Ceramic High Temperature Heat Exchanger Research Articles

Conceptual design and performance evaluation of an innovative high temperature ceramic heat exchanger

The development of an innovative and highly efficient heat exchanger (HE) solution for gas-gas heat recovery is one of the major objectives of the HYDROSOL-beyond project which aims at enhancing the process efficiency for producing H2 from water dissociation with concentrated sunlight. Because of the very high temperature level of the process (up to 1’400°C), an innovative ceramic HE was proposed with an integrated lattice structure, as secondary surface, to maximize the heat transfer. To assist the design of the HE, a multiscale approach was adopted: a 1D model based on global correlations was developed and a 3D computational fluid dynamics model of the secondary surfaces were generated. The former was applied to assess the performance of the entire HE; while, the latter was exploited to study in detail the thermo-fluid dynamics behavior of a HE core element and to provide the global correlations to be integrated into the 1D model. The effect of the number of lattice layers, located into each channel, on the HE effectiveness was evaluated showing that reducing the height of the secondary structure allows to improve the HE effectiveness from 72% up to 94%.

HIGH TEMPERATURE COMPACT CERAMIC REGENERATIVE HEAT EXCHANGER

The subject of the research is the high-temperature compact ceramic heat exchanger of a regenerative type with a honeycomb structure. In relation to high-temperature processes of basalt smelting and glass melting, the possibility of its application in a system of high-temperature air combustion is considered. It is noted that heating of the air pursues both energy goal – reduction of natural gas consumption, and technological goal – increasing the amount of free oxygen in the basalt processing zone. The methods of determining the transient temperature field in the wall of the solid heat-storing material of the regenerator and the operating time of the heat exchanger from the condition of ensuring the permissible surface temperature of the heat regenerator are given. It is established that for the range of the Fourier number Fo≤2.5, it is possible not to take into account the temperature distribution in the wall of the solid heat-storing material of the regenerator and to operate with its average temperature. Features of compact ceramic regenerative heat exchangers are given – heat exchanger efficiency, heat recovery coefficient, number of transfer units, power – as applied to the conditions of the heat engineering process. The heat exchanger efficiency is confirmed. The operating time of the heat exchanger and its effect on the surface temperature of the solid heat-storing material are determined. It is shown that in relation to the conditions of the basalt melting and glass melting processes, the material of the regenerative heat exchanger – mullite – is not an optimal solution. Only for one of the considered variants of the technological process, the surface temperature of the regenerative heat exchanger was lower than the permissible temperature of prolonged use of mullite. In other cases, the resulting temperature of the regenerator exceeded the permissible value of long-term use. It is advisable to use a material with a permissible temperature of application of 1525 °C and above as of the solid heat-storing material of the regenerator. Testing of the results of the research was carried out on pilot industrial samples of bath melting furnaces equipped with HiTAC (high-temperature air combustion system).

Numerical analysis of steady state and transient analysis of high temperature ceramic plate-fin heat exchanger

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 1.5MPa. 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 10.08MPa, 9.90MPa and 11.43MPa 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.

Hydraulic and thermal performances of a novel configuration of high temperature ceramic plate-fin heat exchanger

A novel fin configuration for high temperature ceramic plate-fin heat exchanger (PFHE) was developed using the three-dimensional computational fluid dynamics (CFD) FLUENT code. Numerical analysis was carried out for different types of fins and their results were compared with the selected design. The working fluids used in the model were sulfur trioxide, sulfur dioxide, oxygen and water vapor. Fluid flow, heat transfer, pressure drop and properties like Nusselt number, friction factor and j-factor were studied for various fin configurations. The rip saw fin design (case 9) with thickness of 0.05mm gives the maximum heat transfer performance with less pressure drop and friction factor. The numerical result was compared with the analytical result for rectangular fins and they were found to be in reasonable agreement. In addition to it, the results from the selected ripsaw design were compared with the result from the model with no fins (case 1). It was found that thermal enhancement factor of 2.3211 and average Nusselt number of 4.215 was obtained for the selected design. The results of the rip saw fin design were found in good agreement with the analytical results of a rectangular fin. Further effects of Reynolds number on pressure drop and Nusselt number were studied.

Design of a Compact Ceramic High-Temperature Heat Exchanger and Chemical Decomposer for Hydrogen Production

This article describes a compact silicon carbide ceramic, high-temperature heat exchanger for hydrogen production in the sulfur iodine thermochemical cycle, and in particular, to be used as the sulfuric acid decomposer. In this cycle, hot helium from a nuclear reactor is used to heat the SI (sulfuric acid) feed components (H2O, H2SO4, SO3) to obtain appropriate conditions for the SI decomposition reaction. The inner walls of the SI decomposer channels are coated with platinum to catalytically decompose sulfur trioxide into sulfur dioxide and oxygen. Hydrodynamic, thermal, and the sulfur trioxide decomposition reaction were coupled for numerical modeling. Thermal results of this analysis are exported to perform a probabilistic mechanical failure analysis. This article presents the approach used in modeling the chemical decomposition of sulfur trioxide. Stress analysis of the design is also presented. The second part of the article shows the results of parametric study of the baseline design (linear channels). Several alternate designs of the chemical decomposer channels are also explored. The current study summarizes the results of the parametric calculations whose objective is to maximize the sulfur trioxide decomposition by using various channel geometries within the decomposer. Based on these results, a discussion of the possibilities for improving the productivity of the design is also given.

