Heat Transfer Coefficients In Pool Research Articles

An Overview of the Recent Advances in Pool Boiling Enhancement Materials, Structrure, and Devices.

This review attempts to provide a comprehensive assessment of recent methodologies, structures, and devices for pool boiling heat transfer enhancement. Several enhancement approaches relating to the underlying fluid route and the capability to eliminate incipient boiling hysteresis, augment the nucleate boiling heat transfer coefficient, and improve the critical heat flux are assessed. Hence, this study addresses the most relevant issues related to active and passive enhancement techniques and compound enhancement schemes. Passive heat transfer enhancement techniques encompass multiscale surface modification of the heating surface, such as modification with nanoparticles, tunnels, grooves, porous coatings, and enhanced nanostructured surfaces. Also, there are already studies on the employment of a wide range of passive enhancement techniques, like displaced enhancement, swirl flow aids, and bi-thermally conductive surfaces. Moreover, the combined usage of two or more enhancement techniques, commonly known as compound enhancement approaches, is also addressed in this survey. Additionally, the present work highlights the existing scarcity of sufficiently large available databases for a given enhancement methodology regarding the influencing factors derived from the implementation of innovative thermal management systems for temperature-sensitive electronic and power devices, for instance, material, morphology, relative positioning and orientation of the boiling surface, and nucleate boiling heat transfer enhancement pattern and scale. Such scarcity means the available findings are not totally accurate and suitable for the design and implementation of new thermal management systems. The analysis of more than 100 studies in this field shows that all such improvement methodologies aim to enhance the nucleate boiling heat transfer parameters of the critical heat flux and nucleate heat transfer coefficient in pool boiling scenarios. Finally, diverse challenges and prospects for further studies are also pointed out, aimed at developing important in-depth knowledge of the underlying enhancement mechanisms of such techniques.

Experimental study of the effects of horizontal and vertical roughnesses of heater surface on bubble dynamic and heat transfer coefficient in pool boiling

Experimental study of the effects of horizontal and vertical roughnesses of heater surface on bubble dynamic and heat transfer coefficient in pool boiling

Study on effect of nano-fluid on heat transfer coefficient of pool boiling

Study on effect of nano-fluid on heat transfer coefficient of pool boiling

Influence of magnetic field on boiling heat transfer coefficient of a magnetic nanofluid consisting of cobalt oxide and deionized water in nucleate regime: An experimental study

In this paper, the analysis of the boiling process is studied in a nucleate regime on a copper surface through using oxide nanoparticles of cobalt (Co3O4) in deionized water at volume fractions of 0.005, 0.01, 0.05, 0.1, and 0.2% by means of a nucleate boiling device. The nanoparticles’ average size is about 45 nm for cobalt oxide. As the nanofluid concentration increases, the deposition and the boiling surface heat resistance increases, the nucleation points and coefficient of the boiling heat transfer decrease due to deposition. Despite the magnetic field positive effect on dilute liquids, sediment has a more negative effect than the magnetic field on concentrated nanofluids. The results reveal the improvement of the heat transfer coefficient of pool boiling under a magnetic field for low volume fractions. Maximum heat transfer of Co3O4/ DI-water is 58% compared to the DI-water observed at the concentration of 0.005%. This nanofluid can be applied to increase the heat transfer rate at low concentrations.

Experimental investigation of titanium tetrachloride in pool boiling heat transfer

There is a lack of complete set of available experimental data on the boiling characteristics for titanium tetrachloride, becoming barriers to investigate the interaction mechanism of the TiCl4-Mg system. Boiling heat transfer over a copper surface at various heat fluxes is investigated experimentally in the present study. The heat flux and the heat transfer coefficient of the pool boiling experiment are investigated. With increasing the wall superheat temperature, the heat flux and the heat transfer coefficient of pool boiling for titanium tetrachloride are increasing rapidly. And based on experimental data, the Rohsenow’s correlation and a semi-empirical relation regarding the boiling heat transfer coefficient are obtained.

