Boiling rate

All RBMK reactors have positive void coefficients which means that increasing the boiling rate increases the steam fraction in the core which increases reactivity causing more steam void which causes more reactivity and so on. Competing factors provide stability, but startup, shutdown and maneuvering below about 600 MWt are unstable, hence, there is a rule prohibiting extended operation below 700 Mwt. 

Figure 10-102B. Maximum boiling rate in the low pressure region. (Used by permission Cichelli, M. T. and Bonilla, C. E. Transactions. AlChE, V. 41, No. 6, 1945. American Institute of Chemical Engineers. All rights reserved.)...

For liquids boiling from a pool the boiling rate is limited by the heat transfer from the surroundings to the liquid in the pool. Heat is transferred (1) from the ground by conduction, (2) from the air by conduction and convection, and (3) by radiation from the sun and/or adjacent sources such as a fire. 

The key problem now is to find a simple and reasonable expression for the boiling rate W. I have found in a number of simulations that a mass-transfer type of equation ean be conveniently employed. This kind of relationship also makes physical sense. Liquid boils because, at some temperature (and eomposi-tion if more than one component is present), it exerts a vapor pressure P greater than the pressure P in the vapor phase above it. The driving force is this pressure differential... 

The data were obtained by means of an improved Othmer recirculation still (34), as modified for salt effect studies by Johnson and Furter (22,35). Thermal energy was applied to the still by means of a heating mantle controlled by a rheostat in order that the boiling rate could be adjusted effectively. Suppression of bumping of the solution and both thermal and physical homogeneity were maintained by means of a magnetic stirring mechanism. 

Add additional 0.5 to 1.0 g alundum granules to cooled digestion flask. Add a sufficient volume of concentrated NaOH solution, slowly down the side of the flask. More than 45 ml of 45% NaOH is recommended to neutralize 20 ml of concentrated H2S04 standard, and to render the mixture strongly alkaline. Immediately connect digestion flask to the distillation apparatus, mix completely, and distill at a 7.5-min boil rate until >150 ml distillate is collected in titration beaker. 

For liquids with low boiling points, such as most liquefied gases, the vaporization rate is normally driven by the rate of heat transfer from the ground by conduction and, to a lesser extent, by wind speed. Evaporation and boiling rates vary with time as the pool and the surface beneath it are cooled. The ground temperature is strongly influenced by ambient temperature, solar radiation and wind conditions prior to the spill. 

The lower part of the inner vessel had a capacity of about 0.7 ml. It had a small re-entrant tube extending upward about half-way. A 30-gage copper-constantan thermocouple was wound (in several turns) around the outside and the jimction inserted in the re-entrant tube, which was then filled with wax to provide thermal contact. The inner vessel was filled with about 25 ml. of the ozone-o gen mixture and the outer vessel was evacuated to reduce the boiling rate. The liquid nitrogen bath (not shown), was removed, and the mixture allowed to evaporate at atmospheric pressure. The apparatus was tested first with liquid oxygen and gave the correct boiling point down to the last 0.5 ml. of liquid. 

Acetaldehyde is boiled in a flask and passed through a reaction tube maintained by a surrounding furnace at 518°C. The reaction tube is 3.3 cm ID and 80 cm long. The flow rate through the tube is varied by changing the boiling rate. Analysis of the products from the end of the tube gives the results in Table 4-2. 

If overheating is not a concern (e.g., in refrigerated services), a reboiler level controller can replace the overflow weir, and used to control the boiling rate by flooding or unflooding tubes. In some cases, bottom product is drawn from the bottom of the column, and... 

At high boiling rates, liquid carryover may result. A flow indicator in the vapor line will display the cerry-over and provide a warning before damage to the compressor can occur if compressor suction scrubbers are not provided. 

Withdrawing a control rod reduces the neutron absorption and increases core reactivity. Reactor power then increases until the increased steam formation just balances the change in reactivity caused by the rod withdrawal. The increase in boiling rate ends to raise reactor pressure, causing the initial pressure regulator fo open the turbine admission valves sufficiently to maintain a constant pressure. When a control rod is inserted, the converse effect occurs. 

For evaporative crystallizations, the surface area through which evaporation occurs also increases only with a power of 2 with the reactor diameter, again making it necessary to increase the process time to avoid high boiling rates. 

As noted in Section 4.3, the presence of an overlying water pool does not guarantee that the debris will be coolable. A crust may form over the melt or the boiling rate may simply not be sufficient to remove the decay heat. However, it is possible that water will have some beneficial effect and at least slow down the concrete attack. 

The flask shall be heated by means of a nickel reinforced quartz fabric heating mantle on the lower half so that boiling rates of up to ISO mL/h per cm of cross... 

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