Periodic cellular metals with honeycomb and corrugated topologies are widely used for the cores of light weight sandwich panel structures. Honeycombs have closed cell pores and are well suited for thermal protection while also providing efficient load support. Corrugated core structures provide less efficient and highly anisotropic load support, but enable cross flow heat exchange opportunities because their pores are continuous in one direction. Recent advances in topology design and fabrication have led to the emergence of lattice truss structures with open cell structures. These three classes of periodic cellular metals can now be fabricated from a wide variety of structural alloys. Many topologies are found to provide adequate stiffness and strength for structural load support when configured as the cores of sandwich panels. Sandwich panels with core relative densities of 2-10% and cell sizes in the millimetre range are being assessed for use as multifunctional structures. The open, three-dimensional interconnected pore networks of lattice truss topologies provide opportunities for simultaneously supporting high stresses while also enabling cross flow heat exchange. These highly compressible structures also provide opportunities for the mitigation of high intensity dynamic loads created by impacts and shock waves in air or water. By filling the voids with polymers and hard ceramics, these structures have also been found to offer significant resistance to penetration by projectiles.

Multifunctional periodic cellular metals

Hydraulic transients in closed conduits have been a subject of both theoretical stud intense practical interest for more than one hundred years. While straightforward in te of the one-dimensional nature of pipe networks, the full description of transient fluid fl pose interesting problems in fluid dynamics. For example, the response of the turbu structure and strength to transient waves in pipes and the loss of flow axisymme pipes due to hydrodynamic instabilities are currently not understood. Yet, such u standing is important for modeling energy dissipation and water quality in transient flows. This paper presents an overview of both historic developments and presen research and practice in the field of hydraulic transients. In particular, the paper cusses mass and momentum equations for one-dimensional Flows, wavespeed, nu solutions for one-dimensional problems, wall shear stress models; two-dimensional and momentum equations, turbulence models, numerical solutions for two-dimen problems, boundary conditions, transient analysis software, and future practical an search needs in water hammer. The presentation emphasizes the assumptions and tions involved in various governing equations so as to illuminate the range of applic ity as well as the limitations of these equations. Understanding the limitations of cu models is essential for (i) interpreting their results, (ii) judging the reliability of the da obtained from them, (iii) minimizing misuse of water-hammer models in both research practice, and (iv) delineating the contribution of physical processes from the contribu of numerical artifacts to the results of waterhammer models. There are 134 refrences in this review article.@DOI: 10.1115/1.1828050 #

A Review of Water Hammer Theory and Practice

Heat transfer enhancement for thermal energy storage using metal foams embedded within phase change materials (PCMs)

Studies of mixed convection in vertical tubes

The deformations and stresses during squeeze flows are evaluated for a wider class of materials than previously covered in articles on this subject. These include generalised Newtonian fluids, yield stress fluids, as well as elastic and viscoelastic materials. Wherever possible, results are given in a compact mathematical form. The effect of different boundary conditions (no slip, perfect slip and partial slip) and how these interact with different types of material behaviour to give a variety of macroscopic responses is also discussed. The significance of this in using squeeze flow as a rheometry method is highlighted and a state-of-the-art view of squeeze flow rheometry is given.

Squeeze flow theory and applications to rheometry: A review

Fluid flow and convective heat transfer to fluids at supercritical pressure

The effective thermal conductivity of steel alloy FeCrAlY (Fe—20 wt.% Cr—5 wt.% Al—2 wt.% Y—20 wt.%) foams with a range of pore sizes and porosities was measured between 300 and 800 K, under both vacuum and atmospheric conditions. The results show that the effective thermal conductivity increases rapidly as temperature is increased, particularly in the higher temperature range (500–800 K) where the transport of heat is dominated by thermal radiation. The effective conductivity at temperature 800 K can be three times higher than that at room temperature (300 K). Results obtained under vacuum conditions reveal that the effective conductivity increases with increasing pore size or decreasing porosity. The contribution of natural convection to heat conduction was found to be significant, with the effective thermal conductivity at ambient pressure twice the value of vacuum condition. The results also show that natural convection in metal foams is strongly dependent upon porosity.

The temperature dependence of effective thermal conductivity of open-celled steel alloy foams

Experimental Investigation of Convection Heat Transfer of CO2 at Super-Critical Pressures in Vertical Mini Tubes and in Porous Media

A detailed investigation of fully developed transient flow in a pipe has been undertaken using water as the working fluid. Linearly increasing or decreasing excursions of flow rate were imposed between steady initial and final values. A three-beam, two-component laser Doppler anemometer was used to make simultaneous measurements of either axial and radial, or axial and circumferential, components of local velocity. Values of ensemble-averaged mean velocity, root-mean-square velocity fluctuation and turbulent shear stress were found from the measurements.Being the first really detailed study of ramp-type transient turbulent flow, the present investigation has yielded new information and valuable insight into certain fundamental aspects of turbulence dynamics. Some striking features are evident in the response of the turbulence field to the imposed excursions of flow rate. Three different delays have been identified: a delay in the response of turbulence production; a delay in turbulence energy redistribution among its three components; and a delay associated with the propagation of turbulence radially. The last of these is the most pronounced under the conditions of the present study. A dimensionless delay parameter τ+[= √2τUτ0/D] is proposed to describe it. The first response of turbulence is found to occur in the region near the wall where turbulence production peaks. The axial component of turbulence responds earlier than the other two components and builds up faster. The response propagates towards the centre of the pipe through the action of turbulent diffusion at a speed which depends on the Reynolds number at the start of the excursion. In the core region, the three components of turbulence energy respond in a similar manner. Turbulence intensity is reduced in the case of accelerating flow and increased in decelerating flow. This is mainly as a result of the delayed response of turbulence. A dimensionless ramp rate parameter γ[= (dUb/dt)
 (1/Ub0)(D/Uτ0] is proposed, which determines the extent to which the turbulence energy differs from that of pseudo-steady flow as a result of the delay in the propagation of turbulence.

John Derek Jackson

Papers

Studies of mixed convection in vertical tubes

Fluid flow and convective heat transfer to fluids at supercritical pressure

The temperature dependence of effective thermal conductivity of open-celled steel alloy foams

Experimental Investigation of Convection Heat Transfer of CO2 at Super-Critical Pressures in Vertical Mini Tubes and in Porous Media

A study of turbulence under conditions of transient flow in a pipe