Enhancement of heat transfer at boiling in electrohydrodynamic flow

The influence of the electric field strength and interelectrode spacing on the heat transfer intensity at boiling in an electrohydrodynamic flow was studied. It was stated that the heat transfer coefficient increases with the increasing of the field strength. The influence of the interelectrode spacing is ambiguous. The efficiency of the action of a electrohydrodynamic flow on the heat transfer intensity at boiling was evaluated using the ratio of the heat transfer coefficient at boiling in the field to the heat transfer coefficient at boiling without the field. The relationships for calculation were obtained that satisfactorily agree with the experimental data.

Performance Assessment of the Heat Exchanger with and without a Coating of Hybrid Nanoparticles the User Cooling System in Solar Heating Systems

The aim of this article was to examine the effect of hybrid nano – coating that could potentially impact the enhancement of heat transfer coefficient of distilled water, Reynolds number, and temperature through a swirl heat exchanger, as well as the indicator of the effect Zeta voltage in the coating process. In this experimental work, type of coating used was Aluminum (Al) + Aluminum oxide Al2O3. Outcomes of study showed that the coating of heat exchanger is much better than without coating in improving the thermal properties for liquids passing through heat exchanger as well as increasing the heat exchange through the surface of the exchanger. Results in the article indicated that the use of hybrid nano – structure coating is for inducing the feature of super – hydrophobicity for the surface that touches the fluid included within the heating transferring. Such feature can make an increase in the heating transferring factor and a decreasing in power losing produced via friction. This article indicated that the Zeta voltage analysis is to show the stability of the hybrid nanofluids used in the coating process. The enhanced technology depends upon the concept that exists in nature under the name “Lotus effect” to get super-hydrophobic surfaces. The rate of improvement in heat transfer using hybrid nanoparticles is 33% compared to that without coating condition.

Enhancement of heat transfer for boiling in nanofluid

The paper considers heat transfer during boiling of subcooled water with suspended nanoparticles Al2O3 using a suspension from 0.32% to 4%. On a spherical model, the local heat flux per unit area was measured by the method of gradient heatmetry for model temperature of 464 °C and water temperature of 64 °C. The results are compared with the data obtained at the same temperature conditions for pure water. Enchancement of heat transfer was revealed in the entire concentration range - with a maximum at a particle concentration close to 1%.

Effect of Nanofluids on the Enhancement of Boiling Heat Transfer: A Review

Boiling heat transfer can play a vital role in the two-phase flow applications. The analysis of the boiling hat transfer enhancement is of importance in such applications and the enhancement can be mostly conducted by using various active and passive techniques. One type of passive techniques is the enhancement of heat transfer by nanofluids. This article presents an extensive review on the effect of different nanofluids on the enhancement of heat transfer coefficient (HTC) and critical heat flux (CHF) for both pool as well as flow boiling. Nanoparticles addition to a working fluid is done arbitrarily to improve the thermophysical properties which in turn improves heat transfer rate. Numerous works have been done in the studies on nanofluid boiling. Among various nanoparticles, the most frequently used nanoparticles are Al2O3 and TiO2. In the case of binary nanoparticles, the most commonly used combination is Al2O3 and TiO2. After reviewing the relevant literatures, it is found that for pool boiling, the maximum HTC is increased to 138% for TiO2 nanoparticles and the maximum CHF is increased to 274.2% for MWCNTs. Conversely, in flow boiling the maximum HTC is increased to 126% for ZnO nanoparticles and the maximum CHF increased to as 100% for GO nanoparticles. In addition, when two or more nanoparticles in succession or binary nanofluids are used the CHF in pool boiling increased up to 100% for Al2O3 and TiO2 as well as the CHF in flow boiling increased up to 100% for Al2O3, ZnO, and Diamond. Though the information of the coefficient of heat transfer and the critical heat flux varied for different nanofluids and vary from experiment to experiment for each of the nanofluids. This variation happens because the coefficient of heat transfer and the critical heat flux in boiling is dependent upon several factors.

Enhancement of Convection Heat Transfer in Air Using Ultrasound

The use of ultrasound is a new method to enhance convection drying. However, there is little information in the literature on the improvement of convective heat transfer caused by ultrasound. Therefore, the heat transport during ultrasound-assisted convective heating of small samples in a hybrid dryer was experimentally examined. A small Biot number regime of heat transfer was considered. The results confirmed a great enhancement of heat transfer due to the application of ultrasound. Due to the use of ultrasound, the convective heat exchange coefficient increased from 45% to almost 250%. The enhancement is a linear function of applied ultrasound power. It was shown that the energy absorption of ultrasound existed, but the thermal effect of this absorption was very small.

ENHANCEMENT OF HEAT TRANSFER IN DOUBLE PIPE HEAT EXCHANGER USING AL2O3-FE2O3/WATER HYBRID NANOFLUID

This study aims to enhancement of heat transfer in double pipe heat exchanger by improving the thermal properties of base fluid which is water by adding AL2O3-Fe2O3 nanoparticles to the water. Al2O3-Fe2O3/water hybrid Nanofluid were examined experimentally and numerically at different flow rates ranging between (3 -7) Lpm at temperature of 25°C in an external tube while there was a hot water at a temperature of 60°C and a flow rate ranged between (3 – 5) Lpm running in the central tube of a double pipe counter heat exchanger. Also, the effect of various concentrations ranged between (0.05, 0.1, 0.15, 0.2, 0.25 and 0.3%) of Al2O3-Fe2O3 nanoparticles dispersed in water on the rate of heat transfer, friction coefficient were verified experimentally and numerically . The ratio of Al2O3-Fe2O3 is 0.5:0.5. The experimental and numerical study indicated that with the rate of heat transfer increases when the concentration of suspended nanoparticles in the base fluid increases , but on the other hand, the skin friction coefficient and pressure drop increases as well with increasing the concentration of nanoparticles. The maximum enhancement in heat transfer for AL2O3-Fe2O3 is about 6 % . The results from the experimental study were largely consistent with the numerical results.