Heat Transfer Performance Of Water Research Articles

Experimental investigation on boiling heat transfer performance of fractal microchannels for high heat dissipation applications

This study proposes novel fractal microchannels (FMCs) manufactured by additive manufacturing for direct cooling systems with high heat dissipation. The boiling heat transfer performance of water in the FMC was experimentally investigated under various operating conditions. Furthermore, a comparative heat transfer performance evaluation between the FMC and conventional microchannels (CMCs) was conducted. The critical heat flux of water in the FMC was 11 % higher than that in the CMC due to enhanced boiling heat transfer. In the low heat flux region, the boiling heat transfer coefficient (BHTC) of water in the FMC increased as the mass flow rate increased owing to the liquid replenishing and rewetting effects. However, in the moderate and high heat flux regions, the effect of the mass flow rate was not significant owing to the dominance of nucleate boiling. The BHTC of water in the FMC increased as the water temperature decreased due to the increased rewetting frequency. This study provides useful information for improving the design of direct cooling channels and for understanding the fundamental boiling heat transfer characteristics in FMCs. Furthermore, the proposed FMC can be applied in fields requiring high heat dissipation, such as electronic devices, power plants, and hot stamping.

Numerical investigation on heat transfer performance of a confined slot jet impingement with different MEPCM-water slurries using two-phase Eulerian–Eulerian model

An in-house Fortran-based two-phase Eulerian–Eulerian solver is used to study an impinging jet with microencapsulated phase change material (MEPCM)-water slurry in a minichannel. The heat transfer performance of water based n-eicosane and n-octadecane MEPCM slurries are reported here. The melting pattern of the particles within the minichannel are also reported at different parameters. Figure of merit (FOM) is used to quantify the heat transfer performance of the MEPCM-water slurry taking into account both the thermal and flow characteristics of the slurry. The heat transfer enhancement around 72% is found in the average Nusselt number for a 5%-n-eicosane water slurry, compared to that of pure water at a jet Reynolds number of 200. The melting region of MEPCM particles is found to come closer to the heated walls with an increase in Reynolds number. An increase in the Reynolds number from 100 to 300 has brought an increment of around 81% in the Nusselt number at the jet impinging region, while the increment in the average Nusselt number is around 145%. The figure of merit (FOM), increases from 1.34 to 1.64 with an increase in particle concentration from 1% to 10%, at Re = 300. By comparing the figure of merit values, the best heat transfer performance compared to pure water is obtained for water-based n-eicosane slurry at Re = 100, and εs=1%. A parametric study involving Reynolds number, particle concentration, and channel height to jet width ratio has been reported. Present results are validated with numerical and experimental results available in the literature.

Experiment and prediction model study on pool boiling heat transfer of water in the electric field with periodically changing direction

The pool boiling heat transfer performance of water could be greatly improved by the constant electric field with the bar electrode. While, the heat transfer of water enhanced by electric field with periodically changing direction is rarely involved. Therefore, the heat transfer performance of water, mechanism analysis and prediction model for heat transfer characteristic affected by the electric field with periodically changing direction were studied. Individually, the heat transfer coefficient (HTC) and critical heat flux (CHF) were compared. Meanwhile, the difference of droplet shape, size of contact angle, bubbles growth and detachment on heat transfer surface were analyzed. Besides, semi-empirical prediction models for HTC and CHF were proposed. Results show that the HTC and CHF are significantly enhanced with decrease of switch period. While, this enhancement is diminished with increase of heat flux. Furthermore, when compared to the constant direction electric field, mechanism analysis indicates that the electric field with periodically changing direction not only enhances the rate of boiling fluid wetting the boiling heat transfer surface, but also accelerates the growth and detachment of bubbles. Moreover, predicted curves of model agree well with the experimental data, and variation of surface tension is considered as the main factor affecting heat transfer.

Effect of nanostructure on explosive boiling of thin liquid water film on a hot copper surface: a molecular dynamics study

ABSTRACT The explosive boiling characteristics of water on the copper surface are studied based on molecular dynamics simulation. The effects of the size, number and shape of nanostructures on the heat transfer performance of water explosive boiling are analysed. The results show that the heat transfer performance and boiling rate of liquid film increase with the increase of nanostructure size. At the same volume concentration of nanostructures, the boiling rate of the liquid film increases with the increase of the number of nanostructures. Compared with the spherical nanostructure, the water heating rate is higher and the heat flux of water is larger after the cylindrical nanostructure is adopted. Therefore, using cylindrical nanostructures and increasing, the uniformity of nanostructures on the surface can effectively improve the boiling heat transfer performance of water on the copper surface.

