scholarly journals Review on the Surface Heat Transfer Coefficients of Radiant Systems

2019 ◽  
Vol 111 ◽  
pp. 01075 ◽  
Author(s):  
Jun Shinoda ◽  
Ongun B. Kazanci ◽  
Shin-ichi Tanabe ◽  
Bjarne W. Olesen
Keyword(s):  
Heat Transfer ◽  
Heated Surface ◽  
Measurement Data ◽  
Radiant Heat ◽  
Surface Measurement ◽  
Radiant Heat Transfer ◽  
Extensive Literature ◽  
Prediction Errors ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Heat transfer coefficients are often used to describe the thermal behaviour of radiant systems and how it transfers heat between the cooled/heated surface and the room. In addition to current standards, numerous studies have been conducted to obtain the heat transfer coefficients through experiments and simulations. However, inconsistency is evident in the values or expressions suggested. Thus, this study investigated possible sources of discrepancy through an extensive literature review on articles and standards that focused on the heat transfer coefficients at the cooled/heated surface. Measurement data provided by different authors were extracted to compare both the amount of heat transfer and the actual heat transfer coefficients. Consequently, suggested values and expressions were used to predict the measurement data in other articles to examine their accuracy. Comparison of the results showed that the radiant heat transfer coefficients had a consistent value throughout the literature and had prediction error within ±20%. However, larger deviations and prediction errors were seen in the total and convective heat transfer. It was suggested that some of the sources of error may have been the calculation procedure of each heat transfer mechanism, choice of reference temperature and its measurement height/position, and room dimensions.

scholarly journals The study of spray impact on the heated sapphire plate

2021 ◽  
Vol 2119 (1) ◽  
pp. 012172
Author(s):  
T G Gigola ◽  
V V Cheverda
Keyword(s):  
Heat Transfer ◽  
Sapphire Substrate ◽  
Substrate Surface ◽  
Heated Surface ◽  
Local Heat ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Liquid Spray ◽  
Sapphire Plate

Abstract The process of the liquid spray impact on the heated surface is studied experimentally using the IR-transparent sapphire plate method. The spatiotemporal distribution of the temperature field on the sapphire substrate surface during impacting spray is received. The obtained experimental data are an important step in a study of the local characteristics of heat transfer in the areas of the contact lines during liquid spray impact on the heated surface. Further, the local heat fluxes and heat transfer coefficients will be determined by solving the problem of thermal conductivity in the sapphire substrate.

1987 Max Jakob Memorial Award Lecture: Dynamics and Stability of Thin Heated Liquid Films

1990 ◽  
Vol 112 (3) ◽  
pp. 538-546 ◽  
Author(s):  
S. G. Bankoff
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Heated Surface ◽  
Nucleate Boiling ◽  
Liquid Films ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Molecular Forces ◽  
Memorial Award ◽  
Film Heat Transfer

This review covers the dynamics and tendency toward rupture of thin evaporating liquid films on a heated surface. Very large heat transfer coefficients can be obtained. The applications include various boiling heat transfer and film cooling devices. A relatively new area for study is heat transfer through ultrathin films, which are less than 100 nm in thickness, and hence subject to van der Waals and other long-range molecular forces. Some recent work employing lubrication theory to obtain an evolution equation for the growth of a surface wave is described. Earlier phenomenological work is briefly discussed, as well as the connection between forced-convection subcooled nucleate boiling and thin-film heat transfer.

Design of an axially concave pad profile for a large turbine tilting-pad bearing

2016 ◽  
Vol 231 (4) ◽  
pp. 479-488 ◽  
Author(s):  
Sebastian Kukla ◽  
Nico Buchhorn ◽  
Beate Bender
Keyword(s):  
Heat Transfer ◽  
Film Thickness ◽  
Load Capacity ◽  
Measurement Data ◽  
Tangential Direction ◽  
Measured Temperature ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Tilting Pad ◽  
Calculation Results

To improve operational safety and/or achieve a higher load capacity of turbine tilting-pad bearings, an axially concave pad profile is presented. The thermal and mechanical stress of the loaded pads of a test bearing in load between pivot configuration has been analysed. Both film thickness and pressure distribution have been measured at a very high resolution. A fluid film calculation program in combination with a finite-volume-based structural mechanics program is used to simulate the deformation of a single pad under high circumferential speeds. In this context, the axial and tangential heat transfer coefficients of the pad surface, which act as boundary conditions for the calculation of the 3D temperature distribution, are determined using an optimization process. Herein, the match of predicted and measured pad temperatures is the goal. It can be shown that there must be a huge difference in heat transfer in axial and tangential direction in order to match the large measured temperature gradient in circumferential direction. Based on the measured deformed profile the program code is used to derive a concave pad profile, which will result in an axially non-arched sliding surface under the expected thermal load. Therefore, an iterative simulation procedure is used. By decreasing the axial arching of the pad and thus the large film thickness at the axial ends using an improved profile designed for a specific operation point, the minimum film thickness and maximum pad temperature can be influenced beneficially. The comparison of measurement data and calculation results shows very good agreement regarding the pad deformations. The results indicate that by axially concave profiling of the loaded pads of a large tilting-pad bearing for a specific operation point, the static characteristics in the form of temperature, film thickness and load capacity can be improved.

