Showing papers on "Subcooling published in 1981"

Critical Heat Flux in Helically Coiled Tubes

Abstract: A study of boiling R-113 in electrically heated coils of various diameters is reported. Sub-cooled critical heat flux (CHF) is lower with coils than with straight tubes. The differences increases as mass velocity and ratio of tube diameter to coil diameter (d/D) increases. On the contrary, quality CHF is enhanced in increases with d/D;CHF initially increases with increasing mass velocity, but decreases after a maximum is reached. Operational problems, in particular upstream dryouts, can occur if a coiled tube is operated with low to moderate subcooling neat the inlet and with moderately high heat fluxes.

Energy saving refrigeration system

Abstract: A refrigeration system having an increased efficiency of operation and reduction in power consumption. Low head pressure and subcooling the liquid refrigerant emitted from the remote condenser, the efficiency of operation of the compressor of the refrigeration system can be substantially increased. The particular type of refrigeration system of concern generally includes a compressor for compressing a gaseous refrigerant, a condenser for condensing the gaseous refrigerant and subcooling the liquid refrigerant, a receiver for receiving the liquid and a plurality of display cases having evaporators for evaporating the liquid refrigerant. The gaseous refrigerant passing through the condenser is first condensed into a liquid at a condensing temperature of approximately 10° to 25° F. above a preselected cooling temperature. The condensed liquid is then subcooled to the preselected cooling temperature which should be preferably either approximately 50° F. or the temperature of the ambient atmosphere surrounding the condenser, whichever is higher.

Quenching Studies on a Zircaloy Rod Bundle

Abstract: Quenching data are presented for reflooding by cold water of zircaloy and stainless steel clad rod bundles. In particular a filling material (Al/sub 2/O/sub 3/) with thermophysical properties similar to UO/sub 2/ is used. The rods which are 1.1 mm in outside diameter and are 1.2 m high are arranged in a square lattice and are inductively heated. The experiments have been performed with initial rod surface temperatures up to 1400 K and flooding velocity varying over the range 1--30 cm/s. The subcooling of water at inlet was either 75 K and 50 K. Under identical flow conditions zircaloy is observed to quench faster than stainless steel. The quenching temperature and quench front velocity are found to increase with liquid subcooling and flooding velocity. The present data have been correlated and compared with existing models and correlations.

Study of nonequilibrium flashing of water in a converging-diverging nozzle. Volume 2. Modeling

Abstract: A steady water loop with well controlled flow and thermodynamic conditions was designed, built, and made operational for the measurement of net vapor generation rates under nonequilibrium conditions. The test section consists of a converging-diverging nozzle with 49 pressure taps and two observation windows at the exit. Pressure distributions, photographic observations, diametrical averaged centerline void fraction distributions, detailed transverse distributions of the chordal averaged void fractions at 27 axial locations, and area averaged void fraction distributions along the nozzle were recorded under various flashing conditions. The development of voids in nonequilibrium flashing flows is shown to be dependent on three major factors of the void inception point which determines the initial and subsequent liquid superheats and must be accurately described; of the interfacial mass transfer rates, which depend on the local superheat and must be specified; and the local interfacial area density where the mass transfer occurs. The flashing onset correlation of Alamgir and Lienhard was extended to predict flashing inception in pipe and nozzle flows with subcooled inlet conditions. A void development model for bubbly flows was based on a simple concept for interfacial area density in conjunction with a conduction-controlled bubble growth law. A general model of vapormore » generation following flashing inception was also developed. In this model, bubbly flow, bubbly-slug flow, a transitional flow comprising the annular and annular-mist regimes and finally fully dispersed droplet flow were assumed to occur at successively higher void fraction ranges. On the basis that flashing inception occurred at the throat in nozzle flows with subcooled inlet conditions, and that the pressure undershoot can be calculated, a method of calculating the critical mass flow rates through nozzles was proposed, and it was checked with existing data.« less

