Showing papers on "Subcooling published in 1985"

Subcooled Flow Boiling Critical Heat Flux (CHF) and Its Application to Fusion Energy Components. Part I. A Review of Fundamentals of CHF and Related Data Base

Abstract: The present understanding of critical heat flux (CHF) in subcooled flow boiling with water is reviewed and fusion reactor component high-heat flux (HHF) requirements are outlined. This survey (Part...

Subcooled Flow Boiling Critical Heat Flux (CHF) and Its Application to Fusion Energy Components. Part II. A Review of Microconvective, Experimental, and Correlational Aspects

Abstract: Microconvective, instability, experimental, and correlational aspects of subcooled flow boiling critical heat flux (CHF) are summarized. The present understanding of CHF in subcooled flow boiling i...

Melting Around a Migrating Heat Source

Abstract: The problem of melting around a moving heat source arises in many different situations such as nuclear reactor technology (i.e., “self-burial” process of nuclear waste materials and reactor core “melt-down”), process metallurgy, and geophysics. Experiments were undertaken with a horizontal cylindrical heat source that melted its way through a phase-change material (n-octadecane) under its own weight. The heat source velocity and solid-liquid interface motion for a constant surface temperature source were measured. Effects of heat source density and surface temperature as well as the effects of the initial subcooling of the solid were investigated and are reported. The flow structure in the melt was visualized using a dye. Timewise variation of temperature distribution in the solid and the melt were also measured and are discussed. Results for the heat source migration velocity and the volume of the material melted are correlated in terms of the relevant problem parameters.

Deep flash LNG cycle

Abstract: A system for liquefying and subcooling natural gas wherein compression power is shifted off the closed cycle refrigerant by subcooling the liquid natural gas to a relatively warm exit temperature and subsequently reducing the pressure and flashing the liquefied natural gas to recover a gaseous phase natural gas in excess of plant fuel requirements, the excess being recompressed and recycled to the feed to the process.

Pool Boiling Heat Transfer in Narrow Horizontal Annular Crevices

Abstract: Experimental results of the pool boiling in horizontal narrow annuli are reported. The effects of fluid properties, pool subcooling, crevice length, and gap size on the boiling behavior and the critical heat flux (CHF) are also studied. The CHF decreases with decreasing gap size or increasing length of the annuli. The lower CHF of narrow crevices may be explained by the thin film evaporation. A semi-empirical correlation is established for the CHF of pool boiling in horizontal confined spaces. This correlation is compared with the CHF data of the present experiment. Satisfactory agreement is obtained.

Experiments on fluid flow induced by melting around a migrating heat source

Abstract: A series of melting experiments with a moving horizontal cylindrical heat source at constant surface heat flux have been performed. The heat source was designed in such a way that it could descend under its weight while melting the phase-change material (n-octadecane) surrounding it. The heat-source velocity was measured and the motion and shape of the solid–liquid interface were determined photographically. The effects of the surface heat flux, the density and initial position of the heat source, and the initial subcooling of the solid were investigated and are discussed. Conduction was found to be the dominant heat-transfer mechanism around the lower stagnation point and controlled the terminal velocity of the source. The fluid motion in the melt pool above the heat source was mainly induced by the descent of the source, while natural convection played only a relatively minor role in the motion.

Method and apparatus for providing sterilized cryogenic liquids

Abstract: The invention includes a method and apparatus for providing a sterilized cryogenic liquid. A cryogenic liquid is vaporized, and the resulting gas is sterilized. The sterilized gas is then reliquefied and subcooled. The liquid is vaporized by passing the liquid through a heat exchanger, heat being transferred from the previously sterilized gas to the incoming liquid. Sterilization is accomplished either by passing the gas through a microporous filter, or by subjecting the gas to ultraviolet radiation. The sterilized gas, after passing through the heat exchanger, is directed into a pressurized container, wherein the gas is reliquefied and subcooled. The subcooled liquid is then withdrawn from the apparatus.