Augmentation of heat transfer coefficient in pool boiling using compound enhancement techniques

Modern compact electronic chip design demands more efficient and innovative cooling techniques in a limited space. One such method is the immersion cooling by pool boiling heat transfer, which is a highly efficient technique when compared with conventional cooling techniques. The boiling heat transfer coefficient can be enhanced using active and passive techniques. In the present investigation grooves as passive and surface vibration as active techniques were coupled to improve the boiling heat transfer coefficient. The forced vertical vibrations were induced on the copper grooved surface with a mechanical vibrator. The frequency of vibration was varied in the range 0–100Hz and the amplitude of vibration was varied in the range 0–2.5mm. The compound technique gave 62% improvement in heat transfer coefficient at 300kW/m2 heat flux compared to the 29% enhancement due to grooves alone and 10% enhancement due to vibration alone. The experimental results were used to develop a modified Rohsenow correlation which predicts the experimental Nusselt number with an accuracy of ±25%. Boiling visualization was performed and the bubble parameters such as bubble departure diameter, bubble frequency and bubble growth were determined. The bubble departure diameter decreased by almost 36% and the bubble frequency increased by 221% for boiling on vibrated grooved surface.

Enhanced heat transfer performance of alumina sponge-like nano-porous structures through surface wettability control in nucleate pool boiling

For several decades, a porous surface has been recognized as an efficient medium to increase boiling performance in a nucleate boiling regime. Most feasible porous surfaces have been studied in millimeter and micron-sized domains. It has been believed that a higher wall superheat is required to commence incipient nucleate boiling under a submicron regime. In this study, we demonstrate that a significantly enhanced pool boiling heat transfer is observed in a submicron regime through three dimensionally interconnected hybrid pores: the Alumina sponge-like nano-porous structure (ASNPS). The structural uniqueness of the ASNPS leads to an enlarged surface area, increases the potential number of the active nucleation site density, and improves the vapor–liquid menisci through the reentrant pore. Simultaneously, by changing the surface wettability with a hydrophobic self-assembled monolayer (SAM) coating, the number of active nucleation site density is improved. Eventually, the combination of the ASNPS and hydrophobic SAM coating can achieve substantial heat transfer coefficient (HTC) enhancement in the nucleate boiling. Also, the thickness of the ASNPS is a critical issue to adequately augment the HTC in pool boiling. The thickness of the ASNPS is optimized by examining the boiling performance of the ASNPS fabricated in different amounts of anodizing times. A classical mechanistic model from literature was modified and compared with the experimentally obtained data. The modified mechanistic model – with the combination of forced-convection and thin liquid film evaporation – showed reasonable predictions.

Vertically oriented TiO2 nanotube arrays with different anodization times for enhanced boiling heat transfer

Pool boiling of saturated water on a plain Ti surface and surfaces covered with vertically-oriented TiO2 nanotube arrays (NTAs) has been studied. The technique of potentiostatic anodization using non-aqueous electrolytes was adopted to fabricate three types of TiO2 NTAs distinguished by their anodization time. Compared to the bare Ti surface, the incipient boiling wall superheat on the TiO2 NTAs was decreased by 11 K. Both the critical heat flux and heat transfer coefficient of pool boiling on the TiO2 NTAs were higher than those from boiling on a bare Ti surface. The measured maximum critical heat flux and heat transfer coefficient values were 186.7 W/cm2 and 6.22 W/cm2K, respectively. Different performances for the enhancement of heat transfer by the three types of TiO2 NTAs were attributed to the different degrees of deformation in the nanostructure during boiling. Long-term performance of the nanomaterial-coated surfaces for enhanced pool boiling showed degradation of the TiO2 NTAs prepared with an anodization time of 3 hours.

