The Analytical Modeling of Finite-Length Homogonous Micro-Combustor for a Hydrogen-Oxygen Mixture with Wall Temperature Effects

2016 ◽  
Vol 32 (5) ◽  
pp. 631-642 ◽  
Author(s):  
S. A. Fanaee
Keyword(s):  
Reaction Zone ◽  
Finite Length ◽  
Wall Temperature ◽  
Iterative Solution ◽  
Maximum Temperature ◽  
Oxygen Mixture ◽  
Governing Equations ◽  
Computational Data ◽  
Micro Combustor ◽  
Acceptable Agreement

AbstractThis paper analytically investigates the reaction phenomenon in micro-combustors using a two-dimensional model. The length of micro-combustor is considered at finite length that makes a better physical model than other works. The micro-combustor medium is divided into three integral zones composed of preheat, reaction and post flame where the governing equations are solved using the matching conditions of neighboring zones. The reaction zone thickness is considered as a variable and predicted by an iterative solution. In order to validate the model, normalized magnitude of maximum temperature is compared with published computational data for different values of Peclet number that shows an acceptable agreement that confirms the accuracy of the predicted data. Since a higher wall temperature causes the reaction to be faster, increasing the normalized wall temperature will result to reduce reaction zone thickness.

Micro Combustor Development Using Hydrogen As Fuel

2018 ◽  
Author(s):  
Ronak Shah ◽  
Digvijay Kulshreshtha ◽  
Nisarg Chaudhari
Keyword(s):  
Flame Front ◽  
Reaction Zone ◽  
Equivalence Ratio ◽  
Cross Sectional ◽  
Turbine Engine ◽  
Micro Gas Turbine ◽  
Constant Area ◽  
Stable Flame ◽  
Temperature Levels ◽  
Micro Combustor

Swiss Roll Combustor of 1 W capacity for micro gas turbine engine is operated with premixed hydrogen air mixture at ultra-lean equivalence ratio. The reaction zone under consideration has volume of 60 mm3. The reactant passage and product passage are coiled around the reaction zone facilitating the recovery of heat loss, by preheating the reactants. The reactants are entered through an increasing cross-sectional area passage from 0.6mm × 5mm inlet to 1.5mm × 5mm outlet, thereby reducing the velocity levels in the reactant passage, facilitating stable combustor operation. The combustor performance parameters, temperature levels, pattern factor and emissions are measured is operated at ultra-lean equivalence ratio of 0.12 to lean equivalence ratio of 0.43, for premixed hydrogen air combustion. The results are compared at similar (not same) equivalence ratios for constant area reactant passage. The visual inspection shows stable flame front in the combustion zone for variable area passage and extended flame front in the constant area passage combustor. However, the combustor performance deteriorates drastically above equivalence ratio of 0.43, leading to hot spots generation on walls.

Analytical Study of Natural Convection in a Cavity With Volumetric Heat Generation

Volume 1 ◽  
2004 ◽  
Author(s):  
Mandar V. Joshi ◽  
U. N. Gaitonde ◽  
Sushanta K. Mitra
Keyword(s):  
Natural Convection ◽  
Aspect Ratio ◽  
Heat Generation ◽  
Central Region ◽  
Analytical Study ◽  
Vertical Direction ◽  
Maximum Temperature ◽  
Small Aspect Ratio ◽  
Governing Equations ◽  
Volumetric Heat Generation

A semi-analytical method for natural convection in a two dimensional rectangular enclosure, with uniform volumetric heat generation, having insulated horizontal boundaries, and isothermal vertical boundaries, has been studied here. In this method, the governing equations for natural convection, have been solved under the assumption that for a cavity with small aspect ratio, the flow in the central region of the cavity is only in the vertical direction. It is found that for the cavities with small aspect ratio, the temperature in central region of the cavity is nearly constant along the horizontal direction. However, there is a uniform temperature gradient in the vertical direction, which can be related to the maximum temperature in conduction. The velocity profiles and temperature profiles obtained in the present work, are compared with the numerical simulations by Fluent and a fair agreement is found between these results.

scholarly journals Porosity effect on unsteady MHD free convection flow of Jeffrey fluid past an oscillating vertical plate with ramped wall temperature

2017 ◽  
Vol 13 (2) ◽  
Author(s):  
Nor Athirah Mohd Zin ◽  
Ahmad Qushairi Mohamad ◽  
Ilyas Khan ◽  
Sharidan Shafie
Keyword(s):  
Free Convection ◽  
Wall Temperature ◽  
Vertical Plate ◽  
Convection Flow ◽  
Jeffrey Fluid ◽  
Dimensionless Time ◽  
Governing Equations ◽  
Free Convection Flow ◽  
Permeability Parameter ◽  
The Impact

