The Experts below are selected from a list of 939 Experts worldwide ranked by ideXlab platform
Stefan Elbel - One of the best experts on this subject based on the ideXlab platform.
-
an experimental method to quantify local air side heat transfer coefficient through mass transfer measurements utilizing color change coatings
International Journal of Heat and Mass Transfer, 2019Co-Authors: Min Che, Stefan ElbelAbstract:Abstract This paper presents a visualization method to quantify local air-side heat transfer coefficient (HTC). It is challenging to measure local air-side HTC with good accuracy, especially for complicated geometries and real heat exchangers. The present method relies on measuring convective mass transfer and applying the analogy between heat and mass transfer. It is based on the chemical interaction between a pair of coating material and tracer gas. The coating material absorbs tracer gas and changes its color. Therefore, a visualization procedure is developed to correlate color change on the surface to the local mass transfer coefficient. In this research, the coating formulation, coating methods, and surface topography are evaluated to make sure the analogy between heat and mass transfer is valid. The experimental results of the flat plate in laminar flow show that the standard uncertainty of the local heat transfer coefficient is 15%. Furthermore, the results also show good agreement compared with the analytical Blasius Solution except in the vicinity of the leading and trailing edges. Because of these promising results, it seems feasible to use this method to acquire local air-side HTC through a visualization approach for more complicated geometries.
-
development of a new optical method to quantify local air side heat transfer coefficient
Proceedings of the 25th IIR International Congress of Refrigeration: Montréal Canada August 24-30 2019., 2019Co-Authors: Min Che, Stefan ElbelAbstract:Low air-side heat transfer coefficient (HTC) limits the performance of many heat exchangers. A new method is developed to obtain local air-side HTC of real heat exchangers without the use of complex experimental tools. The method relies on measuring mass transfer and applying the analogy between heat and mass transfer to determine heat transfer. A thin film coating is applied to the heat transfer surface which is exposed to a suitable trace gas, in this case, a 50 ppm ammonia-air mixture. The coating absorbs the ammonia and changes color. A detailed description of the new measurement technique is given, including the application of the fundamental heat and mass transfer correlations, evaluation of suitable coating formulations, determination of surface morphologies, and discussion of the optical principle to quantify color change. For laminar flow across flat plates, the new method results in experimental HTC that are within 17% of the Blasius Solution.
-
application of a new method to quantify local air side heat transfer coefficient on fundamental geometries
Proceedings of the 25th IIR International Congress of Refrigeration: Montréal Canada August 24-30 2019., 2019Co-Authors: Min Che, Stefan ElbelAbstract:A new optical method based on the analogy between heat and mass transfer is developed to obtain local air-side heat transfer coefficient (HTC). It uses thin-film coatings applied to the heat transfer surface in combination with a tracer gas. Experiments with fundamental geometries were conducted to calibrate the process and evaluate its accuracy. The local air-side HTCs results for laminar flow over a flat plate are within 20% compared to the Blasius Solution except for the leading and trailing edges. The mass transfer experiments are conducted in a wind tunnel. Calibration for the flat plate experiments takes into account flow velocity, light source, relative humidity of air, tracer gas concentration, and sample aging effects. Correlations for these parameters have been established. The measurements of the basic geometries such as inclined plates, wedges, and cylinders agree with the experimental results of literatures which employed different methods. These promising validation experiments justify the exploration of more complex geometries and entire heat exchangers using this technique.
R J Goldstein - One of the best experts on this subject based on the ideXlab platform.
-
local heat transfer on a finite width surface with laminar boundary layer flow
Applied Thermal Engineering, 2016Co-Authors: Matthew E Taliaferro, Matteo Angelino, F Gori, R J GoldsteinAbstract:Abstract The effect of a lateral discontinuity in the thermal boundary conditions in two dimensional laminar flow on a flat plate is investigated with numerical and analytical modeling. When the thermal and momentum boundary layers start at the same location, the resulting self-similar two dimensional boundary layer equations were solved numerically. For flow with an unheated starting length, three dimensional numerical simulations were required. For both the two and three dimensional thermal simulations, the Blasius Solution for a two dimensional momentum boundary layer was assumed. It is found that all the Nusselt numbers collapse to a single curve when graphed as a function of a spanwise similarity variable. Simple correlations for the local Nusselt number on a rectangular flat plate are presented for a variety of boundary conditions.