Transient Heat Transfer for a Water Drop Impinging on a Heated Surface : 1st Report, Effects of Drop Subcooling on the Liquid-Solid Contact State

Abstract: This paper deals with transient heat transfer for a water drop impinging on a heated surface in the surface temperature range from the maximum boiling rate point to the non-wetting region. The boiling curves were obtained by analyzing the transient temperature variation inside the heated surface taking account of the time variation of the area covered by the drop. Comparing the boiling curves obtained in this way with that for pool boiling, the heat flux in both cases increases with an increasing subcooling, while the heat flux in the present case is several times higher than that for pool boiling. It was proved that the maximum heat flux point of the boiling curve was located on an extension of the nucleate pool boiling curve and that the boiling heat transfer for a drop on the heated surface was classified into four types according to the degree of subcooling and the heated surface temperature.

An Experimental Investigation of the Effect of Subcooling on Bubble Growth and Waiting Time in Nucleate Boiling

Abstract: The effect of subcooling on bubble waiting time and growth time for water boilng on a copper surface was examined in conjunction with measurements obtained over a range of subcooling from 0 to 15/sup 0/C and three different levels of heat flux 166, 228, and 291 kW/m/sup 2/. The growth-time data was successfully correlated with a model that combined the bubble growth theory of Mikic Rohsenow, and Griffith with the bubble departure diameter relationship of Staniszewski, thereby establishing confidence in the measuring procedure. The waiting time data agreed with the predictions of the Han and Griffith waiting time theory at lower levels of subcooling but then showed a behavior contrary to that predicted for higher levels of subcooling.

Thermodynamic properties of water in the subcooled region. II

Abstract: An equation is derived for the free energy difference between water and ice in the subcooled (supercooled) region. The calculated vapor pressure difference between ice and water agrees well with experimental measurements. The free energy difference estimated for water in the form of emulsion droplets and bulk water, although small varies significantly with temperature in the subcooled region and is shown to be proportional to the excess free energy arising from the surface effects inherent to the emulsion systems. The accuracy of emulsion data at temperatures below −20 °C therefore could be much lower than previously assumed. In turn this would distort the anomaly functions and give incorrect critical temperature estimates.

Liquid nitrogen distribution system

Abstract: Apparatus for providing a simulated space environment for the testing of articles under low temperature conditions comprising a liquid nitrogen head tank (D), liquid nitrogen subcooler pumps (H), a liquid nitrogen subcooler coil (G), a liquid nitrogen head tank makeup pumps (B), a low pressure liquid nitrogen storage tank (A), a high pressure liquid nitrogen storage tank (C), a liquid nitrogen transfer pump, a vacuum chamber (E) and thermal simulation heat exchanger shrouds (CC, F) contained within the vacuum chamber (E). Appropriate internal and external piping connects these components so that the apparatus can be operted both in a subcooled pressurized closed loop system and in a gravity convection system. While liquid nitrogen in this apparatus will produce a stable uniform temperature of -173°C (-279°F) within the shrouds (CC, F) containing the article to be tested, other liquids with similar low temperature characteristics may be used. A requirement for such liquids when used as a circulating medium with the apparatus herein is that the boiling point thereof at one atmosphere will produce the required test operating temperature.

Effects of density change and subcooling on the melting of a solid around a horizontal heated cylinder

Abstract: The unsteady two-dimensional heat-transfer problem of melting around a horizontal heated cylinder is studied numerically. The cylinder is heated isothermally. A physical model is introduced which accounts for the effects of density change upon melting and subcooling effect, as well as natural convection. Most previous work has assumed that the density number (ratio of solid density to liquid density) is unity. In practice, all solid materials exhibit some density change upon melting. If the density number is greater than one, this induces a blowing effect at the phase-change boundary. If the density number is less than one, a suction effect is produced. This study indicates that the density-change effect on heat transfer during melting is minor. Subcooling results when the solid is at a temperature below the melting temperature. When the melting process begins, some of the available thermal energy must be used as sensible heat, to raise the solid's temperature to the melting point. As a result, less thermal energy is available for melting. Subcooling effects are found to have a substantial effect on the heat-transfer process. The effects of natural convection have been clearly documented, and indicate that natural convection must be included in any realistic model of the melting process. Detailed predictions of the effects of density change and subcooling on the melting process are given. Information on the temperature and flow fields for representative values of Stefan, Rayleigh, Prandtl, subcooling and density number is given. Further results from the numerical solutions include information on local and average heat-transfer rates and sensibleheat gain as well as melt volume as a function of time. Comparisons are made with earlier numerical and analytical results.

