scholarly journals Critical autoignition conditions for arbitrary reaction order

2019 ◽  
Vol 475 (2227) ◽  
pp. 20180601 ◽  
Author(s):  
V. Yu Filimonov ◽  
K. B. Koshelev
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Arbitrary Order ◽  
Reaction Order ◽  
Exothermic Reaction ◽  
Ignition Limit ◽  
Critical Parameters ◽  
Initial Concentration ◽  
Reacting Systems ◽  
The Relationship

In this paper, the theoretical analysis of the critical autoignition conditions for exothermically reacting systems at any value of the reaction order was conducted. The calculated and approximate analytical dependencies for the relationship between the parameters at the ignition limit were obtained. On the basis of the obtained diagrams of critical parameters, the conditions of thermal explosion (TE) degeneration for reactions of arbitrary order were determined. It was established that the existing theory of TE gives the correct estimates of ignition temperatures for a given condition of exothermic reaction realization (heat transfer coefficient, specific surface area, initial concentration). However, the theory gives unsatisfactory predictions for the mentioned critical TE conditions at a given ambient temperature. Moreover, the classical theory cannot be applied in the intermediate case when the effect of reactant consumption is already significant but the reaction still proceeds with all the signs of a TE.

The Surface Heat Transfer Coefficient Model of 7075 Al-Alloy Extrusion Product and its Temperature Prediction

2013 ◽  
Vol 749 ◽  
pp. 229-236
Author(s):  
Wen Rong Hou ◽  
Wei Bing Ji ◽  
Zhi Hao Zhang ◽  
Jian Xin Xie
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Surface Heat ◽  
Al Alloy ◽  
Surface Heat Transfer ◽  
7075 Al Alloy ◽  
Surface Heat Transfer Coefficient ◽  
Extrusion Product ◽  
The Relationship

Surface heat transfer coefficient is a key parameter for accurately predicting the extrusion product temperature near the die exit and then achieving isothermal extrusion by speed controlling. Based on the heat transfer characteristics of extrusion product during cooling process, a dynamic loading method of heat transfer boundary conditions was proposed. The surface heat transfer coefficient model of 7075 Al-alloy extrusion product was established using the dynamic loading method and inverse calculation comprehensively. The model indicated the relationship among surface heat transfer coefficient h, surface temperature T and initial temperature T0 as h=1.16T-0.97T0. Its accuracy is high enough for calculating the surface temperature of 7075 Al-alloy extrusion product. According to the model and the experimental data, the relationship between the product and the measured temperatures can be established. It provides an effective way to solve the problem that the extrusion product temperature near the die exit cannot be directly measured.

scholarly journals An Experimental Investigation on the Heat Transfer Coefficient of Oscillating Heat Pipes

2013 ◽  
Vol 732-733 ◽  
pp. 78-82
Author(s):  
Ling Gao ◽  
Wen Guang Geng ◽  
Xiao Xu Ma ◽  
Xiu Li Ma ◽  
Guang Liang Luo ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Transfer Coefficient ◽  
Relative Humidity ◽  
Transfer Coefficient ◽  
Convective Heat Transfer Coefficient ◽  
Heat Pipes ◽  
Oscillating Heat Pipe ◽  
Hot Air ◽  
The Relationship

This paper presents an experimental study on total heat transfer coefficient (ht) in oscillating heat pipe heat exchanger hot air flow tunnels, ht plays an important role in the oscillating heat pipes design process. In this paper, ht and the convective heat transfer coefficient (h) was investigated by experimentally and theoretical calculation respectively. From experimental study, the relationship between the ratio of heat transfer coefficient and the relative humidity is obtained. The results show that the ratio of ht to h increases from 5 to 20 as the relative humidity of the hot gas increasing from 19.22% to 60%. According to the experimental data, a matched curve and an empirical equation were presented, which can be described as ht=h(1.87783+0.09631x+0.0032x2).

