Experimental Investigation of Effect of Pore Diameter on Nucleate Boiling Heat Transfer in Reentrant Tunnel Structured Surfaces

2017 ◽  
Author(s):  
Ali Can Ispir ◽  
Tugce Karatas ◽  
Eren Dikec ◽  
Seyhan Onbasioglu
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
High Speed ◽  
Pore Diameter ◽  
Experimental Studies ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Vapor Bubbles ◽  
Structured Surfaces

This paper focuses on experimental studies of boiling heat transfer on surfaces with reentrant tunnels and pores. Three structured surface which have same tunnel width and height but different pore diameter, have been developed for enhancement boiling heat transfer. The experimental studies were carried out for the structured surfaces using distilled water at atmospheric pressure. The narrow reentrant tunnels are parallel to each other and have 3 mm width, 4 mm height. A number of pores whose diameter 1.5 and 2.0 mm were machined on lateral surfaces of tunnels. The surfaces were termed according to their geometric specifications as 3.0W-30-30, 1.5D-3.0W-30-30, 2.0D-3.0W-30-30. D and W capitals represent pore diameter and tunnel width, respectively. 30-30 part of name shows the dimension of square surface. The tunnels were used to increase area of heat transfer and active nucleation sites of vapor bubbles. In addition, sufficient amount of liquid must be supplied and vapor bubbles should be released fast from the boiling surface before they merge on the surfaces under conditions especially with high heat fluxes. Therefore, it was considered that pore structures would help for fluid transition hence the bubble frequency will increase. Pool boiling experiments were held to determine the performance of surfaces in different range of heat fluxes. Besides, high-speed visualization studies were conducted with high speed camera to observe behavior of nucleation of vapor bubbles. Amongst different geometry sizes the surface which has 1.5 mm of pore diameter (1.5D-3.0W-30-30) demonstrated the best nucleate boiling performance at high heat fluxes. However, the pored ones without pores has higher augmentation than pored structures at low heat fluxes. Thus, it is concluded that pored structures caused active nucleation sites to decrease under low heat fluxes.

An Experimental Investigation of Sub-Cooled Flow Boiling in Hypervapotron Cooling Configuration

2004 ◽  
Author(s):  
Peipei Chen ◽  
Barclay G. Jones ◽  
Ty A. Newell
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Flow Boiling ◽  
Experimental Studies ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Subcooled Boiling ◽  
Reduced Pressure

This work reports on experimental studies to visualize nucleate boiling on the enhanced heat transfer surface of the hypervapotron for with application in the International Thermonuclear Experiment Reactor [ITER]. This research uses the simulant fluid Freon (R134A) instead of prototypic water to model the system performance. This results in much lower thermophysical conditions to represent the prototypic phenomena. By using reduced pressure, temperatures, etc, based on the critical physical properties of both working fluids, Freon and water, the dramatic drop in the level of these quantities with Freon allows the use of modest test conditions. The experiment was conducted for both saturated and subcooled boiling with different heat fluxes (from 50 to 300 kW/m2). A comparison of the heat transfer performance of finned structures and flat surfaces were examined under particular fluid conditions. The uniqueness of this work is the visualization method that allows direct observation of the subcooled boiling process of the Hypervapotron surfaces. Working with a high speed (12,000 frames per second), high fidelity digital camera with variable magnifications (from 1×–25×), the sub-cooled boiling phenomena was observed in detail. A major conclusion of this work is the existence of two separate zones linked to different energy removal efficiency in hypervapotron. Under high heat flux condition, enhanced boiling heat transfer (about 20–30% higher than flat surface) was observed for hypervapotron effect, while saturated boiling happened in the cavity, and a large portion of the region was vapor filled. The process of vapor bubble rotation in the slot appeared to be helpful to enhance energy transfer, as evidenced by an improved wetting condition on the heating surfaces.

