scholarly journals Features of Calculating the Characteristics of Energy Complexes Using Low-Grade Energy

2021 ◽  
Vol 18 (6) ◽  
pp. 108-117
Author(s):  
A. V. Dmitrenko ◽  
M. A. Kolosova
Keyword(s):  
Heat Transfer ◽  
Phase Transition ◽  
Phase Transitions ◽  
Turbulent Flows ◽  
Heat Exchangers ◽  
Stochastic Theory ◽  
Fuel Oil ◽  
Low Grade ◽  
Heavy Fuel Oil ◽  
Comparison Results

The development of stationary energy seems to be an important aspect of introduction of energy-saving technologies in transportation sector. In Russia, it is conditioned by the main provisions of the Energy Strategy of the Russian Federation until 2030. In this regard, the problem of efficient use of low-grade heat based on the organic Rankine cycle (ORC) in stationary heat energy supply units in the transport industry is urgent. In particular, this task is typical for boiler houses converted from heavy fuel oil to gas fuel. In this case, the efficiency of ORC application will primarily be determined by the efficiency of the used heat exchangers (HE) with a phase transition, as a result of which, both technically and theoretically, the problem of designing and calculating the optimal characteristics of these HE will be of great interest.The article presents a theoretical and computational model of heat transfer during phase transitions in turbulent flows based on the relations obtained by the stochastic theory of hydrodynamics and heat transfer. The modelling of the effect of turbulence during the phase transition with undeveloped boiling of the bubble mode is considered. The comparison results show satisfactory conformity of the values obtained according to the formula based on stochastic equations with the values calculated according to the empirical formula for the flow in a pipe, used in the engineering method of designing heat exchangers. The results obtained open the prospect for studying the processes of heat transfer during phase transitions in turbulent flows of HE to reduce their overall and mass characteristics, as well as to increase the energy efficiency of both the devices themselves and the efficiency of the entire energy complex.

Radiation Effects on Heat Transfer in the Reactor Core and Heat Exchangers of an HTGR

1975 ◽  
Vol 97 (3) ◽  
pp. 400-405 ◽  
Author(s):  
Y. Mori ◽  
K. Hijikata ◽  
Y. Yamada
Keyword(s):  
Heat Transfer ◽  
Turbulent Flows ◽  
Heat Exchangers ◽  
Radiation Effects ◽  
Heat Transfer Performance ◽  
Reactor Core ◽  
Transfer Performance ◽  
Fundamental Study ◽  
Narrow Region ◽  
Heat Transfer System

A general and fundamental study of the effect of radiation between duct walls on the heat transfer performance of duct flows of nonradiating gas such as helium is made by an approximate analysis and numerical calculations. Laminar and turbulent flows in a duct simulating a coolant passage in an HTGR and flows in counterflow and parallel-flow heat exchangers in an HTGR heat transfer system are investigated. An approximate analytical solution, based on the assumption that radiation from a point of duct wall produces an effect only on the narrow region opposite the point, agrees well with numerical results. The increase of radiative heat transfer causes a decrease of temperature difference between the duct walls and improves the heat transfer performance. For heat exchangers the heat transfer effectiveness is shown to depend on three nondimensional parameters and can be improved by the increase of these parameters.

scholarly journals Matrix method to solve inverse problem of heat transfer in heat exchangers with phase transition in heat carriers

Vestnik IGEU ◽  
2021 ◽  
pp. 68-75
Author(s):  
A.E. Barochkin
Keyword(s):  
Heat Transfer ◽  
Phase Transition ◽  
Inverse Problem ◽  
Heat Exchangers ◽  
Power Plants ◽  
Thermal Power ◽  
Energy Performance ◽  
Steam Boiler ◽  
Resource Saving ◽  
Heat Carriers

The transition to environmentally friendly and resource-saving energy, efficient use of natural resources and energy performance are the key priorities of the state energy policy of the Russian Federation. Maximum use of heat combustion of fuel and simultaneously production of condensate water of the combustion products of natural gas is one of the directions of energy saving policy. Despite many scientific papers on the issues of utilization of flue gas heat, condensation heat exchangers are not used in most gas boiler houses, energy power providers and thermal power plants in this country. And there are several reasons to explain this fact due to the lack of universal methods to calculate and design condensation-type heat exchangers. Thus, the development of new methods to simulate multithreaded heat exchangers considering the phase transition in heat carriers is an urgent task of power engineering and industry sectors. Matrix models of heat transfer based on mass and energy balance equations are applied to solve the inverse problem of heat transfer in heat exchangers, considering the phase transition in heat carriers. A method to calculate and select the designs of multi-threaded heat exchangers, considering the phase transition in heat carriers, has been developed. The author suggests a numerical solution to choose the design of a contact economizer of a heat power plant steam boiler used for heat recovery of flue gases to illustrate the effectiveness of the proposed method. The proposed method to solve the inverse problem of heat transfer provides the possibility to identify simultaneously the most acceptable values of the parameters of heat carriers and design characteristics of heat exchangers for various purposes.

