Subcooled Flow Boiling Heat Transfer Research Articles

Experimental study on sub-cooled flow boiling heat transfer in inclined non-uniform heating tube bundle channel

Since the specific structure of the U-tube, non-uniform heating (NUH) occurs on the shell side of the U-tube steam generator or exchanger. When the above equipment are applied in ocean environments, they may be in an inclined condition. The coupled conditions of NUH and incline can enhance the complexity of the heat transfer on the shell side, especially in terms of the sub-cooled flow boiling, during which the heat transfer mechanism changes. In this paper, sub-cooled flow boiling in a tube bundle channel under the coupled conditions of NUH and incline are performed experimentally. The result shows that the Gungor-Winterson correlation is in good agreement with the experimental data under uniform heating (UH) conditions and the mean relative error is only about 10.05%, while the predicted ability is poor under the coupled conditions of NUH and incline. The heat transfer characteristics are affected by radial heat and mass transfer, convective flow, bubbles behavior, and bubbles migration, which are introduced by the coupled action of NUH and incline. At last, an improved Gungor-Winterson correlation is proposed for UH, NUH, and inclined NUH conditions. Its average relative error is only 5.56% in total, and less than 0.91% of data has a larger deviation than 15%.

Experimental investigation of surface finishing technique impact on subcooled flow boiling heat transfer enhancement: sandpapering and sandblasting

Experimental investigation of surface finishing technique impact on subcooled flow boiling heat transfer enhancement: sandpapering and sandblasting

Forced convective and sub-cooled flow boiling heat transfer in a hypervapotron heat sink under one-side heating condition

Several studies have been conducted on hypervapotron (HV) cooling channels for the application of the fusion tokamak cooling system; however, most of them have focused on the critical heat flux (CHF). To predict the thermal efficiency of the tokamak system of a DEMO or commercial plant, it is necessary to predict the heat transfer performance of the HV. Therefore, in this study, the heat transfer characteristics of a one-side heated hypervapotron cooling channel under subcooled flow conditions were analysed. The subcooled flow boiling experiment was conducted as a method of gradually increasing the applied heat, and the heat transfer performance in all flow regimes from the single-phase regime to the CHF was measured. In subcooled flow boiling, it was found that three flow regimes exist: the single-phase (SP), partially developed nucleate boiling (PDB), and fully developed nucleate boiling (FDB) regimes. Additionally, we analysed different heat transfer mechanisms for each flow regime. The effects of system parameters such as the system pressure, sub-cooling, and mass flow rate on heat transfer were analysed, and the prediction performance of existing heat transfer correlations developed for application to the three flow regimes was evaluated. However, it was difficult to find a correlation reflecting the heat transfer performance enhanced by the fin structure of the HV, and the authors of this study developed heat transfer correlations using Python code and an artificial intelligence regression method

Investigation on subcooled flow boiling heat transfer characteristics in ICE-like conditions

AbstractThe increasing demand of cooling in internal combustion engine (ICE) may require the shift of heat removal method from traditional single phase liquid convection to subcooled flow boiling in order to fulfill the desired functional temperature. Thus, the characteristics of subcooled flow boiling heat transfer should be studied exclusively considering the practical conditions in ICEs. Accordingly, in this article, subcooled flow boiling experiments were conducted in a rectangular channel using 50/50 volume mixture of ethylene glycol and water coolant (EG/W) as working fluid. Aluminum and cast iron surfaces were selected as the heated surfaces to simulate the material of cylinder head in gasoline and diesel engines, respectively. Experimental results showed a trend that the aluminum surface had a better performance than the cast iron surface in terms of heat transfer coefficient in the boiling region. The difference between these two surfaces was concluded as results of different surface thermophysical properties. A modified wall heat flux model was proposed based on the power-type addition method. The proposed model modified the nucleation boiling contribution by introducing a new parameter which accounts for the influence of thermophysical properties of heated surface on the boiling process. Thus, one such modified model could be useful for practical engine cooling applications.

