Showing papers on "Heat transfer coefficient published in 2009"
TL;DR: The high surface tension forces offered by liquids in nanowire arrays made of Si and Cu can be exploited to increase both the critical heat flux (CHF) and the heat transfer coefficient (HTC) by more than 100%.
Abstract: Boiling is a common mechanism for liquid-vapor phase transition and is widely exploited in power generation and refrigeration devices and systems. The efficacy of boiling heat transfer is characterized by two parameters: (a) heat transfer coefficient (HTC) or the thermal conductance; (b) the critical heat flux (CHF) limit that demarcates the transition from high HTC to very low HTC. While increasing the CHF and the HTC has significant impact on system-level energy efficiency, safety, and cost, their values for water and other heat transfer fluids have essentially remained unchanged for many decades. Here we report that the high surface tension forces offered by liquids in nanowire arrays made of Si and Cu can be exploited to increase both the CHF and the HTC by more than 100%.
623 citations
TL;DR: In this article, the authors measured the pressure drop and convective heat transfer coefficient of water-based Al2O3 nanofluids flowing through a uniformly heated circular tube in the fully developed laminar flow regime.
573 citations
TL;DR: In this paper, the effect of particle size on convective heat transfer in laminar developing region was evaluated with alumina-water nanofluids in tube flow with constant heat flux.
528 citations
TL;DR: In this article, the effect of nanofluids on convective heat transfer was investigated through a circular straight tube with a constant heat flux condition in the laminar and turbulent flow regime.
474 citations
TL;DR: In this paper, heat transfer and viscous pressure loss were investigated for alumina-water and zirconia-water nanofluids in a flow loop with a vertical heated tube.
472 citations
TL;DR: In this paper, an experimental study on the forced convective heat transfer and flow characteristics of a nanofluid consisting of water and 0.2 vol.% TiO2 nanoparticles was performed.
458 citations
TL;DR: In this paper, an experimental energy storage system has been designed using a horizontal concentric tube heat exchanger incorporating a medium temperature phase change material (PCM) Erythritol, with a melting point of 117.7°C.
456 citations
TL;DR: In this article, a single-and two-phase model with either constant or temperature-dependent properties is employed to develop laminar forced convection flow of a water-Al2O3 nanofluid in a circular tube, submitted to a constant and uniform heat flux at the wall.
434 citations
TL;DR: In this paper, the influence of surface wettability on nucleate boiling heat transfer was investigated and a new approach of nucleation mechanism was established to clarify the nexus between the surface wetability and the nucleate heating transfer.
397 citations
TL;DR: In this article, the Nusselt number prediction for nanofluids has been validated with existing well established correlations, and it is found that smaller diameter nanoparticles have higher viscosity.
379 citations
TL;DR: In this paper, different viscosity and thermal conductivity models are used to evaluate heat transfer enhancement in horizontal annuli using variable properties of Al2O3-water nanofluid.
TL;DR: In this paper, the heat transfer process during melting (charge) and solidification (discharge) of five small heat exchangers working as latent heat thermal storage systems was investigated experimentally, and the results showed that the double pipe heat exchanger with the PCM embedded in a graphite matrix (DPHX-PCM matrix) is the one with higher values, in the range of 700-800 W/m 2 -K, which are one order of magnitude higher than the ones presented by the second best.
TL;DR: In this article, an integrated microsystem consisting of a single microchannel on one side, and two localized heaters and five polysilicon temperature sensors along the channel on the other side were fabricated.
TL;DR: In this article, a single slope-single basin solar still with and without phase change material (PCM) under the basin liner of the still has been investigated by computer simulation.
TL;DR: In this article, a composite correlation is developed from a database of 3899 data points from 14 studies in the literature covering 12 different wetting and non-wetting fluids, hydraulic diameters ranging from 016 to 292mm, and confinement numbers from 03 to 40.
TL;DR: In this paper, the thermal conductivity of nanofluid has been determined by model proposed by Patel et al. and the fluid was considered as Newtonian as well as non-Newtonian for a wide range of Reynolds number (Re = 5 to 1500) and solid volume fraction (0.00 ⩽ ϕ⩽ 0.050 ).
