* Corresponding author. Tel.: #972-3-640-7829; fax: #972-3-642- 7334. E-mail address: ullmann@eng.tau.ac.il (A. Ullmann) Chemical Engineering Science 55 (2000) 2203}2212 Measurements of solid contaminant emission rates from boiling pools Abraham Dayan, Sylvia Zalmanovich, Amos Ullmann* Department of Fluid Mechanics and Heat Transfer, Tel Aviv University, Ramat Aviv, 69978 Tel Aviv, Israel Received 1 February 1999; accepted 13 September 1999 Abstract An experimental study was performed to measure release rates of solid particles from boiling pools. Sensitivity studies were conducted to reveal the dependence of the particle carry-over rate on the pool depth, the boiling rate and the vertical distance from the pool surface. Experimental data on particle concentrations as a function of size at the pool surface are also provided. The study was conducted in a nucleate boiling regime. Tests were performed with distilled water and solid nickel particles ranging in size from 5 to 40 m. The test apparatus was made of a cylindrical vessel, 30 cm in diameter and 120 cm in height. Slurry particle concentrations were on the order of milligrams per cubic centimeter of slurry. Heat #uxes on the order of 100 kW/m were attained by electrical bottom heating. Corresponding super"cial vapor velocities were on the order of several centimeters per second. The phenomenon of particle emission from the surface of boiling pools pauses major environmental and industrial problems. Such particles are often undesirable contaminants, especially if toxic or radioactive. Exploration of this subject is of considerable importance to the chemical, nuclear, and power generation industries. The current study provides important data to support safety analyses and development of analytical tools. Surface contamination concentrations and particle emission rates are essential data for environmental contamination evaluations of spills and boiling, respectively. The study indicates, among other things, that emission rates intensify as pools get shallower. A released particle #ux is strongest near the surface; and at a decreasing pace, diminishes to a constant rate as the distance from the surface is increased. Decontamination factors of the boiling process were found to be in a range of 10}10.  2000 Elsevier Science Ltd. All rights reserved. Keywords: Particle emission; Boiling pools; Bubble columns; Environmental; Decontamination factors 1. Introduction The emission of particles from boiling pools and bubble columns poses major industrial and environ- mental problems. Such particles are often undesired en- vironmental contaminants, especially if they are of small size with toxic or radioactive properties. Rising bubbles within pools and emerging vapors from the pools could suspend, expel and spread such particles. To substantiate the importance of the problem, few examples are brought. In the power generation industry, the problem is one of turbo-machinery blade erosion by droplets and particle emissions from boilers. In the chemical industry, the concern is related to continuous or accidental chem- ical reactor releases of toxic catalysts, reactants and products. In the nuclear industry, the threat is related to environmental contamination from accidental radioac- tive material releases. The problem is associated with postulated hypothetical core disruptive accidents involv- ing fuel/coolant interactions. In such events, fragmenta- tion of fuel material could produce small size radioactive solid particles. Pools containing such debris could be in a boiling state owing to intense heating from radioactive decay, stored heat and chemical reactions. It is, there- fore, necessary to study the problem and assess the potential for environmental contamination from such emissions. The emission of materials from a boiling pool depends on the pool dispersion characteristics, on surface phe- nomena and on the emerging vapor velocity. The disper- sion characteristics of substances within bubbling pools were studied extensively. Investigations were conducted primarily by the chemical engineering community for the design of chemical reactors. Comprehensive surveys of this subject can be found in the publications of Saxena and Thimmapuram (1992), Viswanathan (1988), Joshi, Pandit and Raghav Rao (1988), Shah, Kelkar, Godbole 0009-2509/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 0 9 - 2 5 0 9 ( 9 9 ) 0 0 4 9 5 - 9