Experimental study on convective heat transfer and entropy generation of carbon black nanofluid turbulent flow in a helical coiled heat exchanger

Journal of Thermal Analysis and Calorimetry - The convective heat transfer coefficient (CHTC) of a fluid is one of the most effective factors on the performance of a fluid in heat transfer...     

An entropy production analysis for electroosmotic flow and convective heat transfer: a numerical investigation

Journal of Thermal Analysis and Calorimetry - In the current numerical study, an entropy production analysis is conducted for the electroosmotic flow and convective heat transfer in the microduct....     

The experimental investigation concerning the heat transfer enhancement via a four-point star swirl generator in the presence of water–ethylene glycol mixtures

Journal of Thermal Analysis and Calorimetry - In the present study, a new swirling flow generator is studied which aims to enhance the convective heat transfer rate in a heat exchanger tube. This...     

Particle dynamics and particle heat and mass transfer in thermal plasmas. Part II. Particle heat and mass transfer in thermal plasmas

This paper is concerned with a review of heat and mass transfer between thermal plasmas and particulate matter. In this situation various effects which are not present in ordinary heat and mass transfer have to be considered, including unsteady conditions, modified convective heat transfer due to strongly varying plasma properties, radiation, internal conduction, particle shape, vaporization and evaporation, noncontinuum conditions, and particle charging. The results indicate that (i) convective heat transfer coefficients have to be modified due to strongly varying plasma properties; (ii) vaporization, defined as a mass transfer process corresponding to particle surface temperatures below the boiling point, describes a different particle heating history than that of the evaporation process which, however, is not a critical control mechanism for interphase mass transfer of particles injected into thermal plasmas; (iii) particle heat transfer under noncontinuum conditions is governed by individual contributions from the species in the plasma (electrons, ions, neutral species) and by particle charging effects.     

Heat transfer characteristics of water flowing through micro-tube heat exchanger with variable fluid properties

Journal of Thermal Analysis and Calorimetry - The heat transfer characteristics of laminar single-phase forced convective water flow through a micro-tube heat exchanger are numerically investigated...     

Laminar heat and mass transfer with arbitrary order heterogeneous and homogeneous reactions: I: In a rectangular duct

Numerical solutions are presented for the problem of simultaneous convective diffusion of reactants, products and heat with arbitrary order heterogeneo The effects of reaction rate parameters, Lewis number, diffusivity ratio, reaction heat parameters, stoichiometric coefficient ratio and reaction order rectangular duct with small aspect ratios.     

Numerical modelling of the spiral plate heat exchanger

The spiral plate heat exchanger (SHE) is widely used in plenty of industrial services in full counter current flow liquid-liquid heat exchange. We have produced a thermal modelling of the heat exchanges in both steady-state and time dependent cases with 2D spiral geometry, allowing computation with different materials, forced convective heat transfer models in turbulent flow and geometrical parameters options. We will display here some results in steady-state conditions in order to improve the exchanger performances.     

Heat transfer and friction factor analysis of MWCNT nanofluids in double helically coiled tube heat exchanger

Journal of Thermal Analysis and Calorimetry - The convective heat transfer rate and friction factor analysis are determined with the help of a double helically coiled tube heat exchanger by...     

Theoretical investigations into heat transfer in laser-welded steel sheets

This study contains mathematical modelling and numerical analysis of heat transfer in laser beam welding process. The temperature field was obtained on the basis of numerical solution into unsteady heat transfer equation with convective term and volumetric heat sources taken into account. Volumetric heat source model describing laser beam power distribution in combined truncated cone?Ccylinder volume was developed. Due to the wide range of temperatures appearing in the process latent heat of fusion, evaporation as well as latent heat of phase transformations in solid state were taken into account in the solution algorithm. On the basis of developed numerical algorithms an analysis of heat transfer in laser butt-welded steel sheets as a three-dimensional initial-boundary problem was performed.     

Radiant heat exchange mediated by gaseous atmosphere

As is well known, the heat exchange between bodies at different temperatures enclosured at vacuum without thermal contact can be described by the Stefan–Boltzmann law of radiation, where each body receives a fraction of radiant heat from the others depending on their distances and individual temperatures, geometrical shapes, emissivities, and absorptivities. However, when these bodies are surrounded by a gaseous atmosphere conductive and convective phenomena enter on the scenario, leading to a complex mechanism of heat exchange. Here, we study an experimental realization of such situation for two bodies employing a kind of vacuum gauge, on a range of surrounding air pressure between 26 and 1035 mbar, and analyze the heat exchange on the framework of Stefan–Boltzmann law. It is verified empirically that the ratio between the thermal power irradiated by the bodies is independent on their individual heat radiances, and depends only on the surrounding gas pressure.     

Numerical simulations for radiated bioconvection flow of nanoparticles with viscous dissipation and exponential heat source

A nonlinear radiative bioconvection flow of nanofluid due to impulsively porous space is investigated. The applications of externa heat source with exponential relations, viscous dissipation and magnetic force are considered for fully developed stretched flow. The microorganisms are uniformly decomposed with the nanofluids. The thermal analysis is observed with interaction of slip phenomenon and convective boundary constraints. The dimensionless system of governing model is obtained with new imposed variables. The numerical computations are performed by using the shooting method. The confirmation of numerical data is achieved with already reported studies. Thermal observations govern to the flow system in view of parameters are suggested. It is observed that declining change in velocity is subject to the stretching parameter and permeability of porous space. The implementation of slip and convective boundary constraints effectively enhanced the transportation phenomenon. Based on interaction of nonlinear thermal radiated phenomenon and porous medium, different applications of problem are claimed in solar systems, extrusion processes, manufacturing systems, soil sciences, petroleum engineering, chemical processes etc.     

