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  • Ndebele (South Africa)  (8)
  • 1
    Online Resource
    Online Resource
    Thermal characteristics of epoxy as a bonding material in a low temperature vessel
    Old City Publishing, Inc ; 2021
    In:  High Temperatures-High Pressures Vol. 50, No. 4-5 ( 2021), p. 265-276
    Details
    In: High Temperatures-High Pressures, Old City Publishing, Inc, Vol. 50, No. 4-5 ( 2021), p. 265-276
    Abstract: One of the main sources of heat leakage in a low temperature vessel is the thermal conduction of the vessel wall between room temperature and the low temperature. The material of the vessel is generally stainless-steel, and it is fabricated by welding. To reduce the amount of the thermal conduction, materials having low thermal conductivity are chosen. Glass fiber reinforced plastic (GFRP) is one of the adequate candidate materials because it has low thermal conductivity and high mechanical strength. We use GFRP pipe instead of stainless-steel pipe, as a neck in a liquid nitrogen vessel (or Dewar). Epoxy, as a bonding material, is inserted between the GFRP neck and the main body of the vessel. Therefore, the thermal characteristics, especially the thermal expansion, are very important because the vessel is cooled and warmed periodically. The experimental results of thermal expansion between room temperature and the low temperature are presented in the paper. Leakage in a vacuum environment is incurred because of different linear thermal expansion coefficients of various materials. The leakage is investigated using a vacuum-level checking method during the thermal cycle. In addition, the amount of boil-off in a low temperature vessel is discussed in terms of the thermal characteristics of the neck’s material.
    Type of Medium: Online Resource
    ISSN: 1472-3441
    URL: Article
    DOI: 10.32908/hthp.v50.1069
    Language: Ndebele (South Africa)
    Publisher: Old City Publishing, Inc
    Publication Date: 2021
    detail.hit.zdb_id: 2022638-X
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  • 2
    Online Resource
    Online Resource
    Push-rod dilatometer calibration and thermal expansion coefficient measurement of standard material
    Old City Publishing, Inc ; 2021
    In:  High Temperatures-High Pressures Vol. 50, No. 4-5 ( 2021), p. 287-293
    Details
    In: High Temperatures-High Pressures, Old City Publishing, Inc, Vol. 50, No. 4-5 ( 2021), p. 287-293
    Abstract: The linear thermal expansion coefficient (LTEC) is a very important thermal property in the field of length standard, precision engineering and novel material science. There are several methods in measuring the LTEC of a material and the push-rod type is a one of the frequently used method. In this work, the calibration and the measurement procedures of the SRM 736 which is a certified material provided from NIST are carried out with push-rod type dilatometer (Dil402, NETZSCH) and the results are presented in the temperature range from 300°C to 500°C. The calibration of thermocouple and a linear variable differential transformer (LVDT) sensor have been performed with the melting point of the pure metals and the calibration device consisting of the rod and micrometer provided from the NETZSH.
    Type of Medium: Online Resource
    ISSN: 1472-3441
    URL: Article
    DOI: 10.32908/hthp.v50.1075
    Language: Ndebele (South Africa)
    Publisher: Old City Publishing, Inc
    Publication Date: 2021
    detail.hit.zdb_id: 2022638-X
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  • 3
    Online Resource
    Online Resource
    Characteristics of forced convection heat transfer of Co0.5Zn0.5Fe2O4 during laminar flow in a tube
    Old City Publishing, Inc ; 2021
    In:  High Temperatures-High Pressures Vol. 50, No. 4-5 ( 2021), p. 335-354
    Details
    In: High Temperatures-High Pressures, Old City Publishing, Inc, Vol. 50, No. 4-5 ( 2021), p. 335-354
    Abstract: The convective heat transfer characteristics of a Co0.5Zn0.5Fe2O4 nanofluid in the laminar flow region based on various concentrations are measured experimentally. The results indicate that the convective heat transfer coefficient increases with the concentration. The maximum heat transfer improved by 24.7% for the Co0.5Zn0.5Fe2O4 nanofluid at concentration 0.2wt% when the Reynolds number (Re) is 1600, compared with that of the base fluid (water/ethylene glycol (EG) = 80:20). Furthermore, the heat transfer improved by 3.6%, 16.2%, 22.5%, and 32.4% at concentrations of 0.025wt%, 0.05wt%, 0.1wt%, and 0.2wt%, respectively, when Re is 1400, compared with that of the base fluid (water/EG = 80:20). The convective heat transfer coefficient ratio of the Co0.5Zn0.5Fe2O4 nanofluid varied from 1.04 to 1.35. This means that the Co0.5Zn0.5Fe2O4 nanofluid had a larger heat transfer coefficient than the base fluid. Additionally, compared with that of the base fluid (water/EG = 80:20), the pressure drop of the Co0.5Zn0.5Fe2O4 nanofluid increased by 1.52%, 4.33%, 5.49%, and 7.32% at concentrations 0.025wt%, 0.05wt%, 0.1wt%, and 0.2wt%, respectively, when Re is 1600.
