Numerical Modeling of Regenerative Cooling System for Large Expansion Ratio Rocket Engines

2015 ◽  
Vol 7 (1) ◽  
Author(s):  
Manikanda Rajagopal
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Expansion Ratio ◽  
Wall Material ◽  
Rocket Engines ◽  
Conductive Heat ◽  
Thermal Failure ◽  
Regenerative Cooling ◽  
Numerical Predictions ◽  
Large Expansion

In this study, the performance of regenerative cooling system for large expansion ratio rocket engines (Ae/At ∼ 100) is investigated numerically. During combustion and gas expansion, the walls of the combustion chamber and the rocket nozzle are exposed to high temperature gas (∼3500 K), which can ultimately lead to structural failure. Therefore, to protect the hardware from thermal failure, a regenerative cooling system for a cryogenic rocket engine that uses fuel (liquid hydrogen (LH)) or oxidizer (liquid oxygen (LOX)) as the cooling medium is considered. Three-dimensional simulations have been performed for both constant and variable fluid properties. The influence of the thermal properties of the material and thickness of the nozzle wall on conductive heat transfer has also been investigated. The effect of radiative heat transfer when there is no regenerative cooling system has been analyzed. In addition, heat transfer enhancement for different turbulence models and the influence of coolant used (both the fuel and oxidizer) is also investigated. It is evident from the results that a properly designed regenerative cooling system can maintain the hot side wall at a temperature well below the melting point of the wall material, which ensures the protection of nozzle hardware from thermal failure. Also, the predicted pressure drop is found to be 0.7 bar, which meets the design requirement. Numerical predictions are validated with the data available in literature.

HP Vane Aerodynamics and Heat Transfer in the Presence of Aggressive Inlet Swirl

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Imran Qureshi ◽  
Andy D. Smith ◽  
Thomas Povey
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Three Dimensional ◽  
Leading Edge ◽  
Good Deal ◽  
Vortex Center ◽  
Research Facility ◽  
Lean Burn ◽  
Numerical Predictions ◽  
The Impact

Modern lean burn combustors now employ aggressive swirlers to enhance fuel-air mixing and improve flame stability. The flow at combustor exit can therefore have high residual swirl. A good deal of research concerning the flow within the combustor is available in open literature. The impact of swirl on the aerodynamic and heat transfer characteristics of an HP turbine stage is not well understood, however. A combustor swirl simulator has been designed and commissioned in the Oxford Turbine Research Facility (OTRF), previously located at QinetiQ, Farnborough UK. The swirl simulator is capable of generating an engine-representative combustor exit swirl pattern. At the turbine inlet plane, yaw and pitch angles of over ±40 deg have been simulated. The turbine research facility used for the study is an engine scale, short duration, rotating transonic turbine, in which the nondimensional parameters for aerodynamics and heat transfer are matched to engine conditions. The research turbine was the unshrouded MT1 design. By design, the center of the vortex from the swirl simulator can be clocked to any circumferential position with respect to HP vane, and the vortex-to-vane count ratio is 1:2. For the current investigation, the clocking position was such that the vortex center was aligned with the vane leading edge (every second vane). Both the aligned vane and the adjacent vane were characterized. This paper presents measurements of HP vane surface and end wall heat transfer for the two vane positions. The results are compared with measurements conducted without swirl. The vane surface pressure distributions are also presented. The experimental measurements are compared with full-stage three-dimensional unsteady numerical predictions obtained using the Rolls Royce in-house code Hydra. The aerodynamic and heat transfer characterization presented in this paper is the first of its kind, and it is hoped to give some insight into the significant changes in the vane flow and heat transfer that occur in the current generation of low NOx combustors. The findings not only have implications for the vane aerodynamic design, but also for the cooling system design.

Computation of flow and heat transfer through channels with periodic dimple/protrusion walls using low-Reynolds number turbulence models

2019 ◽  
Vol 29 (3) ◽  
pp. 1178-1207 ◽  
Author(s):  
Mohammad Fazli ◽  
Mehrdad Raisee
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Correction Term ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Internal Cooling ◽  
Recirculation Bubble ◽  
Content Type ◽  
Flow And Heat Transfer ◽  
Numerical Predictions

