scholarly journals IMPACT OF THE ELECTRIC CABLES INSTALLATION ON THE IGNITION PARAMETERS OF THE SPRUCE WOOD SURFACE

Wood Research ◽  
2021 ◽  
Vol 66 (5) ◽  
pp. 732-745
Author(s):  
ALEŠ NEČAS ◽  
JOZEF MARTINKA ◽  
PETER RANTUCH ◽  
IGOR WACHTER ◽  
TOMÁŠ ŠTEFKO
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Ignition Temperature ◽  
Thermal Inertia ◽  
Thermal Response ◽  
Heat Fluxes ◽  
Wood Board ◽  
Spruce Wood ◽  
Board Surface ◽  
Electrical Cables

This study is aimed to investigate of an impact of electrical cables installed on Norway spruce (Picea abies(L.) Karst.) wood board surface on main ignition parameters (mainly critical heat flux, ignition temperature, thermal response parameter and thermal inertia). Ignition parameters have been determined by dependence of ignition times (raised to the power of -1, -1/2 and -0.547) on heat flux. Initiation times have been measured for three configurations of spruce wood boards with surface dimensions of 100 x 100 mm ± 1 mm (the first configuration: board without cables on surface, the second configuration: board with three electrical cables on surface -spacing between cables was equal to their diameter and the third configuration: board with five electrical cables -spacing between cables was equal to their diameter) at five heat fluxes (30, 35, 40, 45 and 50 kW·m-2). Obtained results proved that installation of the electrical cables on the spruce wood board surface has a significant impact on the ignition parameters. The critical heat flux (8.5 kW·m-2), apparent thermal inertia0.20 ± 0.02 kJ2·m-4·K-2·s-1and ignition temperature 324 ± 105°C of spruce wood board increased up to 18 ± 3 kW·m-2(critical heat flux), 0.68 ± 0.03 kJ2·m-4·K-2·s-1(apparent thermal inertia) and 475 ± 27°C (ignition temperature) by theinstallation of electrical cableson the surface of spruce wood board.

scholarly journals A Study of Critical Heat Flux During Flow Boiling in Microchannel Heat Sinks

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Tailian Chen ◽  
Suresh V. Garimella
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Rate ◽  
Heat Input ◽  
Heat Sink ◽  
Flow Boiling ◽  
Strong Dependence ◽  
Heat Fluxes ◽  
Abrupt Decrease ◽  
Parallel Microchannels

The cooling capacity of two-phase transport in microchannels is limited by the occurrence of critical heat flux (CHF). Due to the nature of the phenomenon, it is challenging to obtain reliable CHF data without causing damage to the device under test. In this work, the critical heat fluxes for flow boiling of FC-77 in a silicon thermal test die containing 60 parallel microchannels were measured at five total flow rates through the microchannels in the range of 20–80 ml/min. CHF is caused by dryout at the wall near the exit of the microchannels, which in turn is attributed to the flow reversal upstream of the microchannels. The bubbles pushed back into the inlet plenum agglomerate; the resulting flow blockage is a likely cause for the occurrence of CHF which is marked by an abrupt increase in wall temperature near the exit and an abrupt decrease in pressure drop across the microchannels. A database of 49 data points obtained from five experiments in four independent studies with water, R-113, and FC-77 as coolants was compiled and analyzed. It is found that the CHF has a strong dependence on the coolant, the flow rate, and the area upon which the heat flux definition is based. However, at a given flow rate, the critical heat input (total heat transfer rate to the coolant when CHF occurs) depends only on the coolant and has minimal dependence on the details of the microchannel heat sink (channel size, number of channels, substrate material, and base area). The critical heat input for flow boiling in multiple parallel microchannels follows a well-defined trend with the product of mass flow rate and latent heat of vaporization. A power-law correlation is proposed which offers a simple, yet accurate method for predicting the CHF. The thermodynamic exit quality at CHF is also analyzed and discussed to provide insights into the CHF phenomenon in a heat sink containing multiple parallel microchannels.

