Heat Transfer Flow Problems Research Articles

Solution of Unsteady Flow Equations for Nanoscale Heat and Mass Transfer in Diverse Applications

Abstract A new innovative stable time-dependent compressible flow solution over the order of nanoseconds is provided here for wide-ranging critically important challenging applications. Specifically, a solution of the highly complex unsteady high speed oscillating compressible flow field inside a cylindrical tube, closed at one end with a piston oscillating at very high resonant frequency at the other end, has been obtained numerically, assuming one-dimensional, viscous, and heat-conducting flow, by solving the appropriate fluid dynamic and energy equations. An iterative implicit finite difference scheme is employed to obtain the solution. The scheme permits arbitrary boundary conditions at the piston and the end wall and allows assumptions for transport properties. In successfully predicting the time-dependent results/data, an innovative simple but stable solution of unsteady fluid dynamic and energy equations is provided here for wide ranging research, design, development, analysis, and industrial applications in solving a variety of complex fluid flow heat transfer problems. The method is directly applicable to pulsed or pulsating flow and wave motion thermal energy transport, fluid-structure interaction heat transfer enhancement, nanoscale heat and mass transfer, diverse range of advanced fluidics, biofluidics/bio-engineering, and fluidic pyrotechnic initiation devices. It can further be easily extended to cover muzzle blasts and high energy nuclear explosion blast wave propagations in one-dimensional and/or radial spherical coordinates with or without including energy generation/addition terms. No other solution exists for such applications.

Solution of Unsteady Fluid Dynamic and Energy Equations for High-Speed Oscillating Compressible Flows and Blast Wave Propagations

Abstract A solution of the highly complex unsteady high-speed oscillating compressible flow field inside a cylindrical tube has been obtained numerically, assuming one-dimensional, viscous, and heat conducting flow, by solving the appropriate fluid dynamic and energy equations. The tube is approximated by a right circular cylinder closed at one end with a piston oscillating at very high resonant frequency at the other end. An iterative implicit finite difference scheme is employed to obtain the solution. The scheme permits arbitrary boundary conditions at the piston and the end wall and allows assumptions for transport properties. The solution would also be valid for tapered tubes if the variations in the cross-sectional area are small. In successfully predicting the time-dependent results, an innovative simple but stable solution of unsteady fluid dynamic and energy equations is provided here for wide-ranging research, design, development, analysis, and industrial applications in solving a variety of complex fluid flow heat transfer problems. The method is directly applicable to pulsed or pulsating flow and wave motion thermal energy transport, fluid–structure interaction heat transfer enhancement, and fluidic pyrotechnic initiation devices. It can further be easily extended to cover muzzle blasts and nuclear explosion blast wave propagations in one-dimensional and/or radial spherical coordinates with or without including energy generation/addition terms.

Analysis of dual solution for MHD flow of Williamson fluid with slippage

This study investigates the numerical solutions of MHD boundary layer and heat transfer of the Williamson fluid flow on the exponentially vertical shrinking sheet, having variable thickness and thermal conductivity under effects of the velocity and thermal slip parameters. It is also assumed that shrinking/stretching velocity, as well as the wall temperature, has the exponential function form. In this study, the continuity, momentum and energy equations with buoyancy parameter and Hartmann number are incorporated especially in the Williamson fluid flow case. Similarity transformation variables have been employed to formulate the ordinary differential equations (ODEs) from partial differential equations (PDEs). The resultant ODEs are solved by shooting method with Runge Kutta of fourth order method in Maple software. The effects of the different applied non-dimensional physical parameters on the boundary layer and heat transfer flow problems are presented in graphs. The effects of Williamson parameter, Prandtl number, and slip parameters on velocity and temperature profiles have been thoroughly demonstrated and discussed. The numerical results show that the buoyancy force and the slip parameters contribute to the occurrence of the dual solutions on the boundary layer and heat transfer flow problems. Furthermore, the stability analysis suggests that the first solution is stable and physically possible.

A ghost-cell immersed boundary method for the simulations of heat transfer in compressible flows under different boundary conditions Part-II: Complex geometries

In this paper, our previous ghost-cell compressible immersed boundary method (Luo et al., 2016) is further implemented to solve heat transfer problems in flows with complex solid geometries. Arbitrary 2D-immersed boundaries are presented by many micro line segments. Each line segment is identified by two vertices. An extension to 3D situation is straightforward, in which arbitrary surfaces can be divided into many triangular surface elements. Two different interpolation schemes for the mirror points, namely inverse distance weighting and bilinear interpolations, are compared. An accurate capture of the secondary vortex street far behind an elliptical cylinder indicates a successful combination of current IB method with the fluid solver. Then, forced convective flow over an inclined non-circle cylinder is used to further validate present method. Finally, Mach>0.3 cases are studied to demonstrate the essentiality of taking compressibility into consideration in high-speed thermal flow problems.

A ghost-cell immersed boundary method for simulations of heat transfer in compressible flows under different boundary conditions

In this paper we describe the implementation of a ghost-cell immersed boundary method for compressible flow with Dirichlet, Neumann and Robin boundary conditions. A general second-order reconstruction scheme is proposed to enforce the boundary conditions via ghost points. The convergence test shows that the present method has a second-order accuracy for three types of boundary conditions. Laminar flow heat transfer problems are used to test the capability of the present method to handle different boundary conditions with stationary and moving boundaries. The compressible effect on the heat transfer process is then studied to illustrate the advantage and necessity of combining IB methods with a compressible flow solver.

