Heat Transfer, Pressure Drop, and Entropy Generation in a Solar Collector Using SiO2/Water Nanofluids: Effects of Nanoparticle Size and pH

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Omid Mahian ◽  
Ali Kianifar ◽  
Ahmet Z. Sahin ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Entropy Generation ◽  
Thermal Efficiency ◽  
Solar Collector ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Transfer Pressure

In this paper, an analytical study is carried out on the heat transfer, pressure drop, and entropy generation in a flat-plate solar collector using SiO2/water nanofluid with volume concentration of 1%. In the study, the effects of two different values of pH, i.e., 5.8 and 6.5, and two different sizes of nanoparticles, i.e., 12 nm and 16 nm, on the entropy generation rate in turbulent flow are investigated. The results are compared with the results obtained for the case of water. The findings show that by using the Brinkman model to calculate the viscosity instead of experimental data one obtains a higher heat transfer coefficient and thermal efficiency than that in the case of water, while, when the experimental data are used, the heat transfer coefficient and thermal efficiency of water are found to be higher than that of nanofluids. The results reveal that using nanofluids increases the outlet temperature and reduces the entropy generation rate. It is also found that for nanofluids containing the particles with a size of 16 nm, the increase in pH value would increase the entropy generation rate, while for nanoparticles with a size of 12 nm the increase in pH would decrease the entropy generation.

Lower Entropy Generation in Microchannels With Laminar Single Phase Flow

2010 ◽  
Author(s):  
E. Galvis ◽  
J. R. Culham
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Entropy Generation ◽  
Entropy Generation Rate ◽  
Channel Geometry ◽  
Micro Channels ◽  
Optimum Channel

In this study the entropy generation minimization method is used to find the optimum channel dimensions in micro heat exchangers with a uniform heat flux. With this approach, pressure drop and heat transfer in the micro channels are considered simultaneously during the optimization analysis. A computational model is developed to find the optimum channel depth knowing other channel geometry dimensions and coolant inlet properties. The flow is assumed laminar and both hydrodynamically and thermally fully developed and incompressible. However, to take into account the effect of the developing length in the friction losses, the Hagenbach’s factor is introduced. The micro channels are assumed to have an isothermal or isoflux boundary condition, non-slip flow, and fluid properties have dependency on temperature accordingly. For these particular case studies, the pressure drop and heat transfer coefficient for the isoflux boundary condition is higher than the isothermal case. Higher heat transfer coefficient and pressure drop were found when the channel size decreased. The optimum channel geometry that minimizes the entropy generation rate tends to be a deep, narrow channel.

Numerical Study on Conjugated Laminar Mixed Convection of Alumina/Water Nanofluid Flow, Heat Transfer, and Entropy Generation Within a Tube-on-Sheet Flat Plate Solar Collector

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Mohammad Charjouei Moghadam ◽  
Mojtaba Edalatpour ◽  
Juan P. Solano
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Entropy Generation ◽  
Solar Collector ◽  
Richardson Number ◽  
Volume Concentration ◽  
Volume Fraction ◽  
Flat Plate Solar Collector

In this research, an inclined three-dimensional nanofluid-based tube-on-sheet flat plate solar collector (FPSC) working under laminar conjugated mixed convection heat transfer is numerically modeled. The working fluid is selected to be alumina/water (Al2O3/water) and results from heat transfer, entropy generation, and pressure drop points of view are being presented for various prominent parameters, namely volume fraction, nanoparticles diameter, Richardson and Reynolds numbers. According to the simulations, Nusselt number decreases as the Richardson number or volume fraction of the nanofluid rises, whereas heat transfer coefficient experiences an augmentation when volume concentration and the Richardson number surge. Also, data reveal that total entropy generation rate of the system declines when the alumina/water nanofluid is utilized inside the system as the volume fraction or the Richardson number increases. Additionally, it is found that increasing the nanoparticle volume concentration or the Richardson number diminishes the pressure drop considerably, whereas friction factor substantially proliferates as the Richardson number or volume fraction rises. Eventually, employment of larger alumina nanoparticles mean diameter eventuates in providing lower Nusselt number and apparent friction factor while it increases the pressure drop and heat transfer coefficient. Finally, comparing the efficiency of the presented FPSC design with those available in the literature shows a superior performance by the present design with its maximum occurring at 2 vol %.

scholarly journals Entropy Generation for Negative Frictional Pressure Drop in Vertical Slug and Churn Flows

