Phase change materials for thermal energy storage

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 ☆

Recent developments in phase change materials for energy storage applications: A review

An overview of thermal energy storage systems

Thermal energy storage (TES) systems using phase change material (PCM) have been recognized as one of the most advanced energy technologies in enhancing the energy efficiency and sustainability of buildings. Now the research is focus on suitable method to incorporate PCMs with building. There are several methods to use phase change materials (PCMs) in thermal energy storage (TES) for different applications. Microencapsulation is one of the well known and advanced technologies for better utilization of PCMs with building parts, such as, wall, roof and floor besides, within the building materials. Phase change materials based microencapsulation for latent heat thermal storage (LHTS) systems for building application offers a challenging option to be employed as effective thermal energy storage and a retrieval device. Since the particular interest in using microencapsulation PCMs for concrete and wall/wallboards, the specific research efforts on both subjects are reviewed separately. This paper presents an overview of the previous research work on microencapsulation technology for thermal energy storage incorporating the phase change materials (PCMs) in the building applications, along with few useful conclusive remarks concluded from the available literature.

Development of phase change materials based microencapsulated technology for buildings: a review

The invention discloses a compact type flue gas waste heat recovery heat exchanger. The compact type flue gas waste heat recovery heat exchanger comprises a flue gas inlet, a flue gas outlet, a waste heat recovery fluid inlet, a waste heat recovery fluid outlet, heat exchange tubes, a tube plate, a sealing box and an outer wall, wherein each heat exchange tube has a multi-channel structure which is provided with 2 to 4 elliptical or flat circulating channels formed by mechanical processing, and the elliptical or flat circulating channels in the same heat exchange tube are separated into single channels by in-tube convex ribs which are formed by extruding and sinking in the heat exchange tube; and the heat exchange tubes are arranged at intervals in horizontal and vertical directions, the separation distance between outer walls of two adjacent heat exchange tubes in the horizontal direction is 1 to 10 millimeters, and the separation distance in the vertical direction is 3 to 10 millimeters. The multi-channel heat exchange tube structure of the compact type flue gas waste heat recovery heat exchanger enhances the heat transfer of flue gases and the heat recovery fluid in the tubes, so that the efficiency of recovering the flue gas waste heat is increased, the volume of a waste heat recovery device is reduced, the manufacturing cost is saved, and the defects of low heat exchange efficiency and large volume of flue gas waste heat recovery heat tubes or fin tubes are overcome.

Compact type flue gas waste heat recovery heat exchanger

The invention provides an inorganic salt-expanded graphite block composite phase change material and a preparation method thereof. The preparation method comprises the following steps: (1) mixing inorganic salt and expanded graphite, and smashing and stirring to obtain a mixture, wherein the revolving speed during smashing and stirring is 15,000 to 20,000r/min; (2) mixing the mixture and the expanded graphite, and stirring to obtain an inorganic salt-expanded graphite mixture, wherein the revolving speed during stirring is 15 to 30r/min; (3) briquetting the inorganic salt-expanded graphite mixture, and performing heat treatment to obtain the inorganic salt-expanded graphite block composite phase change material. In the preparation method, the expanded graphite and the inorganic salt are mixed uniformly through stepwise stirring mixing, so that the expanded graphite and the inorganic salt are connected more firmly after briquetting, and the inorganic salt is fully adsorbed into pores of the expanded graphite after being fused, thereby lowering the volume expansion ratio of the composite phase change material, and enhancing the heat stability.

Inorganic salt-expanded graphite block composite phase change material and preparation method thereof

Method for preparing adsorbent coating of pipe casing fin type heat exchanger

The invention belongs to the field of a phase change material technology for cool storage, and discloses an inorganic/organic composite casing layer nanometer phase-change capsule cool-storage fluid and a preparation method thereof. The preparation method comprises the following steps: hydrolysis and condensation are carried out for metal alkoxide, modification is carried out with an organosilicon coupling agent, modified metal oxide sol is obtained; a styrene monomer, an acrylic ester comonomer, a chain transferring agent, an initiator and an alkane core material are mixed for forming an oil phase, the oil phase is added into an emulsifier and deionized water for forming a water phase, homogeneous emulsification is carried out, and miniemulsion is obtained; the miniemulsion is heated to 40-80 DEG C, in situ polymerization is carried out for 10-50 minutes, the modified metal oxide sol is added drop by drop, and after a reaction, a composite casing layer nanometer phase change capsule emulsion is obtained; the emulsion is added into an antifreeze, water is added for dilution, and the product is obtained. Metal oxide and organic polymers are compounded into a casing layer; the product has the advantages of high heat conduction performance, high specific heat capacity and good mechanical stability at the same time, and the product can be used as phase-change cool-storage fluid for cool storage air-conditionings.

Inorganic/organic composite casing layer nanometer phase-change capsule cool-storage fluid and preparation method thereof

The invention provides a hydrated salt-modified expandable graphite composite phase change material and a preparation method thereof. The material comprises bulk hydrophilic modified expandable graphite and hydrated salt adsorbed in the bulk hydrophilic modified expandable graphite. The density of the bulk hydrophilic modified expandable graphite is 300-600 kg/m . According to the composite phase change material, hydrophilic modified expandable graphite is used for adsorption of hydrated salt. Hydrated salt adsorbing capacity of expandable graphite is increased, and energy storage density of the composite phase change material is enhanced. By using the bulk modified expandable graphite for adsorption of hydrated salt, energy storage density of unit volume of the composite phase change material is further enhanced. Experiments show that mass fraction of hydrated salt in the composite phase change material can reach 85%, energy storage density can reach 300 MJ/m and heat conductivity coefficient can reach 9.86 (W.m .K ).

Yutang Fang

Papers

Compact type flue gas waste heat recovery heat exchanger

Inorganic salt-expanded graphite block composite phase change material and preparation method thereof

Method for preparing adsorbent coating of pipe casing fin type heat exchanger

Inorganic/organic composite casing layer nanometer phase-change capsule cool-storage fluid and preparation method thereof

Hydrated salt-modified expandable graphite composite phase change material and preparation method thereof