Showing papers on "Critical heat flux published in 1971"

Heat transfer apparatus with improved heat transfer surface

Abstract: A heat transfer device, defined here as a heat link, having a capillary vaporizer adjacent a heat source, transfers heat to a heat sink by vaporization and condensation of a heat transfer fluid within the device. A first passage is provided for conveying vapor from the capillary vaporizer to the heat sink. Another passage which is essentially a continuation of the first passage, conveys condensed liquid from the heat sink to the vaporizer, thus allowing the distance that the liquid must flow through capillary material to be quite short. Contact of the returning liquid with the surface of the vaporizer is assured by providing means for maintaining the temperature of the liquid in the return line at a sufficiently low temperature that any vapor will condense; or, alternatively, by having means for extracting any vapor formed in the returning liquid. In this manner, the heat link operates with high heat flux without any substantial resistance to liquid flow through a long capillary flow path. By thus replacing almost all of the liquid return wick, with its high resistance to fluid flow, of heat pipes with a low flow resistance liquid passage or conduit, the heat flux capacity of the heat link is greatly increased over that of the heat pipe while the quantity of porous material used and the heat link weight are considerably reduced so that a heat link typically has 10 to 1,000 times the heat flux capacity of a heat pipe having the same weight. "Boosted" embodiments of the heat link employing additional means for circulating the fluid, such as vapor jet pumps, powered at least in part by vapor from the capillary vaporizer, are also described. Some "boosted" heat links are capable of handling heat fluxes in the multi-megawatt range while having no moving parts except for check valves and the fluid itself.

Heat and mass transfer in the vicinity of the triple interline of a meniscus

Abstract: Heat and mass transfer in triple interline region of stationary evaporating meniscus on flat plate immersed in liquid pool

Mass Fire Model: An Experimental Study of the Heat Transfer to Liquid Fuel Burning from a Sand-Filled Pan Burner

Abstract: The heat transfer and mass transfer phenomena to a burning array of fuel elements are considered for the various phases of the burning episode which are obtained by burning a fixed amount of liquid fuel in a 152 cm sand-wick pan burner. Quantitative experimental measurements include burning rate, wick temperature distribution, and flame radiation heat flux distributions to the fuel surface as a function of time after ignition. The radiation heat flux is measured with four radiometers which view the flame from beneath the fuel bed with a prescribed view-angle. The total heat flux from the fire plume to the fuel surface is determined from the burning rate and wick temperature histories. A comparison of the aforementioned results is given for non-luminous and luminous flames using methanol and acetone respectively. A comparison of the total heat flux data and the radiation heat flux data indicates that radiation contributes between 20 and 40 percent of the thermal load to the fuel surface for the me...

Heat transfer apparatus with immiscible fluids

Abstract: A heat transfer device, defined here as a heat link, having a capillary vaporizer adjacent a heat source, transfers heat to a heat sink by vaporization and condensation of a heat transfer fluid within the device. A first passage is provided for conveying vapor from the capillary vaporizer to the heat sink. Another passage which is essentially a continuation of the first passage, conveys condensed liquid from the heat sink to the vaporizer, thus allowing the distance that the liquid must flow through capillary material to be quite short. Contact of the returning liquid with the surface of the vaporizer is assured by providing means for maintaining the temperature of the liquid in the return line at a sufficiently low temperature that any vapor will condense; or, alternatively, by having means for extracting any vapor formed in the returning liquid. In this manner, the heat link operates with high heat flux without any substantial resistance to liquid flow through a long capillary flow path. By thus replacing almost all of the liquid return wick, with its high resistance to fluid flow, of heat pipes with a low flow resistance liquid passage or conduit, the heat flux capacity of the heat link is greatly increased over that of the heat pipe while the quantity of porous material used and the heat link weight are considerably reduced so that a heat link typically has 10 to 1000 times the heat flux capacity of a heat pipe having the same weight. ''''Boosted'''' embodiments of the heat link employing additional means for circulating the fluid, such as vapor jet pumps, powered at least in part by vapor from the capillary vaporizer, are also described. Some ''''boosted'''' heat links are capable of handling heat fluxes in the multi-megawatt range while having no moving parts except for check valves and the fluid itself.