Ultrasonic augmentation in pool boiling heat transfer over external surfaces: A review

2020 ◽  
pp. 095440622095035
Author(s):  
Abhishek Swarnkar ◽  
Vikas J Lakhera
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
High Heat ◽  
Ultrasonic Field ◽  
Ultrasonic Waves ◽  
Heat Fluxes ◽  
Surface Topology

Boiling heat transfer is known for high heat fluxes at relatively small temperature differences. However, over the decades, technological innovations have demanded further augmentation in heat fluxes associated with boiling. Among the various active and passive methods, use of ultrasonic waves in boiling liquid has emerged as a proven technique for the required heat transfer improvement as demonstrated by a number of researchers. The present article reviews the application of ultrasonic waves in enhancing the heat transfer in various regimes of pool boiling. It has been found that the use of ultrasonic field is more promising in case of sub-cooled boiling as compared to saturated condition. Along with ultrasonic field of lower frequency and higher power, the usage of various passive techniques of surface improvement such as micro channel, surface topology, nano coatings etc. leads to further augmentation of heat transfer. Also, the relative placement of heating surface in ultrasonic wave field must be considered inevitably while designing an ultrasonic field assisted pool boiling system. It requires further investigations to conduct more parametric studies such as effect of pressure along with the usage of ultrasonic waves during sub- cooled boiling. Also during ultrasonic assisted pool boiling, various nano fluids can be tested for improving the heat transfer characteristics particularly in the saturated nucleate boiling regime.

Boiling Heat Transfer Enhancement Using a Submerged, Vibration-Induced Jet

2006 ◽  
Vol 128 (2) ◽  
pp. 145-149 ◽  
Author(s):  
Steven W. Tillery ◽  
Samuel N. Heffington ◽  
Marc K. Smith ◽  
Ari Glezer
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heated Surface ◽  
Horizontal Cell ◽  
Cross Flow ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Bulk Liquid ◽  
Liquid Jet ◽  
Vapor Bubbles

In this paper we describe a new two-phase cooling cell based on channel boiling and a vibration-induced liquid jet whose collective purpose is to delay the onset of critical heat flux by forcibly dislodging the small vapor bubbles that form on the heated surface during nucleate boiling and propelling them into the cooler bulk liquid within the cell. The submerged turbulent vibration-induced jet is generated by a vibrating piezoelectric diaphragm operating at resonance. The piezoelectric driver induces pressure oscillations in the liquid near the surface of the diaphragm, resulting in the time-periodic formation and collapse of cavitation bubbles that entrain surrounding liquid and generate a strong liquid jet. The resultant jet is directed at the heated surface in the channel. The jet enhances boiling heat transfer by removing attached vapor bubbles that insulate the surface and provides additional forced convection heat transfer on the surface. A small cross flow maintained within the cell increases heat transfer even further by sweeping the bubbles downstream, where they condense. In addition, the cross flow keeps the temperature of the liquid within the cell regulated. In the present experiments, the cell dimensions were 51×25×76mm and water was the working liquid. Heat fluxes above 300W∕cm2 were obtained at surface temperatures near 150°C for a horizontal cell.

Concerning the Effect of Surface Material on Nucleate Boiling Heat Transfer of R-113

2011 ◽  
Author(s):  
R. Hosseini ◽  
A. Gholaminejad ◽  
Mahdi Nabil ◽  
Mohammad Hossein Samadinia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Surface Material ◽  
Effect Of Surface

This paper presents results of an experimental investigation carried out to determine the effects of surface material on nucleate pool boiling heat transfer of refrigerant R113. Experiments were performed on horizontal circular plates of brass, copper and aluminum. The heat transfer coefficient was evaluated by measuring wall superheat and effective heat flux removed by boiling. The experiments were carried out in the heat flux range of 8 to 200kW/m2. The obtained results have shown significant effect of surface material, with copper providing the highest heat transfer coefficient among the samples, and aluminum the least. There was negligible difference at low heat fluxes, but copper showed 23% better performance at high heat fluxes than aluminum and 18% better than brass.

