Considerations in Predicting Burnout of Cylinders in Flow Boiling

1992 ◽  
Vol 114 (1) ◽  
pp. 185-193 ◽  
Author(s):  
P. Sadasivan ◽  
J. H. Lienhard
Keyword(s):  
Heat Flux ◽  
Temperature Distribution ◽  
Surface Temperature ◽  
Flow Boiling ◽  
Heater Surface ◽  
Near Surface ◽  
Surface Temperature Distribution ◽  
Peak Heat Flux ◽  
Far Wake ◽  
Gravity Surface

Previous investigations of the critical heat flux in flow boiling have resulted in widely different hydrodynamic mechanisms for the occurrence of burnout. Results of the present study indicate that existing models are not completely realistic representations of the process. The present study sorts out the influences of the far-wake bubble breakoff and vapor sheet characteristics, gravity, surface wettability, and heater surface temperature distribution on the peak heat flux in flow boiling on cylindrical heaters. The results indicate that burnout is dictated by near-surface effects. The controlling factor appears to be the vapor escape pattern close to the heater surface. It is also shown that a deficiency of liquid at the downstream end of the heater surface is not the cause of burnout.

scholarly journals Thermal conductivity of porous ice in hailstone shells

1996 ◽  
Vol 42 (141) ◽  
pp. 195-200
Author(s):  
Guoguang Zheng ◽  
Roland List
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Temperature Distribution ◽  
Surface Temperature ◽  
Linear Dependence ◽  
Internal Heat ◽  
Density Range ◽  
Surface Temperature Distribution ◽  
Temperature Distributions ◽  
Evolving Surface

AbstractThe thermal conductivity and diffusivity of porous ice accreted on spherical and spheroidal hailstone models were measured over a density range of 620–915 kg m−3. By scanning the evolving surface temperature distributions during cooling in a cold airflow the thermal conductivity was varied in iterative fashion until the internal heat flux produced the correct surface temperature distribution. The results indicate a linear dependence of the thermal conductivity,ki, and diffusivity,αi, on density. For example, lowering the density by 10% lowerskiby 15%. Within the range of cloud conditions, the density variations affect the thermal parameters more than temperature does. The results also indicate a continuous decrease of the thermal conductivity from bulk ice via consolidated porous ice to loosely packed snow.

scholarly journals A new method to predict temperature distribution on a tube at constant heat flux

2021 ◽  
Vol 11 (5) ◽  
pp. 363-372
Author(s):  
Ali Habeeb Askar ◽  
Hazim Albedran ◽  
Endre Kovács ◽  
Károly Jármai
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Temperature Distribution ◽  
Surface Temperature ◽  
Optimization Algorithm ◽  
Linear Interpolation ◽  
Electric Heater ◽  
Spline Curve ◽  
Surface Temperature Distribution ◽  
Cubic Spline Curve

Surface temperature distribution on a tube is one of the main factors affecting the calculation of the heat transfer coefficient calculation. When an electric heater heats the tube, a magnetic flux is generated that affects the thermocouples readings; therefore, an efficient fitting technique is needed to represent these readings. This work proposes an interpolated spline method to mathematically represent experimental data of a thermal distribution on a tube with heat flux. Linear regression was compared with a double linear interpolation process with an optimization algorithm and cubic spline curve method on the proposed problem. The results show that the interpolated experimental data can highly improve the regression of the spline curve. Consequently, an interpolated spline curve gives better surface temperature distribution and better estimation for the average temperature. The interpolated points on spline segments are chosen by an optimization algorithm, which is particle swarm optimization, in a way that provides more minor errors.

Subcooled Flow Boiling Heat Transfer of Nanofluids in a Microchannel

2009 ◽  
Author(s):  
Saeid Vafaei ◽  
Dongsheng Wen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Temperature Distribution ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Subcooled Boiling ◽  
Subcooled Flow Boiling ◽  
Surface Temperature Distribution ◽  
Subcooled Flow ◽  
Flow Boiling Heat Transfer

This work investigates the subcooled flow boiling of aqueous based nanofluids in a 510 μm single microchannel with a focus on the effect of nanoparticles on the critical heat flux (CHF). The surface temperature distribution along the pipe, the inlet and outlet pressures and temperatures are measured simultaneously for different concentrations of alumina nanofluids and dionized water. The experiment shows a remarkable increase ∼ 31% in the CHF under very low nanoparticle concentrations (∼0.1v%) and a nonlinear influence of nanoparticles on the subcooled boiling heat transfer.

