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• 1. [Article] Bioaerosol Deposition on an Air-Conditioning Cooling Coil

  This study is concerned with the role of a fin-and-tube heat exchanger in modifying microbial indoor air quality. Specifically, depositional losses of ambient bioaerosols and particles onto dry (not cooled) ...

  Citation × Citation Citation Abstract Copy Title: Bioaerosol Deposition on an Air-Conditioning Cooling Coil Author: Wu, Yan, Chen, Ailu, Luhung, Irvan, Gall, Elliot T., Cao, Qingliang, Wei-Chung Chang, Victor, Nazaroff, William W. Year: 2016 This study is concerned with the role of a fin-and-tube heat exchanger in modifying microbial indoor air quality. Specifically, depositional losses of ambient bioaerosols and particles onto dry (not cooled) and wet (cool) coil surfaces were measured for different airspeeds passing through the test coil. Total, bacterial and fungal DNA concentrations in condensate water produced by a wet coil were also quantified by means of fluorescent dsDNA-binding dye and qPCR assays. Results revealed that the deposition of bioaerosols and total particles is substantial on coil surfaces, especially when wet and cool. The average deposition fraction was 0.14 for total DNA, 0.18 for bacterial DNA and 0.22 for fungal DNA on the dry coil, increasing to 0.51 for total DNA, 0.50 for bacterial DNA and 0.68 for fungal DNA on the wet coil. Overall, as expected, deposition fractions increased with increasing particle size and increasing airspeed. Deposited DNA was removed from the cooling coil surfaces through the flow of condensing water at a rate comparable to the rate of direct deposition from air. A downward trend of bacterial and fungal DNA measured in condensate water over time provides suggestive evidence of biological growth on heat exchangers during nonoperational times of a ventilation system. This investigation provides new information about bioaerosol deposition onto a conventional fin-and-tube cooling coil, a potentially important factor influencing indoor exposure to microbial aerosols in air-conditioned buildings. Title: Bioaerosol Deposition on an Air-Conditioning Cooling Coil Author: Wu, Yan, Chen, Ailu, Luhung, Irvan, Gall, Elliot T., Cao, Qingliang, Wei-Chung Chang, Victor, Nazaroff, William W. Year: 2016 This study is concerned with the role of a fin-and-tube heat exchanger in modifying microbial indoor air quality. Specifically, depositional losses of ambient bioaerosols and particles onto dry (not cooled) and wet (cool) coil surfaces were measured for different airspeeds passing through the test coil. Total, bacterial and fungal DNA concentrations in condensate water produced by a wet coil were also quantified by means of fluorescent dsDNA-binding dye and qPCR assays. Results revealed that the deposition of bioaerosols and total particles is substantial on coil surfaces, especially when wet and cool. The average deposition fraction was 0.14 for total DNA, 0.18 for bacterial DNA and 0.22 for fungal DNA on the dry coil, increasing to 0.51 for total DNA, 0.50 for bacterial DNA and 0.68 for fungal DNA on the wet coil. Overall, as expected, deposition fractions increased with increasing particle size and increasing airspeed. Deposited DNA was removed from the cooling coil surfaces through the flow of condensing water at a rate comparable to the rate of direct deposition from air. A downward trend of bacterial and fungal DNA measured in condensate water over time provides suggestive evidence of biological growth on heat exchangers during nonoperational times of a ventilation system. This investigation provides new information about bioaerosol deposition onto a conventional fin-and-tube cooling coil, a potentially important factor influencing indoor exposure to microbial aerosols in air-conditioned buildings. Close

• 2. [Article] Estimation of Transient Temperature Distribution during Quenching, via a Parabolic Model

  A material-independent model to estimate the transient temperature distribution in a test probe quenched by immersion is presented in this study. This model is based on the assumption that, under one-dimensional ...