Nucleate Boiling Heat Transfer of Binary Mixtures at Low to Moderate Heat Fluxes

1999 ◽  
Vol 121 (2) ◽  
pp. 365-375 ◽  
Author(s):  
R. J. Benjamin ◽  
A. R. Balakrishnan
Keyword(s):  
Heat Transfer ◽  
Stainless Steel ◽  
Binary Mixtures ◽  
Boiling Heat Transfer ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Steel Tube ◽  
Heat Fluxes ◽  
Stainless Steel Tube ◽  
Turbulent Natural Convection

A model for nucleate pool boiling heat transfer of binary mixtures has been proposed based on an additive mechanism. The contributing modes of heat transfer are (i) the heat transferred by microlayer evaporation, (ii) the heat transferred by transient conduction during the reformation of the thermal boundary layer, and (iii) the heat transferred by turbulent natural convection. The model takes into account the microroughness of the heating surface which has been defined quantitatively. The model compares satisfactorily with data obtained in the present study and in the literature. These data were obtained on a variety of heating surfaces such as a vertical platinum wire, a horizontal stainless steel tube and flat horizontal aluminium, and stainless steel surfaces (with various surface finishes) thereby demonstrating the validity of the model.

Experimental Studies of Hydrodynamics and Heat Transfer in Channels With High-Porous Cellular Materials in Single-Phase Forced Convection and Flow Boiling of Working Fluids

1999 ◽  
Author(s):  
Yury F. Gortyshov ◽  
Igor A. Popov ◽  
Konstantin E. Gulitsky
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Pore Diameter ◽  
Flow Boiling ◽  
Experimental Studies ◽  
Internal Heat ◽  
Cellular Materials ◽  
Heat Fluxes ◽  
Working Fluids ◽  
Resistance Surface

Abstract In this paper we consider experimental studies of hydraulic resistance, surface heat transfer, internal heat exchange and critical heat fluxes for the flow of single-phase and boiling working fluids in channels with high-porous inserts. Experiments were carried out with more than 40 samples of high-porous cellular materials with the porosity 0.8...0.98 and mean pore diameter 0.62...4 mm and with more than 10 samples of regular porous inserts and porosity ε = 0.512...0.86 and mean pore diameter 1.5...3.5 mm. These samples were made of porcelain, invar, nichrome, bronze and copper.

Analytical Model Quantifying the Net Coolant Flow Rate to a Microstructured Copper Surface validated with Two-Phase PIV Measurements

2021 ◽  
Author(s):  
Matt Harrison ◽  
Joshua Gess
Keyword(s):  
Heat Transfer ◽  
Analytical Model ◽  
Flow Rate ◽  
Circular Disk ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Coolant Flow ◽  
Coolant Flow Rate ◽  
Two Phase

Abstract Using Particle Image Velocimetry (PIV), the amount of fluid required to sustain nucleate boiling was quantified to a microstructured copper circular disk. Having prepared the disk with preferential nucleation sites, an analytical model of the net coolant flow rate requirements to a single site has been produced and validated against experimental data. The model assumes that there are three primary phenomena contributing to the coolant flow rate requirements at the boiling surface; radial growth of vapor throughout incipience to departure, bubble rise, and natural convection around the periphery. The total mass flowrate is the sum of these contributing portions. The model accurately predicts the quenching fluid flow rate at low and high heat fluxes with 4% and 30% error of the measured value respectively. For the microstructured surface examined in this study, coolant flow rate requirements ranged from 0.1 to 0.16 kg/sec for a range of heat fluxes from 5.5 to 11.0 W/cm2. Under subcooled conditions, the coolant flow rate requirements plummeted to a nearly negligible value due to domination of transient conduction as the primary heat transfer mechanism at the liquid/vapor/surface interface. PIV and the validated analytical model could be used as a test standard where the amount of coolant the surface needs in relation to its heat transfer coefficient or thermal resistance is a benchmark for the efficacy of a standard surface or boiling enhancement coating/surface structure.

