Flow Boiling Heat Transfer Characteristics of a Minichannel Up to Dryout Condition

2009 ◽  
Author(s):  
Rashid Ali ◽  
Bjo¨rn Palm ◽  
Mohammad H. Maqbool
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Working Fluid ◽  
Flow Boiling Heat Transfer ◽  
The Heat Transfer Coefficient

In this paper the experimental flow boiling heat transfer results of a minichannel are presented. A series of experiments was conducted to measure the heat transfer coefficients in a minichannel made of stainless steel (AISI 316) having an internal diameter of 1.7mm and a uniformly heated length of 220mm. R134a was used as working fluid and experiments were performed at two different system pressures corresponding to saturation temperatures of 27 °C and 32 °C. Mass flux was varied from 50 kg/m2 s to 600 kg/m2 s and heat flux ranged from 2kW/m2 to 156kW/m2. The test section was heated directly using a DC power supply. The direct heating of the channel ensured uniform heating and heating was continued until dry out was reached. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux while mass flux and vapour quality have no considerable effect. Increasing the system pressure slightly enhances the heat transfer coefficient. The heat transfer coefficient is reduced as dryout is reached. It is observed that dryout phenomenon is accompanied with fluctuations and a larger standard deviation in outer wall temperatures.

Flow Boiling Heat Transfer Characteristics of a Minichannel up to Dryout Condition

2011 ◽  
Vol 133 (8) ◽  
Author(s):  
Rashid Ali ◽  
Björn Palm ◽  
Mohammad H. Maqbool
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Working Fluid ◽  
Flow Boiling Heat Transfer ◽  
The Heat Transfer Coefficient

In this paper, the experimental flow boiling heat transfer results of a minichannel are presented. A series of experiments was conducted to measure the heat transfer coefficients in a minichannel made of stainless steel (AISI 316) having an internal diameter of 1.70 mm and a uniformly heated length of 220 mm. R134a was used as a working fluid, and experiments were performed at two different system pressures corresponding to saturation temperatures of 27°C and 32°C. Mass flux was varied from 50 kg/m2 s to 600 kg/m2 s, and heat flux ranged from 2 kW/m2 to 156 kW/m2. The test section was heated directly using a dc power supply. The direct heating of the channel ensured uniform heating, which was continued until dryout was reached. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux, while mass flux and vapor quality have no considerable effect. Increasing the system pressure slightly enhances the heat transfer coefficient. The heat transfer coefficient is reduced as dryout is reached. It is observed that the dryout phenomenon is accompanied with fluctuations and a larger standard deviation in outer wall temperatures.

Study on Flow Boiling Heat Transfer of Carbon Dioxide With PAG-Type Lubricating Oil in Pre-Dryout Region Inside Horizontal Tube

2010 ◽  
Author(s):  
Chaobin Dang ◽  
Minxia Li ◽  
Eiji Hihara
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Flow Boiling Heat Transfer ◽  
The Heat Transfer Coefficient

In this study, the boiling heat transfer coefficients of carbon dioxide with a PAG-type lubricating oil entrained from 0 to 5 wt% in a horizontally placed smooth tube with an inner diameter of 2 mm were experimentally investigated under the following operating conditions: mass fluxes from 170 to 320 kg/m2s, heat fluxes from 4.5 to 36 kW/m2, and a saturation temperature of 15 °C. The results show that for a low oil concentration of approximately 0.5% to 1%, no further deterioration of the heat transfer coefficient was observed at higher oil concentrations in spite of a significant decrement of the heat transfer coefficient compared to that under an oil-free condition. The heat flux still had a positive influence on the heat transfer coefficient in low quality regions. However, no obvious influence was observed in high quality regions, which implies that nucleate boiling dominates in the low quality region whereas it is suppressed in the high quality regions. Unlike the mass flux under an oil-free condition, mass flux has a significant influence on the heat transfer coefficient, with a maximum increase of 50% in the heat transfer. On the basis of our experimental measurements of the flow boiling heat transfer of carbon dioxide under wide experimental conditions, a flow boiling heat transfer model for horizontal tubes has been proposed for a mixture of CO2 and polyalkylene glycol (PAG oil) in the pre-dryout region, with consideration of the thermodynamic properties of the mixture. The surface tension and viscosity of the mixture were particularly taken into account. New factors were introduced into the correlation to reflect the suppressive effects of the mass flux and the oil on both the nucleate boiling. It is shown that the calculated results can depict the influence of the mass flux and the heat flux on both nucleate boiling and convection boiling.