Heat Transfer by Natural Convection of Mercury in Enclosed Spaces When Heated From Below and Rotated

1964 ◽  
Vol 86 (2) ◽  
pp. 203-206 ◽  
Author(s):  
David Dropkin ◽  
George Gelb
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Vertical Axis ◽  
Critical Value ◽  
Characteristic Dimension ◽  
Taylor Number ◽  
The Relationship ◽  
Rayleigh Numbers ◽  
The Heat Transfer Coefficient

This paper presents results of an experimental investigation of convective heat transfer in mercury confined by two horizontal plates, heated from below, and spun about its vertical axis. The experiments covered a range of Rayleigh numbers between 1.1(10)6 and 5.17(10)7, and Taylor numbers from 0 to 7.75(10)10. The Prandtl number was practically constant. The results indicate that for low spin rates, up to a certain critical value of Taylor number, the change in the heat-transfer coefficient is insignificant and the equation derived for the stationary case can be used. The critical Taylor number is given by Ta(critical)=0.68(Ra)1.28 Above the critical Taylor number, the heat-transfer coefficient may be computed from the relationship Nu=0.095(Ra)0.852(Ta)−0.463 In this equation the characteristic dimension of length, for Nu, Ra, and Taylor numbers, is the distance between plates.

scholarly journals Market-Oriented Cost-Effectiveness and Energy Analysis of Windows in Portugal

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3720
Author(s):  
António M. Raimundo ◽  
Nuno Baía Saraiva ◽  
Luisa Dias Pereira ◽  
Ana Cristina Rebelo
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Energy Savings ◽  
Energy Performance ◽  
Economic Benefits ◽  
Cost Of Energy ◽  
Cost Efficient ◽  
The Impact ◽  
The Relationship

Glazed systems in buildings can account for a significant part of overall energy consumption. The unfavorable relationship between energy savings and the increased cost of energy-efficient windows is often the main drawback cited by customers to justify its non-acquisition. of glazed windows. This study addresses the relationship between the investment costs in windows and their energy performance and associated costs. Seventeen window manufacturers were contacted. This survey studied the state-of-the-art and the most-used windows in terms of energy efficiency and cost. Calumen and Guardian Configurator software were used to perform this assessment. Additionally, SEnergEd software was used to simulate the energy performance and compute the equivalent annual cost for the entire life cycle of buildings. Besides the economic benefits, the impact of the energy performance of the windows on the energy performance of the building was also studied. In terms of energy, the most efficient glazing system was two windows per span, resulting in a combined solar factor of 0.43 and a 0.55 W/(m2·K) heat-transfer coefficient. On the other hand, one window per span, with a solar factor of 0.79 and a 3.05 W/(m2 K) heat-transfer coefficient is the most cost-efficient to be used in Portugal.

scholarly journals Asymptotic and Dynamical Analyses of Heat Transfer through a Rectangular Longitudinal Fin

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
C. Harley
Keyword(s):  
Heat Transfer ◽  
Differential Equation ◽  
Thermal Conductivity ◽  
Ordinary Differential Equation ◽  
Heat Transfer Coefficient ◽  
Dynamical Analysis ◽  
Temperature Dependent ◽  
Highly Nonlinear ◽  
The Relationship ◽  
Steady Heat

The steady heat transfer through a rectangular longitudinal fin is studied. The thermal conductivity and heat transfer coefficient are assumed to be temperature dependent making the resulting ordinary differential equation (ODE) highly nonlinear. An asymptotic solution is used as a means of understanding the relationship between key parameters. A dynamical analysis is also employed for the same purpose.

scholarly journals Pemodelan pada Pengeringan Pneumatik Mekanis Tepung Kasava: Hubungan Koefisien Pindah Panas dengan Variabel Pengeringan (Modelling on Mechanical Cassava Flour Pneumatic Drying: Correlation of Heat Transfer Coefficient and Drying Variables)

2016 ◽  
Vol 36 (03) ◽  
pp. 362 ◽  
Author(s):  
Yus Witdarko ◽  
Nursigit Bintoro ◽  
Bandul Suratmo ◽  
Budi Rahardjo
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Dimensional Analysis ◽  
Coefficient Of Determination ◽  
Process Variables ◽  
Drying Process ◽  
Cassava Flour ◽  
Pneumatic Drying ◽  
The Relationship

