Nucleate Boiling Performance of Refrigerants and Refrigerant-Oil Mixtures

1980 ◽  
Vol 102 (4) ◽  
pp. 701-705 ◽  
Author(s):  
S. Chongrungreong ◽  
H. J. Sauer
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Significant Influence ◽  
Correlation Equation ◽  
Nucleate Boiling ◽  
Experimental Results ◽  
General Correlation ◽  
Oil Mixtures ◽  
The Heat Transfer Coefficient

Current and previous studies by the authors and others have shown shown that the carryover of oil in refrigeration systems can have a significant influence on the boiling performance in the evaporator of refrigeration systems. This investigation was conducted primarily to develop a general correlation equation for predicting the heat transfer coefficient for refrigerants and refrigerant-oil mixtures under pool boiling conditions. Experimental results were obtained to establish the validity of the correlation equation.

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.

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.

Natural Heat Transfer Coefficients of Chicken Drum Shaped Bodies

2005 ◽  
Vol 1 (3) ◽  
Author(s):  
Michael Ngadi ◽  
Julian N. Ikediala
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Correlation Equation ◽  
Deep Fat Frying ◽  
Heat Transfer Correlation ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Increasing Temperature ◽  
The Heat Transfer Coefficient

Average heat transfer coefficients of chicken drum shaped bodies were estimated using aluminum chicken drum shaped models. Three model drum sizes namely small, medium and large, and three frying oil viscosities for three temperature differences were used. Estimated heat transfer coefficients were in the range from 67 to 163 W/m²K. Increasing temperature difference increased heat transfer coefficient. Conversely, increasing the size of the chicken drum model bodies and oil viscosities decreased the heat transfer coefficient. A heat transfer correlation equation between average Nu and Ra was derived. The methodology developed in this study could be used to estimate heat transfer coefficients of chicken drum during deep-fat frying.

Prediction of the Heat Transfer Coefficient in a Small Channel with the Superposition and Asymptotic Correlations

2018 ◽  
Vol 26 (01) ◽  
pp. 1850001
Author(s):  
Yushazaziah Mohd-Yunos ◽  
Normah Mohd-Ghazali ◽  
Maziah Mohamad ◽  
Agus Sunjarianto Pamitran ◽  
Jong-Taek Oh
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Experimental Work ◽  
Nucleate Boiling ◽  
Vapor Quality ◽  
Two Phase ◽  
Forced Convective Heat Transfer ◽  
Small Channel ◽  
The Heat Transfer Coefficient

Heat transfer coefficient as an important characteristic in heat exchanger design is determined by the correlation developed from previous experimental work or accumulation of published data. Although discrepancies still exist between the existing correlations and practical data, several researchers claimed theirs as a generalized heat transfer correlation. Through optimization method, this study predicts the heat transfer coefficient of two-phase flow of propane in a small channel at the saturation temperature of 10[Formula: see text]C using two categories of correlation — superposition and asymptotic. Both methods consist of the contribution of nucleate boiling and forced convective heat transfer, the mechanisms that contribute to the total two-phase heat transfer coefficient, which become as two objective functions to be maximized. The optimization of experimental parameters of heat flux, mass flux, channel diameter and vapor quality is done by using genetic algorithm within a range of 5–20[Formula: see text]kW/m2, 100–250[Formula: see text]kg/m2[Formula: see text]s, 1.5–3[Formula: see text]mm and 0.009–0.99, respectively. In the result, the selected correlations under optimized condition agreed on the dominant mechanism at low and high vapor qualities are caused by the nucleate boiling and forced convective heat transfer, respectively. The optimization work served as an alternative approach in identifying optimized parameters from different correlations to achieve high heat transfer coefficient by giving a fast prediction of parameter range, particularly for the investigation of any new refrigerant. In parallel with some experimental works, a quick prediction is possible to reduce time and cost. From the four selected generalized correlations, Bertsch et al. show the closer trend with the reference experimental work until vapor quality of 0.6.

