Experimental Measurement of Heat Transfer to a Cylinder Immersed in a Large Aviation-Fuel Fire

1973 ◽  
Vol 95 (3) ◽  
pp. 397-404 ◽  
Author(s):  
L. H. Russell ◽  
J. A. Canfield
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Radiant Heat ◽  
Aviation Fuel ◽  
Temperature History ◽  
Cylinder Surface ◽  
Measured Temperature ◽  
Convection Coefficient ◽  
Transfer Parameters ◽  
Experimental Effort

Presented are the results of an experimental effort to quantify some of the heat transfer parameters pertaining to the luminous flame that results from the uncontrolled combustion of an 8-ft × 16-ft pool of JP-5 aviation fuel. The temperature and effective total radiant heat flux, both as temporal mean quantities, were measured as functions of position within the quasi-steady burning flame as it existed in a quiescent atmosphere. A grid of infrared radiometers and radiation-shielded thermocouples served as the primary sensing equipment. A determination was made of the perimeter-mean convection coefficient applicable to a horizontally oriented, smooth, 8.530-in-dia circular cylinder immersed at a particular location within the JP-5 flame. The value of this coefficient was the result of a solution to a nonlinear, inverse conduction problem in which the convective heat flux at the cylinder surface was estimated by utilizing a measured temperature history inside the cylinder. An expression relating this coefficient to more general flame/cylinder systems was developed.

A Historical Misperception on Calculating the Average Convection Coefficient in Tubes With Constant Wall Heat Flux

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Ted D. Bennett
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Exact Solutions ◽  
Wall Heat Flux ◽  
First Principle ◽  
Convection Coefficient ◽  
Parallel Plates ◽  
Historical Approach ◽  
First Principle Calculations ◽  
Constant Wall Heat Flux

The historical approach to averaging the convection coefficient in tubes of constant wall heat flux leads to quantitative errors in short tubes as high as 12.5% for convection into fully developed flows and 33.3% for convection into hydrodynamically developing flows. This mistake can be found in teaching texts and monographs on heat transfer, as well as in major handbooks. Using the correctly defined relationship between local and average convection coefficients, eight new correlations are presented for fully developed and developing flows in round tubes and between parallel plates for the constant wall heat flux condition. These new correlations are within 2% of exact solutions for fully developed flows and within 6% of first principle calculations for hydrodynamically developing flows.

Radiation Energy Density and Radiation Heat Flux in Small Rectangular Cavities

1972 ◽  
Vol 94 (3) ◽  
pp. 289-294 ◽  
Author(s):  
R. P. Caren
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Energy Density ◽  
Classical Theory ◽  
Radiant Energy ◽  
Radiation Energy ◽  
Radiant Heat ◽  
Radiant Heat Transfer ◽  
Radiation Heat ◽  
Radiation Energy Density

The present paper investigates the impact of one or more small cavity dimensions on the radiation energy density and radiation heat flux in rectangular metallic cavities. The emphasis of the present analysis is the exact treatment of the modal structure of the electromagnetic field in a small cavity in determining the properties of the thermal radiation field in the cavity. The excitation spectrum of the modes is assumed to be given by the Planck distribution function. The Poynting theorem is invoked in order to determine the radiative heat flux absorbed by the walls from the radiation in the cavity. Variation of the dimensions of the rectangular cavity allows the effects of cavity size and shape on the radiant energy density and radiant heat transfer to be assessed, particularly in several interesting limiting cases. It is found that significant deviations from the classical theory occur whenever any of the cavity dimensions satisfy the inequality lT ≤ 1 cm-deg K. It is further found that, when two or more of the cavity dimensions satisfy the above inequality, the radiant energy density and radiant heat transfer are significantly reduced in comparison to the results of classical theory. However, when only one dimension is limited, as in the case of a closely spaced parallel-surface geometry, the radiant energy density and radiant heat transfer are significantly increased compared to the classical theory.

