Deposit Formation and Mitigation in Aircraft Fuels

1999 ◽  
Vol 123 (4) ◽  
pp. 741-746 ◽  
Author(s):  
L. J. Spadaccini ◽  
D. R. Sobel ◽  
H. Huang
Keyword(s):  
Heat Flux ◽  
Heat Exchanger ◽  
Residence Time ◽  
Carbon Deposition ◽  
Operating Conditions ◽  
Coke Deposition ◽  
Jet Fuels ◽  
Fuel Temperature ◽  
Temperature Heat ◽  
Selection Of

The development of a viable strategy for limiting coke deposition involves combining synergistic approaches for suppressing deposit buildup and reducing its impact on performance. Candidate approaches, including selection of favorable operating conditions (viz., pressure, temperature, heat flux, residence time, and passage size) and coke-tolerant heat exchanger designs, were investigated to evaluate their effectiveness and provide a basis for combining them into a single design philosophy. These approaches were evaluated through testing of current jet fuels in single-tubes and segments of heat exchanger configurations at temperatures up to 1000°F, pressures up to 1200 psi and liquid hourly space velocities up to 40,000/h. A key result of this work is the ranking of the importance of heat exchanger operating conditions on carbon deposition, with fuel temperature and those parameters that control species diffusion having the most pronounced impact. Residence time and pressure are of lesser importance. Alternative coke-tolerant heat exchanger designs featuring interchannel communication were evaluated and ranked, with several of these concepts demonstrating improvement over continuous passages.

scholarly journals Deposit Formation and Mitigation in Aircraft Fuels

1999 ◽  
Author(s):  
Louis J. Spadaccini ◽  
David R. Sobel ◽  
He Huang
Keyword(s):  
Heat Flux ◽  
Heat Exchanger ◽  
Residence Time ◽  
Carbon Deposition ◽  
Operating Conditions ◽  
Coke Deposition ◽  
Jet Fuels ◽  
Fuel Temperature ◽  
Temperature Heat ◽  
Selection Of

The development of a viable strategy for limiting coke deposition involves combining synergistic approaches for suppressing deposit buildup and reducing its impact on performance. Candidate approaches, including selection of favorable operating conditions (viz., pressure, temperature, heat flux, residence time and passage size) and coke-tolerant heat exchanger designs, were investigated to evaluate their effectiveness and provide a basis for combining them into a single design philosophy. These approaches were evaluated through testing of current jet fuels in single-tubes and segments of heat exchanger configurations at temperatures up to 1000 F, pressures up to 1200 psi and liquid hourly space velocities up to 40,000/h. A key result of this work is the ranking of the importance of heat exchanger operating conditions on carbon deposition, with fuel temperature and those parameters that control species diffusion having the most pronounced impact. Residence time and pressure are of lesser importance. Alternative coke-tolerant heat exchanger designs featuring inter-channel communication were evaluated and ranked, with several of these concepts demonstrating improvement over continuous passages.

Transient Analysis of a Ceramic High Temperature Heat Exchanger and Chemical Decomposer

2007 ◽  
Author(s):  
Valery Ponyavin ◽  
Taha Mohamed ◽  
Mohamed Trabia ◽  
Yitung Chen ◽  
Anthony E. Hechanova
Keyword(s):  
Steady State ◽  
High Temperature ◽  
Heat Exchanger ◽  
Thermal Stresses ◽  
Three Dimensional ◽  
Failure Criteria ◽  
Operating Conditions ◽  
Finite Element Software ◽  
Micro Channels ◽  
Temperature Heat

