Heat Transfer Coefficient Of Fluid Research Articles

Experimental investigation on the effect of nanofluid on the thermal performance of symmetric sintered U shaped heat pipe

In this study, the impact of Entrance Power and Silver nanofluid concentration (with base fluid ethanol and DI-water) on heat pipe thermal performance are considered. In order to reach the aim a U-shaped sintered heat pipe is utilized which causes occupied space to decline. The length of the heat pipe is 135 mm in each branch. On account of recognition the effect of working fluid on heat pipe thermal performance, thermal resistance and overall heat transfer coefficient in base working fluid and nano-colloidal silver are measured in the shape of thermosyphon. The working fluid is with volume percentages of 70 ethanol and 30 distilled water. The average size pertaining to the nanoparticle applied is 40 nm. In addition, the influences of nanofluid concentrations are measured by comparing three concentrations 0.001, 0.005, 0.1 vol%. The range of entrance power is from 10 to 40 W and the temperature of coolant has been changed from 20 to 40 °C. The results of the experiment indicate that by increasing entrance power, the temperatures of the condenser, evaporator and working temperature experience a rise. Furthermore, this causes a decrease of thermal resistance and an increase of overall heat transfer coefficient. A comparison of three concentrations reveals that in concentration of 50 ppm, thermal resistance compared to the base fluid has decreased to 42.26 % and overall heat transfer coefficient has gone up to 1883 (W/m2·°K) . Also, due to unexpected changes in concentration of 1000 ppm, the existence of an optimized concentration for the silver nanofluid in this heat pipe with this geometry has been clear.

Sensitivity study with respect to direction of ADI method during re-flooding in AHWR

Abstract The Advanced Heavy water Reactor (AHWR) is a natural circulation vertical pressure tube type boiling light water cooled and heavy water moderated reactor. As the AHWR fuel bundle quenching under accident condition is designed primarily with radial jets at several axial locations, bottom re-flooding still remain open as another option. Radial direction injection of emergency core cooling leads to rewetting of AHWR fuel cluster in circumferential direction. A 3D fuel pin model has been developed by using Finite Difference Method (FDM) of transient heat conduction equation. Alternating Direction Implicit technique of Finite Difference Method (FDM) has been used for discretisation of numerical equation in different time step at different direction. Sensitivity numerical study with respect to direction of ADI method has been carried out to optimize the time step during the transient as well as steady state and is found that it is insensitivity with direction of solution. Further, to assess influence of circumferential rewetting vis-à-vis axial rewetting. Both the analyses are carried out with same fluid temperature and heat transfer coefficients as boundary conditions. It has been found from the analyses that for radial jet, the circumferential conduction is significant and overall the fuel temperature falls in the quench plane with the initiation of quenching event. The paper discusses the sensitivity study with respect to direction of ADI solution and comparison of numerical results for circumferential and axial rewetting for single pin.

Investigation of Laminar Convective Heat Transfer of a Novel Tio2–Carbon Nanotube Hybrid Water-Based Nanofluid

The current study was conducted to investigate the convective heat transfer coefficient of a novel TiO2–CNT hybrid nanofluid through the shell-and-tube heat exchanger under a laminar flow and the effects of temperature and mass fraction on it. TiO2–CNT hybrid nanofluids were prepared using a new and modified hydrolysis technique. The thermal conductivity of the TiO2–CNT hybrid nanofluid and other thermo-physical properties were assessed. Results indicate that the effective thermal conductivity and heat transfer coefficient of the base fluid was influenced significantly and increased by the 0.2 wt% of this novel hybrid nanofluid in distilled water.

Numerical Study on the Skin Friction and Heat Transfer Coefficient of Non-Newtonian Power Law Fluid in Boundary Layer

The paper presents a dimensional analysis on the skin friction and heat transfer coefficient of the boundary layer flow in power law fluid. Based on the theoretical analysis the formula of the thickness, the friction coefficient and the heat transfer coefficient in non-Newtonian power law fluid boundary layer are obtained. By means of numerical simulation the phenomenon of power law fluid flowing on an infinite surface is studied. The temperature distribution is obtained numerically by considering the effect of the power law viscosity on thermal diffusivity and the characteristics of the flow and heat transfer are analyzed. The numerical results proved that the proposed estimate formula is reliable and effective. The results of the data analysis show that the estimation formula above mentioned is coincident well with the data from numerical simulation. The results show that the distribution of the thermal boundary layer depends not only on the velocity ratio parameter of the plate, but also on the power law index and Prandtl number of fluids.