PurposeThis paper aims to predict turbulent flow and heat transfer through different channels with periodic dimple/protrusion walls. More specifically, the performance of various low-Rek-ε turbulence models in prediction of local heat transfer coefficient is evaluated.Design/methodology/approachThree low-Re numberk-εturbulence models (the zonalk-ε, the lineark-εand the nonlineark-ε) are used. Computations are performed for three geometries, namely, a channel with a single dimpled wall, a channel with double dimpled walls and a channel with a single dimple/protrusion wall. The predictions are obtained using an in house finite volume code.FindingsThe numerical predictions indicate that the nonlineark-εmodel predicts a larger recirculation bubble inside the dimple with stronger impingement and upwash flow than the zonal and lineark-εmodels. The heat transfer results show that the zonalk-εmodel returns weak thermal predictions in all test cases in comparison to other turbulence models. Use of the lineark-εmodel leads to improvement in heat transfer predictions inside the dimples and their back rim. However, the most accurate thermal predictions are obtained via the nonlineark-εmodel. As expected, the replacement of the algebraic length-scale correction term with the differential version improves the heat transfer predictions of both linear and nonlineark-εmodels.Originality/valueThe most reliable turbulence model of the current study (i.e. nonlineark-εmodel) may be used for design and optimization of various thermal systems using dimples for heat transfer enhancement (e.g. heat exchangers and internal cooling system of gas turbine blades).

Modelling and Simulation Heat Transfer in Wheat Stored in a Simulated Sealed Pit

2008 ◽  
Vol 4 (1) ◽  
Author(s):  
Mohamed A. Ismail ◽  
Michael P. Douglass ◽  
Brian C. Stenning
Keyword(s):  
Heat Transfer ◽  
Finite Difference ◽  
Input Data ◽  
Storage Period ◽  
Conductive Heat Transfer ◽  
Wall Material ◽  
Conductive Heat ◽  
Moisture Contents ◽  
Grain Moisture ◽  
Grain Temperature

A mathematical model was developed to predict the change of temperature distribution with time in the radial and axial directions in a simulated sealed cylindrical pit. The finite difference method was used in the model to calculate the conductive heat transfer. The model predicts the grain temperatures in the pit during the storage period using input data of initial grain temperature, storage time and number of spatial elements in both radial and axial directions. Other input data include the finite difference spatial increment in both directions, the finite time increment, temperatures of soil surrounding the pit and the physical properties of grain, pit wall material and surrounding soil. To validate the model, predicted temperatures were compared with measured data for wheat of Apollo variety being stored in a simulated sealed pit for a period of 70 days. The wheat was stored in a cylindrical mild steel tank with 0.6 m in both diameter and height. The initial uniform grain temperature was 15°C and the initial uniform grain moisture content was 12.45% (w.b.). Both measured and predicted wheat temperatures attained steady state within a short period of storage (2 to 6 days) and this equilibrium was maintained throughout the experiment period. At the end of the storage period, the grain temperatures were decreased by an average of 2.63°C and the grain moisture contents were increased by an average of 1.62% (w.b.) at the top layer of the pit. For the bottom layer of the pit, the grain temperatures increased by an average of 7.04°C and the grain moisture contents were decreased by an average of 0.50% (w.b.) The conductive heat transfer model predicted the grain temperatures with a standard error of estimate between measured and predicted of 0.12°C -0.25°C.

scholarly journals Coupled thermo-physical behaviour of an inorganic intumescent system in cone calorimeter testing

2017 ◽  
Vol 35 (3) ◽  
pp. 207-234 ◽  
Author(s):  
Sungwook Kang ◽  
Sengkwan Choi ◽  
Joung Yoon Choi
Keyword(s):  
Heat Transfer ◽  
Cone Calorimeter ◽  
Test Sample ◽  
Conductive Heat ◽  
Cone Calorimetry ◽  
Scanning Calorimetry ◽  
Element Analysis ◽  
Physical Behaviour ◽  
Numerical Predictions ◽  
Physical Measurements

This article examines the thermo-physical behaviour of an inorganic-based intumescent coating, tested with bench-scale cone calorimetry, in order to promote the understanding of its intumescence and to contribute to the optimisation of its thermal insulation performance. In the test, the specimen underwent the following phenomena simultaneously: (1) thermo-kinetic endothermic water vaporisation; (2) formation of micro-scale pores in its internal volume; (3) expansion of its volume; (4) variations in thermal boundaries. These simultaneous phenomena cause several changes in internal–external conditions given to the test sample: (1) loss of mass (water molecules); (2) reduction of effective thermal conductivity owing to its porous structure; (3) increase in length of the conductive heat transfer path across its expanding volume; (4) irradiance intensification and additional heat transfer generation on its moving boundaries, exposed to the heat source and surroundings. This interacting thermo-physical behaviour impedes the heat transfer to the underlying substrate. It is therefore comprehensively explained by finite element analysis, associated with the experimental data obtained from a thermogravimetric analyser, differential scanning calorimetry, electric furnace and cone calorimeter tests. The numerical predictions agreed with the physical measurements with consistent accuracy, in terms of both histories of substrate temperature and coating-thickness expansion. This combined numerical–experimental approach enables clear interpretation on the process of intumescence, the impediment mechanism of heat transfer and the critical factors of the material’s behaviour.

