Convective Boiling Heat Transfer and Pressure Drop Characteristics of R134a in a Microfinned Helically Coiled Tube

2005 ◽  
Author(s):  
Wenzhi Cui ◽  
Longjian Li ◽  
Mingdao Xin ◽  
Qinghua Chen ◽  
Quan Liao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Annular Flow ◽  
Convective Boiling ◽  
Coiled Tube ◽  
Frictional Pressure Drop ◽  
Helically Coiled Tube

The main purpose of this paper was to experimentally study the heat transfer and pressure drop characteristics of refrigerant R134a boiling inside a new geometry microfin helically coiled tube. Experiments were performed in a range of mass quality from 0.05 up to 0.9, mass velocity 70 ∼ 380 kg/m2s and heat flux 2.0 ∼ 21.8 kW/m2. The local and average convective boiling heat transfer coefficients were reported in this paper, which were found to be dependent on both of mass flux and heat flux. Compared with corresponding smooth helically coiled tube, the microfin helically coiled tube could enhance the convective boiling heat transfer very well. The enhancement factor was up to 2.2 with the variety of mass flux and heat flux. Heat transfer in annular flow was specially studied. A flow boiling heat transfer correlation was presented for the annular flow regime, which had a mean deviation of 9.1%. The frictional pressure drop values were obtained by subtracting acceleration pressure drop and gravitational pressure drop from the measured total pressure drop. The frictional pressure drop data can be well correlated by Lockhart-Martinelli parameter. Considering the corresponding flow regimes, i.e., stratified and annular flow, two frictional pressure drop correlations were proposed, and showed a good agreement with the respective experimental data.

Numerical Investigation of Subcooled Boiling Heat Transfer in Helically-Coiled Tube

2020 ◽  
Vol 17 (1) ◽  
pp. 7675-7686
Author(s):  
Luthfi A. F. Haryoko ◽  
Jundika C. Kurnia ◽  
Agus P. Sasmito
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Operating Pressure ◽  
Subcooled Boiling ◽  
Coiled Tube ◽  
Helically Coiled Tube

Subcooled boiling heat transfer in helically-coiled tubes offers better heat transfer performance than any other types of boiling processes due to its ability to capture high heat flux with a relatively low wall superheat. This study investigates turbulent subcooled forced convection boiling performances of water-vapour in a helically-coiled tube with various operating conditions i.e. operating pressure, heat, and mass flux. Developed CFD model is validated against previously published experimental results using the RPI model. The model is developed based on the Eulerian-Eulerian framework coupled with k-ε RNG turbulence model and Standard Wall-Function. A good agreement is found between numerical prediction and experimental counterpart for the bulk fluid temperature and non-dimensional length. The result indicates that the subcooled boiling heat transfer in a helically-coiled tube tends to improve heat transfer coefficient and pressure drop in the domain. Subcooled boiling starts at the inner side of the helically-coiled tube (f=9900) due to the existence of secondary flow that comes from the coil curvature. Heat transfer coefficient and pressure drop increased with increasing heat flux and decreasing mass flux, and operating pressure. This is caused by the bubble movement and convective heat transfer phenomena in a helically-coiled tube. Finally, this study can provide a guideline for future research of the subcooled boiling in a helically-coiled tube.

Forced Convective Boiling Heat Transfer and Pressure Drop Characteristics of Two-Phase Flow Inside a Small Horizontal Helically Coiled Tubing Once-Through Steam Generator

2003 ◽  
Author(s):  
Liang Zhao ◽  
Liejin Guo ◽  
Bofeng Bai ◽  
Yucheng Hou ◽  
Ximin Zhang
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Pressure Drop ◽  
Boiling Heat Transfer ◽  
Phase Flow ◽  
Two Phase ◽  
Convective Boiling ◽  
Coiled Tube ◽  
Helically Coiled Tube

The pressure drop and boiling heat transfer of steam water two-phase flow were studied in a small horizontal helically coiled tube once-through steam generator of 9-mm inside diameter with 292-mm coil diameter and 30-mm pitch. Experiments were performed at a range of qualities up to 0.95, a system pressure range of 0.5∼3.5MPa, a mass flux range of 236∼943kg/m2s and a heat flux range of 0∼900kW/m2. Based on the experimental results, a new two-phase frictional pressure drop correlation was developed on the basis of Chisholm’s B-coefficient method. In the present experimental range, boiling heat transfer was found to be dependent not only on mass flux but also on heat flux. This result implies that both the nucleation mechanism and the convection mechanism have the same importance to forced convective boiling heat transfer in small horizontal helically coiled tube over the full range of qualities (pre-critical heat flux qualities of 0.1∼0.9) which is contrary to situations in larger helically coiled tube where the convection mechanism dominates at qualities typically > 0.1. Traditional single parameter Lockhart-Martinelli type correlations failed to satisfactorily predict present experimental data and in this paper a new flow boiling heat transfer correlation was put forward to better predict the experimental data of the present study.