Performance enhancement of subcooled flow boiling on graphene nanostructured surfaces with tunable wettability

Modifying the surface wettability at the solid-liquid interface can significantly improve flow boiling heat transfer. The graphene nanoplatelets (GNPs) and epoxy additives form nanocomposites coatings with tunable wettability (superhydrophilic, superhydrophobic and hydrophobic) via a thermal curing process. They are applied for enhancing the subcooled flow boiling heat transfer in a minichannel. By comparing with the uncoated surface, the superhydrophilic GNPs coating shows the highest boiling heat transfer coefficient with a maximum enhancement of 64.9 %. The nanocapillary-networks of the superhydrophilic GNPs coatings facilitate the fast water permeation effect and induce an effective filmwise boiling heat transfer. Moreover, the superhydrophilic GNPs coatings facilitate bubble detachment process and suppress the formation of dry spot during the boiling process. On the contrary, the hydrophobic and superhydrophobic GNPs coatings act as impervious blankets for the intercalation of water and deteriorate the flow boiling rates. The effects of the subcooled degree and the mass flux of the bulk flow on the performance enhancement are also investigated. This study aims to investigate the flow boiling enhancement attributed to the graphene functionalized coatings and provides interesting insights of the ultrafast water permeation mechanism of graphene into the subcooled flow boiling heat transfer.

Exceptional heat transfer performance induced by intrinsic flow oscillations during subcooled flow boiling over a copper mesh surface

An experimental investigation of subcooled flow boiling heat transfer in an orthogonal macro channel (dh = 16 mm) is undertaken. An extraordinary heat transfer performance is observed when a single copper wire mesh screen covers the heating surface of the channel. Experiments are performed with deionized water, at a mass flux range of 100–410 kg/m2s and a heat flux range of 50–850 kW/m2. A series of highly subcooled flow boiling experiments demonstrates the existence of regions of heat transfer enhancement, compared to a smooth reference surface. The addition of the mesh layer triggers a self-sustained flow instability accompanied by intense pressure oscillations which allows for remarkably thermally steady state conditions to take place. While in several heat transfer studies, the appearance of pressure oscillations has been attributed with heat transfer deterioration, in the current study we observe that a self-sustained oscillatory flow leads altogether to heat transfer enhancement, baring close resemblance to the well-known microbubble emission boiling flow phenomenology and heat transfer. Aspects of temperature, pressure and flow regimes are presented and discussed accordingly.

Investigation of Forced Convective and Subcooled Flow Boiling Heat Transfer Coefficients of Water-Ethanol Mixture: Numerical Study

The subcooled flow boiling is related to the operation of electronic devices, Hybrid electric vehicle (HEV) Battery module and small catalytic reactors. It is well known that the operational temperature must be maintained to avoid any malfunction of these heat dissipative devices. In this paper the forced convective and subcooled flow boiling heat transfer coefficients of water-ethanol mixture is determined numerically by Volume of fluid analysis (VOF). The interaction between liquid and local vapour is analysed by solving the bubble volume of fraction in the numerical study. Crank Nicolson implicit scheme is used for discretizing the scalar convection equation for bubble void fraction and transforming into algebraic equation. Thomas Algorithm is used to solve the algebraic equations of bubble void fraction. The corrector predictor equation method is used to solve for bubble void fraction when the value obtained is less than 0 or exceeds 1. The thermodynamic and Thermophysical properties are substituted in the x-momentum and energy equation to determine the values of pressure drop, velocity and temperature of the fluid. From the temperature values, the subcooled flow boiling heat transfer coefficient is obtained. It is found that the addition of ethanol to water decreases the forced convective and subcooled flow boiling heat transfer coefficient of the water-ethanol mixture. The numerically determined heat transfer coefficient of water ethanol mixture is compared with that of the experimental results. The average deviation between the experimentally determined and numerically determined subcooled flow boiling heat transfer coefficient of water ethanol-mixture is found to be 24.13%.

Experimental investigation of a new hybrid structured surface for subcooled flow boiling heat transfer enhancement

A new scheme with hybrid submillimetre/micro/nano-structured surfaces providing both high subcooled flow boiling performance and relatively low flow resistance was proposed to develop highly efficient and reliable water cooling schemes for plasma facing components (PFCs) in future nuclear fusion engineering. Both comparative microscopic surface structure pattern observations and macroscopic mockup subcooled flow boiling experiments under fusion reactor like heat flux conditions were conducted. The proposed technique can create hybrid structures favourable for subcooled flow boiling enhancement: including increasing bubble generation sites and multiscale instability etc. We demonstrated that the heat transfer coefficients of manipulated surfaces in the subcooled flow boiling state were almost doubled and that the critical heat flux (CHF) values were promoted by 80–200% under the tested flow conditions compared with under smooth surface conditions, with the flow path pressure drop deteriorating by less than 12%, indicating better capacities of high heat flux removal and low flow path resistance than those of existing PFC cooling schemes. The results encourage further optimization and development of this new scheme for practical application in nuclear fusion engineering.

