Single-phase natural circulation loop using oils and ternary hybrid nanofluids: Steady-state and transient thermo-hydraulics

2020 ◽  
pp. 1-32
Author(s):  
Mayaram Sahu ◽  
Jahar Sarkar ◽  
Laltu Chandra
Keyword(s):  
Steady State ◽  
Mass Flow Rate ◽  
Entropy Generation ◽  
Mass Flow ◽  
Flow Rate ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Width Ratio ◽  
Total Entropy ◽  
Hybrid Nanofluids

Abstract Steady-state and transient behaviours of single-phase natural circulation loop (SPNCL) are investigated using four thermal oils (Therminol VP1, Paratherm CR, Dowtherm A and Dowtherm Q) and water-based ternary hybrid (various combinations of different nature and shaped nanoparticles: Al2O3, Cu, CNT and Graphene) nanofluids as loop fluid. The influences of nanoparticle volume concentration and loop height to width ratio on the mass flow rate and total entropy generation rate of SPNCL are investigated. Results disclose that ternary hybrid nanofluids enhance flow initiation, reduce fluctuation and are expected to attain a steady-state faster than water. Steady-state mass flow rate increases/decreases for ternary hybrid nanofluid depending on the shape of the nanoparticle and total entropy generation rate decreases as compared to water. Thermal oil shows a higher mass flow rate and total entropy generation rate as compared to water. Al2O3-Cu-CNT-water and paratherm CR show the best result among all ternary hybrid nanofluids and thermal oils, respectively. The nanoparticle shape decides the optimum nanoparticle volume fraction. Increasing the height to width ratio decreases the total entropy generation and upsurges the mass flow rate at specified input power. The optimum height to width ratio depends on fluid.

Steady-State Energetic and Exergetic Performances of Single-Phase Natural Circulation Loop With Hybrid Nanofluids

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Mayaram Sahu ◽  
Jahar Sarkar
Keyword(s):  
Steady State ◽  
Mass Flow Rate ◽  
Entropy Generation ◽  
Mass Flow ◽  
Flow Rate ◽  
Natural Circulation ◽  
Circulation Loop ◽  
Hybrid Nanofluid ◽  
Natural Circulation Loop ◽  
Hybrid Nanofluids

Energy and exergy performances of natural circulation loop (NCL) with various water-based hybrid nanofluids (Al2O3 + TiO2, Al2O3 + CNT, Al2O3 + Ag, Al2O3 + Cu, Al2O3 + CuO, Al2O3 + graphene) with 1% volumetric concentration are compared in this study. New thermophysical property models have been proposed for hybrid nanofluids with different particle shapes and mixture ratio. Effects of power input, loop diameter, loop height, loop inclination and heater/cooler inclination on steady-state mass flow rate, effectiveness, and entropy generation are discussed as well. Results show that both the steady-state mass flow rate and energy–exergy performance are enhanced by using the hybrid nanofluids, except Al2O3 + graphene, which shows the performance decrement within the studied power range. Al2O3 + Ag hybrid nanofluid shows highest enhancement in mass flow rate of 4.8% compared to water. The shape of nanoparticle has shown a significant effect on steady-state performance; hybrid nanofluid having cylindrical and platelet shape nanoparticles yields lower mass flow rate than that of spherical shape. Mass flow rate increases with the increasing loop diameter and height, whereas decreases with the increasing loop and heater/cooler inclinations. Both effectiveness and entropy generation increase with the decreasing loop diameter and height, whereas increasing the loop and heater/cooler inclinations. This study reveals that the particle shape has a significant effect on the performance of hybrid nanofluids in NCL, and the use of hybrid nanofluid is more effective for higher power.

Selecting the cooling water mass flow rate for a power plant under variable load with entropy generation rate minimization

Energy ◽  
2016 ◽  
Vol 107 ◽  
pp. 725-733 ◽  
Author(s):  
Rafał Laskowski ◽  
Adam Smyk ◽  
Janusz Lewandowski ◽  
Artur Rusowicz ◽  
Andrzej Grzebielec
Keyword(s):  
Power Plant ◽  
Mass Flow Rate ◽  
Entropy Generation ◽  
Mass Flow ◽  
Flow Rate ◽  
Water Mass ◽  
Cooling Water ◽  
Entropy Generation Rate ◽  
Variable Load ◽  
Water Mass Flow Rate

scholarly journals Multi-Objective Optimization of Braun-Type Exothermic Reactor for Ammonia Synthesis

