In recent years the fan heater is used for industry and residence, it is necessary for fan heater to become smaller, lighter, and more silent. However there are problems that the fan heater size is very large, and the noise is very high due to air pressure loss of heat exchangers. Therefore we have been developing the centrifugal type fan with function of heat exchanger. The features of this new type fan heater are that the fan heater size is very small and silent because the fan and the heat exchanger are installed in one body. This paper described the effects of number of fan blades on heat transfer characteristics of the centrifugal fan with the function of heat exchanger. The heat transfer characteristics of the centrifugal fan having different number of blades(number of blades：12, 20, 28)were clarified by measuring heat flux and blade's surface temperature. In results, the heat transfer coefficient increased with number of blades.
For centrifugal compressors used in automotive turbochargers, it becomes very important to improve the compressor efficiency and to suppress the compressor surge because of a demand of high boosting at lower engine speed, i.e., smaller mass flow rate. In order to clarify the cause of compressor surge, two different compressors which have different surge characteristics were investigated by both experimental and numerical procedures. In the experimental approach, compressor performance characteristics beyond usual surge line were obtained by setting an orifice at the compressor exit, and wall static pressures were measured at impeller leading edge, trailing edge and diffuser exit respectively. As the numerical approach, compressor full-domain CFD analyses which include impeller and scroll were also conducted for above two compressors. Experimental and CFD results show circumferential pressure distributions in a diffuser and a scroll induce a positive pressure gradient locally and these may increase the compressor instability near the surge for the compressor which has larger surge mass flow rate.
Numerical simulations were conducted by using LES(Large Eddy Simulation) with DSM(Dynamic Smagorinsky Model) about the axial flow small fan for cooling electronic devices. In this study, the tested fan has two kinds of obstacles located in the suction side. One obstacle is infinite plate(Infinite model)，the other obstacle is half of infinite plate which covers lower half region of fan(Half model). Distance from the fan to the obstacles is 20 mm. The flow pattern around the
fan blades and RMS of pressure fluctuation on the fan blade surfaces were compared under the conditions of with and without obstacle. The flow direction into fan was axial under the condition of without obstacle. On the other hand the flow direction into fan was radial under the condition of with obstacle. This radial inflow caused the expansion of negative pressure region due to the separation from the top of casing, which enlarged tip vortex region and increased pressure fluctuation on suction side blade surface. Moreover the radial inflow caused the reduction of axial flow velocity at the blade tip, which increased pressure fluctuation on pressure side blade surface due to the interference between tip vortex and blade surface. The radial inflow and the axial inflow were mixed in the half model. As the result, fan static pressure, fan noise and pressure fluctuation have interim characteristic of no obstacle model and infinite plate model.
Fluid machineries for fluid food have been used in wide variety of field i.e. transportation, filling, and improvement of quality of fluid food. Although, flow conditions of these are quite complicated because fluid food is different from water. Therefore, design method based on the internal flow conditions is not conducted. In this research, the centrifugal pump having small number of blade was used to decrease shear loss and keep wide flow passage. In previous studies, it was found that unsteady internal flow condition occurred in a test pump, but those flow phenomena were not clarified. In order to investigate the unsteady internal flow condition in detail, the numerical analysis using low viscous fluid was conducted. In this paper, the unsteady internal flow conditions of centrifugal pump using low viscous fluid were clarified by experimental and unsteady numerical analysis results. In addition to that, the design method based on the internal flow was considered.
The authors experimentally studied the characteristics of the flow around/inside a cross-flow fan, namely, a cross-flow impeller. In order to eliminate complicated influence of many casing factors, the impeller rotates in open space without any casings. As a result, at the singular aspect ratio L/D2=0.6, at which the outflow rate Q0 out of the impeller and the maximum vorticity ωmax attain the maximum values, the authors reveal minute fluctuating pressures on impeller's end wall. In some pressure measurements, the eccentric vortex inside the impeller is prevented to revolute by the insertion of a tongue, in order to consider the spatial structure of flow more precisely. The authors have confirmed that the influence of the tongue insertion is negligible. And, the authors confirmed such Reynolds-number effect as a time-mean pressure coefficient Cpmean decreases with increasing Reynolds number for Re ≤ 4.0×103. Based on phase-averaging technique by the synchronised measurement of a impeller-rotation-counter signal, the pressure distribution inside the impeller shows that the minimum value is at θ =300deg.
In order to clarify the relation between the aerodynamic noise and the flow regime around the impeller of a propeller fan operated in maximum efficiency point and off-design point, the characteristics of the fan with the impeller of the different solidity were analyzed experimentally. In the case of high solidity fan, the narrowband noise due to the wake vortex was generated at the off-design point since the relative velocity in the wake became high. From results of the analysis, it was indicated that the broadband noise of the low solidity fan at the maximum efficiency point is related for the velocity fluctuation not only due to the wake vortex but the unstable tip vortex.
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