Augmented Performance of Flow Boiling Heat Transfer in a Tube With Axial Micro-Grooves and its Augmentation Mechanisms

1999 ◽  
Author(s):  
Lixin Cheng ◽  
Tingkuan Chen
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Axial Direction ◽  
Smooth Tube ◽  
Absolute Pressure ◽  
Transfer Coefficients ◽  
Frictional Pressure Drop ◽  
Flow Boiling Heat Transfer ◽  
Enhanced Tube

Abstract Experiments of upward flow boiling heat transfer with water in a vertical smooth tube and a tube with axial micro-grooves were respectively conducted. Both of the tested tubes have a length of 2.5 m, an inner diameter of 15 mm and an outlet diameter of 19 mm. The tube with axial micro grooves has many micro rectangle grooves in its inner wall along the axial direction. The grooves have a depth of 0.5 mm and a width of 0.3 mm. The tests were performed at an absolute pressure of 6 bar. The heat flux ranged from 0 to 550 kW/m2 and the mass flux was selected at 410, 610 and 810 kg/m2s, respectively. By comparison, flow boiling heat transfer coefficients in the enhanced tube are 1.6 ∼ 2.7 fold that in the smooth tube while the frictional pressure drop in the enhanced tube is slightly greater than that in the smooth tube. The augmentation of flow boiling heat transfer in the tube with axial micro-grooves is apparent. Based on the experimental data, a correlation of flow boiling heat transfer is proposed for the enhanced tube. Finally, the mechanisms of heat transfer enhancement are analyzed.

Flow Boiling Heat Transfer of CO2 at Low Temperatures in a Horizontal Smooth Tube

2005 ◽  
Vol 127 (12) ◽  
pp. 1305-1312 ◽  
Author(s):  
Chang Yong Park ◽  
Pega S. Hrnjak
Keyword(s):  
Heat Transfer ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Smooth Tube ◽  
High Mass ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer

Flow boiling heat transfer coefficients of CO2 are measured in a horizontal smooth tube with inner diameter 6.1mm. The test tube is heated by a secondary fluid maintaining constant wall temperature conditions. Heat transfer coefficients are measured at evaporation temperatures of −15 and −30°C, mass flux from 100to400kg∕m2s, and heat flux from 5to15kW∕m2 for qualities (vapor mass fractions) ranging from 0.1 to 0.8. The characteristics of CO2 flow boiling are explained by CO2 properties and flow patterns. The measured CO2 heat transfer coefficients are compared to other published data. Experiments with R22 were also conducted in the same system and the results show that the heat transfer coefficients for CO2 are 40 to 150% higher than for R22 at −15°C and low mass flux of 200kg∕m2s mostly due to the characteristics of CO2 nucleate boiling. The presented CO2 heat transfer coefficients indicate the reduction of heat transfer coefficient as mass flux increases at low quality regions and also show that dryout does not occur until the high quality region of 0.8, for mass fluxes of 200 and 400kg∕m2s. The Gungor and Winterton correlation gives a relatively good agreement with measured data; however it deviates more at lower evaporation temperature and high mass flux conditions.

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.

Flow Boiling of Water in Minichannels: Effect of Pressure

2007 ◽  
Author(s):  
Kwang-Hyun Bang ◽  
Kun-Eui Hong ◽  
In-Seon Hwang
Keyword(s):  
Heat Transfer ◽  
Test Section ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Gear Pump ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Effect Of Pressure ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer

This paper reports an experimental study on flow boiling of water in a minichannel. Flow boiling heat transfer coefficients and pressure drops were measured and the data were compared with existing correlations. The effect of pressure was the major objectives in this study and the range of pressure was 1 to 18 bars. The experimental apparatus consisted mainly of a minichannel test section, gear pump, pre-heater, pressurizer, condenser and evaporator. The evaporator was used for variation of vapor quality at the inlet of test section. The pressurizer controls the desired system pressure. The test section is a round tube of 1.73 mm inside diameter, made of 316 stainless steel. The test section and the evaporator tubes were heated by DC electric current through the tubes. The measured flow boiling heat transfer coefficients showed two distinct regions; relatively high heat transfer coefficients at low vapor quality and lower heat transfer coefficients at higher vapor quality. This observation implies the change of flow regime, slug to annular flow. Comparisons of the experimental data and the prediction of correlations (Gungor & Winterton, 1987; Tran et al., 1996; Kandlikar, 2003) showed large discrepancy in both regions.

