scholarly journals The Influence of Droplet Dispersity on Droplet Vaporization in the High-Temperature Wet Gas Flow in the Case of Combined Heating

2021 ◽  
Vol 13 (7) ◽  
pp. 3833
Author(s):  
Gintautas Miliauskas ◽  
Egidijus Puida ◽  
Robertas Poškas ◽  
Povilas Poškas
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Phase Change ◽  
Flue Gas ◽  
Gas Flow ◽  
Internal Heat ◽  
Radiation Absorption ◽  
Water Droplets ◽  
Transfer Processes ◽  
Equilibrium Evaporation

The change in the thermal and energy state of the water droplet is defined numerically. The influence of droplet dispersity on the interaction of the transfer processes was evaluated. In influence of the Stefan flow was considered as well. The internal heat transfer of the droplet was defined by the combined heat transfer through effective conductivity and radiation model. The results of the numerical modeling of heat and mass transfer in water droplets in a wet flue gas flow of 1000 °C highlight the influence of the variation in heat transfer regimes in the droplet on the interaction of the transfer processes in consistently varying phase change regimes. The results of the investigation shows that the inner heat convection diminishes intensively in the transitional phase change regime because of a rapid slowdown of the slipping droplet in the gas. The radiation absorption in the droplet clearly decreases only at the final stage of equilibrium evaporation. The highlighted regularities of the interaction between combined transfer processes in water droplets are also valid for liquid fuel and other semi-transparent liquids sprayed into high-temperature flue gas flow. However, a qualitative evaluation should consider individual influence of dispersity that different liquids have.

scholarly journals Numerical Investigation on Radiation Effect in Transpiration Cooling

2021 ◽  
Vol 2097 (1) ◽  
pp. 012011
Author(s):  
Kang Qian ◽  
Taolue Liu ◽  
Fei He ◽  
Meng Wang ◽  
Longsheng Tang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Gas Flow ◽  
Radiation Effect ◽  
Porous Wall ◽  
Radiation Absorption ◽  
Transpiration Cooling ◽  
Coupled Modeling ◽  
High Temperature Gas ◽  
Numerical Strategy

Abstract This paper proposed a numerical strategy which could achieve the coupled modeling and solving of transpiration cooling with external high-temperature gas flow and especially take the radiation effect into account. Based on the numerical strategy, the heat and mass transfer characteristics of the transpiration cooling in a high-temperature gas channel were studied, and the radiation effect and corresponding influence factors were analyzed. The results indicated that the radiative heat flux takes an important role in the heat transfer between the transpiration cooling and external high-temperature gas flow which may reach 40% under the operating condition considered in this work, and the radiation absorption from the coolant is more obvious near the downstream wall. As the wall emissivity increases, the radiation heat transfer in the downstream area of the porous wall is enhanced significantly and thereby the wall temperature there increases, as the result, the uniformity of the temperature distribution on the whole porous wall is improved to some extent.

Heat Transfer Processes in High-Temperature Flows of Two-Phase Media

2001 ◽  
Vol 32 (7-8) ◽  
pp. 7
Author(s):  
M. I. Osipov ◽  
K. A. Gladoshchuk ◽  
A. N. Arbekov
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Two Phase ◽  
Transfer Processes

INFLUENCE OF FLUE GAS PATTERN FLOW IN BOILER RADIANT SECTION ON HEAT TRANSFER

2021 ◽  
pp. 1-16
Author(s):  
Branislav Jacimovic ◽  
Srbislav Genic ◽  
Nikola Jacimovic
Keyword(s):  
Heat Transfer ◽  
Flue Gas ◽  
Gas Flow ◽  
Plug Flow ◽  
Integral Model ◽  
Engineering Practice ◽  
Conductive Heat ◽  
Small Deviations ◽  
Proposed Model ◽  
Perfect Mixing

Abstract During the sizing of the radiant zone in boilers and furnaces, the most often used method is the Lobo-Evans model. This method is based on the perfect mixing model for flue gas flow inside the fire box, which represents a conservative or pessimistic flow pattern. This paper presents a different, optimistic model which is based on the plug flow for flue gas flow which results in the largest possible heat duty. The proposed model is given in two distinct forms – integral and numerical. As shown in the paper, the integral model results in small deviations with respect to the numerical model and, as such, is well suited for the engineering practice. Paper also presents an engineering approach to the calculation of the conductive heat transfer through the membrane wall, which is shown to be sufficiently accurate and simple for engineering calculations.

Numerical Simulation on Process of Flow and Heat Transfer in Upright Magnesium Reducing Furnace

2011 ◽  
Vol 383-390 ◽  
pp. 6657-6662 ◽  
Author(s):  
Jun Xiao Feng ◽  
Qi Bo Cheng ◽  
Si Jing Yu
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Temperature Field ◽  
Flue Gas ◽  
Gas Flow ◽  
Three Dimensional ◽  
Reaction Heat ◽  
Flow And Heat Transfer ◽  
Major Factors ◽  
High Chemical Reaction

Based on the analysis of structural characteristic superiority, the process of combustion, flue gas flow and heat transfer in the upright magnesium reducing furnace, the three dimensional mathematical model is devoloped. And numerical simulation is performed further with the commercial software FLUENT. Finally, the flow and temperature field in furnace and temperature field in reducing pot have been obtained. The results indicate that the upright magnesium reducing furnace has perfect flue gas flow field and temperature field to meet the challenge of the magnesium reducing process; the major factors that affect the magnesium reducing reaction are the low thermal conductivity of slag and the high chemical reaction heat absorption.

