Measurement of Surface Heat Flux and Surface Temperature in Nucleate Pool Boiling Using Micro-Thermocouples

2009 ◽  
Author(s):  
Wei Liu ◽  
Kazuyuki Takase
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Temperature Change ◽  
Surface Heat Flux ◽  
Heat Conduction Problem ◽  
Pool Boiling ◽  
Surface Heat ◽  
Heat Transfer Analysis ◽  
Boiling Process

In this paper, a measurement system for surface temperature and surface heat flux was developed to study heat transfer mechanism in boiling process. The system was consisted by two parts: (1) inner block temperatures were measured using micro-thermocouples set at two layers inside heating block; (2) with using the measured temperatures, inverse heat transfer analysis was performed to get surface heat flux and surface temperature. For the inner block temperature measurement, special T-type micro thermocouples with a common positive pole were developed. Totally 20 thermocouples were set at two layers at the depths 3.1μm and 4.905mm beneath the boiling surface, in a radius of 5mm. The developed system was used to research the change of surface heat flux and surface temperature in a boiling process. Experiments were performed to pool boiling at atmospheric pressure. The experiments showed the developed special T-type micro thermocouples could trace temperature change in boiling process successfully. With comparison to images from a high-speed camera, temperature change tendencies in boiling process were tried to understand. Then one dimensional inverse heat conduction problem was solved to get surface heat flux and surface temperature. Increase in surface heat flux with the generation of big bubble was derived successfully.

Instantaneous Local Heat Flux Measurements in a Small Utility Engine

2009 ◽  
Author(s):  
Terry Hendricks ◽  
Jaal Ghandhi ◽  
John Brossman
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Model ◽  
Surface Temperature ◽  
Heat Transfer Rate ◽  
Surface Heat Flux ◽  
Transfer Rate ◽  
Surface Heat ◽  
High Load ◽  
Flux Measurements

Heat flux measurements were performed in an air-cooled utility engine using a fast-response coaxial-type surface thermocouple. The surface heat flux was calculated using both analytical and numerical models. The heat flux was found to be a strong function of engine load. The peak heat flux and initial heat flux rise rate increase with engine load. The measured heat flux data were used to estimate a global heat transfer rate, and this was compared with the heat transfer rate calculated by a single-zone heat release analysis. The measured values of heat transfer were higher than the calculated values largely because of the lack of spatial averaging. The high load data showed an unexplainable negative heat flux during the expansion stroke while the gas temperature was still high. A 1D and 2D finite difference numerical model utilizing an adaptive timestep Crank-Nicholson (CN) integration routine was developed to investigate the surface temperature measurement. Applying the measured surface temperature profile to the 1D model, the resultant surface heat flux showed excellent agreement with the analytical inversion solution and captured the reversal of the energy flow back into the cylinder during the expansion stroke. The 2D numerical model was developed to observe transient lateral conduction effects within the probe and incorporated the various materials used in the construction and assembly of the heat flux sensor. The resulting average heat flux profile for the test case is shown to be slightly higher in peak and longer in duration when compared with the results from the 1D analytical inversion, and this is attributed to contributions from the high thermal diffusivity constituents in the sensor. Furthermore, the negative heat flux at high load was not eliminated suggesting that factors other than lateral conduction may be affecting the measurement accuracy.

Determination of Surface Heat Flux in Quenching

1999 ◽  
Author(s):  
M. K. Alam ◽  
H. Pasic ◽  
K. Anagurthi ◽  
R. Zhong
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Analytical Solution ◽  
Surface Heat Flux ◽  
Measurement Errors ◽  
Numerical Solutions ◽  
Heat Conduction Problem ◽  
Initial Guess ◽  
Surface Heat

Abstract Quench probes have been used to collect temperature data in controlled quenching experiments; the data is then used to deduce the heat transfer coefficients in the quenching medium. The process of determination of the heat transfer coefficient at the surface is the inverse heat conduction problem, which is extremely sensitive to measurement errors. This paper reports on an experimental and theoretical study of quenching carried out to determine the surface heat flux history during a quenching process by an inverse algorithm based on an analytical solution. The algorithm is applied to experimental data from a quenching experiment. The surface heat flux is then calculated, and the theoretical curve obtained from the analytical solution is compared with experimental results. The inverse calculation appears to produce fast, stable, but approximate results. These results can be used as the initial guess to improve the efficiency of iterative numerical solutions which are sensitive to the initial guess.

