Increase In Heat Transfer Coefficient Research Articles

Heat transfer performance and electrohydrodynamic characteristics optimization of a dividing-wall-type ionic wind heat exchanger

Heat exchangers play a major role in reducing emissions and conserving energy. There is a plethora of theoretical research on the enhancement of heat transfer caused by ionic wind, but there is still a lack of studies on the practical application of ionic wind in heat exchangers to increase heat exchange capacity. This work developed an original ionic wind heat exchanger with a dividing wall. It may be applied to difficult circumstances when conventional heat exchangers fail for air-to-air heat exchange. The study conducted experiments to investigate the impact of many factors, including intake air velocity, discharge spacing, and electrode distribution scheme, on the ionic wind intensity and the heat exchanger's increased heat transfer coefficient. A two-dimensional model was used to analyze the internal flow and thermal properties of the heat exchangers with wire emitters. By combining active and passive heat exchange technologies, an ionic wind heat exchanger with serrated grounded electrodes was presented. The outcomes demonstrated that a suitable intake air velocity enhances the heat exchanger's capacity for heat exchange. The improved heat exchange effect of ionic wind is more important when the inlet wind speed is less than 1 m/s. When the intake air velocity approaches 1.3 m/s, the ionic wind has less of an impact on the heat exchanger's capacity for heat exchange. The benefits of improved heat transfer are promoted by placing the emitter closer to the channel entry. Increasing the operating voltage further enhances the heat transfer enhancement ratio (HTER). The number and arrangement of wire electrodes should be chosen with consideration for the 'barrier effect' between neighboring emitters and the distance from the entrance when utilizing multiple wire electrodes. In comparison to the three-wire and five-wire electrodes, the four-wire electrode heat exchanger's HTER values were increased by 5.9 % and 14.3 %, respectively. The ionic wind heat exchanger's capacity for heat transfer is further increased using a zigzag grounding electrode. The zigzag uses a decreased aspect ratio, and the emitter is positioned slightly above the tip, improving the system's heat transfer capabilities. When compared to a heat exchanger with a flat plate grounded electrode, the four-wire electrode heat exchanger produced a 158 % increase in HTER value.

Experimental and numerical analysis of heat transfer mechanisms for two-phase oil-refrigerant flow process in the cylinder of rotary compressor

Investigating the heat transfer mechanisms in rolling piston type rotary compressors is crucial for improving their operational efficiency. A thermal test platform was established and steady-state temperature fields of key components were measured under various conditions, revealing a correlation between these temperatures and crank angles, except near the angle of 54° for the cylinder head-up. It provided important boundary conditions for simulation research. A novel three-dimensional fluid–solid-heat coupled simulation method was proposed, calculating heat transfer coefficients at fluid–solid interfaces. The two-phase heat transfer characteristics post oil–gas miscibility was studied, arising from the injection of lubricating oil into the working chamber. Two-phase oil-refrigerant mixtures, compared to single-phase refrigerant, increased heat transfer coefficients by 2.35 % in the suction channel and 2.99 % in the cylinder head-up, but decreased by 5.85 % in the cylinder head-down, 17.42 % in the piston, and 5.63 % in the cylinder. Oil injection was found to significantly enhance convective heat transfer in the suction chamber, increasing suction superheat in the cylinder by up to 29 K and reducing temperature of the compression chamber by up to 17 K. These results provide novel insights into the complex heat transfer in rotary compressors.

An approach for topology optimization of heat sinks for two-phase flow boiling: Part 2 – Model calibration and experimental validation

