Horizontal Minichannel Research Articles

FLOW BOILING IN HORIZONTAL MINICHANNELS: FLOW PATTERN OF CO2 AT HIGH PRESSURE

This paper describes the flow patterns of carbon dioxide two-phase flow at high pressure observed in horizontal minichannels ranging from 0.51 to 3.0 mm in diameter, together with the flow pattern maps and related boiling heat-transfer characteristics. The observed flow patterns are mainly classified into bubbly, slug, slug-annular, and annular flows, similar to conventional pipes, while phase stratification tendency is still significant even in a 1.0 mm tube, so that heat transfer at high pressure shows significant differences in the upper and lower walls, especially in 2.0 and 3.0 mm tubes. Such phase stratification with reference to heat transfer is roughly scaled by means of boiling number and Bond number. The newly developed simulation model by the authors for conventional-sized tubes is successfully applied to 2.0 and 3.0 mm pipes, but not to 0.51 and 1.0 mm tubes. This model suggests that thermal flow behavior at higher Bond number Bo than 8.2 is similar to that of conventional-sized tube, and cases less than Bo = 8.2 show minichannel behavior. The heat transfer in these minichannels is well-predicted with Schrock{Grossman type correlation with nucleate and forced-convective effects, while in larger tubes, e.g., 2.0 and 3.0 mm, the heat transfer is mainly dominated by nucleate boiling in the present experimental ranges.

Flow boiling heat transfer and pressure drop of pure HFC-152a in a horizontal mini-channel

This study investigates boiling heat transfer and two-phase pressure drop of HFC-152a in a horizontal square mini-channel of 1 mm in diameter. Convection heat fluxes were obtained using an inverse heat transfer method. Tests were performed at a nearly constant system pressure of 600 kPa and under saturated conditions. Local heat transfer coefficients were determined as a function of vapor quality along the length of the test section. Tests were carried out for mass flux ranging from 200 to 600 kg/m 2s and for heat flux ranging from 10 to 60 kW/m 2. Experimental results were compared to predictive models from the literature for two-phase flow pressure drop and boiling heat transfer. The correlation of Müller-Steinhagen and Heck (1986) was found to give a good agreement for prediction of mini-channel frictional pressure losses. The heat transfer mechanism was found to be dominated by nucleate boiling, and the heat transfer coefficient independent of vapor quality and mass flux. A new correlation for Nusselt number was developed based on the Tran et al. (1996) correlation, which was able to predict the present experimental data with respective average and maximum absolute deviations of 3.7% and 11%.

The Effect of Gravity and Shear Stress on a Liquid Film Driven in a Horizontal Minichannel at Local Heating

The present study is focused on the investigation of gravity effect on thermocapillary deformations in a film flowing under action of co-current gas flow, which creates the tangential force on the gas–liquid interface. The influence of local heating intensity on the heater at a substrate is also investigated. Effects of surface tension, temperature dependent viscosity and thermocapillarity are taken into account. Investigations have shown that gravity has a significant effect on the film deformations and pattern. Decreasing of gravity level leads to a flow destabilization. 3D liquid film pattern noticeably changes in spanwise direction. Increasing of heat flux leads to increasing of liquid film deformations. Dependence of film thinning on heat flux is strongly nonlinear. The most dangerous deformations (regions of minimum film thickness with possible disruption of liquid) take place behind the downstream edge of the heater at any gravity conditions.

Critical heat flux in a locally heated liquid film driven by gas flow in a minichannel

The rupture of a liquid film driven by friction with a gas flow in a horizontal minichannel and the heat-exchange crisis in this film locally heated by a 1 × 1 cm source in the channel wall has been experimentally studied. A heat flux of 250 W/cm2 is achieved, which is greater by an order of magnitude than the limiting heat flux for a vertically falling liquid film with the same Reynolds number (Rel = 21). These experiments confirmed good prospects for using gas-flow-driven liquid films in cooling systems of devices with intense local heat evolution.