Ceramics are suitable for use in high temperature applications as well as corrosive environment. These characteristics were the reason behind selection silicone carbide for a high temperature heat exchanger and chemical decomposer, which is a part of the Sulphur-Iodine (SI) thermo-chemical cycle. The heat exchanger is expected to operate in the range of 950°C. The proposed design is manufactured using fused ceramic layers that allow creation of micro-channels with dimensions below one millimeter. A proper design of the heat exchanges requires considering possibilities of failure due to stresses under both steady state and transient conditions. Temperature gradients within the heat exchanger ceramic components induce thermal stresses that dominate other stresses. A three-dimensional computational model is developed to investigate the fluid flow, heat transfer and stresses in the decomposer. Temperature distribution in the solid is imported to finite element software and used with pressure loads for stress analysis. The stress results are used to calculate probability of failure based on Weibull failure criteria. Earlier analysis showed that stress results at steady state operating conditions are satisfactory. The focus of this paper is to consider stresses that are induced during transient scenarios. In particular, the cases of startup and shutdown of the heat exchanger are considered. The paper presents an evaluation of the stresses in these two cases.

CFD Simulation of an Alfa-Stirling Engine to Study the Geometrical Parameters on the Engine Performance

2019 ◽  
Author(s):  
Ana C. Ferreira ◽  
Senhorinha F. C. F. Teixeira ◽  
Ricardo F. Oliveira ◽  
José C. Teixeira
Keyword(s):  
Heat Exchanger ◽  
Power Output ◽  
Cfd Simulation ◽  
Engine Performance ◽  
Stirling Engine ◽  
Operating Conditions ◽  
Design Parameters ◽  
Working Fluid ◽  
Cold Temperatures ◽  
Temperature Heat

Abstract An alpha-Stirling configuration was modelled using a Computational Fluid Dynamic (CFD), using ANSYS® software. A Stirling engine is an externally heated engine which has the advantage of working with several heat sources with high efficiencies. The working gas flows between compression and expansion spaces by alternate crossing of, a low-temperature heat exchanger (cooler), a regenerator and a high-temperature heat exchanger (heater). Two pistons positioned at a phase angle of 90 degrees were designed and the heater and cooler were placed on the top of the pistons. The motion of the boundary conditions with displacement was defined through a User Defined Function (UDF) routine, providing the motion for the expansion and compression piston, respectively. In order to define the temperature differential between the engine hot and the cold sources, the walls of the heater and cooler were defined as constant temperatures, whereas the remaining are adiabatic. The objective is to study the thermal behavior of the working fluid considering the piston motion between the hot and cold sources and investigate the effect of operating conditions on engine performance. The influence of regenerator matrix porosity, hot and cold temperatures on the engine performance was investigated through predicting the PV diagram of the engine. The CFD simulation of the thermal engine’s performance provided a Stirling engine with 760W of power output. It was verified that the Stirling engine can be optimized when the best design parameters combination are applied, mostly the regenerator porosity and cylinders volume, which variation directly affect the power output.

scholarly journals Extended Duration Thermal Stability Test of Improved Thermal Stability Jet Fuels

1995 ◽  
Author(s):  
Gordon L. Dieterle ◽  
Kenneth E. Binns
Keyword(s):  
Thermal Stability ◽  
Heat Exchanger ◽  
Jet Fuel ◽  
Stability Test ◽  
Bulk Temperature ◽  
Jet Fuels ◽  
Test Results ◽  
Fuel Temperature ◽  
Extended Duration ◽  
Thermal Stability Of

A single-pass, dual heat exchanger system called the Extended Duration Thermal Stability Test (EDTST) system was developed for evaluating jet fuel thermal stability. Various JP-8 fuels and thermal stability additives have been evaluated in the system. The test results indicate that additives can substantially improve the thermal stability of conventional jet fuels. Relationships of bulk and wetted wall temperatures on coking deposits that form in heated tubes have also been evaluated. To date, tests conducted with EDTST have verified that additives can improve the thermal stability of JP-8 fuels. The goal of operating at wetted wall temperatures of 260°C (500°F) has been achieved. The goal for bulk fuel temperatures of 218°C (425°F) with no deposits has not been achieved. Additional additive candidates are to be evaluated in the EDTST system to identify additives that meet both the wetted wall and bulk fuel temperature goals of this program. However, if the bulk temperature goal cannot be totally achieved, the JP-8 fuel specification will most probably be changed to take advantage of the wetted wall temperature improvement already demonstrated by a JP-8+100 additive candidate.