TL;DR: The present study investigates the effects of heat and mass transfer on peristaltic transport in a porous space with compliant walls under long-wavelength and low-Reynolds number approximations.
TL;DR: A review of the recent experimental, analytical, and numerical work into single bubble heat transfer is presented to determine the contribution of each of the above mechanisms to the overall heat transfer as discussed by the authors.
TL;DR: In this article, the authors investigated the natural convection heat transfer of water-based nanofluids in an inclined square enclosure where the left vertical side is heated with a constant heat flux, the right side is cooled, and the other sides are kept adiabatic.
TL;DR: In this article, the authors present the results of a numerical study on natural convection heat transfer in an inclined enclosure filled with a water-CuO nanofluid, where two opposite walls of the enclosure are insulated and the other two walls are kept at different temperatures.
Abstract: This article presents the results of a numerical study on natural convection heat transfer in an inclined enclosure filled with a water-CuO nanofluid. Two opposite walls of the enclosure are insulated and the other two walls are kept at different temperatures. The transport equations for a Newtonian fluid are solved numerically with a finite volume approach using the SIMPLE algorithm. The influence of pertinent parameters such as Rayleigh number, inclination angle, and solid volume fraction on the heat transfer characteristics of natural convection is studied. The results indicate that adding nanoparticles into pure water improves its heat transfer performance; however, there is an optimum solid volume fraction which maximises the heat transfer rate. The results also show that the inclination angle has a significant impact on the flow and temperature fields and the heat transfer performance at high Rayleigh numbers. In fact, the heat transfer rate is maximised at a specific inclination angle depending on ...
TL;DR: In this article, a combined discrete particle simulation (DPS) and computational fluid dynamics (CFD) approach is extended to study particle-particle and particle-fluid heat transfer in packed and bubbling fluidized beds at an individual particle scale.
Abstract: The approach of combined discrete particle simulation (DPS) and computational fluid dynamics (CFD), which has been increasingly applied to the modeling of particle-fluid flow, is extended to study particle-particle and particle-fluid heat transfer in packed and bubbling fluidized beds at an individual particle scale. The development of this model is described first, involving three heat transfer mechanisms: fluid-particle convection, particle-particle conduction and particle radiation. The model is then validated by comparing the predicted results with those measured in the literature in terms of bed effective thermal conductivity and individual particle heat transfer characteristics. The contribution of each of the three heat transfer mechanisms is quantified and analyzed. The results confirm that under certain conditions, individual particle heat transfer coefficient (HTC) can be constant in a fluidized bed, independent of gas superficial velocities. However, the relationship between HTC and gas superficial velocity varies with flow conditions and material properties such as thermal conductivities. The effectiveness and possible limitation of the hot sphere approach recently used in the experimental studies of heat transfer in fluidized beds are discussed. The results show that the proposed model offers an effective method to elucidate the mechanisms governing the heat transfer in packed and bubbling fluidized beds at a particle scale. The need for further development in this area is also discussed. © 2009 American Institute of Chemical Engineers AIChE J, 2009
TL;DR: In this paper, the effect of surface roughness on pool boiling heat transfer is experimentally explored over a wide range of roughness values in water and Fluorinert ™ FC-77, two fluids with different thermal properties and wetting characteristics.