Finned Metal Foam Heat Sinks for Electronics Cooling in Forced Convection

2002 ◽  
Vol 124 (3) ◽  
pp. 155-163 ◽  
Author(s):  
A. Bhattacharya ◽  
R. L. Mahajan
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Forced Convection ◽  
Metal Foam ◽  
Experimental Results ◽  
Heat Sinks ◽  
The Heat Transfer Coefficient

In this paper, we present recent experimental results on forced convective heat transfer in novel finned metal foam heat sinks. Experiments were conducted on aluminum foams of 90 percent porosity and pore size corresponding to 5 PPI (200 PPM) and 20 PPI (800 PPM) with one, two, four and six fins, where PPI (PPM) stands for pores per inch (pores per meter) and is a measure of the pore density of the porous medium. All of these heat sinks were fabricated in-house. The forced convection results show that heat transfer is significantly enhanced when fins are incorporated in metal foam. The heat transfer coefficient increases with increase in the number of fins until adding more fins retards heat transfer due to interference of thermal boundary layers. For the 20 PPI samples, this maximum was reached for four fins. For the 5 PPI heat sinks, the trends were found to be similar to those for the 20 PPI heat sinks. However, due to larger pore sizes, the pressure drop encountered is much lower at a particular air velocity. As a result, for a given pressure drop, the heat transfer coefficient is higher compared to the 20 PPI heat sink. For example, at a Δp of 105 Pa, the heat transfer coefficients were found to be 1169W/m2-K and 995W/m2-K for the 5 PPI and 20 PPI 4-finned heat sinks, respectively. The finned metal foam heat sinks outperform the longitudinal finned and normal metal foam heat sinks by a factor between 1.5 and 2, respectively. Finally, an analytical expression is formulated based on flow through an open channel and incorporating the effects of thermal dispersion and interfacial heat transfer between the solid and fluid phases of the porous medium. The agreement of the proposed relation with the experimental results is promising.

Effects of Non-Condensable Gas on Characteristics of Natural Circulation Flow of Isolation Condenser

2021 ◽  
Author(s):  
Tetsuya Takada ◽  
Yasunori Yamamoto ◽  
Kosuke Ono
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Natural Circulation ◽  
Nucleate Boiling ◽  
Hydrogen Effect ◽  
Heat Transfer Tube ◽  
System Pressure ◽  
Transfer Tube ◽  
The Heat Transfer Coefficient

Abstract An isolation condenser (IC) is a passive core cooling system in boiling water reactors. The cooling performance of IC is deteriorated when hydrogen generated in the core flows into the IC pipes. In this study, we conducted high pressure experiments using natural circulation loop with non-condensable gas injection, where helium was used to simulate hydrogen effect on the IC. The reaching distance of steam in the heat transfer tube was estimated by observing the region where nucleate boiling occurred on the outer surface of the heat transfer tube, and the heat transfer coefficient was estimated. The heat transfer coefficient hardly changed when helium was injected to the loop that indicates injected helium was not accumulated in the heat transfer tube. The system pressure at quasi-steady state increased with increasing amount of the injected helium. Since the differential pressure at the down comer section increased by helium injection, the injected helium may be accumulated in the section, leading to increment of the system pressure.

Experimental Study on Flow Boiling of HFE-7100 in Wavy Copper Microchannels

2020 ◽  
Author(s):  
Peilin Cui ◽  
Zhenyu Liu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Thin Liquid Film ◽  
Bubbly Flow ◽  
Nucleate Boiling ◽  
Inlet Temperature ◽  
The Heat Transfer Coefficient