Two dimensional heat transfer problem in flow boiling in a rectangular minichannel

The paper presents mathematical modelling of flow boiling heat transfer in a rectangular minichannel asymmetrically heated by a thin and one-sided enhanced foil. Both surfaces are available for observations due to the openings covered with glass sheets. Thus, changes in the colour of the plain foil surface can be registered and then processed. Plain side of the heating foil is covered with a base coat and liquid crystal paint. Observation of the opposite, enhanced surface of the minichannel allows for identification of the gas-liquid two-phase flow patterns and vapour quality. A two-dimensional mathematical model of heat transfer in three subsequent layers (sheet glass, heating foil, liquid) was proposed. Heat transfer in all these layers was described with the respective equations: Laplace equation, Poisson equation and energy equation, subject to boundary conditions corresponding to the observed physical process. The solutions (temperature distributions) in all three layers were obtained by Trefftz method. Additionally, the temperature of the boiling liquid was obtained by homotopy perturbation method (HPM) combined with Trefftz method. The heat transfer coefficient, derived from Robin boundary condition, was estimated in both approaches. In comparison, the results by both methods show very good agreement especially when restricted to the thermal sublayer.

CFD study of heat transfer for oscillating flow in helically coiled tube heat-exchanger

The heat transfer and pressure drop for oscillating flow in helically coiled tube heat-exchanger were numerically investigated based on the Navier–Stokes equations. The correlation of the average Nussel number and average friction factor were proposed considering the frequency and the inlet velocity. The oscillating flow heat transfer problems are influenced by many factors. Hence we need an easy way to reduce the numbers of simulation or experiment. Therefore, the method of uniform design was adopted and the feasibility of this method was verified. The field synergy principle was used to explain the heat transfer enhancement of oscillating flow in helically coiled tube heat-exchanger. The result shows that the smaller the volume average field synergy angle in the helically coiled tube, the better the rate of heat transfer.

Heat Transfer Coefficient Correlation for Convective Boiling Inside Plain and Microfin Tubes Using Genetic Algorithms

Two-phase flow heat transfer has been exhaustively studied in recent years. However, in this field, several questions remain unanswered. Heat transfer coefficient prediction related to nucleate and convective boiling has been studied using different approaches—numerical, analytical, and experimental. In this study, an experimental analysis, data representation, and heat transfer coefficient prediction of two-phase heat transfer in nucleate and convective boiling are presented. An empirical correlation is obtained, based on a genetic algorithms search engine, of a dimensional analysis of the two-phase flow heat transfer problem.

Analytic solution to the conjugate heat transfer problem of flow past a heated block

An analytic solution has been developed for steady laminar two-dimensional conjugated heat transfer across a rectangular block with constant internal heat source and subjected to forced convection on top, different thermal boundary conditions at the sides, and adiabatic wall condition at the bottom. The idealized problem solution is of interest in the basic analysis of single-block cooling. Numerical results presented illustrate the effects of the Peclet number, conductivity ratio and type of thermal boundary condition on the temperature profiles and heat flux distributions along the upper surface of the block.

The effect of heat generation on convective heat transfer for laminar flows in a multi-passage circular pipe maintained under constant wall temperature

A LITERATURE survey [l-lo] indicates that heat transfer studies for laminar flows in multi-passage circular pipes based on temperature distributions including heat generation effects are not available. The existing conventional convective heat transfer problems in flows of multi-passage tubes are based on lumped parameter type analyses [l] which are not rigorous. However, recent interest in the heat generation effect on convective heat transfer properties [ll] has led to this note where the effect of an arbitrary heat generation density in the inner and outer flows on convective heat transfer properties of the multi-passage flow is studied. The thickness of the separating surface and the resistance of heat conductivity of the inner separating wall are neglected. It has been shown that the Nusselt numbers on the outer surface and at the inner separating surface of a multi-passage pipe flow can be defined in three different ways. Also shown was that the Nusselt numbers depend on two dimensionless parameters fl2J: the ratio of the thermal conducti~ties of the fluids in the inner and outer passages, kkr and the product of kk and the ratio of the Peclet numbers of the flows in the inner and outer passages, n = kkkPe, the heat exchanger number of the multi-passage flow. The effect of heat generation is reflected by the dimensionless heat generation numbers yi and y0 for the inner and outer flows, respectively, where y = (~H)/[k~(~e)], L. is the radius of the conduit, H the heat generation volume density, k the thermal conductivity, and Pe the Peclet number [ll, 131. The Nusselt numbers in this multi-passage flow are defined relative to the mixed, combined bulk temperature of the inner and outer region flows.

FLOW CHARACTERISTICS AND HEAT TRANSFER PERFORMANCE OF UNSTEADY TURBULENT FLOW IN A CHANNEL WITH CASCADE PROMOTERS

Abstract The heat transfer problem of flow in a pipe with turbulence promoters on the inside watt has been studied from the standpoint of heat transfer augmentation. Little attention has been given to unsteady flow phenomena in channels with turbulence promoters. In this paper, the periodically oscillating unsteady turbulent flow in a channel with turbulence promoters, which is controlled by the Coanda effect due to fluid injection from the top of the promoters, is studied experimentally. First, the flow control by the Coanda effect is examined for two different promoters and the optimum operating condition is determined. Then the variation of the mean and fluctuating velocity components with space and time is obtained using the conditional sampling technique. The peaks of turbulent intensity correspond well to the gradients of the mean velocity profiles, even in the transient state of the flow oscillation. The heat transfer coefficient for the unsteady flow is constant in the flow direction and slightly ...