Local heat transfer coefficient for pool boiling of R-134a and R-123 on smooth and enhanced tubes

The current paper presents experimental investigation of nucleate pool boiling of R-134a and R-123 on enhanced and smooth tubes. The enhanced tubes used were TBIIHP and TBIILP for R-134a and R-123, respectively. Pool boiling data were taken for smooth and enhanced tubes in a single tube test section. Data were taken at a saturation temperature of 4.44°C. Each test tube had an outside diameter of 19.05mm and a length of 1m. The test section was water heated with an insert in the water passage. The insert allowed measurement of local water temperatures down the length of the test tube. Utilizing this instrumentation, local heat transfer coefficients were determined at five locations along the test tube. The heat flux range was 2.5–157.5kW/m2 for the TBIIHP tube and 3.1–73.2kW/m2 for the TBIILP tube. The resulting heat transfer coefficient range was 4146–23255W/m2.°C and 5331–25950W/m2.°C for both tubes, respectively. For smooth tube testing, the heat flux ranges were 7.3–130.7kW/m2 and 7.5–60.7kW/m2 for R-134a and R-123, respectively; with resulting heat transfer coefficient ranges of 1798.9–11,379W/m2.°C and 535.4–3181.8W/m2.°C. The study provided one of the widest heat flux ranges ever examined for these types of tubes and showed significant structure to the pool boiling curve that had not been traditionally observed. Additionally, this paper presented an investigation of enhanced tubes pool boiling models.

Adaptive fuzzy model identification to predict the heat transfer coefficient in pool boiling of distilled water

In this paper, a modeling technique based on fuzzy system is used to predict the heat transfer coefficient in pool boiling of distilled water. To achieve this, an experimental investigation has been carried out for saturated boiling of distilled water from plain copper heating tube surface at atmospheric and sub-atmospheric pressures. An empirical correlation has been established to predict the boiling heat transfer coefficient. Further, the experimental data has been compared with those determined from the zero-order adaptive fuzzy model with heat flux as input variable. The representation accuracies of the pool boiling heat transfer coefficient for fuzzy model is very high as indicated from the performance index. The prediction performance of zero-order adaptive fuzzy model has also been compared with MATLAB based ANFIS function. Further, the statistical attributes are determined and compared with the experimental data set of pool boiling of distilled water available in open literatures.

The pool boiling heat transfer enhancement from experiments with binary mixtures and porous heating covers

Porous heating covers and positive binary mixture composition reduce the bubbles’ size and their coalescence, while increasing the liquid supply towards the heating surface, causing an increase of the convective heat transfer coefficient for pool boiling. The convective heat transfer coefficient h was calculated for boiling of pure water and three aqueous mixtures with 12%, 16%, and 20% weight of ethanol on seven different porous coverings on the heating element. Maximum h values were 50 kW/m 2 K for pure water, and 65 kW/m 2 K for ethanol–water mixtures on the smooth surface of the heating element; using the porous coverings, 180 kW/m 2 K for boiling of water and 220 kW/m 2 K for boiling of ethanol mixtures were obtained. The maximum values of h correspond to the composition of 16% ethanol (on each porous covering), to pore-surface-densities of 45 pores per square inch and a covering thickness of 5 mm. Greater thicknesses decreased the values of h for the same number of pores per square inch expressing an internal resistance for vapor release. For limited vapor-release conditions, the bubbles grew with no increase in the h values, while for resistance-free vapor escape the bubbles radii increased almost linearly. A 3 2 factorial design generated a response surface and its analysis of variance, which confirmed that the most important factors, defining the values of h , are the porous covering construction and its pore-surface density.

Heat transfer in boiling of multicomponent mixtures

AbstractPool boiling data of multicomponent mixtures show that the heat transfer coefficients can be considerably lower than those of a corresponding pure fluid with the same physical properties as the mixture. The proposed model, which assumes maximum mass transfer resistance in the liquid boundary layer, is confirmed by the comparison between calculated and experimental data. The model allows the prediction of heat transfer coefficients in pool boiling of mixtures using only single component properties and vapour‐liquid equilibrium data. Judging by experience with a number of different systems, the method should be sufficiently accurate for most practical applications.

A gas volumetric technique for the measurement of heat transfer coefficient in pool boiling

A gas volumetric technique for the measurement of heat transfer coefficient in pool boiling