Improvement of Heat Transport in Paraffines for Latent Heat Storage Systems

Abstract: for an efficient use of solar energy a certain heat storage capacity is always required. Often sensible heat has been used requiring large vessels filled with water or a rock bed. For reduce the storage volume latent heat systems are well known. Materials showing a solid/liquid phase change at a suitable temperature are used. Two types of materials are under consideration for this phase change behaviour. One the hydrates of different anorganic salts, like the well known Glauber’s salt having a melting point near 32, 4°C. They have relatively high heats of fusion, however after going through a number of cycles they show segregation of salt and liquid. Also a considerable subcooling during solidification may occur. These factors often reduce the storage capacity considerable. Next to these materials organic homogeneous materials having the right melting temperature can be considered. For the temperature range 30 to 70°C used in solar heating of buildings paraffine waxes can be used as reviewed by Stahl (1) and Bailey (2) . In general they have a lower heat of fusion (180 – 210 kJ/kg versus about 250 kJ/kg for hydrates). However they don’t show any segregation or subcooling effects even after repeated cycling.

Destabilization of Film Boiling Due to Arrival of a Pressure Shock—Part I: Experimental

Abstract: Transient heat transfer from an electrically-heated 3 mm o.d. horizontal tube, initially in subcooled film boiling, was measured immediately after passage of a shock wave of 1 to 5 x 10/sup 5/ N/m/sup 2/ over-pressure. The fluids tested were Freon-113 and 95 percent ethanol-5 percent water at initially 0.5 to 2 x 10/sup 5/ N/m/sup 2/ at 22 to 24/sup 0/C. Transient heat transfer rates, averaged over 0.5 to 1 ms after vapor film collapse, ranged up to 20 times the steady-state value. The maximum transient flux occurred at supercritical contact temperatures, with frequently a minimum in the range of contact temperatures between the homogeneous nucleation and the critical temperature. Photography at 5000 frames/s showed apparently complete vapor film collapse within one or two frames, followed by re-establishment of film boiling in approximately 1 ms, and eventually nucleate boiling in approximately 100 ms. The surface temperature which gave the highest peak transient flux shifted appreciably with increasing shock pressure, which indicates some compressibility even after contact was made. Implications for vapor explosions are discussed.

Jet operated heat pump

Abstract: A jet pump system is shown that utilizes waste heat to provide heating and/or cooling. Waste heat diverted through a boiler causes a refrigerant to evaporate and expand for supersonic discharge through a nozzle thereby creating a vacuum in an evaporator coil. The vacuum draws the refrigerant in a gaseous state into a condensing section of a jet pump along with refrigerant from a reservoir in a subcooled liquid form. This causes condensation of the gas in a condensation section of the jet pump, while moving at constant velocity. The change in momentum of the fluid overcomes the system high side pressure. Some of the condensate is cooled by a subcooler. Refrigerant in a subcooled liquid state from the subcooler is fed back into the evaporator and the condensing section with an adequate supply being insured by the reservoir. The motive portion of the condensate is returned to the boiler sans subcooling. By proper valving start-up is insured, as well as the ability to switch from heating to cooling.

Process for delivering liquid cryogen

Abstract: A process for delivering a liquid cryogen to a use point in an essentially liquid phase at an about constant flow rate in the range of about 1 to about 40 pounds per hour, said use point having a variable internal pressure drop, comprising the following steps: (i) providing said liquid cryogen at a line pressure in the range of about 4 to about 10 times the maximum use point operating pressure; (ii) subcooling the liquid cryogen of step (i) to an equilibrium pressure of no greater than about one atmosphere while maintaining said ine pressure; (iii) passing the liquid cryogen of step (ii) through a device having a flow coefficient in the range of about 0.0002 to about 0.005 while cooling said device externally to a temperature, which will maintain the liquid cryogen in essentially the liquid phase; and (iv) passing the liquid cryogen exiting the device in step (iii) through an insulated tube having an internal diameter in the range of about 0.020 inch to about 0.200 inch to the use point.

