Forced Convection Boiling Heat Transfer Research Articles

The characteristics of forced convective boiling heat transfer of ammonia in microchannel heat exchanger

The characteristics of forced convective boiling heat transfer of ammonia in microchannel heat exchanger

Forced convection boiling heat transfer inside helically-coiled heat exchanger

For decades, forced convection boiling heat transfer has been considered as one of the most efficient type in the heat transfer mechanism. It has been widely utilized in heat transfer equipment of various industries. Meanwhile, helically-coiled heat exchanger has been commonly utilized in numerous industrial applications. Thus, there is an interest to utilize forced convection boiling heat transfer in helically-coiled heat exchanger. Boiling phenomenon inside helically-coiled tube is more complex as compared to the straight tube due to the secondary flow induced by centrifugal force. This study investigates flow boiling heat transfer performance of water-vapor inside helically-coiled tube by using computational fluid dynamic approach. A Eulerian-Eulerian two-fluid model is used to capture interphase exchange forces and heat transfer between liquid and vapor phase. Wall boiling model is adopted to take into account the boiling condition in the vicinity of the wall. The developed model is then validated against the previously published experimental data. Good agreement for the outlet vapor quality and pressure drop between numerical study and experimental measured value is achieved. The result reveals that the boiling starts at the inner wall of the tube (φ=450°) due to the presence of secondary flow induced by coil curvature. The relationship between HTC and vapor quality along the helically-coiled tube are discussed and evaluated. This study serves as a guideline for future study on forced convection boiling heat transfer in the helically-coiled tube.

Evaluation of forced convective boiling heat transfer with layered parallel microchannels

Evaluation of forced convective boiling heat transfer with layered parallel microchannels

Experimental investigation of flow boiling heat transfer performance in zigzag microchannel heat sink for electronic cooling devices

This study proposes an improved microchannel heat sink with offset zigzag cavities to enhance boiling performance. Flow and heat transfer characteristics are experimentally investigated via a microscale boiling heat transfer visualization system using acetone as the working fluid. At mass fluxes of 285, 402, and 684 kg/(m2·s) and heat fluxes of 1.31–80.26 W/cm2, the effects of heat and mass fluxes on flow pattern, heat transfer, wall temperature, and pressure drop of zigzag microchannel heat sink are analyzed and compared with conventional rectangle microchannel heat sink. Results show that the fluctuating amplitude first increases and then decreases with the increment of heat fluxes, thereby causing a quasi-steady and unstable boiling with small fluctuations. Instability becomes increasingly severe for the nucleate boiling area moves toward the inlet and flow reversal intensity increases with heat fluxes under low heat flux. With heat flux increased furtherly. The proportion of steam in the channel increases to reduce fluctuations. Compared with the rectangular microchannel, the zigzag microchannel evidently enhances heat transfer characteristic with lower wall temperature at the onset of nucleate boiling (ONB), higher heat transfer coefficient (HTC) and critical heat flux (CHF) and improves boiling stability by suppressing flow reversal and reducing two-phase pressure drop. The mechanism of zigzag microchannel enhancement boiling performance can be attributed to (1) the improved disturbance of the working fluid, which enhances forced convective boiling heat transfer and mitigates bubble coalescence and flow reversal strength; (2) the continuously developing liquid film and improved wettability maintain a stable liquid film evaporation and delay partial dry out. Increase in mass flux can improve CHF and reduce pressure drop albeit with high wall temperature of ONB. The local HTC is enhanced, except for the low heat fluxes, because the bubbles are condensed by liquid and cannot grow to absorb heat at low heat fluxes.

Enhancement of Forced Convection Subcooled Film Boiling Heat Transfer Using Gas Sheet Collapse by Electric Field Application

Enhancement of forced-convection boiling heat transfer by electric field is investigated experimentally. When a high-temperature horizontal filament is immersed in water, a gas sheet is formed around and the above filament due to liquid boiling, in the early immersion process. This gas-sheet markedly decreases the boiling cooling rate of the filament. Here, forced collapse of the gas sheet is attempted by imposing an electric field to enhance the boiling cooling rate, In the experiments, a horizontal platinum wire of 0.5[Formula: see text]mm in diameter is immersed in pure water under atmospheric pressure, and a DC voltage up to 600[Formula: see text]V is applied between the wire surface and an electrode made of glass placed 10[Formula: see text]mm apart. The whole boiling curve is measured under different applied voltages and wire-falling velocities in 0.5 to 2.0[Formula: see text]m/s range, and at subcooling of 60[Formula: see text]K. The experimental results show that the electric field is effective in promoting the disintegration of the gas sheet. Under the tested conditions, boiling cooling rate increased two-fold for an applied electric field of 600[Formula: see text]V/cm. This result shows that the use of an electric field to break up the gas-sheet has resulted in a remarkable increase in the cooling rate at high superheats during initial cooling period, which is even greater than that used in the existing material manufacturing processes by the rapid cooling method, and therefore, this method may contribute to developing new materials.

