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Showing papers on "Subcooling published in 1994"


Book
01 Jan 1994
TL;DR: In this paper, the basic models of two-phase flow are discussed and empirical treatments of two phase flow are provided. But the authors focus on convective boiling and condensing.
Abstract: Introduction 1. The basic models 2. Empirical treatments of two-phase flow 3. Introduction to convective boiling 4. Subcooled boiling heat transfer 5. Void fraction and pressure drop in subcooled boiling 6. Saturated boiling heat transfer 7. Critical heat flux in forced convective flow - 1. Vertical uniformly heated tubes 8. Critical heat flux in forced convective flow - 2. More complex situations 9. Condensation 10. Conditions influencing the performance of boiling and condensing systems 11. Multi-component boiling and condensation Appendix Index

2,426 citations


Journal ArticleDOI
TL;DR: In this article, an experimental study of pressure drop and CHF in mini-channel (D = 2.54 mm ) and micro-channel heat sinks of 1 cm heated length was performed using R-113.

467 citations


Journal ArticleDOI
TL;DR: In this article, the critical heat flux (CHF) of subcooled flow boiling was analyzed based on the liquid sublayer dryout mechanism, i.e. the dryout of a thin liquid layer beneath an intermittent vapour blanket due to the coalescence of small bubbles.

161 citations



Journal ArticleDOI
TL;DR: In this article, an experimental study of forced convective subcooled boiling heat transfer to water was performed at heat fluxes that ranged beyond 10 8 W m −2, and the predictive ability for the critical heat flux (CHF) at high heat flux was obtained.

123 citations


Journal ArticleDOI
TL;DR: In this article, an analysis of available correlations and models for the prediction of critical heat flux (CHF) in subcooled flow boiling in the range of interest of fusion reactors thermalhydraulic conditions, i.e. high inlet liquid subcooling and velocity and small channel diameter and length, is presented.

102 citations


Journal ArticleDOI
TL;DR: The very high pressures that occur during the final stages of collapse of a cavitation bubble force the water in the vicinity of the bubble wall briefly (∼ 1 ns) into a metastable state of subcooling relative to the equilibrium phase diagram.
Abstract: The very high pressures (≳1 GPa) that occur during the final stages of collapse of a cavitation bubble force the water in the vicinity of the bubble wall briefly (∼1 ns) into a metastable state of subcooling, relative to the equilibrium phase diagram. Estimates show that the subcooling can fall below the critical temperature for homogeneous nucleation of freezing and that high‐pressure ice particles form at a sufficient rate to affect the collapse. Because of the greater density of high‐pressure ice, a sudden drop in pressure occurs that triggers a shock wave that converges at the center of the compressed gas in the bubble. Such microshocks are believed to be the cause of the extremely short duration of the flashes of sonoluminescence (<50 ps) that have been observed from single cavitation bubbles. The occurrence of transient, high‐pressure solidification can explain different phenomena associated with cavitation, specifically the decrease in cavitation erosion and the increase in sonoluminescence as the ...

85 citations


Journal ArticleDOI
TL;DR: In this paper, an experimental and theoretical study of flow and heat transfer regimes during quenching of a heated vertical channel is presented, and the quench front lies in the transition boiling region which spreads into the dry and wet segments.

53 citations


Journal ArticleDOI
TL;DR: In this article, the flow behavior in an open two-phase natural circulation loop was studied experimentally using Freon-113, and three basic circulation modes were observed with variation of the heat flux: periodic circulation, continuous circulation, and periodic circulation.

51 citations


Journal ArticleDOI
TL;DR: In this article, the authors used high-speed photography and digital image processing techniques to obtain a database for the development of interfacial transport models, or correlations, for subcooled water-steam flow in vertical conduits.

50 citations



Patent
28 Oct 1994
TL;DR: In this article, a non-azeotropic mixture refrigerant comprising at least two kinds of refrigerant of different boiling temperatures mixed together is charged in and circulated through the refrigeration cycle.
Abstract: A refrigeration cycle comprises a compressor, an indoor heat exchanger, an outdoor heat exchanger, a liquid receiver; and a pressure reducer connected in series to form a closed loop. The liquid receiver and the pressure reducer connected in series are connected between the indoor heat exchanger and said outdoor heat exchanger. A non-azeotropic mixture refrigerant comprising at least two kinds of refrigerant of different boiling temperatures mixed together is charged in and circulated through the refrigeration cycle. The mixing ratio of the azeotropic mixture refrigerant circulated thorough the refrigeration cycle is controlled substantially constant.

Journal ArticleDOI
TL;DR: In this article, a phenomenological void growth model is presented which accounts for the vapor volume inside a heated channel at atmospheric pressure, and includes the bubble ebullition cycle, formulated on the basis of information obtained from a high speed photographic study.

