Osamu Kawanami

Abstract Objectives Various designs are proposed for pulmonary expanded polytetrafluoroethylene (ePTFE) conduits and have been applied in clinical practice. However, experimental data to support them are limited. We conducted an in vitro experiment using a circulatory simulator to evaluate their haemodynamic performance and hydrodynamic characteristics. Methods Three root models with a 24-mm basal ring (A, straight; B, with small sinuses; C, with large sinuses) were 3D-printed. Cusps were uniformly cut out from a 0.1-mm-thick ePTFE membrane and sewn to the inter wall of the models. Model A had a single suture on the free margins near the commissures. Each model was tested with a pump size of 70 mL, 70 beats/min, and arterial pressure of 30/10 mmHg. The valve behaviour was recorded by a high-speed camera, and particle image velocimetry (PIV) was performed in the region behind the model housing section. Results Peak transvalvular pressure gradients were 4.0, 4.8, and 4.3 mmHg (P = .95), and geometric orifice areas were 2.34, 2.38, and 2.46 cm2 (P = .96) in models A, B, and C, respectively. Particle image velocimetry revealed peak instantaneous velocity was 1.69, 1.69, and 1.65 m/s (P = .74) and peak Reynolds shear stress in the midsystolic phase was 56.8, 49.5, and 25.5 Pa (P = .05) in models A, B, and C, respectively. Model C tended to have a lower distribution of turbulent flow than the other models. Conclusions All models exhibited sufficient opening and acceptable Reynolds shear stress values. The sinus contributed to the suppression of turbulent flow, which may lead to an improvement of conduit durability, but its effect was dependent on the sinus size.

Abstract This paper presents an experimental investigation of local heat transfer characteristics of single-phase flow in a plate heat exchanger (PHE). The local heat transfer coefficient is evaluated using a test section with PHE geometry for measuring wall temperature distribution. The test section of 1.5 mm thickness is employed to consider the heat conduction effect of the heat transfer plate. The results indicated that the local heat transfer coefficient is influenced by the development of the thermal boundary layer along the flow direction and the maldistribution of water flows along both the direction perpendicular to the flow and the stacking direction. The harmonic mean heat transfer coefficient calculated by the measured local heat transfer coefficient agrees with the average heat transfer coefficient evaluated by the modified Wilson plot method within ±25% and within ±16% for the hot side and the cold side, respectively.

From the end of 2019, COVID-19 prevails. Wearing a facial mask was effective in preventing COVID-19 infection. However, there are two problems with facial masks. First, there is gaps between the face and facial masks around the nose and cheeks, through which virus droplets can enter. Second, wearing a facial mask makes breathing difficult. Therefore, the purpose of this study is to establish an evaluation method for the virus droplet invasion ratio and suffocation magnitude. Furthermore, using the established evaluation method, we aim to develop a new facial mask for medical and general use that eliminates the gaps between face and facial mask and releases the suffocation. We measured the invasion ratio of three types of facial masks, when the facial mask is worn normally or when the facial mask is taped to the face to eliminate the gap. We proposed a two-variable index for the mask development that combines the two invasion ratios. When the two invasion ratios are equal, the filter performance of the facial mask might be at its maximum, and such a facial mask is defined as an optimized mask. Finally, we succeeded in developing a new optimized facial mask that solves the problem of commercial products.

This paper reports the visualization of frost formation behavior at fins used in heat exchangers and the investigation of thermal properties of the frost layer surface using infrared thermography. Visualization uses two types of fins to understand the difference in frost formation behavior. In infrared thermography, the Nusselt number on the surface of the frost layer on a flat plate was calculated as a preliminary step to determine the heat transfer coefficient of the frost surface adhering to the fins.

A generator mainly consists of a central rotor and a surrounding stator. The stator has slits for cooling, but when the amount of power generation increases, the entire coil burns out due to heat generation. Therefore, efficient cooling is essential, and it is necessary to know the behavior of the internal fluid. The purpose of this study is to visualize the velocity and pressure fields around slits using a quadrupole butt-pole rotor with PIV for understanding understand the characteristics of the flow inside the generator. In the result, the pressure fluctuation is estimated from the velocity obtained in the PIV experiment for investigating the unsteady velocity fluctuation in the case of a single stator slit. The conditions under which periodic reverse flow occurs are the same as those under which rotating stall occurs. Therefore, frequency analysis was performed using the pressure fluctuation values, and by comparing with previous papers, it was clarified that the phenomenon was a rotating stall.