Experimental study on flow boiling heat transfer characteristics of multi-channel modified filled foam metal small channel

This experiment reports the experimental study on the heat transfer performance of water in the flow-boiling heat transfer process of different modified foam metal-filled channels. In the experiment, the foam metal has subjected to surface hydrophobicity treatment, surface roughness modification treatment, and gradient pore density stacking treatment. The mass flow rate is 50–150 ml/min, and the heat flux is 15 kW/m2 – 25 kW/m2. The pore density of foam metal is 20 PPI, 50 PPI, and 110 PPI. A high-speed camera, micro camera, and electron microscope are used to record and observe the internal flow of the channel, the results after surface treatment, and the related reaction mechanism. The experiment uses different modifications as the basis for grouping and uses heat flux and mass flow rate as variables to perform multiple sets of orthogonal experiments. At the same time, the prediction model of matching heat transfer coefficient and the correlation of pressure drop gradient are proposed. Construct a comprehensive evaluation index of heat exchange of porous foam metal, which is evaluating the heat exchange performance of foam metal that matches the change of resistance.

Enhanced Heat Transfer Performance of the Tube Heat Exchangers Using Carbon-Based Nanofluids

The wet ball milling method was used and a dispersant (gum Arabic) was added to prepare various concentrations (0.05 and 0.2 wt%) of carbon-based nanofluids (CBNFs) by a two-step synthesis method as working fluids for heat exchange. CBNFs were actually used in a tube heat exchanger (THE) for heat transfer performance experiments. The heat transfer performance of water and CBNFs was estimated under different heating powers and flow rates of working fluid. The pump power consumption (Ppe) of 0.05 wt% CBNF was found to be similar to that of water, but the Ppe of 0.2 wt% CBNF was higher than that of water. The convective heat transfer coefficient (HTC) of CBNF in the was higher than that of water, and the HTC of 0.05 wt% and 0.2 wt% CBNF was optimal at the heating power of 120 W and 80 W, respectively. The average HTC of 0.05 wt% CBNFs at 120 W heating power was about 3.33% higher than that of water, while that of 0.2 wt% CBNFs at 80 W heating power was about 4.52% higher than that of water. Considering the Ppe and HTC concomitantly, the best overall system performance was exhibited by 0.05 wt% CBNFs.

Heat transfer enhancement in a rectangular channel with pillars

This paper numerically studied the heat transfer performance of water flowing in a rectangular channel with pillar structures. We systematically investigated the influence of the pitch, inclination angle, shape, and pillar arrangement on the flow and heat transfer characteristics. The results show that adopting spacing with S/d=2 can improve heat transfer performance sufficiently for a low Reynolds number case. Meanwhile, the noticeable enhancement can also be observed by making the pillar inclination direction consistent with the flow direction or staggered rhombic-shaped.

Heat transfer performance of water based nanofluids: A review

Purpose of present study is to provide detailed literature review and status of research in the field of nanofluid technology. Aim of this paper is to understand effect of nanofluids on heat transfer heat transfer performance and then obtaining their effects on heat transfer enhancement over base fluid. Various works related water based nanofluids are studied throughout the process and then analyzed to understand the behavior of these nanofluids.

Comprehensive Study of the Effect of the Addition of Four Drag Reducing Macromolecules on the Pressure Drop and Heat Transfer Performance of Water in a Finned Tube Heat Exchanger

In the present study the effects of the addition of four drag reducing agents (DRA), including carboxy methyl cellulose with high molecular weight (DRA1) and medium molecular weight (DRA2), polyacrylamide (DRA3) and the natural polymer, xanthan gum (DRA4), to water on the pressure drop and heat transfer performance in a finned tube-heat exchanger were compared. Laminar flow (Reynolds number (Re) <1400) was studied to transfer heat between water and air in the finned tube heat exchanger. The results showed that DRA1, with a maximum %DR of 26%, and DRA4, with a maximum %DR of 5%, were the highest and the lowest obtained results, respectively. In the case of heat transfer reduction percentage (%HTR), DRA4, having more than 34.5%, was the highest, and DRA1, with about 13.7%, was the lowest result for the concentration range of 0-100 ppm and temperature range of 40–65 °C.

