Author
Susan McCahan
Other affiliations: Rensselaer Polytechnic Institute, Queen's University
Bio: Susan McCahan is an academic researcher from University of Toronto. The author has contributed to research in topics: Engineering education & Rubric. The author has an hindex of 7, co-authored 47 publications receiving 262 citations. Previous affiliations of Susan McCahan include Rensselaer Polytechnic Institute & Queen's University.
Topics: Engineering education, Rubric, Boiling, Vocabulary, Nucleate boiling
Papers
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TL;DR: In this paper, the effect of adding one of three salts (NaCl, Na 2 SO 4 or MgSO 4 ) to water sprayed on a hot surface was studied experimentally.
Abstract: The effect of adding one of three salts (NaCl, Na 2 SO 4 or MgSO 4 ) to water sprayed on a hot surface was studied experimentally. A copper test surface was heated to 240°C and quenched with a water spray. The variation of surface temperature during cooling was recorded, and the surface heat flux calculated from these measurements. Surface heat flux during cooling with pure water sprays was compared with that obtained using salt solutions. Dissolved NaCI or Na 2 SO 4 increased nucleate boiling heat transfer, but had little effect on transition boiling during spray cooling. MgSO 4 increased both nucleate and transition boiling heat flux. Enhanced nucleate boiling was attributed to foaming in the liquid film generated by the dissolved salts. MgSO 4 produced the largest increase in nucleate boiling heat transfer, Na 2 SO 4 somewhat less and NaCI the least. A concentration of 0.2 mol/l of MgSO 4 produced the greatest heat flux enhancement ; higher salt concentrations did not result in further improvements. During transition boiling particles of MgSO 4 adhered to the heated surface, raising .surface roughness and increasing heat transfer. Addition of MgSO 4 reduced the time required to cool a hot surface from 240°C to 120°C by an order of magnitude.
57 citations
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TL;DR: In this article, the effect of dissolving either a gas (carbon dioxide) or a solid salt (sodium carbonate or sodium bicarbonate) in water droplets boiling on a hot stainless steel surface was investigated.
Abstract: We conducted experiments on the effect of dissolving either a gas (carbon dioxide) or a solid salt (sodium carbonate or sodium bicarbonate) in water droplets boiling on a hot stainless steel surface. Substrate temperatures were varied from 100°C to 300°C. We recorded the boiling of droplets with a video system, and photographed droplet impact using short-duration flash photography. At surface temperatures that were too low to initiate nucleate boiling, dissolved salts were found to reduce the evaporation rate since they lower the vapor pressure of water. Dissolved gas had the opposite effect: it came out of solution and formed bubbles in the liquid, enhancing evaporation. In the nucleate boiling regime dissolved carbon dioxide enhanced heat transfer by a small amount. However, sodium carbonate prevented coalescence of vapor bubbles and produced foaming in the droplet, greatly enhancing heat transfer and reducing the droplet lifetime to approximately half that of a pure water drop. Sodium bicarbonate, which decomposes to give carbon dioxide and sodium carbonate when heated, produced an even larger enhancement of heat transfer. When the surface temperature was raised above the Leidenfrost temperature of water, droplets went into film boiling and bounced off the surface follow-ing impact. Dissolved carbon dioxide was found to suppress heterogeneous bubble formation in the droplet during impact. However, dissolved salts promoted bubble formation and led to droplet break-up during impact.
56 citations
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TL;DR: In this paper, the effect of dissolving three different salts (NaCI, Na 2 SO 4 and MgSO 4 ) in water droplets boiling on a hot stainless steel surface was investigated.