Abstract This study experimentally investigated the flow boiling of HFE-7100 in wavy copper microchannel heat sink (20 mm × 10 mm), which was fabricated with the ultrafast laser micromachining approach, consisting of 20 wavy microchannels with wavelength of 2000 μm and wave amplitude of 100 μm with triangular cross section (200 μm × 573 μm). The experiment was conducted with the mass fluxes of 330.07–550.11 kg/(m2·s) and heat flux of 14.5–411.3 kW/m2 at an inlet temperature of 15°C. Four flow patterns including bubbly flow, slug flow, churn flow and annular flow were captured with the visualization technique. Several confined bubbles with irregular shape were observed. In the low heat flux region, the dominant flow regime of heat transfer in the microchannels is the nucleate boiling and the heat transfer coefficient increases with increasing heat flux. With the nucleate boiling suppressed gradually, the evaporation of thin liquid film begins to dominate and the heat transfer coefficient decreases with the increase of heat flux. The heat flux has a significant effect on heat transfer coefficient compared with the mass flux and vapor quality.

scholarly journals Flow Boiling in a 1.1 mm Tube With R134A: Experimental Results and Comparison With Model

2007 ◽  
Author(s):  
D. Shiferaw ◽  
T. G. Karayiannis ◽  
D. B. R. Kenning
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Film Thickness ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Flow Boiling ◽  
Experimental Results ◽  
Vapour Quality ◽  
The Heat Transfer Coefficient

A detailed comparison of the three-zone evaporation model, proposed by Thome et al. (2004), with experimental heat transfer results of two stainless steel tubes of internal diameter 4.26 mm and 2.01 mm using R134a fluid was presented by Shiferaw et al. (2006). In the current paper the comparison is extended to flow boiling in a 1.1 mm tube using R134a as the working fluid. Other parameters were varied in the range: mass flux 100–600 kg/m2.s; heat flux 16–150 kW/m2 and pressure 6–12 bar. The experimental results demonstrate that the heat transfer coefficient increases with heat flux and system pressure, but does not change with vapour quality when the quality is less than about 50% for low heat and mass flux values. The effect of mass flux is observed to be insignificant. For vapour quality values greater than 50% and at high heat flux values, the heat transfer coefficient does not depend on heat flux and decreases with vapour quality. This could be caused by partial dryout. The three-zone evaporation model predicts the experimental results fairly well, especially at relatively low pressure. However, the partial dryout region is highly over-predicted by the model. The sensitivity of the performance of the model to the three optimized parameters (confined bubble frequency, initial film thickness and end film thickness) and some preliminary investigation relating the critical film thickness for dryout to measured tube roughness are also discussed.

scholarly journals Convective Bubbly Flow of Water in an Annular Pipe: Role of Total Dissolved Solids on Heat Transfer Characteristics and Bubble Formation

Water ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 1566 ◽  
Author(s):  
M. M. Sarafraz ◽  
M. S. Shadloo ◽  
Zhe Tian ◽  
Iskander Tlili ◽  
Tawfeeq Abdullah Alkanhal ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Contact Angle ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Rate ◽  
Bubble Diameter ◽  
Nucleate Boiling ◽  
Heat Transfer Characteristics ◽  
The Heat Transfer Coefficient

Formation of bubbles in water inside an annulus pipe in a flow boiling regime was experimentally investigated. The effect of various variables, such as total dissolved solid materials (TDS) in terms of mass fraction, flow rate of water, and applied heat flux (HF) on the heat transfer coefficient (HTC) and bubble behavior of water, was experimentally investigated. A regression formula was fitted to estimate the average bubble diameter at various TDS values, with accuracy of <4.1% up to heat flux of 90 kW/m2. Results show that the presence of TDS materials can increase the contact angle of bubble and bubble diameter, and also promotes the HTC value of the system. However, flow rate of water suppressed bubble generation, and increased the heat transfer coefficient due to the renewal of the thermal boundary layer around the boiling surface. Likewise, it was identified that forced convective and nucleate boiling heat transfer mechanisms contribute to the flow of boiling water, and heat flux is a key parameter in determining the mechanism of heat transfer. In the present study, heat flux of 15 kW/m2 at 50 °C was the heat flux in which onset of nucleate boiling was identified inside the annulus pipe. The contact angle of water at TDS values of 300 mg/L and 1200 mg/L was 74° and 124°, respectively, showing the improvement in heat transfer characteristics of water due to the presence of TDS materials.

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