  Citation × Citation Citation Abstract Copy Title: Estimation of Transient Temperature Distribution during Quenching, via a Parabolic Model Author: Lozano, Diego E., Martinez-Solis, Gabriela, Mercado-Solis, Rafael David, Colás, Rafael, Totten, George E. Year: 2015 A material-independent model to estimate the transient temperature distribution in a test probe quenched by immersion is presented in this study. This model is based on the assumption that, under one-dimensional unsteady heat conduction, the radial temperature distribution at the end of an interval belongs to the equation of a parabola. The model was validated using AISI 304 stainless steel test probes (Φ8×40 mm and Φ12×60 mm) quenched from 850 to 900 °C in water and in water-based NaNO2 solutions at 25 °C and in canola oil at 50 °C. Additionally, square test probes (20×20×100 mm) were quenched from 550 °C in water. The test probes were equipped with embedded thermocouples for temperature-versus-time data logging at the core, one-quarter thickness and 1 mm below the surface. In each experiment, the data recordings from the core and near-surface thermocouples were employed for the temperature calculations while the data from the one-quarter thickness thermocouple were employed for model validity verifications. In all cases, the calculated temperature distributions showed good correlations with the experimentally obtained values. Based on the results of this work, it is concluded that this approach constitutes a simple, quick and efficient tool for estimating transient surface and radial temperature distributions and represents a useful resource for quenchant cooling rate calculations and heat transfer characterizations. Title: Estimation of Transient Temperature Distribution during Quenching, via a Parabolic Model Author: Lozano, Diego E., Martinez-Solis, Gabriela, Mercado-Solis, Rafael David, Colás, Rafael, Totten, George E. Year: 2015 A material-independent model to estimate the transient temperature distribution in a test probe quenched by immersion is presented in this study. This model is based on the assumption that, under one-dimensional unsteady heat conduction, the radial temperature distribution at the end of an interval belongs to the equation of a parabola. The model was validated using AISI 304 stainless steel test probes (Φ8×40 mm and Φ12×60 mm) quenched from 850 to 900 °C in water and in water-based NaNO2 solutions at 25 °C and in canola oil at 50 °C. Additionally, square test probes (20×20×100 mm) were quenched from 550 °C in water. The test probes were equipped with embedded thermocouples for temperature-versus-time data logging at the core, one-quarter thickness and 1 mm below the surface. In each experiment, the data recordings from the core and near-surface thermocouples were employed for the temperature calculations while the data from the one-quarter thickness thermocouple were employed for model validity verifications. In all cases, the calculated temperature distributions showed good correlations with the experimentally obtained values. Based on the results of this work, it is concluded that this approach constitutes a simple, quick and efficient tool for estimating transient surface and radial temperature distributions and represents a useful resource for quenchant cooling rate calculations and heat transfer characterizations. Close

• 3. [Article] High-Speed Quenching of High Carbon Steel

  Medium and high carbon steels are usually quenched in polymer and oil in order to avoid cracking and distortion; however, recent studies have proved that it is possible to minimize cracking using water ...

