Numerical simulation of snow melting using geothermal energy assisted by heat storage during seasons

Numerical simulation programs were developed for estimating temperature field and snow depth on a snow‐melting system using geothermal energy assisted by heat storage during seasons. The system utilized a group of piles underground as a heat exchanger and heat dissipation pipes near the pavement surface, realizing underground solar heat storage from the surface through the seasons. Verification experiments for this system were conducted not only in a relatively mild snowy region, Fukui, but also in a frigid region, Sapporo. Numerical simulation results demonstrated the existence of an optimum space of a group of piles, where snow melting power becomes maximal. The obtained simulation results showed good agreement with the experimental data of both regions, demonstrating the utility and validity of the programs. Also shown was that the proposed system can melt snow well in a frigid region, Sapporo, without the help of a heat pump. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 42(8): 724–744, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20393     

A study on latent heat storage exchangers with the high‐temperature phase‐change material

This paper presents a theoretical analysis and an experimental test on a shell‐and‐tube latent heat storage exchanger. The heat exchanger is used to recover high‐temperature waste heat from industrial furnaces and off‐peak electricity. It can also be integrated into a renewable energy system as an energy storage component. A mathematical model describing the unsteady freezing problem coupled with forced convection is solved numerically to predict the performance of the heat exchanger. It provides the basis for an optimum design of the heat exchanger. The experimental study on the heat exchanger is carried out under various operating conditions. Effects of various parameters, such as the inlet temperature, the mass flow rate, the thickness of the phase‐change material and the length of the pipes, on the heat transfer performance of the unit are discussed combined with theoretical prediction. The criterion for analyzing and evaluating the performance of heat exchanger is also proposed. Copyright © 2001 John Wiley & Sons, Ltd.     

Thermal radiation effects of a high‐temperature developing laminar flow in a tube

The thermal radiation effects of a high‐temperature developing laminar flow in a tube are investigated numerically. The two‐dimensional steady flow and heat transfer are considered for an absorbing‐emitting gray medium, whose density is dependent on the temperature. The governing equations of the coupled process are simultaneously solved by the discrete ordinate method combined with the control volume method. For a moderate optical thickness, the velocity distribution, the temperature distribution, and the radial heat flux distribution in the medium as well as the heat flux distribution on the tube wall are presented and discussed. The results show that the thermal radiation effects of a high‐temperature medium are significant under a moderate optical thickness. The flow and convective heat transfer are weakened, and the development of temperature distribution is accelerated noticeably. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(5): 299–306, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20018     

Two dimensional numerical simulation of transient natural convection in freezer

A two dimensional model of the transient natural convection in a freezer is studied numerically by finite volume approach. The temperatures of the freezer outside surfaces and the evaporator vary in specified manners, which were taken from an experimental work. The fluid in the freezer is of the Bousinnesq type and the flow is assumed laminar. The transient heat conduction in the insulating layers and the temperature and velocity fields of the fluid are solved conjugately. The radiation heat transfer between the freezer inner surfaces is taken into account by using the additional source term method. The distributions of the local Nusselt number along the upper and lower surfaces of the evaporator and their average values in the period of periodically unsteady operation are calculated. Comparisons are made between the results with and without consideration of inner surface radiative heat transfer. It is found that the radiative heat transfer between the inner surfaces has a profound effect on the evaporator heat transfer characteristics.     

Prediction of skin temperature of externally water cooled pipes under intense fires

A multiphase, multimode heat transfer numerical model was used to estimate the maximum skin temperature of a stagnant water‐filled pipe structure subject to an intense flame. This transient two‐dimensional mathematical model takes into account conduction, convection and radiation as well as evaporation of cooling water. Results have been obtained based on practical data and experimental field findings. The cooling water film that surrounds the pipe structure attacked by the flames, can originate from fire‐fighting water hoses or from a sprinkler water system. Two different values of water film thickness of 3 and 5 mm are analysed. The simulation results indicate that the main parameter which controls the pipe skin temperature, is the water film thickness covering the pipe. Indeed the maximum steel pipe skin temperature drops from 175.5 to 108.8°C when the water film thickness is increased from 3 to 5 mm for the 20 inch‐water‐filled pipes. However the water presence inside the pipe has negligible effect on the pipe skin temperature. Copyright © 2004 John Wiley & Sons, Ltd.     

