Showing papers on "Subcooling published in 2002"
TL;DR: In this paper, both single-phase forced convection and sub-cooled and saturated nucleate boiling experiments have been performed in small rectangular channels using FC-84 as test fluid.
327 citations
TL;DR: In this paper, a correlation for predicting the wall superheat and wall heat flux at ONB has been developed from the data obtained in this study and that reported in the literature.
Abstract: The partitioning of the heat flux supplied at the wall is one of the key issues that needs to be resolved if one is to model subcooled flow boiling accurately. The first step in studying wall heat flux partitioning is to account for the various heat transfer mechanisms involved and to know the location at which the onset of nucleate boiling (ONB) occurs. Active nucleation site density data is required to account for the energy carried away by the bubbles departing from the wall. Subcooled flow boiling experiments were conducted using a flat plate copper surface and a nine-rod (zircalloy-4) bundle. The location of ONB during the experiments was determined from visual observations as well as from the thermocouple output. From the data obtained it is found that the heat flux and wall superheat required for inception are dependent on flow rate, liquid subcooling, and contact angle. The existing correlations for ONB underpredict the wall superheat at ONB in most cases. A correlation for predicting the wall superheat and wall heat flux at ONB has been developed from the data obtained in this study and that reported in the literature. Experimental data are within630 percent of that predicted from the correlation. Active nucleation site density was determined by manually counting the individual sites in pictures obtained using a CCD camera. Correlations for nucleation site density, which are independent of flow rate and liquid subcooling, but dependent on contact angle have been developed for two ranges of wall superheat—one below 15°C and another above 15°C. @DOI: 10.1115/1.1471522#
300 citations
TL;DR: In this article, experimental data for subcooled flow boiling of water at pressures from 105 to 3 bar, bulk liquid velocities ranging from 008 to 08 m/s, and subcooling from 10 to 30 K were presented.
227 citations
TL;DR: In this article, a two-fluid model was used for predicting subcooled boiling flow at high pressure into being applicable for low-pressure conditions, and the following closure relationships or parameters are important for an accurate prediction of void fraction distributions at low pressures: (i) partition of the wall heat flux; (ii) bubble size distribution and interfacial area concentration; and (iii) bubble departure diameter and its relationship with bubble frequency.
191 citations
TL;DR: In this paper, the radial profiles of local void fraction and velocities of both phases were measured in subcooled boiling flow of water in a vertical concentric annulus with a heated inner tube.
139 citations
TL;DR: In this article, a dimensionless correlation based on Buckingham π theorem was developed to predict the mass flow rate through the capillary tubes for R22, R407C and R410A.
Abstract: The objective of this study is to present test results and to develop a dimensionless correlation on the basis of the experimental data of adiabatic capillary tubes for R22 and its alternatives, R407C (R32/125/134a, 23/25/52 wt.%) and R410A (R32/125, 50/50 wt.%). Several capillary tubes with different length and inner diameter were selected as test sections. Mass flow rate through the capillary tube was measured for several condensing temperatures and various degrees of subcooling at the inlet of each capillary tube. Experimental conditions for the condensing temperatures were selected as 40, 45 and 50°C, and the degrees of subcooling were adjusted to 1.5, 5 and 10°C. Mass flow rates of R407C and R410A were compared with those of R22 for the same test conditions. The results for straight capillary tubes were also compared with those of coiled capillary tubes. A new correlation based on Buckingham π theorem to predict the mass flow rate through the capillary tubes was presented based on extensive experimental data for R22, R407C and R410A. Dimensionless parameters were chosen considering the effects of tube geometry, capillary tube inlet conditions, and refrigerant properties. Dimensionless correlation predicted experimental data within relative deviations ranging from −12% to +12% for every test condition for R22, R407C and R410A. The predictions by the developed correlation were in good agreement with the results in the open literature.
129 citations
TL;DR: In this paper, measurements of space and time resolved subcooled pool boiling of FC-72 in low, earth, and high gravity environments were made using a microscale heater array.
120 citations
Patent•
02 Apr 2002
TL;DR: In this article, a method of determining refrigerant charge level in a space temperature conditioning system includes the steps of establishing a relationship between at least one selected system operating parameter and refrigerant level, independent of ambient temperature conditions; measuring the selected parameter(s) while the system is in operation; and using the established relationship and the measured parameters(s).
Abstract: In accordance with the present invention, a method of determining refrigerant charge level in a space temperature conditioning system includes the steps of establishing a relationship between at least one selected system operating parameter and refrigerant charge level, independent of ambient temperature conditions; measuring the selected parameter(s) while the system is in operation; and using the established relationship and the measured parameter(s) to determine the refrigerant charge level. In one embodiment of the invention, both condenser subcooling and evaporator superheat parameters are measured and the predetermined relationship between charge level and each of these parameters is used to determine the actual refrigerant charge level.
