of temperature ranging from 0 to 150 °C. The obtained results showed that increasing both length and diameter of the U-shaped tubes of the solar collector enhances its thermal efficiency. Moreover, it is found that using oxide nanofluids results in an enhancement in the collector thermal performance which using water–CuO nanofluid causes 13.8, 1.5 and 1.3% higher collector thermal efficiency in comparison with employing pure water, water–TiO
2
and water–Al
2
O
3
nanofluids, respectively. It is also observed that the working fluid heat capacity plays an important role in the thermal performance of the evacuated tube solar collector.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This numerical study on the effect of microchannels with porous medium and nanofluid on the solar concentrator photovoltaic (CPV) system with a solar concentration ratio of 10 is presented. Numerical ...simulation is two-dimensional and different layers of CPV are modeled. The effect of the position of the porous layer in the microchannel on the cooling of the PV system is investigated. The thermal behavior of the microchannel with the porous layer varies with the change of Darcy number, and the porosity coefficient according to the position of the porous layer in the microchannel is studied. The consequences demonstrate that the solar cell temperature is reduced by about 17% using the microchannel. The development of the microchannel cooling capacity is related to the rise in thermal conductivity in the porous layer. Also, in the porous layer cases, located in a block width across the microchannel, the maximum electrical efficiency rate and the minimum of the solar cell temperature occurred. The raising of the nanofluid volume fraction has improved the CPV system's electrical efficiency. Consequently, the solar cell temperature can be reduced from 1 to 52% with the increment of radiation intensity from 100 to 1000 Wm
−2
. The proposed cooling method is about 30% more effective than the conventional fin cooling method.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The present review paper aims to document the latest developments on the applications of nanofluids as working fluid in parabolic trough collectors (PTCs). The influence of many factors such as ...nanoparticles and base fluid type as well as volume fraction and size of nanoparticles on the performance of PTCs has been investigated. The reviewed studies were mainly categorized into three different types of experimental, modeling (semi-analytical), and computational fluid dynamics (CFD). The main focus was to evaluate the effect of nanofluids on thermal efficiency, entropy generation, heat transfer coefficient enhancement, as well as pressure drop in PTCs. It was revealed that nanofluids not only enhance (in most of the cases) the thermal efficiency, convection heat transfer coefficient, and exergy efficiency of the system but also can decrease the entropy generation of the system. The only drawback in application of nanofluids in PTCs was found to be pressure drop increase that can be controlled by optimization in nanoparticles volume fraction and mass flow rate.
The increasing need of the modern era of technology for better ways to increase the heat transfer performance of thermal systems has made nanoliquids much more critical than they have been for the ...previous two decades. With such demand in mind, the Carreau-Yasuda nanofluid in the presence of motile microorganisms and thermal radiation along with Robin’s boundary conditions has been scrutinized. The controlling PDEs are cracked into ordinary differentials through suitable similarity transformation. The transformed ODEs are solved numerically utilizing bvp4c built-in MATLAB computational software. The graphical results of the main parameters against the velocity profile, temperature profile, and solutal field of nanoparticles and motile microorganisms' concentration are illustrated through graphs. Furthermore, the consequence of the involved parameters on the heat transfer rate is also deliberated and offered through table values. This study analyzed that velocity is a declining function of magnetic parameter and buoyancy ratio parameter. Besides, the additional amount of thermal radiation improves the heat transport rate. The concentration field is an escalating function of the thermophoresis parameter. Furthermore, microorganisms’ profile is boosted up by enlarging the magnitudes of microorganism’s Biot number.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The main purpose of this research is the numerical modeling of laminar mixed convection heat transfer inside an open square cavity with different heat transfer areas. In the considered geometry, cold ...fluid enters the cavity. At the middle of the cavity, there is a hot isothermal circular heat source. For increasing the heat transfer, solid silver nanoparticles with volume fractions (
φ
) of 0, 2 and 4% are added to water. Studied Re numbers are 10, 50, 120 and 200. The location of the hot zone changes the temperature distribution in the fluid layers. If the heat transfer area is located in an appropriate location, temperature distribution becomes more uniform. Increasing Re leads to smaller temperature gradients in regions near the hot surface and higher temperature at fluid layers close to the surface. By increasing fluid velocity, backflows do not improve heat transfer but it is able to change the heat transfer mechanism. By decreasing the fluid velocity, the effects of velocity gradients and extension of the velocity boundary layer increase and friction coefficient attains the maximum value.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In the present study, a set of experiments were accomplished to appraise the thermal performance and heat transfer of
n
-pentane-acetone and
n
-pentane-methanol mixtures inside a gravity-assisted ...thermosyphon heat pipe. Pure
n
-pentane, acetone and methanol were also tested as the carrying fluid to produce some reference data. The heat pipe was manufactured from copper with length and diameter of 290 and 20 mm, respectively. The effect of multiple factors covering the input heat to the evaporator section, the filling ratio of the carrying fluid, heat pipe tilt angle and also the type of the carrying fluid on temperature distribution and thermal performance of the heat pipe was investigated. The results demonstrated that the thermo-physical properties of the carrying fluid were the key factor controlling the heat pipe efficiency. The vapour pressure and boiling temperature of the carrying fluid controlled the thermal efficiency of the system such that for
n
-pentane-acetone, the highest thermal efficiency was obtained. Also, it was identified that the filling ratio of the system is a key operating factor such that the value of the filling ratio was small for the evaporative carrying fluid (binary mixtures), while it was large for the non-evaporative carrying fluids. Also, heat pipe tilt angle was impressed by the type of the carrying fluid; the optimum tilt angle was 55 degree for the binary mixtures, while it was 65° for the pure liquids.
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