    Type of Medium: Online Resource
    ISSN: 1472-3441
    URL: Article
    DOI: 10.32908/hthp.v50.1063
    Language: Ndebele (South Africa)
    Publisher: Old City Publishing, Inc
    Publication Date: 2021
    detail.hit.zdb_id: 2022638-X
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  • 4
    Online Resource
    Online Resource
    Thermophysical properties of nickel-based single crystal of René N5
    Old City Publishing, Inc ; 2021
    In:  High Temperatures-High Pressures Vol. 50, No. 4-5 ( 2021), p. 311-323
    Details
    In: High Temperatures-High Pressures, Old City Publishing, Inc, Vol. 50, No. 4-5 ( 2021), p. 311-323
    Abstract: Nickel-based superalloys have been widely used for various high-temperature and high-pressure applications such as gas-turbines, power plants, and boiler housings. In this study, we report new experimental results for thermophysical properties of René N5 alloy in a temperature range of room temperature to 1000 °C. Especially, specimens of René N5 alloy were studied in directions [001] and [111] from the same batch of commercial alloy bar. Thermal diffusivity, specific heat capacity, thermal conductivity, and coefficient of thermal expansion (CTE) with correction data of density were evaluated for each measurement method, and detailed data are provided in tables. Thermal conductivity of the [001] alloy had a higher trend than that of the [111] alloy, with relative deviation of 0.7% to 4.8%. Coefficient of thermal expansion values showed good agreement (within 5.3%) and had a curve similar to that of the specific heat capacity. All thermophysical property results were described and compared with those of single crystal alloy of CMSX-4, René N5 and conventional cast René 80 of reference data. The microstructures of alloys [001] and [111] of René N5 were observed by SEM and found to have phase of γ/γ′, which affects the thermophysical properties.
    Type of Medium: Online Resource
    ISSN: 1472-3441
    URL: Article
    DOI: 10.32908/hthp.v50.1085
    Language: Ndebele (South Africa)
    Publisher: Old City Publishing, Inc
    Publication Date: 2021
    detail.hit.zdb_id: 2022638-X
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  • 5
    Online Resource
    Online Resource
    Thermal conductivity measurement of VO2 nanofluid using bidirectional 3ω method
    Old City Publishing, Inc ; 2021
    In:  High Temperatures-High Pressures Vol. 50, No. 4-5 ( 2021), p. 355-367
    Details
    In: High Temperatures-High Pressures, Old City Publishing, Inc, Vol. 50, No. 4-5 ( 2021), p. 355-367
    Abstract: Nanofluids containing vanadium dioxide (VO2) are used in applications such as actuators, smart windows, and gastrointestinal tracts. Therefore, measuring the thermal conductivity of nanofluids with VO2 characteristics is important in various environmental industries. In this study, the bidirectional 3 omega (3ω) method was used to measure the thermal conductivity of nanofluids. Experimental equipment for measuring VO2 nanofluids in various environments was designed and fabricated. The effectiveness of the bidirectional 3ω equipment was verified by measuring the thermal conductivity of ethylene glycol, which has been extensively reported in the literature. The effects of elapsed time, specimen thickness, and operation temperature on the thermal conductivity are discussed in this paper. In addition, the measuring error was investigated with regard to the precipitation of particles in the suspension.
    Type of Medium: Online Resource
    ISSN: 1472-3441
    URL: Article
    DOI: 10.32908/hthp.v50.1071
    Language: Ndebele (South Africa)
    Publisher: Old City Publishing, Inc
    Publication Date: 2021
    detail.hit.zdb_id: 2022638-X
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  • 6
    Online Resource
    Online Resource
    Evaluation of heat transfer performance of a laboratory-scale polymer rotary air preheater
    Old City Publishing, Inc ; 2021
    In:  High Temperatures-High Pressures Vol. 50, No. 4-5 ( 2021), p. 369-381
    Details
    In: High Temperatures-High Pressures, Old City Publishing, Inc, Vol. 50, No. 4-5 ( 2021), p. 369-381
    Abstract: Regenerative heat exchangers, which increase the temperature of newly supplied air using the waste heat of exhaust gas, are installed in large thermal systems, such as thermal power plants and industrial boilers, to improve their thermal efficiency. These devices are also known as air preheaters, and the rotary regenerative type has been widely used. The heat transfer performance of a rotary regenerator is enhanced as the heat capacity, which is the product of the density and specific heat, increases rather than the thermal conductivity of heat exchanging plates (HEPs). Studies to replace the existing metal materials with polymers, which are resistant to corrosion and inexpensive, have garnered attention. In this study, the heat transfer performance of HEPs fabricated using polytetrafluoroethylene, Mono Cast nylon, stainless steel, and aluminum is experimentally compared using a laboratory-scale experimental setup. It is confirmed that the polymer materials have similar or larger effectiveness compared to metals within the experimental error.