Experimental investigation of the subcooled flow boiling heat transfer of water and nanofluids in a horizontal metal foam tube

The present article experimentally explored heat transfer through a horizontal metal foam tube with a constant wall heat flux during the subcooled flow boiling of water, Al2O3/H2O, and CuO/H2O nanofluids. To investigate the effect of using metallic foam on the subcooled flow boiling heat transfer, the results have been compared with a simple tube. Besides, The impacts of significant parameters, including subcooled inlet temperature (25–60 °C), mass flux (150–310 kg m−2 s−1), wall heat flux (100–230 kW m−2), particle type (CuO and Al2O3), and nanofluids concentration (0.5% wt., 1% wt.) were investigated on the transfer of boiling heat while measuring pressure loss and rate of heat transfer. The results show that the use of metal foam increases the heat transfer rate by 3.5–5.8 times compared to the simple tube. Comparing the subcooled flow boiling heat transfer of water and nanofluids in both metal foam and simple tubes, it was found that water has superiority over the nanofluids. Besides, the value of the thermal performance index defined as a ratio of the heat transfer enhancement to the pressure loss degradation is more than one for water and the nanofluids.

Experimental study on sub-cooled flow boiling heat transfer characteristics in non-uniform heating tube bundle channel

Since the primary coolant temperature decreases along the U-tube, so the secondary side fluid in the steam generator tubes will receive non-uniform heating (NUH) from the primary side. Compared with uniform heating (UH), NUH has a great influence on the heat transfer characteristics of the secondary side, especially in terms of the sub-cooled flow boiling, during which the heat transfer mechanism changes. In this paper, sub-cooled flow boiling in a tube bundle channel under NUH and UH conditions are performed experimentally. The results show that NUH makes the onset of nucleate boiling (ONB) occur ahead of time, and it also leads to a greater radial inhomogeneity of fluid temperature field than UH. Four Chen-type correlations were evaluated, and it is found that the Gungor-Winterton correlation is most suitable for experiments under UH condition. However, the Gungor-Winterton correlation has a relatively large deviation under NUH condition, and it is also difficult to capture the predicted trend, which means that it is not applicable to NUH conditions. Therefore, an improved Gungor-Winterton correlation is proposed for NUH conditions. Its average relative error is 8.02%, and less than 2.18% of data has larger deviation than 20%.

Experimental Investigation of Sub-Cooled Flow Boiling Heat Transfer in Single Rectangular Metallic Micro-Channel

In this study, an experimental investigation on the flow boiling heat transfer in single rectangular micro-channel was carried out. The micro-channel was formed by machining 300 μm wide x 700 μm deep groove (i.e. a hydraulic diameter 420 μm) into the surface of brass block having length of 60 mm. The working fluid was deionized water. The experiments were carried out with the mass flux range (300-600 kg/m2.sec), and flux of heat (based on wall) 5.4 to 376.5 kW/m2, inlet sub-cooling of 20 K and 1 atm. working pressure. The results of this study have shown that at heat fluxes with lower range, the local coefficient of heat transfer increased with increasing the flux of heat. This trend is reversed when heat fluxes exceed 64.2, 77.9, 93.8 and 116.7 kW/m2 for mass fluxes 300, 400, 500 and 600 kg/m2.s respectively, where the heat transfer coefficient decreases as the heat flux increases and reach a constant value at the highest heat flux. The experimental results are compared to heat transfer correlations of minichannel and microscale, these correlations gave the results reasonably well.

Enhancement of Subcooled Flow Boiling Heat Transfer with High Porosity Sintered Fiber Metal

We conducted experimental research using high-porosity sintered fiber attached on the surface, as a passive method to increase the heat flux for subcooled flow boiling. Two different porous thicknesses (1 and 0.5 mm) and one bare surface (0 mm) were compared under three different inlet subcooling temperatures (30, 50 and 70 K) and low mass flux (150–600 kg·m−2·s−1) using deionized water as the working fluid under atmospheric pressure. The test section was a rectangular channel, and the hydraulic diameter was 10 mm. The results showed that the heat flux on porous surfaces with a thickness of 1 and 0.5 mm increased by 60% and 40%, respectively, compared to bare surfaces at ΔTsat = 40 K at a subcooled temperature of 50 K and mass flux of 300 kg·m−2·s−1. An abrupt increase in the wall superheat was avoided, and critical heat flux (CHF) was not reached on the porous surfaces. The flow pattern and bubble were recorded with a high-speed camera, and the bubble dynamics are discussed.

