Mathematical Modeling of Direct Flame Impingement Heat Transfer

2006 ◽  
Author(s):  
German Malikov ◽  
Vladimir Lisienko ◽  
Yuri Malikov ◽  
John Wagner ◽  
Harry Kurek ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Radiation Transfer ◽  
Convective Diffusion ◽  
Heat Fluxes ◽  
Nox Emissions ◽  
Gas Temperature ◽  
Fine Grid ◽  
Combustion Gas ◽  
Calculation Domain ◽  
Diffusion Transfer

Direct flame impingement (DFI) furnaces consist of large arrays of high velocity combusting jets with temperatures up to 1700 K and impinging on complex configuration surfaces of the work pieces. This results in serious convergence problems DFI modeling and computational efforts. A new method of modeling convective-diffusion transfer (CDT) and zone radiation transfer (RT) employing different calculation schemes with a multi-scale grid is presented. Relatively coarse grid calculation domain allows use of conservative and accurate zone radiation transfer method with only modest computational efforts. A fine grid calculation domain is used to predict convective -diffusion transfer for a representative furnace section, containing a small number of jets that allows to significantly decrease the computer time. The main difficulty of coupling between convective-diffusion transfer (CDT) and radiation heat transfer numerical computations is successfully overcome using a relatively simple algorithm. The method allows one to model the physicochemical process taking place in the DFI and reveals as well as explains many features that are difficult to evaluate from experiments. The results were obtained for high velocities (up to 400 m/s) and high firing rates. Maximum (available for natural gas-air firing) total heat fluxes up to 500 kW/m2 and convective heat fluxes of up to 300 kW/m2 were obtained with relatively 'cold' refractory wall temperatures not exceeding 1300 K. The combustion gas temperature range was 1400-1700 K. A simplified analysis for NOx emissions has been developed as post-processing and shows extremely low NOx emissions (under 15 ppm volume) in DFI systems. Good agreement between measurements and calculations has been obtained. The model developed may be regarded as an efficient tool to compute and optimize industrial furnaces designs in limited time.

On the Computation of Convective Heat Transfer in Complex Turbulent Flows

1988 ◽  
Vol 110 (4b) ◽  
pp. 1112-1128 ◽  
Author(s):  
B. E. Launder
Keyword(s):  
Heat Transfer ◽  
Turbulent Flows ◽  
Heat Fluxes ◽  
Future Research ◽  
Transfer Coefficients ◽  
Fine Grid ◽  
Wall Functions ◽  
Thermal Turbulence ◽  
Averaged Equations ◽  
Thermal Diffusivities

The paper summarizes current strategies for computing heat transfer coefficients in complex turbulent flows based on numerical solution of the averaged equations for momentum and enthalpy and corresponding equations for averaged properties of the turbulent flow field. It argues that, for accuracy and width of applicability, a fine-grid low-Reynolds-number treatment should be employed near the wall in place of wall functions, despite the attractive simplicity of the latter approach. Several examples are provided that bring out the benefit from adopting second-moment closures, in which attention is focused on the turbulent stresses and heat fluxes themselves rather than on effective viscosities and thermal diffusivities. Directions for future research are briefly discussed, an important contribution to this effort being the direct numerical simulation of the near-wall dynamic and thermal turbulence field.

scholarly journals ANALISIS PERPINDAHAN PANAS PADA EKONOMISER DI PLTU PULANG PISAU

JTAM ROTARY ◽  
2020 ◽  
Vol 2 (1) ◽  
pp. 1
Author(s):  
Syahrul Fajar Setiawan ◽  
Aqli Mursadin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flue Gas ◽  
High Heat ◽  
Study Data ◽  
Feed Water ◽  
Gas Temperature ◽  
Combustion Gas ◽  
High Heat Transfer

Ekonomiser adalah alat yang digunakan untuk memanaskan air umpan sebelum memasuki boiler dengan memanfaatkan panas dari gas pembakaran di boiler. Dengan meningkatnya suhu air pengisi boiler, juga diharapkan meningkatkan efisiensi boiler. Dalam penelitian ini, pengumpulan data dilakukan di ruang kontrol dan data yang diambil, yaitu Tc.i (suhu economizer air yang masuk), Tc.o (suhu air keluar dari economizer), Th.i (suhu gas buang sebelum memasuki economizer) dan Th.o (suhu gas asap keluar dari economizer). Koefisien perpindahan panas tertinggi 4260.492 Btu / h.ft2. ° F dan koefisien perpindahan panas terendah 4251.243 Btu / h.ft2. ° F. Efisiensi tertinggi 87,43% dan terendah 80,76%. Economizer is a tool used to heat feed water before entering boiler by utilizing heat from the combustion gas in the boiler. With the increasing temperature of boiler filler water, it is also expected to increase boiler efficiency. In this study, data collection was carried out in the control room and the data that was taken, Tc.i (the temperature of the incoming water economizer), Tc.o (the exit water temperature of the economizer), Th.i (flue gas temperature before entering economizer) and Th.o (flue gas temperature exit the economizer). High heat transfer coefficient 4260,492 Btu/h.ft2.°F and low heat transfer coefficient 4251,243 Btu/h.ft2.°F. Highest the efficiency 87,43 % and the lowest 80,76 %.