The unsteady magnetohydrodynamic (MHD) free convection flow of Jeffrey fluid embedded in porous medium past an oscillating vertical plate generated by thermal radiation with ramped wall temperature is investigated. The incompressible fluid is taken electrically conducting under the action of transverse magnetic field towards the flow. Constitutive relation of Jeffrey fluid is employed to model the governing equations in terms of partial differential equations with some physical conditions. The transformed dimensionless governing equations are solved analytically using Laplace transform technique. The impact of various pertinent parameters namely material parameter of Jeffrey fluid , dimensionless parameter of Jeffrey fluid , phase angle , Hartmann number , permeability parameter , Grashof number , Prandtl number , radiation parameter  and dimensionless time  on velocity and temperature distributions are presented graphically and discussed in details. It is observed that, the permeability parameter tend to retard the fluid velocity for ramped wall temperature but enhance the velocity for an isothermal plate. Besides that, this study shows, the amplitude of velocity and temperature fields for ramped wall temperature are always lower than isothermal plate. A comparison with the existing published work is also provided to confirm the validity of the present results and an excellent agreement are found. 

scholarly journals Validation of Current Practice and a near Patient Testing Method for Oral-Anticoagulant Control in General Practice

1997 ◽  
Vol 90 (12) ◽  
pp. 657-660 ◽  
Author(s):  
David A Seamark ◽  
Susan Backhouse ◽  
Paul Barber ◽  
John Hichens ◽  
Richard Lee ◽  
...  
Keyword(s):  
General Practice ◽  
Whole Blood ◽  
Oral Anticoagulant ◽  
Control Method ◽  
Oral Anticoagulants ◽  
Maximum Temperature ◽  
Routine Method ◽  
Blood Samples ◽  
Acceptable Agreement ◽  
Near Patient Testing

When oral anticoagulant control is monitored in general practice, venous blood samples are usually transported to a central laboratory for determination of international normalized ratio (INR). An alternative is near patient testing by a commercial method. In a rural general practice 27 km from a central haematology laboratory, whole blood samples were drawn from patients receiving oral anticoagulants and analysed by three methods: after centrifugation, plasma separated and frozen in liquid nitrogen, transported to the laboratory, thawed and immediately analysed (control); courier transport of citrated sample to the laboratory for analysis (routine); near patient testing of whole blood sample (NPT). Maximum temperature achieved and time to analysis for routine samples were recorded. 306 complete sets of data were obtained. Comparison between the routine method and the control method revealed acceptable agreement. On multiple regression analysis, maximum temperature achieved did not contribute to differences observed but time to analysis of over 5 hours did make a significant contribution. Comparison between the NPT method and control method showed acceptable agreement, with persistent under-recording by the NPT method. The routine method for INR determination was validated as robust and reproducible with the proviso that needle-to-analysis time should be kept below 5 hours. The NPT method was valid under conditions of normal general practice. Strict quality control of NPT methods is essential if performance is to be comparable with that of established methods.

The Modeling of Constant/Variable Solar Heat Flux Into a Porous Coil With Concentrator

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Sayyed Aboozar Fanaee ◽  
Mojtaba Rezapour
Keyword(s):  
Heat Flux ◽  
Heat Fluxes ◽  
The Finite Element Method ◽  
Governing Equations ◽  
Solar Heat ◽  
Clear Sky ◽  
Alumina Nanofluid ◽  
Solar Heat Flux ◽  
The City ◽  
Acceptable Agreement

In this paper, thermal-fluid modeling of nonporous/porous thermal coil filled by alumina nanofluid is discussed considering constant/variable solar heat fluxes. The fluxes are calculated for a parabolic concentrator at the solar paths for the city with a longitude of 59.20 deg and latitude of 32.87 deg in the clear sky at spring season. The governing equations are included as continuity, momentum, and energy conservations with considering variable solar flux by shadow effects of the coil on the parabolic concentrator. The numerical model is based on the finite element method by LU algorithm using the mumps solver. The results show that, in a porous medium, that the normalized temperature of the presented model has an acceptable agreement with experimental data with maximum errors of 3%. The existence of porosity significantly increases heat transfer parameters that improve transferred solar heat from the wall of the coil to nanofluid. The variable solar heat flux increases the temperature in the length of the coil rather than constant heat fluxes because of increasing exchanged heat to nanofluid.

Film Boiling Around a Vertical Cylinder With Top and Bottom Horizontal Surfaces

2007 ◽  
Author(s):  
Satoru Momoki ◽  
Takashi Yamada ◽  
Toru Shigechi ◽  
Kuniyasu Kanemaru ◽  
Tomohiko Yamaguchi
Keyword(s):  
Heat Transfer ◽  
Lower Limit ◽  
Finite Length ◽  
Wall Temperature ◽  
Vertical Cylinder ◽  
Cooling Curve ◽  
Film Boiling ◽  
Heated Cylinder ◽  
Subcooled Water ◽  
Saturated Water

