scholarly journals Network of thermal cracks in meteorites due to temperature variations: new experimental evidence and implications for asteroid surfaces

2020 ◽  
Vol 500 (2) ◽  
pp. 1905-1920
Author(s):  
Guy Libourel ◽  
Clément Ganino ◽  
Marco Delbo ◽  
Mathieu Niezgoda ◽  
Benjamin Remy ◽  
...  
Keyword(s):  
Thermal Cracking ◽  
Temperature Variations ◽  
Hydrous Minerals ◽  
Thermal Cracks ◽  
Temperature Cycles ◽  
Rapid Temperature ◽  
Thermal Fracturing ◽  
Cracking Process ◽  
Near Earth Asteroids ◽  
Highly Porous

ABSTRACT In recent years, several studies have shown the importance of thermal fracturing of rocks due to temperature variations, on The Earth and Mars. Rock thermal cracking might also be a process at play on the lunar surface. These temperature variations as well as change rates can reach important amplitude on bodies without an atmosphere, in particular on those that reach small perihelion distances such as near-Earth asteroids. On the other hand, the formation, geometry, and extension of cracks on these bodies have not been fully investigated yet. Here, we show results of thermal cracking laboratory experiments on chondrite meteorites, which develop networks of cracks when subjected to rapid temperature cycles with amplitudes similar to those experienced by asteroids with low perihelion distances. The depth of the cracks can reach a few hundred of microns in some hundreds of temperature cycles, in agreement with theoretical studies. We find that dehydration of hydrous minerals enhances the cracking process. The formation of crack networks increases the porosity both at the surface and in the sub-surface of our specimens. We propose that this process could help explaining the recent finding of the very highly porous surfaces of most of the boulders on the asteroids Ryugu and Bennu.

scholarly journals XFEM for Thermal Crack of Massive Concrete

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Guowei Liu ◽  
Yu Hu ◽  
Qingbin Li ◽  
Zheng Zuo
Keyword(s):  
Cooling System ◽  
Concrete Structures ◽  
Thermal Cracking ◽  
Pipe System ◽  
Degree Of Hydration ◽  
Thermal Cracks ◽  
Massive Concrete ◽  
Cooling Pipe ◽  
Equivalent Equation ◽  
Viscoelastic Constitutive Model

Thermal cracking of massive concrete structures occurs as a result of stresses caused by hydration in real environment conditions. The extended finite element method that combines thermal fields and creep is used in this study to analyze the thermal cracking of massive concrete structures. The temperature field is accurately simulated through an equivalent equation of heat conduction that considers the effect of a cooling pipe system. The time-dependent creep behavior of massive concrete is determined by the viscoelastic constitutive model with Prony series. Based on the degree of hydration, we consider the main properties related to cracking evolving with time. Numerical simulations of a real massive concrete structure are conducted. Results show that the developed method is efficient for numerical calculations of thermal cracks on massive concrete. Further analyses indicate that a cooling system and appropriate heat preservation measures can efficiently prevent the occurrence of thermal cracks.

scholarly journals Prediction of products yield at the thermal cracking of vegetable oil

2014 ◽  
Vol 25 (2) ◽  
pp. 81-84
Author(s):  
Doinita Roxana Cioroiu ◽  
Claudia Irina Koncsag
Keyword(s):  
Vegetable Oil ◽  
Energy Savings ◽  
Raw Materials ◽  
Thermal Cracking ◽  
Raw Material ◽  
Semiempirical Model ◽  
University Of Florida ◽  
Steam Cracking ◽  
Cracking Process ◽  
The University

Abstract According to previous studies on the pyrolysis of vegetable oils, it resulted that the thermal cracking process is prone to produce large yields of ethylene, propylene, hydrogen and methane, comparable with the gas proceeding from the steam cracking of naphtha, but at much lower process temperature, this ensuring important energy savings. The studies are performed on very different raw materials and different reaction conditions, that being why at this moment it is very difficult to predict the products yield. This paper uses an analytical semiempirical model (ASEM) developed at the University of Florida, by applying it to a different raw material. The ASEM model fits very well to our experimental data, obtained at higher temperature but some parameters have to be adjusted. In the end we confirm a set of systemic parameters to be used for the prediction of main products yield proceeding from vegetable oil in an extended range of temperatures.

scholarly journals Studies on Naphtha Thermal Cracking Process used Slit Burner

1966 ◽  
Vol 30 (5) ◽  
pp. 415-421,a1
Author(s):  
Ryosuke Hashimoto ◽  
Hirao Fukushima ◽  
Daizo Kunii
Keyword(s):  
Thermal Cracking ◽  
Cracking Process

DeNOx mechanism caused by thermal cracking hydrocarbons in the stratified rich zone during diesel combustion

2005 ◽  
Vol 6 (6) ◽  
pp. 547-555 ◽  
Author(s):  
Y Kidoguchi ◽  
K Miwa ◽  
H Noge
Keyword(s):  
Flow Reactor ◽  
Reduction Process ◽  
Thermal Cracking ◽  
Chemical Kinetic ◽  
Diffusion Combustion ◽  
Diesel Combustion ◽  
Rapid Compression Machine ◽  
Combustion Phase ◽  
Rapid Compression ◽  
Cracking Process

