**4. Conclusion**

162 Heat Exchangers – Basics Design Applications

deposit for such heating conditions. Figure 15 indicate the graphite coating can inhibit

Fig. 18. Effect of TIT on chamber pressure for Expander Cycled Rocket Engine.

Fig. 19. Effect of TIT on Vacuum Isp for Expander Cycled Rocket Engine.

coking to thermal decomposition in those temperature ranges.

In the present chapter, the experimental and numerical studies on fundamental chemical phenomena of CH4 and LNG pyrolysis are conducted. CH4 pyrolysis is promoted by the catalytic effects of chamber material and the addition of C3H8. CH4 pyrolysis can begin at temperature of 800 to 900 0C, however, the catalytic effect of combustion chamber materials can reduce the temperature which CH4 pyrolysis begins by 200 0C. In addition, the addition of C3H8 can promote the coking on the test pieces, especially it is apparent if the volumetric fraction of C3H8 is more than 3.0 %. The numerical simulation can predict the experimental results of CH4 and C3H8 pyrolysis.

Based on those experimental results, the effective coking inhibition method by graphite coating for LNG rocket engine can be developed and confine pyrolysis temperature up to 700 0C. INCONEL 600 with the graphite coating did not have their catalytic effect on LNG pyrolysis absolutely.

If this method can be applied to expander cycle rocket engine, the improvement of vacuum Isp can be achieved from 338.6 to 342.5 sec when the nozzle expansion ratio is 40. However, it is expected that the size of combustion chamber may be dramatically reduced. In the next phase, more detailed investigations for heat transfer in regenerative cooling passage and

**7** 

*Poland* 

Agnieszka A. Chudzik

**Numerical Analysis of the Structural Stability of** 

A demand for improved computational methods of complex systems used in modern structures has been followed by development of theory and analysis in the field of stability of shell structures. Nonlinear problems, in which, for instance, shape imperfections, complex loads, nonelastic properties of the material used in the structure are accounted for, are of deep interest. Thanks to an advance in computer technology and numerical methods, a possibility to conduct more precise analysis which corresponds better to actual structures of mathematical models arises. In the linear and nonlinear analysis of structures, stability occupies a special place. To test the load carrying capacity of the structure, the phenomena that occur during a stability loss and after it should be recognized. An application of thinwall elements results in advantages such as light weight, a possibility to carry high loads, thermo-insulating properties, etc. Here, analysis and recognition of transfer phases since an appearance of plastic strains up to a complete reduction of the load carrying capacity is essential. A demand for such complex analysis that includes stability and leads to more actual evaluation of the structure safety has been observed in many disciplines of technology, e.g., in designing of ships, airplanes, pressure chemical apparatus, in modern construction industry and in power and heat generation. Heat exchangers that are widely applied in, e.g., power and heat generation, operate under very high temperatures. The principal elements of these devices are perforated walls – perforated plates in which heating cartridge pipes are fixed. The number of pipes, i.e., of holes in the plate, is very high and these holes are separated from one another by a thin bridge. The issue of differences in temperatures in individual parts of the heat exchanger and in various media that flow in the device is a source of considerable design difficulties. Heat exchangers usually operate under pressure or in vacuum. Independently of the fact that not only the knowledge of material strength properties is needed for computations of heat exchangers, there are legal regulations that standardize the calculations of the devices operating under pressure. They define the way the basic parts are calculated, providing thus hints concerning the structure of the devices under control. A decrease in the safety factor due to stability, i.e., a rapprochement to the real state of stress up to the critical one, is the way the modern engineering structures can be characterized by. Therefore, the calculations of stability, stiffness of thin-walled structural elements are becoming more and more important nowadays in designing and performance of many devices. A heat exchange is a common phenomenon in technology and nature – it occurs when there are differences in

**1. Introduction** 

**Heat Exchangers – The FEM Approach** 

*Technical University of Lodz/Department of Machine Dynamics* 

turbopump must be done for practical application of the graphite coating on the expander cycle LNG rocket engine.