Bypass system for a dual refrigeration cycle air conditioner

Abstract: An air conditioner includes a first refrigeration cycle with a capacity-variable type compressor, and a second refrigeration cycle with a constant rotation type compressor, both refrigeration cycles having outdoor heat exchangers while utilizing a single common indoor heat exchanger. The first refrigeration cycle has a bypass passage connected, at one end, between the suction side of the compressor and the indoor heat exchanger, and, at the other end, between the indoor heat exchanger and the outdoor heat exchanger. When the second refrigeration cycle is stopped, or the capacity variable compressor operated at a low operation frequency, a part of the coolant which passes through the outdoor heat exchanger in the first refrigeration cycle flows into the suction side of the compressor through the bypass passage.

Steam explosion experiments with single drops of iron oxide melted with a CO/sub 2/ laser. Part II. Parametric studies

Abstract: The steam explosion experiments performed with single drops of molten iron oxide melted with a CO/sub 2/ laser, described in Part I of this report, were extended here. The following major parameters were varied: ambient pressure, water temperature and subcooling, melt temperature,and melt composition. Also, a few scoping experiments were performed to explore the effects of changing the nature of the coolant, and the viscosity of the melt. As each of the four major parameters was varied, thresholds could be located beyond which explosions were suppressed. However, in general, the explosions could be reinitiated by increasing the magnitude of the triggering pulse. The effects of increasing the ambient pressure up to 1.12 MPa were faster and finer melt fragmentation, and faster and more complete transfer of heat from melt to water. Moreover, triggering became easier over the range of ambient pressure between about 0.15 MPa and approximately 0.7 MPa.

Method of obtaining low temperatures and apparatus for implementing the same

Abstract: A method of obtaining low temperatures comprising pulse-feeding a refrigerant within a step-wise pressure range where boiling occurs, and its vapors are formed at a low pressure. The refrigerant vapors are subsequently compressed and condensed until the formation of a liquid refrigerant. The liquid refrigerant is subcooled and boiled at a low pressure and a temperature out of the boiling temperature step-wise range with the number of steps depending on the final temperature of the refrigerated medium. An apparatus for obtaining low temperatures comprises, successively interconnected in a closed path, an evaporator, a means to separate a liquid refrigerant, associated with at least two differential pressure relays through pressure transducers, a compressor, a condenser, a receiver, a means for pulse feeding of the liquid refrigerant, and a means for uniform distribution of the liquid refrigerant. The evaporator comprises interconnected suction header and at least two heat-exchange plates, one of which is associated with at least two temperature relays through temperature transducers.

NUFREQ-NP: a digital computer code for the linear stability analysis of boiling water nuclear reactors

Abstract: The phenomena of nuclear-coupled density-wave oscillations are of considerable importance in boiling water nuclear reactor (BWR) stability analysis. A state-of-the-art linear frequency domain digital computer code, NUFREQ-NP, has been developed for either forced or natural circulation BWR stability analysis. The NUFREQ-NP code can be excited by many external perturbations, including system pressure perturbation. It is based on one dimensional drift-flux thermal hydraulics, and allows for subcooled boiling, arbitrary nonuniform axial and radial power shapes, distributed local losses (e.g., spacers), point or multi-dimensional neutron kinetics, and detailed fuel element dynamics. It has been compared with both out-of-core and in-core data, and good agreement has been found.

Subcooled boiling heat transfer in four types of boiling systems by combining flow pattern and surface orientation.

Abstract: 伝熱面へ鉛直方向から液体を供給する吹き付け沸騰・伝熱面周囲から鉛直方向へ液体を吸い上げる吸込み沸騰の流動様式のそれぞれに,水平上向きおよび下向きの伝熱面姿勢を組合わせた四つの特殊サブクール沸騰系の実験をおこない,サブクール度80Kの熱伝達特性について比較考察した.とくにDNB点以降でそれぞれの沸騰系に特徴が現れ,上向きの吹込み流れでは気泡の微細化現象を伴う高熱流束の熱伝達を示した.