Entropy ◽  
2021 ◽  
Vol 24 (1) ◽  
pp. 52
Author(s):  
Tianchao Xie ◽  
Shaojun Xia ◽  
Chao Wang
Keyword(s):  
Entropy Generation ◽  
Flow Rate ◽  
Ammonia Synthesis ◽  
Storage System ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Inlet Temperature ◽  
Total Entropy ◽  
Nsga Ii ◽  
Molar Flow Rate

The exothermic reactor for ammonia synthesis is a primary device determining the performance of the energy storage system. The Braun-type ammonia synthesis reactor is used as the exothermic reactor to improve the heat release rate. Due to the entirely different usage scenarios and design objectives, its parameters need to be redesigned and optimized. Based on finite-time thermodynamics, a one-dimensional model is established to analyze the effects of inlet gas molar flow rate, hydrogen–nitrogen ratio, reactor length and inlet temperature on the total entropy generation rate and the total exothermic rate of the reactor. It’s found that the total exothermic rate mainly depends on the inlet molar flow rate. Furthermore, considering the minimum total entropy generation rate and maximum total exothermic rate, the NSGA-II algorithm is applied to optimize seven reactor parameters including the inlet molar flow rate, lengths and temperatures of the three reactors. Lastly, the optimized reactor is obtained from the Pareto front using three fuzzy decision methods and deviation index. Compared with the reference reactor, the total exothermic rate of the optimized reactor is improved by 12.6% while the total entropy generation rate is reduced by 3.4%. The results in this paper can provide some guidance for the optimal design and application of exothermic reactors in practical engineering.

Aerodynamic Performance of Tip Injections for a Winglet-Shrouded Linear Turbine Cascade

2017 ◽  
Author(s):  
Min Zhang ◽  
Yan Liu ◽  
Meng-Chao Zhang ◽  
Bao-Xi Mo ◽  
Jing-Guang Yang
Keyword(s):  
Energy Loss ◽  
Mass Flow Rate ◽  
Entropy Generation ◽  
Mass Flow ◽  
Flow Rate ◽  
Aerodynamic Performance ◽  
Loss Coefficient ◽  
Entropy Generation Rate ◽  
Turbine Cascade ◽  
Tip Injection

Tip injection is applied in high pressure gas turbine blades to improve the tip surface heat transfer, while it also alters the flow fields in the tip gap and near the tip regions. This paper evaluates the aerodynamic performance of tip injections for a linear turbine cascade. A previously investigated winglet shroud tip without (WS) and with seals (WSS) and a flat tip are considered as datum cases. Five jet holes are distributed on the winglet shroud tips but they are not constructed on the flat tip geometry. Four injection mass flow ratios, Mr,d, of the injection mass flow rate to the mainstream mass flow rate being 0.1%, 0.2%, 0.3% and 0.5% are examined using both experiments and CFD, while three additional Mr,d including 0.7%, 0.9% and 1.0% are further numerically studied. Influences of tip injections on loss changes under various jet mass flow ratios are pinpointed via analyzing the entropy generation rate and energy loss coefficient. For Mr,d being 0.3%, the jet fluid penetrates into the near-tip region and enhances the upper passage vortex, especially for the WSS case due to the blockage effect of the seals. More severe velocity gradients and larger entropy generation rates are observed in the cascade for the WS and WSS tips with the tip jet (simply named by WSJ and WSSJ respectively). Compared with the flat tip, the WS and WSS tips reduce the energy loss coefficient by 18.98% and 33.86% respectively, while the WSJ and WSSJ bring smaller decrements of 15.89% and 27.08% separately. Contrast to the energy loss changes, tip injection can help prevent the over-tip leakage (OTL) flow from entering into the tip gap. For Mr,d being 0.3%, the WSJ and WSSJ decrease the OTL mass flow rates at a gap inlet plane by 16.97% and 65.37% respectively relative to the flat tip. When compared to the corresponding non-injection WS and WSS cases, the WSJ and WSSJ achieve further reductions of 11.43% and 29.00% separately. However, in the WSJ and WSSJ cases, the OTL mass flow rate at a tip exit plane is not noticeably lessened as it also includes the increased injection mass flow apart from the leakage main fluid. With the increase in jet mass flow ratio (Mr,d), the aerodynamic performance of the cascade with WSJ and WSSJ is gradually deteriorated. Particularly, the energy loss coefficient of the injection cases even becomes larger than that of the flat tip when Mr,d exceeds 0.7%. This change trend of the energy loss is also confirmed by an one-dimensional loss model analysis for the mixing process between the injected and the main streams.