    Type of Medium: Online Resource
    ISSN: 1472-3441
    URL: Article
    DOI: 10.32908/hthp.v50.1077
    Language: Ndebele (South Africa)
    Publisher: Old City Publishing, Inc
    Publication Date: 2021
    detail.hit.zdb_id: 2022638-X
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  • 7
    Online Resource
    Online Resource
    The effect of flow regime on surface oscillations during electromagnetic levitation experiments
    Old City Publishing, Inc ; 2020
    In:  High Temperatures-High Pressures Vol. 49, No. 1-2 ( 2020), p. 49-60
    Details
    In: High Temperatures-High Pressures, Old City Publishing, Inc, Vol. 49, No. 1-2 ( 2020), p. 49-60
    Abstract: During containerless processing, the oscillating drop method can be used to measure the surface tension and viscosity of a levitated melt. Through containerless processing, reactive melts that cannot be measured through conventional methods can be accurately measured; however, the accuracy of this method is dependent on the internal flow within the drop. While laminar flow does not redistribute the momentum of the oscillations, turbulent flow does redistribute the momentum of the flow and, as a result, dominates the damping. As a result, it is important to understand the internal flow behavior and the factors that affect the flow during these experiments. Models are used for the indirect quantification and characterization of the internal flow using the experimental parameters and material properties. In some cases, such as Cu50Zr50, the flow is laminar over the full range of the experiment. In other cases, including Al75Ni25, the sample is dominated by turbulent flow at high temperatures and applied electromagnetic fields, but upon cooling, transitions to laminar flow. Additionally, cases exist in which the flow is fully turbulent over the range of interest and valid measurements using the oscillating drop method are not possible. During the design phase of the experiment, the experimental parameters should be modeled to characterize the flow behavior and ensure a clean experiment.
    Type of Medium: Online Resource
    ISSN: 1472-3441
    URL: Article
    DOI: 10.32908/hthp.v49.817
    Language: Ndebele (South Africa)
    Publisher: Old City Publishing, Inc
    Publication Date: 2020
    detail.hit.zdb_id: 2022638-X
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  • 8
    Online Resource
    Online Resource
    High-temperature cyclic fatigue in air of SiCf/SiC ceramic matrix composite with a pyrolytic carbon interface
    Old City Publishing, Inc ; 2021
    In:  High Temperatures-High Pressures Vol. 50, No. 4-5 ( 2021), p. 325-334
    Details
    In: High Temperatures-High Pressures, Old City Publishing, Inc, Vol. 50, No. 4-5 ( 2021), p. 325-334
    Abstract: A cyclic fatigue test of SiCf/SiC ceramic matrix composites was conducted at 1400°C and compared to the monotonic tensile test. The specimens were prepared with an interface layer of pyrolytic carbon and densified through chemical vapor infiltration. In the monotonic tensile test, at 1400°C, the specimen fractured at a strain of 0.35% with a proportional limit stress of 175 MPa, showing a typical fiber pull-out. However, after a prolonged cyclic test with increasing stresses from 65 to 95 MPa, the specimen fractured brittlely with almost no fiber pull-out. The microstructure analysis of the fracture surface showed different oxidation levels with respect to fracture locations, indicating that the crack propagated during the cyclic fatigue test. Transmission electron microscopy analysis revealed that the interface layer of pyrolytic carbon was removed by oxidation and oxide layers were formed on both sides of the fiber and matrix at the later stage of the cyclic test, resulting in a strong interface between the fibers and matrix and brittle fracture during the cyclic test at 1400°C.
    Type of Medium: Online Resource
    ISSN: 1472-3441
    URL: Article
    DOI: 10.32908/hthp.v50.1079
    Language: Ndebele (South Africa)
    Publisher: Old City Publishing, Inc
    Publication Date: 2021
    detail.hit.zdb_id: 2022638-X
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