MHD Mixed Convection and Mass Transfer Due to Unsteady Stretching Sheet

Heat and mass transfer in the flow of a viscous incompressible fluid along a vertical isothermal unsteady stretching sheet in the presence of heat generation and a transverse magnetic field is investigated. The governing equations of continuity, momentum, energy, and species concentration are transformed into a system of nonlinear ordinary differential equations and solved numerically by using the Runge–Kutta fourth‐order method with shooting technique. The velocity, temperature, and concentration distributions are discussed numerically and shown through graphs. The expressions of skin‐friction coefficient, Nusselt number, and Sherwood number at the sheet are discussed numerically and their variations are presented through tables. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(5): 447–458, 2014; Published online 3 October 2013 in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21088     

An experimental and theoretical investigation into the heat transfer of a finned water wall tube in a circulating fluidized bed boiler

Heat transfer improvement in a water wall tube with fins was investigated in a circulating fluidized bed (CFB) boiler. Experiments were first conducted in a 6 MWth CFB boiler then a model was developed to analyse and interpolate the results. Temperatures at some discrete points within the wall cross‐section of the tube were measured by burying 0.8 mm thermocouples within a tube. Experimental data showed an increase in heat absorption up to 45 per cent. A good agreement between measured and predicted values was noted. The distribution of temperature in the metal wall and of heat flux around the outer wall of a tube with longitudinal and lateral fins was analysed by numerical solution of a two‐dimensional heat conduction equation. Effects of bed‐to‐wall heat transfer coefficient, water‐to‐tube inside heat transfer coefficient, bed temperature, water temperature and thermal conductivity of the tube material on the heat flux around the water tube are discussed. The present work also examines the influence of the length of the longitudinal fin and the water tube thickness. Heat flux was highest at the tip of the longitudinal fin. It dropped, but increased again near the root of the lateral fin. Copyright © 2000 John Wiley & Sons, Ltd.     

Numerical study of the intensified heat transfer of an internally longitudinal ridged finned tube under pulsating flow

The turbulent pulsating flow and heat transfer in an internally longitudinal protuberant finned tube was numerically investigated by solving unsteady three‐dimensional elliptical Navier–Stokes equations. The realized k–? turbulent model was adopted. The dynamic behaviors of velocity field, average Nusselt number, and friction number of the internally longitudinal protuberant finned tube were numerically analyzed in a pulsating period, and it was further investigated by changing the frequency of the pulsating flow. It was found that the intensity of heat transfer enhancement increases with an increase of pulsating frequency, while the pressure drop will be increased simultaneously, the intensification of heat transfer in internally longitudinal protuberant finned tubes are gradually better than the pressure drop with an increase of pulsating frequency. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20253     

Numerical study of radiation‐convection heat transfer

In this study, the authors attempted to introduce a simulation technique for radiation‐convection heat transfer in the high‐temperature fields of industrial furnaces, boilers, and gas turbine combustors. The convection effect was analyzed by a differential equation, but the radiation effect was analyzed by an integral equation. Thus, it was not easy to arrange both effects using the same type of equations. Then, the authors introduced the zone method and Monte Carlo method for the integral equation of the radiation effect and the finite difference method for the differential equation of the convection effect. A three‐dimensional analysis of the high‐temperature furnace was performed by this simulation technique to obtain its temperature distribution. Furthermore, another radiation‐convection heat transfer analysis in the low‐temperature living room was performed by the same technique. Finally, the authors tried to develop a computer software for radiation‐convection heat transfer and described their idea of software construction for the above. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(5): 391–407, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10042     

双圆柱坐标下垂直埋管土壤热湿耦合迁移理论模型与数值模拟

以土壤热湿迁移理论为基础,建立双圆柱坐标系下U型垂直埋地换热器周围土壤内三维非稳态热湿耦合迁移模型,并考虑土壤内热湿迁移的相互影响,编制相应的计算软件.进行不同土壤物性、不同运行工况、不同初始含湿量对U型垂直埋地换热器周围土壤内热湿迁移影响的研究.将模拟值与实验结果进行比较,表明该模型可用于实际应用的模拟分析.     