Journal ArticleDOI
TL;DR: In this article, the optimum value of the subcooling evaporator temperature is predicted using an ideal dedicated sub-cooling cycle, which leads to a design rule for the optimum distribution of heat exchange area for the dedicated sub cooling cycle.
Abstract: Dedicated mechanical subcooling cycles utilize a small mechanical vapour-compression cycle, coupled to the main cycle at the exit of the condenser, to provide subcooling to the main refrigeration cycle. The amount of subcooling, the thermal lift of the subcooling cycle, and consequently the performance of the overall cycle, can be directly related to the temperature of the subcooling cycle evaporator. In this paper, the optimum value of the subcooling evaporator temperature is predicted using an ideal dedicated subcooling cycle. These results are then compared with those generated from a property-dependent model. The consideration of this optimum subcooling evaporator temperature leads to a design rule for the optimum distribution of heat exchange area for the dedicated subcooling cycle.

Journal ArticleDOI
TL;DR: In this article, the effects of reduced gravity on the flow regime and the heat transfer characteristics of a boiling two-phase horizontal flow were studied by using an aircraft in parabolic flight experiments.


Journal ArticleDOI
TL;DR: In this paper, the critical heat flux (CHF) in forced convection over a flat surface at relatively low flow velocities has been found, not unexpectedly, to depend upon the orientation of the buoyancy.
Abstract: The critical heat flux (CHF) in forced convection over a flat surface at relatively low flow velocities has been found, not unexpectedly, to depend upon the orientation of the buoyancy. The CHF for R-113 was measured at various heating surface orientations for test section Reynolds numbers ranging between 3000 and 6500. In this flow range, the buoyancy force acting on the vapor generally dominates over the flow inertia, yet the inertia would still be substantial were gravity to be reduced. In the experiments of this study, the CHF is determined for heating surface orientations ranging from 0 deg to 360 deg, for flow velocities between 4 cm/s and 35 cm/s, and for subcoolings between 2.8 C and 22.2 C. The results presented here demonstrate the strong influence of buoyancy at low flow velocities, which diminishes as the flow velocity and subcooling are increased. 15 refs.

Journal ArticleDOI
01 Jun 1994-Energy
TL;DR: In this article, a vapor-compression refrigeration cycle with a mechanical subcooling loop was investigated by using both the first and second laws of thermodynamics, and it was found that the performance of the system can be significantly improved by reducing the irreversibilities due to the expansion process.

Journal ArticleDOI
TL;DR: In this article, the authors reported the results of an experimental investigation about the occurrence of the critical heat flux (CHF) in subcooled flow boiling of water, carried out to ascertain the influence of thermal hydraulic parameters on CHF under conditions typical of thermonuclear fusion divertor thermal hydraulic design.

Journal ArticleDOI
TL;DR: In this paper, a correlation is formulated for the prediction of limiting heat flux and quality of density-wave-type oscillations in a single-channel, high-pressure forced-convection boiling upflow system using water as working fluid.

Patent
04 Feb 1994
TL;DR: In this paper, a closed-loop mixed-refrigerant cycle was proposed to provide efficient low-level refrigeration for recovering ethylene from a mixed gas feed, which allowed advantageous operation of the feed chilling train at pressures between 150 and 400 psia.
Abstract: A closed-loop mixed refrigerant cycle provides efficient low-level refrigeration for recovering ethylene from a mixed gas feed. Compressed mixed refrigerant vapor is condensed at -20° F. to -50° F. and is subcooled to -175° F. to -225° F. by indirect heat exchange with cold H 2 , methane, and expander streams from elsewhere in the ethylene plant. A portion of the subcooled refrigerant may be flashed to provide additional subcooling of the main mixed refrigerant stream. Subcooled mixed refrigerant is subsequently flashed to provide very low temperature level refrigeration for feed condensation and demethanizer overhead condenser duties. The invention allows advantageous operation of the feed chilling train at pressures between 150 and 400 psia.

Journal ArticleDOI
TL;DR: In this article, eight void fraction models were used in a refrigeration system model to evaluate their impact on the estimation of important system variables in an air conditioner as a function of charging.
Abstract: One variable required for modelling the heat transfer and pressure drop of refrigerant inside air conditioner evaporators and condensers is the void fraction. Eight void fraction models were used in a refrigeration system model to evaluate their impact on the estimation of important system variables in an air conditioner as a function of charging. The void fraction models included: (i) homogeneous, (ii) Lockhart and Martinelli, (iii) Thom, (iv) Zivi, (v) Baroczy, (vi) Hughmark, (vii) Premoli and (viii) Tandon. The system variables considered included: power, capacity, refrigerant flow, subcooling and superheat. Comparisons were made with a 10.6 kW capacity air conditioner with capillary tube expansion. Results indicate that the Hughmark void fraction model appeared to provide the best comparison to measured data over the range of charging conditions considered.