The Effect of Inlet Orifice on Critical Heat Flux and Flow Boiling Heat Transfer in Single Horizontal Microtube

2013 ◽  
Author(s):  
Yanfeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Saturation Pressure ◽  
Working Fluid ◽  
Flow Boiling Heat Transfer

Flow oscillation is a crucial issue for the development of flow boiling heat transfer in the applications. Inlet orifice has been proven be an option to eliminate the oscillation. However, the effects of inlet orifice on critical heat flux and flow boiling heat transfer coefficient are lack of study. In this work, the effects of inlet restriction on critical heat flux and heat transfer coefficient in single horizontal microtube under uniform heating condition is experimentally investigated using FC-72 as working fluid. A stainless steel microtube with an inner diameter of 889 μm is selected as main microtube. Two smaller microtubes are assembled at the inlet of main microtube to achieve the restriction configurations of 50% and 20% area ratios. The experimental measurement is carried out at mass fluxes ranging from 160–870 kg/m2·s and heat fluxes varying from 6–170 kW/m2. Two saturation pressures, 10 and 45 kPa, are tested. The experimental results of critical heat flux and two phase heat transfer coefficient obtained in the microtube without orifice are compared with the existing correlations. The addition of an orifice does not enhance the normal critical heat flux but increases the premature critical heat flux. In aspect of heat transfer, the orifice shows improvement on heat transfer coefficient at low mass flux and high saturation pressure.

Flow Boiling Heat Transfer of R-22 in Small-Diameter Horizontal Round Tubes

2003 ◽  
Author(s):  
K. S. Park ◽  
W. H. Choo ◽  
K. H. Bang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Vapor Quality ◽  
Flow Boiling Heat Transfer ◽  
Boiling Heat Transfer Coefficient

The flow boiling heat transfer coefficient of R-22 in small hydraulic diameter tubes has been experimentally studied. Both brass and aluminum round tubes of 1.66 mm inside diameter are used for the test section. The ranges of the major experimental parameters are 300∼600 kg/m2s of refrigerant mass flux, 10∼20 kW/m2 of the wall heat flux, 0.0∼0.9 of the inlet vapor quality. The experimental result showed that the flow boiling heat transfer coefficient in this small tubes are in the range of 2∼4 kW/m2K and it varies only by heat flux, independent of mass flux and vapor quality. It is also observed that the heat transfer coefficients in the aluminum tube are up to 50% higher than in the brass tube.

scholarly journals Experimental Study on the Flow Boiling Heat Transfer Characteristics in a Mini-Channel with Offset Fins

Proceedings ◽  
2018 ◽  
Vol 2 (22) ◽  
pp. 1376
Author(s):  
Tao Wen ◽  
Hongbo Zhan ◽  
Yimo Luo ◽  
Dalin Zhang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Saturation Pressure ◽  
Rectangular Channels ◽  
Flow Boiling Heat Transfer

The present study studied the flow boiling heat transfer performance of a mini channel with offset fins experimentally. The hydraulic diameter for it is 1.59 mm with 9 offset rectangular channels. The influences of saturation pressure, mass flux and heat flux on heat transfer coefficient were investigated. The experimental results reveal that when the vapor quality of refrigerant is less than 0.6, the mass flux has negligible influence on heat transfer coefficient. While it increases with both the saturation pressure and heat flux. Differently, in the high quality region, the heat transfer coefficient has an ascending trend with the increase of mass flux and is not affected by heat flux and saturation pressure.

scholarly journals Impact of selected thermal and flow parameters on flow boiling heat transfer in a minichannel

