Showing papers in "Thermal Science in 2016"

New Fractional Derivatives with Nonlocal and Non-Singular Kernel: Theory and Application to Heat Transfer Model

Abstract: In this manuscript we proposed a new fractional derivative with non-local and no-singular kernel. We presented some useful properties of the new derivative and applied it to solve the fractional heat transfer model.

Transient heat diffusion with a non-singular fading memory: From the Cattaneo constitutive equation with Jeffrey’s Kernel to the Caputo-Fabrizio time-fractional derivative

Abstract: Starting from the Cattaneo constitutive relation with a Jeffrey’s kernel the derivation of a transient heat diffusion equation with relaxation term expressed through the Caputo-Fabrizio time fractional derivative has been developed. This approach allows seeing the physical background of the newly defined Caputo-Fabrizio time fractional derivative and demonstrates how other constitutive equations could be modified with non-singular fading memories.

A NEW FRACTIONAL DERIVATIVE WITHOUT SINGULAR KERNEL Application to the Modelling of the Steady Heat Flow

Abstract: In this article we propose a new fractional derivative without singular kernel. We consider the potential application for modeling the steady heat-conduction problem. The analytical solution of the fractional-order heat flow is also obtained by means of the Laplace transform.

A new integral transform method for solving steady heat-transfer problem

Abstract: In this paper, we propose a new integral transform method for the first time. It is used to find the solution for the differential equation in the steady heat-transfer problem. The proposed technology is accurate and efficient.

On fractal space-time and fractional calculus

Abstract: This paper gives an explanation of fractional calculus in fractal space-time. On observable scales, continuum models can be used, however, when the scale tends to a smaller threshold, a fractional model has to be adopted to describe phenomena in micro/nano structure. A time-fractional Fornberg-Whitham equation is used as an example to elucidate the physical meaning of the fractional order, and its solution process is given by the fractional complex transform.

Performance study of conical strip inserts in tube heat exchanger using water based titanium oxide nanofluid

Abstract: The objective of the study is to observe the Nusselt number and friction factor behavior in a tube heat exchanger fitted with staggered and non-staggered conical strip inserts using water based titanium oxide nanofluid under laminar flow conditions. Water based titanium oxide nanofluid was prepared using a two-step method with a volume concentration of 0.1% and 0.5%. The tube inserts used were staggered and non-staggered conical strips having three different twist ratios of 2, 3, and 5. The experimental results indicated that the Nusselt number increased in the presence of water based titanium oxide nanofluid compared to the base fluid. Nusselt number further increased enormously with the use of conical strip inserts than a tube with no inserts. It was observed that the strip geometry and the nanofluid had a major effect on the thermal performance of the circular tube heat exchanger. It was found that with the staggered conical strip having a twist ratio of Y = 3 and 0.5% volume concentration of nanofluid provided the highest heat transfer. Correlations have been derived using regression analysis.

Chemically reacting on MHD boundary-layer flow of nanofluids over a non-linear stretching sheet with heat source/sink and thermal radiation

Abstract: CITATION: Makinde, O. D., Mabood, F. & Ibrahim, S. M. 2018. Chemically reacting on MHD boundary-layer flow of nanofluids over a non-linear stretching sheet with heat source/sink and thermal radiation. Thermal Science, 22(1):495-506, doi:10.2298/TSCI151003284M.

Fractional Maxwell fluid with fractional derivative without singular kernel

Abstract: In this paper we propose a new model for the fractional Maxwell fluid within fractional Caputo-Fabrizio derivative operator. We present the fractional Maxwell fluid in the differential form for the first time. The analytical results for the proposed model with the fractional Losada-Nieto integral operator are given to illustrate the efficiency of the fractional order operators to the line viscoelasticity.

On steady heat flow problem involving Yang-Srivastava-Machado fractional derivative without singular kernel

Abstract: In this article, we present a new application for the Yang-Srivastava-Machado fractional derivative without singular kernel to the steady heat flow problem. The Sumudu transform is used to find the analytical solution of the fractional-order heat flow.