Numerical simulation of nanofluids for improved cooling efficiency in a 3D copper microchannel heat sink (MCHS)

In this paper, laminar nanofluid flow in 3D copper microchannel heat sink (MCHS) with rectangular cross section, and a constant heat flux, has been treated numerically using the computational fluid dynamics software (FLUENT). Results for the temperature and velocity distributions in the investigated MCHS are presented. In addition, experimental and numerical values are compared in terms of friction factors, convective heat transfer coefficients, wall temperature and pressure drops, for various particle volume concentrations and Reynolds numbers. The numerical results show that enhancing the heat flux has a very weak effect on the heat transfer coefficient for pure water, but an appreciable effect for the case of a nanofluid. For all considered volume fractions, the sink friction factor decreases by increasing the Reynolds number and slightly increases by increasing the volume fractions, and, with increasing the volume fractions and the Reynolds number, the pressure drop increases.     

Calculation of heat transfer and uniformity of chemical amplification during post-exposure bake

Heat transfer in a resist-coated silicon wafer using a bake process is theoretically evaluated by modeling the three-dimensional diffusion process, focusing on the controllability of the lithographic performance of chemically amplified resists. Six models of various ambient conditions are used. The proximity gap between the hotplate and the wafer is found to have a dominant influence on the heat transfer process for the whole system. Because the atmosphere near the wafer acts as a thermal diffusion buffer layer, no temperature gradient occurs in the resist, even when it is subjected to convective heat transfer from the resist surface. Experimental results obtained by X-ray lithography confirm the calculation results.     

Investigation of nanofluids on heat transfer enhancement in a louvered microchannel with lattice Boltzmann method

Numerical studies of laminar forced convective heat transfer and fluid flow in a 2D louvered microchannel with Al₂O₃/water nanofluids are performed by the lattice Boltzmann method (LBM). Eight louvers are arranged in tandem within the single-pass microchannel. The Reynolds number based on channel hydraulic diameter and bulk mean velocity ranges from 100 to 400, where the Al₂O₃ fraction varies from 0 to 4%. A double distribution function approach is adopted for modeling fluid flow and heat transfer. Code validations are performed by comparing the streamwise Nusselt number (Nu) profiles and Fanning friction factors of the present LBM and those of the analytical solutions. Good agreements are obtained. Simulated results show that the louver microstructure can disturb the core flow and guide coolant toward the heated walls, thus enhancing the heat transfer significantly. Furthermore, the addition of nanoparticles in microchannels can also augment the heat transfer, but it creates an unnoticeable pressure loss. With both the louver microstructure and nanofluid, a maximum overall Nu enhancement of 7.06 is found relative to that of the fully developed smooth channel.

     

Diffusion of a passive impurity through a porous media: fractal model in an unsaturated medium

The theory of fractal sets is used to describe convective diffusion of a passive impurity in a partly-saturated porous medium.     

Preparation of calcium peroxide in a UHF field at atmospheric pressure

The kinetics of free moisture removal from a CaO₂ paste under the conditions of convective drying and UHF field at atmospheric pressure were compared. Drying under the action of UHF radiation is characterized by the absence of the heat-up period. The use of the microwave radiation at atmospheric pressure decreases the drying time in production of anhydrous calcium peroxide by a factor of approximately 10 compared to convective drying.

     

The numerical simulation and sensitivity analysis of a non-Newtonian fluid flow inside a square chamber exposed to a magnetic field using the FDLBM approach

Journal of Thermal Analysis and Calorimetry - This paper simulated the free convective heat transfer (CHT) and generation of entropy (GOE) of a non-Newtonian fluid (NNF) in a square chamber using...     

Convective drying of a moist porous object under the effects of a rotating cylinder in a channel

Journal of Thermal Analysis and Calorimetry - Numerical study of evaporation in porous medium during convective drying process was examined, and heat and mass transfer of liquid water and water...     

Non-Steady-State Processes Under Conditions of Natural Convection in an Electrochemical Cell with Horizontal Electrodes: The Critical Time of the Onset of a Convective Instability at Large Rayleigh Numbers

Theoretical analysis of a model electrochemical system is performed. An equation for the critical time of the onset of a convective instability and natural convection in a plane electrolyte layer between two horizontal electrodes is derived. The cessation of damping of fluctuations of the electroactive-ion concentration is taken as the condition for the onset of a convective instability.     

A novel thin-film temperature and heat-flux microsensor for heat transfer measurements in microchannels

Temperature and heat-flux measurement at the microscale for convective heat-transfer studies requires highly precise, minimally intrusive sensors. For this purpose, a new generic temperature and heat-flux sensor was designed, calibrated and tested. The sensor allows measurement of temperature and heat flux distributions along the direction of flow. It is composed of forty gold thermoresistances, 85 nm thick, deposited on both sides of a borosilicate substrate. Their sensitivities are about 37.8 μV K(-1), close to those of a K-type wire thermocouple. Using a thermoelectrical model, temperature biases due to the Joule effect were calculated using the current crossing each thermoresistance and the heat-transfer coefficient. Finally, heat-transfer measurements were performed with deionized water flowing in a straight PDMS microchannel for various Reynolds numbers. The Nusselt number was obtained for microchannels of 50 to 10 μm span. The results were found to be in good agreement with classical Nu-Re macroscopic correlations.