Measurement of Transient Natural Convection in Non-Ventilated Aircraft Compartments

2008 ◽  
Author(s):  
V. Egan ◽  
T. W. Confrey ◽  
D. Newport ◽  
V. Lacarac
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Temperature Distribution ◽  
Secondary Flows ◽  
Flow Structures ◽  
Flow Visualisation ◽  
Transient Effects ◽  
Aircraft Wing ◽  
Full Field ◽  
Side Walls

The present study focuses on heat transfer behaviour in aircraft compartments. The objectives of the analysis were to investigate the transient effects on fluid flow structures and heat transfer mechanisms in aircraft wing boxes relative to aircraft turnaround times. Experimental methods employed were flow visualisation and thermocouple measurements. A simplified air filled aluminium rectangular enclosure of aspect ratio 0.25 was constructed to replicate an aircraft wing box. Rubber insulation was used between wall surfaces to maintain separate thermal boundary conditions at each wall. Flow visualisation was used to illustrate the transient evolution of full field flow structures and thermocouple measurements were recorded to investigate the full field transient temperature distribution. Experiments were carried out from time zero to steady state and were conducted for Rayleigh numbers of 2.87×106, 4.81×106 and 7.39×106 based on enclosure height. Fluid flow patterns revealed the presence of two counter acting flows in the cavity with a downward motion adjacent to the front and rear sides of the enclosure. The downward motions were present due to the cooling of the warm air inside the cavity by the adjacent cooler aluminium side walls. Secondary flows existed in the lower region of the cavity specifically prominent to the front and rear surfaces where the height of detachment of the flow varied with time and temperature of the adjacent side walls. Transient spatial temperature distribution plots confirmed the approach to steady state was gradual, that a vertically thermal stratified distribution existed in the cavity and the presence of the thermal boundary layers along the horizontal and vertical walls were clearly evident. It was concluded that transient effects are significant relative to aircraft turnaround times as it was observed that the flow structures change over the initial transient phase of analysis and remain similar thereafter. Wing box material thermophysical properties influenced the developed flow structures causing two secondary flows to exist along the front and rear spar walls. Vertical temperature distribution results were generalised using a power law based on dimensionless time (t*), dimensionless temperature (T*) and Rayleigh number.

Heat transfer enhancement in microchannels using ribs and secondary flows

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Karthikeyan Paramanandam ◽  
Venkatachalapathy S. ◽  
Balamurugan Srinivasan
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Content Type ◽  
Flow And Heat Transfer

Purpose The purpose of this paper is to study the flow and heat transfer characteristics of microchannel heatsinks with ribs, cavities and secondary channels. The influence of length and width of the ribs on heat transfer enhancement, secondary flows, flow distribution and temperature distribution are examined at different Reynolds numbers. The effectiveness of each heatsink is evaluated using the performance factor. Design/methodology/approach A three-dimensional solid-fluid conjugate heat transfer numerical model is used to study the flow and heat transfer characteristics in microchannels. One symmetrical channel is adopted for the simulation to reduce the computational cost and time. Flow inside the channels is assumed to be single-phase and laminar. The governing equations are solved using finite volume method. Findings The numerical results are analyzed in terms of average Nusselt number ratio, average base temperature, friction factor ratio, pressure variation inside the channel, temperature distribution, velocity distribution inside the channel, mass flow rate distribution inside the secondary channels and performance factor of each microchannels. Results indicate that impact of rib width is higher in enhancing the heat transfer when compared with its length but with a penalty on the pressure drop. The combined effects of secondary channels, ribs and cavities helps to lower the temperature of the microchannel heat sink and enhances the heat transfer rate. Practical implications The fabrication of microchannels are complex, but recent advancements in the additive manufacturing techniques makes the fabrication of the design considered in this numerical study feasible. Originality/value The proposed microchannel heatsink can be used in practical applications to reduce the thermal resistance, and it augments the heat transfer rate when compared with the baseline design.

Jet Engine Gas Path Analysis Based on Takeoff Performance Snapshots

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
A. Putz ◽  
S. Staudacher ◽  
C. Koch ◽  
T. Brandes
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Performance Model ◽  
Operating Conditions ◽  
Medium Size ◽  
Jet Engines ◽  
Transient Effects ◽  
Steady State Analysis ◽  
Simulation Results ◽  
State Analysis

