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).

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.

Comparison of 30 Boiling and Condensation Correlations for Two-Phase Flows in Compact Plate-Fin Heat Exchangers

2017 ◽  
Author(s):  
Wenhai Li ◽  
Ken Alabi ◽  
Foluso Ladeinde
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Flow Boiling ◽  
Transfer Coefficients ◽  
Two Phase Flows ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Heat Exchanger Design ◽  
Micro Channels ◽  
Vertical Tubes

Over the years, empirical correlations have been developed for predicting saturated flow boiling [1–15] and condensation [16–30] heat transfer coefficients inside horizontal/vertical tubes or micro-channels. In the present work, we have examined 30 of these models, and modified many of them for use in compact plate-fin heat exchangers. However, the various correlations, which have been developed for pipes and ducts, have been modified in our work to make them applicable to extended fin surfaces. The various correlations have been used in a low-order, one-dimensional, finite-volume type numerical integration of the flow and heat transfer equations in heat exchangers. The NIST’s REFPROP database [31] is used to account for the large variations in the fluid thermo-physical properties during phase change. The numerical results are compared with Yara’s experimental data [32]. The validity of the various boiling and condensation models for a real plate-fin heat exchanger design is discussed. The results show that some of the modified boiling and condensation correlations can provide acceptable prediction of heat transfer coefficient for two-phase flows in compact plate-fin heat exchangers.

An Experimental Investigation of the Rib Surface-Averaged Heat Transfer Coefficient in a Rib-Roughened Square Passage

1997 ◽  
Vol 119 (2) ◽  
pp. 381-389 ◽  
Author(s):  
M. E. Taslim ◽  
C. M. Wadsworth
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Performance ◽  
Blockage Ratio ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Average Heat ◽  
Heat Transfer Coefficients ◽  
The Heat Transfer Coefficient

Turbine blade cooling, a common practice in modern aircraft engines, is accomplished, among other methods, by passing the cooling air through an often serpentine passage in the core of the blade. Furthermore, to enhance the heat transfer coefficient, these passages are roughened with rib-shaped turbulence promoters (turbulators). Considerable data are available on the heat transfer coefficient on the passage surface between the ribs. However, the heat transfer coefficients on the surface of the ribs themselves have not been investigated to the same extent. In small aircraft engines with small cooling passages and relatively large ribs, the rib surfaces comprise a large portion of the passage heat transfer area. Therefore, an accurate account of the heat transfer coefficient on the rib surfaces is critical in the overall design of the blade cooling system. The objective of this experimental investigation was to conduct a series of 13 tests to measure the rib surface-averaged heat transfer coefficient, hrib, in a square duct roughened with staggered 90 deg ribs. To investigate the effects that blockage ratio, e/Dh and pitch-to-height ratio, S/e, have on hrib and passage friction factor, three rib geometries corresponding to blockage ratios of 0.133, 0.167, and 0.25 were tested for pitch-to-height ratios of 5, 7, 8.5, and 10. Comparisons were made between the rib average heat transfer coefficient and that on the wall surface between two ribs, hfloor, reported previously. Heat transfer coefficients of the upstream-most rib and that of a typical rib located in the middle of the rib-roughened region of the passage wall were also compared. It is concluded that: 1 The rib average heat transfer coefficient is much higher than that for the area between the ribs; 2 similar to the heat transfer coefficient on the surface between the ribs, the average rib heat transfer coefficient increases with the blockage ratio; 3 a pitch-to-height ratios of 8.5 consistently produced the highest rib average heat transfer coefficients amongst all tested; 4 under otherwise identical conditions, ribs in upstream-most position produced lower heat transfer coefficients than the midchannel positions, 5 the upstream-most rib average heat transfer coefficients decreased with the blockage ratio; and 6 thermal performance decreased with increased blockage ratio. While a pitch-to-height ratio of 8.5 and 10 had the highest thermal performance for the smallest rib geometry, thermal performance of high blockage ribs did not change significantly with the pitch-to-height ratio.