102 citations
TL;DR: In this paper, a high-speed CCD camera was used to record the bubble collapse in the bulk subcooled liquid and the experimental data were in turn used to correlate bubble collapse rate and the interfacial heat transfer rate.
100 citations
TL;DR: In this article, an inverse heat conduction problem is used to calculate the local heat flux and corresponding temperature up to a distance of 55 mm from the stagnation line of a planar jet of water.
98 citations
TL;DR: In this paper, an analytical model for predicting film condensation of vapor flowing inside a vertical mini triangular channel is presented, where the concurrent liquid-vapor two-phase flow field is divided into three zones: the thin liquid film flow on the sidewall, the condensate flow in the corners, and the vapor core flow in center.
TL;DR: In this article, sliding bubble dynamics and associated flow pattern and heat transfer over a downward facing inclined heater surface were experimentally investigated in the subcooled and nearly saturated high performance liquid PF-5060.
TL;DR: In this paper, the effects of body forces perpendicular to a heated wall were examined by conducting 1g flow boiling experiments at different orientations, with the heated surface facing upward or downward relative to gravity.
TL;DR: In this article, a combined power/refrigeration thermodynamic cycle is optimized for thermal performance, which uses ammonia-water binary mixture as a working fluid and can be driven by various heat sources, such as solar, geothermal and low temperature waste heat.
Abstract: A novel combined power/refrigeration thermodynamic cycle is optimized for thermal performance in this paper. The cycle uses ammonia-water binary mixture as a working fluid and can be driven by various heat sources, such as solar, geothermal and low temperature waste heat. It could produce power as well as refrigeration with power output as a primary goal. The optimization program, which is based on the Generalized Reduced Gradient (GRG) algorithm, can be used to optimize for different objective functions. Examples that maximize second law efficiency, work output and refrigeration output are presented, showing the cycle may be optimized for any desired performance parameter. In addition, cycle performance over a range of ambient temperatures was investigated. It was found that for a source temperature of 360K, which is in the range of flat plate solar collectors, both power and refrigeration outputs are achieved under optimum conditions. All performance parameters, including first and second law efficiencies, power and refrigeration output decrease as the ambient temperature goes up. On the other hand, for a source of 440K, optimum conditions do not provide any refrigeration. However, refrigeration can be obtained even for this temperature under non-optimum performance conditions.Copyright © 2002 by ASME
TL;DR: In this paper, experiments and simulations were carried out in this investigation of turbulent subcooled boiling flow of Refrigerant-113 through a vertical annular channel whose inner wall only was heated.
Abstract: Experiments and simulations were carried out in this investigation of turbulent subcooled boiling flow of Refrigerant-113 through a vertical annular channel whose inner wall only was heated. The measurements used, simultaneously, a two-component laser Doppler velocimeter for the liquid velocity field and a fast-response cold-wire for the temperature field, and a dual-sensor fiberoptic probe for the vapor fraction and vapor axial velocity. In the numerical simulation, the two-fluid model equations were solved by the solver ASTRID developed at Electricite de France. Wall laws for the liquid phase time-average axial velocity and temperature were developed from the experimental data, and the turbulent Prandtl number in the liquid was determined from the wall laws. The wall laws and turbulent Prandtl number were used in the simulations. The wall heat transfer model utilized the measured turbulent heat flux distribution in the liquid. Results from the simulations were compared with the measurements
TL;DR: In this article, the transition from partial to fully developed flow boiling with regard to bubble growth rates and the time that individual bubbles spend attached to the heater surface was investigated, and it was shown that bubble agitation becomes a leading heat transfer mode with increasing heat flux.
TL;DR: In this article, a theoretical and experimental study of density wave oscillation (DWO) in natural circulation is presented, which is a function of non-dimensional parameters, such as phase change number Npch, subcooling number Nsub, Froude number, Fr, geometry number Nl and friction number τ.
TL;DR: In this paper, the authors carried out an experimental study of the absorption of water vapour over a wavy laminar falling film of water-lithium bromide on the inner wall of a smooth vertical tube.
TL;DR: In this article, an experimental study on growth and detachment mechanisms of a single bubble on a heated surface conducted during the parabola flight of the KC-135 aircraft is described.