Numerical Simulation of Heat Transfer Coefficient on Turbine Blade using Intermittency Factor Equation

This paper deals with the numerical simulation of fluid flow and heat transfer coefficient on a gas turbine blade. The mathematical model of flow is based on the Reynolds Averaged Navier-Stokes (RANS) equations completed with the formulation of transition model by using an intermittency transport equation. An intermittency based transition model, which is critical for invoking transition onset according to Abu-Ghannam and Shaw correlation, is implemented into the proven Reynolds-Averaged N-S (RANS) solver. The intermittent behavior of the transitional flow is incorporated into the computation by modifying the eddy viscosity μt, obtained from a turbulence model. Wilcox [4] low Reynolds k−ω turbulence model is employed to calculate the eddy viscosity and others turbulent quantities. This model is designated for the prediction of flow transition under the influence of freestream turbulence (FST). The current model is applied to prediction of a modern high pressure turbine experiment, and detail comparisons of the computational results with the experimental data are presented. The model has been shown to be capable of predicting the high pressure turbine flow transition under a variety of Reynolds number and free stream turbulence conditions.

A novel numerical cubic filament model and method for the two-energy equation in porous media

Abstract A consistent rule, which requires the flow and heat transfer of both a numerical model and real porous media should simultaneously satisfy the same governing equations as well as the same or consistent transport properties, is proposed for establishing a numerical model by which the flow and heat transfer of real porous media can be simulated. A cubic filament model (CFM) with regular geometry solid matrix is modeled. In the procedure of modeling, transport properties of both the cubic filament model (CFM) and real porous media, including porosity, permeability, tortuosity, specific surface, inertial coefficient, surface heat transfer coefficient and thermal conductivity of both fluid and solid, are analyzed and developed. According to analysis of transport properties and the consistent rule, structure parameters of the cubic filament model (CFM) are determined. To avoid complexity of determining the effective conductivity, it is proposed that solid matrix and fluid are divided into two independent control volumes for the cubic filament model (CFM). Meanwhile, equivalent conductivity of solid matrix and average temperature differences of the source terms are derived for the cubic filament model (CFM).

Performance Optimization of Co-current Gas-to-Gas Micro Heat Exchanger Considering Radiation

Optimization of a parallel flow gas-to-gas tubular micro heat exchanger with hot core and cold annulus fluid is numerically analyzed, considering the beneficial role of surface radiation. Operating and geometric parameters are varied for fixed overall mass flow rate and temperature of cold core fluid, to study the effects on the following performance parameters: heat transferred to annulus fluid, logarithmic mean temperature difference, effectiveness, and volumetric heat transfer coefficient. The micro heat exchanger is optimized for high heat transfer to annulus fluid and volumetric heat transfer coefficient, for different operating and geometric conditions. Optimization for high volumetric heat transfer coefficient maximizes the micro heat exchanger effectiveness, heat transferred and improves logarithmic mean temperature difference.

Thermo-Physical Properties of Magnetic Fluid and its Natural Convection Heat Transfer in a Horizontal Enclosed Rectangular Container

Thermo-physical properties of magnetic fluid were measured experimentally at various temperatures, in order to evaluate their temperature dependencies. Heat transfer by natural convection was also investigated in a horizontal enclosed rectangular container filled with the tested magnetic fluid. It was found that the heat transfer coefficient of the magnetic fluid keeps good agreement with the conventional heat-transfer correlation of natural convection heat transfer in a horizontal enclosed rectangular container by applying the values of thermo-physical properties obtained in the present work. Therefore, the measured thermo-physical properties are reliable and can be used as a thermo-physical database of the magnetic fluid.

Magnesium based metal hydride reactor incorporating helical coil heat exchanger: Simulation study and optimal design