A new integral transform with an application in heat-transfer problem

Abstract: In this paper, an new integral transform J[Φ(τ)] =1/μ ∫0∞Φ(τ)e−μτ dτ is proposed for the first time. The integral transform is used to solve the differential equation arising in heat-transfer problem.

Temperature and time influence on the waste plastics pyrolysis in the fixed bed reactor

Abstract: Pyrolysis as a technique of chemical recycling of plastic materials is causing an increasing level of interest as an environmentally and economically acceptable option for the processing of waste materials. Studies of these processes are carried out under different experimental conditions, in different types of reactors and with different raw materials, which makes the comparison of different processes and the direct application of process parameters quite complex. This paper presents the results of investigation of the influence of temperature in the range of 450°C to 525°C, on the yield of the process of pyrolysis of waste plastics mixture, composed of 45% polypropylene, 35% low density polyethylene and 25% high density polyethylene. Also, this paper presents results of the investigation of the effect of the reaction, atintervals of 30-90 [min], on the yield of pyrolysis of the mentioned waste plastics mixture. Research was conducted in a fixed bed pilot reactor, which was developed for this purpose. The results of the research show that at a temperature of 500°C, complete conversion of raw materials was achieved, for a period of 45 [min], with a maximum yield of the pyrolysis oil of 32.80%, yield of the gaseous products of 65.75% and the solid remains of 1.46%. Afurther increase of temperature increases the yield of gaseous products, at the expense of reducing the yield of pyrolysis oil. Obtained pyrolysis oil has a high calorific value of 45.96 [MJ/kg], and in this regard has potential applications as an alternative fuel.

Design, simulation and optimization of a solar dish collector with spiral-coil thermal absorber

Abstract: The efficient conversion of solar radiation into heat at high temperature levels requires the use of concentrating solar collectors. The goal of this paper is to present the optical and the thermal analysis of a parabolic dish concentrator with a spiral coil receiver. The parabolic dish reflector consists of 11 curvilinear trapezoidal reflective petals constructed by PMMA with silvered mirror layer and has a diameter of 3.8 m, while its focal distance is 2.26m. This collector is designed with commercial software SolidWorks and simulated, optically and thermally in its Flow Simulation Studio. The optical analysis proved that the ideal position of the absorber is at 2.1m from the reflector in order to maximize the optical efficiency and to create a relative uniform heat flux over the absorber. In thermal part of the analysis, the energetic efficiency was calculated approximately 65%, while the exergetic efficiency is varied from 4% to 15% according to the water inlet temperature. Moreover, other important parameters as the heat flux and temperature distribution over the absorber are presented. The pressure drop of the absorber coil is calculated at 0.07bar, an acceptable value.

A study of heat transfer in power law nanofluid

Abstract: The purpose of this paper is to study the effects of nanoparticles on mixed convection flow of power law fluid. The shear thinning fluid is considered as base fluid. The nanoparticles of copper for nanofluid are taken into account. To analysis the flow and temperature behavior, various mass concentrations of polyvinyl alcohol in water, different sizes and concentrations of nanoparticles are used. The effects of nanoparticle concentrations on shear stress, heat flux and thermal resistance are also presented.

The effect of surfactant on stability and thermal conductivity of carbon nanotube based nanofluids

Abstract: The addition of highly conductive substance such as carbon nanotubes into a traditional heat transfer fluid will enhance the fluids’ thermal conductivity. However, dispersion process of carbon nanotubes into base fluids is not an easy task due to hydrophobic characteristic of its surface. This study attempts to investigate the stability and thermal conductivity of carbon nanotube based ethylene glycol/water nanofluids with and without surfactants. Stability investigation was conducted through observation and zeta potential measurement methods. As for the thermal conductivity, the samples were measured based on transient line heat source. The results showed that 0.01 wt.% of carbon nanotube based nanofluid, containing 0.01wt.% hexadecyltrimethylammonium bromide possess highest zeta potential value compared to the other tested samples. 0.5 wt. % of carbon nanotube based nanofluids with gum arabic exhibit 25.7% thermal conductivity enhancement.