Forced Convective Boiling of Refrigerant HCFC123 in a Mini-Tube

2010 ◽  
Author(s):  
Koichi Araga ◽  
Keisuke Okamoto ◽  
Keiji Murata
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Pool Boiling ◽  
Constant Heat Flux ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Convective Boiling ◽  
Frictional Pressure Drop ◽  
Heat Transfer Coefficients

This paper presents an experimental investigation of the forced convective boiling of refrigerant HCFC123 in a mini-tube. The inner diameters of the test tubes, D, were 0.51 mm and 0.30 mm. First, two-phase frictional pressure drops were measured under adiabatic conditions and compared with the correlations for conventional tubes. The frictional pressure drop data were lower than the correlation for conventional tubes. However, the data were qualitatively in accord with those for conventional tubes and were correlated in the form φL2−1/Xtt. Next, heat transfer coefficients were measured under the conditions of constant heat flux and compared with those for conventional tubes and for pool boiling. The heat transfer characteristics for mini-tubes were different from those for conventional tubes and quite complicated. The heat transfer coefficients for D = 0.51 mm increased with heat flux but were almost independent of mass flux. Although the heat transfer coefficients were higher than those for a conventional tube with D = 10.3 mm and for pool boiling in the low quality region, they decreased gradually with increasing quality. The heat transfer coefficients for D = 0.30 mm were higher than those for D = 0.51 mm and were almost independent of both mass flux and heat flux.

Effect of Inlet Restriction on Flow Boiling Heat Transfer in a Horizontal Microtube

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
YanFeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Mass Fluxes ◽  
Flow Boiling Heat Transfer ◽  
Low Mass

Flow boiling heat transfer in a horizontal microtube with inlet restriction (orifice) 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 microtubes with smaller diameters are assembled at the inlet of main microtube to achieve the restriction ratios of 50% and 20%. The experimental measurement is carried out at mass fluxes ranging from 160 to 870 kg/m2·s, heat fluxes varying from 6 to 170 kW/m2, inlet temperatures of 23 and 35 °C, and saturation pressures of 10 and 45 kPa. The effects of the orifices on two-phase pressure drop, critical heat flux (CHF), and flow boiling heat transfer coefficient are studied. The results show that the pressure drop caused by the orifice takes a considerable portion in the total pressure drop at low mass fluxes. This ratio decreases as the vapor quality or mass flux increases. The difference of normal critical heat flux in the microtubes with different orifice sizes is negligible. In the aspect of flow boiling heat transfer, the orifice is able to enhance the heat transfer at low mass flux and high saturation pressure, which indicates the contribution of orifice in the nucleate boiling dominated regime. However, the effect of orifice on flow boiling heat transfer is negligible in the forced convective boiling dominated regime.

Experimental Investigation on Flow Characteristics of Supercritical CO2 in a Helically Coiled Tube

2013 ◽  
Vol 368-370 ◽  
pp. 631-635
Author(s):  
Shu Xiang Wang ◽  
Wei Zhang ◽  
Jin Liang Xu
Keyword(s):  
Heat Flux ◽  
Fluid Flow ◽  
Mass Flux ◽  
Flow Characteristics ◽  
Experimental Investigations ◽  
Coiled Tube ◽  
Frictional Pressure Drop ◽  
Helically Coiled Tube ◽  
Coil Diameter ◽  
Fluid Flow Characteristics

Under the background of global warming, carbon dioxide among natural refrigerants has attracted considerable attention as an alternative refrigerant. In the present study, experimental investigations of the fluid flow characteristic of supercritical CO2in a helically coiled tube with the inner diameter 9.0 mm, coil diameter 283 mm and coil pitch 32 mm were carried out. Both frictional pressure drop and friction factor were obtained under the pressure of 8.0 MPa, mass flux from 0 to 600 kg/m2s and inner heat flux from 0 to 20 kW/m2. The results indicate that inner wall heat flux and mass flux had significant effects on fluid flow characteristics. The study provides experimental data that could be used for the design and development of more efficient exchangers for refrigeration conditioning, heat pump and some other systems.

scholarly journals Experimental Investigation on Flow Boiling Heat Transfer and Pressure Drop of a Low-GWP Refrigerant R1234ze(E) in a Horizontal Minichannel

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5972
Author(s):  
Yu Xu ◽  
Zihao Yan ◽  
Ling Li
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Experimental Investigation ◽  
Pressure Drop ◽  
Mass Flux ◽  
Flow Boiling ◽  
Saturation Pressure ◽  
Nucleate Boiling ◽  
Vapor Quality ◽  
Frictional Pressure Drop