Magnesium based metal hydride has been viewed as one of the most commonly-used materials in the practical applications of hydrogen energy systems. The heat and mass transfer processes have significant effects on the hydrogen storage performance of magnesium based metal hydride reactors. Incorporating helical coil heat exchanger into the reactor could be an effective way to improve the performance of heat and mass transfer. In this work, a new three-dimensional model for magnesium based metal hydride reactor with helical coil heat exchanger is proposed and solved using the commercial software package COMSOL Multiphysics V3.5a. The comparison of hydrogen storage behaviors between the reactors incorporating the traditional straight pipe and new helical coil heat exchangers is firstly conducted based on the numerical simulation. The comparison results show that the helical coil heat exchanger has better effect on improving the characteristics of reactor than the straight pipe heat exchanger due to its secondary circulation. The effects of key parameters, including the initial conditions, heat transfer coefficients of heat transfer fluid and helical coil geometry on the characteristics of reactor with the helical coil heat exchanger are also analyzed systematically. It is discovered that larger initial hydrogen pressure and lower initial temperature are beneficial to the improvement of hydrogen absorption kinetics, because of the greater driving force for the hydriding reaction. The results of optimal design suggest that smaller non-dimensional pitch, the ratio of helical pitch to helical diameter, improves the heat and mass transfer performance. The reactor with 0.333 of non-dimensional pitch exhibits the best hydrogen storage behaviors under 3.0MPa and 523K, when the heat transfer coefficient of heat transfer fluid is 500Wm−2K−1. Approximately 95% of hydrogen absorption process is completed within about 1000s in this case.

Numerical Study on Influence of Cross Flow on Rewetting of AHWR Fuel Bundle

Numerical study on AHWR fuel bundle has been carried out to assess influence of circumferential and cross flow rewetting on the conduction heat transfer. The AHWR fuel bundle quenching under accident condition is designed primarily with radial jets at several axial locations. A 3D (r, θ, z) transient conduction fuel pin model has been developed to carry out the study with a finite difference method (FDM) technique with alternating direction implicit (ADI) scheme. The single pin has been considered to study effect of circumferential conduction and multipins have been considered to study the influence of cross flow. Both analyses are carried out with the same fluid temperature and heat transfer coefficients as boundary conditions. It has been found from the analyses that, for radial jet, the circumferential conduction is significant and due to influence of overall cross flow the reductions in fuel temperature in the same quench plane in different rings are different with same initial surface temperature. Influence of cross flow on rewetting is found to be very significant. Outer fuel pins rewetting time is higher than inner.

Pool Boiling Heat Transfer Performance of a Dielectric Fluid With Low Global Warming Potential

Due to growing concerns over anthropogenic effects on the climate, there is increasing need to replace engineered fluids of high global warming potentials (GWPs), such as hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs), with more environmentally friendly alternatives in thermal management systems. This article presents experimental data and compares various correlations for predicting the pool boiling heat transfer coefficient of a new low-GWP fluid, FK-649. Using a pressurized boiling facility with a smooth aluminum heater, the critical heat flux (CHF) and heat transfer coefficient were measured for the pool boiling of FK-649 at various saturation conditions. The commonly used refrigerant tetrafluoroethane (R-134a) is tested in the same pressurized facility to act as a benchmark for the new fluid. While R-134a exhibited a higher heat transfer coefficient and CHF, this behavior is expected from the fluid properties. Two-phase heat transfer performance of FK-649 is expected to be similar to that of the fluorocarbon FC-72. Experimental data are compared to predictions using the Rohsenow, Borishanskii–Mostinski, Stephan and Abdelsalam, Cooper, and Leiner correlations. Where applicable, empirical constants are obtained by using a least-squares fit to experimental data. The Rohsenow correlation yielded the best result with a new surface–fluid constant C s,f of 0.0037 for FK-649.

Evaluation of the Heat Transfer Correlations for Supercritical Pressure Water in Vertical Tubes

A large number of studies have been carried out on the flow and heat transfer of supercritical pressure fluids in the past decades. However, there are still some uncertainties and deficiencies in the accurate prediction for supercritical fluid heat transfer coefficient due to the large and fast variations of fluids properties in the so-called pseudo-critical region. In this paper, 15 correlations were selected from the literature and were compared with each other to verify their capability in predicting heat transfer coefficient of supercritical pressure water in vertical tubes. Based on the comparison between the calculation results of the existing heat transfer correlations and the experimental data obtained from the open literature, it was found that the Swenson et al. correlation and the Hu correlation can reasonably predict the heat transfer coefficient of supercritical water in the pseudo-critical region. After evaluating these correlations, the authors conducted polynomial fitting for the collected experimental data and got a new correlation for heat transfer coefficient of water at supercritical pressures. The new correlation can fit well with the experimental data even in the neighborhood of pseudo-critical temperature.