The Role of Atomizing Medium in the Effectiveness of Water-Oil Emulsions to Reduce Unburned Carbon Particles

2007 ◽  
Author(s):  
Antonio Diego-Marin ◽  
Carlos Melendez-Cervantes ◽  
Alejandro Mani-Gonzalez
Keyword(s):  
Fluid Dynamic ◽  
Computer Code ◽  
Fuel Oil ◽  
Compressed Air ◽  
Saturated Steam ◽  
Unburned Carbon ◽  
Experimental Program ◽  
Low Grade ◽  
Heavy Fuel Oil ◽  
Carbon Particles

Two older boilers were burning low grade heavy fuel oil (number 6) and emitting large amounts of unburned carbon particles. Owing to the short life remaining of the units and economic constrains, it was not possible to change to a better fuel or install new burners. To contribute to the solution of this problem, an experimental program was carried out by emulsifying water in the fuel oil. Tests were performed in a scale furnace (0.35MWth) and the emulsions that produced the best results were assessed in the two boilers, 28 and 34 MWe capacity with Y-jet atomizer type. The system to prepare the emulsion was very simple: water was added into the oil before the fuel oil pump, no chemical products were added and a static mixed was used to improve the water size distribution, which 90% ranged from 1 to 9 micron. In the pilot furnace the emulsions were prepared with 5 and 10% water and atomized with compressed air. Particle reductions of 43 and 67% were obtained compared with the net heavy fuel oil. In the boilers, the emulsions were prepared with the same amount of water, and were atomized with saturated steam. In the 28 MWe boiler, a similar particle reduction was obtained to that of the scale furnace. However, in the 34 MWe boiler there was no particle abatement. By using a commercial fluid dynamic computer code, it was found that the combustion air transferred heat to the steam raising its temperature. Thus, in the mixing chamber of the Y-jet atomizers, the steam was superheated and destroyed the water droplets of the emulsion. Compressed air and saturated steam as atomizing medium of the emulsions had similar effect on the unburned particle reduction. However, the effectiveness of the emulsions may be affected by the steam. Care should be taken to avoid the use of steam with a temperature higher than the saturated water temperature.

Turbulent flows in a spiral double-pipe heat exchanger

2019 ◽  
Vol 30 (1) ◽  
pp. 39-53 ◽  
Author(s):  
Zhe Tian ◽  
Ali Abdollahi ◽  
Mahmoud Shariati ◽  
Atefeh Amindoust ◽  
Hossein Arasteh ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Turbulent Flows ◽  
Heat Exchangers ◽  
Volume Fraction ◽  
Inlet Temperature ◽  
Content Type ◽  
Tube Heat Exchanger ◽  
Double Pipe ◽  
Pipe Heat

Purpose This paper aims to study the fluid flow and heat transfer through a spiral double-pipe heat exchanger. Nowadays using spiral double-pipe heat exchangers has become popular in different industrial segments due to its complex and spiral structure, which causes an enhancement in heat transfer. Design/methodology/approach In these heat exchangers, by converting the fluid motion to the secondary motion, the heat transfer coefficient is greater than that of the straight double-pipe heat exchangers and cause increased heat transfer between fluids. Findings The present study, by using the Fluent software and nanofluid heat transfer simulation in a spiral double-tube heat exchanger, investigates the effects of operating parameters including fluid inlet velocity, volume fraction of nanoparticles, type of nanoparticles and fluid inlet temperature on heat transfer efficiency. Originality/value After presenting the results derived from the fluid numerical simulation and finding the optimal performance conditions using a genetic algorithm, it was found that water–Al2O3 and water–SiO2 nanofluids are the best choices for the Reynolds numbers ranging from 10,551 to 17,220 and 17,220 to 31,910, respectively.

A Review of Forced Convective Heat Transfer in Stationary and Rotating Annuli

1996 ◽  
Vol 210 (2) ◽  
pp. 123-134 ◽  
Author(s):  
P R N Childs ◽  
C A Long
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Forced Convection ◽  
Turbulent Flows ◽  
Convective Heat ◽  
Heat Exchangers ◽  
Outer Cylinder ◽  
Forced Convective Heat Transfer ◽  
Analytical Research ◽  
Laminar And Turbulent Flows

The study of heat transfer by forced convection in annular passages is of interest across the range of process and aeronautical industries, for example from annular heat exchangers to the various configurations of annuli found in turbomachinery. The aim of this paper is to review relevant experimental, numerical and analytical research of heat transfer in both stationary and rotating annuli, with an emphasis on presenting useful information for designers. The geometries considered are the stationary annulus with superposed axial throughflow and the rotating annulus with rotation of either the inner or outer cylinder (both with and without throughflow). The work presented covers laminar and turbulent flows as well as flow regimes where transition occurs or vortex flows are present.

