skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Boiling on horizontal surfaces coated with porous metal wicks

Abstract

Boiling experiments intended to simulate heat pipe operating conditions were conducted on a copper surface covered with copper foametal and nickel fiber wicks 3.175 and 4.760 mm thick. The experiments were conducted on a horizontal surface open to the atmosphere with water as the working fluid. The experimental surface was operated like a heat pipe with distilled water supplied upstream of the heated section and transported by capillary action across a section which was adiabatic to the heated section where boiling took place. At low excess temperature, less than 10 to 20 C, the heat flux from the porous coated surfaces is comparable to or greater than that predicted for a smooth surface using the Rohsenow correlation. At higher excess temperatures corresponding to heat fluxes between 10{sup 5} and 10{sup 6} W/m{sup 2} the increase in heat flux with excess temperature is much less than that predicted by the Rohsenow correlation. When the wicks were vented by cutting slots covering 10 to 20% of the total surface area the heat flux increased, in some cases by a factor of three, for a given excess temperature. The heat flux at which the slope of the boiling curve decreased also increased formore » the vented surfaces. This is attributed to the provision of a low resistance path for the steam to escape providing a surface that is more highly wetted. A mathematical model for the transport with boiling in the porous wick is developed in an attempt to gain further understanding of the processes involved. The model predicts dryout conditions that are in reasonable agreement with experimental observations. However, the model predicts decreasing vapor pressure, and hence temperature, adjacent to the heated surface with increasing heat flux as a result of the decrease in relative permeability of the partially saturated wick.« less

Authors:
;
Publication Date:
Research Org.:
Faculty of Engineering-Mataria, Cairo (EG)
OSTI Identifier:
20014425
Resource Type:
Conference
Resource Relation:
Conference: 32nd National Heat Transfer Conference, Baltimore, MD (US), 08/08/1997--08/12/1997; Other Information: PBD: 1997; Related Information: In: ASME proceedings of the 32nd national heat transfer conference (HTD-Vol. 349). Volume 11: Interfacial thermal phenomena in thin films; Heat pipes and thermosyphons; Heat and mass transfer in porous media, by Goodson, K.; Chang, W.S.; Charmchi, M.; Hadim, H. [eds.], 211 pages.
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; BOILING; OPERATION; SIMULATION; HEAT PIPES; HEAT PIPE WICKS; POROUS MATERIALS; EXPERIMENTAL DATA; WORKING FLUIDS; DRYOUT; HEAT TRANSFER

Citation Formats

Abou-Zyan, H.Z., and Plumb, O.A.. Boiling on horizontal surfaces coated with porous metal wicks. United States: N. p., 1997. Web.
Abou-Zyan, H.Z., & Plumb, O.A.. Boiling on horizontal surfaces coated with porous metal wicks. United States.
Abou-Zyan, H.Z., and Plumb, O.A.. 1997. "Boiling on horizontal surfaces coated with porous metal wicks". United States. doi:.
@article{osti_20014425,
title = {Boiling on horizontal surfaces coated with porous metal wicks},
author = {Abou-Zyan, H.Z. and Plumb, O.A.},
abstractNote = {Boiling experiments intended to simulate heat pipe operating conditions were conducted on a copper surface covered with copper foametal and nickel fiber wicks 3.175 and 4.760 mm thick. The experiments were conducted on a horizontal surface open to the atmosphere with water as the working fluid. The experimental surface was operated like a heat pipe with distilled water supplied upstream of the heated section and transported by capillary action across a section which was adiabatic to the heated section where boiling took place. At low excess temperature, less than 10 to 20 C, the heat flux from the porous coated surfaces is comparable to or greater than that predicted for a smooth surface using the Rohsenow correlation. At higher excess temperatures corresponding to heat fluxes between 10{sup 5} and 10{sup 6} W/m{sup 2} the increase in heat flux with excess temperature is much less than that predicted by the Rohsenow correlation. When the wicks were vented by cutting slots covering 10 to 20% of the total surface area the heat flux increased, in some cases by a factor of three, for a given excess temperature. The heat flux at which the slope of the boiling curve decreased also increased for the vented surfaces. This is attributed to the provision of a low resistance path for the steam to escape providing a surface that is more highly wetted. A mathematical model for the transport with boiling in the porous wick is developed in an attempt to gain further understanding of the processes involved. The model predicts dryout conditions that are in reasonable agreement with experimental observations. However, the model predicts decreasing vapor pressure, and hence temperature, adjacent to the heated surface with increasing heat flux as a result of the decrease in relative permeability of the partially saturated wick.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1997,
month = 7
}

Conference:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that hold this conference proceeding.