Flow boiling offers increased heat transfer coefficients and effective heat capacity rates that can be leveraged by topology optimization (TO) to generate high-performance microchannel heat sinks. Topology optimization of heat sinks having two-phase flows can be accomplished using the homogenization approach wherein designs are represented as spatially varying distributions of microstructures, as demonstrated in Part 1 of this two-part study. Flow and heat transfer within the microstructures are captured using a two-phase mixture model featuring an effective porous medium formulation. However, closure of these governing equations requires empirical correlations for pressure drop and heat transfer that are specific to the operating conditions, geometry, and surface finish. Therefore, it must be demonstrated these available correlations can be successfully calibrated over a range of microstructural variations present within the homogenization framework, so as to attain the required prediction generality and accuracy needed to ensure the resulting designs achieve Pareto-optimality. This Part 2 of our study successfully demonstrates a comprehensive end-to-end process for two-phase flow model calibration, topology optimized design generation, and experimental validation of optimized performance for flow boiling heat sinks. To this end, a TO algorithm with the homogenization approach and a two-phase mixture model is implemented using available flow boiling correlations for microchannels. A set of uniform pin fin calibration samples are additively manufactured and experimentally tested under flow boiling at various flow rates and heat inputs for model calibration. All of the unknown/free coefficients in the adopted correlations are determined by minimizing the error between the model predictions and the experimental measurements using gradient-based optimization. The calibrated topology optimization algorithm is then used to generate a Pareto-optimal set of heat sinks optimized for minimum pressure drop and thermal resistance during flow boiling. Experimental characterization of these additively manufactured heat sinks, unseen during the model coefficient calibration process, reveals that the measured Pareto optimality curve matches that predicted by the topology optimization algorithm. Lastly, a heat sink design is generated for a design space involving multiple hot spots and background heating to showcase the capability of the experimentally calibrated two-phase topology optimization algorithm at handling complex boundary conditions. The optimized heat sink intelligently distributes an adequate amount of coolant flow to each of the heated regions to avoid local dry-out. This work demonstrates a complete framework for two-phase topology optimization of heat sinks through experimental calibration of flow boiling correlations to the porous medium used by the homogenization approach.

Numerical investigation of the thermal-hydraulic performance of a novel parabolic trough wavy tubular receiver by using FMWNCT/oil-nanofluid coupled with fins

This study employs a computational fluid dynamics (CFD) approach to assess the performance of a novel wavy profile tube receiver. It integrates rectangular fins and an Oil-based nanofluid, specifically utilizing Thermodyne GG-03 synthetic oil combined with Functionalized Multi-Wall Carbon Tubes (FMWNCT). The synthesis involves rigorous experimental procedures to characterize the thermophysical properties of the oil and nanofluid. Empirical correlations, validated against Bitam et al.'s model [1], guide the numerical analysis. The investigation, utilizing a steady-state κ - ω SST turbulence model with a non-uniform Gaussian thermal flux distribution, explores thermohydraulic performance in fully developed turbulent flow (Reynolds number range: 2 × 104 – 5 × 104). Comparative analysis with Bitam et al.'s work, employing Syltherm 800 oil as a reference, reveals a 25.76% average Nusselt number enhancement with Thermodyne GG-03. Additional improvements are observed: 124.69% with FMWNCT/oil-nanofluid, 137.04% with fins, and 236.54% with combined FMWNCT/oil-nanofluid and fins. These enhancements lead to increased heat transfer coefficients and rates. The friction coefficient rises by less than 60%, mainly attributed to the Nusselt number improvement. At RE = 20000, the Maximum Performance Evaluation Criteria (PEC) is 5.5, signifying significant improvement. Notably, a 300% PEC enhancement is observed compared to Roger and Mayhew's curved tube model [1]. In conclusion, these findings offer valuable insights for efficiently designing wavy tubular receivers in PTR collectors.

An investigation shell and tube heat exchanger for cooling system: A case study of biodiesel plants using lauric acid

Shell and Tube Heat Exchanger (STHE) is a commonly used type of heat exchanger in various industries due to its cost-effectiveness and ease of maintenance. Continuous washing and maintenance of STHE play an important role in influencing both the quality and quantity of production from biodiesel plants. In this particular investigation, the STHE serves as a cooling medium for biodiesel production, with cooling water circulating on the tube side and biodiesel flowing on the shell side. This study focuses on removing silica crust buildup caused by cooling water in the Shell and Tube Heat Exchanger. Furthermore, a Clean-in-Place machine and a 10 % citric acid solution with variable washing times of 2 h, 4 h, 6 h, 8 h, 10 h, and 12 h were used for the cleaning process. The results indicate a significant 250 % increase in the volumetric flow rate of the cooling tower along with an increase in the overall Heat Transfer Coefficient after 10 h of washing. Further analysis at the hours mark showed consistent results, suggesting a steady state. Beyond this point, no additional temperature decrease was observed, with temperature stabilizing at 32 °C. The results of the Scanning Electron Microscope analysis show that the crust formed in the STHE comes from silica found in cooling water.