Transient heat transfer characteristics and process intensification with Al2O3-water and TiO2-water nanofluids: An experimental investigation

This paper aims to provide an experimental investigation on the thermal conductivity enhancement and heat transfer performance of water based Al2O3 and TiO2nanofluids. Nanofluids at different concentrations of 0.125 %, 0.25 %, 0.5 % and 1.5 % of m/V were prepared by two-step method adding Polyvinyl alcohol and Polyvinylpyrrolidone as surfactants. Then, the stability of nanofluids was examined using visual inspection and zeta potential analysis. The thermal conductivity value of test samples was measured using sound velocities in test samples over 25 °C–55 °C for each10 °C rise. Heat transfer performance of nanofluids was examined under transient condition through an experimental setup over 25 °C–60 °C. Stable nanofluids with little sedimentation were obtained. Enhancements in Thermal conductivity and heat transfer performance of nanofluids were achieved. Al2O3 nanofluids have shown the best results with a maximum of 44 % increment in thermal conductivity and a maximum of 21 % increment in transient heat transfer performance. Polyvinylpyrrolidone showed better effect than Polyvinyl alcohol on improving the stability of nanofluids. However, superiority of any surfactant in context of the thermal conductivity and heat transfer performance of nanofluids was ambiguous. Finally, enhanced thermal conductivity and heat transfer performance compared to their basefluids enables them as a potential cooling medium.

Numerical investigation of heat transfer performance of water flowing through a reservoir with two intersecting fractures

Understanding the water flow and heat transfer process in rock fractures is crucial for the development and utilization of geothermal reservoirs. This study develops a numerical model of a granite reservoir with two intersecting fractures to evaluate the heat production performance. Then, the evolution of the distribution of the rock and fluid temperatures is investigated. In addition, the effect of the injection temperature, heat transfer coefficient and injection flow velocity on the heat transfer characteristics are analyzed. Additionally, in order to study heat transfer performance with different fracture distributions, four cases of intersecting fractures with different angles are designed. The results indicate that, at different locations along the direction of seepage, the water temperature changes with time follow different rules. The results also show that, when the distribution of fractures is more uniform in the reservoir, the heat extraction rate of flowing water from the surrounding reservoir is faster. These results provided theoretical basis for geothermal system location selection, optimal selection of the reservoir stimulation scheme and reservoir thermal output prediction.

Towards experimental and modeling study of heat transfer performance of water- SiO2 nanofluid in quadrangular cross-section channels

ABSTRACTNanofluids have found extended applications in different industrial and engineering systems nowadays. This study aims to investigate the accurate prediction of SiO2 nanofluid effect on the heat transfer performance, specifically convective heat transfer coefficient (H), of a quadrangular cross-section channel by considering affecting fluid flow specifications factors of Re, Pr, and concentration of nanoparticles (x) in the employing working fluid. An experimental setup is used to prepare a database consisting of 270 data points on the H, of SiO2 nanofluids. These data are then applied to develop predictive models based on three intelligent algorithms, namely multi-layer perceptron (MLP), adaptive neuro-fuzzy inference system (ANFIS), and least squares support vector machine (LSSVM), respectively. Graphical and statistical error criterions are carried out to evaluate the credibility of the proposed approaches. The LSSVM method had the precise performance regarding the mean squared error (MSE) and the coefficient of determination (R2) of 59.7 and 0.9992, respectively. A sensitivity analysis is also carried out to assess the impact of different parameters on the H demonstrating that the Prandtl number has the highest impact with a relevancy factor (r) of 0.524.

Experimental and LBM simulation study on the effect of bubbles merging on flow boiling

Abstract Surfactant additives can prevent bubbles merging and change the flow mode in flow boiling. This work presented the effect of bubbles merging on flow boiling heat transfer performance of water. Flow boiling experiment and lattice Boltzmann method (LBM) were carried out in a rectangular channel. With a high speed camera, the flow boiling process has been recorded. D2Q9 model and the Peng-Robinson (P-R) equation of two phase state (EOS) were used to simulate flow boiling process. The present experimental results showed that surfactant addition could enhance the flow boiling heat transfer and increased the critical heat flux (CHF). And there were more nucleation sites, larger bubbles density and smaller bubble size in surfactant solution. The present simulation results showed that the flow boiling without bubbles merging has higher and more stable average Nu number. The bubbles merging made the middle nucleation sites lose effectiveness. It implies that preventing bubbles merging is another factor of surfactant addition enhancing boiling heat transfer.