-
Local heat transfer on a finite width surface with laminar boundary layer flow [journal paper]
2016Co-Authors: Matthew E Taliaferro, Matteo Angelino, F Gori, R J GoldsteinAbstract:The effect of a lateral discontinuity in the thermal boundary conditions in two dimensional laminar flow on a flat plate is investigated with numerical and analytical modeling. When the thermal and momentum boundary layers start at the same location, the resulting self-similar two dimensional boundary layer equations were solved numerically. For flow with an unheated starting length, three dimensional numerical simulations were required. For both the two and three dimensional thermal simulations, the Blasius Solution for a two dimensional momentum boundary layer was assumed. It is found that all the Nusselt numbers collapse to a single curve when graphed as a function of a spanwise similarity variable. Simple correlations for the local Nusselt number on a rectangular flat plate are presented for a variety of boundary conditions
Min Che - One of the best experts on this subject based on the ideXlab platform.
-
an experimental method to quantify local air side heat transfer coefficient through mass transfer measurements utilizing color change coatings
International Journal of Heat and Mass Transfer, 2019Co-Authors: Min Che, Stefan ElbelAbstract:Abstract This paper presents a visualization method to quantify local air-side heat transfer coefficient (HTC). It is challenging to measure local air-side HTC with good accuracy, especially for complicated geometries and real heat exchangers. The present method relies on measuring convective mass transfer and applying the analogy between heat and mass transfer. It is based on the chemical interaction between a pair of coating material and tracer gas. The coating material absorbs tracer gas and changes its color. Therefore, a visualization procedure is developed to correlate color change on the surface to the local mass transfer coefficient. In this research, the coating formulation, coating methods, and surface topography are evaluated to make sure the analogy between heat and mass transfer is valid. The experimental results of the flat plate in laminar flow show that the standard uncertainty of the local heat transfer coefficient is 15%. Furthermore, the results also show good agreement compared with the analytical Blasius Solution except in the vicinity of the leading and trailing edges. Because of these promising results, it seems feasible to use this method to acquire local air-side HTC through a visualization approach for more complicated geometries.
-
development of a new optical method to quantify local air side heat transfer coefficient
Proceedings of the 25th IIR International Congress of Refrigeration: Montréal Canada August 24-30 2019., 2019Co-Authors: Min Che, Stefan ElbelAbstract:Low air-side heat transfer coefficient (HTC) limits the performance of many heat exchangers. A new method is developed to obtain local air-side HTC of real heat exchangers without the use of complex experimental tools. The method relies on measuring mass transfer and applying the analogy between heat and mass transfer to determine heat transfer. A thin film coating is applied to the heat transfer surface which is exposed to a suitable trace gas, in this case, a 50 ppm ammonia-air mixture. The coating absorbs the ammonia and changes color. A detailed description of the new measurement technique is given, including the application of the fundamental heat and mass transfer correlations, evaluation of suitable coating formulations, determination of surface morphologies, and discussion of the optical principle to quantify color change. For laminar flow across flat plates, the new method results in experimental HTC that are within 17% of the Blasius Solution.
-
application of a new method to quantify local air side heat transfer coefficient on fundamental geometries
Proceedings of the 25th IIR International Congress of Refrigeration: Montréal Canada August 24-30 2019., 2019Co-Authors: Min Che, Stefan ElbelAbstract:A new optical method based on the analogy between heat and mass transfer is developed to obtain local air-side heat transfer coefficient (HTC). It uses thin-film coatings applied to the heat transfer surface in combination with a tracer gas. Experiments with fundamental geometries were conducted to calibrate the process and evaluate its accuracy. The local air-side HTCs results for laminar flow over a flat plate are within 20% compared to the Blasius Solution except for the leading and trailing edges. The mass transfer experiments are conducted in a wind tunnel. Calibration for the flat plate experiments takes into account flow velocity, light source, relative humidity of air, tracer gas concentration, and sample aging effects. Correlations for these parameters have been established. The measurements of the basic geometries such as inclined plates, wedges, and cylinders agree with the experimental results of literatures which employed different methods. These promising validation experiments justify the exploration of more complex geometries and entire heat exchangers using this technique.
Matthew E Taliaferro - One of the best experts on this subject based on the ideXlab platform.
-
local heat transfer on a finite width surface with laminar boundary layer flow
Applied Thermal Engineering, 2016Co-Authors: Matthew E Taliaferro, Matteo Angelino, F Gori, R J GoldsteinAbstract:Abstract The effect of a lateral discontinuity in the thermal boundary conditions in two dimensional laminar flow on a flat plate is investigated with numerical and analytical modeling. When the thermal and momentum boundary layers start at the same location, the resulting self-similar two dimensional boundary layer equations were solved numerically. For flow with an unheated starting length, three dimensional numerical simulations were required. For both the two and three dimensional thermal simulations, the Blasius Solution for a two dimensional momentum boundary layer was assumed. It is found that all the Nusselt numbers collapse to a single curve when graphed as a function of a spanwise similarity variable. Simple correlations for the local Nusselt number on a rectangular flat plate are presented for a variety of boundary conditions.