Abstract: We conducted experiments on the effect of dissolving three different salts sodium chloride (NaCI), sodium sulfate (Na 2 SO 4 ) and magnesium sulfate (MgSO 4 ) in water droplets boiling on a hot stainless steel surface. Substrate temperatures were varied from 90°C to 220°C We photographed droplets as they evaporated, and recorded their evaporation time. At surface temperatures that were too low to initiate nucleate boiling all three salts were found to reduce droplet evaporation rates because they lower the vapor pressure of water. In the nucleate boiling regime, low concentrations (<0.1 mol/l) of Na 2 SO 4 and MgSO 4 enhanced heat transfer because they prevented coalescence of vapor bubbles and produced foaming in the droplet, significantly reducing droplet lifetimes, increasing the salt concentration further did not produce a corresponding increase in droplet boiling rate. Dissolved salts prevent bubble coalescence because they increase surface tension and stabilize the liquid film separating bubbles, and because electric charge that accumulates on the surfaces of bubbles produces a repulsive force, preventing them from approaching each other, Na 2 SO 4 and MgSO 4 , which have high ionic strengths, produced a large amount of foaming in droplets and increased their boiling rate significantly. NaCl, which has low ionic strength, had little effect on droplet boiling.
42 citations
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22 Jun 2011TL;DR: The Engineering Graduate Attribute Development (EGAD) project as mentioned in this paper is a Canadian collaborative project sponsored by the National Council of Deans of Engineering and Applied Science (NCDEAS), in collaboration with Engineers Canada.
Abstract: This paper describes the objectives and progress of the Engineering Graduate Attribute Development (EGAD) project. This is a Canadian collaborative project sponsored by the National Council of Deans of Engineering and Applied Science (NCDEAS), in collaboration with Engineers Canada. EGAD's mandate is to develop resources and training for assessing graduating student attributes in undergraduate engineering programs for the purpose of improving the quality of engineering education in Canada, specifically in response to CEAB's graduate attribute requirements.
21 citations
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20 Jun 2012
TL;DR: In this article, the authors describe and compare the different approaches of seven Canadian institutions to the Canadian Engineering Accreditation Board (CEAB) requirements for continuous quality improvement using graduate attributes.
Abstract: This paper describes and compares the different approaches of seven Canadian institutions to the Canadian Engineering Accreditation Board (CEAB) requirements for continuous quality improvement using graduate attributes. Program approaches are compared by: program objectives & management, indicators, curriculum mapping, assessment & data collection and curriculum improvement. The significant differences include approaches to curriculum mapping, data collection and curriculum improvement.
15 citations
Cited by
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01 Jan 2002
TL;DR: For instance, Schofield et al. as discussed by the authors studied the influence of L1 influences on L2 vocabulary acquisition and the formal aspects of vocabulary acquisition in the context of the syllabus.
Abstract: 1. Word frequency and vocabulary size Paul Nation and Rob Waring 2. Variation in spoken and written language Michael McCarthy and Ron Carter 3. Vocabulary connections Rosamund Moon 4. Vocabulary and context William Nagy 5. Productive vs. receptive aspects of vocabulary Francine Melka 6. Models of lexical acquisition Paul Meara 7. Cognitive constraints on vocabulary acquisition Nick Ellis 8. Intralexical factors affecting the difficulty of vocabulary acquisition Batia Laufer 9. L1 influences on L2 vocabulary acquisition 10. Acquisition of the formal aspects of vocabulary Michael Swan 11. Vocabulary learning strategies Ann Ryan 12. Vocabulary and the syllabus Norbert Schmitt 13. Teaching vocabulary: most recent trends Felicity O'Dell 14. Vocabulary and testing John Read 15. Dictionaries, thesauruses, lexical resources Phil Schofield.
905 citations
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TL;DR: In this paper, a comprehensive review of published literatures concerning the fluid mechanics and heat transfer mechanisms of liquid drop impact on a heated wall is provided, divided into four parts, each centered on one of the main heat transfer regimes: film evaporation, nucleate boiling, transition boiling, and film boiling.
357 citations
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TL;DR: In this article, a review of spray cooling is presented, focusing on the relatively high-flux, low-temperature mechanisms and predictive tools associated with the single-phase liquid cooling and nucleate boiling regimes, as well as critical heat flux (CHF).
346 citations
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TL;DR: In this article, a single- nozzle spray cooling heat transfer mechanism with varying amounts of dissolved gas was investigated using two powerful techniques: time and space resolved heat transfer distributions produced by a single nozzle were measured using an array of individually controlled microheaters, while visualization and measurements of the liquid-solid contact area and the three phase contact line length were made using a total internal reflectance technique.
228 citations