EXPERIMENTAL INVESTIGATION OF THE EFFECTS OF POROUS MEDIUM ON SUBCOOLED FLOW BOILING HEAT TRANSFER IN A VERTICAL ANNULUS TUBE

EXPERIMENTAL INVESTIGATION OF THE EFFECTS OF POROUS MEDIUM ON SUBCOOLED FLOW BOILING HEAT TRANSFER IN A VERTICAL ANNULUS TUBE

Heat-transfer characteristics of screw tube in one-side high heat load condition for fusion reactor divertor application

In this study, the heat transfer characteristics of one-side heated screw tubes were analyzed using subcooled flow boiling experiments. The experiments were performed until the critical heat flux was reached, while the applied heat flux was gradually increased. Subsequently, the boiling curves derived from the experimental results were divided into partial nucleate boiling (PDB) and fully developed nucleate boiling (FDB) regimes. As the flow rate increases, the forced convective heat transfer is enhanced, improving the single-phase heat transfer performance. However, as the FDB region is approached, most of the heat transfer proceeds via nucleate boiling heat transfer, so the heat transfer coefficient curve converges into the same straight line. The same trend was observed when analyzing the effect of the degree of subcooling. However, as the system pressure increased, and the liquid surface tension and latent heat decreased, a faster transition was observed from the single-phase regime to the PDB regime. From evaluating the prediction performance of the existing subcooled flow boiling heat transfer correlations, among the PDB regime; Liu and Winterton correlation, a kind of Chen-type correlation, showed the highest accuracy with mean absolute error (MAE) of 13.62% and root mean square error (RMSE) of 16.13%. However, most of the FDB correlations did not accurately predict the heat transfer performance of the one-side heated screw tube under a high heat flux load of several MW/m2. Therefore, a new screw tube FDB correlation was developed using Python code combined with artificial intelligence technology. The authors believe that the proposed correlation will be useful for not only predicting the heat transfer performance in the FDB region, but also establishing an operating map of the screw tube in the future.

Subcooled Flow Boiling of Carbon Dioxide Near the Critical Point Inside a Microchannel

Subcooled flow boiling heat transfer of carbon dioxide (${\mathrm{CO}}_{2}$) at the microscale near the critical pressure is experimentally studied. The onset of nucleate boiling and the local heat-transfer coefficient are obtained under 26 experimental conditions, consisting of 17 sample points each, yielding 442 data points. Excess temperatures of about 1 K at the onset of nucleate boiling and heat-transfer coefficients of up to $200\phantom{\rule{0.25em}{0ex}}\mathrm{kW}/{\mathrm{m}}^{2}\phantom{\rule{0.25em}{0ex}}\mathrm{K}$ are recorded. The heat-transfer coefficient and the onset of nucleate boiling models and correlations developed for low reduced pressures are compared to current experimental results. Modifications to these models are introduced to account for conditions pertinent to reduced pressures around unity. Overall, the correlations do not fully capture current measurements, suggesting that the physics of flow boiling heat transfer near the critical conditions exhibits some unique characteristics. Furthermore, it is observed that the experimentally obtained heat-transfer coefficient is better predicted by a model developed for flow boiling of ${\mathrm{CO}}_{2}$. However, with increasing pressure, deviations between experiments and predictions increase.

Experimental study of hypervapotron channel with square fin structure for divertor cooling by one-side, electric joule heating system

The lack of cooling capacity to maintain the thermal steady state of the divertor is becoming a severe engineering problem in preparation for DEMO fusion reactor. But, there is not much literature comparing with the existing sub-cooled flow boilng heat transfer correlation and analyzing the Hypervapotron boiling curve. To simulate the fusion thermal condition, experimental loop that can withstand high temperature (150℃) and high pressure (20 bar) was constructed. And one-side electric joule heating system that can apply heat flux of up to 10.4 MW/m2 was developed. In addition, it was verified that stable operation is possible by confirming that the flow rate and the channel inlet temperature fluctuation rate are 1% or less, respectively. This experiment was carried out to evaluate the boiling heat transfer of Hypervapotron cooling channel at 10 bar, 40 ∼ 80 subcooling, 0.108 ∼ 0.284 kg /s and maximum effective heat flux of 6.87 MW/m2. Among the sub-cooled flow boiling heat transfer correlations, Thom correlation (1965), Jens & Lottes correlation (1951), and Aaladiev correlation (1957) differed significantly from the experimental data. But Shah 1977 (error rate: 4.75 %) and Kandlikar 1998 (error rate: 16.57 %) correlations were well predicted.