-
Local heat transfer on a finite width surface with laminar boundary layer flow [journal paper]
2016Co-Authors: Matthew E Taliaferro, Matteo Angelino, F Gori, R J GoldsteinAbstract:The effect of a lateral discontinuity in the thermal boundary conditions in two dimensional laminar flow on a flat plate is investigated with numerical and analytical modeling. When the thermal and momentum boundary layers start at the same location, the resulting self-similar two dimensional boundary layer equations were solved numerically. For flow with an unheated starting length, three dimensional numerical simulations were required. For both the two and three dimensional thermal simulations, the Blasius Solution for a two dimensional momentum boundary layer was assumed. It is found that all the Nusselt numbers collapse to a single curve when graphed as a function of a spanwise similarity variable. Simple correlations for the local Nusselt number on a rectangular flat plate are presented for a variety of boundary conditions
Van Oudheusden B.w. - One of the best experts on this subject based on the ideXlab platform.
-
High-reSolution PIV measurements of a transitional shock wave–boundary layer interaction
Springer, 2015Co-Authors: Giepman R.h.m., Schrijer F.f.j., Van Oudheusden B.w.Abstract:This study investigates the effects of boundary layer transition on an oblique shock wave reflection. The Mach number was 1.7, the unit Reynolds number was 35 × 106 m?1, and the pressure ratio over the interaction was 1.35. Particle image velocimetry is used as the main flow diagnostics tool, supported by oil-flow and Schlieren visualizations. At these conditions, the thickness of the laminar boundary layer is only 0.2 mm, and seeding proved to be problematic as practically no seeding was recorded in the lower 40 % of the boundary layer. The top 60 % could, however, still be resolved with good accuracy and is found to be in good agreement with the compressible Blasius Solution. Due to the effects of turbulent mixing, the near-wall seeding deficiency disappears when the boundary layer transitions to a turbulent state. This allowed the seeding distribution to be used as an indicator for the state of the boundary layer, permitting to obtain an approximate intermittency distribution for the boundary layer transition region. This knowledge was then used for positioning the oblique shock wave in the laminar, transitional (50 % intermittency) or turbulent region of the boundary layer. Separation is only recorded for the laminar and transitional interactions. For the laminar interaction, a large separation bubble is found, with a streamwise length of 96 ??i,0 . The incoming boundary layer is lifted over the separation bubble and remains in a laminar state up to the impingement point of the shock wave. After the shock, transition starts and a turbulent profile is reached approximately 80–90 ??i,0 downstream of the shock. Under the same shock conditions, the transitional interaction displays a smaller separation bubble (43 ??i,0 ), and transition is found to be accelerated over the separation bubble
-
High-reSolution PIV measurements of a transitional shock wave–boundary layer interaction
'Springer Science and Business Media LLC', 2015Co-Authors: Giepman R.h.m., Schrijer F.f.j., Van Oudheusden B.w.Abstract:This study investigates the effects of boundary layer transition on an oblique shock wave reflection. The Mach number was 1.7, the unit Reynolds number was 35 × 106 m?1, and the pressure ratio over the interaction was 1.35. Particle image velocimetry is used as the main flow diagnostics tool, supported by oil-flow and Schlieren visualizations. At these conditions, the thickness of the laminar boundary layer is only 0.2 mm, and seeding proved to be problematic as practically no seeding was recorded in the lower 40 % of the boundary layer. The top 60 % could, however, still be resolved with good accuracy and is found to be in good agreement with the compressible Blasius Solution. Due to the effects of turbulent mixing, the near-wall seeding deficiency disappears when the boundary layer transitions to a turbulent state. This allowed the seeding distribution to be used as an indicator for the state of the boundary layer, permitting to obtain an approximate intermittency distribution for the boundary layer transition region. This knowledge was then used for positioning the oblique shock wave in the laminar, transitional (50 % intermittency) or turbulent region of the boundary layer. Separation is only recorded for the laminar and transitional interactions. For the laminar interaction, a large separation bubble is found, with a streamwise length of 96 ??i,0 . The incoming boundary layer is lifted over the separation bubble and remains in a laminar state up to the impingement point of the shock wave. After the shock, transition starts and a turbulent profile is reached approximately 80–90 ??i,0 downstream of the shock. Under the same shock conditions, the transitional interaction displays a smaller separation bubble (43 ??i,0 ), and transition is found to be accelerated over the separation bubble.Aerodynamics, Wind Energy & PropulsionAerospace Engineerin