Mechanical Work at a Boundary and its Associated Exergy Transfer

1996 ◽  
Vol 210 (6) ◽  
pp. 541-547
Author(s):  
J A McGovern ◽  
E I Yantovski
Keyword(s):  
Energy Transfer ◽  
Mechanical Stress ◽  
Stress Tensor ◽  
Continuum Mechanics ◽  
Velocity Vector ◽  
Exergy Analysis ◽  
Mechanical Work ◽  
Flux Vector ◽  
Exergy Transfer ◽  
Energy Flux Vector

This paper is a didactic discussion of mechanical work at a boundary from the standpoint of exergy analysis. It is shown that the use of the material velocity vector and the mechanical stress tensor of continuum mechanics allows the magnitude and direction of the energy flux vector at a point to be determined unambiguously. Hence, the amount and direction of the energy transfer at a boundary can be established. This methodology is then extended to the calculation of the associated exergy flux vector and the exergy transfer at the boundary. It is noted that the exergy transfer is not always equal to the energy transfer as mechanical work. In general, the exergy transfer also involves a term consisting of the product of the environmental pressure and a volume displacement or transfer.

scholarly journals The theory of the chain fountain revisited

2021 ◽  
Vol 2090 (1) ◽  
pp. 012166
Author(s):  
Dragos-Victor Anghel
Keyword(s):  
Energy Transfer ◽  
Kinetic Energy ◽  
Significant Role ◽  
Mechanical Work ◽  
Scientific Consensus ◽  
Energy And Momentum ◽  
Work Done

Abstract We analyze the chain fountain effect-the chain siphoning when falling from a container onto the floor. We argue that the main reason for this effect is the inertia of the chain, whereas the momentum received by the beads of the chain from the bottom of the container (typically called “kicks”) plays no significant role. The inertia of the chain leads to an effect similar to pulling the chain over a pulley placed up in the air, above the container. In another model (the so called “scientific consensus”), it was assumed that up to half of the mechanical work done by the tension in the chain may be wasted when transformed into kinetic energy during the pickup process. This prevented the chain to rise unless the energy transfer in the pickup process is improved by the “kicks” from the bottom of the container. Here we show that the “kicks” are unnecessary and both, energy and momentum are conserved-as they should be, in the absence of dissipation-if one properly considers the tension and the movement of the chain. By doing so, we conclude that the velocity acquired by the chain is high enough to produce the fountain effect. Simple experiments validate our model and certain configurations produce the highest chain fountain, although “kicks” are impossible.

Exergy Analysis of 330MW Thermal Power Unit

2012 ◽  
Vol 246-247 ◽  
pp. 505-508
Author(s):  
Jian Meng Yang ◽  
Wang Wei ◽  
Nian Zhe Qi
Keyword(s):  
Energy Transfer ◽  
Power Plant ◽  
Power Unit ◽  
Thermal Power Plant ◽  
Exergy Analysis ◽  
Thermal Power ◽  
Flow Equation ◽  
Energy Utilization ◽  
Plant Production ◽  
System Energy

This paper took one 330MW unit boiler in one power plant as an example, then doing some research about the boiler system energy change through doing exergy analysis. After this, the exergy flow equation was established, the energy transfer, utilize and loss of the thermal power plant production was revealed, the exergy efficiency of the boiler was defined. So the paper can provide a basis for energy utilization of power plant.

ENERGY-FLUX VECTOR OF SURFACE THERMOELASTIC WAVES

1991 ◽  
Vol 14 (4) ◽  
pp. 563-570
Author(s):  
Tsolo P. Ivanov ◽  
Radiianka Savova
Keyword(s):  
Energy Flux ◽  
Flux Vector ◽  
Thermoelastic Waves ◽  
Energy Flux Vector

Domains In Nematic Elastomers

1993 ◽  
Vol 328 ◽  
Author(s):  
A. Ten Bosch ◽  
L. Varichon
Keyword(s):  
Liquid Crystal ◽  
Mechanical Stress ◽  
Stress Tensor ◽  
Elastic Deformation ◽  
Order Parameter ◽  
Side Chain ◽  
Elastic Model ◽  
Liquid Crystal Elastomer ◽  
Nematic Order ◽  
Nematic Elastomers

ABSTRACTA theory based on an elastic model and including coupling between elastic deformation and nematic order parameter as well as an interaction between crosslinks and orientation is given. The nematic order parameter and the stress tensor have been determined on elongation and as a function of temperature as well as he anisotropy of the conformation of a side chain liquid crystal elastomer on application of a mechanical stress. A transition from a turbid, low ordered polydomain phase to a transparent, Monodomain is shown to occur.