Abstract: The effect of surface roughness on pool boiling heat transfer is experimentally explored over a wide range of roughness values in water and Fluorinert ™ FC-77, two fluids with different thermal properties and wetting characteristics. The test surfaces ranged from a polished surface (Ra between 0.027 m and 0.038 m) to electrical discharge machined (EDM) surfaces with a roughness Ra ranging from 1.08 m to 10.0 m. Different trends were observed in the heat transfer coefficient with respect to the surface roughness between the two fluids on the same set of surfaces. For FC-77, the heat transfer coefficient was found to continually increase with increasing roughness. For water, on the other hand, EDM surfaces of intermediate roughness displayed similar heat transfer coefficients that were higher than for the polished surface, while the roughest surface showed the highest heat transfer coefficients. The heat transfer coefficients were more strongly influenced by surface roughness with FC-77 than with water. For FC-77, the roughest surface produced 210% higher heat transfer coefficients than the polished surface while for water, a more modest 100% enhancement was measured between the same set of surfaces. Although the results highlight the inadequacy of characterizing nucleate pool boiling data using Ra, the observed effect of roughness was correlated using h Ra as has been done in several prior studies. The experimental results were compared with predictions from several widely used correlations in the literature. DOI: 10.1115/1.3220144
Journal Article•
TL;DR: In this paper, the problem of steady laminar two-dimensional boundary layer flow and heat transfer of an incompressible viscous fluid with a presence of thermal radiation over an exponentially stretching sheet is investigated numerically.
Abstract: In this paper, the problem of steady laminar two-dimensional boundary layer flow and heat transfer of an incompressible viscous fluid with a presence of thermal radiation over an exponentially stretching sheet is investigated numerically. The governing boundary layer equations are reduced into ordinary differential equations by a similarity transformation. The transformed equations are solved numerically using an implicit finitedifference scheme known as the Keller-box method. The numerical solutions for the wall skin friction coefficient, the heat transfer coefficient, and the velocity and temperature profiles are computed, analyzed and discussed.
TL;DR: In this paper, the effects of channel dimensions, channel wall thickness, bottom thickness and inlet velocity on the pressure drop, thermal resistance and the maximum allowable heat flux are presented.
TL;DR: In this paper, a regression equation is developed to estimate the Nusselt number valid for both water and nanofluid flowing in the transition flow Reynolds number range in circular plain tube and with tape inserts.
TL;DR: In this paper, the nucleate pool boiling heat transfer of a refrigerant-based nanofluid was investigated at different nanoparticle concentrations and pressures, and the results indicated that the boiling temperature of nucleate pools deteriorated with increasing particle concentrations, especially at high heat flux.
TL;DR: The results for velocity, temperature, stream function and heat transfer coefficient obtained in the analysis have been evaluated numerically and discussed briefly and the numerical result shows that more trapped bolus appears with increasing Knudsen number.
TL;DR: In this paper, the authors evaluated the performance of nanofluid convective heat transfer and viscosity measurements and evaluated how they performed heating buildings in cold regions, and found that the heat transfer coefficient increases with volume concentration, and that using nanoparticles in heat exchangers could reduce volumetric and mass flow rates, and result in an overall pumping power savings.
TL;DR: In this article, the influence of nanoparticles on the heat transfer characteristics of refrigerant-based nanofluid flow boiling inside a horizontal smooth tube was investigated, and a correlation for predicting heat transfer performance was presented.
Abstract: The objective of this paper is to investigate the influence of nanoparticles on the heat transfer characteristics of refrigerant-based nanofluid flow boiling inside a horizontal smooth tube, and to present a correlation for predicting heat transfer performance of refrigerant-based nanofluid. For the convenience of preparing refrigerant-based nanofluid, R113 refrigerant and CuO nanoparticles were used. Experimental conditions include an evaporation pressure of 78.25 kPa, mass fluxes from 100 to 200 kg m−2 s−1, heat fluxes from 3.08 to 6.16 kW m−2, inlet vapor qualities from 0.2 to 0.7, and mass fractions of nanoparticles from 0 to 0.5 wt%. The experimental results show that the heat transfer coefficient of refrigerant-based nanofluid is larger than that of pure refrigerant, and the maximum enhancement of heat transfer coefficient is 29.7%. A heat transfer correlation for refrigerant-based nanofluid is proposed, and the predictions agree with 93% of the experimental data within the deviation of ±20%.
TL;DR: In this paper, the inlet/outlet arrangement effects on the fluid flow and heat transfer inside the heat sinks are numerically investigated, and it is suggested that better heat sink performance can be achieved when the coolant is supplied and collected vertically.