Intensification of thermal characteristics of flat plate solar water heater using triangular perforated wavy tape

The efficiency of the flat Plate Solar water heater has improved experimentally using passive methods. Experiments have shown that the addition of wavy tape (WT), 6 mm perforated wavy tape (PWT), and 9 mm perforated wavy tape (PWT) to a forced circulation solar water heater improves rate of heat transfer (Nu), friction factor (f), and effectiveness. Wavy tape inside the pipes induces secondary swirl flow, which improves mixing and increases heat transfer coefficients. The heat transfer rate (Nu) is increased by the incorporation of wavy tape; FPC with 6 PWT was higher than FPC without WT, FPC with plain WT, and FPC with 9 PWT by 20.83%, 14.85% and 6.25%, respectively. The maximum temperature difference of FPC with 6 PWT was higher than FPC without WT, FPC with plain WT, and FPC with 9 PWT by 61.9%, 22.9%, and 12.62% respectively. The maximum efficiencies value observed was 37.55%, 49.46%, 54.013%, and 51.03% for FPC without WT, FPC with plain WT, FPC with 6 PWT, and FPC with 9 PWT, respectively.

Transient behavior of flow boiling in structured microchannels under sudden and highly variable heat loads

In practice, heat sinks are sometimes exposed to sudden and irregular or highly variable heat loads. Therefore, here, for expanding micro-pin-fin heat sinks having micro cavities (heat sink code: MD) transient flow boiling characteristics are investigated under sudden and highly variable heat loads. Results are compared with those of conventional parallel channel heat sink (SD). Experiments can be grouped into two categories: (1) For a specified mass flux (G = 200 kg m−2 s−1) and inlet temperature (Ti = 78 °C), different heat loads (150 W, 30 W, 200 W, 150 W and 30 W, respectively) are applied. Every heat load is applied for three minutes, successively. (2) For a given mass flux (G = 200 kg m−2 s−1) and different inlet temperatures (Ti = 36 °C, Ti = 57 °C and Ti = 78 °C), the heat sinks are suddenly exposed to heating power of 200 W for ten minutes. It is deduced that MD increases heat transfer coefficient, decreases pressure drop and enhances thermal response characteristics compared to SD. In whole experimental range, heat transfer coefficient increases up to 11,802%, decrease in surface temperature reaches up to 39.2 °C, decrease in pressure drop reaches up to 4.05 kPa, and time passed for stable thermal conditions reduces from 48 s to 25 s. Decreasing inlet temperature increases thermal performance, however, leads higher fluctuations.

On convection vive in mixing-controlled combustion with thermal barrier coatings

Thermal barrier coatings (TBCs) could improve the efficiency of internal combustion engines by reducing heat losses. TBC modeling has demonstrated efficiency gains at all loads in compression ignition, including in gasoline compression ignition (GCI). However, after GCI testing of 13 coated pistons of various materials, thicknesses, and surface preparations in this work, a clear trend was observed: TBCs result in an efficiency gain at 6 bar IMEPn (low load) and an efficiency penalty at 15 bar IMEPn (high load). This can be explained by “convective vive”, which was originally presented by Woschni for engines with TBCs. Convection vive refers to a reduction in the quench distance of a reacting flame when the quenching surface temperature is elevated, resulting in an increased heat transfer coefficient and heat transfer rate despite the lower temperature difference between the gas and the wall. Although this work is unable to provide direct experimental evidence for convection vive, several experiments were performed to rule out alternate theories including differences in heat release rate, radiation heat transfer, combustion chamber deposits, and surface catalytic effects. Experiments also showed that at 6 bar IMEPn, injection pressure did not impact the performance of the TBC compared to the metal baseline, but at 15 bar IMEPn, the efficiency penalty increased with rail pressure. These results provide indirect evidence of convection vive: as the surface temperature of the TBC increases with load past a threshold, the quench distance decreases to the point where exothermic reactions can occur in the boundary layer, which raises the convective heat transfer coefficient. This implies that in mixing controlled combustion systems, the TBC should not be present on combustion chamber surfaces that experience high fuel-wall interaction during combustion.

Preparation and thermal properties of nano-microcapsule and simulation heat storage application

The prevention of material leakage and improvement of thermal conductivity are very important for thermal energy storage application. In this work, nano-TiO2@n-docosane microcapsules were synthesized by the fine emulsion interface polymerization method using tetra-n-butyl titanate (TBT). This approach enhances the encapsulation rate and efficiency of phase change microcapsules. The microcapsules formation process was observed using a biological microscope. The diameter of the microcapsules decreased significantly with the increase of stirring rate. The phase transition temperature of the optimal microcapsules is 42.4 °C. The encapsulation rate and efficiency reach up to 90.7% and 91.0%, respectively. The average thermal conductivity of nano-TiO2@n-docosane microcapsules is 215% higher than that of n-docosane. SEM and infrared spectroscopy testing results confirm the successful coating of n-docosane by TiO2. Thermogravimetric analysis presents that TiO2 forms a shell, which reduces the leakage of n-docosane. The melting and solidification processes of n-docosane and nano-TiO2@n-docosane microcapsules were simulated numerically. In comparison to n-docosane, nano-TiO2@n-docosane microcapsules exhibit a 14.89% increase in peak storage power and a 12.47% increase in heat transfer coefficient during charging. Additionally, during discharging, these values rise by 3.23% and 6.46%, respectively. Nano-TiO2@n-docosane microcapsules enhance heat transfer and the charging/discharging process of phase change materials.