The Effect of Liquid Film Evaporation on Flow Boiling Heat Transfer in a Micro Tube

2010 ◽  
Author(s):  
Youngbae Han ◽  
Naoki Shikazono ◽  
Nobuhide Kasagi
Keyword(s):  
Heat Transfer ◽  
Film Thickness ◽  
Liquid Film ◽  
Flow Boiling ◽  
Liquid Film Thickness ◽  
Periodic Pattern ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Micro Channels ◽  
Measured Liquid

Flow boiling in micro channels is attracting large attention since it leads to large heat transfer area per unit volume. Generated vapor bubbles in micro channels are elongated due to the restriction of channel wall, and thus slug flow becomes one of the main flow regimes. In slug flow, sequential bubbles are confined by the liquid slugs, and thin liquid film is formed between tube wall and bubble. Liquid film evaporation is one of the main heat transfer mechanisms in micro channels and liquid film thickness is a very important parameter to determine heat transfer coefficient. In the present study, liquid film thickness is measured under flow boiling condition and compared with the correlation proposed under adiabatic condition. The relationship between liquid film thickness and heat transfer coefficient is also investigated. Pyrex glass tube with inner diameter of D = 0.5 mm is used as a test tube. Working fluids are water and ethanol. Laser focus displacement meter is used to measure the liquid film thickness. Initial liquid film thickness under flow boiling condition can be predicted well by the correlation proposed under adiabatic condition. However, measured liquid film thickness becomes thinner than the predicted values in the cases of back flow and short slugs. These are considered to be due to the change of velocity profile in the liquid slug. Under flow boiling condition, liquid film profile fluctuates due to high vapor velocity and shows periodic pattern against time. Frequency of periodic pattern increases with heat flux. At low quality, heat transfer coefficients calculated from measured liquid film thickness show good accordance with heat transfer coefficients obtained directly from wall temperature measurements.

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.

Rib Heat Transfer Coefficient Measurements in a Rib-Roughened Square Passage

1998 ◽  
Vol 120 (2) ◽  
pp. 376-385 ◽  
Author(s):  
G. J. Korotky ◽  
M. E. Taslim
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Performance ◽  
Blockage Ratio ◽  
Average Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Average Heat ◽  
Heat Transfer Coefficients

Three staggered 90 deg rib geometries corresponding to blockage ratios of 0.133, 0.167, and 0.25 were tested for pitch-to-height ratios of 5, 8.5, and 10, and for two distinct thermal boundary conditions of heated and unheated channel walls. Comparisons were made between the surface-averaged heat transfer coefficients and friction factors for ribs with rounded corners and those with sharp corners, reported previously. Heat transfer coefficients of the furthest upstream rib and that of a typical rib located in the middle of the rib-roughened region of the passage wall were also compared. It was concluded that: (a) For the geometries tested, the rib average heat transfer coefficient was much higher than that for the area between the ribs. For the sharp-corner ribs, the rib average heat transfer coefficient increased with blockage ratio. However, when the corners were rounded, the trend depended on the level of roundness. (b) High-blockage-ratio (e/Dh = 0.25) ribs were insensitive to the pitch-to-height ratio. For the other two blockage ratios, the pitch-to-height ratio of 5 produced the lowest heat transfer coefficient. Results of the other two pitch-to-height ratios were very close, with the results of S/e = 10 slightly higher than those of S/e = 8.5. (c) Under otherwise identical conditions, ribs in the furthest upstream position produced lower heat transfer coefficients for all cases except that of the smallest blockage ratio with S/e of 5. In that position, for the rib geometries tested, while the sharp-corner rib average heat transfer coefficients increased with the blockage ratio, the trend of the round-corner ribs depended on the level of roundness, r/e. (d) Thermal performance decreased with the blockage ratio. While the smallest rib geometry at a pitch-to-height ratio of 10 had the highest thermal performance, thermal performance of high blockage ribs at a pitch-to-height ratio of 5 was the lowest. (e) The general effects of rounding were a decrease in heat transfer coefficient for the midstream ribs and an increase in heat transfer coefficient for ribs in the furthest upstream position.

