Prediction of heat transfer during boiling of cryogenic fluids flowing in tubes

Data from eleven sources for nitrogen, neon, helium, and argon boiling in horizontal and vertical tubes were compared with the correlations of Shah and Klimenko as well as the superposition correlation of Rohsenow. Best agreement was found with the Shah correlation which agrees with nine of the data sets. Each of the other two correlations gives satisfactory agreement with only four of the twelve data sets. The results of data analysis are presented and discussed.     

Two-phase heat transfer and pressure drop of LNG during saturated flow boiling in a horizontal tube

Two-phase heat transfer and pressure drop of LNG (liquefied natural gas) have been measured in a horizontal smooth tube with an inner diameter of 8 mm. The experiments were conducted at inlet pressures from 0.3 to 0.7 MPa with a heat flux of 8–36 kW m⁻², and mass flux of 49.2–201.8 kg m⁻² s⁻¹. The effect of vapor quality, inlet pressure, heat flux and mass flux on the heat transfer characteristic are discussed. The comparisons of the experimental data with the predicted value by existing correlations are analyzed. Zou et al. (2010) correlation shows the best accuracy with 24.1% RMS deviation among them. Moreover four frictional pressure drop methods are also chosen to compare with the experimental database.     

水平管内四氟甲烷流动沸腾传热实验研究

实验测定了四氟甲烷(R14)在内径为6 mm的水平管内两相流动沸腾传热特性.实验测试的压力范围为0.22-0.60 MPa,热流密度范围19.9-73.6 kW/m2,质量流量范围370-862 kg/m2s.实验结果表明,传热系数随质量流量的增大而有一定程度的上升,而热流密度及饱和压力与传热系数呈明显的正相关关系.将实验数据与已有文献模型的计算结果进行比较发现,Kandlikar模型、Gungor-Winterton模型以及Shah模型与实验数据的关联性较好,平均偏差均在15％以内.     

Investigation on the heat transfer characteristics during flow boiling of liquefied natural gas in a vertical micro-fin tube

This paper presents an experimental investigation on the heat transfer characteristics of liquefied natural gas flow boiling in a vertical micro-fin tube. The effect of heat flux, mass flux and inlet pressure on the flow boiling heat transfer coefficients was analyzed. The Kim, Koyama, and two kinds of Wellsandt correlations with different F_tp coefficients were used to predict the flow boiling heat transfer coefficients. The predicted results showed that the Koyama correlation was the most accurate over the range of experimental conditions.     

Experimental investigation on downward flow boiling heat transfer characteristics of propane in shell side of LNG spiral wound heat exchanger

For designing LNG spiral wound heat exchangers (SWHE), the boiling heat transfer mechanism of two-phase hydrocarbon refrigerant flowing downward in shell side should be known. In this study, an explosion-proof experimental rig was established for measuring heat transfer coefficients (HTC) and observing flow patterns. The test section contains three-layer tube bundles to emulate the actual structure and flow conditions of an SWHE. Propane as one main component of shell-side refrigerant is used as the tested fluid. The experimental conditions cover heat fluxes of 4~10 kW⋅m⁻², mass fluxes of 40~80 kg (m²⋅s)⁻¹ and vapor qualities of 0.2~1.0. The results indicate that HTC initially increases and then decreases with the increment of vapor quality, representing a maximum at a vapor quality of 0.8~0.9; the effect of heat flux on HTC increases with the increment of heat flux. A correlation of HTC was developed covering 98% of the experimental data within a deviation of ±20%.     

Flow pattern and heat transfer characteristics during flow boiling of CO2 in a horizontal micro fin tube and comparison with smooth tube data

Flow pattern observations and measurements of the heat transfer in a helical grooved micro fin tube are presented and compared with results for a smooth tube. The micro fin tube used (OD of 9.52 mm) was a Wieland Cuprofin EDX tube with 60 fins (height 0.25 mm) and a helix angle of 18°. The flow pattern observations at 39.7 bar (T_s=+5 °C, p_r=0.54) and 26.4 bar (T_s=−10 °C, p_r=0.36) show a wide range of the annular flow region. The transition from slug to annular flow does not occur, as expected, at constant vapour quality for all mass fluxes but there is an interdependence between transition vapour quality and mass flux. For the heat transfer in the micro fin tube, measurements at 39.7 bar are presented for heat fluxes up to 120 kW m⁻², mass fluxes between 75 and 250 kg m⁻² s⁻¹ and vapour qualities between 0.1 and 0.9.     