Exact solutions of micropolar SWCNTs nanofluid with heat transfer

The present study is aimed to analyze the unsteady micropolar nanofluid flow passing over an oscillating infinite vertical plate. The flow is affected by thermal radiation and Newtonian heating. Single‐walled carbon nanotubes (SWCNTs) are added to enrich the thermal properties of the micropolar fluid. Kerosene is taken as the base liquid to enhance heat transfer. By using dimensional analysis, the governing equations for temperature, velocity, and microrotation are reduced to dimensionless form and after that, these equations have been solved by applying Laplace transform method to get the exact solutions. Finally, we have presented the effects of material and flow parameters and illustrated graphically by the Mathcad software. We found that microrotation, temperature, and velocity are decreasing functions of Prandtl number but have shown increasing behavior for Grashof number. Furthermore, we found that SWCNTs‐water‐based nanofluid has a comparatively higher heat transfer rate than SWCNTs‐kerosene and SWCNTs‐engine oil‐based nanofluids.     

Numerical simulation of coupled radiation‐convection heat transfer of high‐temperature developing flow in tube

By combining the discrete ordinate method with the control volume method, the coupled radiation‐convection heat transfer of high‐temperature developing laminar flow in a tube is investigated numerically. The radiative transfer is solved by the discrete ordinate method and its contribution to thermal balance is dealt with as a source term in the energy equation, which is solved, as well as the momentum equation, by the control volume method. The effects of medium optical thickness and tube wall temperature on the temperature distribution in medium as well as the heat flux and local Nusselt number on wall are analyzed. The results show that the radiation heat transfer of high‐temperature medium influences the temperature distribution and convection heat transfer greatly, and plays an important role in the heat transfer of developing laminar flow in a tube. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(1): 53–63, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10135     

Coupled radiation‐convection heat transfer of high‐temperature participating medium in heated/cooled tubes

The coupled radiation‐convection heat transfer of high‐temperature participating medium in heated/cooled tubes is investigated numerically. The medium flows in a laminar and fully developed state with a Poiseuille velocity distribution, but the thermal status is developing. By the discrete ordinate method, the nonlinear integrodifferential radiative transfer equation in a cylindrical coordinate form is solved to give the radiative source term in the energy equation of coupled heat transfer. The energy equation is solved by the control volume method. The local Nusselt number and wall heat flux of convection as well as the total wall heat flux are employed to evaluate the influence of radiation heat transfer on convection. The analysis shows that the radiation heat transfer weakens the convection effect, promotes the temperature development, and significantly shortens the tube length with obvious heated/cooled effect. There is an obvious difference between the coupled heat transfer in a heated tube and that in a cooled tube, even though the medium properties are kept constant. The wall emissivity, the medium thermal conductivity and scattering albedo have significant influences on the coupled heat transfer, but the effect of medium scattering phase function is small. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(1): 64–72, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10137     

Steam absorption into aqueous lithium bromide solution films falling inside vertical pipes

The realization of a compact and efficient air‐cooled absorber is the key technology for the small‐capacity absorption refrigerator for domestic use. A vertical pipe with absorbent flowing inside and air flowing outside is the best choice for the air‐cooled absorber due to the easy addition of fins to enhance heat transfer on the air side. In this paper, first, the modeling of the absorption process in the vertical pipe for a constant heat transfer coefficient on the outer surface is described. Then, experimental results are presented for pipes of inner diameters 8 to 26 mm, pressure 5 and 6 mm Hg, and outer surface heat transfer coefficient 2000 and 3300W/(m²·K). It was found that for pipes of diameter 13 mm or more, the absorption process is well estimated by the proposed model. The absorption with addition of surfactant is estimated by the pseudo‐turbulent method. The necessary heat transfer area for the air‐cooled condition is about three times that for the water‐cooled condition. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(8): 740–752, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10128     

Unsteady free convection of second‐grade nanofluid with a new time‐space fractional heat conduction

The Caputo and Caputo–Fabrizio derivative are applied to study a second‐grade nanofluid over a vertical plate. A comparative analysis is presented to study the unsteady free convection of a second‐grade nanofluid with a new time–space fractional heat conduction. The governing equations with mixed time–space fractional derivatives are non‐dimensionalized and solved numerically, and a comparison between the Caputo and the Caputo–Fabrizio models is made. It is found that the temperature is higher for the Caputo–Fabrizio fractional model than the Caputo model, but the higher velocity only exists near the vertical plate for the Caputo–Fabrizio model than the Caputo model. Moreover, the velocity for the Caputo model will exceed the Caputo–Fabrizio model as y evolves.     

