Quenching of a Heated Rod: Physical Phenomena, Heat Transfer, and Effect of Nanofluids

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Arnab Dasgupta ◽  
A. S. Chinchole ◽  
P. P. Kulkarni ◽  
D. K. Chandraker ◽  
A. K. Nayak
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Surface Heat Flux ◽  
High Speed ◽  
Ad Hoc ◽  
Marked Change ◽  
Surface Heat ◽  
High Speed Photography ◽  
Physical Phenomena

The physical phenomena of rewetting and quenching are of prime importance in nuclear reactor safety in the event of a loss of coolant accident (LOCA). Generally, top spray or bottom flooding concepts are used in reactors. Numerical simulation of these processes entails the use of the concept of a rewetting velocity. However, heat transfer just before and after the rewetting front is often assumed in an ad hoc fashion. The present work aims to evaluate the surface heat flux during quenching as a function of surface temperature. The experiments presented herein are primarily applicable to the bottom flooding scenario with high flooding rate. In the experiments, a rod heated above Leidenfrost point is immersed in a pool of water. The surface temperature was recorded using a surface-mounted thermocouple. The surface heat flux was then determined numerically and hence can be related to a particular value of surface temperature. This type of data is useful for numerical simulations of quenching phenomena. In addition to this, high-speed photography was undertaken to visualize the phenomena taking place during the rewetting and quenching. Both subcooled and saturated water pools have been used and compared in the experiments. Surface finish was seen to influence rewetting process by a mechanism which here is termed as “transition boiling enhanced film boiling.” The effect of using nanofluids was also studied. No marked change is observed in the overall quenching time with nanofluids, however, the initial cooling is apparently faster.

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.

Experimental and Numerical Characterization of Droplet-Induced Spreading-Splashing Transition in Surface Cooling

2016 ◽  
Author(s):  
Taolue Zhang ◽  
J. P. Muthusamy ◽  
Jorge Alvarado ◽  
Anoop Kanjirakat ◽  
Reza Sadr
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Weber Number ◽  
High Speed ◽  
Single Phase ◽  
Surface Heat ◽  
Droplet Impingement ◽  
Surface Heat Transfer ◽  
Dry Out

The effects of droplet train impingement on spreading-splashing transition and surface heat transfer were investigated experimentally and numerically. Experimentally, a single stream of HFE-7100 droplet train was generated using a piezo-electric droplet generator with the ability to adjust parameters such as droplet impingement frequency, droplet diameter and droplet impingement velocity. A thin layer of Indium Tin Oxide (ITO) was coated on a translucent sapphire substrate, which was used as heating element. High-speed and infrared imaging techniques were employed to characterize the hydrodynamics and heat transfer of droplet train impingement. Numerically, the high frequency droplet train impingement process was simulated using ANSYS-Fluent with the Volume of Fluid (VOF) method [1]. The heat transfer process was simulated by applying constant heat flux conditions on the droplet receiving surface. Droplet-induced spreading-splashing transition behavior was investigated by increasing the droplet Weber number while holding flow rate constant. High speed crown propagation images showed that at low-Weber number (We < 400), droplet impingements resulted in smooth spreading of the droplet-induced crown. However, within the transitional droplet Weber number range (We = 400–500), fingering and splashing (i.e. emergence of secondary droplets) could be observed at the crown’s rim. At high droplet Weber number (We > 800), breakup of the crown was observed during the crown propagation process in which the liquid film behaved chaotically. Droplet-induced spreading-splashing transition phenomena were also investigated numerically. Reasonable agreement was reached between the experimental and numerical results in terms of crown morphology at different droplet Weber number values. The effects of spreading-splashing transition on surface heat transfer were also investigated at fixed flow rate conditions. Time-averaged Infrared (IR) temperature measurements indicate that heat flux-surface temperature curves are linear at low surface temperatures and before the onset of dry-out, which indicate that single phase forced convection is the primary heat transfer mechanism under those conditions. Numerical heat transfer simulations were performed within the single phase forced convection regime only. Instantaneous numerical results reveal that droplet-induced crown propagation effectively convect heat radially outward within the droplet impingement zone. Under high heat flux conditions, a sharp increase in surface temperature was observed experimentally when dry-out appeared on the heater surface. It was also found that strong splashing (We > 800) is unfavorable for heat transfer at high surface temperature due to the onset of instabilities seen in the liquid film, which leads to dry-out conditions. In summary, the results indicate that droplet Weber number is a significant factor in the spreading-splashing transition and surface heat transfer.

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.

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.

