| 1. |
- Badinand, T., et al.
(författare)
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Radiative heat transfer in film-cooled liquid rocket engine nozzles
- 2003
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Ingår i: Journal of thermophysics and heat transfer. - : American Institute of Aeronautics and Astronautics (AIAA). - 0887-8722 .- 1533-6808. ; 17:1, s. 29-34
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Tidskriftsartikel (refereegranskat)abstract
- A radiation model has been implemented in a Navier-Stokes flow solver to investigate the importance of thermal radiation in film-cooled liquid hydrogen/liquid oxygen rocket engine thrust chambers. Two running conditions were computed: high-altitude and sea-level conditions. For high altitudes, the smalls are heated by radiation approximately 3 K, and the flow is not influenced. At sea level, the flow separates from the nozzle walls and a Mach disk is formed inside the nozzle. This extra source of radiation is clearly observable and, combined with the cold atmospheric air pocket created behind the separation, contributes importantly to the wall temperatures. An increase of up to 140 K is observed in the zone after the separation. Moreover, the position of the shock is slightly affected by radiative transfer. It is shown that radiative heat transfer does play an important role in the case of a shocked film-cooled nozzle. In the unshocked case, its effects are noticeable, but may be neglected.
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| 2. |
- Gkoutzamanis, V. G., et al.
(författare)
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Thermal Management System Considerations for a Hybrid-Electric Commuter Aircraft
- 2022
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Ingår i: Journal of thermophysics and heat transfer. - : AIAA International. - 0887-8722 .- 1533-6808. ; 36:3, s. 650-666
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Tidskriftsartikel (refereegranskat)abstract
- When it comes to novel aircraft concepts, thermal management system (TMS) design is a ubiquitous task, even at the conceptual design phase. This is owing to its impact on the total weight of the aircraft, cooling drag, and overall performance. The commuter air transportation has recently regained attention and is seen as a solution to employ partial or full electrification in the upcoming decades due to its low power requirement and potential benefit of faster “door-to-door” traveling. This work examines the TMS characteristics to cool a battery-powered aft-fan engine. A literature review is initially performed on other research associated with TMS design. The development and weight evaluation of the baseline TMS for this type of propulsive technology are then presented, including the characterization of system redundancy effects on the overall TMS weight. Results show that the TMS design is a function of the selected propulsive configuration and energy management throughout the mission. Primarily, this relates to the cooling method selected, the heat exchangers as the major mass contributors of the TMS, the positioning of components used for the propulsive configuration, and the imposed certification constraints. Finally, the selected TMS design is calculated to have a combined specific cooling of 0.79 kW∕kg.
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| 3. |
- Hartwig, Jason, et al.
(författare)
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Screen Channel Liquid-Acquisition-Device Bubble Point Tests in Liquid Oxygen
- 2015
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Ingår i: Journal of Thermophysics and Heat Transfer. - 0887-8722. ; 29:2, s. 353-363
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Tidskriftsartikel (refereegranskat)abstract
- This paper examines the key parameters that affect the bubble point pressure for screen channel liquid acquisition devices in cryogenic liquid oxygen at elevated pressures and temperatures typical of a high-pressure propellant tank. An in-depth analysis of the effect of varying liquid temperature, pressure, and pressurization gas type on the bubble point is presented. Testing of a 200 x 1400 and 325 x 2300 Dutch twill screen sample was conducted at the NASA John H. Glenn Research Center at Lewis Field in Cleveland, Ohio. Test conditions ranged from 92 to 130 K and 0.138 to 1.79 MPa. The bubble point is shown to be a strong function of temperature with a secondary dependence on the amount of liquid subcooling. The subcooling dependence is believed to be a function of the amount of evaporation and condensation occurring at the liquid-gas interface at the screen. Good agreement exists between the data and theory for normally saturated liquid, but the model generally underpredicts the bubble point in subcooled liquid. Using the liquid temperature at the screen as opposed to the bulk liquid temperature to determine the surface tension of the fluid results in better correlation with the data.
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| 4. |
- Li, Yong, et al.
(författare)
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Buoyancy and Thermal Acceleration of Supercritical n-Decane in a Rectangular Channel
- 2022
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Ingår i: Journal of Thermophysics and Heat Transfer. - 0887-8722. ; 36:2, s. 419-430
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Tidskriftsartikel (refereegranskat)abstract
- In this work, supercritical n-decane flowing in ducts with different orientations is thoroughly investigated in terms of secondary flow, wall shear stress, and thermal acceleration. It is known that the secondary flow strength hardly plays a role in cases of flowing upward, flowing downward, or flowing horizontally at a small heat flux/mass flux. Still, an attachment point can be found at the center for cases of flowing upward and flowing downward, and this enhances the heat transfer. For a large heat flux/mass flux, thermal transport depends not only on the secondary flow strength but also on the secondary flow structure. Besides, a separation point is found at the center for flowing up/downward cases, and the more adjacent the attachment point is to the heated wall, the more serious is the thermal transport. The wall shear stress is beneficial to heat transfer but also relies on the distribution profile. Thermal acceleration can really diminish or even restrain the HTD phenomenon, but it is not the reason to cause the difference of heat transfer behavior for channels with different orientations.
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| 5. |
- Monsivais, Ian, et al.
(författare)
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Conjugate Heat Transfer in a Thin Microchannel Filled with a Porous Medium
- 2022
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Ingår i: Journal of thermophysics and heat transfer. - : AIAA International. - 0887-8722 .- 1533-6808. ; 36:1, s. 40-50
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Tidskriftsartikel (refereegranskat)abstract
- We study numerically the conjugate heat transfer between the walls of a parallel plate microchannel and ahomogeneous porous medium fully saturated with a liquid that is found in motion due to an external pressuregradient. The origin of this problem is caused by a uniform heat flux imposed at the external surfaces of the walls of themicrochannel that have a finite thermal conductivity. In this manner, the competition and heat transfer mechanismsbetween both regions characterized by the thermal resistances, conduct to a conjugate formulation that originates adimensionless conjugate parameter αc. This parameter measures the ratio of both thermal resistances, and, for largevalues of this parameter, the longitudinal heat conduction effects in the walls are very important and suffer significantdeviations when compared with the case with finite values for this parameter. The dimensionless governing equationsfor both regions are established with the corresponding boundary conditions, and the numerical results show that theaspect ratios of both regions, controlled through the dimensionless parameters ϵh and ϵ, play an important role indistinguishing the presence of the longitudinal heat conduction effects in the walls. For instance, if the ratios αc∕ϵ2h25 and αc∕ϵ2 1, the longitudinal effects of heat transfer are very important in the walls of the microchannel,whereas in the porous matrix there are effects of heat transfer in both directions, whereas if αc∕ϵ2h αc∕ϵ2 25 onlythe longitudinal conduction effects are significant for both regions.
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