Experimental Study of Thermal Performance of Nanofluids During Flow in Microchannels Using Surface Temperature-Nano-Sensors

2011 ◽  
Author(s):  
Seok-Won Kang ◽  
Saeil Jeon ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Soft Lithography ◽  
Rectangular Cross Section ◽  
Critical Concentration ◽  
Heated Surface ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Micro Channels ◽  
Nano Sensors

The thermal performance of nanofluids in microchannel of rectangular cross-section was experimentally investigated in this study. In the previous studies, a threshold nanoparticle concentration exists where the critical concentration separates the heat transfer performance of the nanofluid during a flow through microchannels. Thus, the emphasis of our study is to find the optimum concentration value of nanoparticles for enhancing the forced convective heat transfer coefficients. In this study, thin-film thermocouple array (TFTA) of K-Type (Chromel/ Alumel) was employed to measure the temperature profile on the heated surface in the microchannel (while the top and wall was sufficiently insulated). The TFTA deposited on a silicon wafer is bonded with a polymer substrate containing the molded microchannel. The microchannel was made using the Poly Di-Methyl Siloxane (PDMS). The mold for the microchannel in order to cure the PDMS onto it was fabricated using soft-lithography technique on an atomically stable silicon substrate. To assess the thermal performance of nanofluids in micro-channels, the temperature profiles in the heated bottom wall of the micro-channel was monitored using the TFTA which was then used to estimate the wall heat flux values. The concentration and size of the silica nanoparticles in the aqueous nanofluids are parametrically varied in this study (e.g. at weight concentrations of 0.5%, 0.1% and 0.2%). These parametric experiments were performed by varying the wall temperatures (e.g. 30, 50 and 70 °C) and flow rates (e.g. 5, 7 and 9 μl/min).

Inverse Determination of Steady Heat Convection Coefficient Distributions

1998 ◽  
Vol 120 (2) ◽  
pp. 328-334 ◽  
Author(s):  
T. J. Martin ◽  
G. S. Dulikravich
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Boundary Conditions ◽  
Measurement Data ◽  
Cost Effective ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Simple Modification ◽  
Heat Transfer Coefficients ◽  
Thermal Boundary Conditions

An inverse Boundary Element Method (BEM) procedure has been used to determine unknown heat transfer coefficients on surfaces of arbitrarily shaped solids. The procedure is noniterative and cost effective, involving only a simple modification to any existing steady-state heat conduction BEM algorithm. Its main advantage is that this method does not require any knowledge of, or solution to, the fluid flow field. Thermal boundary conditions can be prescribed on only part of the boundary of the solid object, while the heat transfer coefficients on boundaries exposed to a moving fluid can be partially or entirely unknown. Over-specified boundary conditions or internal temperature measurements on other, more accessible boundaries are required in order to compensate for the unknown conditions. An ill-conditioned matrix results from the inverse BEM formulation, which must be properly inverted to obtain the solution to the ill-posed problem. Accuracy of numerical results has been demonstrated for several steady two-dimensional heat conduction problems including sensitivity of the algorithm to errors in the measurement data of surface temperatures and heat fluxes.

Water Droplet Vaporization on Superhydrophilic Nanostructured Surfaces at High and Low Superheat

2014 ◽  
Author(s):  
Jorge Padilla ◽  
Van P. Carey
Keyword(s):  
Heat Transfer ◽  
Water Droplet ◽  
Heated Surface ◽  
Thin Liquid Film ◽  
Contact Angles ◽  
Bubble Nucleation ◽  
Transfer Coefficients ◽  
Droplet Vaporization ◽  
Heat Transfer Coefficients ◽  
Low Superheat

This paper summarizes results of an experimental exploration of heat transfer during vaporization of a water droplet deposited on a superhydrophilic nanostructured surface at high and low superheat conditions. The superhydrophilic surface is composed of a vast array of zinc oxide (ZnO) nanostructures grown by hydrothermal synthesis on a smooth copper substrate. The individual nanostructures are randomly-oriented and have a mean diameter of about 400 nm, a mean length of 2 μm and a mean centerline spacing of about 700 nm. The macroscopic wetting characteristics of the surface were measured and scanning electron microscope imaging was used to document the nanoscale features of the surface before and after the experiments. These surfaces typically exhibited water contact angles less than 5 degrees. In single droplet deposition experiments at atmospheric pressure, a high-speed video camera was used to document the droplet-surface interaction, and the heat transfer coefficients were simultaneously determined from thermal measurements in the test apparatus. At low superheat levels (10–20°C), droplets spread rapidly over the heated surface when deposited. For these conditions, no bubble nucleation was observed, and we nevertheless observed extremely high heat transfer coefficients resulting from rapid evaporation of the thin liquid film formed by the spreading droplet. At high wall superheat levels, the vaporization process exhibited Leidenfrost droplet vaporization. The extreme wetting for these surfaces resulted in extremely high Leidenfrost transition temperatures. The results document a trend of increasing Leidenfrost temperature with decreasing contact angle, which is consistent with earlier studies. The results of this study are compared with early work in this area and the implications for applications are discussed.