Saturated and subcooled film boiling heat transfer around a vertical finite-length silver cylinder with top and bottom horizontal surfaces has been investigated, experimentally and analytically, in terms of cooling curve, and the correlations of heat transfer were proposed in the present paper. Pool film boiling experiments were carried out by quenching method. Cooling curves are obtained for saturated water at atmospheric pressure. The heated cylinder is made of silver and 18 kinds of cylinder are tested in the ranges of the diameter from 8 to 100 mm and the length from 8 to 160 mm. For subcooled water, the experiments were carried out in the similar method to the case of saturated water. The ranges of the diameter and length of the cylinder are 32 to 50 mm and 16 to 64 mm, respectively. The degree of liquid subcooling ranges from 2 to 30 K. In order to predict the film boiling characteristics, the overall heat transfer rate from a cylinder with finite length was modelled by taking into account each convective heat transfer on the bottom, side and top surfaces of the vertical cylinder. Present correlation equations for heat transfer and the lower limit of film boiling are good agreement with the experimental data for saturated and subcooled water. The values of wall heat flux and temperature at the lower limit of film boiling are obtained as the point where the cooling rate has a minimum value on the cooling curve. For the case of saturated water, wall temperature at the lower limit of film boiling is about 136 K and irrespective of the configuration of a cylinder. For subcooled water, the correlation is proposed for the effect of liquid subcooling on wall temperature at the lower limit of film boiling.

Mathematical Modeling of Biomass Pyrolysis

2009 ◽  
Author(s):  
A. Rahbari ◽  
M. Bidabadi ◽  
M. Azimi
Keyword(s):  
Reaction Zone ◽  
Burning Velocity ◽  
Flame Temperature ◽  
Governing Equations ◽  
Flame Zone ◽  
Conservation Equations ◽  
One Dimensional ◽  
Preheat Zone ◽  
Rate Of Reaction ◽  
Fuel Particles

In this research, the structure of laminar, one-dimensional and steady flame propagation in uniformly premixed particle-wood is analyzed. The structure of the flame is composed of three zones: a preheat zone, a narrow reaction zone and a post flame zone. In the preheat zone, the rate of reaction between fuel and oxidizer is assumed to be small and also it is presumed that the fuel particles vaporize to yield a gaseous fuel of known chemical structure when enter the reaction zone. Then in the reaction zone, composed of gas, tar and char combustion, the convective terms and vaporization terms in the conservation equations are presumed to be small and in the post flame zone, the diffusive terms in the conservation equations are assumed to be small in comparison with other parameters. The governing equations in each zone, considering these assumptions, are solved using the required boundary and matching conditions. Consequently, the variation of burning velocity and flame temperature as a function of equivalence ratio are presented as the outcome of this research.

Heat Transfer Enhancement Using Cu-Water Nanofluid in an Enclosure with Moving Cold Sidewalls

2012 ◽  
Vol 326-328 ◽  
pp. 440-445
Author(s):  
Ghanbar Ali Sheikhzadeh ◽  
M. Tavakoli ◽  
H. Alizadeh
Keyword(s):  
Heat Source ◽  
Richardson Number ◽  
Volume Fraction ◽  
Maximum Temperature ◽  
Source Surface ◽  
Governing Equations ◽  
Transfer Enhancement ◽  
Square Cavity ◽  
Simpler Algorithm ◽  
Volume Method

Mixed convection of Cu-water nanofluid in a lid-driven square cavity with a heat source embedded in the bottom wall is studied numerically. The governing equations together with the respective boundary conditions are solved numerically using the finite volume method and the SIMPLER algorithm. The computations are performed for various Richardson numbers (), heat source length () and volume fraction of the nanoparticles (). It is observed from the results that the average Nusselt number is increased by increasing the Richardson number and the volume fraction of the nanoparticles. Moreover, the maximum temperature at the heat source surface decreases by increasing the Richardson number and the volume fraction of the nanoparticles.

scholarly journals Experimental study of the adiabatic wall temperature of a cylinder in a supersonic cross flow

2021 ◽  
Vol 2039 (1) ◽  
pp. 012029
Author(s):  
S S Popovich ◽  
N A Kiselev ◽  
A G Zditovets ◽  
Y A Vinogradov
Keyword(s):  
Experimental Study ◽  
Wall Temperature ◽  
High Speed ◽  
Cross Flow ◽  
Maximum Temperature ◽  
Thermal Imager ◽  
State University ◽  
Adiabatic Wall ◽  
Speed Flow ◽  
Total Temperature

Abstract The results of an experimental study of the adiabatic wall temperature for a supersonic air flow across the cylinder are presented. The temperature was measured contactlessly using an InfraTEC ImageIR 8855 thermal imager through a ZnSe infrared illuminator. The freestream Mach number was 3.0, input flow total temperature was 295 K, and the total pressure 615 kPa. The Reynolds number calculated from the cylinder diameter (30 mm) was about 106. It is shown that it is possible in principle to determine the high-speed flow total temperature by defining the maximum temperature of a cylindrical probe at the front critical point. Thermograms of the wall temperature distribution along the profile of the cylinder were obtained. The research was performed at the experimental facilities of the Institute of Mechanics of Lomonosov Moscow State University.

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