A General Correlation for Saturated Two-Phase Flow Boiling Heat Transfer Inside Horizontal and Vertical Tubes

1990 ◽  
Vol 112 (1) ◽  
pp. 219-228 ◽  
Author(s):  
S. G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Experimental Investigations ◽  
Mean Deviation ◽  
Transfer Coefficients ◽  
Flow Boiling Heat Transfer ◽  
Dependent Parameter ◽  
Vertical Tubes

A simple correlation was developed earlier by Kandlikar (1983) for predicting saturated flow boiling heat transfer coefficients inside horizontal and vertical tubes. It was based on a model utilizing the contributions due to nucleate boiling and convective mechanisms. It incorporated a fluid-dependent parameter Ffl in the nucleate boiling term. The predictive ability of the correlation for different refrigerants was confirmed by comparing it with the recent data on R-113 by Jensen and Bensler (1986) and Khanpara et al. (1986). In the present work, the earlier correlation is further refined by expanding the data base to 5246 data points from 24 experimental investigations with ten fluids. The proposed correlation, equations (4) and (5), along with the constants given in Tables 3 and 4, gives a mean deviation of 15.9 percent with water data, and 18.8 percent with all refrigerant data, and it also predicts the correct hTP versus x trend as verified with water and R-113 data. Additional testing with recent R-22 and R-113 data yielded the lowest mean deviations among correlations tested. The proposed correlation can be extended to other fluids by evaluating the fluid-dependent parameter Ffl for that fluid from its flow boiling or pool boiling data.

scholarly journals Flow Boiling Heat Transfer in Microchannels

2006 ◽  
Vol 129 (10) ◽  
pp. 1321-1332 ◽  
Author(s):  
Dong Liu ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Transfer Coefficients ◽  
Convective Boiling ◽  
Maximum Heat ◽  
Flow Boiling Heat Transfer ◽  
Microchannel Flows ◽  
Saturated Boiling

Flow boiling heat transfer to water in microchannels is experimentally investigated. The dimensions of the microchannels considered are 275×636 and 406×1063μm2. The experiments are conducted at inlet water temperatures in the range of 67–95°C and mass fluxes of 221–1283kg∕m2s. The maximum heat flux investigated in the tests is 129W∕cm2 and the maximum exit quality is 0.2. Convective boiling heat transfer coefficients are measured and compared to predictions from existing correlations for larger channels. While an existing correlation was found to provide satisfactory prediction of the heat transfer coefficient in subcooled boiling in microchannels, saturated boiling was not well predicted by the correlations for macrochannels. A new superposition model is developed to correlate the heat transfer data in the saturated boiling regime in microchannel flows. In this model, specific features of flow boiling in microchannels are incorporated while deriving analytical solutions for the convection enhancement factor and nucleate boiling suppression factor. Good agreement with the experimental measurements indicates that this model is suitable for use in analyzing boiling heat transfer in microchannel flows.

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.

An Experimental Study on Flow Boiling Heat Transfer Outside Horizontal Enhanced Tubes

2020 ◽  
Author(s):  
Liangxiang Ma ◽  
Jianghui Zhang ◽  
Xiang Ma ◽  
Zongbao Gu ◽  
Yan He ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Outer Surface ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Smooth Tube ◽  
Flow Boiling Heat Transfer ◽  
Enhanced Tubes ◽  
Inner Surface

Abstract A flow boiling heat transfer experimental investigation on the shell-side of a smooth tube and two enhanced tubes (C-EHT, P-EHT) was performed using R410A as working fluid. The outer surface of the C-EHT tube is covered with special fins having a salient height, and the inner surface has a thread structure with the same distribution density. The outer surface of the P-EHT tube has lots of tiny pits formed by high-strength sandblasting and smooth inner surface. The inlet and outlet vapor quality is 0.2 and 0.8 at a saturation temperature of 279K. The flow boiling experimental results show that the evaporation heat transfer coefficient of C-EHT tube is the largest among the tested tubes. However, for the P-EHT tube, its heat transfer coefficient is lower than that of smooth tube. C-EHT tube with special fins has higher heat transfer area, which can also intensify the interfacial turbulence with increasing fins. The reason why the flow boiling heat transfer coefficient of the P-EHT tube is lower than that of the smooth tube is that the diameter of the pit on P-EHT tube is too small to form the nucleation cites, which results in bubble retention under the condition of low mass flux and deteriorates the flow boiling heat transfer performance.

Sign in / Sign up

Export Citation Format

Share Document