LEE- Malzeme Bilimi ve Mühendisliği Lisansüstü Programı

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http://hdl.handle.net/11527/19374

Gözat

Yazar "Erol, Ahmet Furkan" ile LEE- Malzeme Bilimi ve Mühendisliği Lisansüstü Programı'a göz atma
  • Öge
    Development of diffusion bonding processes for metal alloys to use production of pche
    (Graduate School, 2022-07-29) Erol, Ahmet Furkan ; Kazmanlı, M Kürşat ; 521171018 ; Material Science and Engineering
    The phase state of carbon dioxide above the critical pressure and critical temperature is called supercritical CO2 (sCO2). Since the density of sCO2 at the critical point is higher than the density of the liquids at the critical point, it allows the pumping power in the compressor to be greatly reduced, thus increasing the efficiency of thermalelectrical energy conversion. The sCO2 cycle has great potential in waste heat recovery systems, air-independent propulsion systems, due to its high power density, high efficiency, compact and modular structure. In order to use a heat exchanger in the sCO2 cycle, a compact heat exchanger resistant to high pressure and temperature should be developed. In order to develop a heat exchanger that will meet these requirements, the diffusion bonding process, which can be applied in complex geometries, provides strength as much as the base material, and has high corrosion resistance, comes to the fore. Since the heat exchangers that can meet the high pressure and high temperature requirements of sCO2 are printed circuit heat exchangers (PCHE) type heat exchangers, the diffusion coupling method developed within the scope of the thesis has been used in the production of printed circuit heat exchangers. Heat exchangers are equipment that allow the heat energies of two fluids to pass from a high temperature fluid to a low temperature fluid. In some areas of use, it is of great importance that the heat exchanger designs be compact and resistant to high pressure and high temperature. Printed circuit heat exchangers (Printed Circuit Heax Exchanger-PCHE) come to the fore because they are one of the types of heat exchangers that meet these conditions. The compactness, high pressure and temperature resistance of this type of heat exchanger is directly related to the production method of the heat exchanger. Diffusion bonding has been used in the production of micro-channel heat exchanger, which is the subject of this thesis, because of the precision welding process requirement. In addition, the strength of the weld in the region of diffusion bonding is in some cases as much as the base material. In printed circuit heat exchangers, micro-channel plates are placed on top of each other to ensure heat transfer between the fluids with counterflow in the channel. When two plates are welded together in order to withstand high pressure and temperature, the strength of the weld area must be either the same or close to the base material. In addition to the fact that traditional welding methods (melt welding, solder, etc.) cannot provide as much strength as diffusion bonding welding, the material pairs that can be used in traditional welding methods are limited. Not every material can be welded with each other. Material selection possibilities are wider in diffusion bonding method. The diffusion bonding process, which plays a critical role in the production of heat exchangers mainly due to such advantages, has been developed within the scope of this thesis. The basis of the diffusion bonding process is explained by the diffusion mechanism. Concentration and concentration changes, which are the basic parameters in the diffusion process, are revealed by Fick's laws. Diffusion takes place on an atomic scale between the materials to be used in diffusion bonding. The diffusion coupling mechanism has been studied in this context. The parameters affecting the diffusion bonding are: temperature, pressure, time, surface quality and atmosphere where diffusion bonding takes place. The parameters optimized in the thesis work are temperature, pressure and time. Surface quality and atmosphere were kept constant in each sample. 316L stainless steel material was chosen for use in heat exchanger design due to reasons such as resistance to high temperature, resistance to high pressure, that is, high strength, cheap and easy availability, and suitability for the diffusion bonding process. For this reason, 316L stainless steel is used in the diffusion bonding process. The properties of 316L stainless steel material are explained in the thesis. In addition to diffusion bonding of 316L-316L material pair, samples using nickel as intermediate material were also examined. The test matrices of the relevant samples were prepared and sample optimization was made. Temperature, pressure and time were used as optimization parameters. 316L-316L and 316L-Ni-316L samples were also tested with destructive and non-destructive examinations using these optimization parameters, and the test results were also compared. Tensile test and microhardness test were performed as tests of samples prepared within the scope of destructive testing. Optical microstructure examinations, SEM and EDS examinations were also carried out within the scope of non-destructive examination. The prepared samples were examined and evaluated. As a result of the literature search, all samples were prepared under 8.5 MPa pressure and in Argon atmosphere. In the study, first of all, temperature optimization was made. The samples prepared at 950°C and 1050°C were fixed for 60 minutes and compared. As a result of the temperature optimization, it was observed that the samples prepared at 950°C and 60 minutes failed the tensile tests. In the second optimization phase, the temperature was kept constant at 1050°C and the optimization was made for 120 and 180 minutes and the results were evaluated. It has been seen in tensile tests, 316L-Ni316L diffusion bonding sample produced at 1050°C for 180 minutes, under 8.5 MPa pressure and argon atmosphere gave the best results. In the tensile test, the maximum tensile stress was measured as 407 MPa. As a result of the development of the diffusion bonding process, a printed circuit heat exchanger (PCHE) was produced by using the sample parameters that gave the best results as a result of the tensile tests. The heat exchanger was tested in a test bench installed at 80 bar, 453°C. The parameters have been measured. It has been seen that it meets the technical requirements in terms of performance. In addition, the hydrostatic test of the heat exchanger was carried out at 200 bar at room temperature using water as a fluid, and the leak test was carried out under 10 bar pressure at room temperature by blowing air into the heat exchanger and foaming the outside with a special solution. The heat exchanger has successfully passed these tests as well. Thus, the diffusion bonding process developed for the designed printed circuit heat exchanger (PCHE) was successfully carried out.