Calculation of Fluid Flow Distribution Inside a Compact Ceramic High Temperature Heat Exchanger and Chemical Decomposer

Numerical analysis of flow distribution inside a compact ceramic high temperature heat exchanger and chemical decomposer (thereafter, heat exchanger), which will be used for hydrogen production, wherein the sulfur iodine thermochemical cycle is performed. To validate the numerical model, experimental investigation of the heat exchanger is accomplished. The study of the flow distribution in the base line design heat exchanger shows that the design has large-flow maldistribution and the reverse flow may occur at poor inlet and outlet manifold configurations. To enhance uniformity of the flow rate distribution among the heat exchanger internal channels, several improved designs of the heat exchanger manifolds and supply channels are proposed. The proposed designs have a sufficiently uniform flow rate distribution among the internal channels, with an appropriate pressure drop.

Parametric study of sulfuric acid decomposer for hydrogen production

It is proposed to use a ceramic high-temperature heat exchanger as a sulfuric acid decomposer for hydrogen production within the sulfur–iodine thermo-chemical cycle portion of the hydrogen production process. In this cycle, hot helium from a nuclear reactor is used to heat the SI (sulfuric acid) feed components (H 2O, H 2SO 4, SO 3) to obtain appropriate conditions for the SI decomposition reaction. The inner walls of the SI decomposition channels of the decomposer are coated by a catalyst to decompose sulfur trioxide into sulfur dioxide and oxygen. The heat exchanger and decomposer are made of silicon carbide (SiC). A three-dimensional computational model is developed to investigate fluid flow, heat transfer, chemical reaction, and stress analysis within the decomposer. Fluid/thermal/chemical analysis of the decomposer is conducted using FLUENT software. Thermal results of this analysis are exported to ANSYS software to perform a probabilistic failure analysis. Effects of using various channel geometries of the decomposer are investigated.

An Assessment of the Performance of Closed Cycles With and Without Heat Rejection at Cryogenic Temperatures

This paper presents optimized cycle performance that can be obtained with systems including a closed cycle gas turbine (CCGT). The influence of maximum temperature, minimum temperature, and recuperator effectiveness on cycle performance is illustrated, Several power-plant arrangements are analyzed and compared based on thermodynamic performance (thermal efficiency and specific work); enabling technologies (available at present); and developing technologies (available in the near term or future). The work includes the effects of utilization of high temperature ceramic heat exchangers and of coupling of CCGT systems with plants vaporizing liquid hydrogen (LH2) or liquefied natural gas (LNG). Given the versatility of energy addition and rejection sources that can be utilized in closed gas-cycle systems, the thermodynamic performance of power plants shown in this paper indicate the remarkable capabilities and possibilities for closed gas-cycle systems.

Characterization of metallic and ceramic high-temperature materials for energy systems by means of atomic spectroscopy

In nuclear and non-nuclear energy systems high-temperature alloys and structural ceramics are used. The development and characterization of high temperature materials for use in advanced high temperature gas-cooled reactors, in metallic and ceramic high temperature heat exchanger components and in Tokamak fusion reactor designs are reported. In these areas, the development of materials, in general, and materials characterization using modern physico-chemical methods, in particular, are crucial. The investigations for the high temperature reaction (HTR) are concentrated on the optimization and the verification of the long time behaviour of the materials. In the field of high resistant structural materials, the oxidation and corrosion mechanisms and the stability of protective scales and coatings are of high importance. The fusion reactor materials work is concerned with fundamental development stages and with plasma-wall interactions. It is for the characterization of materials and for investigation of reaction mechanisms that modern analytical techniques are required. In addition to the use and specific optimization of modern physicochemical techniques for bulk and surface analysis, especially spectroscopic methods, the application potential for the methods is outlined and the available results are discussed.

High-Temperature Ceramic Heat Exchanger Element for a Solar Thermal Receiver

A study has been completed on the development of a high-temperature ceramic heat exchanger element to be integrated into a solar receiver producing heated air. A number of conceptual designs were developed for heat exchanger elements of differing configuration. These were evaluated with respect to thermal performance, pressure drop, structural integrity, and fabricability. The final design selection identified a finned ceramic shell as the most favorable concept. The ceramic shell is surrounded by a larger metallic shell. The flanges of the two shells are sealed to provide a leak-tight pressure vessel. The ceramic shell is fabricated by an innovative combination of slip casting the receiver walls and precision casting the heat transfer finned plates. The fins are bonded to the shell during firing. Fabrication of a one-half scale demonstrator ceramic receiver has been completed.