Optimizing Laminar Natural Convection for a Heat Generating Cylinder in a Channel

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Corey E. Clifford ◽  
Mark L. Kimber
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Spent Nuclear Fuel ◽  
Reactor Core ◽  
Horizontal Cylinder ◽  
Cylinder Surface ◽  
Transfer Program ◽  
Wet Storage

Natural convection heat transfer from a horizontal cylinder is of importance in a large number of applications. Although the topic has a rich history for unconfined cylinders, maximizing the free convective cooling through the introduction of sidewalls and creation of a chimney effect is considerably less studied. In this investigation, a numerical model of a heated horizontal cylinder confined between two vertical adiabatic walls is employed to evaluate the natural convective heat transfer. Two different treatments of the cylinder surface are investigated: constant temperature (isothermal) and constant surface heat flux (isoflux). To quantify the effect of wall distance on the effective heat transfer from the cylinder surface, 18 different confinement ratios are selected in varying increments from 1.125 to 18.0. All of these geometrical configurations are evaluated at seven distinct Rayleigh numbers ranging from 102 to 105. Maximum values of the surface-averaged Nusselt number are observed at an optimum confinement ratio for each analyzed Rayleigh number. Relative to the “pseudo-unconfined” cylinder at the largest confinement ratio, a 74.2% improvement in the heat transfer from an isothermal cylinder surface is observed at the optimum wall spacing for the highest analyzed Rayleigh number. An analogous improvement of 60.9% is determined for the same conditions with a constant heat flux surface. Several correlations are proposed to evaluate the optimal confinement ratio and the effective rate of heat transfer at that optimal confinement level for both thermal boundary conditions. One of the main application targets for this work is spent nuclear fuel, which after removal from the reactor core is placed in wet storage and then later transferred to cylindrical dry storage canisters. In light of enhanced safety, many are proposing to decrease the amount of time the fuel spends in wet storage conditions. The current study helps to establish a fundamental understanding of the buoyancy-induced flows around these dry cask storage canisters to address the anticipated needs from an accelerated fuel transfer program.

Approach to Heat Transfer Mechanism Beneath Boiling Bubble With MEMS Sensor

2009 ◽  
Author(s):  
Tomohide Yabuki ◽  
Osamu Nakabeppu
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Heat Flux ◽  
Heated Surface ◽  
Bubble Nucleation ◽  
Temperature Data ◽  
Heated Wall ◽  
Measured Temperature ◽  
Back Side ◽  
Mems Sensor

Temperature variation beneath isolated bubble during saturated boiling of water was measured with a MEMS (Micro-Electro-Mechanical Systems) sensor having high temporal and spatial resolution. Then, local heat transfer from the heated surface was evaluated by a transient heat conduction analysis of the wall with measured temperature data as a boundary condition. The MEMS sensor on a 20 × 20 mm2 silicon substrate includes an electrolysis trigger and eight thin film thermocouples on the top side, and two thin film heaters on the back side. The thin film thermocouple was calibrated with a thermal scan method using two alloy samples with different melting point. The condition of the sensor was smoothly controlled with the heater. The bubble is initiated with electrolysis at a gap of the trigger electrode, where slight hydrogen gasses are supplied as bubble nuclei. Then, local and fast temperature variations in wide region are measured with the thermocouples with cutoff frequency of 100 kHz arranged in a line at 40 – 2000 μm far from the trigger gap. Measured temperature data presents formation of microlayer and expansion of dryout area in bubble growth process and rewetting in bubble departure process. The numerical analysis showed that average heat flux beneath the bubble indicated the maximum value of 19 W/cm2 during the microlayer evaporation, and then after hitting a bottom slightly lower than a heat flux at the bubble nucleation, recovers to the nucleation level. The contribution of the heat transfer from the heated wall was evaluated to approximately one-fourth of latent heat in the bubble at departure.

scholarly journals Наножидкости для энергетики: механизм влияния диспергентов на тепловые параметры и кризисные явления при кипении

2020 ◽  
Vol 90 (2) ◽  
pp. 175
Author(s):  
В.Н. Морару ◽  
Б.И. Бондаренко ◽  
С.В. Сидоренко ◽  
Д.В. Комыш
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Direct Current ◽  
Sedimentation Stability ◽  
Boiling Crisis ◽  
Transfer Parameters ◽  
The Heat Transfer Coefficient

