Sub-cooled boiling

If bubbles are formed in a liquid which is much below its boiling point, then the bubbles will collapse in the bulk of the liquid. Thus if a liquid flows over a very hot surface then 

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Sub-cooled boiling in this region the liquid next to the wall has reached boiling point, but not the bulk of the liquid. Local boiling takes place at the wall, which increases the rate of heat transfer over that given by forced convection alone. 

SINGLE- PHASE FORCED CON- VECTION SUB- COOLED BOILING BUBBLE COAGU- LATION SLUG FORMA- TION SLUG COAGU- LATION ANNULAR FLOW ANNULAR FLOW WITH DROPLETS... 

Inside a heated duct, the liquid vaporizes in several stages sub-cooled boiling, saturated or bulk boiling, and the dry wall regime. 

H. J. Ivey and D. J. Morris, On the Relevance of the Vapour-Liquid Exchange Mechanism for Sub-Cooled Boiling Heat Transfer at High Pressure, UKAEA Report AEEW-R137,1962. 

A model was developed [Onifer and Knudsen 1993] for reaction fouling under sub-cooled boiling conditions for the polymerisation of styrene. It is similar to the... 

Under accident conditions, the Automatic Depressurization System (ADS) depressurizes the reactor vessel, and equalizes the reactor vessel and containment vessel pressure. Feedwater flow to the steam generator is secured and a new heat transport path is established. The coolant in the core reaches sub-cooled boiling conditions and produces a steam filled region in the upper portion of the reactor vessel. The steam is vented to the containment via the upper ADS vent lines. Once in the containment, the steam condenses on the walls of the containment vessel and pools at the bottom of the containment. This pooled fluid enters the reactor vessel either by sump recirculation lines or the submerged ADS lines, completing the flow path. A simple schematic of the accident condition heat transport system is shown in Fig. I-15(b). 

Thermal condition of feed (at boiling point, all vapor, sub-cooled liquid). 

The condition of the feed as it enters the column has an effect on the number of trays, reflux requirements and heat duties for a given separation. Figure 8-15 illustrates the possible situations, i.e., sub-cooled liquid feed, feed at the boiling point of the column feed tray, part vapor and part liquid, all vapor but not superheated, and superheated vapor. The thermal condition is designated as q, and... 

When the vapour entering the condenser is superheated, and the condensate leaving the condenser is cooled below its boiling point (sub-cooled), the temperature profile will be as shown in Figure 12.46. 

Single-phase flow region at the inlet the liquid is below its boiling point (sub-cooled) and heat is transferred by forced convection. The equations for forced convection can be used to estimate the heat-transfer coefficient in this region. 

If the feed is sub-cooled, the mean temperature difference should still be based on the boiling point of the liquid, as the feed will rapidly mix with the boiling pool of liquid the quantity of heat required to bring the feed to its boiling point must be included in the total duty. 

ZUBER, N., Tribus, M. and Westwater, J. W. (1961) Second International Heat Transfer Conference, Paper 27, p. 230, Am. Soc. Mech. Eng. The hydrodynamic crisis in pool boiling of saturated and sub-cooled liquids. 

Problem. A mixture of methanol and water containing 40 mol per cent of methanol is to be separated to give a product of at least 90 mol per cent of methanol at the top, and a bottom product with no more than 10 mol per cent of methanol. The feed flow rate is 100 kmol h 1 and the feed is heated so that it enters the column at its boiling point. The vapour leaving the column is condensed, but not sub-cooled, and provides reflux and product. Since all the vapour from the column is condensed, the composition of the vapour from the top plate must equal that of the top product as well as that returned as reflux. 

Y. Elkassabgi and J. H. Lienhard, The Peak Pool Boiling Heat Fluxes From Horizontal Cylinders in Sub-Cooled Liquid, J. Heat Transfer (110) 479 196,1988. 

C. H. Lee and I. A. Mudawwar, A Mechanistic CHF Model for Sub-Cooled Flow Boiling Based on Local Bulk Flow Conditions, Int J. Multiphase Flow (14) 711,1988. 

H. Nariai and F. Inasaka, Critical Heat Flux of Sub-Cooled Flow Boiling in Tube With and Without Internal Twisted Tape Under Uniform and Non-Uniform Heat Flux Conditions, in Convective Flow Boiling, J. C. Chen ed., pp. 207-212, Taylor Francis, Washington, DC, 1996. 

N. Hammouda, D. C. Groeneveld, and S. C. Cheng, An Experimental Study of Sub-Cooled Film Boiling of Refrigerants in Vertical Up-Flow, Int. J. Heat Mass Transfer (39) 3799-3812,1996. 

The solvent vapor is condensed, and is often sub-cooled below its normal boiling point. It should be quite free of soil, but laden with water. 

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