Performance investigation of photovoltaic modules by back surface water cooling

Abstract: The temperature of the photovoltaic module has an adverse effect on the performance of photovoltaic modules. The photovoltaic module converts a small portion of energy from solar radiations into electricity while the remaining energy wastes in the form of heat. In this study, water cooled photovoltaic/thermal system was analyzed to enhance the efficiency by absorbing the heat generated by the photovoltaic modules and allowing the photovoltaic module to work at comparatively low temperature. For this system, four photovoltaic modules of two different types were used. To investigate the cooling effect, two modules were modified by making ducts at their back surface having inlet and outlet manifolds for water-flow. The measurements were taken with cooling and without cooling of photovoltaic modules. The temperature was measured at inlet, outlet, and at different points at the back of photovoltaic modules. It was found that there was a linear trend between the module efficiency and temperature. The average module temperature of c-Si and p-Si modules without cooling was 13.6% and 7.2% lower, respectively, than the same modules without cooling. As a result of temperature drop, the average module electrical efficiency of c-Si and p-Si was 13% and 6.2% higher, respectively, compared to the modules without cooling. Flowing water also gains useful heat from photovoltaic module so the resultant overall energy of the system was much higher.

Impact of CO2 concentration on indoor air quality and correlation with relative humidity and indoor air temperature in school buildings in Serbia

Abstract: Previous studies have shown that poorly ventilated classrooms can have negative impact on the health of children and school staff. In most cases, schools in Serbia are ventilated naturally. Considering their high occupancy, classroom air quality test determines the level of air pollution, after which it is possible to implement corrective measures. The research presented in this study was conducted in four schools which are located in different areas and have different architecture designs. Measurements in these schools have been performed during the winter (heating season) and spring (non-heating season) and the following results were presented: indoor air temperature, relative humidity and carbon dioxide concentration. These results show that the classroom average concentration of carbon dioxide often exceeds the value of 1500 ppm, during its full occupancy, which indicates inadequate ventilation. Measurement campaigns show that carbon dioxide concentration increased significantly from non-heating to heating season in three of the four schools. Analysis of measurements also determined high correlation between relative humidity and carbon dioxide concentration in all schools in winter season. This fact may constitute a solid basis for the fresh air supply strategy. [Projekat Ministarstva nauke Republike Srbije, br. III42008: SINPHONIE - Schools Indoor Pollution and Health: Observatory Network in Europe]

Energy and exergy efficiency of heat pipe evacuated tube solar collectors

Abstract: In this paper, a heat pipe evacuated tube solar collector has been investigated both theoretically and experimentally. A detailed theoretical method for energy and exergy analysis of the collector is provided. The method is also evaluated by experiments. The results showed a good agreement between the experiment and theory. Using the theoretical model, the effect of different parameters on the collector’s energy and exergy efficiency has been investigated. It is concluded that inlet water temperature, inlet water mass flow rate, the transmittance of tubes and absorptance of the absorber surface have a direct effect on the energy and exergy efficiency of the heat pipe evacuated tube solar collector. Increasing water inlet temperature in heat pipe evacuated solar collectors leads to a decrease in heat transfer rate between the heat pipe’s condenser and water.

Water-based squeezing flow in the presence of carbon nanotubes between two parallel disks

Abstract: Present study is dedicated to investigate the water functionalized carbon nanotubes squeezing flow between two parallel discs. Moreover, we have considered magnetohydrodynamics effects normal to the disks. In addition we have considered two kind of carbon nanotubes named: single wall carbon nanotubes (SWCNT) and multiple wall carbon nanotubes (MWCNT) with in the base fluid. Under this squeezing flow mechanism model has been constructed in the form of partial differential equation. Transformed ordinary differential equations are solved numerically with the help of Runge-Kutta-Fehlberg method. Results for velocity and temperature are constructed against all the emerging parameters. Comparison among the SWCNT and MWCNT are drawn for skin friction coefficient and local Nusselt number. Conclusion remarks are drawn under the observation of whole analysis.

