Induced subcooling

Maulbetsch, J. S., and P. Griffith, 1965, A Study of System-Induced Instabilities in Forced Convection Flows with Subcooled Boiling, MIT Engineering Projects Lab. Rep. 5382-35, Massachusetts Institute of Technology, Cambridge, MA. (5)... 

Fig. 14 shows the comparison of the photographs from Chandra and Avedisian (1991) with simulated images of this study for a subcooled 1.5 mm n-heptane droplet impact onto a stainless-steel surface of 200 °C. The impact velocity is 93 cm/s, which gives a Weber number of 43 and a Reynolds number of 2300. The initial temperature of the droplet is room temperature (20 °C). In Fig. 14, it can be seen that the evolution of droplet shapes are well simulated by the computation. In the first 2.5 ms of the impact (frames 1-2), the droplet spreads out right after the impact, and a disk-like shape liquid film is formed on the surface. After the droplet reaches the maximum diameter at about 2.1ms, the liquid film starts to retreat back to its center (frame 2 and 3) due to the surface-tension force induced from the periphery of the droplet. Beyond 6.0 ms, the droplet continues to recoil and forms an upward flow in the center of the... 

The development of the freeze concentration process for fruit juices has been hampered by the fact that solute concentrate is entrained by the ice crystals. This incomplete separation of the entrained concentrate from the ice results in a considerable increase of the cost of the process. In this investigation sucrose solutions were concentrated by the formation of an ice layer on the externally cooled walls of the crystallizer. The formation of the layer was initiated by secondary nuclei induced by rotating ice seeds, at subcoolings smaller than the critical subcooling needed for spontaneous nucleation. A minimum in the amount of sucrose entrapped in the ice layer was observed at a subcooling smaller than the critical subcooling for spontaneous nucleation. The effect of soluble pectins on the minimum was also studied. 

In order to understand and control lipid crystallization, one should know the thermodynamic driving force for crystallization. In a pure system, like a single TAG, the melting point, T, defines the driving force and a temperature below is required to induce crystallization. That is, the subcooling or the melting temperature minus the actual temperature (Tm — T) defines the driving force for crystallization. 

A poorly piped variation of this system (Fig. 17.5e) caused pressure fluctuations and inability to keep column pressure constant in one case (194). The author is familiar with two more troublesome cases with a similar piping arrangement, while a fourth similar case was reported by Hollander (164). With the Fig. 17.5e scheme, subcooled liquid mixes with dew point vapor. Collapse of vapor takes place at the point of mixing. The rate of vapor collapse varies with changes in subcooling, overhead temperature, and condensation rate. Variation of this collapse rate induces pressure fluctuations. The above problem (194) was completely eliminated by separating the liquid line from the vapor line, and extending the liquid line well below the liquid surface. The vapor line entered at the previous inlet. 

As the heat input is increased, geysering is suppressed and another instability called natural circulation instability is induced due to hydrostatic head fluctuation (caused by PDO), which varies the natural circulation force. As the heat flux is further increased, density wave instabilities appear. The period of natural circulahon oscillations is much longer than that of density wave instabilities, and reduces with an increase in heat flux and with a decrease in inlet subcooling. 

Calculate the reflux induced on Tray (Dl - 1) as the amount of vapor from Tray (Dl - 2) which enters and is condensed on Tray (Dl - 1) for the purpose of converting the subcooled pumpback reflux liquid to its bubble point. 

The wide variation in the temperature distribution patterns, as a function of pressure, indicates the presence of two different boiling heat transfer mechanisms. For self-pressurization, the heat is absorbed in an essentially saturated liquid and more complete mixing occurs because of complete bubble detachment from the wall and subsequent passage through the liquid. For the higher top pressures, which created a subcooled liquid, the bubbles do not detach from the wall but collapse and induce high heat transfer rates to the liquid directly. This in turn... 

The operators asserted during interviews that they were concerned about a inducing a LOCA by a reactor coolant pump seal failure, and decided to go on natural circulation. To establish natural circulation would have required (among other things) subcooled reactor coolant. The operators assumed that, because the pressurizer level was high, the core must be covered. In actuality, natural circulation was precluded by the steam that had formed in the reactor coolant system. It was the higher... 

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