Journal ArticleDOI
TL;DR: In this article, a theory of thermal choking due to nonequilibrium condensation in a nozzles is presented and an explicit equation for the critical quantity of heat in condensing flow has been derived.
Abstract: A theory of thermal choking due to nonequilibrium condensation in a nozzle is presented. An explicit equation for the critical quantity of heat in condensing flow has been derived. The equation is of general validity and applies to vapor-droplet flow with or without a carrier gas. It has been usually assumed in the literature that the classical gas dynamics result for the critical quantity of heat applies in condensing flow as well. The classical result is, however, obtained by considering external heat addition to an ideal gas in a constant area duct. In this paper it is shown that the area variation across the condensation zone (although small) and the depletion in the mass of vapor as a result of condensation have profound effects on the critical quantity of heat. The present equation (derived from an integral, control-volume approach) agrees very well with results from full time-marching solution of the nonequilibrium, differential gas dynamic equations. The classical gas dynamics result, on the other hand, seriously underpredicts the critical heat for condensing flow in nozzles (by a factor of three in the example calculation presented).


Journal Article
TL;DR: In this article, the authors compared experimental mass flow results with HFC-134a and CFC-12 for a variety of inlet conditions and short-tube geometries.
Abstract: Short-tube orifices have been widely used as an expansion device on automotive and residential-sized air conditioners in the United States. The design for optimum performance of these systems requires predicting correct flow characteristics through short tubes for a given set of operating conditions. Insufficient data are available on how any of the new replacement refrigerants will perform in short-tube orifices relative to conventional refrigerants. This paper compares experimental mass flow results with HFC-134a and CFC-12 for a variety of inlet conditions and short-tube geometries. Five sharp-edged short-tube orifices with 7 < LID < 20 and 1.10 mm (0.0435 in.) < D < 1.72 mm (0.0676 in.) were tested with HFC-134a and CFC-12. Both two-phase and subcooled liquid flow conditions entering the short tube were examined for condensing temperatures ranging from 35.4 C (96 F) to 53.8 C (129 F), for subcooling as high as 13.9 C (25 F), and for qualities as high as 10% at the inlet of the short tube. The effects of downstream pressure were also investigated by lowering the downstream pressure from the upstream saturation pressure down to 310 kPa (45 psia). For HFC-134a, two types of measurements were made during this study-mass flow tests andmore » pressure distribution inside the orifice. For CFC-12, only mass flow tests were performed The results with CFC-12 were compared with those of HFC-134a with the same upstream temperature conditions. A comparison of these two refrigerants was made as a function of the main operating variables (upstream pressure, subcooling, and downstream pressure) and short-tube geometry. Semi-empirical models for both HFC-134a and CFC-12 were developed for the prediction of mass flow rate through short tubes.« less

01 Jun 1994
TL;DR: In this paper, the effect of mixing on the depressurization of a large liquid hydrogen storage tank was investigated, and it was shown that the rate of tank pressure change is controlled by the competing effects of subcooled jet flow and the free convection boundary layer flow due to external tank wall heating.
Abstract: Experiments have been conducted to investigate the effect of fluid mixing on the depressurization of a large liquid hydrogen storage tank The test tank is approximately ellipsoidal, having a volume of 489 m(exp 3) and an average wall heat flux of 42 W/m(exp 2) due to external heat input A mixer unit was installed near the bottom of the tank to generate an upward directed axial jet flow normal to the liquid-vapor interface Mixing tests were initiated after achieving thermally stratified conditions in the tank either by the introduction of hydrogen gas into the tank or by self-pressurization due to ambient heat leak through the tank wall The subcooled liquid jet directed towards the liquid-vapor interface by the mixer induced vapor condensation and caused a reduction in tank pressure Tests were conducted at two jet submergence depths for jet Reynolds numbers from 80,000 to 495,000 and Richardson numbers from 0014 to 052 Results show that the rate of tank pressure change is controlled by the competing effects of subcooled jet flow and the free convection boundary layer flow due to external tank wall heating It is shown that existing correlations for mixing time and vapor condensation rate based on small scale tanks may not be applicable to large scale liquid hydrogen systems

