Journal of Thermophysics and Heat Transfer
ISSN / EISSN : 0887-8722 / 1533-6808
Published by: American Institute of Aeronautics and Astronautics (AIAA) (10.2514)
Total articles ≅ 3,696
Latest articles in this journal
Published: 6 September 2021
Journal of Thermophysics and Heat Transfer pp 1-11; https://doi.org/10.2514/1.t6175
Transient thermochromic liquid crystal (TLC) experiments can provide high-fidelity spatially resolved heat transfer data for complex geometries, particularly where infrared techniques cannot be applied. One challenge when applying transient methods to internal geometries is the local definition of the driving gas temperature. The transient nature of the streamwise driving gas temperature profile has led to comparisons with steady-state computational fluid dynamics being questioned. This paper explores simulating the temporal behavior of transient TLC experiments directly. A novel technique is developed to account for differences in the gas and solid time scales, where surface temperature is calculated at each spatial location analytically from the surface heat flux, using an impulse response method assuming one dimensional, semi-infinite conduction. Postprocessing of the simulated surface temperature history is performed using the same method as experimentally, allowing for direct comparison. This analytical thermal boundary condition (ATBC) is applied to simulate a transient TLC experiment of a stationary superscaled rib turbulated internal cooling passage in a gas turbine engine. Traditional steady-state simulations were also performed with constant temporal and spatial temperature boundary conditions. Results show that calculations using the new ATBC and traditional steady-state method give very similar Nusselt number distributions and mean values in relation to the experimental data, suggesting the larger discrepancy between simulations and the experiments is not the definition of the driving gas temperature. Analysis of transient variation of Nusselt number indicated brief highly localized maximum variations up to 40%, although this was not found to significantly affect the mean values, and passage-averaged values converged to within 0.5% of the final value within 0.2 s.
Published: 6 September 2021
Journal of Thermophysics and Heat Transfer pp 1-10; https://doi.org/10.2514/1.t6269
The knowledge of surface heat flux over aerodynamic surfaces is highly desirable for high-speed applications. Impulse test facilities like shock tubes and shock tunnels are invariantly employed for this where the aerodynamic test models experience step/ramp heat loads. Contrary to conventional methods, the usage of an advanced soft computing technique through an adaptive neuro-fuzzy inference system (ANFIS), for recovery of such surface heat loads, is theme of this paper. A coaxial thermal sensor is fabricated in house from chromel and constantan alloy. This E-type thermal probe is subjected to known heat flux (2–3.5 W) of laser light in an exclusive experimental setup, and the temperature responses are recorded. The simulations are also performed to get the temperature history for these heat loads. The experimental and computational results, either separately or together, are used to train the ANFIS network. The time-averaged values of heat flux obtained from ANFIS-based recovery shows excellent agreement in trend and magnitude (uncertainty band of ±5%) with the applied heat load. The present studies demonstrate the possible use of a soft computing technique for heat flux recovery in short-duration experiments within a desired accuracy level by using training data obtained experimentally or computationally or both.
Published: 31 August 2021
Journal of Thermophysics and Heat Transfer pp 1-14; https://doi.org/10.2514/1.t6363
On 7 September 2017, the U.S. Air Force Research Laboratory launched the second Advanced Structurally Embedded Thermal Spreader (ASETS-II) flight experiment on the fifth flight [Orbital Test Vehicle 5 (OTV-5)] of the Air Force’s X-37B spaceplane. OTV-5 landed on 27 October 2019 after 780 days on orbit. The ASETS-II flight experiment accomplished its mission to demonstrate functionality, characterize behavior, and explore the predicted limits of operation of oscillating heat pipes (OHPs) in a long-term microgravity environment. The three science objectives were to measure initial on-orbit thermal performance, long-duration thermal performance, and any lifetime degradation. The three OHPs on ASETS-II have varying configuration (center heating with large and small heaters and with single- and double-ended cooling) and heat pipe fluids (butane and R-134a) to isolate performance parameters of interest. Data collected during on-orbit operation are presented and favorably compared to predicted OHP limits of operation. Each OHP performed as expected with no notable differences between horizontal and microgravity flight data. All three OHPs started easily, had similar performance on ground and on orbit, showed no hysteresis effects or degradation on orbit, and performed well in several six-week-duration continuous operation tests both on the ground and in orbit.
Published: 30 August 2021
Journal of Thermophysics and Heat Transfer pp 1-14; https://doi.org/10.2514/1.t6199
In the present study, the effect of conical obstacles on heat transfer and flow characteristics in a circular tube was investigated. In most previous studies, stationary obstacles were used to stimulate the flow and to investigate heat transfer and pressure drop. In the present paper, in addition to investigating the effect of a stationary obstacle, the effect of using moving obstacles was studied, both empirically and numerically, as a new topic on heat transfer and pressure drop in turbulent flow inside the pipe. In this study, the rotating speed of the obstacle ranged from 50 to 100 rpm, and the Re ranged from 4000 to 24,000. The results revealed that the heat transfer and friction factor changed by 2.2–3.95 and 17.2–22.2 times relative to the smooth tube, respectively. Also, the thermal performance coefficient was 120% more than the stationary obstacles. According to the findings of the current study, studying the effect of obstacle rotation on thermohydraulic characteristics is an innovative and useful topic. Altogether, besides its easy construction, compared to previous reports, the conical obstacle is a suitable obstacle that can be employed to improve thermal performance.
