This paper reviews the development of latent heat thermal energy storage systems studied detailing various phase change materials (PCMs) investigated over the last three decades, the heat transfer and enhancement techniques employed in PCMs to effectively charge and discharge latent heat energy and the formulation of the phase change problem. It also examines the geometry and configurations of PCM containers and a series of numerical and experimental tests undertaken to assess the effects of parameters such as the inlet temperature and the mass flow rate of the heat transfer fluid (HTF). It is concluded that most of the phase change problems have been carried out at temperature ranges between 0 °C and 60 °C suitable for domestic heating applications. In terms of problem formulation, the common approach has been the use of enthalpy formulation. Heat transfer in the phase change problem was previously formulated using pure conduction approach but the problem has moved to a different level of complexity with added convection in the melt being accounted for. There is no standard method (such as British Standards or EU standards) developed to test for PCMs, making it difficult for comparison to be made to assess the suitability of PCMs to particular applications. A unified platform such as British Standards, EU standards needs to be developed to ensure same or similar procedure and analysis (performance curves) to allow comparison and knowledge gained from one test to be applied to another.

A review of materials, heat transfer and phase change problem formulation for latent heat thermal energy storage systems (LHTESS)

A review of experimental/computational studies to enhance the thermal conductivity of phase change materials (PCM) that were conducted over many decades is presented. Thermal management of electronics for aeronautics and space exploration appears to be the original intended application, with later extension to storage of thermal energy for solar thermal applications. The present review will focus on studies that concern with positioning of fixed, stationary high conductivity inserts/structures. Copper, aluminum, nickel, stainless steel and carbon fiber in various forms (fins, honeycomb, wool, brush, etc.) were generally utilized as the materials of the thermal conductivity promoters. The reviewed research studies covered a variety of PCM, operating conditions, heat exchange and thermal energy storage arrangements. The energy storage vessels included isolated thermal storage units (rectangular boxes, cylindrical and annular tubes and spheres) and containers that transferred heat to a moving fluid medium passing through it. A few studies have focused on the marked role of flow regimes that are formed due to the presence of thermally unstable fluid layers that in turn give rise to greater convective mixing and thus expedited melting of PCM. In general, it can be stated that due to utilization of fixed high conductivity inserts/structures, the conducting pathways linking the hot and cold ends must be minimized.

Thermal conductivity enhancement of phase change materials for thermal energy storage: A review ☆

Methods and apparatuses for operating a portable device based on an accelerometer are described. According to one embodiment of the invention, an accelerometer attached to a portable device detects a movement of the portable device. In response, a machine executable code is executed within the portable device to perform one or more predetermined user configurable operations. Other methods and apparatuses are also described.

Methods and apparatuses for operating a portable device based on an accelerometer

Methods of manufacturing a liquid crystal device including depositing a layer of liquid crystal material on a substrate and imprinting a pattern on the layer of liquid crystal material using an imprint template are disclosed. The liquid crystal material can be jet deposited. The imprint template can include surface relief features, Pancharatnam-Berry Phase Effect (PBPE) structures or diffractive structures. The liquid crystal device manufactured by the methods described herein can be used to manipulate light, such as for beam steering, wavefront shaping, separating wavelengths and/or polarizations, and combining different wavelengths and/or polarizations.

Virtual and augmented reality systems and methods

A continuum model for momentum, heat and species transport in binary solid-liquid phase change systems. II: Application to solidification in a rectangular cavity

A disk drive has a fall detection control system that detects when a disk drive is in a free fall, and takes precautionary protective action to minimize physical damage from any resulting shock upon impact. The disk drive includes an accelerometer device that measures acceleration of the disk drive along three mutually orthogonal axes x, y, and z and resolves the measurement into respective vectors a x , a y , and a z . In one embodiment, a processor is programmed to (1) compute a net acceleration a net of the disk drive, (2) compare the net acceleration a net with the selected acceleration threshold level, (3) measure a duration that the net acceleration a net exceeds the acceleration threshold level, (4) compare the measured duration with a selected reference time period, and (5) output the warning signal when the measured duration exceeds the reference time period. Upon receipt of the warning signal, a controller initiates protective routines in preparation for shock.

Disk drive and method for minimizing shock-induced damage

A data retention system is described that has a plurality of access protocols. The system comprises a memory store accessible through a virtual address space, a controller communicatively coupled to the memory store, and an interface. The controller is adapted to implement a memory access protocol for accessing at least a first portion of the virtual address space and a secondary storage protocol for accessing at least a second portion of the virtual address space. The interface is communicatively coupled to the controller, and is able to be communicatively coupled to a communications link.

Data retention system with a plurality of access protocols

Phase-change energy storage devices have an inherent disadvantage due to the insulating properties of the phase-change materials (PCM's) used. Such systems are difficult to analyze theoretically due to the nonlinearities of the moving liquid-solid interface and the presence of natural convection as shown by several recent numerical and experimental investigations. Previous work has been unsuccessful in predicting the performance of phase-change devices in the presence of fins and natural convection. This study presents a simplified numerical model based on a quasi-linear, transient, thin fin equation, which predicts the fraction of melted PCM, and the shape of the liquid-solid interface as a function of time with sufficient accuracy for engineering purposes. Experimental results are compared in dimensionless form with model predictions, and show fairly good agreement. To achieve high heat-transfer rates with a fixed amount of PCM and metal fin material, the model indicates that melting the PCM in a pure conduction mode with closely spaced thin fins is preferable to melting PCM with thicker fins spread further apart, even in the presence of natural convection.

Enhanced heat conduction in phase-change thermal energy storage devices

A process and apparatus is described to break down the Position Error Signal (PES) of a magnetic or optical disk or tape drive to its contributing components (In the case of the optical disk drive, the method is actually two different PESs, Focus Error Signal (FES) and Tracking Error Signal (TES)) This method is based on three concepts: an understanding of how Bode's Integral Theorem ties into noise measurements, a measurement methodology that allows for the isolation of individual noise sources, and a system model that allows these sources to be recombined to form the drive's Position Error Signal The method measures frequency response functions and output power spectra of each servo system element Each input noise spectrum can then be inferred and applied to the closed loop model to determine its effect on the PES uncertainty The method allows the user to identify and rank the most critical noise sources in the positioning mechanism of a drive This allows for optimization of the drive positioning control loop(s) by suitable design choices Such choices may include--but are not limited to--optimization of the position encoding on the data storage surface (such as groove dimensions in an optical drive), optimization of the position signal detection method (such as the demodulation method on a magnetic disk or tape drive), and optimization of the actuator design Such optimization is far more difficult without this invention because it is very difficult to identify which improvements are most helpful

Richard H. Henze

Papers

Disk drive and method for minimizing shock-induced damage

Data retention system with a plurality of access protocols

Enhanced heat conduction in phase-change thermal energy storage devices

Enhanced heat conduction in phase-change thermal energy storage devices

Method and apparatus for decomposing drive error signal noise sources