A Coupled Solution Procedure for Zonal Radiative and Convective Heat Transfer in 3-D Enclosures With Blockages and Screens

2007 ◽  
Author(s):  
German Malikov ◽  
Vladimir Lisienko ◽  
Yuri Malikov ◽  
Yaroslav Chudnovsky ◽  
Raymond Viskanta
Keyword(s):  
Heat Transfer ◽  
Radiation Transfer ◽  
Simple Algorithm ◽  
Solution Procedure ◽  
Computational Effort ◽  
Fine Grid ◽  
Multi Scale ◽  
Curvilinear Grids ◽  
Transfer Method ◽  
Coupled Solution

A new 3D method of modeling convective-diffusive (CDT) heat transfer and zonal radiation transfer (ZRT) employing different calculation schemes and multi-scale curvilinear grids is presented. The coarse multiblock unstructured grid calculation domain allows use of a conservative and an accurate zonal radiation transfer method with only modest computational effort that requires only a small fraction of total processor CPU time. The blockages (e.g., bars in a furnace) and screens have their own very coarse grids. This reduces the time for defining their intersections with rays. Structured fine grid is used for convective-diffusive (CDT) calculations. The main difficulty (i.e., in coupling between CDT and ZRT numerical computations) is successfully overcome using a simple algorithm. The zonal radiation transfer method is based on a fast algorithm for calculating view factors and total exchange areas. The present approach is fast, efficient and accurate for gas fired furnaces and complex internal configurations of the work pieces with many blockages and screens. The utility of the method is demonstrated by calculating the heating of a hundred round metal bars arranged in a continuous natural gas fired furnace. Good agreement between calculations and industrial experiments is demonstrated.

Improvement Of Free Convection From Three horizontal Finned Cylinders Fixed Between Two Walls

2018 ◽  
Vol 6 (2) ◽  
pp. 98-114 ◽  
Author(s):  
Hassan K. Abdullah ◽  
Haneen H. Rahman
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Prandtl Number ◽  
Convection Heat Transfer ◽  
Constant Heat Flux ◽  
Heat Fluxes ◽  
Head Orientation ◽  
Outer Diameter ◽  
Gravitational Acceleration ◽  
Convection Heat

Improvement of  free convection heat transfer from three finned cylinders arranged at a triangle shape fixed between two walls has been investigated in this study. Three mild steel finned cylinders fixed between two walls from Pyrex glass have been used as a test rig. It has been changed the spacing between the cylinders (X/D=1,2,3 & S/D=2,4,6) and the head orientation of a triangle to the top under constant heat flux values (38, 254, 660, 1268) W/m2 and compare with case of three finned cylinders arranged in vertical array in line fixed between two wall. The experiments are carried for Rayleigh number (Ra) from (15x103 to 14 x104 ) and Prandtl  number from (0.706-0.714 ). The results indicated an increase in Nu with increasing Ra for all cylinders. Furthermore,hx and Nu increased proportionally with the increasing of cylinder spacings for all heat fluxes. Also the experimental results show the case of triangle arrangement is improvement the heat transfer more than case of vertical arrangement. Heat transfer dimensionless correlating equation is also proposed.              Nomeclature: Ax: surface area(m2), T∞: surrounding temperature(k), D: the outer diameter of fin (m), Kf: the thermal conductivity for air at film temperature(W/m.k), hx: Local convection heat transfer(W/m2.k),  Gravitational acceleration(m/s2), I: Electric current (Amp), Nu: Nusselt number, Pr: Prandtl number

scholarly journals Assessing IDDES-Based Wall-Modeled Large-Eddy Simulation (WMLES) for Separated Flows with Heat Transfer

Fluids ◽  
2021 ◽  
Vol 6 (7) ◽  
pp. 246
Author(s):  
Rozie Zangeneh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Large Eddy Simulation ◽  
Skin Friction ◽  
Heat Fluxes ◽  
Separated Flows ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Isothermal Wall