A221 パワーモジュール向け強制流動沸騰冷却における旋回流による伝熱促進の検討

A221 パワーモジュール向け強制流動沸騰冷却における旋回流による伝熱促進の検討

Mechanistic Multidimensional Modeling of Forced Convection Boiling Heat Transfer

Due to the importance of boiling heat transfer in general, and boiling crisis in particular, for the analysis of operation and safety of both nuclear reactors and conventional thermal power systems, extensive efforts have been made in the past to develop a variety of methods and tools to evaluate the boiling heat transfer coefficient and to assess the onset of temperature excursion and critical heat flux (CHF) at various operating conditions of boiling channels. The objective of this paper is to present mathematical modeling concepts behind the development of mechanistic multidimensional models of low-quality forced convection boiling, including the mechanisms leading to temperature excursion and the onset of CHF.

2618 臨界圧近傍における二酸化炭素の細管内強制対流沸騰熱伝達(S32 高効率ヒートポンプの要素技術とその応用,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

2618 臨界圧近傍における二酸化炭素の細管内強制対流沸騰熱伝達(S32 高効率ヒートポンプの要素技術とその応用,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

D223 臨界圧近傍における二酸化炭素の水平管内強制対流沸騰熱伝達(管内沸騰・凝縮)

D223 臨界圧近傍における二酸化炭素の水平管内強制対流沸騰熱伝達(管内沸騰・凝縮)

1204 マイクロチャンネルにおける二酸化炭素の強制対流沸騰熱伝達(GS-6 強制対流・沸騰,研究発表講演)

1204 マイクロチャンネルにおける二酸化炭素の強制対流沸騰熱伝達(GS-6 強制対流・沸騰,研究発表講演)

Prediction of forced convective boiling heat transfer coefficient of pure refrigerants and binary refrigerant mixtures inside a horizontal tube

Forced convective boiling heat transfer coefficients were predicted for an annular flow inside a horizontal tube for pure refrigerants and nonazeotropic binary refrigerant mixtures. The heat transfer coefficients were calculated based on the turbulent temperature profile in liquid film and vapor core considering the composition difference in vapor and liquid phases, and the nonlinearity in mixing rules for the calculation of mixture properties. The heat transfer coefficients of pure refrigerants were estimated within a standard deviation of 14% compared with available experimental data. For nonazeotropic binary refrigerant mixtures, prediction of the heat transfer coefficients was made with a standard deviation of 18%. The heat transfer coefficients of refrigerant mixtures were lower than linearly interpolated values calculated from the heat transfer coefficients of pure refrigerants. This degradation was represented by several factors such as the difference between the liquid and the overall compositions, the conductivity ratio and the viscosity ratio of both components in refrigerant mixtures. The temperature change due to the concentration gradient was a major factor for the heat transfer degradation and the mass flux itself at the interface had a minor effect.

Forced Convective Boiling of a Fluorocarbon Liquid in Reduced Size Channels--an Experimental Study

The present paper reports the results of an experimental study of forced convection boiling heat transfer from a 2 cm x 2 cm simulated chip to a fluorocarbon coolant (FX-3250) in a parallel-plate channel. The experimental parameters were the channel height (1 and 5 mm), the surface geometry of the simulated chip (flat and microfinned), and the coolant velocity (0.125-4 m/s). Longitudinal microfins (0.5 mm high x 0.5 mm wide) on the finned chip increased the actual surface area to about twice that of the flat surface. Attention was focused on the data of the 1-mm high channel. When compared with the flat chip data on the footprint area basis, the microfins produced 40% of heat transfer enhancement at coolant velocities less than 1 m/s; however, the enhancement diminishes at higher velocities. The boiling curves of the finned chip, based on the actual area, seem to reflect that there is an effect due to the bypassing of flow through the cross-section over the fins. For both the flat chip and the finned chip...

The Influence of Vapor Bubble Sliding on Forced Convection Boiling Heat Transfer

This paper describes experimental efforts aimed at examining the effect of vapor bubble sliding on forced convection boiling heat transfer. Flow boiling experiments using FC-87 were conducted for vertical upflow and downflow configurations. Both slightly subcooled single-phase and saturated annular flow boiling were considered. Significantly higher heat transfer rates were measured for vertical upflow than for downflow with the same wall superheat and slightly subcooled single-phase inlet conditions. This increase in heat transfer is directly attributable to sliding vapor bubbles, which remain attached to the wall during upflow and lift off the wall during downflow. Differences in the measured upflow and downflow heat transfer rates are not as significant for annular flow boiling, which is due in part to the similar vapor bubble dynamics which have been observed for upflow and downflow. Heat transfer experiments in single-phase subcooled upflow with air bubble injection at the heating surface suggest that sliding bubbles enhance the bulk liquid turbulence at the wall, which contributes significantly to the macroscale heat transfer. It is concluded from this work that vapor bubble sliding heat transport can be a significant heat transfer mechanism, and should be considered in the development of mechanistic flow boiling heat transfer models.