Entropy ◽  
2021 ◽  
Vol 23 (2) ◽  
pp. 156
Author(s):  
Lei Liu ◽  
Dongxu Liu ◽  
Na Huang
Keyword(s):  
Experimental Data ◽  
Pressure Drop ◽  
Energy Loss ◽  
Entropy Generation ◽  
Mechanical Energy ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Pressure Drops ◽  
Frictional Pressure Drop ◽  
Mechanical Energy Loss

It is widely accepted that the frictional pressure drop is impossible to be negative for pipe flow. However, the negative frictional pressure drops were observed for some cases of two-phase slug and churn flows in pipes, challenging the general sense of thermodynamic irreversibility. In order to solve this puzzling problem, theoretical investigations were performed for the entropy generation in slug and churn flows. It is found that the frictional pressure drop along with a buoyancy-like term contributes to the entropy generation due to mechanical energy loss for steady, incompressible slug and churn flows in vertical and inclined pipes. Experiments were conducted in a vertical pipe with diameter as 0.04 m for slug and churn flows. Most of the experimental data obtained for frictional pressure drop are negative at high gas–liquid ratios from 100 to 10,000. Entropy generation rates were calculated from experimental data. The results show that the buoyancy-like term is positive and responsible for a major part of entropy generation rate while the frictional pressure drop is responsible for a little part of entropy generation rate, because of which the overall entropy generation due to mechanical energy loss is still positive even if the frictional pressure drop is negative in vertical slug and churn flows. It is clear that the negative frictional pressure drops observed in slug and churn flows are not against the thermodynamics irreversibility.

scholarly journals Application of Nanofluids in Thermal Performance Enhancement of Parabolic Trough Solar Collector: State-of-the-Art

2019 ◽  
Vol 9 (3) ◽  
pp. 463 ◽  
Author(s):  
Hamed Olia ◽  
Mohammadamin Torabi ◽  
Mehdi Bahiraei ◽  
Mohammad Hossein Ahmadi ◽  
Marjan Goodarzi ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Entropy Generation ◽  
Thermal Efficiency ◽  
Performance Enhancement ◽  
Volume Fraction ◽  
Working Fluid ◽  
Parabolic Trough

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.

Entropy Generation Rate in Forced Convection Flow About Inclined Surfaces in a Porous Medium

2011 ◽  
Author(s):  
Bourhan Tashtoush ◽  
B. S. Yilbas
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Pressure Drop ◽  
Forced Convection ◽  
Entropy Generation ◽  
Operating Conditions ◽  
Generation Rate ◽  
Optimum Operating ◽  
Entropy Generation Rate ◽  
Thermal System

Entropy generation rate has been the attraction of research, since it provides information on the thermodynamic irreversibility associated with the thermal systems. The exergy distraction in the thermal system increases entropy generation rate while lowering the second law efficiency of the thermal system. The heat transferring devices, such as heat exchangers, operates better when temperature difference between the transferring device and the heat sink is maintained high. In addition, the use of porous material in these devices enhances the heat transfer rates due to the achievement of high heat transfer coefficients. However, the presence of the porous material also increases the pump power because of the high pressure drop in the flow system. This increases the operational costs. Consequently, entropy generation rate due to pressure drop needs to be minimized to reduce the cost; however, heat transfer rates from the thermal system needs to be enhanced to improve the thermal performance of the heat transferring device. Therefore, a balance between the entropy generation rates due to pressure drop and heat transfer needs to be attained to achieve optimum operating conditions of such devices. To investigate the optimum operating conditions, the forced convection problem about inclined surfaces (or wedges) in saturated porous medium is considered. The flow in the porous medium is described by the Darcy-Brinkman momentum equation. An exact analytical solution of the governing equations using Kummer function is developed for the velocity, temperature, Nusselt Number, and entropy generation rate for the case where the free stream velocity and wall temperature distribution of the inclined surface vary according to the same power function of distance x, along the plate. It is demonstrated that the entropy generation number is weakly dependent on the Brinkman-Darcy number for forced convection flow, which is particularly true near the wall region.