In the cassava flour pneumatic drying process, mostly heat transfer occurred in convective mode. One of variables which could be used to evaluate the effectiveness of drying processperformance is heat transfer coefficient (h) during drying. The objectives of the research was to formulate a mathematical relationship between h and various pneumatic drying process variables of cassava flour by applying dimensional analysis. In the following research it had been constructed a pneumatic drying machine which was able to be according to the needed data that will be collected. Several parameters related to physical and thermal properties as well as operation of the drying machine were measured and used as the analysis variables was solved using dimensional analysis. Based on the result of the data, it was obtained that the relationship between h and the drying process variables could be expressed as follows  This equation had quite high coefficient of determination, so that it could be used to predict the heat transfer coefficient in pneumatic drying process. Sensitivity analysis indicated that the dimensionless product which had the largest effect on h was   .ABSTRAKPada proses pengeringan tepung kasava secara pneumatik, perpindahan panas terjadi terutama secara konveksi. Salah satu parameter yang digunakan untuk mengevaluasi efektivitas kinerja proses pengeringan tersebut adalah koefisien perpindahan panas (h) yang terjadi selama pengeringan. Tujuan dari penelitian ini adalah untuk menghubungkan secara matematis antara nilai h dengan beberapa variabel proses pengeringan pneumatik tepung kasava dengan menggunakan metode analisis dimensi. Pada penelitian ini telah dikonstruksi suatu mesin pengering pneumatik yang dirancang untuk dapat dilakukan pengaturan-pengaturan sesuai dengan kebutuhan data penelitian yang akan dikumpulkan. Beberapa parameter yang terkait dengan sifat fisik dan sifat thermis bahan serta operasional mesin pengering diukur dan digunakan sebagai variabel-variabel analisis yang diselesaikan dengan metode analisis dimensi. Berdasarkan hasil analisis data diperoleh hubungan antara nilai h dengan variabel-variabel proses pengeringan sebagai berikut    Persamaan tersebut mempunyai nilai koefisien determinasi yang cukup besar, sehingga dapat digunakan untuk memprediksi koefisien perpindahan panas pada pengeringan pneumatic. Hasil uji sensitivitas menunjukkan bahwa dimensionless product yang paling berpengaruh terhadap nilai h adalah    .Kata kunci: Tepung kasava; analisis dimensi; koefisisen perpindahan panas; pneumatic drying

Evaporation of lignin-lean black liquor

TAPPI Journal ◽  
2015 ◽  
Vol 14 (7) ◽  
pp. 441-450
Author(s):  
HENRIK WALLMO, ◽  
ULF ANDERSSON ◽  
MATHIAS GOURDON ◽  
MARTIN WIMBY
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Black Liquor ◽  
Salt Content ◽  
Solubility Limit ◽  
Lignin Removal ◽  
Kraft Black Liquor ◽  
Black Liquors ◽  
The Heat Transfer Coefficient

Many of the pulp mill biorefinery concepts recently presented include removal of lignin from black liquor. In this work, the aim was to study how the change in liquor chemistry affected the evaporation of kraft black liquor when lignin was removed using the LignoBoost process. Lignin was removed from a softwood kraft black liquor and four different black liquors were studied: one reference black liquor (with no lignin extracted); two ligninlean black liquors with a lignin removal rate of 5.5% and 21%, respectively; and one liquor with maximum lignin removal of 60%. Evaporation tests were carried out at the research evaporator in Chalmers University of Technology. Studied parameters were liquor viscosity, boiling point rise, heat transfer coefficient, scaling propensity, changes in liquor chemical composition, and tube incrustation. It was found that the solubility limit for incrustation changed towards lower dry solids for the lignin-lean black liquors due to an increased salt content. The scaling obtained on the tubes was easily cleaned with thin liquor at 105°C. It was also shown that the liquor viscosity decreased exponentially with increased lignin outtake and hence, the heat transfer coefficient increased with increased lignin outtake. Long term tests, operated about 6 percentage dry solids units above the solubility limit for incrustation for all liquors, showed that the heat transfer coefficient increased from 650 W/m2K for the reference liquor to 1500 W/m2K for the liquor with highest lignin separation degree, 60%.

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