Flow boiling heat transfer coefficients at cryogenic temperatures for multi-component refrigerant mixtures of nitrogen–hydrocarbons

The recuperative heat exchanger governs the overall performance of the mixed refrigerant Joule–Thomson cryocooler. In these heat exchangers, the non-azeotropic refrigerant mixture of nitrogen–hydrocarbons undergoes boiling and condensation simultaneously at cryogenic temperature. Hence, the design of such heat exchanger is crucial. However, due to lack of empirical correlations to predict two-phase heat transfer coefficients of multi-component mixtures at low temperature, the design of such heat exchanger is difficult.The present study aims to assess the existing methods for prediction of flow boiling heat transfer coefficients. Many correlations are evaluated against available experimental data of flow boiling of refrigerant mixtures. Silver-Bell-Ghaly correlation and Granryd correlation are found to be more suitable to estimate local heat transfer coefficients. A modified Granryd correlation is recommended for further use.     

垂直管内沸腾传热实验研究

重点介绍垂直管内低过热度下沸腾传热性能的测试装置和方法、数据处理及相关计算方法。实验装置采用套管换热器模型,以蒸汽为热源,整体构成一逆流换热空间。通过测取蒸发速度、温度等相关参数,得到在不同蒸汽压力、温度下的总传热系数、沸腾传热系数与热流密度、蒸汽侧压力的关系曲线,从而得出单管在何种状态下沸腾传热性能,并对两试件(光管和高通量管)进行性能对比实验研究,比较其传热性能。     

The influence of electric field on heat transfer in a boiling cryogenic liquid

An experimental technique to investigate how an electric field affects heat transfer in boiling nitrogen is described. Experiments were performed in natural convection and nucleate boiling zones using cylindrical surfaces to simulate wires conducting a current.     

Pool boiling heat transfer of carbon dioxide on a horizontal tube

Carbon dioxide is again becoming an important refrigerant. While the thermophysical properties are well known there is a lack of data on its heat transfer characteristics.

In this study, heat transfer coefficients for nucleate boiling of carbon dioxide are determined using a standard apparatus for the investigation of pool boiling based on a set-up from Karlsruhe [D. Gorenflo, J. Goetz, K. Bier. Vorschlag für eine Standard-Apparatur zur Messung des Wärmeübergangs beim Blasensieden. Wärme-und Stoffübertragung 16 (1982), 69–78; J. Goetz, Entwicklung und Erprobung einer Normapparatur zur Messung des Wärmeübergangs beim Blasensieden. Dissertation Universität Karlsruhe (1980).] and built at our institute. Electrically heated horizontal cylinders with an outer diameter of 16 mm and a length of 100 mm are used as heating elements. Measurements with constant heat flux are performed for different wall materials and surface roughnesses. The heat transfer is investigated within the pressure range of 0.53≤ p ≤1.43 MPa (0.072≤ p/p_c ≤0.190) and a temperature range of −56≤ t ≤−30 °C, respectively. Heat fluxes of up to 80,000 W m⁻² are applied.

The influences of wall material and roughness on the heat transfer coefficient are evaluated separately. The obtained coefficients are compared to generally accepted correlations and to experimental results of other authors, who used similar configurations with copper tubes and carbon dioxide. These are the only previous experimental data, which could be found. Results for copper, stainless steel and aluminium as wall materials are presented.     

Phase slip and heat transfer to the liquid in film boiling of a cryogenic liquid in piston flow

Published data are examined and results are given from a survey of experiments on phase slip and heat transfer to liquids.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 3, pp. 442–448, September, 1980.     

Flow boiling heat transfer in microgravity: Recent results

Flow boiling heat transfer (FBHT) allows high performance heat transfer due to latent heat transportation and its use is therefore important to reduce size and weight of space platforms and satellites. Its knowledge is also important for the safe operation of existing single-phase systems in case of accidental increase of heat generation rate. The number of existing researches on flow boiling in reduced gravity is very small due to both larger heat loads and available room in a 0-g apparatus for experiments. Consequently, coherence in existing data is somewhat missing. This lecture will summarize the results of the few research carried out on FBHT in microgravity, with special emphasis to the recent research carried out at ENEA, in the frame of an ESA (European Space Agency) project.     

Forced convection heat transfer to boiling helium in a tube

This paper describes a study carried out to obtain the heat transfer characteristics of liquid helium l in a vertical tube under forced convection conditions. The test section was a straight stainless-steel tube with a length of 8.5 cm and an id of 0.109 cm. Helium pressures ranged from 1.1 to 1.9 atm (0.11 to 0.19 MN m^?2) and qualities (vapour mass fractions) ranged from zero to 1.Results were correlated using conventional equations and compared with the data already obtained. The hysteresis observed in the nucleate boiling region is qualitatively discussed. The quality dependence of two-phase flow heat transfer was clearly observed during an increase, but not during a decrease, of heat flux or quality.     