High Temperature Heat Exchangers (HTHX) for Nuclear Applications

2006 ◽  
Author(s):  
James C. Govern ◽  
Cila V. Herman ◽  
Dennis C. Nagle
Keyword(s):  
High Temperature ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Operating Conditions ◽  
Heat Exchanger Design ◽  
Performance Requirements ◽  
Starting Point ◽  
Temperature Heat ◽  
And Performance ◽  
Design Challenges

Many nuclear engineering applications, current and future, require heat exchangers operating at high temperatures. The operating conditions and performance requirements of these heat exchangers present special design challenges. This paper considers these challenges with respect to a simple heat exchanger design manufactured of a novel carbon material. Heat transfer and effectiveness calculations are performed for several parametric studies regarding heat exchanger parameters. These results are used to better understand the design challenges of high temperature heat exchangers as well as provide a starting point for future optimization work on more complex heat exchanger designs.

Quantitative Assessment of the Overall Heat Transfer Coefficient U

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Eph Sparrow ◽  
John Gorman ◽  
John Abraham
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Transfer Coefficient ◽  
Numerical Simulations ◽  
Operating Conditions ◽  
Overall Heat Transfer Coefficient

This investigation was performed in order to quantify the validity of the assumed constancy of the overall heat transfer coefficient U in heat exchanger design. The prototypical two-fluid heat exchanger, the double-pipe configuration, was selected for study. Heat transfer rates based on the U = constant model were compared with those from highly accurate numerical simulations for 60 different operating conditions. These conditions included: (a) parallel and counter flow, (b) turbulent flow in both the pipe and the annulus, (c) turbulent flow in the pipe and laminar flow in the annulus and the vice versa situation, (d) laminar flow in both the pipe and the annulus, and (e) different heat exchanger lengths. For increased generality, these categories were further broken down into matched and unmatched Reynolds numbers in the individual flow passages. The numerical simulations eschewed the unrealistic uniform-inlet-velocity-profile model by focusing on pressure-driven flows. The largest errors attributable to the U = constant model were encountered for laminar flow in both the pipe and the annulus and for laminar flow in one of these passages and turbulent flow in the other passage. This finding is relevant to microchannel flows and other low-speed flow scenarios. Errors as large as 50% occurred. The least impacted were cases in which the flow is turbulent in both the pipe and the annulus. The general level of the errors due to the U = constant model were on the order of 10% and less for those cases. This outcome is of great practical importance because heat-exchanger flows are more commonly turbulent than laminar. Another significant outcome of this investigation is the quantification of the axial variations of the temperature and heat flux along the wall separating the pipe and annulus flows. It is noteworthy that these distributions do not fit either the uniform wall temperature or uniform heat flux models.

Numerical and Analytical Analyses of a High Temperature Heat Exchanger

2006 ◽  
Author(s):  
Donato Aquaro ◽  
Franco Donatini ◽  
Maurizio Pieve
Keyword(s):  
High Temperature ◽  
Heat Exchanger ◽  
Analytical Model ◽  
Electric Utility ◽  
Combined Cycle ◽  
Operating Conditions ◽  
Working Fluid ◽  
Fluid Temperature ◽  
Test Loop ◽  
Temperature Heat

In this paper some analytical and numeric analyses of a high temperature heat exchanger are performed. This heat exchanger should be employed in a test loop of a EFCC (Externally Fired Combined Cycle), placed in a experimental facility owned by the Italian electric utility, ENEL. The heat exchanger is the crucial element in this cycle, as it undergoes temperatures above 1000°C and pressures of about 7 bars. The enthalpy of the combustion products of low cost fuels, such as coal, bottom tar, residuals from refineries, is used to heat a clean working fluid, in this case pressurized air. There are some outstanding benefits for the turbine, in regard to the manufacturing and maintenance costs, and also for its life. The heat transfer components are some bayonet tubes, assembled in 4 modules. A half of them is made of ceramic materials, the others of an advanced metallic material (ODS), due to the burdensome operating conditions. First of all, the heat exchanges are evaluated by means of a simplified analytical model. The radiant contribution also has been taken into account, due to the presence of non-transparent gases. Subsequently, the in-tube fluid temperature increase is calculated for all the heat exchanger modules, through an enthalpy balance and with some simplifying assumptions. Moreover, a comparison is made between the analytical solution and the results of a numerical model implemented in a CFD code. A good agreement is found, which indicates that the analytical model is reasonably valid. In fact, the whole heat exchanger temperature change is determined by means of the two methods with a difference of about 7% for both the streams. Finally, these results are to be compared with the experimental data which should be available in the near future, when the facility will begin working. Also, by this way, the developed calculation model would get a validation.

