Finite-Temperature Properties of Ba(Zr,Ti)O3_3 Relaxors From First Principles

A first-principles-based technique is developed to investigate properties of Ba(Zr,Ti)O$_3$ relaxor ferroelectrics as a function of temperature. The use of this scheme provides answers to important, unresolved and/or controversial questions, such as: what do the different critical temperatures usually found in relaxors correspond to? Do polar nanoregions really exist in relaxors? If yes, do they only form inside chemically-ordered regions? Is it necessary that antiferroelectricity develops in order for the relaxor behavior to occur? Are random fields and random strains really the mechanisms responsible for relaxor behavior? If not, what are these mechanisms? These {\it ab-initio-based} calculations also leads to a deep microscopic insight into relaxors.Comment: 3 figures + Supplemen

Miniature loop heat pipe with flat evaporator for cooling computer CPU

This paper presents an experimental investigation on a copper miniature loop heat pipe (mLHP) with a flat disk shaped evaporator, 30mm in diameter and 10-mm thick, designed for thermal control of computer microprocessors. Tests were conducted with water as the heat transfer fluid. The device was capable of transferring a heat load of 70W through a distance up to 150mm using 2-mm diameter transport lines. For a range of power applied to the evaporator, the system demonstrated very reliable startup and was able to achieve steady state without any symptoms of wick dry-out. Unlike cylindrical evaporators, flat evaporators are easy to attach to the heat source without need of any cylinder-to-plane reducer material at the interface and thus offer very low thermal resistance to the heat acquisition process. In the horizontal configuration, under air cooling, the minimum value for the mLHP thermal resistance is 0.17degC/W with the corresponding evaporator thermal resistance of 0.06degC/W. It is concluded from the outcomes of the current study that a mLHP with flat evaporator geometry can be effectively used for the thermal control of electronic equipment including notebooks with limited space and high heat flux chipsets. The results also confirm the superior heat transfer characteristics of the copper-water configuration in mLHP

Thermal peformance of miniature loop heat pipe operating under different heating modes

In the new generation microprocessors, it is observed that the power density over the active surface can vary from uniform to non uniform modes depending on the clock speed and the processing load on the chipset. The latter mode of operation can result in hot spots on the microprocessors that can result in the increase of the local temperature above the permissible limit and ultimately in the failure of the electronic device. In order to propose a solution for this problem a miniature loop heat pipe (mLHP) with the flat disk shaped evaporator, 30 mm in diameter and 10 mm thick, was developed. The proposed mLHP was tested under uniformly as well as non-uniformly heating mode. In the uniform heating, the entire active area of the evaporator was heated while in the non-uniform mode only 14% of the evaporator active area was heated locally. The thermal performance of the mLHP under these heating modes was compared on the basis of the evaporator wall temperature and thermal resistance between different loop components. The results of the experiment help to classify mLHP as the viable thermal solution for the cooling of microprocessors with local hot spots and non-uniform heating pattern