Heat transfer intensity at forced flow boiling of cryogenic liquids in tubes

A generalized correlation for heat transfer with forced flow boiling of cryogenic liquids (nitrogen, hydrogen and neon) in tubes is presented. The correlation describes, with a ± 35% accuracy, all known experimental data for vertical and horizontal channels (without stratified regimes) in the pressure range 0.9 – 22 bar, mass flow rates from 20 to 2200 kg m^?2 S^?1, and heat fluxes from 400 to 210 000 W m^?2. The boundary line between channels of a large and a small diameter has been established; a simple method of taking into account the higher heat transfer intensity in capillaries has been suggested.     

Unsteady free-convection heat transfer during vortex flow in a horizontal tube

We conducted a theoretical and experimental investigation of the hydrodynamic structure and unsteady free-convection heat transfer in a round horizontal tube under different conditions of the second kind. During the experiment the Grashof number varied from Gr=1.54·10⁵ to Gr=7.9·10⁵. Using the interferometric method we investigated the distribution of the temperature field for different structures of free-convection flow in the tube.Academic Scientific Complex A. V. Luikov Heat and Mass Transfer Institute of the Academy of Sciences of Belarus, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 1, pp. 3–8, January–February, 1995.     

Effect of tube diameter on boiling heat transfer and flow characteristic of refrigerant R32 in horizontal small-diameter tubes

This study investigated the effect of tube diameter on flow boiling characteristics of refrigerant R32 in horizontal small-diameter tubes with 1.0, 2.2, and 3.5 mm inner diameters. The boiling heat transfer coefficient and pressure drop were measured at 15 °C saturation temperature. The effects of mass velocity, heat flux, quality, and tube diameter were clarified. The flow pattern of R32 for adiabatic two-phase flow in a horizontal glass tube with an inner diameter of 3.5 mm at saturation temperature of 15 °C was investigated. Flow patterns such as plug, wavy, churn, and annular flows were observed. The heat transfer mechanisms of forced convection and nucleate boiling were similar to those in conventional-diameter tubes. In addition, evaporation heat transfer through a thin liquid film in the plug flow region for low quality, mass velocity, and heat flux was observed. The heat transfer coefficient increased with decreasing tube diameter under the same experimental condition. The fictional pressure drop increased with increasing mass velocity and quality and decreasing tube diameter. The experimental values of the heat transfer coefficient and frictional pressure drop were compared with the values calculated by the empirical correlations in the open literature.     

Flow boiling heat transfer of carbon dioxide with PAG-type lubricating oil in pre-dryout region inside horizontal tube

A flow boiling heat transfer model for horizontal tubes is proposed for CO₂ with entrained polyalkylene glycol (PAG) type lubricating oil in the pre-dryout region. A general power law-type model with a power number of 3 is used together with the average thermodynamic properties of the CO₂–oil mixture. A convective enhancement factor (F) is recommended according to the relationship between the Lockhart–Martinelli parameter and the ratio α_tp/α_l, which was obtained based on previous experimental results for CO₂ and oil. A new suppression factor (S) is introduced that comprises a suppression term for forced convection and oil concentration term for bubble generation. A comparison of six correlations showed that the proposed correlation can depict the influence of the mass and heat fluxes on both nucleate and convection boiling reasonably well.     

An experimental study on flow patterns and heat transfer characteristics during cryogenic chilldown in a vertical pipe

In the present paper, the experimental results of a cryogenic chilldown process are reported. The physical phenomena involve unsteady two-phase vapor–liquid flow and intense boiling heat transfer of the cryogenic fluid that is coupled with the transient heat conduction inside pipe walls. The objective for the present study is to compare the chilldown rates and flow patterns between the upward flow and downward flow in a vertical pipe. Liquid nitrogen is employed as the working fluid and the test section is a vertical straight segment of a Pyrex glass pipe with an inner diameter of 8 mm. The effects of mass flow rate on the flow patterns, heat transfer characteristics and interface movement were determined through experiments performed under several different mass flow rates. Through flow visualization, measurement and analysis on the flow patterns and temperature variations, a physical explanation of the vertical chilldown is given. By observing the process and analyzing the results, it is concluded that pipe chilldown in a vertical flow is similar to that in microgravity to some extent.     

Flow structure and heat transfer during the separation of a pulsating flow

The results of experimental studies of heat transfer in the separation region and the kinematic structure of the air flow in a channel behind a rib under superimposed discharge pulsations are presented. The effect of heat transfer enhancement of up to1.5 times in comparison with the stationary regime has been established. In the near wake behind the obstacle, it was up to five times. An observable decrease in the reat-tachment length (of up to two times) has been revealed under the pulsating flow regimes. The mechanism of these phenomena has been established, and typical features of the structure of pulsating separated flows have been described on the basis of the results of visualization experiments. The classification of these flows is proposed, and a regime map has been drawn up.