Flow Boiling Heat Transfer of R123/R134a Mixture in a Micro-Channel

2010 ◽  
Author(s):  
Sehwan In ◽  
Sangkwon Jeong
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Micro Channel ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Transfer Characteristics ◽  
Flow Boiling Heat Transfer ◽  
Micro Channels

This paper describes the flow boiling heat transfer of R123/R134a mixture in a single round micro-channel with 0.19 mm ID. The flow boiling heat transfer coefficients were measured with the variation of mixture composition (R123 mole fraction: 0.502, 0.746) at various experimental conditions: mass velocities (314, 392, 470 kg/m2-s), heat fluxes (10, 15, 20 kW/m2) and vapor qualities (0.2–0.85). The heat transfer characteristics of R123/R134a mixture are similar to those of pure R123 observed in the previous flow boiling experiment. The similarity of heat transfer characteristics denotes that the heat transfer is governed by evaporation of thin liquid film around the elongated bubbles like the case of pure R123. The heat transfer coefficients of R123/R134a mixture are compared with those of equivalent pure refrigerant by the correlation developed from pure R123 experimental results. The large reduction of heat transfer coefficients compared with pure refrigerant is found in micro-channels flow boiling by the mass transfer effect of mixed refrigerant. In addition, macro-channel correlations for mixed refrigerant do not make accurate prediction about the reduction of heat transfer coefficients.

Flow Boiling Heat Transfer of CO2 at Low Temperatures: Challenges and Opportunities

2007 ◽  
Author(s):  
Pradeep Bansal ◽  
Xiumin Zhao
Keyword(s):  
Heat Transfer ◽  
Low Temperatures ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Stainless Steel Tube ◽  
Limited Information ◽  
Heat Transfer Characteristics ◽  
Transfer Coefficients ◽  
Transfer Characteristics ◽  
Flow Boiling Heat Transfer

There is a growing use of CO2 refrigeration to achieve low temperatures, particularly in the food industry, however, very limited information is available in the open literature on its boiling heat transfer characteristics below (−)30°C. This paper presents an overview of the flow boiling heat transfer characteristics of pure CO2 at low temperatures, its special thermal properties and their effect on the boiling heat transfer. The paper also presents an analysis of the experimental data collected from (−)24.3°C to (−)40°C in a novel experimental rig, specifically designed to achieve low temperatures down to (−)50°C, using 4.5m long horizontal stainless steel tube of 4.57mm inner diameter. The paper highlights the limitations of existing empirical correlations by comparing their predictions with the experimental boiling heat transfer coefficients. It is expected that the data presented in this study would be beneficial to industry and designers of compact heat exchangers for CO2 at low temperatures.

Flow Boiling Heat Transfer Characteristic of Ternary Mixture in a Micro-Channel

2011 ◽  
Author(s):  
Inmyong Park ◽  
Sehwan In ◽  
Sangkwon Jeong
Keyword(s):  
Heat Transfer ◽  
Mole Fraction ◽  
Boiling Heat Transfer ◽  
Ternary Mixture ◽  
Flow Boiling ◽  
Thin Liquid Film ◽  
Micro Channel ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer

This paper describes the flow boiling heat transfer of R123/R134a/R22 mixture in a single round micro-channel with 0.19 mm ID. The flow boiling heat transfer coefficients were measured for ternary mixture (R123/R134a/R22 mole fraction: 0.194/0.62/0.186) at various experimental conditions: mass velocities (314, 392, 470 kg/m2-s), heat fluxes (10, 15, 20 kW/m2) and vapor qualities (0.2–0.8). The heat transfer characteristics of the R123/R134a/R22 mixture are similar to those of the R123/R134a mixture (mole fraction: 0.502/0.498) observed in the previous flow boiling experiment which indicates that major heat transfer mechanism in the microchannel is dominated by evaporation of thin liquid film around the elongated bubbles. The large reduction of heat transfer coefficients compared with pure refrigerant is observed in micro-channel flow boiling by mass transfer effect of mixed refrigerant.

scholarly journals Flow Boiling Heat Transfer Characteristics in Horizontal, Three-Dimensional Enhanced Tubes

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 927 ◽  
Author(s):  
Zhi-Chuan Sun ◽  
Xiang Ma ◽  
Lian-Xiang Ma ◽  
Wei Li ◽  
David Kukulka
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Tube Length ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow Boiling Heat Transfer ◽  
Developed Surface ◽  
Enhanced Tubes ◽  
Surface Patterns

An experimental investigation was conducted to explore the flow boiling heat transfer characteristics of refrigerants R134A and R410A inside a smooth tube, as well as inside two newly developed surface-enhanced tubes. The internal surface structures of the two enhanced tubes are comprised of protrusions/dimples and petal-shaped bumps/cavities. The equivalent inner diameter of all tested tubes is 11.5 mm, and the tube length is 2 m. The experimental test conditions included saturation temperatures of 6 °C and 10 °C; mass velocities ranging from 70 to 200 kg/(m2s); and heat fluxes ranging from 10 to 35 kW/m2, with inlet and outlet vapor quality of 0.2 and 0.8. It was observed that the enhanced tubes exhibit excellent flow boiling heat transfer performance. This can be attributed to the complex surface patterns of dimples and petal arrays that increase the active heat transfer area; in addition, more nucleation sites are produced, and there is also an increased interfacial turbulence. Results showed that the boiling heat transfer coefficient of the enhanced surface tubes was 1.15–1.66 times that of the smooth tubing. Also, effects of the flow pattern and saturated temperature are discussed. Finally, a comparison of several existing flow boiling heat transfer models using the data from the current study is presented.

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.

Flow Boiling Heat Transfer, Pressure Drop, and Flow Pattern for CO2 in a 3.5mm Horizontal Smooth Tube

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Chang Yong Park ◽  
Pega Hrnjak
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer

Abstract C O 2 flow boiling heat transfer coefficients and pressure drop in a 3.5mm horizontal smooth tube are presented. Also, flow patterns were visualized and studied at adiabatic conditions in a 3mm glass tube located immediately after a heat transfer section. Heat was applied by a secondary fluid through two brass half cylinders to the test section tubes. This research was performed at evaporation temperatures of −15°C and −30°C, mass fluxes of 200kg∕m2s and 400kg∕m2s, and heat flux from 5kW∕m2 to 15kW∕m2 for vapor qualities ranging from 0.1 to 0.8. The CO2 heat transfer coefficients indicated the nucleate boiling dominant heat transfer characteristics such as the strong dependence on heat fluxes at a mass flux of 200kg∕m2s. However, enhanced convective boiling contribution was observed at 400kg∕m2s. Surface conditions for two different tubes were investigated with a profilometer, atomic force microscope, and scanning electron microscope images, and their possible effects on heat transfer are discussed. Pressure drop, measured at adiabatic conditions, increased with the increase of mass flux and quality, and with the decrease of evaporation temperature. The measured heat transfer coefficients and pressure drop were compared with general correlations. Some of these correlations showed relatively good agreements with measured values. Visualized flow patterns were compared with two flow pattern maps and the comparison showed that the flow pattern maps need improvement in the transition regions from intermittent to annular flow.

Sign in / Sign up

Export Citation Format

Share Document