An Experimental Investigation of the Effects of Using Hexagonal BN–Water Nanofluids on the Thermal Performance and Pressure Drop of a Concentric Tube Heat Exchanger

The thermal conductivity of recently produced hexagonal boron nitride (hBN)-containing nanofluids is comparatively higher than their viscosity, indicating that these materials belong to a relatively novel class. In this study, hBN–water nanofluids in stable and dispersed concentrations were used in parallel and counterflow experiments at volumes of 0.01%, 0.1%, and 1%, as well as at various flow rates and Reynolds numbers. When employing hBN–water nanofluid in a counter-flow heat exchanger instead of distilled water, the results showed a 16.7% increase in the overall heat transfer coefficient. The findings also showed that, in comparison to a counter-flow heat exchanger, employing hBN nanofluid as the cold fluid in a parallel-flow heat exchanger produced superior results in terms of an increase in heat transfer. The effects of nanofluid concentration on pressure drops were investigated through experiments conducted in both parallel- and counter-flow conditions.

Flow Boiling Heat Transfer in Enhanced Tubes With Composite Structure

Abstract To fill the research gaps in the study of flow boiling on composite surfaces, four heat exchange tubes with different structures were investigated: an enhanced tube with herringbone teeth (EHT_HB), a tube with a dimple structure (EHT_DIM), a tube with a composite herringbone tooth/dimple structure (EHT_HB/DIM), and a smooth tube as a baseline for comparison purposes. The experimental conditions were set as follows: saturation temperature 6 °C, mass flux 50–205 kg/(m2 · s), and vapor quality 0.2–0.8. After confirming the validity of the experimental results, the effects of the mass flux on the flow boiling heat transfer and pressure drop characteristics were examined. Results showed that the flow boiling heat transfer coefficient and pressure drop increase with the increase of the mass flux and the vapor quality in the tested tubes. The EHT_HB/DIM tube was found to combine the advantages of the two structures and to have the highest heat transfer coefficient. The average value of the heat transfer coefficient was found to be 43.75% higher than that of the smooth tube. Also, the average flow boiling heat transfer coefficients of the EHT_HB and the EHT_DIM tubes were found to be 15% and 35% higher than that of the smooth tube, respectively. From the perspective of the frictional pressure drop, it was found that the EHT_HB/DIM tube exhibited the maximum frictional pressure drop. The optimum working conditions of the enhanced tubes were determined by introducing a performance factor that captures the combined effects of heat transfer and pressure drop.

Study on the effect of pressure in humid air dehumidificationournal

In this paper, there are problems such as large energy consumption and complex system in the field of condensation dehumidification. It is found that increasing pressure can strengthen the effect of condensation dehumidification, simplify the system and reduce energy consumption. So this paper simulates the condensation and dehumidification process of humid air in horizontal pipe under positive pressure. The results show that the dehumidification capacity increases by 25%∼30% when the pressure increases by 100kPa on average. The increase of pressure has little effect on the heat transfer coefficient, but the increase of humidity increases the heat transfer coefficient more obvious. When the humidity of wet air increases by 20%, the heat transfer coefficient increases by 18% ∼ 33%. The dehumidification capacity and heat transfer coefficient increase with the increase of pipe diameter and fluid flow rate.