Heat transfer performance of water and Nanoencapsulated n-nonadecane based Nanofluids in a double pipe heat exchanger

The heat transfer and pressure drop characteristics for the flow of water, which is base fluid, and nanoencapsulated n-nonadecane based nanofluids in a double pipe heat exchanger were investigated. The results showed that no improvement in overall heat transfer coefficient was observed for the nanofluids containing 0.42% and 0.84% solid volume ratios with reference to the base fluid, while an improvement of about 10% was obtained for the nanofluids containing 1.68% solid volume ratio. It was found that the friction factors for the nanofluids exhibited a slight increase reference to the base fluid. A performance analysis based on constant pumping power was also performed.

Intensification of convective heat transfer in water/ethylene glycol based nanofluids containing TiO2 nanoparticles

This paper presents a study of heat transfer performance of water, ethylene glycol (EG) and their mixtures of varying compositions and comparison thereof. The present work demonstrates the enhancement in convective heat transfer in nanofluids. The nanofluids were prepared by adding TiO2 nanoparticles (having a particle size below 100nm) in a base fluid. A binary mixture of EG (40%) and water (60%) was used as a base fluid. Nanofluids with varied volume fraction between 0 and 0.5 (volume fraction of TiO2 nanoparticles) were considered in the present study. The experimental setup used was consisting of a test section that includes 750mm long copper pipe with 8mm inner diameter and a heater. The test section was covered with an insulation layer to minimize the heat losses. Temperature measurement was done with thermocouples. The experiments were conducted to study the effects of solid volume fraction, nanofluid flow rate and the inlet temperature on the heat transfer performance of the nanofluids. The results show an enhancement in heat transfer coefficient with increased volume fraction of TiO2 nanoparticles. The maximum enhancement of 105% in heat transfer coefficient was observed for the nanofluid with solid volume fraction of 0.5.

Heat Transfer in Coiled Square Tubes for Laminar Flow of Slurry of Microencapsulated Phase Change Material

Passive heat transfer enhancement using a slurry of microencapsulated phase-change material (MEPCM) flowing in a laminar regime through a coiled duct of square cross section was evaluated. The phase-change material is n-octadecane. The flow behavior and heat transfer performance of water and MEPCM suspensions in various configurations (conical spiral, in-plane spiral, and helical spiral) of coiled tubes of square cross section was investigated. The results are compared with those for water as the base fluid flowing through a straight tube. A computational fluid dynamics (CFD) approach is used to simulate the laminar flow of water with MEPCM suspension in these geometries. The liquid suspension properties are expressed as functions of the volumetric concentration of MEPCM particles and the temperature. Improved heat transfer performance was obtained as the concentration of MEPCM suspension increased from 1 to 10%. However, the overall performance in terms of the pumping power consumed for unit heat transferred worsened.

Heat transfer characteristics of water flow in microtubes

This study provides an experimental investigation on forced convective heat transfer performance of water flowing through six microtubes with inner diameters ranging from 123 to 962 μm. A non-contacted liquid crystal thermography (LCT) temperature measurement method that proposed by Lin and Yang [T.-Y. Lin, C.-Y. Yang, An experimental investigation on forced convection heat transfer performance in microtubes by the method of liquid crystal thermography, International Journal of Heat and Mass Transfer (2007), doi:10.1016/j.ijheatmasstransfer.2007.03.038] was used in this study to measure the surface temperature of microtubes. The test results show that the conventional heat transfer correlations for laminar and turbulent flow can be well applied for predicting the fully developed heat transfer performance in microtubes. The transition occurs at Reynolds number from 2300 to 3000. This is also the same range as that for conventional tubes. There is no significant size effect for water flow in tubes within this diameter range. The laminar thermal entrance length for microtubes is longer than that estimated by the conventional correlation. The developing Nusselt numbers for 962 μm tube agree well with those predicted by the Shah and Bhatti [R.K. Shah, M.S. Bhatti, Laminar convective heat transfer in ducts, in: S. Kakac, R.K. Shah, W. Aung, (Eds.), Handbook of Single-Phase Convective Heat Transfer, Willy, New York, 1987] correlations. However, as the tube size decreases, the discrepancy between the test results and the predicting value increases.

Experimental Studies of Free Convection Heat Transfer in a Vertical Tube With Uniform Wall Heat Flux

Abstract The heat-transfer performance of water in a vertical tube closed at the bottom, with a length-radius ratio of 21 was experimentally determined for the case of uniform heat flux. The average performance was found to agree with the uniform wall-temperature results of Martin. This suggests that the uniform wall-temperature results of Martin for other fluids and other length-radius ratios may be utilized to predict the average performance for the uniform heat-flux boundary conditions.