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In this study numerical analysis was carried out for four different types of fins namely rectangular, triangular, inverted bolt fins and ripsaw fins and three different types of arrangements namely straight, staggered and top and bottom arrangement. The obtained results were compared with each other and the design with the highest decomposition percentage of sulfur trioxide was selected. The working fluids used in the model were sulfur trioxide, sulfur dioxide, oxygen and water vapor. The operating pressure was 1.5 MPa and the operating temperature ranges from 973 K to 1223 K. From the results it was found that the ripsaw fin design with thickness of 0.05 mm gives the highest decomposition percentage of sulfur trioxide. The inverted bolt fins gives a good heat transfer rate but due to the fin arrangement and the flow disturbances caused by the arrangement the pressure drop was the highest compared to the other fins. The pressure drop and heat transfer obtained for the rectangular and triangular fins were similar to each other. The obtained decomposition percentage of sulfur trioxide for straight, staggered and top and bottom arrangement were 17.60%, 16.74% and 20.55%. The obtained decomposition percentage increased from 16.74% to 85.15% when the channel length of the heat exchanger was increased ten times. [ABSTRACT FROM AUTHOR]

In this study three-dimensional model of ceramic plate-fin high temperature heat exchanger with different fin designs and arrangements is analyzed numerically using ANSYS FLUENT and ANSYS structural module. The ability of ceramics to withstand high temperature and corrosion makes silicon carbide (SiC) suitable candidate material to be used in high temperature heat exchanger. The operating temperature of heat exchanger is 950 °C and the operating pressure is 1.5 MPa. The working fluids are helium, sulfur trioxide, sulfur dioxide, oxygen and the water vapor. Fluid flow and heat transfer analysis are carried out for steady and transient state in FLUENT. The obtained thermal and pressure load for the steady and transient state from ANSYS FLUENT are imported to ANSYS structural module to obtain the principal stress and the factor of safety. Different arrangements of rectangular fins, triangular fins, inverted bolt fins and ripsaw fins are studied. From the results it is found that the minimum stress and the maximum safety factor are obtained for inverted bolt fins. The triangular fins have the maximum principal stress and minimum factor of safety. However, the fluid flow and heat transfer analysis show inverted bolt fins and triangular fins produce higher pressure drop and friction factor. The steady state maximum principal stress is 10.08 MPa, 9.90 MPa and 11.43 MPa for straight, staggered and top and bottom ripsaw fin arrangement. The corresponding safety factors are 21.80, 21.95 and 19.01, respectively. The ripsaw fin design is chosen to be the best design since it gives less stress, more safety factor, less pressure drop, friction factor and reasonable heat transfer rate. From the results it is also found that thermal stress is more significant than the mechanical stress. [ABSTRACT FROM AUTHOR]

Highlights: [•] Rip saw fin design (case 9) was considered to be the best because it has thin fins and has higher heat transfer coefficient. [•] Due to higher surface area density the heat transfer coefficient and Nusselt number obtained for case 7 is lower than other fin types. [•] The values of the average Nusselt number obtained for all the cases vary in small order of magnitude. [•] The maximum Nusselt number was obtained for the ripsaw fin design (case 9). [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the effects of inlet temperature and rib height on the fluid flow and heat transfer performances of the ribbed channel inside the high temperature heat exchanger are presented. The inlet temperature varies from 850K to 1250K and the ratio of rib height to channel height varies from 0.083 to 0.333. The results indicate that increasing the rib height can enhance the flow disturbance and hence improve the heat transfer performance. The inlet temperature has little effect on the basic structure of fluid flow and the heat transfer is enhanced due to the increased velocity. Compared to increasing the rib height, more heat can be transferred by increasing the inlet temperature with less pressure drop. The high pressure drop is more serious as the inlet temperature increases. It is proposed to use the compact heat transfer structure at the low temperature region and replace it by loose heat transfer structure at the high temperature region. It also demonstrates that the Nusselt number and friction factor are unsuitable to compare the heat transfer and pressure drop performances among different temperature conditions because the physical properties of fluid change with temperature variation. [Copyright &y& Elsevier]