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ABSTRACT
Regenerative cooling is being used to meet the high cooling requirements of advanced hypersonic flight vehicles using the fuel at supercritical pressures as the coolant. The heat transfer and thermal cracking characteristics vary with the pressure, mass flow rate and heat flux. This work presents an experimental investigation of the thermal cracking and the heat transfer characteristics of supercritical pressure hydrocarbon fuels and their interactions. A proportional production distribution chemical model was developed for the thermal cracking with the pre-exponential factor and activation energy to describe the reactions. Numerical results show good agreement with experimental data at low conversions (<25%). The heat transfer for supercritical pressure fuels with thermal cracking is very different from that without thermal cracking. Thermal cracking near the wall enhances the heat transfer by adding an extra heat sink, while coking and a bubble layer add thermal resistances to reduce the convective heat transfer.
Nomenclature
| A | = | pre-exponential factor [1/s] |
| Bo* | = | buoyancy number |
| CFD | = | computational fluid dynamics |
| cp | = | specific heat capacity [J/K] |
| d | = | tube diameter [m] |
| Ea | = | activation energy [kJ/mol] |
| G | = | mass flow rate [kg/h] |
| GCMS | = | gas chromatography–mass spectrometry |
| hf | = | fluid bulk specific enthalpy [J/kg] |
| hx | = | local heat transfer coefficient [W/(m2·K)] |
| i | = | species |
| I | = | current [A] |
| k | = | reaction rate [1/s] |
| = | mass flow rate [kg/s] | |
| Nu | = | Nusselt number |
| p | = | pressure [MPa] |
| PPD | = | proportional product distribution |
| qw | = | heat flux [W/m2] |
| qv | = | volumetric heat source [W/m3] |
| Q | = | heat loss [W] |
| R | = | universal gas constant, 8.314 × 10−3 [kJ/(K·mol)] |
| Rx | = | resistance [Ω] |
| Re | = | Reynolds number |
| T | = | temperature [K or °C] |
| x | = | axial coordinate [m] |
| xi | = | mass fraction of product i in each phase [%] |
| Xi | = | mass fraction of product i [%] |
Greek symbols
| ϵ | = | conversion [%] |
| λ | = | thermal conductivity [W/(m·K)] |
| μ | = | dynamic viscosity [Pa·s] |
| ρ | = | resistivity [Ω·m] |
| Ψg | = | gas yield rate [%] |
Subscripts
| b | = | bulk value |
| c | = | supercritical |
| f | = | fluid |
| i | = | inner |
| in | = | inlet |
| o | = | outer |
| out | = | outlet |
| pc | = | pseudo critical |
| w | = | wall |
Acknowledgements
This project was supported by the National Natural Science Foundation of China (No. 51536004) and the Science Fund for Creative Research Groups of NSFC (No. 51621062). We thank Prof. David Christopher for editing the English.
Additional information
Funding
Notes on contributors
Peixue Jiang
Pei-Xue Jiang is a professor in the Department of Thermal Engineering, Tsinghua University, China. He received his Ph.D. in the Department of Thermo-Power Engineering of Moscow Power Engineering Institute in 1991. He then joined the faculty of Tsinghua University and took the professor post in 1997. His main research interests include convection heat transfer in porous media and enhanced heat transfer, convection heat transfer at supercritical pressures, transpiration cooling and film cooling, thermal transport in nanoscale structures, trans-critical CO2 air conditioning systems, and heat pumps. He has published more than 100 papers in international journals and conferences.
Junjie Yan
Junjie Yan is a Ph.D. student in the Department of Thermal Engineering, Tsinghua University, under the supervision of Prof. Peixue Jiang. He received the degree of Bachelor of Engineering for Energy, Power System and Automation from Tsinghua University in 2013. He is currently working on heat transfer of supercritical pressure fuels.
Shuai Yan
Shuai Yan is a M.S. student in the Department of Thermal Engineering, Tsinghua University, under the supervision of Prof. Yinhai Zhu. He received the degree of Bachelor of Engineering for Energy, Power System and Automation from Tsinghua University in 2015. He is currently working on heat transfer and coke deposition of supercritical pressure hydrocarbon fuels.
Zelong Lu
Zelong Lu is a Ph.D. student in the Department of Thermal Engineering, Tsinghua University, under the supervision of Prof. Peixue Jiang. He received the degree of Bachelor of Engineering for Energy, Power System and Automation from Tsinghua University in 2013. He is currently working on heat transfer of supercritical pressure fuels under rotation conditions.
Yinhai Zhu
Yinhai Zhu is an associate professor in the Department of Thermal Engineering, Tsinghua University, China. He received his Ph.D. in engineering thermophysics from Xi'an Jiaotong University in 2009. His main research interests are ejectors and refrigeration systems, and thermal protection techniques.