Pitfalls for Accurate Steady-State Port Flow Simulations

2012 ◽  
Author(s):  
Xiaofeng Yang ◽  
Zhaohui Chen ◽  
Tang-Wei Kuo
Keyword(s):  
Steady State ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Measured Data ◽  
Steady State Flow ◽  
Bench Tests ◽  
Flow Simulations ◽  
Mesh Topology ◽  
State Flow

Steady-state port flow simulations were carried out with a commercial three dimensional (3D) Computational Fluid Dynamics (CFD) code using Cartesian mesh with cut cells to study the prediction accuracy. The accuracy is assessed by comparing predicted and measured mass-flow rate and swirl and tumble torques at various valve lifts using different boundary condition setup and mesh topology relative to port orientation. The measured data is taken from standard steady-state flow bench tests of a production intake port. The predicted mass-flow rates agree to within 1% with the measured data between the intermediate and high valve lifts. At low valve lifts, slight over prediction in mass-flow rate can be observed. The predicted swirl and tumble torques are within 25% of the flow bench measurements. Several meshing parameters were examined in this study. These include: inlet plenum shape and outlet plenum/extension size, embedded sphere with varying minimum mesh size, finer meshes on port and valve surface, orientation of valve and port centerline relative to the mesh lines. For all model orientations examined, only the mesh topology with the valve axis aligned closely with the mesh lines can capture the mass-flow rate drop for very high valve lifts due to flow separation. This study further demonstrated that it is possible to perform 3D CFD flow analyses to adequately simulate steady-state flow bench tests.

Predictions of Flow Separation at the Valve-Seat for Steady-State Port-Flow Simulation

2014 ◽  
Author(s):  
Tao Fang ◽  
Satbir Singh
Keyword(s):  
Steady State ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Flow Separation ◽  
Combustion Engine ◽  
Flow Simulation ◽  
Valve Lift ◽  
Valve Seat ◽  
Mesh Density

Steady-state port-flow simulations with static valve lift are often utilized to optimize the performance of intake system of an internal combustion engine. Generally, increase in valve lift results in higher mass flow rate through the valve. But in certain cases, mass flow rate can actually decrease with increased valve lift, caused by separation of turbulent flow at the valve-seat. Prediction of this phenomenon using computational fluid dynamics (CFD) models is not trivial. It is found that the computational mesh significantly influences the simulation results. A series of steady-state port flow simulation are carried out using a commercial CFD code. Several mesh topologies are applied for the simulations. The predicted results are compared with available experimental data from flow bench measurements. It is found that the flow separation and reduction in mass flow rate with increased valve lift can be predicted when high mesh density is used in the proximity of the valve seat and the walls of the intake port. Higher mesh density also gives better predictions of mass flow rate compared to the experiments, but only for high valve lifts. For low valve lifts, the error in predicted flow rate is close to 13%.

MHD Transient Free Convection Flow in Vertical Concentric Annulus with Isothermal and Adiabatic Boundaries

2017 ◽  
Vol 11 ◽  
pp. 40-52 ◽  
Author(s):  
Basant K. Jha ◽  
Taiwo S. Yusuf
Keyword(s):  
Steady State ◽  
Free Convection ◽  
Skin Friction ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Steady State Solution ◽  
State Solution ◽  
Concentric Annulus ◽  
Riemann Sum

This paper presents MHD transient flow in an infinite vertical concentric annulus when the fluid is set in motion by free convection current occurring in the annulus as a result of application of isothermal heating on the inner surface of the outer cylinder while the outer surface of the inner cylinder is thermally insulated. The solution of the governing equations are obtained using the well-known Laplace transform technique while the Riemann-sum approximation method has been used to invert the solution from Laplace domain to time domain. The numerical values obtained using Riemann-sum approximation approach is validated by presenting a comparison with the values obtained using the implicit finite difference method as well as the steady-state solution. These comparisons with the steady state solution shows a remarkable agreement at large value of time. The effect of the governing parameters on the velocity field, temperature field, mass flow rate as well as the skin-friction on both surfaces of the annulus have been analysed and presented with the aid of line graph. Generally, we observed that the mass flow rate and skin friction at the isothermally heated surface increases with increase in radius ratio. However, the reverse is seen at the thermally insulated surface as the skin-friction decreases with increase in radius ratio.