Abstract: Results of an experimental study on growth and detachment mechanisms of a single bubble on a heated surface conducted during the parabola e ights of the KC-135 aircraft are described. An artie cial cylindrical cavity 10 πm in diameter was etched in the center of a silicon wafer. The wafer was heated on the back side, and the wall superheat was controlled. Degassed distilled water was used as the test liquid. Bubble growth time, bubble size and shape from nucleation to liftoff were measured under subcooled and saturation conditions at system pressures varying from 0.101 to 0.115 MPa. The wall superheats were varied from 2.5 to 8.0 ±C. Signie cantly larger bubble diametersand longerbubble growth periods than thoseat Earth normal gravity were measured. Bubblediameters as large as 20 mm at liftoff were observed as opposed to about 2.5 mm at Earth normal gravity. Consistent with results of numerical simulations, it is found that for the same wall superheat and liquid subcooling the bubble liftoff diameter can be approximately related to the gravity level through the relation Dd / g i 0:5 and the growth period as tg / g i 1:05 . The effect of wall superheat and liquid subcooling on bubble liftoff diameter is found to be small. However, the growth periods are found to be very sensitive to liquid subcooling at a given wall superheat. Small accelerations along the heater surface can lead to sliding motion of the bubble prior to liftoff. At the same gravitational acceleration the liftoff diameter of sliding bubbles is smaller than that of nonsliding bubbles.
TL;DR: In this paper, a flat aluminium multiport extruded tube composed of 11 parallel rectangular channels (3.28 mm × 1.47 mm) with hydraulic diameter of 2.01 mm was used.
TL;DR: In this article, a study on the crystal growth of dendrite ice in water-ethyleneglycol solution was carried out, experimentally, and it was shown that the shape of the crystal was different from that of the one in pure water.
Abstract: Study on the crystal growth of ice in water-ethyleneglycol solution was carried out, experimentally. The ice crystal, which was seeded on top of the capillary tube, propagated inside the tube slowly and began to grow freely at the tip of the tube in subcooled solution. The outer diameter of the tip of the capillary tube was less than 0.1 mm, which was much smaller than that of other researchers. Hence, considerable reduction of the influence of the existence of a capillary was accomplished and the initial growth of a single crystal was observed, precisely. Under the condition of subcooling of less than 8 K, the shape of the crystal was observed to be different from that of the one in pure water. The velocity of dendrite ice growth and the radius of the curvature of the tip were measured. It was found that after the dendrite ice developed to a certain size, the velocity of the dendritic growth and the radius of curvature were kept steady, and its values were dependent on the degree of subcooling and the concentration of the solution.
TL;DR: In this paper, the onset of flow instability and critical heat flux (CHF) in heated thin horizontal annular flow passages cooled by subcooled water were investigated and the effect of dissolved noncondensables on OFI was examined by performing similar experiments with degassed water and water saturated with air at test section inlet temperature and exit pressure.
TL;DR: In this article, a vertical plate heat exchanger with a corrugated sinusoidal shape of a chevron angle of 60° was used to visualize the boiling flow in a vertical PHE.
TL;DR: In this article, the functioning of the subcooled boiling model adopted in a thermal-hydraulic computer program has been investigated in detail, for low-pressure conditions, and necessary refinements have been incorporated into the code.
TL;DR: In this article, a numerical model of simultaneous mass and heat transfers between the liquid and gas phases in the jet ejector was developed, and the steady-state model was based on unidimensional balance equations of mass, energy and momentum.
TL;DR: In this article, the feasibility of a vapor compression/absorption hybrid refrigeration cycle for energy saving and utilization of waste heat is discussed, and a prototype of the cycle is constructed, in which a compressor and an absorption unit are combined in series.
Abstract: This paper discusses the feasibility of a vapor compression/absorption hybrid refrigeration cycle for energy saving and utilization of waste heat. The cycle employs propane as a natural refrigerant and a refrigeration oil as an absorbent. A prototype of the cycle is constructed, in which a compressor and an absorption unit are combined in series. The performance of the cycle is examined both theoretically and experimentally. Although the solubility of the propane with the oil is not enough as a working pair in the absorption unit, the theoretical calculation shows that the hybrid cycle has a potential to achieve a higher performance in comparison with a simple vapor compression cycle by using the waste heat. In the experiment, the prototype cycle is operated successfully and it is found that an improvement of an absorber is necessary to achieve the good performance close to the theoretical one. The application of an AHE (absorber heat exchanger) can reduce the heat input to a generator. Further examinations on some other combinations of refrigerant/refrigeration oil and additives are desirable.
TL;DR: In this paper, the experimental investigation of two phase flow instabilities in a horizontal in-tube flow boiling system whose test tube is relatively long was conducted at constant heat input, system pressure and exit restriction.
TL;DR: In this article, an experimental investigation of the dynamics of, and the heat transfer to, the vapor bubbles condensing in a miscible or an immiscible liquid is presented.
TL;DR: In this paper, an experimental facility for forced convective subcooled boiling of water was constructed and built up for water at low system pressure using optical measurement techniques, and the imaging and observation techniques presented in [1] were further developed by combining the high speed camera with an additional low speed, high resolution CCD camera.
TL;DR: In this paper, a microscale heater array 2: 7m m� 2:7 mm in size along with a video camera was used to provide subcooled pool boiling heat transfer measurements at gravity levels ranging from 1.8g to 10 � 6 g.