Parameter estimation applied to the heat transfer characterisation of Scraped Surface Heat Exchangers for food applications

A parameter estimation approach was applied to characterise the heat transfer of Scraped Surface Heat Exchangers (SSHEs) specifically designed for the food industry. It is difficult to apply the data available in the literature to SSHEs, due to the specificity of each product, thermal treatment and geometrical configuration, making the thermal design of these apparatuses critical. Therefore, it appears to be more useful to assess the methodology used to derive a proper heat transfer correlation than to assess the form of the heat transfer correlation itself, as the correlation often cannot be transferred to other heat exchangers, even those that belong to the same class.This study enabled successful and robust estimation of the heat transfer correlation for the product side Nusselt number and the external side heat transfer coefficient; this approach differs from Wilson plot methods, as no assumption is made regarding the functional dependence of the external side heat transfer coefficient.The procedure was validated through application to both synthetic data and experimental data acquired from a coaxial SSHE pilot plant for the treatment of highly viscous fluid foods.The procedure was optimised with the aid of sensitivity and uncertainty analysis, which provided considerable insight into the problem.The application to synthetic data demonstrated that under typical operating conditions, areas of insensitivity to certain parameters are present. The application to the experimental data acquired under both heating and cooling conditions confirmed that the measured values of the overall heat transfer coefficient can be used to estimate the secondary fluid heat transfer coefficient, as well as the power law dependence of the internal fluid Nusselt number on the rotational Reynolds number and the Prandtl number together with the multiplicative constant. The uncertainty analysis provided the confidence intervals associated with each estimated parameter, thereby enabling the quality and robustness of the resulting heat transfer correlations to be determined.

The effect of nanoparticles on laminar heat transfer in a horizontal tube

Heat transfer coefficient in laminar flow of water-based alumina, titania and carbon nanotube nanofluids in a straight pipe with constant heat flux at the wall have been investigated independently by two universities. The nanoparticles affect the thermo-physical properties of the suspensions, however, nanoparticles presence and movement due to Brownian diffusion and thermophoresis seemed to have insignificant effect on heat transfer coefficient. The Nusselt number of all investigated nanofluids followed standard heat transfer correlations developed for liquids within ±10% suggesting that all investigated nanofluids can be treated as homogenous fluids. Different methods of comparison between heat transfer coefficient in nanofluids and base fluid are also critically discussed.

Experimental Investigation on Heat Transfer Characteristics of CO<sub>2</sub>-Based Foam Fracturing Fluid

Heat transfer characteristics of the CO2-based foam fracturing fluid were investigated on the large-scale test loop of foam fracturing fluid. The relationship between thermal conductivity coefficient and shear rate was introduced into the expression of the convective heat transfer coefficient. Thus the expression of the convective heat transfer coefficient of power-law fluid was revised. The results show that the convective heat transfer coefficient of the fracturing fluid increases with the increase of the pressure, the foam quality and the shear rate. The convective heat transfer coefficient of the foam fracturing fluid calculated by the revised calculation formula is highly consistent with the experimental data at low pressure. The deviation is bigger at high pressure, but still within 20%.

Numerical analysis of transient laminar forced convection of nanofluids in circular ducts

In this study, forced convection heat transfer characteristics of nanofluids are investigated by numerical analysis of incompressible transient laminar flow in a circular duct under step change in wall temperature and wall heat flux. The thermal responses of the system are obtained by solving energy equation under both transient and steady-state conditions for hydro-dynamically fully-developed flow. In the analyses, temperature dependent thermo-physical properties are also considered. In the numerical analysis, Al2O3/water nanofluid is assumed as a homogenous single-phase fluid. For the effective thermal conductivity of nanofluids, Hamilton–Crosser model is used together with a model for Brownian motion in the analysis which takes the effects of temperature and the particle diameter into account. Temperature distributions across the tube for a step jump of wall temperature and also wall heat flux are obtained for various times during the transient calculations at a given location for a constant value of Peclet number and a particle diameter. Variations of thermal conductivity in turn, heat transfer enhancement is obtained at various times as a function of nanoparticle volume fractions, at a given nanoparticle diameter and Peclet number. The results are given under transient and steady-state conditions; steady-state conditions are obtained at larger times and enhancements are found by comparison to the base fluid heat transfer coefficient under the same conditions.

Heat transfer analysis of a finned-tube evaporator for engine exhaust heat recovery

The organic Rankine cycle (ORC) can be used to recover waste heat from an internal combustion engine. In such a system, the evaporator design is critical. Determining the amount of heat that can be transferred in a designed evaporator is extremely important for a successful ORC system. In this paper, the performance of a finned-tube evaporator used to recover exhaust waste heat from a diesel engine is presented. First, the exhaust heat of the chosen diesel engine is evaluated based on the measured data. Subsequently, a mathematical model of the evaporator is created based on the detailed geometry and the specific ORC working conditions. Then, the heat transfer of the evaporator is estimated as the diesel engine runs through all of its operating regions defined by the engine speed and the engine load. The results show that the exhaust temperature at the evaporator outlet increases with engine speed and engine load. Although the convective heat transfer coefficient of the organic working fluid is significantly larger than that of the exhaust gas, the overall heat transfer coefficient is slightly greater than that of the exhaust gas. Furthermore, the heat transfer rate is the greatest in the preheated zone and least in the superheated zone. Consequently, the heat transfer area for the preheated zone is nearly half of the total area. In addition, the area of the superheated zone is slightly greater than that of the two-phase zone. It is concluded that the heat transfer area for a finned tube evaporator should be selected carefully based on the engine’s most typical operating region.