Development of a novel solar dryer with an incorporated heat exchanger

This study analyzes the thermal performance of an indirect-type solar dryer incorporated with a heat exchanger to recover heat from the exhaust. Data were recorded for 8 h from 9:00 to 17:00 from November to January to determine the drying rate for varying airflows from 2 l/s to 12 l/s under the weather conditions of Nepal and Bhutan. The air temperatures in multiple locations in the dryer were recorded and logged for 30-second intervals. The results indicated that incorporating a simple heat exchanger can achieve 78 % and 81 % effectiveness for the lowest tested airflow of 2.5 l/s and 2 l/s in Nepal and Bhutan. The heat transfer effectiveness increases with decreasing flow, resulting in a higher cold side outlet temperature of the heat exchanger for lower airflows. The solar air collector demonstrated efficient performance, achieving 80 % and 90 % efficiencies for the highest tested airflows of 12 l/s and 10 l/s in Nepal and Bhutan, respectively. Due to an increased heat transfer coefficient, the incoming air can effectively remove the accumulated heat from the absorber plate for higher airflows. The drying rates were observed to be the highest for 12 l/s, with a value of 85 g/(h × m2) for apples and 10 l/s, with a value of 56 g/(h × m2) for gingers in Nepal and Bhutan, respectively. From both cases, it can be concluded that the highest tested airflows provide higher air circulation for effective heat and mass transfer from the product to the surrounding air for drying.

Numerical investigation of thermal-hydraulic characteristics in cross-flow heat exchangers with different twisted oval tubes

This study presents a new strategy to strengthen the flow and thermal performance of gas-liquid tube bundle heat exchangers by combining oval tubes with variable-direction twist method. The effects of twist direction, twist angle and flow velocity on the overall performance were investigated. The variable-direction twisted oval tube enhances the mixing degree of the main stream and the tail vortex, thereby improving the thermal performance and reducing the pressure drop. Both heat transfer coefficient and pressure drop increase with the increase of twist angle, and the overall performance is negatively correlated. Twist period has little effect on overall performance. Convective heat transfer coefficient of the variable-direction twisted oval tube with a twist angle of 120° is increased by 5.8%–10.2%, pressure drop is reduced by 5.0%–7.8% and overall performance is increased by 7.4%–10.7%, as compared circular tube bundle. The proposed variable-direction twisted oval tube realizes the synergistic enhancement of thermal-hydraulic performance, and can directly replace the traditional circular tube. The work of this paper provides technical guidance for improving the processing technology of twisted oval tube and developing new heat exchangers.

Investigation of heat transfer and pressure drop characteristics in metal-foam filled channels in a plate heat exchanger: A comparative experimental study

An experiment was conducted on a single-phase system using water as the working fluid in a Gasket Plate Heat Exchanger (GPHE). The copper metal foam was employed on the corrugated profile in this experiment. The experiment was calibrated using iterative multiple linear regression analysis to find the coefficient of heat transfer on the hot water side for the given heat exchanger with a 60° corrugation angle. A comparative study was carried out between channels that were plain and modified with metal foam. The analysis focused on various factors, including the heat transfer coefficient, frictional pressure drop characteristics, pumping power, and volume goodness factor. The experiments were performed within a Reynolds number range of 200 to 1000, with the hot and cold water temperatures set at 60 °C and 30 °C, respectively. The experiments used copper metal foam with 50 pores per inch (PPI). The foam had a porosity ranging from 0.6 to 0.9, with a pore size of 1 mm. The Nusselt number for the modified GPHE was 1.97 times higher than that of the plain GPHE. Additionally, the frictional pressure drop for the modified heat exchanger was 1.89 times higher than that of the plain heat exchangers. The rate of frictional pressure drop increases at higher Reynolds numbers was higher than the heat transfer coefficient increase for both the plain and modified GPHE. The modified plate heat exchanger shows superior thermal performance compared to a plain GPHE at any given friction power conditions. Additionally, using metal foam-filled channels in contrast to plain corrugated plate channels suggests that the modified GPHE can achieve a more compact design for the same heat-duty application.

Heat transfer in the melting of ice slurry during flow in a vertical slit channel

The article concerns the heat transfer process of ethanol ice slurry during downward and upward flow in a vertical slit channel (3x35.8x700mm) under constant heat flux density conditions. Experimental studies were conducted for three initial concentrations of ethanol (Xvai = 10.5 %, 13.2 %, 15.8 %) and mass fractions of ice of 0 ≤ xs ≤ 30 %. For upward flow, heat transfer coefficients were 6–14 % higher than for downward flow. For laminar flow, a greater effect of the melting process was observed, and for turbulent flow, the convection process had a greater effect on heat transfer coefficients. For laminar flow, the heat transfer coefficients of the ice slurry can be 200 % higher than the corresponding values for the carrier fluid. In turbulent flow, the corresponding increase in heat transfer coefficients did not exceed 15 %. For generalised non-Newtonian flow of ice slurry, criterion relationships were proposed for calculating heat transfer coefficients, taking into account the effect of the concentration of the carrier fluid, mass fractions of ice, its melting process, as well as the nature and direction of the flow.