Stability and Enhancement of Boiling in Microchannels

2011 ◽  
Author(s):  
A. E. Bergles
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
High Heat ◽  
Heat Fluxes ◽  
Transfer Enhancement ◽  
The Past ◽  
The Stability ◽  
Saturated Boiling ◽  
Microelectronic Components

During the past 20 years, there has been intense worldwide interest in microchannel heat exchangers, particularly for cooling of microelectronic components. Saturated boiling of the coolant is usually indicated in order to accommodate high heat fluxes and to have uniformity of temperature. However, boiling is accompanied by several instabilities, the most severe of which can sharply limit the maximum, or critical, heat flux. These stability phenomena are reviewed, and recent studies will be discussed. Elevation of the critical heat flux will be discussed within the context of heat transfer enhancement. Means to improve the stability of boiling and the enhancement of boiling heat transfer, in general, are discussed.

Flammability of Solid Materials: An Experimental Calorimetric Approach

2011 ◽  
Author(s):  
Paolo E. Santangelo ◽  
Noah L. Ryder ◽  
Andre´ W. Marshall ◽  
Christopher F. Schemel
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Quantitative Estimation ◽  
Hazard Analysis ◽  
Thermal Inertia ◽  
Fire Risk ◽  
Solid Materials ◽  
General Applicability ◽  
Plastic Materials ◽  
Validity Range

Flammability properties of solid materials are necessary to be a known parameter for many purposes: among them, forensic investigations of fire and explosion events, fire risk or hazard analysis, design and development of combustion-based systems. However, despite the large quantity of data in the literature, the flammability properties of many materials still appear not to be available or show a degree of uncertainty associated with them, which makes their value limited. The present work is aimed at proposing a calorimetric-based approach to determine some flammability and thermophysical properties of solids, with specific regard to time-to-ignition as a function of the imposed heat flux. Plastic materials have been here chosen as test cases, even though this approach has a general applicability. The two mentioned parameters have been analyzed to provide a quantitative estimation of the critical heat flux (minimum heat flux resulting in ignition). A cone calorimeter has been employed to conduct the experiments: the facility complies with standard ASTM E 1354; the related uncertainty and validity range has been evaluated through an appropriate error analysis. Finally, thermal inertia has been thereby calculated for the considered materials through a simple thermodynamic model, which is based upon critical heat flux and energy conservation.

scholarly journals Novel active method for the estimation of a building wall thermal resistance

2020 ◽  
Vol 172 ◽  
pp. 14008
Author(s):  
Adrien François ◽  
Laurent Ibos ◽  
Vincent Feuillet ◽  
Johann Meulemans
Keyword(s):  
Steady State ◽  
Thermal Resistance ◽  
Building Materials ◽  
Thermal Inertia ◽  
Thermal Response ◽  
Heat Fluxes ◽  
External Temperature ◽  
Building Wall ◽  
High Thermal Inertia

The thermal resistance of a wall can be readily measured in steady-state. However, such a state is seldomly achieved in a building because of the variation of outdoor conditions as well as the high thermal inertia of building materials. This paper introduces a novel active (dynamic) method to measure the thermal resistance of a building wall. Not only are active approaches less sensitive to external temperature variations, they also enable to perform measurements within only a few hours. In the proposed methodology, an artificial thermal load is applied to a wall (heating of the indoor air) and its thermal response is monitored. Inverse techniques are used with a reduced model to estimate the value of the thermal resistance of a wall from the measured temperatures and heat fluxes. The methodology was validated on a known load-bearing wall built inside a climate chamber. The results were in good agreement with reference values derived from a steady-state characterization of the wall. The method also demonstrated a good reproducibility.

Critical Heat Fluxes and Flow Patterns in High-Pressure Boiling Water Flows

1964 ◽  
Vol 86 (1) ◽  
pp. 12-22 ◽  
Author(s):  
F. E. Tippets
Keyword(s):  
Heat Flux ◽  
High Pressure ◽  
Critical Heat Flux ◽  
Rectangular Channel ◽  
Motion Pictures ◽  
Flow Patterns ◽  
Heat Fluxes ◽  
Boiling Water ◽  
Forced Flow ◽  
Flux Level

High-speed motion pictures (4300 pictures/sec) of boiling water flow patterns in conditions of forced flow at 1000 psia pressure in a vertical heated rectangular channel were taken over the range of mass velocities from 50 to 400 lb/sec-ft2, fluid states from bulk subcooled liquid flow to bulk boiling flow at 0.66 steam quality, and heat fluxes up to and including the critical heat flux level. Eighty critical heat flux determinations were made in the course of the experiment at 1000 psia in conditions of bulk boiling. The motion pictures provide photographic evidence of the general arrangement of the flow in conditions of bulk boiling at high pressure with heat fluxes near and including the critical heat flux level.