Inverted annular flow experimental study

Abstract: Steady-state inverted annular flow of Freon 113 in up flow was established in a transparent test section. Using a special inlet configuration consisting of long aspect-ratio liquid nozzles coaxially centered within a heated quartz tube, idealized inverted annular flow initial geometry (cylindrical liquid core surrounded by coaxial annulus of gas) could be established. Inlet liquid and gas flowrates, liquid subcooling, and gas density (using various gas species) were measured and varied systematically. The hydrodynamic behavior of the liquid core, and the subsequent downstream break-up of this core into slugs, ligaments and/or droplets of various sizes, was observed. In general, for low inlet liquid velocities it was observed that after the initial formation of roll waves on the liquid core surface, an agitated region of high surface area, with attendant high momentum and energy transfers, occurs. This agitated region appears to propagate downsteam in a quasi-periodic pattern. Increased inlet liquid flow rates, and high gas annulus flow rates tend to diminish the significance of this agitated region. Observed inverted annular flow (and subsequent downstream flow pattern) hydrodynamic behavior is reported, and comparisons are drawn to data generated by previous experimenters studying post-CHF flow.

Study on Dropwise Condensation Curves : Measurement of Propylene Glycol Vapor on PTFE Coated Surface

Abstract: By realizing dropwise condensation of propylene glycol vapor on PTFE coated surface, dropwise condensation curves were measured over a wide range of surface subcooling and the modes of condensate were observed using video recording and photography simultaneously. The parametric trends were presented by the experiments conducted for the four cases i.e., two values each for departing drop diameters and vapor pressures. Although the curve shapes of propylene glycol vapor were similar to those of steam on oleic acid promoted copper surface, the values of heat transfer coefficient and heat flux were much smaller and the transition mode from drop type to film type was quite different. Further, the effect of non-condesable gas on heat transfer was demonstrated to be negligible in the measurement.

Corium quench in deep pool mixing experiments

Abstract: The results of two recent corium-water thermal interaction (CWTI) tests are described in which a stream of molten corium was poured into a deep pool of water in order to determine the mixing behavior, the corium-to-water heat transfer rates, and the characteristic sizes of the quenched debris. The corium composition was 60% UO/sub 2/, 16% ZrO/sub 2/, and 24% stainless steel by weight; its initial temperature was 3080 K, approx.160 K above the oxide phase liquidus temperature. The corium pour stream was a single-phase 2.2 cm dia liquid column which entered the water pool in film boiling at approx.4 m/s. The water subcooling was 6 and 75C in the two tests. Test results showed that with low subcooling, rapid steam generation caused the pool to boil up into a high void fraction regime. In contrast, with large subcooling no net steam generation occurred, and the pool remained relatively quiescent. Breakup of the jet appeared to occur by surface stripping. In neither test was the breakup complete during transit through the 32 cm deep water pool, and molten corium channeled to the base where it formed a melt layer. The characteristic heat transfer rates measured 3.5 MJ/s and 2.7 MJ/s during more » the fall stage for small and large subcooling, respectively; during the initial stage of bed quench, the surface heat fluxes measured 2.4 MW/m/sup 2/ and 3.7 MW/m/sup 2/, respectively. A small mass of particles was formed in each test, measuring typically 0.1 to 1 mm and 1 to 5 mm dia for the large and small subcooling conditions, respectively. 9 refs., 13 figs., 1 tab. « less

Pressure noise in pressurized water reactors

Abstract: A general study of pressure fluctuations (noise) in the primary coolant loop of pressurized water reactors (PWRs) was performed. The study included noise sources, PWR pressure dynamics, and pressure-noise measurements. A detailed model of noise in the Loss-of-Fluid Test (LOFT) Facility was developed and compared against measurements. The potential of pressure-noise measurements for reactor monitoring and diagnosis of problems was assessed, particularly collapse of the pressurizer steam bubble, loss of subcooling, and sensing-line defects. 26 refs., 30 figs., 12 tabs.