Coupling Process Analysis on the Flow and Heat Transfer of Hydrocarbon Fuel With Pyrolysis and Pyrolytic Coking Under Supercritical Pressures

2018 ◽  
Author(s):  
Chaofan Zhao ◽  
Xizhuo Hu ◽  
Jianqin Zhu ◽  
Zhi Tao
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Cooling System ◽  
Process Analysis ◽  
Hydrocarbon Fuel ◽  
Strong Impact ◽  
Regenerative Cooling ◽  
Flow And Heat Transfer ◽  
Cooling Tube ◽  
Scramjet Engine

The regenerative cooling technology has become the most effective method to reduce the high-temperature of the scramjet engine. With physical and chemical heat sink, the endothermic hydrocarbon fuel has excellent performance in the regenerative cooling system of the scramjet engine which operates under extremely high temperature. The pyrolytic reactions not only absorb a large amount of heat, but also produce some kinds of coking precursors, mainly alkenes and aromatics. Because of the coking precursors and the coking reactions, a lot of coke would be generated on the wall and exert strong impact on the heat transfer, as the conductivity of the coke is much lower than that of the metal wall. Meanwhile, the surface coking changes the geometric parameters of the cooling tube, which leads to the flow field variations with the thickening coking layer. So, it is needed to find out the interaction between these variations. In this paper, a one-dimensional (1D) model has been developed to calculate the flow and heat transfer parameters distributions of the pyrolytically reacted RP-3 along the regenerative cooling tube with the pyrolytic coking. The 24-step pyrolytic reaction model and the coking kinetic model are applied to predict the pyrolysis and pyrolytic coking process of RP-3, with accurate computations of the physical properties of fluid mixture which undergo drastic variations during the transcritical process. Comparisons between the current predictions and the open published experimental data are carried out and good agreement is achieved. Calculations on the coupling relationships between the flow, heat transfer, pyrolysis and pyrolytic coking within 20 min in the circular tube have been conducted. With the heat flux increased, the coke mass is rising sharply and the temperature of the outer tube wall rises rapidly owing to the increasing thermal resistance of the coke layer. Moreover, the flow velocity becomes faster during the narrowing process of the tube caused by surface coking. In order to better understand the coking characteristics, further investigations on distributions of the surface coking under heat fluxes of 1.2–2.0MW/m2, pressures of 2.6–7.4 MPa and with inlet velocities of 0–5m/s have been performed. Results reveal that all these factors play an important role in the pyrolytic reactions and the coking rate distributions. The results in this paper have significant reference value in the design of the regenerative cooling system.

Study of Hybrid Wet/Dry Cooling With Different Surface Morphology: Analyses on Pressure Drop and Thermal Performances

2020 ◽  
Author(s):  
Sudipta Saha ◽  
Jamil Khan ◽  
Tanvir Farouk
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Pressure Drop ◽  
Surface Morphology ◽  
Thermal Resistance ◽  
Cooling System ◽  
Numerical Study ◽  
Mathematical Framework ◽  
Current Effort ◽  
Numerical Predictions

Abstract This work conducts a multiphase multi-physics numerical study on this mixed mode cooling system, where evaporation of a liquid water film augments the convective cooling by evaporative heat and mass transfer. The mathematical framework consists of coupled mass, momentum, energy equation with species transport of air and evaporated water in the gas phase. Author’s prior works on perfectly flat surface predicted a minimum 500% increase of heat transfer coefficient in presence of a dual mode heat transfer. Current effort conducts a parametric study based on the different surface roughness structures over a broad range of Reynolds number condition. Array of circular, squared and triangular shaped grooves have been introduced along the surface exposed to the evaporating liquid. The cooling performances have been analyzed for different surface roughness structures and then compared against the flat film configuration. Furthermore, pressure drop across the liquid-gas interface has also been analyzed to predict the pumping power of the system. Model predicts that triangular shaped grooves exhibits a maximum ∼22% decrease in thermal resistance with a minimum pressure drop (∼5.5 times) across the interface. The square shaped surface morphology achieves 18% reduction in thermal resistance, with a penalty of pressure drop increase by a factor of ∼8. In comparison, circular grooves exhibit similar thermal performance but with a slightly a lower pressure drop (∼7 times). The numerical predictions have been compared with similar experimental findings and qualitative agreement was observed.

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