Nucleate Boiling From Micro-Machined Surfaces

2003 ◽  
Author(s):  
Adrian M. Holland ◽  
Colin P. Garner
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Imaging System ◽  
Laser System ◽  
Ccd Camera ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Frame Rate ◽  
High Speed Imaging ◽  
Machined Surfaces

This paper discusses the production and use of laser-machined surfaces that provide enhanced nucleate boiling and heat transfer characteristics. The surface features of heated plates are known to have a significant effect on nucleate boiling heat transfer and bubble growth dynamics. Nucleate boiling starts from discrete bubbles that form on surface imperfections, such as cavities or scratches. The gas or vapours trapped in these imperfections serve as nuclei for the bubbles. After inception, the bubbles grow to a certain size and depart from the surface. In this work, special heated surfaces were manufactured by laser machining cavities into polished aluminium plates. This was accomplished with a Nd:YAG laser system, which allowed drilling of cavities of a known diameter. The size range of cavities was 20 to 250 micrometers. The resulting nucleate pool boiling was analysed using a novel high-speed imaging system comprising an infrared laser and high resolution CCD camera. This system was operated up to a 2 kHz frame rate and digital image processing allowed bubbles to be analysed statistically in terms of departure diameter, departure frequency, growth rate, shape and velocity. Data was obtained for heat fluxes up to 60 kW.m−2. Bubble measurements were obtained working with water at atmospheric pressure. The surface cavity diameters were selected to control the temperature at which vapour bubbles started to grow on the surface. The selected size and spacing of the cavities was also explored to provide optimal heat transfer.

Experimental Study of Enhanced Pool Boiling Heat Transfer Using Graphite Foam Inserts

2011 ◽  
Vol 312-315 ◽  
pp. 352-357 ◽  
Author(s):  
K.C. Leong ◽  
L.W. Jin ◽  
I. Pranoto ◽  
H.Y Li ◽  
J.C. Chai
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Boiling Heat Transfer ◽  
High Speed ◽  
Bubble Formation ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Copper Block ◽  
Different Types ◽  
Graphite Foam

This paper presents the results of an experimental study of heat transfer in a pool boiling evaporator with porous insert. Different types of graphite foams were tested with the phase change coolant FC-72 in a designed thermosyphon. Comparisons between the graphite foams and a solid copper block show that the porous structure enhances pool boiling significantly. The boiling thermal resistance of the tested graphite foams was found to be about 2 times lower than that of the copper block. The bubble formation recorded by a high speed camera indicates that boiling from a graphite foam is more vigorous than from a copper block. The designed thermosyphon with graphite foam insert can remove heat fluxes of up to 112 W/cm2 with the maximum heater temperature maintained below 100°C.

Oil Effects on In-Tube Evaporation of CO2 by Altering Flow Regime and Properties

2013 ◽  
Author(s):  
Pega Hrnjak ◽  
Seongho Kim
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Circulation Rate ◽  
Convective Boiling ◽  
Mass Fluxes

Flow boiling heat transfer characteristics of CO2 with and without oil were investigated experimentally in horizontal smooth and enhanced tubes with an inner diameter of 11.2 mm. The visualization of flow pattern provides a detailed attributes of the nucleate and the convective boiling heat transfer. In order to investigate the effect of the miscible oil on the heat transfer of CO2, POE (polyolester) RENSIO C85E oil is added to give an oil circulation rate (OCR) between 0.5% and 2%. Results are compared with those of pure CO2. The experimental conditions include evaporation temperatures of −15 °C, mass fluxes from 40 to 200 kg/m2 s, heat fluxes from 0.5 to 10 kW/m2, and vapor qualities from 0.1 to 0.8. Oil generally deteriorates the heat transfer coefficient of pure CO2. The reduction in heat transfer coefficient is most apparent at low vapor qualities, 0.1 to 0.4, and at low mass fluxes, 100 and 200 kg/m2. It is caused by the suppression of nucleate boiling due to increased surface tension. At conditions where the convective boiling contribution is dominant, vapor qualities above 0.5, oil increases heat transfer coefficients. Through visualization, it is shown that the wetted area on the perimeter of inner tube is enhanced due to formation of foaming in the smooth tube. However, such enhancement of heat transfer due to forming is negligible in the enhanced tube, because the enhanced factor due to micro-finned structures is dominant.

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