Current engine condition monitoring (ECM) systems for jet engines include the analysis of on-wing gas path data using steady-state performance models. Such data, which are also referred to as performance snapshots, usually are taken during cruise flight and during takeoff. Using steady-state analysis, it is assumed that these snapshots have been taken under stabilized operating conditions. However, this assumption is reasonable only for cruise snapshots. During takeoff, jet engines operate in highly transient conditions with significant heat transfer occurring between the fluid and the engine structure. Hence, steady-state analysis of takeoff snapshots is subject to high uncertainty. Because of this, takeoff snapshots are not used for performance analysis in current ECM systems. We quantify the analysis uncertainty by transient simulation of a generic takeoff maneuver using a performance model of a medium size two-shaft turbofan engine with high bypass ratio. Taking into account the influence of the preceding operating regimes on the transient heat transfer effects, this takeoff maneuver is extended backward in time to cover the aircraft turnaround as well as the end of the last flight mission. We present a hybrid approach for thermal calculation of both the fired engine and the shutdown engine. The simulation results show that takeoff derate, ambient temperature, taxi-out (XO) duration and the duration of the preceding aircraft turnaround have a major influence on the transient effects occurring during takeoff. The analysis uncertainty caused by the transient effects is significant. Based on the simulation results, we propose a method for correction of takeoff snapshots to steady-state operating conditions. Furthermore, we show that the simultaneous analysis of cruise and corrected takeoff snapshots leads to significant improvements in observability.

Two-Way Coupling Simulation of Heat Transfer in ADS Windowless Spallation Target

2013 ◽  
Author(s):  
Jie Liu ◽  
Lei Gao ◽  
Huan Chen ◽  
Zeng-hui Wang ◽  
Wen-qiang Lu
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Temperature Distribution ◽  
Nuclear Physics ◽  
Phase Distribution ◽  
Structural Parameters ◽  
Heat Transfer Process ◽  
Flow Process ◽  
Large Power ◽  
Spallation Target

The steady-state phase distribution and the structural parameters have been taken as the input for the nuclear physics calculation in the ADS windowless spallation target. The distribution of the extreme large power density of the heat load is imported back as the source term in the energy equation. Then temperature distribution is obtained based on the flow process and heat transfer. The preliminary results show that the temperature distribution reaches the steady-state and its shape is like the broken wings of the butterfly. This is very important for the further design and optimization of the ADS windowless spallation target. So the two-way coupling simulation of the heat transfer process is successfully performed between the computational fluid dynamics and the nuclear physics simulation.

Quasi-Steady-State Temperature Distribution in Periodically Contacting Finite Regions

1981 ◽  
Vol 103 (4) ◽  
pp. 739-744 ◽  
Author(s):  
B. Vick ◽  
M. N. O¨zis¸ik
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Steady State ◽  
Temperature Distribution ◽  
Interface Temperature ◽  
Quasi Steady State ◽  
Exact Analytical Solutions ◽  
One Dimensional ◽  
Steady State Temperature ◽  
Regular Cycle

Heat transfer across two surfaces which make and break contact periodically according to a continuous regular cycle is investigated theoretically and exact analytical solutions are developed for the quasi-steady-state temperature distribution for a two-region, one-dimensional, periodically contacting model. The effects of the Biot number, the thermal conductivity and thermal diffusivity of the materials and the duration of contact and break periods on the interface temperature and the temperature distribution within the solids are illustrated with representative temperature charts.

Effect of Nanofluid Properties on Magnetohydrodynamic Pump (MHD)

2011 ◽  
Vol 403-408 ◽  
pp. 663-669 ◽  
Author(s):  
Azadeh Shahidian ◽  
Majid Ghassemi ◽  
Rafat Mohammadi
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Temperature Distribution ◽  
Finite Difference ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Al2o3 Nanoparticles ◽  
Nacl Solution ◽  
Navier Stokes Equations ◽  
Side Walls

A Magnetohydrodynamic pump uses the Lorentz effect. It is based on the injection of an electric field into two electrodes located at facing side walls of a channel. The purpose of this study is to numerically investigate the effect of Nanofluid properties on the flow field as well as the temperature distribution in a MHD pump. To solve the non-linear governing differential equations, a finite difference based code is developed and utilized. The temperature and velocity are calculated by solving the energy and Navier-Stokes equations. Result shows that temperature stays almost constant with magnetic field. Furthermore velocity and temperature behaviours are similar for each period. However heat transfer inside the MHD pump varies with nanofluid (NaCl solution and Al2O3 nanoparticles) in comparison with the NaCl solution.

Field Mach-Zehnder Interferometer for Heat-Transfer Studies

1968 ◽  
Vol 1 (1) ◽  
pp. T9-T16 ◽  
Author(s):  
R. G. Brooks ◽  
S. D. Probert ◽  
J. Maxwell
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Minor Axis ◽  
Test Cell ◽  
Field Of View ◽  
Zehnder Interferometer ◽  
Full Field ◽  
Temperature Distributions ◽  
Complete Field ◽  
Mach Zehnder Interferometer

The use of interferometry for heat transfer studies enables a complete field of view to be quantitatively examined at one time without disturbing the temperature distribution being measured. The Mach-Zehnder interferometer described has an elliptical field, with a 15cm minor axis and is capable of accommodating test chambers 102cm in length using the full field of view. The sensitivity of the instrument for various air pressures and temperature distributions within the test cell has been evaluated. The use of the instrument for identifying isotherms in the neighbourhood of a heated slab supported on skid bars is described. A Moiré technique which eliminates the effects of imperfections in the interferometer plates has also been used.

