The characteristics of heat transfer and flow patterns are investigated experimentally for the vertical falling film evaporation of pure refrigerant HCFC123 in a rectangular minichannels consisting of offset strip fins. The refrigerant liquid is uniformly supplied to the channel through a distributor. The liquid flowing down vertically is heated electrically from the rear wall of the channel and evaporated. To observe the flow patterns during the evaporation process directly, a transparent vinyl chloride resin plate is placed as the front wall. The experimental parameters are as follows: the mass velocity G = 28∼70 kg/(m 2 s), the heat flux q = 20∼50 kW/m 2 and the pressure P ≈ 100 kPa. It is clarified that the heat transfer coefficient α depends on G and q in the region of vapor quality x ≥ 0.3 while there is little influence of G and q in the region x ≤ 0.3. From the direct observation using a high speed video camera and a digital still camera, flow patterns are classified into five types. Then the empirical correlation equations for evaporation heat transfer coefficient on a vertical falling film plate fin evaporator with minichannels are proposed. From the physical model to evaluate the heat transfer coefficient of the minichannel surface with fins, the characteristics of fin efficiency is clarified that the average value of fin efficiency is about 0.6 and the distributive characteristics of fin efficiency is roughly inverse of heat transfer coefficient characteristics.

A periodic microstructure of the cubic cavity 6.0 μm wide, 6.0 μm deep, and 6.0 μm high is built on an ultraviolet curable resin via UV nanoimprinting. The 200 nm thick gold film is sputtered on the periodic micro structure. The hemispherical spectroscopic transmittance and reflectance of the periodic microstructure with the gold film are measured using a Fourier transform infrared spectrometer with an integrating sphere. The hemispherical spectroscopic transmittance is 0.0 from 2 to 15 μm wavelength. The hemispherical spectroscopic reflectance is 1.0 from 2 to 8 μm wavelength and from 12 to 15 μm wavelength. The bottom of the hemispherical spectroscopic reflectance is 0.4 near 10 μm. Assuming Kirchhoff’s law, the maximum normal emissivity of the periodic microstructure is 0.6 near 10 μm. It is clarified that the periodic microcavities with a gold film built via UV nanoimprinting and sputtering can enhance maximum spectral emissive power of radiation.

In a polymer electrolyte fuel cell (PEFC), the catalyst degradation on cathodic side is one of the fatal problems caused by mal-distributed hydrogen supply into each channel on active area in a fuel cell, especially in a fuel cell stack for automotive fuel cell systems which consist of several hundreds of fuel cells stacked. For example, before getting the fuel cell system started-up, the gas in all the anodic flow passage including channels in each fuel cell is occupied by air instead of hydrogen due to cross leak from cathodic side to anodic side through the membrane employed as an electrolyte. In this situation, if hydrogen is supplied partially or unevenly between cells to start up the system, a concentration interface of air and hydrogen will be made within a fuel cell. This causes a state of local cell within a single fuel cell and the catalyst degradation (carbon corrosion or Pt dissolution) occurs. In this paper, to avoid this catalyst degradation, the gas distribution is investigated with pressurized hydrogen supply into channels located on the hundreds stacked fuel cells statically filled with air initially. A transient computational fluid analysis was applied to the flow fields of anodic side which consist of channels on fuel cells, both distributing and collecting manifold connected to the fuel cells under parameters: 1) number of stacked fuel cells (i.e. manifold length), 2) the rate of pressure rising (Pa/sec.) which makes the gas flow velocity. A gas analysis experiment was also carried out for a validation with mass spectrometer taking gas sample from several points along the gas channels on alternative fuel cells which are made of transparent acrylic resin. The results show that the uniform distribution in concentration between cells and its profile within the channels along the flow direction are strongly affected by flow field formed within the distributing manifold located upstream of stacked plates with channels.

In this paper the feasibility of obtaining optical access for micro devices made by stereolithography is investigated, to meet demands set by microfluidic research efforts. A commercially available resin SL5530 was selected for the UV polymerisation process. By optimising the design of the CAD models and the fabrication process, the suitability of the final product was improved for optical metrology. Transparent T-shaped microchannels were manufactured for future application in gas mixing study on interferometric system. Fringes patterns were first obtained from interferometric experiments and then the signals were extracted from the fringes pattern to analyse its suitability.

This paper demonstrates the design, Fabrication, and characterization of a novel electrohydrodynamic (EHD) conduction micropump. The device is based on LCP MEMS microfabrication technology. The novelty of design is due to its micro scale space between two electrodes. The pump consists of high voltage electrode, ground electrode, gasket, input/output ports, and electrical connections. The high voltage electrode consists of 75 centric annulus that were patterned on a 1.5mm LCP film with 30 μm copper clad layer as a substrate. The ground electrode was patterned using the same technology in the shape of a single circular plane avoiding any sharp point. A 230 μm -annuals liquid crystal polymer (LCP) gasket was used to fix the distance between the two substrates. Using 56 μm -resin epoxy film, two substrates are bonded together with constant distance 286 μm. The overall dimension of the micro pump is 65mm × 70mm. The flow direction in the pump was from ground electrode toward positive voltage electrode. In the absence of net flow, the device tests showed a maximum head of 105 Pa with 18 mW power consumption in absence of direct ion injection. The low level of power consumption with this pressure head generation promises a good chance to use the micropump in microgravity micro lubrication applications.

In the present study, the characteristics of heat transfer and flow patterns are experimentally investigated on the falling film evaporation of pure refrigerant HCFC123 in a vertical rectangular minichannel consisting of offset strop fins. The refrigerant liquid is supplied to the channel through 37 holes of a distributor. The liquid flowing down vertically is heated electrically from the rear wall of the channel and evaporated. To observe the flow patterns during the evaporation process directly, a transparent vinyl chloride resin plate is placed as the front wall. The experimental parameters are as follows: the mass velocity G = 28∼70 kg/(m 2 s), the heat flux q = 20∼50 kW/m 2 and the pressure P ≈ 100 kPa. It is clarified that the heat transfer coefficient α depends on G and q in the region of vapor quality x ≥ 0.3 while there is little influence of G and q in the region x ≤ 0.3. From the direct observation using a high speed video camera and a digital still camera, flow patterns are classified into five typical ones: plane liquid film, wavy liquid film, liquid film accompanied with dry patch, liquid film accompanied with dripping and liquid film accompanied with mist. Then the relation between heat transfer and flow pattern is clarified. The results of heat transfer characteristics are also compared with some previous correlation equations.

The frictional pressure drops of gas-liquid two-phase flow in mini-pipes and mini-rectangular channels were investigated experimentally. The following test channels were used in the present experiments: commercial stainless-steel circular tubes with 0.6, 0.5 and 0.25 mm in inner diameter, FEP circular tube of 0.4 mm in inner diameter and rectangular channels, made of Acrylic resin, with 0.39 × 20.4 mm, 0.21 × 9.75 mm, 0.26 × 4.28 mm and 0.18 × 1.87 mm in height and width, respectively. The pressure drops of straight pipe, sudden enlargement and sudden contraction of gas-liquid two-phase flow in mini-pipes were measured for the test mini-channels. The pressure drops of rectangular minichannel were also measured. Experimental result showed that measured two-phase friction multipliers agreed well with a conventional Lockhart-Martinelli correlation for circular tubes and Mishima-Hibiki’s correlation for rectangular channels. Observed flow patterns by visualization were bubbly, slug, churn, ring and annular flow; the flow patterns in the present experiments were reproduced well by Baker’s flow pattern map.