Heat Transfer Characteristics of Downward Facing Hot Horizontal Surfaces Using Mist Jet Impingement

2017 ◽  
Author(s):  
Ashutosh Kumar Yadav ◽  
Parantak Sharma ◽  
Avadhesh Kumar Sharma ◽  
Mayank Modak ◽  
Vishal Nirgude ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Heat Flux ◽  
Cooling System ◽  
Water Pressure ◽  
Jet Impingement ◽  
Surface Heat ◽  
Heat Transfer Characteristics ◽  
Impingement Cooling ◽  
Transfer Characteristics

Impinging jet cooling technique has been widely used extensively in various industrial processes, namely, cooling and drying of films and papers, processing of metals and glasses, cooling of gas turbine blades and most recently cooling of various components of electronic devices. Due to high heat removal rate the jet impingement cooling of the hot surfaces is being used in nuclear industries. During the loss of coolant accidents (LOCA) in nuclear power plant, an emergency core cooling system (ECCS) cool the cluster of clad tubes using consisting of fuel rods. Controlled cooling, as an important procedure of thermal-mechanical control processing technology, is helpful to improve the microstructure and mechanical properties of steel. In industries for heat transfer efficiency and homogeneous cooling performance which usually requires a jet impingement with improved heat transfer capacity and controllability. It provides better cooling in comparison to air. Rapid quenching by water jet, sometimes, may lead to formation of cracks and poor ductility to the quenched surface. Spray and mist jet impingement offers an alternative method to uncontrolled rapid cooling, particularly in steel and electronics industries. Mist jet impingement cooling of downward facing hot surface has not been extensively studied in the literature. The present experimental study analyzes the heat transfer characteristics a 0.15mm thick hot horizontal stainless steel (SS-304) foil using Internal mixing full cone (spray angle 20 deg) mist nozzle from the bottom side. Experiments have been performed for the varied range of water pressure (0.7–4.0 bar) and air pressure (0.4–5.8 bar). The effect of water and air inlet pressures, on the surface heat flux has been examined in this study. The maximum surface heat flux is achieved at stagnation point and is not affected by the change in nozzle to plate distance, Air and Water flow rates.

scholarly journals Nanofluid Flow on a Shrinking Cylinder with Al2O3 Nanoparticles

Mathematics ◽  
2021 ◽  
Vol 9 (14) ◽  
pp. 1612
Author(s):  
Iskandar Waini ◽  
Anuar Ishak ◽  
Ioan Pop
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Friction Factor ◽  
Surface Heat Flux ◽  
Transfer Rate ◽  
Surface Heat ◽  
Al2o3 Nanoparticles ◽  
Nanofluid Flow ◽  
Curvature Parameter ◽  
Over Time

This study investigates the nanofluid flow towards a shrinking cylinder consisting of Al2O3 nanoparticles. Here, the flow is subjected to prescribed surface heat flux. The similarity variables are employed to gain the similarity equations. These equations are solved via the bvp4c solver. From the findings, a unique solution is found for the shrinking strength λ≥−1. Meanwhile, the dual solutions are observed when λc<λ<−1. Furthermore, the friction factor Rex1/2Cf and the heat transfer rate Rex−1/2Nux increase with the rise of Al2O3 nanoparticles φ and the curvature parameter γ. Quantitatively, the rates of heat transfer Rex−1/2Nux increase up to 3.87% when φ increases from 0 to 0.04, and 6.69% when γ increases from 0.05 to 0.2. Besides, the profiles of the temperature θ(η) and the velocity f’(η) on the first solution incline for larger γ, but their second solutions decline. Moreover, it is noticed that the streamlines are separated into two regions. Finally, it is found that the first solution is stable over time.

scholarly journals Operating temperatures of oil-lubricated medium-speed gears: Numerical models and experimental results

2003 ◽  
Vol 217 (2) ◽  
pp. 87-106 ◽  
Author(s):  
H Long ◽  
A A Lord ◽  
D T Gethin ◽  
B J Roylance
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Rotational Speed ◽  
High Speed ◽  
Applied Load ◽  
Frictional Heat ◽  
Transfer Coefficients ◽  
Gear Teeth ◽  
Heat Transfer Coefficients

This paper investigates the effects of gear geometry, rotational speed and applied load, as well as lubrication conditions on surface temperature of high-speed gear teeth. The analytical approach and procedure for estimating frictional heat flux and heat transfer coefficients of gear teeth in high-speed operational conditions was developed and accounts for the effect of oil mist as a cooling medium. Numerical simulations of tooth temperature based on finite element analysis were established to investigate temperature distributions and variations over a range of applied load and rotational speed, which compared well with experimental measurements. A sensitivity analysis of surface temperature to gear configuration, frictional heat flux, heat transfer coefficients, and oil and ambient temperatures was conducted and the major parameters influencing surface temperature were evaluated.

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