Entropy Generation Analysis and Cooling Time Estimation for a Rotating Vertical Hollow Tube in the Air Medium

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Basanta Kumar Rana ◽  
Jnana Ranjan Senapati
Keyword(s):  
Heat Transfer ◽  
Entropy Generation ◽  
Thermodynamic Characteristics ◽  
Time Estimation ◽  
Rotating Cylinder ◽  
Cooling Time ◽  
Variation Pattern ◽  
Fluid Friction ◽  
Thermodynamic Performance ◽  
D 20

Abstract An objective function combining the first and second laws of thermodynamics has been employed to delineate the thermodynamic performance on mixed convection around a vertical hollow, rotating cylinder within the laminar range with the variation of Rayleigh number (104 ≤ Ra ≤ 108), Reynolds number (ReD < 2100), and aspect ratio (1 ≤ L/D ≤ 20). Entropy generation in the system is predominantly triggered by heat transfer in comparison to fluid friction. The irreversibility incurred progressively increases with an increase in Ra and ReD. The variation pattern of (I/Q)Rotation/(I/Q)Non−Rotation has been demonstrated to find out the optimized regime where heat transfer is maximum within the laminar range. The contribution of fluid friction irreversibility toward total irreversibility rises abruptly with an increase in ReD for all cases of L/D and Ra. To demonstrate this study's thermodynamic characteristics, the static temperature contours as well as the contours of entropy generation have been represented pictorially. The estimation of cooling time has been reported by using the method of lumped capacitance.

Heat Transfer and Entropy Generation Characteristics of a Non-Newtonian Fluid Squeezed and Extruded Between Two Parallel Plates

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
P Kaushik ◽  
Pranab Kumar Mondal ◽  
Sukumar Pati ◽  
Suman Chakraborty
Keyword(s):  
Heat Transfer ◽  
Newtonian Fluid ◽  
Entropy Generation ◽  
Bejan Number ◽  
Engineering Systems ◽  
Power Law Model ◽  
Parallel Plates ◽  
Unsteady Heat Transfer ◽  
Thermodynamic Performance ◽  
Fluid Rheology

This study investigates the unsteady heat transfer and entropy generation characteristics of a non-Newtonian fluid, squeezed and extruded between two parallel plates. In an effort to capture the underlying thermo-hydrodynamics, the power-law model is used here to describe the constitutive behavior of the non-Newtonian fluid. The results obtained from the present analysis reveal the intricate interplay between the fluid rheology and the squeezing dynamics, toward altering the Nusselt number and Bejan number characteristics. Findings from this study may be utilized to design optimal process parameters for enhanced thermodynamic performance of engineering systems handling complex fluids undergoing simultaneous extrusion and squeezing.

Effects of Thermal Boundary Conditions on Entropy Generation During Natural Convection in a Differentially Heated Square Cavity

2010 ◽  
Author(s):  
Ram Satish Kaluri ◽  
Tanmay Basak ◽  
A. R. Balakrishnan
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Boundary Conditions ◽  
Entropy Generation ◽  
Bottom Wall ◽  
Convection Flow ◽  
Uniform Heating ◽  
Square Cavity ◽  
Fluid Friction ◽  
Thermal Boundary Conditions

Natural convection is a widely occurring phenomena which has important applications in material processing, energy storage devices, electronic cooling, building ventilation etc. The concept of ‘entropy generation minimization’, which is a thermodynamic approach for optimization, may be very useful in designing efficient thermal systems. In the current study, entropy generation in steady laminar natural convection flow in a square cavity is studied with following isothermal boundary conditions: (1) Bottom wall is uniformly heated (2) Bottom wall is sinusoidally heated. The side walls are maintained cold and the top wall is maintained adiabatic. The thermal boundary condition in non-uniform heating case (case 2) is such that the dimensionless average temperature of the bottom wall is equal to that of uniform heating case (case 1). The prime objective of this work is to investigate the influence of uniform and non-uniform heating on entropy generation. The governing mass, momentum and energy equations are solved using Galerkin finite element method. Streamlines, isotherms, contour maps of entropy generation due to heat transfer and fluid friction are studied for Pr = 0.01 (molten metals) and 7 (water) in range of Ra = 103–105. Detailed analysis on the effect of uniform and non-uniform thermal boundary conditions on entropy generation due to heat transfer and fluid friction has been presented. Also, the average Bejan’s number which indicates the relative dominance of entropy generation due to heat transfer or fluid friction and the total entropy generation are studied for each case.