Stagnation‐point flow of Maxwell fluid with magnetic field and radiation effects

The effect of heat transfer on the steady two‐dimensional stagnation point flow of a Maxwell fluid over a stretching sheet is discussed. The fluid is electrically conducting in the presence of a uniform applied magnetic field. The radiation effect in the energy equation is taken into account. The arising nonlinear problem is solved by a homotopy analysis method (HAM). Convergence of the series solutions is checked. The values of skin friction coefficient and local Nusselt number have been computed and discussed. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20385     

埋地换热器理论模型与周围土壤温度数值模拟

提出内热源型埋地换热器理论模型，建立换热器周围土壤热湿传递物理数学模型。内热源模型综合考虑热湿迁移、土壤物性等各方面因素，将埋设于土壤中的换热器处理为等效内热源。采用专业多孔介质计算软件Autough2对模型进行模拟计算。着重模拟计算不同土壤物性、不同换热器运行方式对单根U型垂直埋管换热器周围土壤温度场影响的模拟计算与分析。     

Numerical analysis of unsteady heat conduction in regular solid bodies comprising natural convection to nearby fluids

The present paper addresses unsteady, unidirectional heat conduction in regular solid bodies (vertical plate, horizontal cylinder, and sphere) that exchange heat by natural convection with a neighboring fluid. From thermal physics, natural convection constitutes a worst-case scenario for forced convection cooling. Under the premises of natural convection heat transfer, the unsteady, 1-dimensional heat conduction equation consists in a linear parabolic partial differential equation with a dominant natural convection boundary condition represented by the mean convective coefficient that depends upon temperature. As expected, the nonlinear unsteady, unidirectional heat conduction problem is complex and does not admit an exact, analytical solution. Instead, the nonlinear unsteady, unidirectional heat conduction problem forcibly necessitates approximate numerical treatment with the finite difference method. The computed dimensionless center, surface, and mean temperatures varying with dimensionless time are obtained numerically and are graphed for 3 solids: iron, aluminum, copper exposed to 3 fluids: air, water, oil; the 6 media are used in numerous engineering applications.     

Transient heat transfer in a heat‐generating fin with radiation and convection with temperature‐dependent heat transfer coefficient

The transient heat transfer in a heat‐generating fin with simultaneous surface convection and radiation is studied numerically for a step change in base temperature. The convection heat transfer coefficient is assumed to be a power law function of the local temperature difference between the fin and its surrounding fluid. The values of the power exponent n are chosen to include simulation of natural convection (laminar and turbulent) and nucleate boiling among other convective heat transfer modes. The fin is assumed to have uniform internal heat generation. The transient response of the fin depends on the convection‐conduction parameter, radiation‐conduction parameter, heat generation parameter, power exponent, and the dimensionless sink temperature. The instantaneous heat transfer characteristics such as the base heat transfer, surface heat loss, and energy stored are reported for a range of values of these parameters. When the internal heat generation exceeds a threshold the fin acts as a heat sink instead of a heat source. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21012     

Development of a simplified heat pipe numerical model and case study/experimental validation using a long ‘wicked’ heat pipe

This paper describes existing numerical techniques used for simulating heat pipe operation, and the development of a simplified numerical model for normal wicked/wickless heat pipes based on the analysis of current modelling methods. Vapour flow was treated as a two‐dimensional flow. Heat transfers through the liquid–wick region and wall region were computed by solving a one‐dimensional heat conduction equation. Flow in the liquid–wick region was treated as a one‐dimensional problem. The liquid and vapour flows were coupled using a set of governing equations, incorporating thermal compressibility, hydro‐dynamical and capillary relationship, as well as geometrical correlation. The finite‐difference method was employed to carry out the numerical analysis, and FORTRAN language was used to develop a computer program. The model was used to investigate the operating characteristics of a long ‘wicked’ heat pipe, including variation of cross‐sectional area, axial/radial velocity, pressure and temperature of liquid/vapour flows with height position above the liquid level. To validate the modelling predictions, a test rig was constructed to carry out experimental testing. This included measurement of surface temperatures and heat flow associated with heat‐pipe heat transfer. The results from tests were found to be in general agreement with the numerical predictions when the test conditions were close to the simulation assumptions. Copyright © 2004 John Wiley & Sons, Ltd.