Abstract: The effect of dispersants organic (CTAB) and inorganic nature (sodium pyrophosphate and sodium silicate) on the critical heat flux (CHF) and heat-transfer coefficient (HTC) of boiling various aqueous nanofluids (NFs) under conditions of free convection is studied. It has been established that the addition of ionic dispersants to aluminosilicate NFs, increasing their aggregative and sedimentation stability, as a rule, worsens their heat-transfer parameters during boiling, causing a sudden pre-crisis heater burnout in a test unit powered by direct current. The mechanism of the phenomenon is revealed. On the contrary, the addition of dispersants and surfactants to carbon-containing NFs with high thermal conductivity, improving their stability, at the same time increases the heat transfer coefficient during boiling of NFs, but also cause pre-crisis heater burnout in the case of direct current heating. The effect of dispersants on crisis phenomena during boiling of water and NFs is analyzed and the causes of sudden pre-crisis heater burnout have been elucidated. Several mechanisms have been proposed for interpreting the observed effects, from which the expediency of using alternating heating current and non-ionic, non-foaming surfactants and dispersants to avoid an early onset of the boiling crisis in order to achieve higher values of the critical heat flux and the heat transfer coefficient during the NFs boiling.

Optimization of Confined Laminar Natural Convection for Dry Cask Storage Systems

2014 ◽  
Author(s):  
Corey E. Clifford ◽  
Mark L. Kimber
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Rayleigh Number ◽  
Effective Rate ◽  
Horizontal Cylinder ◽  
Constant Heat Flux ◽  
Thermal Capacity ◽  
Cylinder Surface ◽  
Transfer Program ◽  
Dry Storage

Although high-density pool storage provides an acceptable method for housing used fuel elements, a number of concerns have triggered a call for the reduction of current inventories by mandating a maximum permissible time in which assemblies may be placed in wet storage before transfer to passive, dry storage conditions. In anticipation of an accelerated fuel transfer program, the principal goal of this investigation is to develop a fundamental understanding of the physics associated with the buoyancy-induced flow around dry casks in an effort to improve the heat rejection capability of the overall system. The aim of this research initiative is to minimize the amount of active pool cooling necessary by maximizing the thermal capacity of dry storage casks. A simplified geometry of a heated horizontal cylinder confined between two, vertical adiabatic walls is employed to evaluate the coupled heat and mass transfer. Two different treatments of the cylinder surface are investigated: constant temperature (isothermal) and constant surface heat flux (isoflux). To quantify the effect of wall distance on the effective heat transfer from the cylinder surface, 18 different confinement ratios are selected in varying increments from 1.125 to 18.0. Each of these geometrical configurations are evaluated at seven distinct Rayleigh numbers ranging from 102 to 105. Maximum values of the surface-averaged Nusselt number are observed at an optimum confinement ratio for each analyzed Rayleigh number. Relative to the pseudo-unconfined cylinder at the largest confinement ratio, a 54.2% improvement in the heat transfer from an isothermal cylinder surface is observed at the optimum wall spacing for the highest analyzed Rayleigh number. An analogous improvement of 46.6% is determined for the same conditions with a constant heat flux surface. Several correlations are proposed to evaluate the optimal confinement ratio and the effective rate of heat transfer at that optimal confinement level for both thermal boundary conditions.

scholarly journals High Pressure Turbine Vane Annular Cascade Heat Flux and Aerodynamic Measurements With Comparisons to Predictions

1998 ◽  
Author(s):  
Christopher R. Joe ◽  
Xavier A. Montesdeoca ◽  
Friedrich O. Soechting ◽  
Charles D. MacArthur ◽  
Matthew Meininger
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Pressure ◽  
Heat Loss ◽  
Short Duration ◽  
Wall Temperature ◽  
Measured Temperature ◽  
Unique Contribution ◽  
Pressure Measurements ◽  
High Pressure Turbine