Experimental studies on heat transfer to Newtonian and non-Newtonian fluids in helical coils with laminar and turbulent flow

Experimental studies on isothermal steady state and non-isothermal unsteady state conditions were carried out in helical coils for Newtonian and non-Newtonian fluids. Water, glycerol–water mixture as Newtonian fluids and dilute aqueous polymer solutions of sodium carboxymethyl cellulose (SCMC), sodium alginate (SA) as non-Newtonian fluids were used in this study. These experiments were performed for coils with curvature ratios δ=0.0757, 0.064 and 0.055 in laminar and turbulent regimes. An innovative approach of correlating Nusselt number to dimensionless number ‘M’ for Newtonian fluids based on experimental data is presented which is not available in the literature. Several correlations for the first time are proposed based on heat transfer data generated from the experiments performed for Newtonian fluids under isothermal and non-isothermal conditions (total 138 tests). These developed correlations were compared with the work of earlier investigators and were found in good agreement. Further, comparison of overall heat transfer coefficient Uo, and Nusselt numbers for Newtonian and non-Newtonian fluids under isothermal and non-isothermal conditions (total 276 tests) is presented in this paper. From the experimental results, it was found that overall heat transfer coefficient and Nusselt numbers for water are higher than glycerol–water mixture and non-Newtonian fluids. It was also observed from experimental results that as helix diameter increases, overall heat transfer coefficient and Nusselt numbers of both fluids decreases for the same flow rates.

Evaluation of the convective heat transfer coefficient for minimum quantity lubrication (MQL)

PurposeThe purpose of this paper is to evaluate the cooling ability of minimum quantity lubrication (MQL) cutting fluid.Design/methodology/approachAn experimental system is devised to find the heat transfer coefficient of MQL under simulated reaming conditions. Cooling rate of the specimen is measured with an infrared camera. The effect of air pressure and oil volume on cooling rate is tested. Metal cutting tests are performed to evaluate the effect of heat transfer coefficient on workpiece temperature.FindingsConvective heat transfer coefficient for MQL increases with increasing air pressure. Oil volume has an indeterminate effect on the heat transfer coefficient; however, it is a dominant factor for controlling temperature during reaming.Practical implicationsThe results of the study can provide guidance to optimize the temperature controlling ability of MQL for production.Originality/valueThere is limited information available in literature regarding the heat transfer coefficient of metal working fluids, particularly for MQL. In particular, experiments designed to investigate the effect of air pressure and oil volume on the heat transfer coefficient of the mist have not been previously documented. This information may be used to improve the overall cooling ability of MQL mist, thus increasing its effectiveness at controlling tool wear and maintaining part quality. The other major contribution of this work is to separate the role of the cooling and lubrication for controlling temperature while reaming aluminum. Prior to this study, there has been relatively little research performed for the reaming metal cutting operation, and still less for reaming with MQL. The nature of how metal working fluids control temperature is not fully understood, and this work provides insight as to whether cooling or lubrication plays the dominant role for reaming.

Nano-Cutting Fluid for Enhancement of Metal Cutting Performance

Nano-cutting fluids are the mixtures of conventional cutting fluid and nanoparticles. Addition of the nanoparticles can alter wettability, lubricating properties, and convective heat transfer coefficient (cooling properties) of nano-cutting fluids. In the present work, nano-cutting fluid is made by adding 1% Al2O3 nanoparticles to conventional cutting fluid. The wettability characteristic of this nano-cutting fluid on a carbide tool tip is measured using the macroscopic contact angle method. Comparative study of tool wear, cutting force, workpiece surface roughness, and chip thickness among dry machining, machining with conventional cutting fluid as well as nano-cutting fluid has been undertaken. This study clearly reveals that the cutting force, workpiece surface roughness, tool wear, and chip thickness are reduced by the using nano-cutting fluid compared to dry machining and machining with conventional cutting fluid.