Subcooled flow boiling of seawater in a vertical annulus

The present study investigates experimentally subcooled flow boiling heat transfer characteristics of 3.5 wt% artificial seawater and de-ionized water in an annulus. Boiling behaviors through a high-speed video camera reveals significantly different two-phase flow patterns in the heated annulus between artificial seawater and de-ionized water. Bubbles in de-ionized water tend to merge each other to form large bubbles or slug bubbles, while bubble coalescence is absent in seawater and bubble foam may eventually be formed. Subcooled boiling results in the quick rise of void fraction in the flow direction downstream of the net vapor generation point, as evident through flow visualizations and the evaluation of Saha and Zuber's model and Pan's model. Fluid temperature measurements at the inlet and exit of the annulus enable the evaluation of qualities and corresponding void fractions at the exit of the annulus through energy balance. Calculated void fraction as high as 50–70% is demonstrated and is consistent with the prediction of models. Correspondingly, the pressure drop rises very quickly after the heat flux exceeding the initiation of boiling two-phase flow and reaches a plateau of constant pressure drop in seawater, indicating the appearance of bubble foam. Generally, the pressure drops of artificial seawater under the same operating condition are much higher than those of de-ionized water in two-phase boiling region due to its unique bubbly flow pattern. The subcooled flow boiling heat transfer coefficients with the mass flux of 564, 874, and 1200 kg/m2s in artificial seawater are slightly higher than those in de-ionized water, possibly due to strong bubble agitation. The heat transfer coefficients obtained in the present study agree well with the predictions of the correlation of Papel in the early literature.

Convective flow boiling heat transfer in an annular space: N-heptane/water case in a bubbly sub-cooled flow

The subcooled flow boiling heat transfer characteristics of n-heptane and water is conducted for an upward flow inside the vertical annulus with an inner gap of 30 mm, in different heat fluxes up to 132kW.m-2, subcooling max.:30C, flow rate: 1.5 to 3.5lit.min-1 under the atmospheric pressure. The measured data indicate that the subcooled flow boiling heat transfer coefficient significantly increases with increasing liquid flow rate and heat flux and slightly decreases with decreasing the subcooling level. Although results demonstrate that subcooling is the most effective operation parameter on onset of nucleate boiling such that with decreasing the subcooling level, the inception heat flux significantly decreases. Besides, recorded results from the visualization of flow show that the mean diameter of the bubbles departing from the heating surface decreases slightly with increasing the flow rate and slightly decreases with decreasing the subcooling level. Meanwhile, comparisons of the present heat transfer data for n-heptane and water in the same annulus and with some existing correlations are investigated. Results of comparisons reveal an excellent agreement between experimental data and those of calculated by Chen Type model and Gungor–Winterton predicting correlation.

The applicability of heat transfer correlations to flows in minichannels and new correlation for subcooled flow boiling

This paper focuses on the applicability of heat transfer correlations to flows in minichannels. The data were taken from own research conducted at the experimental stand for subcooled flow boiling heat transfer in an asymmetrically heated rectangular minichannel oriented with seven inclination angles (0°, 30°, 60°, 90°, 120°, 150°, and 180°) relative to the horizontal plane. Various cooling liquids (FC-72, HFE-649, HFE-7100 or HFE-7000) flowing along a minichannel were heated by a thin plate. The plate had a smooth or enhanced surface on the side that was in contact with the fluid. The enhanced surfaces were obtained by vibration-assisted laser surface texturing or electromachining. Porous surfaces produced by soldering or sintering iron powder to the heated surface were also tested. Infrared thermography was used to determine changes in temperature on the outer smooth surface of the plate. Local heat transfer coefficients in the contact surface between the heated plate and the cooling fluid were determined using the one-dimensional mathematical method. A dozen or so heat transfer correlations selected from the literature have been used in calculations. It was found that the majority of correlations enabled the predicting of Nusselt number within error bands of ±25%. The smallest mean absolute percentage error in determining the Nusselt number was obtained using Mikielewicz J. correlation. A new correlation for subcooled flow boiling heat transfer in minichannels was proposed. The mean absolute percentage error of the Nusselt number, amount to 14%, was achieved according to own correlation.

Application of general multilevel factorial design approach in forced convection and subcooled flow boiling heat transfer to CuO/water nanofluids

In this research, heat transfer in forced convection and subcooled flow boiling to CuO/water nanofluids was experimentally and theoretically investigated. The effects of various parameters comprising subcooling temperature, nanoparticle concentration, heat flux, and fluid flow rate on the heat transfer performance of the system were studied. The general multilevel factorial design approach was applied in order to design the experiments and statistically analyze the results. Results showed that all the aforementioned factors were statistically significant. A reduced quadratic model was presented to predict the heat transfer coefficient. The suggested model was in good agreement with the experimental data. It was found the heat transfer coefficient increase as the heat flux and fluid flow rate increase while the trend was reversed for the effect of subcooling temperature. Raising the nanoparticle concentration initially deteriorated the heat transfer coefficient while a further increase in concentration enhanced the heat transfer coefficient.