Experimental tests were performed at the USAF Turbine Research Facility (TRF) to obtain heat transfer and aerodynamic data on a first stage vane of a modern high pressure turbine. This is a transient blowdown facility that provides data from short duration tests. Data for a matrix of test conditions were obtained to document the effect of inlet Reynolds number, the stage pressure ratio across the vane, and the gas-to-wall temperature ratio. The objectives of these tests were to assess the capability of obtaining accurate aerodynamic total pressure loss measurements and airfoil static pressure measurements as well as determine the heat transfer coefficient distributions on the vanes. Results from these tests were compared to analytical predictions and are presented. The unique contribution of the work presented herein is: 1) demonstration of circumferential traversing temperature and pressure data in a short duration facility test, and 2) heat loss closure during a short duration test using heat flux gauges and the measured temperature loss. The transient heat loss during a short duration test is a fundamental requirement to determine turbine efficiency when work extraction is determined from the temperature drop across the turbine stage. Heat transfer data were acquired from heat flux gauges that were fabricated using thin-film sputtering techniques and placed on the airfoil surfaces. The surface temperature of the gauge was measured and heat flux was determined from a closed form transient semi-infinite solution that included the resistance of the heat flux gauge and the underlying metal substrate. Circumferentially, pressure measurements were obtained on the airfoil surfaces and on traversing rakes at the inlet and exit of the vane test section. Total and differential pressure rake instrumentation was required to obtain accurate aerodynamic loss measurements over a range of gas-to-wall temperature ratios.

scholarly journals Effect of concentric and eccentric porous layer on forced convection heat transfer and fluid flow around a solid cylinder

2021 ◽  
Author(s):  
Alireza Alinezhad ◽  
Ataallah Soltani Goharrizi ◽  
Ataallah Kamyabi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Porous Layer ◽  
Darcy Number ◽  
Local Thermal Equilibrium ◽  
Cylinder Surface ◽  
Solid Cylinder ◽  
Number Range

Abstract In this paper, heat transfer and fluid flow around a solid cylinder wrapped with a porous layer in the channel were studied numerically by computational fluid dynamics (CFD). The homogeneous concentric and eccentric porous medium round a rigid, solid cylinder are supposed at local thermal equilibrium. The transport phenomena within the porous layer, volume averaged equations were employed, however the conservation laws of mass, momentum and energy were applied in the channel. This current numerical analysis, the effects of eccentricity ( ), the variable diameter of porous layer (d=0.07,0.08,0.09), permeability, as well as the different Reynolds number and Darcy number on the heat transfer parameters and fluid flow was investigated. The main purpose of this study is analyzed and compared the heat flux of concentric and eccentric porous layer in Reynolds number range of 1 to 40 and Darcy numbers of to . It is found that with the decline of Darcy number, the vortex length is increased behind the solid cylinder surface. In addition, the heat flux rate of the cylinder is raised with the increase of Reynolds number. Finally, The results have demonstrated that with raising Reynolds and Darcy numbers, the increase of the average Nusselt numbers in the eccentric porous layer is higher than the concentric porous layer.

Tool Heat Fluxes During Cutting of A360 Using Beck’s Method

2009 ◽  
Author(s):  
Sean C. McCarty ◽  
Keith A. Woodbury ◽  
Y. Kevin Chou
Keyword(s):  
Heat Flux ◽  
Temperature Response ◽  
Heat Fluxes ◽  
Temperature History ◽  
Measured Temperature ◽  
Detailed Model ◽  
Sensitivity Coefficients ◽  
Metal Chips ◽  
Cutting Zone ◽  
Mechanical Cutting

The energy released during mechanical cutting is carried away by the metal chips and conduction into the tool. This report focuses on determination of the heat fluxes into the tool during cutting using Beck’s method. A small thermocouple is used to measure the temperature rise on the surface of a cutting tool during turning of aluminum A360 cylinders. A detailed model of the tool in FLUENT is used to compute the sensitivity coefficients for the temperature response at the sensor location due to a unit heat flux disturbance at the cutting zone. These sensitivity coefficients are used in Beck’s method along with the measured temperature history, to determine the heat flux history at the cutting zone.

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