The Wall-modeled Large-eddy Simulation (WMLES) methods are commonly accompanied with an underprediction of the skin friction and a deviation of the velocity profile. The widely-used Improved Delayed Detached Eddy Simulation (IDDES) method is suggested to improve the prediction of the mean skin friction when it acts as WMLES, as claimed by the original authors. However, the model tested only on flow configurations with no heat transfer. This study takes a systematic approach to assess the performance of the IDDES model for separated flows with heat transfer. Separated flows on an isothermal wall and walls with mild and intense heat fluxes are considered. For the case of the wall with heat flux, the skin friction and Stanton number are underpredicted by the IDDES model however, the underprediction is less significant for the isothermal wall case. The simulations of the cases with intense wall heat transfer reveal an interesting dependence on the heat flux level supplied; as the heat flux increases, the IDDES model declines to predict the accurate skin friction.

scholarly journals Pool Boiling Heat Transfer Coefficients in Mixtures of Water and Glycerin

Processes ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 830
Author(s):  
Viktor Vajc ◽  
Radek Šulc ◽  
Martin Dostál
Keyword(s):  
Heat Transfer ◽  
Dynamic Method ◽  
Water Mass ◽  
Heat Fluxes ◽  
Static Method ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mean Relative Error ◽  
Mixture Effects ◽  
Mass Fractions

Heat transfer coefficients were investigated for saturated nucleate pool boiling of binary mixtures of water and glycerin at atmospheric pressure in a wide range of concentrations and heat fluxes. Mixtures with water mass fractions from 100% to 40% were boiled on a horizontal flat copper surface at heat fluxes from about 25 up to 270kWm−2. Experiments were carried out by static and dynamic method of measurement. Results of the static method show that the impact of mixture effects on heat transfer coefficient cannot be neglected and ideal heat transfer coefficient has to be corrected for all investigated concentrations and heat fluxes. Experimental data are correlated with the empirical correlation α=0.59q0.714+0.130ωw with mean relative error of 6%. Taking mixture effects into account, data are also successfully correlated with the combination of Stephan and Abdelsalam (1980) and Schlünder (1982) correlations with mean relative error of about 15%. Recommended coefficients of Schlünder correlation C0=1 and βL=2×10−4ms−1 were found to be acceptable for all investigated mixtures. The dynamic method was developed for fast measurement of heat transfer coefficients at continuous change of composition of boiling mixture. The dynamic method was tested for water–glycerin mixtures with water mass fractions from 70% down to 35%. Results of the dynamic method were found to be comparable with the static method. For water–glycerin mixtures with higher water mass fractions, precise temperature measurements are needed.

scholarly journals Systematic heat transfer measurements in highly viscous binary fluids

2021 ◽  
Author(s):  
Ann-Christin Fleer ◽  
Markus Richter ◽  
Roland Span
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volatile Component ◽  
Test Tube ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Low Viscosity ◽  
The Heat Transfer Coefficient

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

Experimental investigation of wall heat transfer due to spray combustion in a high-pressure/high-temperature vessel

2021 ◽  
pp. 146808742110072
Author(s):  
Karri Keskinen ◽  
Walter Vera-Tudela ◽  
Yuri M Wright ◽  
Konstantinos Boulouchos
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Pressure ◽  
High Temperature ◽  
High Speed ◽  
Transfer Problem ◽  
Wall Heat Transfer ◽  
Gas Temperature ◽  
Reference Case ◽  
High Pressure High Temperature

Combustion chamber wall heat transfer is a major contributor to efficiency losses in diesel engines. In this context, thermal swing materials (adapting to the surrounding gas temperature) have been pinpointed as a promising mitigative solution. In this study, experiments are carried out in a high-pressure/high-temperature vessel to (a) characterise the wall heat transfer process ensuing from wall impingement of a combusting fuel spray, and (b) evaluate insulative improvements provided by a coating that promotes thermal swing. The baseline experimental condition resembles that of Spray A from the Engine Combustion Network, while additional variations are generated by modifying the ambient temperature as well as the injection pressure and duration. Wall heat transfer and wall temperature measurements are time-resolved and accompanied by concurrent high-speed imaging of natural luminosity. An investigation with an uncoated wall is carried out with several sensor locations around the stagnation point, elucidating sensor-to-sensor variability and setup symmetry. Surface heat flux follows three phases: (i) an initial peak, (ii) a slightly lower plateau dependent on the injection duration, and (iii) a slow decline. In addition to the uncoated reference case, the investigation involves a coating made of porous zirconia, an established thermal swing material. With a coated setup, the projection of surface quantities (heat flux and temperature) from the immersed measurement location requires additional numerical analysis of conjugate heat transfer. Starting from the traces measured beneath the coating, the surface quantities are obtained by solving a one-dimensional inverse heat transfer problem. The present measurements are complemented by CFD simulations supplemented with recent rough-wall models. The surface roughness of the coated specimen is indicated to have a significant impact on the wall heat flux, offsetting the expected benefit from the thermal swing material.

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