Combined Effect of Structured Surface and Biosurfactant in Pool Boiling Heat Transfer Enhancement

An attempt has been made to explore the combined effect of structured surfaces (segmented finned surface and uniform cross-section surface) and Rhamnolipid biosurfactant to improve heat transfer rate in pool boiling. Experimental investigations were performed at normal atmospheric condition and till reaching critical heat flux. The results shows that the segmented finned surface has shown better heat transfer than plain surfaces, with a 200% increase in heat transfer coefficient. In contrast, a uniform cross-section surface showed an improvement in heat transfer coefficient of 107% over a plain surface. The reasons for better thermal performance in segmented finned configuration can be associated to the reduced surface tension of the working fluid increasing more nucleation sites. Additionally, better rewetting phenomena and bubble evolution from the segmented finned surface have also assisted in improving the heat transfer rate. Moreover, the pool boiling results of all the heating surfaces with surfactant solution is compared with pure water. It has been observed that all heating surfaces have performed better with surfactant solution compared to pure water. However, the CHF obtained on all heating surfaces with surfactant solution were lesser than pure water. Low CHF is due to the foamability of the surfactant solution.

Comprehensive Evaluation of the Performances of Heat Exchangers with Aluminum and Copper Finned Tubes

The finned-tube heat exchanger is the core part of an air conditioning system. Its heat exchange performance directly affects the energy consumption and efficiency of the air conditioner. The shortage and rising price of copper have led to increasing replacement of copper tubes with aluminum tubes in finned-tube heat exchangers. This paper studies two kinds of such heat exchangers, one consisting of copper tubes and aluminum fins and the other consisting of aluminum tubes and aluminum fins. The influences of the different base tube materials on heat transfer are compared and analyzed in terms of heat transfer strength and cost per unit heat transfer. The results show that the heat transfer and heat transfer coefficient increase with increasing inlet wind speed. Under different inlet wind speeds, the heat transfer and heat transfer coefficient of the finned-tube heat exchanger with aluminum tubes are 4%–12% and 7%%–9% lower than those of an identically structured heat exchanger with copper tubes, respectively. The aluminum-aluminum exchanger achieves 67% higher heat transfer than that of the copper-aluminum exchanger at only 8% of the cost. These results are significant for guiding the development and application of finned-tube heat exchangers.

Numerical simulation study on heat transfer and fluid performance of novel calcium carbide heat collection system

This article proposes a novel recovery system for the substantial waste heat from the hot calcium carbide (CA). The study employs numerical simulation to investigate the heat transfer performance of the heat collection system (HCS). The research explores the effects of outlet position, inlet velocity, and inlet temperature on the operational characteristics and heat transfer performance of the HCS. The results indicate that optimal heat transfer performance is achieved when the outlet position is at the center of the collector. Instantaneous efficiency (IE), exergy loss (EL), pressure drop (PD), and heat transfer coefficient (HTC) increase with the velocity, while effectiveness decreases with the velocity. The peak values for IE, effectiveness, and HTC are 28.22%, 29.69%, and 1212.45 W/(m2*K), respectively. The heat transfer performance of the HCS is highest when the inlet temperature is 280K. The proposed CA HCS holds significant importance for recovering waste heat from electric stone production, providing a theoretical basis for subsequent experimental work.

Effect of nanoparticle concentration and surfactants on nanofluid pool boiling

Silica nanofluids are prepared with a concentration varying from 0.001 vol.% to 0.003 vol.%, and pool boiling of the nanofluids is experimentally investigated. It is found that critical heat flux and heat transfer coefficient increase by a maximum of 62.66% and 45.88% compared with deionized water. The best boiling performance is achieved with the nanofluid of 0.002 vol.%. In addition, the paper further investigated the effect of surfactants on nanofluid boiling, i.e., cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and polysorbate 20 (Tween 20). The heat transfer coefficients of the nanofluids with CATB and with SDS increase by 55.45% and 9.73% compared to the nanofluid without surfactant. However, the heat transfer coefficient of the nanofluid with Tween 20 is lower than that of the nanofluid without surfactant. Finally, surface characterizations and bubble dynamics are carried out to reveal the mechanism of nanofluid boiling enhancement, as well as the effect of surfactants on nanofluid boiling. The results show that nanoparticles deposited on the surface during boiling, which increases surface roughness and reduces surface contact angles, promoting bubble nucleation and departure as well as liquid supply.