The Influence of Plasma Arc Behavior on Ingot Top Surface Temperature Distribution during PAM Process

2013 ◽  
Vol 709 ◽  
pp. 313-319 ◽  
Author(s):  
Hai Song Li ◽  
Hong Chao Kou ◽  
Feng Xu ◽  
Hui Chang
Keyword(s):  
Heat Flux ◽  
Temperature Distribution ◽  
Surface Temperature ◽  
Element Model ◽  
Plasma Arc ◽  
Temperature Changes ◽  
Surface Temperature Distribution ◽  
Regional Center ◽  
Arc Behavior ◽  
Arc Heating

A 3D finite element model was established to simulate the top surface temperature evolution of Ti45Al8Nb (at.%) alloy ingot under the effect of plasma arc behavior during plasma arc cold hearth melting (PAM) process. According to the model, the top surface temperature distribution and its evolution was analyzed under different heat flux densities. Simulation results show that the position of maximum top surface temperature changes with plasma arc motion, and always located in the plasma arc heating regional center, and it increases first with time elapse and then decreases in the rest of time within one cycle. The results also show that the top surface temperature is increased with the increase in heat flux densities, but the extent is not significant, and meanwhile the temperature distribution is more non-uniform and temperature gradient is greater with the increase in heat flux densities.

Thermal conductivity of porous ice in hailstone shells

1996 ◽  
Vol 42 (141) ◽  
pp. 195-200
Author(s):  
Guoguang Zheng ◽  
Roland List
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Temperature Distribution ◽  
Surface Temperature ◽  
Linear Dependence ◽  
Internal Heat ◽  
Density Range ◽  
Surface Temperature Distribution ◽  
Temperature Distributions ◽  
Evolving Surface

AbstractThe thermal conductivity and diffusivity of porous ice accreted on spherical and spheroidal hailstone models were measured over a density range of 620–915 kg m−3. By scanning the evolving surface temperature distributions during cooling in a cold airflow the thermal conductivity was varied in iterative fashion until the internal heat flux produced the correct surface temperature distribution. The results indicate a linear dependence of the thermal conductivity, ki, and diffusivity, αi, on density. For example, lowering the density by 10% lowers ki by 15%. Within the range of cloud conditions, the density variations affect the thermal parameters more than temperature does. The results also indicate a continuous decrease of the thermal conductivity from bulk ice via consolidated porous ice to loosely packed snow.

scholarly journals Relative Role of Turbulent and Radiative Flux on the Near-Surface Temperature in a Single-Layer Urban Canopy Model over Houston

2017 ◽  
Vol 56 (8) ◽  
pp. 2173-2187 ◽  
Author(s):  
James Brownlee ◽  
Pallav Ray ◽  
Mukul Tewari ◽  
Haochen Tan
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Single Layer ◽  
Urban Canopy ◽  
Heat Fluxes ◽  
Radiative Flux ◽  
Hydrological Processes ◽  
Urban Canopy Model ◽  
Near Surface ◽  
Canopy Model

AbstractNumerical simulations without hydrological processes tend to overestimate the near-surface temperatures over urban areas. This is presumably due to underestimation of surface latent heat flux. To test this hypothesis, the existing single-layer urban canopy model (SLUCM) within the Weather Research and Forecasting Model is evaluated over Houston, Texas. Three simulations were conducted during 24–26 August 2000. The simulations include the use of the default “BULK” urban scheme, the SLUCM without hydrological processes, and the SLUCM with hydrological processes. The results show that the BULK scheme was least accurate, and it overestimated the near-surface temperatures and winds over the urban regions. In the presence of urban hydrological processes, the SLUCM underestimates these parameters. An analysis of the surface heat fluxes suggests that the error in the BULK scheme is due to a lack of moisture at the urban surface, whereas the error in the SLUCM with hydrological processes is due to increases in moisture at the urban surface. These results confirm earlier studies in which changes in near-surface temperature were primarily due to the changes in the turbulent (latent and sensible heat) fluxes in the presence of hydrological processes. The contribution from radiative flux was about one-third of that from turbulent flux. In the absence of hydrological processes, however, the results indicate that the changes in radiative flux contribute more to the near-surface temperature changes than the turbulent heat flux. The implications of these results are discussed.

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