An Experimental Study on the Thermal Properties of Concrete under the Load Ratio Condition in a Fire

2012 ◽  
Vol 446-449 ◽  
pp. 1231-1242
Author(s):  
Heung Youl Kim ◽  
Hyung Jun Kim ◽  
Jea Sung Lee ◽  
Ki Hyuk Kwon
Keyword(s):  
Thermal Properties ◽  
Temperature Rise ◽  
Heated Surface ◽  
Load Ratio ◽  
Constant Load ◽  
Concrete Lining ◽  
Small Scale ◽  
Ratio Condition ◽  
Rapid Temperature ◽  
Heating Test

When a fire occurs, the strength of the concrete structure deteriorates due to temperature rise under the condition of constant load. The deterioration in strength causes the change in axial load ratio, so the structure is deformed. In this study, loaded heating test of concrete lining was conducted to realize the condition of an actual fire outbreak in a tunnel where heating and loading affect the structure simultaneously. The shape of the specimens was planned in compliance with the standard for small scale test prescribed in the EFNARC and 24 MPa, 40 MPa and 50MPa were used to analyze the thermal properties associated with different concrete strengths. Constant loading condition was provided based on the load ratios equivalent to 20 % and 40 % of the sectional stress in the concrete and the MHC fire scenario was selected to realize the thermal impact on the concrete by rapid temperature rise. Under each load ratio, more cracks were observed in higher strength and spalling occurred in 50MPa. In terms of fire damage range, 50mm points from heated surface of the 200mm lining did not satisfy the ITA standard for concrete lining upon a fire.

An Experimental Study on the Thermal Properties of Concrete under the Load Ratio Condition in a Fire

2012 ◽  
Vol 446-449 ◽  
pp. 1231-1242
Author(s):  
Heung Youl Kim ◽  
Hyung Jun Kim ◽  
Jea Sung Lee ◽  
Ki Hyuk Kwon
Keyword(s):  
Experimental Study ◽  
Thermal Properties ◽  
Load Ratio ◽  
Ratio Condition

Temperature Rise Times in Pneumatic Tires

1976 ◽  
Vol 4 (3) ◽  
pp. 181-189 ◽  
Author(s):  
S. K. Clark
Keyword(s):  
Heat Transfer ◽  
Thermal Properties ◽  
Temperature Rise ◽  
Thermal Equilibrium ◽  
Transfer Coefficients ◽  
Pneumatic Tire ◽  
Heat Transfer Coefficients ◽  
Idealized Model ◽  
Pneumatic Tires

Abstract An idealized model is proposed for heating of a pneumatic tire. A solution is obtained for the temperature rise of such a model. Using known thermal properties of rubber and known heat transfer coefficients, the time to reach thermal equilibrium is estimated.

Micro Fluidic Jets for Thermal Management of Electronics

Volume 4 ◽  
2004 ◽  
Author(s):  
Jivtesh Garg ◽  
Mehmet Arik ◽  
Stanton Weaver ◽  
Seyed Saddoughi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heated Surface ◽  
Turbulent Jets ◽  
Harmonic Signal ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Small Scale ◽  
Air Cooling ◽  
Infrared Thermal Imaging

Micro fluidics devices are conventionally used for boundary layer control in many aerospace applications. Synthetic Jets are intense small scale turbulent jets formed from entrainment and expulsion of the fluid in which they are embedded. The idea of using synthetic jets in confined electronic cooling applications started in late 1990s. These micro fluidic devices offer very efficient, high magnitude direct air-cooling on the heated surface. A proprietary synthetic jet designed in General Electric Company was able to provide a maximum air velocity of 90 m/s from a 1.2 mm hydraulic diameter rectangular orifice. An experimental study for determining the thermal performance of a meso scale synthetic jet was carried out. The synthetic jets are driven by a time harmonic signal. During the experiments, the operating frequency for jets was set between 3 and 4.5 kHz. The resonance frequency for a particular jet was determined through the effect on the exit velocity magnitude. An infrared thermal imaging technique was used to acquire fine scale temperature measurements. A square heater with a surface area of 156 mm2 was used to mimic the hot component and extensive temperature maps were obtained. The parameters varied during the experiments were jet location, driving jet voltage, driving jet frequency and heater power. The output parameters were point wise temperatures (pixel size = 30 μm), and heat transfer enhancement over natural convection. A maximum of approximately 8 times enhancement over natural convection heat transfer was measured. The maximum coefficient of cooling performance obtained was approximately 6.6 due to the low power consumption of the synthetic jets.