scholarly journals Second Law Analysis for the Experimental Performances of a Cold Heat Exchanger of a Stirling Refrigeration Machine

Entropy ◽  
2020 ◽  
Vol 22 (2) ◽  
pp. 215 ◽  
Author(s):  
Steve Djetel-Gothe ◽  
François Lanzetta ◽  
Sylvie Bégot
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Entropy Generation ◽  
Mass Flow ◽  
Hydraulic Diameter ◽  
Entropy Generation Rate ◽  
Second Law ◽  
Water Mixture ◽  
Fluid Friction ◽  
Refrigeration Machine

The second law of thermodynamics is applied to evaluate the influence of entropy generation on the performances of a cold heat exchanger of an experimental Stirling refrigeration machine by means of three factors: the entropy generation rate N S , the irreversibility distribution ratio ϕ and the Bejan number B e | N S based on a dimensionless entropy ratio that we introduced. These factors are investigated as functions of characteristic dimensions of the heat exchanger (hydraulic diameter and length), coolant mass flow and cold gas temperature. We have demonstrated the role of these factors on the thermal and fluid friction irreversibilities. The conclusions are derived from the behavior of the entropy generation factors concerning the heat transfer and fluid friction characteristics of a double-pipe type heat exchanger crossed by a coolant liquid (55/45 by mass ethylene glycol/water mixture) in the temperature range 240 K < TC < 300 K. The mathematical model of entropy generation includes experimental measurements of pressures, temperatures and coolant mass flow, and the characteristic dimensions of the heat exchanger. A large characteristic length and small hydraulic diameter generate large entropy production, especially at a low mean temperature, because the high value of the coolant liquid viscosity increases the fluid frictions. The model and experiments showed the dominance of heat transfer over viscous friction in the cold heat exchanger and B e | N S → 1 and ϕ → 0 for mass flow rates m ˙ → 0.1 kg.s−1.

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.

Role of Heating Location on the Performance of a Natural Convection Driven Melting Process Inside a Square-Shaped Thermal Energy Storage System

2018 ◽  
Vol 10 (6) ◽  
Author(s):  
Ojas Satbhai ◽  
Subhransu Roy ◽  
Sudipto Ghosh
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Energy Storage ◽  
Entropy Generation ◽  
Thermal Energy ◽  
Storage System ◽  
Melting Process ◽  
Energy Storage System ◽  
Thermodynamic Performance ◽  
Thermal Energy Storage System

Abstract In this work, numerical experiments were performed to compare the heat transfer and thermodynamic performance of melting process inside the square-shaped thermal energy storage system with three different heating configurations: an isothermal heating from left side-wall or bottom-wall or top-wall and with three adiabatic walls. The hot wall is maintained at a temperature higher than the melting temperature of the phase change material (PCM), while all other walls are perfectly insulated. The transient numerical simulations were performed for melting Gallium (a low Prandtl number Pr = 0.0216, low Stefan number, Ste = 0.014, PCM with high latent heat to density ratio) at moderate Rayleigh number (Ra ≊ 105). The transient numerical simulations consist of solving coupled continuity, momentum, and energy equation in the unstructured formulation using the PISO algorithm. In this work, the fixed grid, a source-based enthalpy-porosity approach has been adopted. The heat transfer performance of the melting process was analyzed by studying the time evolution of global fluid fraction, Nusselt number at the hot wall, and volume-averaged normalized flow-kinetic-energy. The thermodynamic performance was analyzed by calculating the local volumetric entropy generation rates and absolute entropy generation considering both irreversibilities due to the finite temperature gradient and viscous dissipation. The bottom-heating configuration yielded the maximum Nusselt number but has a slightly higher total change in entropy generation compared to other heating configurations.

scholarly journals Local Entropy Generation Analysis of a Rotary Magnetic Heat Pump Regenerator