Destabilization of Film Boiling Due to Arrival of a Pressure Shock: Part II—Analytical

Abstract: Part 1 of this work the heat transfer during the first two ms after passage of a shock past a hot nickel tube surrounded by subcooled Freon-113 or ethanol was studied. The following important results were obtained: (1) the peak heat flux exhibits a maximum of a heater surface temperature of 280 to 350/sup 0/C, depending upon the strength of the shock. This is well above the critical temperature, so that nucleation considerations are irrelevant. (2) The maximum of the peak heat flux envelope depends upon the shock ..delta..P, indicating that only partial contact is made upon collapse of the vapor film. (3) The collapse is rapid (1 to 2 frame at 5000 f/s), and is produced by relatively weak shocks (..delta..P = 2 to 3 atm.). In the present work, the vapor film collapse is studied analytically, in order to obtain additional insight into the mechanism. A Lagrangian transformation due to Hamill and Bankoff is introduced to immobilize the moving boundary, and a polynomial temperature distribution in the transformed mass variable is assumed in the vapor region, as well as in the liquid region. This leads to a set of coupled nonlinear ordinary differential equations in the three regions,more » which are solved numerically. Two models were developed: (1) a detailed model, taking into account the Knudsen layers at the vapor-liquid and vapor-solid interfaces, and (2) a simplified model, in which these layers were neglected, and a linear temperature profile in the Lagrangian vapor phase variable was assumed. It is found that the initial vapor mass is a key variable determining whether collapse is achieved. In practice, this is a stochastic variable due to bubble departure, which explains the observed heat flux data scatter. The analytical results are in general agreement with the experimental data.« less

Forced Convection Film Boiling Heat Transfer from a Horizontal Cylinder to Liquid Cross-flowing Upward : 1st Report, Saturated Liquid

Abstract: Forced convection film boiling heat transfer from a horizontal cylinder to a subcooled liquid cross-flowing upward is analysed based on the two-phase boundary-layer theory Numerical solution of the conservation equations is determined for subcooled water, ethanol and hexane under the atmospheric pressure by the method similar to that of the first report for saturated liquid The velocity profile, the separation point in the vapor film, the thickness of the boundary-layer and the average Nusselt number are discussed in the same manner as in the previous report and the effects of the subcooling and the approaching velocity on them are also examined The calculated results on heat transfer are compared with the experimental data

Prediction Method of Flow Patterns in Subcooled and Low Quality Boiling Regions

Abstract: A new parameter is proposed for prediction of the transition between flow patterns such as bubble, froth and annular flow, in both the subcooled and low quality regions of boiling flow. This parameter is derived from the theoretical calculation method of void fraction, which has been reported, on the assumption that the flow pattern transition occurs at a value of average void fraction over the cross section of the flow. A flow map is also presented which reasonably correlates the experimental results covering the following conditions ; pressure : 1∼98 ata, heat flux : 2×104∼5×106kcal/m2h, and mass velocity : 40∼5400kg/m2s.

Rapid solidification of subcooled small metallic drops

Abstract: Accurate rapidly and slowly varying analytical solutions are obtained for the problem of the rapid solidification by convection of subcooled small metallic drops. These solutions, which were suggested by the approximate results obtained by using a quasi-moving-boundary approach, are useful in estimating metallurgical parameters in rapid rate solidification technology. The rapidly varying regular perturbation solution describes recalescence during which the liquid core increases very quickly from the nucleation temperature to the melting point. Enormous internal heat transfer rates dominate the process, and the solid-liquid interface is morphologically unstable, during recalescence. External convective heat transfer dominates after recalescence, and the slowly varying solution shows that this period begins when the dimensionless thickness of the solidified region is approximately equal to 1 − (1 − S)1/3. The position of the interface after recalescense is given by (1 − S − 3Hθ)1/3 Complete freezing of the ...

Refrigeration system condenser heat recovery at higher temperature than normal condensing temperature

Abstract: Heat is recovered in a medium at higher than normal condensing temperature of a refrigeration system by using two cascade connected refrigeration systems and heating the medium in isolated stages by refrigerant subcooling and refrigerant condensing stages of the higher temperature system.

Method for cooling plastics hollow profiles

Abstract: 1. Process for cooling of hollow synthetic material profiles during extrusion by means of direct heat exchange with liquid nitrogen, which is introduced via a boring in the mandrel (3) of the extrusion tool into the interior of the hollow synthetic material (6), characterised in that the nitrogen has a pressure of 2 to 8 bar and a temperature below its boiling point, what means that it is subcooled, and that the liquid in the extrusion tool moves through a capillary tube (4) with a maximum inside diameter of 1,2 mm, which capillary tube is enclosed by an insulation tube (5).