Thermal Effects Due to Surface Films in Sliding Contact

1994 ◽  
Vol 116 (2) ◽  
pp. 238-245 ◽  
Author(s):  
Brian Vick ◽  
L. P. Golan ◽  
M. J. Furey
Keyword(s):  
Thermal Properties ◽  
Temperature Rise ◽  
Thermal Effects ◽  
Three Dimensional ◽  
Sliding Contact ◽  
Frictional Heat ◽  
Solution Technique ◽  
Surface Films ◽  
Thermal Coupling ◽  
Efficient Manner

The present work examines theoretically the influence of surface coatings on the temperatures produced by friction due to sliding contact. A generalized thermal model is developed which incorporates three-dimensional, transient heat transfer between layered media with thermal coupling at multiple, interacting contact patches. A solution technique based on a variation of the boundary element method is developed and utilized. The method allows for the solution of the distribution of frictional heat and the resulting temperature rise in an accurate yet numerically efficient manner. Results are presented showing the influence of film thickness, thermal properties, velocity, and contact area on the division of heat and surface temperature rise. The results show that a film with thermal properties different than those of the substrate can have a pronounced effect on the predicted temperature rise.

Large-scale correction and thermal properties of holographic dual background of an adaptive graphene model

2020 ◽  
Vol 17 (09) ◽  
pp. 2050135
Author(s):  
Z. Zali ◽  
J. Sadeghi
Keyword(s):  
Thermal Properties ◽  
Energy Spectrum ◽  
Large Scale ◽  
Correction Term ◽  
Gaussian Function ◽  
Beltrami Equation ◽  
Additional Term ◽  
Order Equation ◽  
Small Scale ◽  
Corrected Entropy

In this paper, we consider the particle on curved graphene space-time. In that case, we calculate the geometric form of potential which is known as Gaussian function. Here, we introduce the metric background which completely corresponds to curved graphene space-times. This metric leads us to obtain the geometry potential and we make the Laplace Beltrami equation in the mentioned metric background. We also rearrange such relation in terms of the second-order equation. By using the known polynomial, we solve the particle equation of motion in graphene background. In that case, we arrive the energy spectrum which has three terms. We take advantage from energy spectrum and investigate the thermal properties of system. The additional terms give us an opportunity to obtain the corrected entropy and free energy. So, we show that the additional term comes from geometry potential. This correction is important for the large scale. Hence, we show that correction term is logarithmic as well as small scale corrections.

scholarly journals Thermal Contact Conductance-Based Thermal Behavior Analytical Model for a Hybrid Floor at Elevated Temperatures

Materials ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 4257 ◽  
Author(s):  
Min Jae Park ◽  
Jeong Ki Min ◽  
Jaehoon Bae ◽  
Young K. Ju
Keyword(s):  
Thermal Behavior ◽  
Elevated Temperatures ◽  
Heated Surface ◽  
Thermal Contact ◽  
Polymeric Materials ◽  
Steel Plates ◽  
Thermal Contact Conductance ◽  
Small Scale ◽  
Element Analysis ◽  
Contact Conductance

Hybrid floors infilled with polymeric materials between two steel plates were developed as a prefabricated floor system in the construction industry. However, the floor’s fire resistance performance has not been investigated. To evaluate this, fire tests suggested by the Korean Standards should be performed. As these tests are costly and time consuming, the number of variables were limited. However, many variables can be investigated in other ways such as furnace tests and finite element analysis (FEA) with less cost and time. In this study, furnace tests on heated surface areas smaller than 1 m2 were conducted to investigate the thermal behavior of the hybrid floor at elevated temperatures. To obtain the reliability of the proposed thermal behavior analytical (TBA) model, verifications were conducted by FEAs. Thermal contact conductance including interfacial thermal properties between two materials was adopted in the TBA model, and the values at elevated temperatures were suggested based on thermo-gravimetric analyses results and verified by FEA. Errors between the tests and TBA model indicated that the model was adequate in predicting the temperature distribution in small-scale hybrids. Furthermore, larger furnace tests and analysis results were compared to verify the TBA model’s application to different sized hybrid floors.