Enhancement of Critical Heat Flux From High Power Microelectronic Heat Sources in a Flow Channel

1990 ◽  
Vol 112 (3) ◽  
pp. 241-248 ◽  
Author(s):  
Issam Mudawar ◽  
Douglas E. Maddox
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Vertical Channel ◽  
Heat Fluxes ◽  
Semiempirical Model ◽  
High Profile ◽  
Low Profile ◽  
Pin Fins ◽  
Augmentation Techniques ◽  
Discrete Heat Source

Several surface augmentation techniques were examined in an investigation of enhancement of critical heat flux (CHF) from a simulated electronic chip to a fluorocarbon (FC-72) liquid in a vertical channel. A parametric comparison of boiling performances is presented for a smooth surface and for surfaces with low-profile microgrooves, low-profile microstuds, and high-profile pin fins. Critical heat fluxes as high as 361 W/cm2 were achieved using a combination of moderate flow velocity, high subcooling and surface enhancement. A semiempirical model constructed previously for CHF from a smooth discrete heat source to saturated or subcooled liquid flow, was found successful in correlating CHF data for the three enhanced surfaces.

Flammability Parameters of Materials: Ignition, Combustion, and Fire Propagation

1994 ◽  
Vol 12 (4) ◽  
pp. 329-356 ◽  
Author(s):  
A. Tewarson
Keyword(s):  
Heat Flux ◽  
Heat Release ◽  
Critical Heat Flux ◽  
Thermal Response ◽  
Fire Propagation ◽  
Flammability Parameters ◽  
Param Eters

In this paper, flammability parameters associated with the igni tion, combustion, and fire propagation processes and their usefulness for the development of fire resistant materials are discussed. The flammability param eters discussed are: (a) Critical Heat Flux (CHF) and Thermal Response Param eter (TRP), associated with ignition, (b) Heat Release Parameter (HRP) and Fire Propagation Index (FPI), associated with combustion and fire propagation.

Critical Heat Flux of R-123 in Silicon-Based Microchannels

2006 ◽  
Vol 129 (7) ◽  
pp. 844-851 ◽  
Author(s):  
Ali Koşar ◽  
Yoav Peles
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Heat Sink ◽  
Mass Velocity ◽  
Heat Fluxes ◽  
Microchannel Heat Sink ◽  
New Correlation ◽  
Mass Fluxes ◽  
System Pressure ◽  
Silicon Based

Critical heat flux (CHF) of R-123 in a silicon-based microchannel heat sink was investigated at exit pressures ranging from 227kPato520kPa. Critical heat flux data were obtained over effective heat fluxes ranging from 53W∕cm2to196W∕cm2 and mass fluxes from 291kg∕m2sto1118kg∕m2s. Flow images and high exit qualities suggest that dryout is the leading CHF mechanism. The effect of mass velocity, exit quality, and system pressure were also examined, and a new correlation is presented to represent the effect of these parameters.

Critical Heat Flux in Helically Coiled Tubes

1981 ◽  
Vol 103 (4) ◽  
pp. 660-666 ◽  
Author(s):  
M. K. Jensen ◽  
A. E. Bergles
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Velocity ◽  
High Heat ◽  
Heat Fluxes ◽  
Tube Diameter ◽  
Coiled Tube ◽  
Coil Diameter ◽  
The Difference

A study of boiling R-113 in electrically heated coils of various diameters is reported. Subcooled critical heat flux (CHF) is lower with coils than with straight tubes. The difference increases as mass velocity and ratio of tube diameter to coil diameter (d/D) increases. On the contrary, quality CHF is enhanced and increases with d/D; CHF initially increases with increasing mass velocity, but decreases after a maximum is reached. Operational problems, in particular upstream dryouts, can occur if a coiled tube is operated with low to moderate subcooling near the inlet and with moderately high heat fluxes.

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