1994 ◽  
Vol 116 (2) ◽  
pp. 140-147 ◽  
Author(s):  
M. K. Drost ◽  
M. D. White
Keyword(s):  
Heat Transfer ◽  
Heat Pump ◽  
Entropy Generation ◽  
Efficiency Index ◽  
Local Entropy ◽  
Enhancement Technique ◽  
Viscous Losses ◽  
Thermodynamic Performance ◽  
Improve Heat Transfer ◽  
Local Entropy Generation

The rotary magnetic heat pump has attractive thermodynamic performance, but it is strongly influenced by the effectiveness of the regenerator. This study uses local entropy generation analysis to evaluate the regenerator design and to suggest design improvements. The results show that performance of the proposed design is dominated by heat-transfer-related entropy generation. This suggests that enhancement concepts that improve heat transfer should be considered, even if the enhancement causes a significant increase in viscous losses (pressure drop). One enhancement technique, the use of flow disruptors, was evaluated and the results showed that flow disruptors can significantly reduce thermodynamic losses. The results of this study also suggest that, in this case, the widely used efficiency index is an inappropriate thermodynamic measure of the performance of a heat transfer enhancement technique and that a figure-of-merit based on second law considerations should be used.

scholarly journals Gas Turbine Model Scaling

1995 ◽  
Author(s):  
Mark R. D. Davies ◽  
John D. Wallace
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Gas Turbine ◽  
Entropy Generation ◽  
Three Dimensional ◽  
Relative Magnitude ◽  
Fluid Friction ◽  
Measured Velocity ◽  
Velocity Boundary Layer ◽  
Layer Flow

A dimensional analysis, of both the equations governing boundary-layer flow with heat transfer and of the steady and unsteady boundary conditions, demonstrates that twelve non-geometric, dimensionless parameters are required for the complete similarity of a three-dimensional, compressible, viscous flow with a freestream pressure gradient. The analysis shows that non-dimensional groups describing the machine can be reduced to a function of metal angles and twelve fundamentally derived, dimensionless scaling parameters. The equation describing the rate of local entropy generation caused by fluid friction and heat transfer is also non-dimensionalised. This leads to an estimate of the relative magnitude of entropy generation due to fluid friction and heat transfer. A comparison of the principle operating parameters for a number of existing gas turbine test facilities, designed to model the aerodynamic and heat transfer conditions in real engines, suggests that full modelling of engine boundary-layer phenomena has not been achieved. A semi-empirical, boundary-layer analysis suggests that measured velocity boundary-layer profiles from adiabatic test facilities differ significantly with those from a gas turbine operating at engine gas to wall temperature ratios. Similarly, the analysis established the shape of the velocity boundary-layer to be dependent upon the specific-heat ratio.

Three-Dimensional Numerical Investigation of Thermodynamic Performance Due to Conjugate Natural Convection From Horizontal Cylinder With Annular Fins

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
Jnana Ranjan Senapati ◽  
Sukanta Kumar Dash ◽  
Subhransu Roy
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Entropy Generation ◽  
Horizontal Cylinder ◽  
Diameter Ratio ◽  
Tube Diameter ◽  
Wide Range ◽  
Thermodynamic Performance ◽  
Annular Fins ◽  
Fin Spacing

Entropy generation due to natural convection has been computed for a wide range of Rayleigh numbers based on fin spacing, RaS in the entire laminar range 5≤RaS≤108, and diameter ratio 2 ≤ D/d ≤ 5 for an isothermal horizontal cylinder fitted with vertical annular fins. Entropy generation in the tube-fin system is predominantly due to heat transfer rather than fluid friction. The results demonstrate that the degree of irreversibility is higher in the case of the finned configuration when compared with the unfinned one. With the deployment of a merit function combining the first and second laws of thermodynamics, we have tried to show the thermodynamic performance of finned cylinder with natural convection. So, we have defined the ratio (I/Q)finned/(I/Q)unfinned which gets its minimum value at optimum fin spacing where heat transfer is maximum. A detailed view of the entropy generation around the finned cylinder has been shown for various S/d (fin spacing to tube diameter ratio) at a particular D/d (fin to tube diameter ratio) and Rayleigh number, which explains the nature and reason of entropy production.

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