Patent
04 Feb 1994
TL;DR: In this article, an open-loop mixed refrigeration cycle was proposed for an ethylene recovery plant, which utilizes components present in the ethylene-containing feed gas as the mixed refrigerant.
Abstract: Refrigeration is provided in an ethylene recovery plant by an open-loop mixed refrigeration cycle which utilizes components present in the ethylene-containing feed gas as the mixed refrigerant Refrigeration is provided by subcooled mixed refrigerant at -175° to -225° F for the demethanizer overhead condenser and for initial cooling and condensation of the ethylene-containing feed gas Overall ethylene recoveries of up to 999% can be achieved at reduced power consumption compared with conventional ethylene recovery cycles In addition, significant capital savings can be realized due to the simplification of equipment with the open-loop mixed refrigerant cycle, which can be operated advantageously at pressures between 150 and 400 psia

01 Sep 1994
TL;DR: The feasibility of using densification or subcooling with respect to standard temperature propellants on the Space Transportation System (STS) in order to achieve a payload gain is discussed in this article.
Abstract: The feasibility of using densification or subcooling with respect to standard temperature propellants on the Space Transportation System (STS) in order to achieve a payload gain is discussed in this report. The objective is to determine the magnitude of the payload gain and to identify any system impacts to the space shuttle on either flight systems or ground systems. Results show that a payload benefit can be obtained by subcooling the liquid hydrogen (LH2) from a nominal temperature of 36.4 R to 28.5 R and by subcooling the liquid oxygen (LO2) from a nominal temperature of 164 R to either 132.1 R or 141.4 R. When the propellants are subcooled to 28.5 R and 132.1 R for the LH2 and LO2, respectively, a maximum payload gain of 7,324 lb can be achieved, and when the propellants are subcooled to 28.5 R and 141.5 R for the LH2 and LO2, respectively, a maximum payload gain of 6,841 lb can be achieved. If the LH2 is subcooled to 28.5 R while the LH2 and LO2 remains at the nominal conditions, a maximum payload gain of 1,303 lb can be achieved.

Journal ArticleDOI
TL;DR: In this paper, an integrated model of the TOPAZ-II space nuclear reactor system is developed and compared with measurements from the V-71 unit tests, and the model calculates the coolant flow rate, temperature, and pressure throughout the system; load electric power; and overall system efficiency.
Abstract: An integrated model of the TOPAZ-II space nuclear reactor system is developed and compared with measurements from the TOPAZ-II, V-71 unit tests. For a given reactor thermal power, the model calculates the coolant flow rate, temperature, and pressure throughout the system; load electric power; and overall system efficiency. Model predictions showed good agreement with the experimental data. The calculated coolant temperatures and pressure are within 15 K (< 2%) and 12% of the measurements, respectively. Analysis showed that at the nominal operating thermal power of the system (115 kW), and NaK coolant is highly subcooled. The largest subcooling of 365 K occurs at the exit of the electromagnetic pump, where coolant pressure is highest, and the lowest subcooling of 275 K occurs at the exit of the reactor core, where coolant temperature is highest.

Journal ArticleDOI
TL;DR: In this paper, a number of partially fluorinated alkanes and ethers were identified from earlier technical publications and from a joint Electric Power Research Institute/Environmental Protection Agency (EPRI/EPA) project as potential alternatives for chloroflurocarbon (CFC) and hydrogen-containing CFC refrigerants.
Abstract: A number of partially fluorinated alkanes and ethers were identified from earlier technical publications and from a joint Electric Power Research Institute/Environmental Protection Agency (EPRI/EPA) project as potential alternatives for chloroflurocarbon (CFC) and hydrogen-containing CFC refrigerants. These larger molecules, by virtue of their more elaborate structure, have larger vapour phase heat capacities ( C p s) and larger molecular weights than currently used refrigerants, which result in decreased volumetric capacities and greater flash gas losses in simple cycle applications. The compounds were fitted to the Lee-Kessler-Plocker and Carnahan-Starling-DeSantis equations of state, and refrigerant property routines based on these equations were used to simulate their performance in a single-stage centrifugal chiller as pure refrigerants and nearly azeotropic refrigerant mixtures. Consideration was given to the effects of acoustic velocity in the refrigerant, rotational mach numbers, the application of superheat prior to the compressor inlet to avoid ‘wet isentropic compression’, and liquid subcooling before isenthalpic expansion. Results indicate that several chlorine-free compounds give modelled chiller performance comparable to R11 and R123 and better than R12 and R134a. Blends of these refrigerants may be required to mitigate the inflammability of alternatives that show the best performance. Modifications to the basic chiller cycle — such as liquid subcooling and suction gas superheat — may offer unique advantages for more complicated, larger refrigerant molecules. An algorithm based on molecular bond energies and vapour phase C p s was used to estimate the flammability of these alternatives and of blends made from them. Depending on desirable and permissible deviations from the currently used chiller operating conditions and on the acceptability of flammable refrigerant combinations, ideal coefficients of performance comparable to R11 and 5–10% better than R12 are indicated.