Enhancement of Convective Heat Transfer in Internal Viscous Flows by Inserting Motionless Mixers

2009 ◽  
Author(s):  
Ramin K. Rahmani ◽  
Anahita Ayasoufi ◽  
Theo G. Keith
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Turbulent Flows ◽  
Heat Exchangers ◽  
Convection Heat Transfer ◽  
Viscous Fluids ◽  
High Rate ◽  
Working Fluid ◽  
Static Mixer ◽  
Shell And Tube

In chemical processing industries, heating, cooling and other thermal processing of viscous fluids are an integral part of the unit operations. Enhancement of the natural and forced convection heat transfer rates has been the subject of numerous academic and industrial studies. Motionless mixers, also known as static mixers, are often used in continuous mixing, heat transfer, and chemical reactions applications. These mixers have low maintenance and operating costs, low space requirements, and have no moving parts. Heat exchangers equipped with mixing elements are especially well suited for heating or cooling highly viscous fluids. Shell and tube heat exchangers incorporate static mixing elements in the tubes to produce a heat transfer rate significantly higher than that of conventional heat exchangers. The mixing elements continuously create a new interface between the working fluid and tube wall, thereby producing a uniform heat history in the fluid. It is desired to employ motionless mixers in heat transfer applications to provide a high rate of heat transfer from a thermally homogenous fluid with low pressure drop. In the past, laboratory experimentation has been a fundamental part of the design process of a new static mixer for a given application as well as the selection of an existing static mixer. It is possible to use powerful computational fluid dynamics (CFD) tools to study the performance of these mixers without resorting to experimentation. In this paper, which is an extension to the previous work of the authors, the enhancement of performance of shell and tube heat exchangers by inserting motionless mixers (SMX and helical) is studied for creeping, laminar, and low-Re turbulent flows. It is shown that the studied mixers produced similar flow histories for the working fluid considered. Both SMX and helical mixers are able to increase thermal performance of heat exchangers. The SMX mixer manifests a higher performance in temperature blending and in heat transfer enhancement compared to the helical mixer. However, the pressure drop created by SMX elements, and consequently the required energy to maintain the flow in tube, is significantly higher.

scholarly journals Теплофизические свойства мультиферроиков Bi-=SUB=-1-x-=/SUB=-Tm-=SUB=-x-=/SUB=-FeO-=SUB=-3-=/SUB=-

2022 ◽  
Vol 64 (2) ◽  
pp. 305
Author(s):  
С.Н. Каллаев ◽  
А.Г. Бакмаев ◽  
З.М. Омаров ◽  
Л.А. Резниченко
Keyword(s):  
Heat Transfer ◽  
Phase Transition ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Phase Transitions ◽  
Thermal Diffusivity ◽  
Mean Free Path ◽  
Antiferromagnetic Phase ◽  
Temperature Dependences ◽  
Additional Anomaly

Investigations of the heat capacity, thermal diffusivity, and thermal conductivity of multiferroics Bi1-xTmxFeO3 (x = 0, 0.05, 0.10, 0.20) have been carried out in the high temperature range of 300-1200 K. and thermal conductivity in the region of phase transitions. The temperature dependences of the specific heat for compositions with x = 0.10 and 0.20 exhibit an additional anomaly characteristic of the phase transition at T = 580 K. The dominant mechanisms of phonon heat transfer in the region of ferroelectric and antiferromagnetic phase transitions are considered. The temperature dependence of the average phonon mean free path is determined.

scholarly journals THERMOPHYSICAL PROPERTIES OF POLYMER MICROAND NANOCOMPOSITES BASED ON POLYCARBONATE

2015 ◽  
Vol 37 (2) ◽  
pp. 12-19
Author(s):  
A. A. Dolinskiy ◽  
N. M. Fialko ◽  
R. V. Dinzhos ◽  
R. A. Navrodskaya
Keyword(s):  
Heat Transfer ◽  
Carbon Nanotubes ◽  
Thermophysical Properties ◽  
Percolation Theory ◽  
Heat Exchangers ◽  
Experimental Studies ◽  
Low Grade ◽  
Thermophysical Characteristics ◽  
Hostile Environments ◽  
Low Grade Heat

The results of experimental studies by the performed complex of thermophysical characteristics of created polymeric microand polycarbonate-based nanocomposites, which comprise from 0.2 to 10% carbon nanotubes and microparticles of aluminum are presented. Materials on the interpretation of the data based on the percolation theory are submitted. The possibilities of using of offered composites for the production of heat exchangers, focused on low-grade heat transfer and operating in hostile environments are previewed.  

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