Two-phase flow heat transfer of propane vaporization in horizontal minichannels

Experiments were performed on the convective boiling heat transfer in horizontal minichannels using propane. The test section was made of stainless steel tubes with inner diameters of 1.5 mm and 3.0 mm and lengths of 1000 mm and 2000 mm, respectively, and it was uniformly heated by applying an electric current directly to the tubes. Local heat transfer coefficients were obtained for a heat flux range of 5–20 kW m−2, a mass flux range of 50–400 kg m−2 s−1, saturation temperatures of 10, 5, and 0°C and quality ranges of up to 1.0. The nucleate boiling heat transfer contribution was predominant, particularly at the low quality region. Decreases in the heat transfer coefficient occurred at a lower vapor quality with a rise of heat flux and mass flux, and with a lower saturation temperature and inner tube diameter. Laminar flow appeared in the minichannel flows. A new boiling heat transfer coefficient correlation that is based on the superposition model for propane was developed with 8.27% mean deviation.

F211 二酸化炭素の水平細管内二相流動(次世代冷凍空調技術に関わる伝熱過程I)

F211 二酸化炭素の水平細管内二相流動(次世代冷凍空調技術に関わる伝熱過程I)

Pressure drop and heat transfer during two-phase flow vaporization of propane in horizontal smooth minichannels

This study examined the two-phase flow boiling pressure drop and heat transfer for propane, as a long term alternative refrigerant, in horizontal minichannels. The pressure drop and local heat transfer coefficients were obtained for heat fluxes ranging from 5–20 kW m −2, mass fluxes ranging from 50–400 kg m −2 s −1, saturation temperatures of 10, 5 and 0 °C, and quality up to 1.0. The test section was made of stainless steel tubes with inner diameters of 1.5 mm and 3.0 mm, and lengths of 1000 mm and 2000 mm, respectively. The present study showed the effect of mass flux, heat flux, inner tube diameter and saturation temperature on pressure drop and heat transfer coefficient. The experimental results were compared against several existing pressure drop and heat transfer coefficient prediction methods. Because the study on evaporation with propane in minichannels was limited, new correlations of pressure drop and boiling heat transfer coefficient were developed in this present study.

Two-phase pressure drop during CO 2 vaporization in horizontal smooth minichannels

Pressure drop experiments for a natural refrigerant vaporization of CO 2 were performed in horizontal minichannels. The test section was made of stainless steel tubes with inner diameters of 1.5 mm and 3.0 mm and with lengths of 2000 and 3000 mm. This test section was uniformly heated by applying electric current directly to the tubes. Experiments were performed at inlet saturation temperatures of −10, −5 and 10 °C, mass flux ranges from 200 to 600 kg m −2 s −1 and heat flux ranges from 10 to 30 kW m −2. The current study showed the significant effect of mass flux, tube diameter, and saturation temperature on the pressure drop. The experimental results were compared against 13 existing two-phase pressure drop prediction methods. A new pressure drop prediction method based on the Lockhart–Martinelli method was developed with 9.41% mean deviation.

Two-phase pressure drop of R-410A in horizontal smooth minichannels

Convective boiling pressure drop experiments were performed in horizontal minichannels with a binary mixture refrigerant, R-410A. The test section was made of stainless steel tubes with inner diameters of 1.5 mm and 3.0 mm and with lengths of 1500 mm and 3000 mm, respectively. This test section was uniformly heated by applying electric current directly to the tubes. Experiments were performed at inlet saturation temperature of 10 °C, mass flux ranges from 300 to 600 kg m −2 s −1 and heat flux ranges from 10 to 40 kW m −2. The current study showed the significant effect of mass flux and tube diameter on pressure drop. The experimental results were compared against 15 two-phase pressure drop prediction methods. The homogeneous model predicted well the experimental pressure drop, generally. A new pressure drop prediction method based on the Lockhart–Martinelli method was developed with 4.02% mean deviation.

Boiling heat transfer of R-22, R-134a, and CO 2 in horizontal smooth minichannels

This study examined convective boiling heat transfer in horizontal minichannels using R-22, R-134a, and CO 2. The local heat transfer coefficients were obtained for heat fluxes ranging from 10 to 40 kW m −2, mass fluxes ranging from 200 to 600 kg m −2 s −1, a saturation temperature of 10 °C, and quality up to 1.0. The test section was made of stainless steel tubes with inner diameters of 1.5 mm and 3.0 mm, and a length of 2000 mm. The section was heated uniformly by applying an electric current to the tubes directly. Nucleate boiling heat transfer was the main contribution, particularly at the low quality region. An increasing and decreasing heat transfer coefficient occurred at the lower vapor quality with increasing heat flux and mass flux. The mean heat transfer coefficient ratio of R-22:R-134a:CO 2 was approximately 1.0:0.8:2.0. Laminar flow was observed in the minichannels. A new boiling heat transfer coefficient correlation based on the superposition model for refrigerants in minichannels was developed with a mean deviation of 11.21%.