Thermally Induced Flow Structures in Aircraft Wing Compartments

2008 ◽  
Author(s):  
D. Newport ◽  
V. Egan ◽  
M. Aguanno ◽  
V. Lacarac ◽  
B. Estebe ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Composite Material ◽  
Composite Materials ◽  
Thermal Environment ◽  
Flow Structures ◽  
Heat Transfer Mechanism ◽  
Commercial Aircraft ◽  
Aircraft Wing ◽  
Thermally Induced ◽  
Induced Flow

The use of composite material in modern commercial aircraft has increased significantly in recent years. The very low conductivity relative to Aluminium of composite materials means that the thermal environment experienced in an aircraft, during flight and on the apron, are significantly altered. The heat transfer mechanism is complex: natural and mixed convection flows established in compartments. This paper presents the thermally induced flow structures under representative conditions for a rectangular cavity representative of wing boxes and horizontal tail planes. The paper highlights the sensitivity to boundary conditions, the effect of structural stiffeners. The results indicate it may be possible to incorporate the effect of stringers and heating from above into existing correlations.

A Study of Heat Transfer Augmentation for Recuperative Heat Exchangers: Comparison Between Three Dimple Geometries

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
Michelle I. Valentino ◽  
Lucky V. Tran ◽  
Mark Ricklick ◽  
J. S. Kapat
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Waste Heat ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Low Reynolds Numbers ◽  
Heat Transfer Augmentation ◽  
Flow Disturbances ◽  
Side Walls

This study presents an investigation of the heat transfer augmentation for the purpose of obtaining high effectiveness recuperative heat exchangers for waste heat recovery. The focus of the present work is in the fully developed portion of a 2:1 aspect ratio rectangular channel characterized by dimples applied to one wall at channel Reynolds numbers of 10,000, 18,000, 28,000, and 36,000. The dimples are applied in a staggered-row, racetrack configuration. In this study, a segmented copper test section was embedded with insulated dimples in order to isolate the heat transfer within the dimpled feature. The insulated material used to create a dimpled geometry isolates the heat transfer within the dimple cavity from the heat transfer augmentation on the surrounding smooth walls promoted by the flow disturbances induced by the dimple. Results for three different geometries are presented, a small dimple feature, a large dimple, and a double dimple. The results of this study indicate that there is significant heat transfer augmentation even on the nonfeatured portion of the channel wall resulting from the secondary flows created by the features. Overall heat transfer augmentations for the small dimples are between 13–27%, large dimples between 33–54%, and double dimples between 22–39%, with the highest heat transfer augmentation at the lowest Reynolds number for all three dimple geometries tested. Heat transfer within the dimple was shown to be less than that of the surrounding flat regions at low Reynolds numbers. Results for each dimple geometry show that dimples are capable of promoting heat transfer over the entire bottom wall surface as well as the side walls; thus the effects are not confined to within the dimple cavity.

scholarly journals The Effect of Beam Intensity on Temperature Distribution in ADS Windowless Lead-Bismuth Eutectic Spallation Target

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Jie Liu ◽  
Lei Gao ◽  
Wen-qiang Lu
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Temperature Distribution ◽  
Heat Transfer Process ◽  
Beam Intensity ◽  
Maximum Temperature ◽  
Flow Process ◽  
Large Power ◽  
Spallation Target ◽  
Lead Bismuth Eutectic

The spallation target is the component coupling the accelerator and the reactor and is regarded as the “heart” of the accelerator driven system (ADS). Heavy liquid metal lead-bismuth eutectic (LBE) is served as core coolant and spallation material to carry away heat deposition of spallation reaction and produce high flux neutron. So it is very important to study the heat transfer process in the target. In this paper, the steady-state flow pattern has been numerically obtained and taken as the input for the nuclear physics calculation, and then the distribution of the extreme large power density of the heat load is imported back to the computational fluid dynamics as the source term in the energy equation. Through the coupling, the transient and steady-state temperature distribution in the windowless spallation target is obtained and analyzed based on the flow process and heat transfer. Comparison of the temperature distribution with the different beam intensity shows that its shape is the same as broken wing of the butterfly. Nevertheless, the maximum temperature as well as the temperature gradient is different. The results play an important role and can be applied to the further design and optimization of the ADS windowless spallation target.

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