  Citation × Citation Citation Abstract Copy Title: High-Speed Quenching of High Carbon Steel Author: Martínez-Cázares, Gabriela M., Lozano, Diego E., Guerrero-Mata, Martha, Colás, Rafael, Totten, George E. Year: 2014 Medium and high carbon steels are usually quenched in polymer and oil in order to avoid cracking and distortion; however, recent studies have proved that it is possible to minimize cracking using water as a coolant of these steels by promoting extremely high cooling rates. By great agitation and velocity of quenchant, the vapor blanket is reduced or prevented during water quench, allowing uniform hardening of the surface. In this study, the cooling severity of a spray quenching system and a high-speed quenching chamber are studied. Cylindrical samples of AISI 304 stainless steel (20 mm in diameter and 100 mm length) were employed to characterize the cooling severity. Thermal data was acquired through K-type thermocouples placed in the sample at three positions, 1 mm below surface, mid-radius and at center of the specimen, connected to a data acquisition system. High thermal gradients were observed in both systems, being the high-speed chamber the severest cooling. The maximum cooling rate obtained at the surface was 470 and 300°C/s for the high-speed chamber and the spray system, respectively. In addition, 5160 spring steel samples were quenched for short times in both systems; the cooling was interrupted to avoid through transformation and to produce a case-core type microstructure. Different cooling times were used for the interrupted quenching to modify the martensite case thickness. No cracks were observed. Thermal results and microstructures are discussed. Title: High-Speed Quenching of High Carbon Steel Author: Martínez-Cázares, Gabriela M., Lozano, Diego E., Guerrero-Mata, Martha, Colás, Rafael, Totten, George E. Year: 2014 Medium and high carbon steels are usually quenched in polymer and oil in order to avoid cracking and distortion; however, recent studies have proved that it is possible to minimize cracking using water as a coolant of these steels by promoting extremely high cooling rates. By great agitation and velocity of quenchant, the vapor blanket is reduced or prevented during water quench, allowing uniform hardening of the surface. In this study, the cooling severity of a spray quenching system and a high-speed quenching chamber are studied. Cylindrical samples of AISI 304 stainless steel (20 mm in diameter and 100 mm length) were employed to characterize the cooling severity. Thermal data was acquired through K-type thermocouples placed in the sample at three positions, 1 mm below surface, mid-radius and at center of the specimen, connected to a data acquisition system. High thermal gradients were observed in both systems, being the high-speed chamber the severest cooling. The maximum cooling rate obtained at the surface was 470 and 300°C/s for the high-speed chamber and the spray system, respectively. In addition, 5160 spring steel samples were quenched for short times in both systems; the cooling was interrupted to avoid through transformation and to produce a case-core type microstructure. Different cooling times were used for the interrupted quenching to modify the martensite case thickness. No cracks were observed. Thermal results and microstructures are discussed. Close

• 4. [Article] Quantum Yield Optimization for Semiconductor Photocatalysis Systems

  The utilization of photocatalysis has a well-known potential for mineralizing organic contaminants in water purification processes. A continuous flow photocatalytic reactor was developed in order to test ...

  Citation × Citation Citation Abstract Copy Title: Quantum Yield Optimization for Semiconductor Photocatalysis Systems Author: Catabay, Ryan Year: 2016 The utilization of photocatalysis has a well-known potential for mineralizing organic contaminants in water purification processes. A continuous flow photocatalytic reactor was developed in order to test the quantum yield of titanium dioxide, a semiconductor material well known for its photocatalytic properties. In order to build this reactor, multiple manufacturing methods were performed: manual and CNC machining, laser cutting, waterjet cutting, and chemical synthesis. A continuous flow reactor was particularly designed for a controlled, variable radiant flux of ultraviolet light. This continuous UV radiation excites the photocatalyst, generating electron hole pairs that form hydroxyl radicals, which in turn mineralize organic pollutants. The design of the reactor also included a variable catalyst cartridge, allowing multiple catalyst thicknesses and positions to be tested. In having these controlled variables, this reactor allows for a consistent measurement of contaminant degradation. This information relates directly to the quantum yield of the catalyst, allowing for a higher understanding of the material and its photocatalytic activity. Results from testing will be compared to Monte Carlo simulations of electron hole pair generation that have been produced. Further, several testing methods were used in the characterization of the semiconductor thin-films, such as UV-Vis spectrophotometry, scanning electron microscopy and energy dispersive x-ray spectroscopy. Title: Quantum Yield Optimization for Semiconductor Photocatalysis Systems Author: Catabay, Ryan Year: 2016 The utilization of photocatalysis has a well-known potential for mineralizing organic contaminants in water purification processes. A continuous flow photocatalytic reactor was developed in order to test the quantum yield of titanium dioxide, a semiconductor material well known for its photocatalytic properties. In order to build this reactor, multiple manufacturing methods were performed: manual and CNC machining, laser cutting, waterjet cutting, and chemical synthesis. A continuous flow reactor was particularly designed for a controlled, variable radiant flux of ultraviolet light. This continuous UV radiation excites the photocatalyst, generating electron hole pairs that form hydroxyl radicals, which in turn mineralize organic pollutants. The design of the reactor also included a variable catalyst cartridge, allowing multiple catalyst thicknesses and positions to be tested. In having these controlled variables, this reactor allows for a consistent measurement of contaminant degradation. This information relates directly to the quantum yield of the catalyst, allowing for a higher understanding of the material and its photocatalytic activity. Results from testing will be compared to Monte Carlo simulations of electron hole pair generation that have been produced. Further, several testing methods were used in the characterization of the semiconductor thin-films, such as UV-Vis spectrophotometry, scanning electron microscopy and energy dispersive x-ray spectroscopy. Close