Published: 30 August 2021
Journal of Thermophysics and Heat Transfer pp 1-5; https://doi.org/10.2514/1.t6326
Emission spectroscopy was conducted in a miniature arc heater in China Aerodynamics Research and Development Center to study the erosion of water-cooled copper electrode due to the high-temperature environment. With a 2-mm-diam viewpoint, emission signal of plasma torch at the exit of the nozzle was collected. Three tests were implemented under different conditions with arc currents of 400, 600, and 800 A. Temperature under each condition was determined as 4680±300, 4560±300, and 4650±300 K. By absolute irradiance calibration, the number density of copper atoms in the flowfield was determined; combined with the estimate of the plasma torch volume and the flow velocity, the erosion rate of copper electrode was given. Apparently, the erosion rate increases with the raise of the current, as shown in the result. Based on experience and the results of previous studies by other researchers, the value of the erosion rate is reliable, which verified a new approach with optical method to investigate the electrode erosion of arc-heated facilities.
Published: 13 August 2021
Journal of Thermophysics and Heat Transfer pp 1-7; https://doi.org/10.2514/1.t6359
Published: 9 August 2021
Journal of Thermophysics and Heat Transfer pp 1-11; https://doi.org/10.2514/1.t6332
This study numerically investigates the effects of the geometrical and operational parameters of an air channel, with an inclined baffle mounted opposite the heating plate, on its thermohydraulic performance and entropy generation. The Reynolds number (Re) was examined in the range from 1000 to 20,000 and the baffle angle α from 0 to 60°, and the clearance ratio C/H was studied in the range from 0.6 to 1.4. The response surface method was applied to determine the optimal design and operating parameters needed to maximize thermohydraulic performance and minimize the entropy generated. The results show that the parameter of thermohydraulic performance (η) of the channel increased with a decreasing Reynolds number and increasing values of the baffle angle and clearance ratio. By contrast, the entropy generation number Ns decreased with an increase in the Reynolds number and the baffle angle and a decrease in the clearance ratio. The results of multi-objective optimization yielded optimum values of Re=14,500, C/H=0.6, and α=59 deg, corresponding to η=0.7374 and Ns=3.683.
Published: 30 July 2021
Journal of Thermophysics and Heat Transfer pp 1-12; https://doi.org/10.2514/1.t6137
Metal effectiveness measurements (or overall cooling effectiveness measurements) are becoming increasingly used to understand complex coupled systems in gas turbine experimental research. Unlike traditional techniques in which individual boundary conditions are measured in isolation and superposed using a thermal model, metal effectiveness measurements give the final result of a complex coupled system. In correctly scaled experiments this allows aerothermal performance at near-engine conditions to be evaluated directly, and is thus powerful both as a research technique and for derisking engine development programs. The technique is particularly useful for evaluating the thermal performance of internally cooled turbine components, because of the complexity and degree of interaction of the underlying boundary conditions. An intrinsic limitation of metal effectiveness measurement data is that the individual boundary conditions (e.g., the internal and external heat transfer coefficients) cannot be directly obtained from the final measurement. Decoupling of these boundary conditions would allow deeper understanding of the systems that are the subject of experiments. The objective of this paper is to present methods to extract the individual underlying boundary conditions from data available in typical metal effectiveness experimental measurements, and to assess the uncertainty associated with decoupling techniques. Although we reference experimental data from advanced facilities for metal effectiveness research throughout, much of the analysis is performed using a low-order heat transfer model to allow the impact of experiment design and measurement errors to be clearly separated at each stage of the analysis.
Published: 30 July 2021
Journal of Thermophysics and Heat Transfer pp 1-11; https://doi.org/10.2514/1.t6254
Nonintrusive laser diagnostics are used for the measurements of metastable nitrogen molecules in the lowest excited electronic state, N2(A3Σu+), in a nonequilibrium flow, blowdown supersonic wind tunnel. The tunnel is operated with nitrogen at plenum pressures of P0=200–250 Torr, with the flow expanding through a two-dimensional contoured nozzle to the Mach number of M=3.6–4.6. The steady-state run time of the tunnel is approximately 10 s. The flow is excited by a repetitive nanosecond pulse discharge operated in the plenum or in the nozzle throat. Time-resolved absolute N2(A3Σu+,v=0) populations in the plenum are measured by single-pass, continuous wave tunable diode laser absorption spectroscopy (TDLAS). In the supersonic test section, absolute N2(A3Σu+,v=0–2) populations are measured by cavity ring down spectroscopy (CRDS), using a tunable pulsed laser system operated at 10 Hz. During each run, 50 single-shot ring down traces are acquired, demonstrating good shot-to-shot reproducibility. The results demonstrate that the cavity ring down time is not affected by the supersonic flow. N2(A3Σu+,v=0–2) populations and the flow temperature are inferred from the single-shot CRDS data. At the conditions when the flow is excited by the discharge in the nozzle throat, N2(A3Σu+,v=0) population in the supersonic test section is measured by both CRDS and TDLAS diagnostics. The two diagnostic techniques are complementary and can be used for characterization of nonequilibrium reacting flows over a wide range of pressures, including short-run-time high-enthalpy flow facilities.
Published: 14 July 2021
Journal of Thermophysics and Heat Transfer pp 1-10; https://doi.org/10.2514/1.t6337
Radiative heat transfer in a concentric cylinder system with a participating medium is demonstrated to be inherently two-dimensional, even for the consideration of heat transfer to the total inner or outer surface with uniform boundary conditions. For the evaluation of two-dimensional nongray radiative heat transfer, the zonal exchange factor, together with the concept of point mean beam length, is shown to be an effective solution approach. Optimal point mean beam length for radiative heat transfer between a differential area and a finite area with different geometrical configurations within the concentric cylindrical enclosure is generated. Numerical data for an example calculation is presented to illustrate the characteristics of nongray two-dimensional radiative heat transfer.