Boiling heat transfer in small horizontal tube bundles at low cross-flow velocities

An experimental investigation has been carried out to determine the local forced convective boiling heat transfer coefficient in small tube bundles consisting of horizontal tubes in a vertical column arranged in a large channel under low cross-flow velocities in saturated distilled water at atmospheric pressure. The effects of the impressed heat flux, cross-flow velocity and tube geometry on the heat transfer characteristics have been investigated. While no significant effect of the bundle geometry was observed on the heat transfer coefficient of the bottom tube compared to that of the single tube, vapour bubbles rising from the lower tubes and agitating the liquid around the upper tubes were found to yield higher values for heat transfer coefficients on the upper tubes. A Chen-type relation has been used to correlate the data on local forced convective heat transfer coefficients of upper tubes with reasonably accuracy.

A Correlation for Forced Convective Boiling Heat Transfer of Binary Refrigerant Mixtures.

A correlation, which does not involve any empirical constants dependent on refrigerants, is developed for forced convective boiling heat transfer inside a smooth tube. The correlation is based on the model where the heat transfer coefficient of a mixture is lower than that of the equivalent pure fluid due to the mixture effects on nucleate boiling and to the heat transfer resistance in the vapor phase. The predicted heat transfer coefficients agreed with the experimental data with mean deviation of 5.9 and 6.5% for pure refrigerants (R11, R114, R123, R12) and binary mixtures (R11/R114, R123/R134a, R11/R12), respectively.

Heat Transfer Characteristics of an Earth Probe Model for a Ground-Source Heat Pump. Experiments on Forced Convection Boiling Heat Transfer in a Vertical Double Tube:the Case of Small Flow Rate.

An experimental investigation was conducted to determine the heat transfer characteristics of HCFC-22 for a two-phase double tube connected to a heat pump. This study focussed on the forced convection boiling heat transfer of small flow rate in a double tube. It was clarified that the quality at the dry-out point increases as mass velocity increases, and that the heat transfer coefficient of two-phase flow is about 30 times as large as that of the liquid single-phase laminar flow. Furthermore, it was found that the heat transfer performance of the double tube is superior to that of a single tube.

Experimental results of maximum transition boiling temperature during upflow in a circular tube at medium pressure

Temperature-controlled measurements of forced convective boiling heat transfer during upflow of water in a vertically mounted short circular tube were performed between saturation and 400°C wall temperature. From these experimental results, 343 data points of the maximum transition boiling temperature, which corresponds to the minimum heat flux condition, were deduced. The parametric effects of pressure (range 0.11–1.2 MPa), local quality (−0.04–0.8), mass flux [10−1000 kg/(m 2·s)], and inlet subcolling (5–57 K) as comprised in these data are discussed. The present data are compared with experimental data and correlations of the true quench temperature available from the literature. Extrapolating the data to zero flow and comparing the resultant pseudodata with pertinent theories and experimental data for the minimum film boiling temperature reveals fair agreement over the entire pressure range with recent data by Sakurai et al, only.

Boiling heat transfer to an impinging jet spurted into a narrow space. (1st report Space with an open end)

An experimental study has been made on the forced convection boiling heat transfer in a narrow space The heated surface diameter was 20.0mm. The distance between the nozzle plate and the heated surface was changed within a range from 0.3 mm to 0.6 mm and the nozzle diameter was 2.2 mm. Saturated water was impinged on the center of the heated surface and flowed radially on it. In this report the nozzle plate had a flat bottom which was parallel to the heated surface. It is clarified in the present study that heat transfer characteristics varied with the change of space and mass flow-rate of the impinging jet, especially in the region of transition boiling. The quantity of maximum heat flux increased as the space decreased.

Correlation of forced convection boiling heat transfer data

The method of superposition for correlating forced convection boiling heat transfer data is extended to cover subcooled to high quality ranges using single phase and two phase forced convection equations, a pool boiling equation, and an incipient boiling criterion. Only one empirically determined coefficient is needed. Agreement with water data is better than that provided by the Chen correlation.

An alternate to the Dengler and Addoms convection concept of forced convection boiling heat transfer

AbstractCurrent literature describes forced convecting, boiling heat transfer as primarily convective heat transfer. The original evidence for this concept, reported by Dengler and Addoms, was reexamined and found misinterpreted. Nucleate boiling data, instead, correlate with their data. Subsequent use of the concept in correlations and models now requires close scrutiny.