• 5. [Article] “Reference QuenchProbe”—An Alternative Probe Design for In-Situ Estimation of Cooling Rates, Heat Flux, and Hardenability During Immersion Quenching of Hardenable Steels

  This article reviews some of the limitations of the standard cooling curve analysis and the Jominy hardenability test in extending the results to actual quenching in industrial setups and reports the development ...

  Citation × Citation Citation Abstract Copy Title: “Reference QuenchProbe”—An Alternative Probe Design for In-Situ Estimation of Cooling Rates, Heat Flux, and Hardenability During Immersion Quenching of Hardenable Steels Author: Prasanna Kumar, T. S., Hernández-Morales, B., Totten, George E. Year: 2014 This article reviews some of the limitations of the standard cooling curve analysis and the Jominy hardenability test in extending the results to actual quenching in industrial setups and reports the development of a new portable tool—Reference QuenchProbe—for estimating cooling rates, hardness, and microstructure distributions in hardenable steel grades during immersion quenching, which can be used by the heat treater in the plant. The specimen is made of the same grade of steel as the quenched component with section thickness matching that of the component, which is a departure from standard laboratory tests. The test is carried out in the plant under actual conditions dispensing the need to correlate the standard cooling curve data and end quench hardenability tests done in the laboratory to industrial practice. To test the suite of mathematical models associated with the Reference QuenchProbe hardware and software, specimens of different grades of steels were instrumented with a single thermocouple near the surface of the specimen. Using the cooling data at the point of measurement, the cooling rates, microstructure, and hardness at other critical locations were computed. An enthalpy-based non-linear inverse heat conduction model was coupled with austenite decomposition models for handling the latent heat liberated during quenching. Several steels ranging from low carbon to medium alloy steels were both end-quenched by water and immersion quenched in several industrial quenchants. The computed hardness of end quenched and immersion quenched specimens were shown to be in good agreement with the measured values. The Reference QuenchProbe is thus shown to generate data needed for heat treatment process design including quenchant selection, which can be directly used in practice. Title: “Reference QuenchProbe”—An Alternative Probe Design for In-Situ Estimation of Cooling Rates, Heat Flux, and Hardenability During Immersion Quenching of Hardenable Steels Author: Prasanna Kumar, T. S., Hernández-Morales, B., Totten, George E. Year: 2014 This article reviews some of the limitations of the standard cooling curve analysis and the Jominy hardenability test in extending the results to actual quenching in industrial setups and reports the development of a new portable tool—Reference QuenchProbe—for estimating cooling rates, hardness, and microstructure distributions in hardenable steel grades during immersion quenching, which can be used by the heat treater in the plant. The specimen is made of the same grade of steel as the quenched component with section thickness matching that of the component, which is a departure from standard laboratory tests. The test is carried out in the plant under actual conditions dispensing the need to correlate the standard cooling curve data and end quench hardenability tests done in the laboratory to industrial practice. To test the suite of mathematical models associated with the Reference QuenchProbe hardware and software, specimens of different grades of steels were instrumented with a single thermocouple near the surface of the specimen. Using the cooling data at the point of measurement, the cooling rates, microstructure, and hardness at other critical locations were computed. An enthalpy-based non-linear inverse heat conduction model was coupled with austenite decomposition models for handling the latent heat liberated during quenching. Several steels ranging from low carbon to medium alloy steels were both end-quenched by water and immersion quenched in several industrial quenchants. The computed hardness of end quenched and immersion quenched specimens were shown to be in good agreement with the measured values. The Reference QuenchProbe is thus shown to generate data needed for heat treatment process design including quenchant selection, which can be directly used in practice. Close