This study concerns an experimental and theoretical investigation of the deNO x mechanism caused by thermal cracking hydrocarbons during diesel combustion. A total gas sampling experiment using a rapid compression machine showed that NO x can be reduced under fuel-rich and high-swirl conditions. It was found that under these conditions, a large amount of thermal cracking hydrocarbons, including unsaturated hydrocarbons such as C2H4, are produced during the ignition delay period, and that stratified fuel-rich combustion regions that contain these thermal cracking hydrocarbons are distributed widely throughout the combustion chamber. During the diffusion combustion phase, the CH4 concentration surpasses that of C2H4 and becomes the dominant hydrocarbon species. These thermal cracking hydrocarbons are supposed to be active in NO x reduction chemistry. To confirm the assumption, a flow reactor experiment was conducted focusing on the thermal cracking process of diesel fuel and the NO x reduction process. The experiment showed that when a solvent was used as fuel, light hydrocarbons similar to those observed in the rapid compression experiment are formed, and that about 60 per cent of NO x was reduced at equivalence ratios over 2.5 and a temperature of 1500 K. In addition to the above experiments, a chemical kinetic calculation using CHEMKIN III was carried out. The calculation revealed that C2H4 is easily decomposed during its oxidation process, forming HCCO or CHC2, which reacts promptly with NO and that in this reaction path, C2H22 formed through the thermal cracking process of C2H4 is an essential species to the formation of HCCO and CH2.

Olefins and Ethanol from Polyolefins: Analysis of Potential Chemical Recycling of Poly(ethylene) Mexican Case

2016 ◽  
Vol 14 (6) ◽  
pp. 1289-1300 ◽  
Author(s):  
A. Vargas Santillán ◽  
J. C. Farias Sanchez ◽  
M. G. Pineda Pimentel ◽  
A. J. Castro Montoya
Keyword(s):  
Thermal Cracking ◽  
Added Value ◽  
Cost Ratio ◽  
Chemical Recycling ◽  
Total Production ◽  
Process Economics ◽  
Technological Advances ◽  
Challenges And Opportunities ◽  
Cracking Process ◽  
Number Of Treatment

Abstract Plastic solid waste (PSW) presents challenges and opportunities to society regardless of their sustainability awareness and technological advances. A special emphasis is paid on waste generated from polyolefin sources, which makes up a great percentage of our daily commodities’ plastic products. In Mexico 7.6 millions of tons of plastic in 2012 were wasted, which low density polyethylene LDPE, and high density polyethylene HDPE were the most abundant. Increasing cost, and decreasing space of landfills are forcing considerations of alternative options for PSW disposal. Years of research, study and testing have resulted in a number of treatment, recycling and recovery methods for plastics that can be economically, and environmentally viable. The following work studies the possibilities of polyethylene recycling. Nowadays, non-catalytic thermal cracking (Pyrolysis) is receiving renewed attention, due to the fact of added value on a crude oil barrel and its very valuable yielded products, but a fact remains that advanced thermo-chemical recycling of polyolefin still lacks the proper design, and kinetic background to target certain desired products and/or chemicals. On the other hand some research have shown a good performance that can be used in a real plant. ASPEN Plus is used to simulate a non-catalytic thermal cracking process. The process behavior of simulation is similar to the experimental data from other authors. Using gibbs free energy to identify the chemical equilibrium in system, its global minimization allows identifying the amount of substances present in the process. The simulation results demonstrate that it could be produced 49 % and 34 % wt of ethylene and propylene respectively from gas yield at 850 °C. Then scale the plant to produce ethylene and propylene from the pyrolysis and ethanol from a direct hydration of ethylene. Aspen Process Economics Analyzer is used in order to find the feasibility of the pyrolysis and ethanol production. The total sales/total production cost ratio obtained for the integrated process approaches was 2.55.

Melioration of Pyroelectric Cells for Power Conversion

2012 ◽  
Vol 479-481 ◽  
pp. 2199-2205
Author(s):  
Chun Ching Hsiao ◽  
Chin Yu Chang ◽  
An Shen Siao ◽  
Jing Chih Ciou
Keyword(s):  
Temperature Variation ◽  
Power Conversion ◽  
Temperature Gradients ◽  
Electrode Design ◽  
Cutting Depth ◽  
Temperature Variations ◽  
Variation Rate ◽  
Rapid Temperature ◽  
Temperature Variation Rate ◽  
Lateral Temperature

Trenching PZT material in a thicker PZT pyroelectric cell to improve the temperature variation rate was proposed in this study to enhance the efficiency of thermal energy-harvesting conversion by pyroelectricity. A thicker pyroelectric cell is beneficial in generating electricity pyroelectrically, but it opposes rapid temperature variations. Therefore, the PZT sheet was fabricated to produce deeper trenches to cause lateral temperature gradients induced by the trenched electrode, enhancing the temperature variation rate under homogeneous heat irradiation. When the trenched electrode type with an electrode width of 200 μm and a cutting depth of 150 μm was used to fabricate the PZT pyroelectric cell with a 200 μm thick PZT sheet, the temperature variation rate was improved by about 55%. Therefore, the trenched electrode design did indeed enhance the temperature variation rate and the efficiency of pyroelectric energy converters.

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