Proposed Experimental Technique for Measuring Heat Transfer Coefficients Using a Pulsed Periodic Surface Heat Flux

1999 ◽  
Author(s):  
Wayne N. O. Turnbull ◽  
William E. Carscallen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Phase Behavior ◽  
Experimental Technique ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Transfer Coefficients ◽  
Periodic Surface ◽  
Heat Transfer Coefficients

Abstract An analytical and numerical investigation has been carried out to ascertain the possibility of using a pulsed periodic surface heat flux to measure local surface heat transfer coefficients. The proposed technique is an extension of a previously proven experimental method. It is based upon the premise that the harmonics of a surface temperature response to an imposed periodic pulse will display phase shifting behavior that is a function of the thermophysical properties of the surface, the local heat transfer coefficient and the harmonic frequency. The phase behavior is not a function of the magnitude of the energy deposited by the pulse. Since phase behavior is being investigated there is no requirement to calibrate the surface temperature-sensing device. The numerical solution confirms the analytical results, which were obtained using a non-rigorous mathematical assumption. Results indicate that in order to maximize the sensitivity of the proposed experimental technique the pulse frequency should be kept low, the surface layer thin and the substrate thermal conductivity and diffusivity as low as possible.

scholarly journals Analysis of One Dimensional Inverse Heat Conduction Problem : A Review

2012 ◽  
pp. 126-131
Author(s):  
Rakesh Kumar ◽  
Jayesh. P ◽  
Niranjan Sahoo
Keyword(s):  
Heat Flux ◽  
Heat Conduction ◽  
Temperature Change ◽  
Surface Heat Flux ◽  
Working Condition ◽  
Heat Conduction Problem ◽  
Inverse Heat Conduction Problem ◽  
Surface Heat ◽  
Inverse Heat Conduction ◽  
One Dimensional

A procedure to solve inverse heat conduction problem (IHCP) is to derive surface heat flux and temperature from temperature change inside a solid. The method proves to be very useful and powerful when a direct measurement of surface heat flux and temperature is difficult, owing to several working condition. The literature reviewed here discussion one dimensional inverse heat conduction problem. Procedure, criteria, methods and important results of other investigation are briefly discussed.

A Microscale Study of the Impact of Bubble Growth Dynamics on Surface Heat Flux in Microchannel Flow Boiling Process

2015 ◽  
Author(s):  
Sajjad Bigham ◽  
Saeed Moghaddam
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Surface Heat Flux ◽  
Flow Boiling ◽  
Surface Heat ◽  
Bubble Wall ◽  
Average Surface ◽  
Boiling Process ◽  
The Impact

In this study, the physics of microscale heat transfer events at the wall-fluid interface during the growth of a moving bubble in a microchannel is analyzed. The study is enabled through development of a novel device that utilizes 53 microscale platinum resistance temperature detectors (RTDs) embedded in a composite substrate made of a high thermal conductivity material coated by a thin layer of a low thermal conductivity material. This sensors arrangement enables resolving the thermal field at the bubble-wall interface with unprecedented spatial and temporal resolutions of 40–65 μm and 50 μs, respectively. To prevent random bubble inception, a 300 nm in diameter cavity is fabricated using a focused ion beam (FIB) at the center of a pulsed function microheater. A detailed analysis of the surface heat transfer events and their relations to time scale of formation and dimensions of bubbles are conducted to decipher the underlying physics of the flow boiling process. Experimental results show that four mechanisms of heat transfer are active as a bubble grows and flows through the channel. These mechanisms of heat transfer are 1) microlayer evaporation, 2) interline evaporation, 3) transient conduction, and 4) micro-convection. The results suggest that the average surface heat flux enhances as the bubble grows in size resulting in expansion of the surface area over which the thin film evaporation mechanism is active. Above a certain bubble size, the average surface heat flux declines due to the formation of a dry region at the bubble-wall interface. Hence, the results indicate that there is an optimal bubble length at which the average surface heat flux is maximum.

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