Save / Share:
  • The elementary processes responsible for impurity enrichment of the liquid in the immediate vicinity of the heating surface are investigated in connection with boiling on a porous-coated surface. A simple theory is proposed for calculating the degree of impurity enrichment of the liquid on the surface. It turns out that the investigated effects can account for 10/sup 2/- to 10/sup 3/-fold enrichment, resulting in corrosion of the heating surface if surface-inactive impurities are corrosion-prone. These effects are a potential cause of recent steam generator accidents in a number of plants using PWR reactors.
  • The external, nucleate pool-boiling heat-transfer coefficient in R-114 with up to 10% oil (by mass) was measured on a smooth copper tube and on a porous-coated copper-nickel tube. The heat flux was varied from 160 to 30,000 Btu/hr . ft/sup 2/ (0.5 to 95 kW/m/sup 2/) at boiling temperatures of 28 F and 44 F (-2.2/sup 0/C and 6.7/sup 0/C). The porous-coated surface was found to improve the heat-transfer coefficient over the smooth surface by a factor of 7 to 10 in oil-free R-114. The presence of up to 3% oil caused about a 35% reduction in the heat-transfer coefficientmore » of the porous-coated surface at all heat fluxes. With 6% or more oil, the boiling performance of this surface declined drastically at heat fluxes in excess of 9500 Btu/hr . ft/sup 2/ (30 kW/m/sup 2/). Some plausible mechanisms to explain the observed behavior are described.« less
  • In this study a vertical sintering oven is constructed and instrumented to enable a realization of sintering experiments of bronze inside capper tubes. The sintering oven consists of ceramic core around which is rolled helical electrical resistance of KW in power. The outside shell is made up of an iron tube and is thermically isolated. A thermocouple passes through the top cover and is perfectly isolated and sealed. This thermocouple is used to measure the average temperature of the oven. The tube to be sintered is hung inside the ceramic tube. In order to ensure an inert atmosphere, a smallmore » diameter tube is soldered to the top cover and is connected to a helium gas cylinder fitted with a pressure regulator. In these experiments various particle sizes were used. Various sintering temperature and times. After the tubes are sintered, they are removed and tested hydrodynamically to verify the pressure drop and measure the permeability. Results are plotted showing the effect of temperature and residence time on these parameters. Selected tubes are then prepared as heat pipes and put for testing to determine the thermal performance of the tubes. Parameters such as working temperature, mass of working fluid, angle of inclination are investigated, analysed and discussed. It is found that heat pipes with sintered material have a reasonably good thermal performance as compared to mesh wicked tubes. Another advantage is that sintered tubes are easy to fabricate and prepare and thus the fabrication cost is much below mesh wicked tubes. It is hoped that this cost reduction will allow large scale use of these tubes in heat exchangers and energy recuperators.« less
  • Precision metal felts are made of filaments of microndiameter wires that are chopped and layered onto a flat surface to form a wool-like material. Metal felts are commonly used as filters for micron-sized particles. The small diameters of the wires and the relatively open structure of these non-woven materials provide porosities on the order of 90% and greater. The high porosities of metal felts make them interesting candidate materials for heat pipe applications. Property measurements on selected samples of metal felts have demonstrated that typical effective pore radii range from 40 to 120 {mu}m and the respective Darcy permeabilities rangemore » from 30 to 300 {mu}m{sup 2}. Through careful compaction of these materials, it is possible to tailor the flow characteristics of the materials to specific applications. Recently, a series of tests have been conducted at Sandia to measure the flow characteristics and pore structures of these materials as a function of compaction. Results from these tests and a discussion of the current applications of these materials in liquid-metal heat pipes for solar power conversion systems are presented in this paper.« less
  • An interesting problem is the effect of an immiscible liquid heating surface on the process of film boiling. Such surfaces raise questions concerning interface stability to disturbances, effects of gas bubbling, and vapor explosions in layered systems. The specific motivation for this study was to investigate film boiling from a liquid surface with application to cooling of molten reactor core debris by an overlying pool of reactor coolant. To investigate this phenomenon, and apparatus consisting of a nominal six-inch diameter steel vessel to hold the liquid metal and boiling fluid was constructed; coolant reservoirs, heaters, controllers, and allied instrumentation weremore » attached. A transient energy balance was performed on the liquid metal pool by a submerged assembly of microthermocouples in the liquid metal and an array of thermocouples on the wall of the test vessel. The thermocouple data were used to determine the boiling heat flux as well as the boiling superheat. On an average basis, the deviation between the prediction of the Berenson model and the experimental data was less than one percent when Berenson was corrected for thermal radiation effects. Evidence from visualization tests of R-11 in film boiling over molten metal pools to superheats in excess of 600 K supports this conclusion. 13 refs.« less