Vol.3 No.2 2010

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Research paper : Establishment of compact processes (A. Suzuki et al.)−154−Synthesiology - English edition Vol.3 No.2 (2010) the low-temperature fluid that flows in from the bottom part is mixed with the supercritical water that flows from the left, a temperature transition zone is formed at the bottom of the flow channel, and a temperature gradient forms within the flow channel. On the other hand, in the LDV, the homogeneous temperature fluid is formed in the micro flow channel with inside diameter of 300 m and length of 1.3 mm, and quick fluid mixing is achieved. Figure 4 shows the plot of the maximum and minimum temperatures in the vertical cross sections from the center of the mixer to the downstream direction of the mixed fluid. It can be seen from the figure that the temperature difference is shown at the mixer exit in the STD (9.2 mm from the mixing point), while the temperature is homogenized rapidly at the mixer exit that is only 1.3 mm from the mixing point in the LDV. Estimating the average heating rate in the flow channel, the STD is 31,000 ºC/s while LDV is 270,000 ºC/s, and there is a 9 times difference. The difference in the heating rate, or the mixing rate, indicates that it is possible to precisely control the delicate synthesis reaction in which side reactions may occur.Figure 5 shows the photograph of the micro swirl mixer that we developed and the result of the CFD simulations[10]. The raw material at ordinary temperature is supplied from the left, and supercritical water divided into two is supplied at 60° angle from the central axis. Further, the supercritical water is connected eccentrically and mutually from the center of the mixer, and the swirl flow can be generated by the divided supercritical water at the center of the mixer. The raw material is given the inertial force in the circumferential direction as well as the axial direction by the swirl flow, and it is considered to enhance the mixing performance. In the T-shaped mixer, a vortex is formed at the bend as the fluid makes a right angle turn. Since this vortex region may cause accumulation, the increase of unexpected retention time is a concern. On the other hand, in the micro swirl mixer, the accumulation region does not form in the center of the mixer since the mixed fluid is rotating and flowing out at all times. The central collision mixer shown in Fig. 6 is composed of the raw material supply channel with a needle that moves up and down in the upper part (the raw material is introduced through the thin film channel along the exterior surface of the needle) and the fluid mixing chamber with several supercritical water streams in the bottom part (central collision area), and is capable of realizing quick mixing and heating[11]. The raw material is not affected by the heat transfer from the supercritical water (due to the cooling effects by the cooling medium in the inner tube of the needle, the radiation effect by the air cooling fin, and the heat transfer limitations by a small metal seal ring), and is introduced into Fig. 3 Result of the CFD simulation of fluid mixing using the T-shaped mixer (temperature contour diagram)In the STD TEE, the temperature was not even at the exit (length 9.2 mm from mixing point) of the mixer, while in the LDV TEE, mixing was almost entirely even at the exit (length 1.3 mm from mixing point) of the micro flow channel.LDV TEESTD TEESupercritical waterSupercritical waterRaw materialRaw material(Standard T-shaped mixer)(Low Dead Volume T-shaped mixer)Axial distance from mixing point (mm)Temperature (ºC)0024681012100200300400500Local min. temp. (STD TEE)Local max. temp. (STD TEE)Local min. temp. (LDV TEE)Local max. temp. (LDV TEE)Supercritical water 33 g/min, raw material 12 g/minSTD TEE (Standard T-shaped mixer)LDV TEE (Low Dead Volume T-shaped mixer)Fig. 4 Temperature profile of fluid after mixingThe temperature did not converge in the STD TEE, while it rapidly evened out in the LDV TEE.Raw materialMassless particles are flown from the raw materialRaw material1/2 supercritical water1/2 supercritical water1/2 supercritical water1/2 supercritical waterFig. 5 Photograph of the micro swirl mixer and the result of the CFD simulation (flow line of raw material)The supercritical water is mixed with the raw material by forming a swirl flow by dividing the supercritical water. The structure prevents the generation of vortex of the T-shaped mixing.L 0.8mm 1mm 1/4 1/4 NeedleCooling waterCooling waterRaw material1/4 Supercriticalwater1/4 Supercritical water1/4 Supercritical water1/4 Supercritical waterNeedleCooling waterCooling waterRaw materialNeedle position1/4 Supercriticalwater1/4 SupercriticalwaterInside diameter0.8 mm at exit Inside diameter 1 mm LFig. 6 Central collision mixerThe supercritical water is divided into four, and the raw material is introduced from the top into the central collision section. The needle is inserted from the top to allow adjustment of the mixing state.

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