Recently, the fuel consumption of automobiles has been reduced, and the demand for turbochargers has increased. A heat exchanger called an intercooler is used with this equipment. The problem is that the intercooler may be destroyed by the condensation and solidification of the steam in the compressed air when using it in a low temperature environment. Previous studies have conducted frosting and defrosting experiments on fin-and-tube heat exchangers. However, there are few studies on frost formation in the internal channel, and the frost formation process is not clearly known. The purpose of this research is to reproduce the frosting phenomenon on the fins installed inside the flow path and to understand the frost formation phenomenon in more detail by visualizing the frost formation process. We conducted an experiment using two types of fins and investigated the effect of the fin shape on the frost formation phenomenon. In the experiment, we measured temperature, humidity, flow rate, and flow path differential pressure, and calculated heat transfer rate to understand the frost phenomenon. As a result of the experiment, in the triangular fin, water droplets were likely to stay between the fins, and the flow path was clogged earlier.

To improve the heat transfer performance of the heat exchanger, it is effective to install a vortex generator on the heat transfer surface and break the temperature boundary layer by fluid mixing. The purpose of this research is to investigate the behavioral changes of the flow inside the offset channel with the vortex generator and its effect on the heat transport property. In this report, we show the numerical calculation result of the case where the installation position is offset, considering the interference between the vortex generator fin attached in the channel and the wall boundary layer. The results were compared using the Fanning's friction coefficient and Colburn's j-factor. The reason for the model showing the best heat transfer performance from the distribution of vortex structure and local Nusselt number was investigated. It has been clarified that it is advantageous to improve the heat transfer performance by installing the upstream fin close to the wall surface in the inclined direction. This is because this condition is effective in maintaining the amount of rotation of the vertical vortex extending between the fins and at the same time promoting the development of the horseshoe vortex.

For the promotion of heat transfer, various measures have been taken to induce stirring flow until now. It was confirmed that the dimple can restrain the pressure loss to the same level as the bare tube and obtain the heat transfer effect equal to or more than that of the fin⁽¹⁾. However, it is hardly mentioned what sort of flow style was formed by the dimples and so what influence was brought out on the main flow. In addition to this question, many studies have dealt with typical circular dimples and arrangements of multiple dimples to adapt to the actual machine⁽²⁾⁽³⁾, so the performance in the cases of other shape and single dimple have not been clarified yet. The purpose of this study is expose the mixing flow characteristics generated by simplex dimple of different shape was evaluated. In this paper, it described the external mean flow around the dimples, which is circular, elliptical and teardrop shape, in the three-dimensional flow field by PIV measurement⁽⁴⁾. As a result, with respect to the Reynolds stresses u’v’, the circular and elliptical dimples had distributed from the center of dimple to the backward. The teardrop-shaped dimple had a generated region extending backward from the trailing edge near the sidewall. The Second invariant of velocity gradient Q value was distributed along the trailing edge of the dimple. In the elliptical, it was also confirmed at the leading edge.

In order to improve the performance of the heat exchanger, it is important to enhance the heat transfer coefficient at the wall surface. It has been reported that the dimples are used in the heat exchanger to increase the cross-sectional area and agitate the fluid motion for enhancing the heat transfer coefficient. There are many experimental studies on effects of multiple dimples on flow characteristics. However, there are few experimental reports which comparing the turbulent-flow characteristics on dimple shapes. Regarding the turbulent-flow characteristics which are exerted a single elliptical dimple, three-dimensional flow and Reynolds stress measured by a particle image velocimetry experiments. Furthermore, in order to explore the effect of installation angle of dimple on heat transfer, it investigated the difference in the characteristics of the flow field on dimple which installed different angle and the factors that improve the heat transfer performance and the flow agitation performance.

<p>In recent years, EGR coolers, which are heat exchangers for automobiles, are required to improve heat transfer performance and reduce size and weight for the purpose of improving fuel efficiency and reducing nitrogen oxides. Previous studies have revealed that longitudinal vortices induced by vortex generators installed near the surface of the heat exchanger promote heat transfer from the main vortex to the boundary layer. In this study, the heat transfer performance by the shape of the vortex generator (VG) using CFD is compared for the flow in the rectangular pipe channel. Moreover, the effect of the continuous shape is clarified from the calculation result of the case where the VG is installed in the offset fin channel.</p>

<p>The micro-tube heat exchanger efficiently exchanges heat by flowing fluid into the flow path and small diameter tube. In recent years, thanks to 3D printers, it has become possible to easily mold even shapes that could not be realized in the past. Based on these points, we investigated the flow of the rhomboid tube group that could not be created before and the effect of self-excited vibration on the temperature field.</p>

<p>EGR coolers installed in automobiles are required to improve heat exchange performance and to be smaller and lighter. Conventionally, a method has been adopted in which heat transfer fins generate vortices to promote heat transfer. In recent years, however, soot accumulation in exhaust gas has been regarded as a problem. Therefore, the purpose of this study is to clarify the relationship between the heat flow and the flow field formed by the shape and flow path arrangement of the flow path with the protruding vortex generator, and compare the performance with the conventional product.</p>

<p>The micro-tube heat exchanger efficiently exchanges heat by flowing fluid into the flow path and small diameter tube. In recent years, thanks to 3D printers, it has become possible to mold easily even shapes that could not be realized in the past. Based on these points, we investigated the flow of the rhomboid tube group that could not be created before and the effect of self-excited vibration on the temperature field.</p>