Heat and mass transfer analysis on MHD blood flow of Casson fluid model due to peristaltic wave

Abstract: In this article, heat and mass transfer analysis on MHD blood flow of Casson fluid model due to peristaltic wave has been investigated. The governing equations of blood flow for Casson fluid model, temperature, and energy equation have been solved by taking the assumption of long wavelength and neglecting the inertial forces. The resulting coupled differential equations have been solved analytically and the exact solutions are presented. The impact of various pertinent parameters is plotted and discussed. It is found that the influence of magnetic field and fluid parameter shows similar behavior on velocity profile while its behavior is opposite for pressure rise and pressure gradient profile. Trapping phenomena have also taken into account by sketching the streamlines. The expression for pressure rise and friction forces are evaluated numerically.

Emission estimation of neat paradise tree oil combustion assisted with superheated hydrogen in a 4-stroke natural aspirated DICI engine

Abstract: This research work investigates the use of neat paradise tree oil in a 4-stroke natural aspirated direct injection compression ignition engine assisted with the help of superheated hydrogen (hydrogen in gaseous state or above its saturation temperature) as a combustion improver. The high calorific gaseous fuel hydrogen gas was used as a combustion improver and admitted into the engine during the suction stroke. A 4-stroke single cylinder Diesel engine was chosen and its operating parameters were suitably modified. Neat paradise tree oil was admitted through standard injector of the engine and hydrogen was admitted through induction manifold. Inducted superheated hydrogen was initiated the intermediate compounds combustion of neat paradise tree oil. This process offers higher temperature combustion and results in complete combustion of heavier molecules of neat paradise tree oil within shorter duration. The results of the experiment reveal that 40% higher NOx, 20% lower smoke, 5% lower CO, and 45% lower HC than that of neat paradise tree oil fuel operation and the admission of superheated hydrogen has improved the combustion characteristics of neat paradise tree oil. The investigation successfully proved that the application of neat paradise tree oil with 15% of hydrogen improver is possible under a regular Diesel engine with minimal engine modification.

Experimental investigation on overall thermal performance of fluid-flow in a rectangular channel with discrete V-pattern baffle

Abstract: This work presents the results of an experimental study of thermohydraulic performance of rectangular channel having discrete V-pattern baffle attached on the broad wall. Measurements have been carried out for the aspect channel ratio of 10, Reynolds number from 3000 to 21000, relative baffle height value of 0.50, relative baffle pitch value of 1.5, relative gap width value of 1.0, flow attack angle value of 60°, and relative discrete distance values of 0.26 to 0.83. The heat transfer and friction factor data obtained were compared with the data obtained from a smooth wall channel under similar operating conditions. In comparison to the smooth wall channel the discrete V-pattern baffle channel enhanced the Nusselt number and friction factor by 3.89 and 6.08 times, respectively. The overall thermal performance parameter is found superior for the relative discrete distance of 0.67. Discrete V-pattern baffle roughness shape has also been shown to be overall thermal performance higher in comparison to other continuous (without discrete) V-pattern baffle shape rectangular channel.

The role of hybrid nanofluids in improving the thermal characteristics of screen mesh cylindrical heat pipes

Abstract: Experiments were conducted to study the thermal performance of meshed wick heat pipe by varying the working fluid and heat input. In this work four screen mesh wicked heat pipes were fabricated and tested. All the heat pipes were tested for heat input from 50W to 250W each with an increment of 50W in each step. The heat input range selected in this study is commonly encountered in most of the electronic application devices. The thermal resistance of all the heat pipes charged with different working fluids such as DI water, Al2O3/DI water nanofluid of volume concentration 0.1 % and hybrid nanofluid volume concentration 0.1%( with two different combinations of (Al2O3 50%- CuO 50%)/DI water and (Al2O3 25%- CuO 75%)/DI water)was determined. The maximum percentage reduction was found to be 58.87% for the hybrid nanofluid of (Al2O3 25%- CuO 75%)/DI water compared to base fluid. An important observation from the study is that, use of hybrid nanofluid can raise the operating range of the heat pipe beyond 250W which makes hybrid nanofluid as a potential substitute for the conventional working fluid.