Evaluation of Thermal Performance for Vacuum Glazing by Using Three-Dimensional Finite Element Model

2011 ◽  
Vol 492 ◽  
pp. 328-332 ◽  
Author(s):  
Zhi Ming Han ◽  
Yi Wang Bao ◽  
Wei Dong Wu ◽  
Zheng Quan Liu ◽  
Xiao Gen Liu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Simulation Analysis ◽  
Three Dimensional ◽  
Central Area ◽  
Element Model ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Vacuum Glazing ◽  
Three Dimensional Finite Element

Simulation analysis of thermal performance for vacuum glazing was conducted in this paper. The heat conduction through the support pillars and edge seal and the radiation between two glass sheets were considered. The heat conductance of residual gas in vacuum gap was ignored for a low pressure of less than 0.1Pa. Two pieces of vacuum glazing with sizes of 0.3 × 0.3 m and 1.0 × 1.0 m were simulated. In order to check the accuracy of simulations with specified mesh number, the thermal performance of a small central area (4mm×4mm) with a single pillar in the center was simulated using a graded mesh of 41×41×5 nodes. The heat transfer coefficients of this unit obtained from simulation and analytic prediction were 2.194Wm-2K-1and 2.257Wm-2K-1respectively, with a deviation of 2.79%. The three dimensional (3D) isotherms and two dimensional (2D) isotherms on the cold and hot surfaces of the specimens were also presented. For a validity of simulated results, a guarded hot box calorimeter was used to determine the experimental thermal performance of 1.0m×1.0m vacuum glazing. The overall heat transfer coefficients obtained from experiment and simulation were 2.55Wm-2K-1 and 2.47Wm-2K-1respectively, with a deviation of 3.14%.

Simulation of Two-Phase Flow and Heat Transfer in Mini- and Micro-Channels for Concentrating Photovoltaics Cooling

2011 ◽  
Author(s):  
Devin Pellicone ◽  
Alfonso Ortega ◽  
Marcelo del Valle ◽  
Steven Schon
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Single Phase ◽  
Phase Flow ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Micro Scale ◽  
Heat Transfer Coefficients ◽  
Flow And Heat Transfer ◽  
Micro Channels

Advances in concentrating photovoltaics technology have generated a need for more effective thermal management techniques. Research in photovoltaics has shown that there is a more than 50% decrease in PV cell efficiency when operating temperatures approach 60°C. It is estimated that a waste heat load in excess of 500 W/cm2 will need to be dissipated at a solar concentration of 10,000 suns. Mini- and micro-scale heat exchangers provide the means for large heat transfer coefficients with single phase flow due to the inverse proportionality of Nusselt number with respect to the hydraulic diameter. For very high heat flux situations, single phase forced convection in micro-channels may not be sufficient and hence convective flow boiling in small scale heat exchangers has gained wider scrutiny due to the much higher achievable heat transfer coefficients due to latent heat of vaporization and convective boiling. The purpose of this investigation is to explore a practical and accurate modeling approach for simulating multiphase flow and heat transfer in mini- and micro-channel heat exchangers. The work is specifically aimed at providing a modeling tool to assist in the design of a mini/micro-scale stacked heat exchanger to operate in the boiling regime. The flow side energy and momentum equations have been implemented using a one-dimensional homogeneous approach, with local heat transfer coefficients and friction factors supplied by literature correlations. The channel flow solver has been implemented in MATLAB™ and embedded within the COMSOL™ FEM solver which is used to model the solid side conduction problem. The COMSOL environment allows for parameterization of design variables leading to a fully customizable model of a two-phase heat exchanger.

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.

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