On-Line Fuel Deoxygenation for Coke Suppression

2002 ◽  
Author(s):  
Louis J. Spadaccini ◽  
He Huang
Keyword(s):  
Dissolved Oxygen ◽  
Membrane Filter ◽  
Coke Formation ◽  
Cooling Capacity ◽  
Coke Deposition ◽  
Jet Fuels ◽  
Fuel Temperature ◽  
Steady State Condition ◽  
Order Of Magnitude ◽  
On Line

Fuel deoxygenation is being developed as a means for suppressing autoxidative coke formation in aircraft fuel systems, thereby increasing the exploitable cooling capacity of the fuel, enabling major increases in engine operating temperature and cycle efficiency. Reduced maintenance is an added benefit. A prototype membrane filter module for on-line removal of dissolved oxygen, which would otherwise react to form coke precursors, was constructed and successfully demonstrated. The fuel flows over the membrane, while oxygen diffuses through it at a rate that is proportional to the difference in oxygen partial pressures across the surface. Tests were conducted over a range of fuel flow rates (residence times) and temperatures. The filter was operated with air-saturated jet fuel for several hours at a steady-state condition, verifying the capability to remove essentially all of the dissolved oxygen (to <1 ppm) and proving the viability of the concept. A convincing demonstration of coke suppression was performed when air-saturated (normal) and deoxygenated jet fuels were tested in a standard ASTM heated tube apparatus at wall temperatures as high as 850 F. With deoxygenated fuel, there was a dramatic reduction (more than an order of magnitude) in coke deposition relative to air-saturated Jet A, which will allow the maximum fuel temperature to be increased by more than 200 F, doubling the available heat sink. Moreover, deoxygenated Jet A was shown to perform as well as JP-7, the Air Force’s highest thermal stability fuel. An analytical model for oxygen permeation through the membrane was formulated, and used in conjunction with the test data to estimate the filter size required for a practical (i.e., low-volume/high-flowrate) deoxygenator.

Mechanical Properties and Cracking Behavior of High-Temperature Heat-Exchanger Materials

2005 ◽  
Author(s):  
Ajit K. Roy ◽  
Lalit Savalia ◽  
Narendra Kothapalli ◽  
Raghunandan Karamcheti
Keyword(s):  
High Temperature ◽  
Heat Exchanger ◽  
Elevated Temperatures ◽  
Hydrogen Generation ◽  
Acidic Solution ◽  
Structural Materials ◽  
Operating Conditions ◽  
Time To Failure ◽  
Cracking Behavior ◽  
Temperature Heat

The structural materials selected for high-temperature heat-exchanger applications are expected to withstand very severe operating conditions including elevated temperatures and aggressive chemical species during hydrogen generation using nuclear power. Three different cycles namely sulfur-iodine, calcium-bromine and high temperature electrolysis have been identified for hydrogen generation. Three different structural materials namely Alloy C-22, Alloy C-276 and Waspaloy have been tested to evaluate their high-temperature tensile properties and stress corrosion cracking (SCC) resistance in an acidic solution. The data indicate that all three alloys are capable of maintaining appreciably high tensile strength upto a temperature of 600°C. The results of SCC testing indicate that all three materials are highly resistant to cracking in an acidic solution retaining much of their ductility and time to failure in the tested environment. Fractographic evaluation by scanning electron microscopy revealed dimple microstructure indicating significant ductility in all three alloys.

Sign in / Sign up

Export Citation Format

Share Document