To protect the environment, a new low-GWP refrigerant R1234ze(E) was created to substitute R134a. However, its flow boiling performances have not received sufficient attention so far, which hinders its popularization to some extent. In view of this, an experimental investigation was carried out in a 1.88 mm horizontal circular minichannel. The saturation pressures were maintained at 0.6 and 0.7 MPa, accompanied by mass flux within 540–870 kg/m2 s and heat flux within 25–65 kW/m2. For nucleate boiling, a larger heat flux brings about a larger heat transfer coefficient (HTC), while for convective boiling, the mass flux and vapor quality appear to take the lead role. The threshold vapor quality of different heat transfer mechanisms is around 0.4. Additionally, larger saturation pressure results in large HTC. As for the frictional pressure drop (FPD), it is positively influenced by mass flux and vapor quality, while negatively affected by saturation pressure, and the influence of heat flux is negligible. Furthermore, with the measured data, several existing correlations are compared. The results indicate that the correlations of Saitoh et al. (2007) and Müller-Steinhagen and Heck (1986) perform best on flow boiling HTC and FPD with mean absolute deviations of 5.4% and 10.9%.

A Heat Transfer Correlation of Flow Boiling In Micro-Finned Helically Coiled Tube

2005 ◽  
Author(s):  
Wenzhi Cui ◽  
Longjian Li ◽  
Mingdao Xin ◽  
Tien-Chien Jen ◽  
Qinghua Chen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Straight Tube ◽  
Heat Transfer Correlation ◽  
Convective Boiling ◽  
Coiled Tube ◽  
Helically Coiled Tube ◽  
Flow Boiling Heat Transfer

In the research of intube flow boiling, a widely accepted factor is that there are two main mechanisms participating in the heat transfer. One is nucleate boiling, which is dependent on the presence of active nuclei on the heated wall and the heat transfer coefficient is much influenced by the heat flux, much similar to pool boiling. In the other heat transfer mode, the boiling nuclei are fully suppressed and heat is transferred by the liquid evaporation through the interface of liquid film and vapor core. This is also called forced convective evaporation or convective boiling. In the evaporation region, the dependence of heat transfer on heat flux is not distinct and governed mainly by the mass flux and vapor quality. In the open literature on convective boiling heat transfer of refrigerant researches have been extensively conducted in straight tube. The studies, however, on two-phase flow boiling heat transfer in helically coiled tube are far less than that in straight tube. Because of the high efficiency in heat transfer and compactness in volume, helically coiled tubes are used extensively in practical industries. Therefore, it is important for application to obtain the correlations of flow boiling heat transfer coefficient in helically coiled tube. A new kind of micro-finned helically coiled tube was developed by the present authors and the flow boiling heat transfer characteristics are experimental studied in this paper, using R134a, an environment-friendly refrigerant as experimental fluid. By introducing convective boiling number NCB, as suggested by V. V. Klimenko (in Ref. [8]), the transition boundary between nucleate boiling and forced convective boiling in helically coiled tube is examined, which is much different with that in straight tube. Based on the analysis of the mechanisms of flow boiling, heat transfer correlation of the specific micro-finned helically coiled tubes is obtained, which has a mean absolute deviation of 13.8%.

Flow Boiling of R134a and R245fa in a 1.1 mm Diameter Tube

2013 ◽  
Author(s):  
Emily A. Pike-Wilson ◽  
Mohamed M. Mahmoud ◽  
Tassos G. Karayiannis
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Experimental Conditions ◽  
Local Flow ◽  
Flow Boiling Heat Transfer ◽  
Vapour Quality

New refrigerants are required for cooling systems due to the fact that refrigerants like R134a are about to be phased out. This paper presents a comparison between the flow boiling heat transfer and pressure drop results of refrigerants R245fa and R134a. The experiments with R245fa were conducted in a vertical cold drawn stainless steel tube with an inner diameter of 1.1 mm and heated length of 150 mm. Experimental conditions include: mass flux range 100–400 kg/m2s, heat flux range 10–60 kW/m2, pressures of 8 and 10 bar and 1.9 and 2.5 bar for R134a and R245fa corresponding to saturated temperatures 31 °C and 39 °C and exit vapour quality range 0–0.95. The data for R134a were obtained earlier using the same experimental facility at the same experimental conditions and with the same test tube. The results demonstrated that refrigerant properties have a significant effect on heat transfer and pressure drop. The pressure drop of R245fa is higher by up to 300% compared to that of R134a at similar conditions. In addition, the effect of mass flux and heat flux on the local flow boiling heat transfer coefficient was different. Heat transfer coefficients of R245fa showed a greater dependence on vapour quality. The agreement with past heat transfer correlations is better with R134a than with R245fa.

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