Heat sink capability of jet A fuel - Heat transfer and coking studies

Abstract: The operation of supersonic turbine a i r c ra f t can be err:tended by using more heat sink of the fuel for cooling. Experiments were run wi%h J e t A fuel t o determine the heat t ransfer character is t ics and coking problems associated with t h i s application. Selection of the fuel used was based on coker t e s t s of fuels from several sources. Heat t ransfer t o the fuel was studied and correlations were developed for both laminar and Lwbden t flow of the fuel. Considerable free convection i n laminar flow e&aneed the heat t ransfer and s tabi l ized the flaw a t Reynolds numbers up t o 15,000. Coke deposits were measured for both deoxygenated and aerated fuel in t e s t s up t o 100 hours duration. A 100-hour t e s t run with deoxygen~ted fuel a t a heat flux of about 1 ~tu /secin2 (1.6 Plw/m2) was completed wi.e"n coke deposits l e s s than 1 m i l thick. The maximum tube temperature a t the end of the run was 1 4 0 0 " ~ (760°c), l e s s than the 1 4 5 0 " ~ (788"~) maximum a% the s t a r t of the t e s t . Deposits were found t o be more severe and more irregular with the aerated fuel, and carburization of the tube accmred at the higher temperatures reached i n t h i s case. Different tube materials were screened i n coker t e s t s , and selected ones were tested further i n %he heat t ransfer t e s t r ig . Results of these experiments d i d not indicate any obvious relationship between coking tendency and tube material. Tests showed tha t the tube temperature was the most important variable i n determining deposition rate . Coke deposits were found t o have two ef fec ts on hea"cmns-. fer , a beneficial e f fec t by acting as a turbulence promoter t o kcpease the convective heat t ransfer coefficient and a detrimental e f fec t by increasbg the resistance t o heat transfer. Pressure osci l la t ions i n the t e s t section were audible at certain turbulent flow conditions when the ex i t fuel was near its pseudocritical temperature. Amplitudes ranged up t o 350 ps i (2.4 M N / ~ ~ ) and primlay frequenc ies varied from 1000 t o 5000 Hz.

Film cooling effectiveness and heat transfer with injection through holes

Abstract: An experimental investigation of the local film cooling effectiveness and heat transfer downstream of injection of air through discrete holes into a turbulent boundary layer of air on a flat plate is reported. Secondary air is injected through a single hole normal to the main flow and through both a single hole and a row of holes spaced at three diameter intervals with an injection angle of 35 deg to the main flow. Two values of the mainstream Reynolds number are used; the blowing rate is varied from 0.1 to 2.0. Photographs of a carbon dioxide-water fog injected into the main flow at an angle of 90 deg are also presented to show interaction between the jet and mainstream.

Experimental Study on the Mechanism of Transition Boiling Heat Transfer : 1st Report, Measurements of Local Solid-Liquid Contact and Temperature Fluctuations on the Heating Surface

Abstract: Measurement of solid-liquid contact and surface temperature fluctuations is conducted in case of nucleate and transition boiling of water on the horizontal copper surface of 8 mm diameter. From these measurements it is inferred that the mechanism of transition boiling is closely related to the behavior of vapor bubbles. The results obtained from the analysis of surface temperature records are as follows. (1) Transition boiling is distinguished by intermittent solid-liquid contact and the fluctuation of heat flux corresponding to the periodic departure of vapor bubbles from heating surface. (2) Local time rate of solid-liquid contact, which is smallest at the center of heating surface and largest at he circumference, decreases rapidly with the increase of wall superheat. (3) Transition boiling heat transfer can be explained as the coexistence of nucleate boiling heat transfer in the solid-liquid contact part and film boiling heat transfer in the solid-vapor contact part.

Heat transfer in a cylindrical cavity

Abstract: An analytical solution is developed to describe the unsteady-state heat transfer to a cylindrical cavity with circulating flow induced by a moving wall. The previously derived velocity field at low Reynolds numbers is incorporated into the energy equation, and the case of heat transfer to a fluid segmented by highly conducting plugs flowing in a tube with constant wall temperature is considered. Calculations of temperature distributions, average temperatures, and heat transfer coefficients as functions of time and Peclet number are presented for a specific cavity geometry, and the degree of enhancement in heat transfer caused by the recirculating flow is determined.The methods developed in this study may be useful in obtaining analytical solutions to a variety of closed-streamline heat and mass transfer problems with known velocity fields.

Convective heat transfer measurements of plants in a wind tunnel

Abstract: Heat transfer was studied between intact leaves of various sizes and shapes in vivo under free and forced air conditions. Use of a wind tunnel and a microwave transmitter to heat the leaves facilitated measurements of convective, along with radiative and evaporative, heat losses from plant leaves. Knowledge of input energy, analysis of cooling curves, and established formulae, respectively, formed the basis of the steady-state, unsteady-state, and analytical methods for the determination of heat transfer coefficients.

Fuel elements for use in thermionic nuclear reactors

Abstract: 1,185,583. Nuclear power plant. EUROPEAN ATOMIC ENERGY COMMUNITY. 7 March, 1968 [14 April, 1967], No. 11145/68. Heading G6C. In a nuclear reactor thermionic fuel element, heat is removed by a heat pipe in which the thermionic elements are mounted. The thermionic units 10 are supported in the heat pipe 11, in which sodium vapour flows from the fission zone 16 to the condensing end 18. The condensate is returned to 16 through the capillary structure 19. Each thermionic unit is formed of nuclear fuel 12 in emitter envelope 13 which is supported in the heat pipe by the electrically insulating ring 17 which engages the emitter screen and cover 14, 15. The thermionic collector is formed by the pipe 11. With fuel elements stacked vertically, the emitter covers 15 of one element are connected in parallel by the heat pipe 11 of element above. In a further embodiment, the thermionic units have planar electrodes and are mounted in the upper surface of a heat pipe.

A review of basic aspects of heat transfer under impinging air jets

Abstract: The literature on the heat transfer occurring from impinging hot air jets, now employed in many driers is reviewed. Variations in average and local heat transfer coefficients and other parameters are discussed in respect to jet air velocity, distance from jet to the impinged surface, and jet turbulence level. Areas which require additional research are pointed out, in addition to a discussion on elementary heat transfer and a brief review of research on mass transfer occurring under impinging jets.