Transitional flow, whereby the motion of a fluid changes from laminar to turbulent flow, was successfully identified by Reynolds (1883) almost 130 years ago. According to ASHRAE (2009), for a round pipe, in general, laminar flow exists when the Reynolds number is less than 2 300. Fully turbulent flow exists when the Reynolds number is larger than 10 000 and transitional flow exists for Reynolds...

There are a number of systems in which supercritical cryogenic fluids are used as coolants or propellant fluids. In some modern military aircraft, the fuel is pressurized above its critical point and used as a coolant to remove heat from the aircraft engine. Accurate prediction of heat transfer coefficients to turbulent flows of supercritical fluids is essential in design of such systems. One o...

The Lagrangian thermodynamic equations of irreversible processes are extended to convective heat transfer. This generalization provides equations for the unified analysis of transient heat flow in complex systems comprising solid structures and moving fluids in either laminar or turbulent flow. The concept of a surface-heat-transfer coefficient is eliminated from the formulation. The theory is ...

Due to its distinct capability to improve the efficiency of shale gas production, supercritical carbon dioxide (SC-CO2) fracturing has attracted increased attention in recent years. Heat transfer occurs in the transportation and fracture processes. To better predict and understand the heat transfer of SC-CO2 near the critical region, numerical simulations focusing on a vertical flow pipe were p...

An experimental investigation is conducted to determine the effect of repeated-plate blockages of variable streamwise spacing on heat transfer characteristics of turbulent flow in rectangular ducts. The plates are attached to the upper and lower walls in a staggered arrangement. The experiments are carried out by mass transfer and the analogy between heat and mass transfer provides the necessar...

research in convective heat transfer using suspensions of nanometer-sized solid particles in base liquids started only over the past decade. recent investigations on nanofluid, as such suspensions are often called, indicate that the suspended nanoparticles remarkably change the transport properties and heat transfer characteristics of the suspension. bending walls can also improve heat transfer...

flow structure and heat transfer characteristics around two-equal in-tandem square cylinders in the two dimensional laminar and turbulent flow regimes are simulated numerically for reynolds and prandtl numbers, re=1-1×10 5 , pr=0.71, respectively. the investigation is based on an implicit finite volume scheme for integrating the unsteady navier-stokes equations and use of standard κ-ε model to ...

A quad inserted into a turbulent boundary layer of a flat plate and its effect on average heat transfer and the friction coefficient is studied. To optimize this effect, the edge sizes and distance of the quad from the flat plate are continually modified. In each case, simultaneously the heat transfer enhancement and reduction in skin friction are analyzed. For optimization, the genetic algorit...

the present paper deals with the prediction of three-dimensional fluid flow and heat transfer in rib-roughened ducts of square cross-section. such flows are of direct relevance to the internal cooling system of modern gas turbine blades. the main objective is to assess how a recently developed variant of a cubic non-linear model (proposed by craft et al. (1999)), that has been shown to produce ...

The present paper reports on the application of Principal Component Analysis (PCA) on the flow and thermal fields generated by the large-eddy simulation (LES) of a square ribbed duct heated by a constant heat flux applied over the bottom surface of the duct. PCA allows to understand the complexity of the resulting turbulent heat transfer process, identifying the flow and thermal quantities whic...