Optimal Analysis of Entropy Generation and Heat Transfer in Parabolic Trough Collector Using Green-Synthesized TiO2/Water Nanofluids

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Eric C. Okonkwo ◽  
Muhammad Abid ◽  
Tahir A. H. Ratlamwala ◽  
Serkan Abbasoglu ◽  
Mustafa Dagbasi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Entropy Generation ◽  
Mass Flow ◽  
Flow Rate ◽  
Entropy Generation Rate ◽  
Convection Coefficient ◽  
Parabolic Trough ◽  
Volumetric Concentration ◽  
Flow Rates

This study presents an experimental nanoparticle synthesis and the numerical analysis of a parabolic trough collector (PTC) operating with olive leaf synthesized TiO2/water nanofluid. The PTC is modeled after the LS-2 collector for various operating conditions. An analysis of the heat transfer and entropy generation in the PTC is carried out based on the first and second laws of thermodynamics for various parameters of nanoparticle volumetric concentration (0 ≤ φ ≤ 8%), mass flow rate (0.1 ≤ m˙ ≤ 1.1 kg/s), and inlet temperatures (350–450 K) under turbulent flow regime. The effect of these parameters is evaluated on the Nusselt number, thermal losses, heat convection coefficient, outlet temperature, pressure drop, entropy generation rate, and Bejan number. The results show that the values of the Nusselt number decrease with higher concentrations of the nanoparticles. Also, the addition of nanoparticles increases the heat convection coefficient of the nanofluid compared to water. The thermal efficiency of the system is improved with the use of the new nanofluid by 0.27% at flow rates of 0.1 kg/s. The entropy generation study shows that increasing the concentration of nanoparticles considerably decreases the rate of entropy generation in the system. It is also observed that increasing the volumetric concentration of nanoparticles at low mass flow rates has minimal effect on the rate of entropy generation. Finally, a correlation that provides a value of mass flow rate that minimizes the entropy generation rate is also presented for each values of inlet temperature and nanoparticle volumetric concentration.

scholarly journals Validating Spray Coverage Rate Using Liquid Mass on a Spray Card

2018 ◽  
Vol 61 (3) ◽  
pp. 887-895
Author(s):  
Michael P. Sama ◽  
Austin M. Weiss ◽  
Emma K. Benedict
Keyword(s):  
Steady State ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Evaporation Rate ◽  
Initial Mass ◽  
Field Validation ◽  
Steady State Method ◽  
State Method ◽  
Coverage Rates

Abstract. Validation of agricultural sprayers is important for quantifying as-applied coverage rates under field conditions. The complexity of modern sprayer control systems presents a challenge for precise field validation due to the use of nozzle control technologies, such as pulse width modulation, to meter chemical flow rates at individual nozzles. Non-uniform flow over time may result in local variations at high spatial resolutions that are ignored when estimating as-applied coverage rates across a field. The purpose of this study was to test several methods for estimating the mass of water applied to a water-sensitive paper spray card target using steady-state and instantaneous measurement techniques. The steady-state method consisted of a spray patternator table used to quantify the mass flow rate distribution across the nozzle width at varying nozzle pressures. The mass flow rate was then projected onto a two-dimensional area traveling across the spray width to calculate the mass of water that was deposited in the area. Two instantaneous sampling methods were used. The first method directly measured the mass of the spray card and water for 5 min after exposure to model the evaporation rate and solve for the initial mass at the time of exposure. The second method indirectly used the percent coverage of the exposed spray card by droplets. Results showed that the error between the calculated mass of water from the mass flow rate and the estimated initial mass of water from the evaporation rate varied between 2% and 8%. The relationships between the calculated and estimated initial mass of water methods and the spray card percent coverage were highly linear (R2 > 0.98). Both instantaneous methods produced results with higher variability between replications than the steady-state method, but the number of replications resulted in acceptably small differences between average mass measurements. These results show the potential for using evaporation rates for laboratory validation and percent coverage for laboratory or field validation of as-applied coverage rates. Keywords: Evaporation rate, Flow measurement, Precision agriculture, Sprayers, Water-sensitive paper.

The Equivalence of Maximum Power and Minimum Entropy Generation Rate in the Optimization of Power Plants

1996 ◽  
Vol 118 (2) ◽  
pp. 98-101 ◽  
Author(s):  
Adrian Bejan
Keyword(s):  
Heat Transfer ◽  
Power Plant ◽  
Entropy Generation ◽  
Heat Input ◽  
Power Plants ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Total Entropy ◽  
Minimum Entropy ◽  
Minimum Entropy Generation

It is shown that to maximize the power output of a power plant is equivalent to minimizing the total entropy generation rate associated with the power plant. This equivalence is illustrated by using two of the oldest and simplest models of power plants with heat transfer irreversibilities. To calculate the total entropy generation rate correctly, one must recognize that the optimization process (e.g., the variability of the heat input) requires “room to move,” i.e., an additional, usually overlooked, contribution to the total entropy generation rate.

Sign in / Sign up

Export Citation Format

Share Document