Numerical Investigation of Local Entropy Generation for Laminar Flow in Rotating-Disk Systems

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Mohammad Shanbghazani ◽  
Vahid Heidarpoor ◽  
Marc A. Rosen ◽  
Iraj Mirzaee
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Laminar Flow ◽  
Entropy Generation ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Bejan Number ◽  
Local Entropy ◽  
Fluid Friction ◽  
Local Entropy Generation

The entropy generation is investigated numerically in axisymmetric, steady-state, and incompressible laminar flow in a rotating single free disk. The finite-volume method is used for solving the momentum and energy equations needed for the determination of the entropy generation due to heat transfer and fluid friction. The numerical model is validated by comparing it to previously reported analytical and experimental data for momentum and energy. Results are presented in terms of velocity distribution, temperature, local entropy generation rate, Bejan number, and irreversibility ratio distribution for various rotational Reynolds number and physical cases, using dimensionless parameters. It is demonstrated that increasing rotational Reynolds number increases the local entropy generation rate and irreversibility rate, and that the irreversibility is mainly due to heat transfer while the irreversibility associated with fluid friction is minor.

Entropy Generation Minimization in a Pressure-Driven Microflow of Viscoelastic Fluid With Slippage at the Wall: Effect of Conjugate Heat Transfer

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Rajkumar Sarma ◽  
Pranab Kumar Mondal
Keyword(s):  
Heat Transfer ◽  
Viscoelastic Fluid ◽  
Entropy Generation ◽  
Conjugate Heat Transfer ◽  
Applied Pressure ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Minimum Entropy ◽  
Viscoelastic Parameter ◽  
Entropy Generation Minimization

We focus on the entropy generation minimization for the flow of a viscoelastic fluid through a parallel plate microchannel under the combined influences of applied pressure gradient, interfacial slip, and conjugate heat transfer. We use the simplified Phan–Thien–Tanner model (s-PTT) to represent the rheological behavior of the viscoelastic fluid. Using thermal boundary conditions of the third kind, we solve the transport equations analytically to obtain the velocity and temperature distributions in the flow field, which are further used to calculate the entropy generation rate in the analysis. In this study, the influential role of the following dimensionless parameters on entropy generation rate is examined: the viscoelastic parameter (εDe2), slip coefficient (k¯), channel wall thickness (δ), thermal conductivity of the wall (γ), Biot number (Bi) and Peclet number (Pe). We show that there exists a particular value of the abovementioned parameters that lead to a minimum entropy generation rate in the system. We believe the results of this analysis could be of helpful in the optimum design of microfluidic system/devices typically used in thermal management, such as micro-electronic devices, microreactors, and microheat exchangers.

Modeling heat transfer of nanofluid flow in microchannels with electrokinetic and slippery effects using Buongiorno’s model

2019 ◽  
Vol 29 (8) ◽  
pp. 2566-2587 ◽  
Author(s):  
Hang Xu ◽  
Huang Huang ◽  
Xiao-Hang Xu ◽  
Qiang Sun
Keyword(s):  
Heat Transfer ◽  
Entropy Generation ◽  
Slip Length ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Lower Wall ◽  
Volumetric Concentration ◽  
Nanofluid Flow ◽  
Cross Sectional ◽  
Content Type

PurposeThis paper aims to study the heat transfer of nanofluid flow driven by the move of channel walls in a microchannel under the effects of the electrical double layer and slippery properties of channel walls. The distributions of velocity, temperature and nanoparticle volumetric concentration are analyzed under different slip-length. Also, the variation rates of flow velocity, temperature, concentration of nanoparticle, the pressure constant, the local volumetric entropy generation rate and the total cross-sectional entropy generation are analyzed.Design/methodology/approachA recently developed model is chosen which is robust and reasonable from the point of view of physics, as it does not impose nonphysical boundary conditions, for instance, the zero electrical potential in the middle plane of the channel or the artificial pressure constant. The governing equations of flow motion, energy, electrical double layer and stream potential are derived with slip boundary condition presented. The model is non-dimensionalized and solved by using the homotopy analysis method.FindingsSlip-length has significant influences on the velocity, temperature and nanoparticle volumetric concentration of the nanofluid. It also has strong effects on the pressure constant. With the increase of the slip-length, the pressure constant of the nanofluid in the horizontal microchannel decreases. Both the local volumetric entropy generation rate and total cross-sectional entropy generation rate are significantly affected by both the slip-length of the lower wall and the thermal diffusion. The local volumetric entropy generation rate at the upper wall is always higher than that around the lower wall. Also, the larger the slip-length is, the lower the total cross-sectional entropy generation rate is when the thermal diffusion is moderate.Originality/valueThe findings in this work on the heat transfer and flow phenomena of the nanofluid in microchannel are expected to make a contribution to guide the design of micro-electro-mechanical systems.

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