Two-phase flow heat transfer of CO 2 vaporization in smooth horizontal minichannels

Experiments were performed on the convective boiling heat transfer in horizontal minichannels with CO 2. The test section is made of stainless steel tubes with inner diameters of 1.5 and 3.0 mm and with lengths of 2000 and 3000 mm, respectively, and it is uniformly heated by applying an electric current directly to the tubes. Local heat transfer coefficients were obtained for a heat flux range of 20–40 kW m −2, a mass flux range of 200–600 kg m −2 s −1, saturation temperatures of 10, 0, −5, and −10 °C and quality ranges of up to 1.0. Nucleate boiling heat transfer contribution was predominant, especially at low quality region. The reduction of heat transfer coefficient occurred at a lower vapor quality with a rise of heat flux, mass flux and saturation temperature, and with a smaller inner tube diameter. The experimental heat transfer coefficient of CO 2 is about three times higher than that of R-134a. Laminar flow appears in the minichannel flows. A new boiling heat transfer coefficient correlation that is based on the superposition model for CO 2 was developed with 8.41% mean deviation.

F41 水平ミニチャンネル内気液二相流に及ぼす表面張力の影響(F4 流体工学11)

F41 水平ミニチャンネル内気液二相流に及ぼす表面張力の影響(F4 流体工学11)

Forced convective boiling heat transfer of R-410A in horizontal minichannels

Convective boiling heat transfer experiments were performed in horizontal minichannels with binary mixture refrigerant, R-410A. The test section is made of stainless steel tubes with inner diameters of 1.5 mm and 3.0 mm and with lengths of 1500 mm and 3000 mm, respectively, and is uniformly heated by applying electric current directly to the tubes. Local heat transfer coefficients were obtained for a heat flux range of 10–30 kW m −2, a mass flux range of 300–600 kg m −2 s −1, and quality ranges of up to 1.0. The experimental results were mapped on Wang et al.'s (C.C. Wang, C.S. Chiang, D.C. Lu, Visual observation of two-phase flow pattern of R-22, R-134a, and R-407C in a 6.5-mm smooth tube, Experimental, Thermal and Fluid Science 15 (1997) 395–405) and Wojtan et al.'s (L. Wojtan, T. Ursenbacher, J.R. Thome, Investigation of flow boiling in horizontal tubes: part I – a new diabatic two-phase flow pattern map, International Journal of Heat and Mass Transfer 48 (2005) 2955–2969) flow pattern maps to observe the flow regimes. Laminar flow appears in flow with minichannels. A new boiling heat transfer coefficient correlation based on the superposition model for R-410A was developed with 11.20% mean deviation; it showed a good agreement between the measured data and the calculated heat transfer coefficients.

Rheology and convective heat transfer of colloidal gas aphrons in horizontal mini-channels

Colloidal gas aphrons (CGA) consists of closely packed minute gas bubbles with diameter ranging from 10 to 100 μm. It is produced by stirring a surfactant solution at high speed in a fully baffled beaker. CGA can be used in various applications such as bioremediation, bioreactors, oil recovery, and fire fighting. This paper reports experimental data for (1) adiabatic flow and (2) laminar convective heat transfer of CGA in five 1.58 × 0.76 mm 2 mini-rectangular channels. First, it is shown that CGA is a shear thinning fluid. Correlation for the friction factor as a function of Reynolds number is compared with that of water and macrofoams. Then, the local temperature and heat transfer coefficient along the mini-channels are reported as a function of the mass flow rates and imposed heat flux. The heat transfer coefficients for CGA appears to be constant and independent of mass flow rate and imposed heat flux as well known for single phase laminar flow.

작은 유로 내에서의 흐름응축 열전달 (II) -원형 및 사각유로에서의 실험적 연구-

By using unique experimental techniques and careful construction of the experimental apparatus, the characteristics of the local heat transfer were investigated using the condensing R134a two-phase flow, in horizontal single mini-channels. The circular channels (D