The use of heat transfer coefficients in estimating sensible heat loss from the pig

1977 ◽  
Vol 25 (3) ◽  
pp. 271-279 ◽  
Author(s):  
L. E. Mount
Keyword(s):  
Heat Transfer ◽  
Body Weight ◽  
Heat Loss ◽  
Radiant Heat ◽  
Heat Losses ◽  
Sensible Heat ◽  
Transfer Coefficients ◽  
Wind Speeds ◽  
Heat Transfer Coefficients ◽  
Environmental Temperatures

SUMMARYHeat transfer coefficients are used to calculate convective and radiant heat losses from pigs of 4, 20 and 60 kg body weight at 20 and 30 °C environmental temperatures for different wind speeds. Comparisons with heat losses estimated from whole-animal calorimetry suggest that calculations with heat transfer coefficients can lead to useful approximate estimates of heat loss from the pig.

Heat Transfer Coefficients and Dynamical Thermal Models for Variable Flow Rates in Pipes and Ducts

2013 ◽  
Vol 291-294 ◽  
pp. 1760-1771
Author(s):  
Bjørn R Sørensen
Keyword(s):  
Heat Transfer ◽  
Heat Loss ◽  
Dynamic Performance ◽  
Measurement Data ◽  
Transfer Coefficients ◽  
Flow Rates ◽  
Variable Flow ◽  
Thermal Models ◽  
Heat Transfer Coefficients ◽  
Ventilation Ducts

This study presents thermal models of pipes or ventilation ducts with variable flow rates. The models are based on dynamic thermodynamic heat balances, and much attention has been put into developing accurate heat transfer coefficients. MATLAB/Simulink environment has been used for modeling, but the model is however universal and can be implemented into any software. The model has been validated against measurement data, and found to be quite accurate for use in typical HVAC applications. Accuracy is particularly good if taking thermal damping into account. Thermal damping of pipe or duct mass has shown to be significant for dynamic performance. The model is suited for control simulations or accurate heat loss simulations, where dynamic conditions are important.

Buoyant Convection in Superposed Metal Foam and Water Layers

2008 ◽  
Author(s):  
V. Kathare ◽  
F. A. Kulacki ◽  
Jane H. Davidson
Keyword(s):  
Heat Transfer ◽  
Metal Foam ◽  
Heated Surface ◽  
Transfer System ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Water Layers ◽  
Heat Transfer System ◽  
Vertical Cavity

Experiments on natural convection in superposed metal foam and water layers are reported. The heat transfer system comprises a vertical cavity heated from below and held at constant temperature at the top. Two systems are considered: a water-filled cavity with a foam layer on the heated surface and a water-filled cavity with foam layers on the upper and lower surfaces. The present experiments use open cell copper foams with a nominal porosity of 92%, and the relative thicknesses of the water and foam layers are varied. Steady state Nusselt numbers show the presence of foam on the boundaries enhances overall heat transfer coefficients over that for the water-only layer. Enhancement of overall Nusselt numbers varies from 12 to 60% depending on Rayleigh number. Sub-layer configurations with foam on both heat transfer surfaces are more effective for enhancement than a configuration with foam only on the heated surface.

Microjet Impingement Cooling With Phase Change

2004 ◽  
Author(s):  
Evelyn N. Wang ◽  
Juan G. Santiago ◽  
Kenneth E. Goodson ◽  
Thomas W. Kenny
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Heated Surface ◽  
Heat Removal ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Impingement Cooling ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Wall Superheat

The large heat generation rates in contemporary microprocessors require new thermal management solutions. Two-phase microjet impingement cooling promises high heat transfer coefficients and effective cooling of hotspots. We have fabricated integrated microjet structures with heaters and temperature sensors to study local heat transfer at the impingement surface of a confined microjet. Circular jets with diameters less than 100 μm are machined in glass. Preliminary temperature measurements (for Rej = 100–500) suggest that heat transfer coefficients of 1000 W/m2C close to the jet stagnation zone can be achieved. As the flowrate of the jet is increased, a tradeoff in heat removal capability and wall superheat is observed. To aid in understanding the mechanism for wall superheat during boiling at the heated surface, the devices allow for optical access through the top of the device. However, the formation of vapor from the top reservoir makes visualization difficult. This study aids in the design of microjet heat sinks used for integration into a closed-loop cooling system.

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