2019 ◽  
Vol 213 ◽  
pp. 02079
Author(s):  
Kinga Strąk ◽  
Magdalena Piasecka
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Inlet Pressure ◽  
Flow Parameters ◽  
Flow Boiling Heat Transfer

This paper reports an impact of selected thermal and flow parameters i.e., mass flux and inlet pressure on flow boiling heat transfer in a minichannel. Research was carried out on the experimental set up with the test section fitted with a single, rectangular and vertically oriented minichannel 1.7 mm deep. Infrared thermography was used to determine changes in the temperature on the outer side of the heated minichannel wall in the central part of the minichannel. The heated element for HFE-649 flowing in the minichannel was a thin alloy plate, made of Haynes-230. Local values of heat transfer coefficient for stationary state conditions were calculated using a simple one-dimensional method. Analysis of the results was based on experimental series obtained for the same heat flux, various mass fluxes and average inlet pressures. The experimental results are presented as the relationship between the heat transfer coefficient and the distance along the minichannel length and boiling curves. The highest local heat transfer coefficients were obtained for the lower average inlet pressure and for the highest mass flux at lower heat flux.

A Fundamental View of the Flow Boiling Heat Transfer Characteristics of Nano-Refrigerants

2012 ◽  
Author(s):  
Lorenzo Cremaschi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Phase ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Working Fluid ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow Boiling Heat Transfer

Driven by higher energy efficiency targets and industrial needs of process intensification and miniaturization, nanofluids have been proposed in energy conversion, power generation, chemical, electronic cooling, biological, and environmental systems. In space conditioning and in cooling systems for high power density electronics, vapor compression cycles provide cooling. The working fluid is a refrigerant and oil mixture. A small amount of lubricating oil is needed to lubricate and to seal the sliding parts of the compressors. In heat exchangers the oil in excess penalizes the heat transfer and increases the flow losses: both effects are highly undesired but yet unavoidable. This paper studies the heat transfer characteristics of nanorefrigerants, a new class of nanofluids defined as refrigerant and lubricant mixtures in which nano-size particles are dispersed in the high-viscosity liquid phase. The heat transfer coefficient is strongly governed by the viscous film excess layer that resides at the wall surface. In the state-of-the-art knowledge, while nanoparticles in the refrigerant and lubricant mixtures were recently experimentally studied and yielded convective in-tube flow boiling heat transfer enhancements by as much as 101%, the interactions of nanoparticles with the mixture still pose several open questions. The model developed in this work suggested that the nanoparticles in this excess layer generate a micro-convective mass flux transverse to the flow direction that augments the thermal energy transport within the oil film in addition to the macroscopic heat conduction and fluid convection effects. The nanoparticles motion in the shearing-induced and non-uniform shear rate field is added to the motion of the nanoparticles due to their own Brownian diffusion. The augmentation of the liquid phase thermal conductivity was predicted by the developed model but alone it did not fully explain the intensification on the two-phase flow boiling heat transfer coefficient reported in previous work in the literature. Thus, additional nano- and micro-scale heat transfer intensification mechanisms were proposed.

Two Phase Heat Transfer of Ammonia in a Mini/Micro Channel

2010 ◽  
Author(s):  
M. Hamayun Maqbool ◽  
Bjo¨rn Palm ◽  
R. Khodabandeh ◽  
Rashid Ali
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Experimental Results ◽  
Working Fluid ◽  
Internal Diameter ◽  
Vapour Quality ◽  
The Heat Transfer Coefficient

Experiments have been performed to investigate heat transfer in a circular vertical mini channel made of stainless steel (AISI 316) with internal diameter of 1.70 mm and a uniformly heated length of 245 mm using ammonia as working fluid. The experiments are conducted for a heat flux range of 15 to 350 kW/m2 and mass flux range of 100 to 500 kg/m2s. The effects of heat flux, mass flux and vapour quality on the heat transfer coefficient are explored in detail. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux while mass flux and vapour quality have no considerable effect. Experimental results are compared to predictive methods available in the literature for boiling heat transfer. The correlations of Cooper et al. [1] and Shah [3] are in good agreement with our experimental data.

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