<p>Micro-tube heat exchangers are often used for heat exchange between fluid and gas. This heat exchanger is equipped with fine circular tubes to perform heat exchange efficiently and the miniaturization of tube diameter and the increase of installation density are promoted with the recent development of processing technology. However, the miniaturization of the circular tube leads to an increase in the wall thickness, it is necessary to calculate the temperature considering not only the heat transfer in the radial direction of the pipe but also the heat transfer in the axial direction of the pipe. Therefore, in this analysis, numerical analysis of tubes with wall thicknesses was conducted, and the flow characteristics of the fluid and the heat transfer characteristics inside the tube were investigated.</p>

<p>When dimples are installed on the heat transfer surface of the heat exchanger, the heat transfer efficiency is expected to be improved because the flow is mixed while suppressing the pressure loss. However, the performance of single dimple, which is the most basic, has not been clarified yet. In this study, for the purpose of quantitative evaluation of turbulence property generated by circular dimple in a flow field, local flow velocity was measured using PIV. As a result of evaluating Reynolds stress in three-dimension around the dimple, the stirring effect generated in dimple was confirmed.</p>

<p>EGR cooler is a heat exchanger that reduces NOx emissions and improves fuel consumption of cars. Up to now, fin shape Vortex generator have been used to improve the heat transfer performance, but in recent years, raised dimple shape have attracted attention. Although this dimple is effective for reducing of soot deposits, it does not generate vortices that improve heat transfer performance. The purpose of this research is to compare the shapes of protrusions using CFD for cost reduction, and propose the shapes of protrusions that meet the requirements.</p>

<p>Heat exchangers are installed in the cycle of car air conditioners to improve the fuel efficiency of automobiles. This higher performance of the internal heat exchanger leads to further improvement of fuel consumption and reduction of the influence of global warming. As the way to do it, research and development of laying dimples inside equipment is attracting attention for the purpose of increasing the heat transfer area and disturbing the fluid with low pressure loss to improve the heat exchange efficiency. However, there are still many unclear matters such as optimum arrangement and optimum shape of dimples, and the Reynolds number of the actual machine is on the order of hundreds of thousands, so it is necessary to clarify the influence of dimples on the turbulent flow field. Therefore, in this research, numerical analysis was performed by using in-house code in the channel where multiple dimples were laid to clarify the effect of laying dimples and the relationship between turbulence statistics and heat transfer characteristics. As a result, it was found that the Nusselt number at the bottom and the Reynolds stress in the vicinity become larger near the dimple trailing edge. In addition, it was found that the magnitude of the local Nusselt number between dimples in the center of the flow field and the peak value of Reynolds stress near the bottom decrease as going downstream.</p>

<p>Boiling heat transfer using immiscible liquid mixtures is an innovative cooling technique for high-heat-density electronic devices. Immiscible liquid mixtures which are composed of more-volatile liquid with higher density and less-volatile liquid with lower density such as combination of FC-72 and Water are discussed here. In the case of pool boiling using immiscible liquid mixtures, more-volatile liquid on the heating surface is started boiling firstly, and then the more-volatile liquid reaches the critical heat flux as the heat flux increases. Subsequently, the less-volatile liquid is replaced with the more-volatile liquid and moves onto the heating surface, and this liquid is started boiling. This phenomenon is called a Boiling Refrigerant Transition, and the characteristics of heat transfer and flow behavior during Boiling Refrigerant Transition are not clear. Therefore, here the experiments under the conditions of various heights of more-volatile liquid layer and various mixture composed ratio by using two combinations of immiscible mixtures are carried out. The experimental results show that characteristics of heat transfer including Boiling Refrigerant Transition are only depending on the height of more-volatile liquid layer. And the relation between the observation of boiling behavior on the heating surface and characteristics of heat transfer is discussed.</p>

Experiments were performed to verify the performance of experimental apparatus for the acquisition of reference data for flow boiling heat transfer under the terrestrial condition which is to be compared with that obtained under the microgravity condition onboard International Space Station (ISS) by using another apparatus with the same specification. Test section is a circular tube made of copper with an inner diameter of 4 mm and a heated length of 368 mm and oriented vertically on ground. To improve the accuracy of local heat fluxes, the compensation of heat flux distribution along the tube axis is discussed on the basis of the experimental results on the local heat transfer coefficients for a single-phase liquid flow. Correlations for local heat transfer coefficient of flow boiling are proposed here as functions of boiling number and Martinelli parameter in the regions of nucleate boiling and two-phase forced convection, respectively. Because the discrepancy of local heat transfer coefficient obtained from the apparatus for the terrestrial and the space experiments is caused by the difference of surface roughness in nucleate boiling region, a compensation factor is introduced in the correlation. The local heat transfer coefficients predicted by the proposed correlation are agreed well with those obtained by both apparatus.