Effect of conventional degumming methods on Eri silk fibers produced in Kenya

2020 ◽  
Vol 24 (2) ◽  
pp. 163-182
Author(s):  
Edison Omollo Oduor ◽  
Lucy Wanjiru Ciera ◽  
Vijay Adolkar ◽  
Odoch Pido
Keyword(s):  
Thermal Properties ◽  
Rural Areas ◽  
Fiber Strength ◽  
Silk Fiber ◽  
Small Scale ◽  
Content Type ◽  
Silk Fibers ◽  
Fiber Production ◽  
Alkali Medium ◽  
Eri Silk

Purpose This paper aims to determine the best conventional degumming technique for use by rural farmers practicing Eri silk fiber production in Kenya. Design/methodology/approach Three conventional silk degumming methods (water, soap and alkali) were analyzed under the factors, namely, time, pressure and degumming media, following the multilevel factorial design of experiments. The effect of variables on degumming weight loss was determined. The effects of the conventional degumming methods that produced complete sericin removal on chemical structure, surface morphology, thermal properties, crystallinity and fiber strength on Eri silk fibers produced in Kenya were then determined. The optimal degumming condition was then evaluated. Findings Soap and water degumming led to incomplete sericin removal. Alkali degumming media had the most effect, especially when pressure cooked at 103 kPa. Increasing time during alkali degumming beyond 30 min did not to have any major difference on degumming loss (at p 0.05). There were no major changes in chemical and thermal properties after degumming. However, the tensile strength and elongation deteriorated especially on alkali medium. Decreasing degumming time in alkali medium from 120 min to 30 min reduced the strength loss from 45% to 33%. Optimal degumming was found to be in an alkali media at 103 kPa for 30 min. Originality/value There is very little information available on Eri silk fibers produced in Kenya. Results of this study provide an optimized conventional degumming procedure suitable for small scale farmers in rural areas practicing Eri silk fiber production.

A Copper Microchannel Heat Exchanger for MEMS-Based Waste Heat Thermal Scavenging

2014 ◽  
Author(s):  
E. Borquist ◽  
A. Baniya ◽  
S. Thapa ◽  
D. Wood ◽  
L. Weiss
Keyword(s):  
Heat Exchanger ◽  
Thermal Energy ◽  
Waste Heat ◽  
Heated Surface ◽  
Copper Substrate ◽  
Working Fluid ◽  
Bottom Plate ◽  
Small Scale ◽  
Thermal Source ◽  
Micro Channels

The growing necessity for increased efficiency and sustainability in energy systems such as MEMS devices has driven research in waste heat scavenging. This approach uses thermal energy, which is typically rejected to the surrounding environment, transferred to a secondary device to produce useful power output. This paper investigates a MEMS-based micro-channel heat exchanger (MHE) designed to operate as part of a micro-scale thermal energy scavenging system. Fabrication and operation of the MHE is presented. MHE operation relies on capillary action which drives working fluid from surrounding reservoirs via micro-channels above a heated surface. Energy absorption by the MHE is increased through the use of a working fluid which undergoes phase change as a result of thermal input. In a real-world implementation, the efficiency at which the MHE operates contributes to the thermal efficiency of connected small-scale devices, such as those powered by thermoelectrics which require continual heat transfer. This full system can then more efficiently power MEMS-based sensors or other devices in diverse applications. In this work, the MHE and micro-channels are fabricated entirely of copper with 300μm width channels. Copper electro-deposition onto a copper substrate provides enhanced thermal conductivity when compared to other materials such as silicon or aluminum. The deposition process also increases the surface area of the channels due to porosity. Fabrication with copper produces a robust device, which is not limited to environments where fragility is a concern. The MHE operation has been designed for widespread use in varied environments. The exchanger working fluid is also non-specific, allowing for fluid flexibility for a range of temperatures, depending on the thermal source potential. In these tests, the exchanger shows approximately 8.7 kW/m2 of thermal absorption and 7.6 kW/m2 of thermal transfer for a dry MHE while the wetted MHE had an energy throughput of 8.3 kW/m2. The temperature gradient maintained across the MHE bottom plate and lid is approximately 30 °C for both the dry and wetted MHE tests though overall temperatures were lower for the wetted MHE.

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