A direct algorithm of exp-function method for non-linear evolution equations in fluids

Abstract: In this paper, a direct algorithm of the exp-function method is proposed for exactly solving non-linear evolution equations. To illustrate the validity and advantages of the algorithm, the Korteweg-de Vries and Jimbo-Miwa equations are considered. As a result, exact solutions are obtained. It is shown that the exp-function method with the direct algorithm provides a simpler but effective mathematical tool for constructing exact solutions of non-linear evolution equations in fluids.

Developments in fluidized bed conversion of solid fuels

Abstract: A summary is given on the development of fluidized bed conversion (combustion and gasification) of solid fuels. First, gasification is mentioned, following the line of development from the Winkler gasifier to recent designs. The combustors were initially bubbling beds, which were found unsuitable for combustion of coal because of various drawbacks, but they proved more useful for biomass where these drawbacks were absent. Instead, circulating fluidized bed boilers became the most important coal converters, whose design now is quite mature, and presently the increments in size and efficiency are the most important development tasks. The new modifications of these conversion devices are related to CO2 capture. Proposed methods with this purpose, involving fluidized bed, are single-reactor systems like oxy-fuel combustion, and dual-reactor systems, including also indirect biomass gasifiers.

Heat input effect of friction stir welding on aluminium alloy AA 6061-T6 welded joint

Abstract: This paper deals with the heat input and maximum temperature developed during friction stir welding with different parameters. Aluminium alloy (AA 6061-T6) has been used for experimental and numerical analysis. Experimental analysis is based on temperature measurements by using infrared camera, whereas numerical analysis was based on empirical expressions and finite element method. Different types of defects have been observed in respect to different levels of heat input.

A fractional model for insulation clothings with cocoon-like porous structure

Abstract: Both silkworm cocoons and wild silkworm cocoons have excellent mechanical properties, as a protective barrier against environmental damage and attack by natural predators. In particular, this multilayer porous structure can be exceptionally tough to enhance the chance of survival for pupas while supporting their metabolic activity. Here, a fractional derivative is defined through the variational iteration method, and its application to explaining the outstanding thermal protection of insulation clothings with cocoon-like porous structure is elucidated. The fractal hierarchic structure of insulation clothings makes human body mathematically adapted for extreme temperature environment.

Studies on orange oil methyl ester in diesel engine with hemispherical and toroidal combustion chamber

Abstract: An investigation has been made to compare the emission characteristics of 20% orange oil methyl ester and 80% diesel in volumetric basis with Neat diesel in hemispherical combustion chamber and toroidal combustion chamber. Non-edible orange oil is selected and utilized to prepare alternative fuel to be utilized in Diesel engine. The traditional method of transestrification is employed for preparation orange oil methyl ester. The chemical properties of prepared methyl ester were determined using fouriertransform infrared spectroscopy method. Further its fuel properties were found based on American Society for Testing and Materials standards and compared with Neat diesel fuel properties. A compression ignition engine with electrical dynamometer test rig with gas analyzer has been used. It is observed that 1% of NOx and 4% of HC emission reduced in toroidal combustion chamber engine. However, smoke emission is found to be lower in hemispherical combustion chamber engine.

Some new applications for heat and fluid flows via fractional derivatives without singular kernel

Abstract: This paper addresses the mathematical models for the heat-conduction equations and the Navier-Stokes equations via fractional derivatives without singular kernel.

Radially varying magnetic field effect on peristaltic motion with heat and mass transfer of a non-newtonian fluid between two co-axial tubes

Abstract: The present analysis discusses the effects of thermal-diffusion with thermal radiation, Joule heating and internal heat generation on peristaltic flow of a non-Newtonian fluid obeying Jeffery model. Heat and mass transfer are also taken into consideration, the flow is between two co-axial tubes under the effect of radially varying magnetic field. The inner tube is uniform and at rest, while the outer tube is flexible with sinusoidal wave traveling. The problem is modulated mathematically by a system of partial differential equations which describes the equations of momentum, heat, and mass transfer. These equations are solved analytically under the assumptions of long wave length and low-Reynolds number in non-dimensional form. The solutions are obtained as a functions of physical parameters of the problem. The radially varying magnetic field effect on the temperature and concentration distributions is analyzed and it is shown that the increase of Hartman number tends to reduce the temperature, while it increases the concentration.