On sound generated aerodynamically I. General theory

1952 ◽  
Vol 211 (1107) ◽  
pp. 564-587 ◽  
Keyword(s):  
Fluid Flow ◽  
Mach Number ◽  
General Theory ◽  
Stress Tensor ◽  
High Power ◽  
Velocity Vector ◽  
Unit Volume ◽  
Equations Of Motion ◽  
Sound Field ◽  
Velocity Of Sound

A theory is initiated, based on the equations of motion of a gas, for the purpose of estimating the sound radiated from a fluid flow, with rigid boundaries, which as a result of instability contains regular fluctuations or turbulence. The sound field is that which would be produced by a static distribution of acoustic quadrupoles whose instantaneous strength per unit volume is ρv i v j + p ij - a 2 0 ρ δ ij , where ρ is the density, v i the velocity vector, p ij the compressive stress tensor, and a 0 the velocity of sound outside the flow. This quadrupole strength density may be approximated in many cases as ρ 0 v i v j . The radiation field is deduced by means of retarded potential solutions. In it, the intensity depends crucially on the frequency as well as on the strength of the quadrupoles, and as a result increases in proportion to a high power, near the eighth, of a typical velocity U in the flow. Physically, the mechanism of conversion of energy from kinetic to acoustic is based on fluctuations in the flow of momentum across fixed surfaces, and it is explained in § 2 how this accounts both for the relative inefficiency of the process and for the increase of efficiency with U . It is shown in § 7 how the efficiency is also increased, particularly for the sound emitted forwards, in the case of fluctuations convected at a not negligible Mach number.

scholarly journals Crystallite fusion in nanocellulose aggregates

2021 ◽  
Author(s):  
Kazuho Daicho ◽  
Kayoko Kobayashi ◽  
Shuji Fujisawa ◽  
Tsuguyuki Saito
Keyword(s):  
Energy Transfer ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Mechanical Stress ◽  
Thermal Energy ◽  
Structural Defect ◽  
Single Crystalline ◽  
Naturally Occurring

Abstract Crystallite refers to a single crystalline grain in crystal aggregates, and multiple crystallites form a grain boundary or the inter-crystallite interface. A grain boundary is a structural defect that hinders the efficient directional transfer of mechanical stress or thermal phonons in crystal aggregates. We observed that grain boundaries within an aggregate of a-few-nanometers-wide fibrillar crystallites of cellulose were crystallized by enhancing their inter-crystallite interactions; multiple crystallites were coupled into single fusion crystals without passing through a melting or dissolving state. Accordingly, the crystallinity of naturally occurring cellulose, which has previously been considered irreversible once decreased, was recovered, and the thermal energy transfer in the aggregate was significantly improved. Other fibrillar crystallites of chitin also showed a similar fusion phenomenon by enhancing the inter-crystallite interactions. Crystallite fusion in aggregates may occur for other biopolymers.

CFD-Code Evaluation for Complex Interior Flows

2002 ◽  
Author(s):  
H. Herwig ◽  
H. Mocikat ◽  
T. Gu¨rtler
Keyword(s):  
Boundary Condition ◽  
Numerical Solution ◽  
Stress Tensor ◽  
Forced Convection ◽  
Cross Sections ◽  
Velocity Vector ◽  
Main Flow ◽  
Test Facility ◽  
Flow Section ◽  
Interior Flow

Measurements in a test facility for a complex interior flow are provided as a data basis for CFD code evaluation. For forced convection flows the three time averaged components of the velocity vector and all components of the Reynolds stress tensor are measured in selected cross sections. Special attention is given to the inflow into the main flow section since it is the important part of the boundary condition for a numerical solution.

scholarly journals Analysis of Energy Flux Vector on Natural Convection Heat Transfer in Porous Wavy-Wall Square Cavity with Partially-Heated Surface

Energies ◽  
2019 ◽  
Vol 12 (23) ◽  
pp. 4456 ◽  
Author(s):  
Yan-Ting Lin ◽  
Ching-Chang Cho
Keyword(s):  
Nusselt Number ◽  
Rayleigh Number ◽  
Energy Flux ◽  
Darcy Number ◽  
Bottom Surface ◽  
Flux Vector ◽  
Square Cavity ◽  
Vector Distribution ◽  
The Mean ◽  
Energy Flux Vector

The study utilizes the energy-flux-vector method to analyze the heat transfer characteristics of natural convection in a wavy-wall porous square cavity with a partially-heated bottom surface. The effects of the modified Darcy number, modified Rayleigh number, modified Prandtl number, and length of the partially-heated bottom surface on the energy-flux-vector distribution and mean Nusselt number are examined. The results show that when a low modified Darcy number with any value of modified Rayleigh number is given, the recirculation regions are not formed in the energy-flux-vector distribution within the porous cavity. Therefore, a low mean Nusselt number is presented. The recirculation regions do still not form, and thus the mean Nusselt number has a low value when a low modified Darcy number with a high modified Rayleigh number is given. However, when the values of the modified Darcy number and modified Rayleigh number are high, the energy flux vectors generate recirculation regions, and thus a high mean Nusselt number is obtained. In addition, in a convection-dominated region, the mean Nusselt number increases with an increasing modified Prandtl number. Furthermore, as the length of the partially-heated bottom surface lengthens, a higher mean Nusselt number is presented.

Sign in / Sign up

Export Citation Format

Share Document