Thermal Modeling of High Temperature Energy Storage Using Encapsulated Phase Change Materials

2012 ◽  
Author(s):  
Ali F. Elmozughi ◽  
Weihuan Zhao ◽  
Sudhakar Neti ◽  
Alparslan Oztekin
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Energy Storage ◽  
Phase Change ◽  
Phase Change Materials ◽  
Front Tracking ◽  
System Level ◽  
Flow Conditions ◽  
Tracking Method ◽  
Front Tracking Method

Transient heat transfer analysis is conducted to investigate high temperature energy storage using encapsulated phase change materials (EPCMs) for concentrated solar power applications. The phase change material considered is the eutectic mixture of NaCl-MgCl2 (57 mole% NaCl and 43 mole% MgCl2) encapsulated by stainless steel in a cylindrical shaped capsule (or tube). Energy storage into EPCM and energy retrieval from EPCM is simulated for various flow conditions of the heat transfer fluid. Heat storage/retrieval times are determined from numerical simulations for various sizes of capsules and flow conditions by an accurate modeling of propagating solid/liquid interface. Numerical simulations are conducted by employing a front tracking method and the enthalpy–porosity approach. A two-dimensional horizontally placed cylindrical shaped EPCM capsule is considered in simulations using gas (air) and liquid (VP1-Therminol) as heat transfer fluids. The results predicted by the front tracking method agree well with those predicted by the enthalpy–porosity method. It is illustrated by the present work that enthalpy–porosity method can be employed to simulate the modeling at the single capsule level and system level. System level storage unit is a thermocline that includes an arrangement of several EPCMs.

Heat Transfer Enhancement of Phase Change Materials (PCMs) in Low and High Temperature Thermal Storage by Using Porous Materials

2010 ◽  
Author(s):  
C. Y. Zhao ◽  
D. Zhou ◽  
Z. G. Wu
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Phase Change ◽  
Porous Materials ◽  
Phase Change Materials ◽  
Heat Transfer Performance ◽  
Expanded Graphite ◽  
Metal Foams ◽  
Transfer Performance ◽  
Solid Liquid

In this paper the solid/liquid phase change heat transfer in porous materials (metal foams and expanded graphite) at low and high temperatures is experimentally investigated, in an attempt to examine the feasibility of using metal foams to enhance the heat transfer capability of phase change materials for use with both the low and high temperature thermal energy storage systems. In this research, the organic commercial paraffin wax and inorganic hydrate calcium chloride hydrate salts were employed as the low-temperature materials, while the sodium nitrate is used as the high-temperature PCM in the experiment. The heat transfer characteristics of these PCMs embedded with open-cell metal foams were studied experimentally. The composites of paraffin and expanded graphite with different graphite mass ratios, namely, 3%, 6% and 9%, were also made and the heat transfer performances of these composites were tested and compared with metal foams. Overall metal foams can provide better heat transfer performance than expanded graphite due to their continuous inter-connected structures. But the porous materials can suppress the natural convection effect in liquid zone, particularly for the PCMs with low viscosities, thereby leading to the different heat transfer performance at different regimes (solid, solid/liquid and liquid regions). This implies that the porous materials don’t necessarily mean they can always enhance heat transfer in every regime.

Effect of Inclination on Freezing in a Sealed Cylindrical Capsule

1984 ◽  
Vol 106 (2) ◽  
pp. 394-401 ◽  
Author(s):  
E. D. Larson ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Liquid Phase ◽  
Phase Change ◽  
Layer Thickness ◽  
Relative Importance ◽  
Fusion Temperature ◽  
Capsule Wall ◽  
Transfer Processes ◽  
Freezing Period

Experiments were performed to study the heat transfer processes that occur during freezing inside of a sealed cylindrical capsule when the inclination of the capsule is varied parametrically from vertical to horizontal. The phase-change medium was 99 percent pure n-eicosane paraffin. It was found that the amount of mass that solidified during a given freezing period was insensitive to the inclination of the capsule, as was the amount of energy extracted from the capsule. Only highly localized quantities such as the local frozen layer thickness reflected the inclination of the cylinder. Parametric variations were also performed for the degree of sub-cooling of the capsule wall below the fusion temperature and for the degree of superheating of the liquid phase at the onset of freezing. These variations facilitated the identification of the relative importance of the latent and sensible energies to the total extracted energy.

Computational Analysis of Gas Flow and Heat Transport Phenomena in Monolithic Structures for High Temperature Processes

2005 ◽  
Author(s):  
Faruk Selimovic ◽  
Tor Bruun ◽  
Bengt Sunde´n
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Power Density ◽  
Gas Flow ◽  
Gas Temperature ◽  
Oxidation Of Methane ◽  
Steam Methane ◽  
High Temperature Processes ◽  
Efficient Heat Transfer ◽  
Flow Maldistribution

High-temperature catalytic processes such as partial oxidation of Methane (POX) and steam Methane reforming (SMR) may benefit from use of reactor systems using monolithic honeycomb structures. Hereby, process performance is enhanced through more efficient heat transfer and considerable smaller reactor foot-prints than for conventional reactor concepts. Compact ceramic heat exchange structures may also be an interesting option for increasing the energy efficiency of high temperature processes in general. One example is single cycle turbines where these structures can be used as recuperators. The purpose of this paper is to describe modelling of gas flow pattern and heat transfer in reactors and heat exchangers with monolithic based structures. This technology is currently under development in a partnership of European companies and academia, with financial support from the EC and Swiss Government. The mathematical model developed for heat transfer and flow maldistribution has been used for counter-current checkerboard channel-arrangement. Pressure drop has been analyzed both experimentally and numerically (computation fluid dynamics, CFD). Power density has been shown to depend on various reactor parameters. Channel geometry, inlet gas temperature difference and channel wall thickness have been calculated to find the influence on power density.

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