The continuous increase in the level of greenhouse gas emissions and the climb in fuel prices are the main driving forces behind efforts to more effectively utilise various sources of renewable energy. In many parts of the world, direct solar radiation is considered to be one of the most prospective sources of energy. However, the large-scale utilisation of this form of energy is possible only if the effective technology for its storage can be developed with acceptable capital and running costs. One of prospective techniques of storing solar energy is the application of phase change materials (PCMs). Unfortunately, prior to the large-scale practical application of this technology, it is necessary to resolve numerous problems at the research and development stage. This paper looks at the current state of research in this particular field, with the main focus being on the assessment of the thermal properties of various PCMs, methods of heat transfer enhancement and design configurations of heat storage facilities to be used as a part of solar passive and active space heating systems, greenhouses and solar cooking.

Solar energy storage using phase change materials

The use of a latent heat storage system using Phase Change Materials (PCM) is an effective way of storing thermal energy (solar energy, off-peak electricity, industrial waste heat) and has the advantages of high storage density and the isothermal nature of the storage process. It has been demonstrated that, for the development of a latent heat storage system, choice of the PCM plays an important role in addition to heat transfer mechanism. The information on the latent heat storage materials and systems is enormous and published widely in the literatures. In this paper, we make an effort to gather the information from the previous works on PCMs and latent heat storage systems. This review will help to find a suitable PCM for various purposes a suitable heat exchanger with ways to enhance the heat transfer, and it will also help to provide a variety of designs to store the heat using PCMs for different applications, i.e. space heating & cooling, solar cooking, greenhouses, solar water heating and waste heat recovery systems. Measurement techniques of thermophysical properties, studies on thermal cycles for long term stability, corrosion of the PCMs and enhancement of heat transfer in PCM are discussed. New PCM innovations are also included for the awareness of new applications. This paper contains a list of about 250 PCMs and more than 250 references.

Latent Heat Storage Materials and Systems: A Review

Developments in organic solid–liquid phase change materials and their applications in thermal energy storage

Process intensification (PI) is commonly seen as one of the most promising development paths for the chemical process industry and one of the most important progress areas for modern chemical engineering. Often illustrated with spectacular examples, process intensification struggles, however, with its definition and interpretation. Instead of narrowing the scientific discussion down to finding a commonly accepted definition of PI, it is more important to determine its position within chemical engineering and to identify its fundamentals. Accordingly, the paper presents a fundamental vision on process intensification. The vision encompasses four approaches in spatial, thermodynamic, functional, and temporal domains, which are used to realize four generic principles of PI. The approaches refer to all scales existing in chemical processes, from molecular to meso- and macroscale, and are illustrated with relevant examples with special attention given to the molecular scale.

Structure, energy, synergy, time - the fundamentals of Process Intensification

Adsorbents for the post-combustion capture of CO2 using rapid temperature swing or vacuum swing adsorption

Rotating packed beds have received considerable attention as a means of process intensification for gas−liquid mass transfer over the past 2 decades. In this work, we take a critical view of the de...

Process Intensification in Rotating Packed Beds (HIGEE): An Appraisal

The liquid-side mass transfer rate in a centrifugal gas-liquid contactor has been reported to be several times higher than that in conventional packed beds. However, no direct measurement of the gas-side mass transfer coefficient has been reported. We present experimental studies on gas-side mass transfer in a rotating packed bed with wire-gauze packing. Contrary to expectations, the gas-side mass transfer coefficient was much lower than that in conventional packed columns. An analysis of the gas flow, based on the equations of motion, revealed that the gas undergoes solid-body-like rotation in the rotor because of the drag offered by the packing. Therefore, the mass transfer coefficient should be in the same range as that in conventional packed columns. The lower value of the coefficient found experimentally is attributed to liquid maldistribution. The possibility of enhancing the mass transfer coefficient by enhancing the slip between the gas and the packing was explored by using a stack of closely spaced disks as the packing. Mass transfer studies with a pair of disks were conducted. Higher throughputs and mass transfer rates than those with the wire-gauze packing were obtained. A stack of disks as packing appears to hold promise.

Gas-Phase Mass Transfer in a Centrifugal Contactor

HiGee technology is emerging as an alternative to conventional tray and packed towers for mass-transfer applications. To evaluate the process intensification (volume reduction) potential of the technology, a systematic design procedure is developed in this work. HiGee designs using split packing innovation of Chandra et al. [Ind. Eng. Chem. Res. 2005, 44, 4051−4060] are developed for four industrially relevant distillation and absorption systems. Comparison with conventional packed or tray tower designs shows that significant volume reduction is possible. For the systems studied, the process intensification achieved is particularly impressive when the gas side mass-transfer resistance is dominant. The results suggest that split packing design innovation may be particularly suitable for intensification of gas side mass-transfer resistance controlled processes.

Process Intensification in HiGee Absorption and Distillation: Design Procedure and Applications

The flooding and mass transfer characteristics of a rotating packed bed (RPB) incorporating the split packing design innovation is studied. The air−water system is used for characterizing the flooding behavior, while mass transfer is studied for the chemisorption of CO2 in aqueous NaOH. Danckwert’s chemical method is used to infer the effective specific interfacial area (ae) for mass transfer. The variation in the liquid side volumetric mass transfer coefficient (kLae) with operating conditions is also measured. Consistently higher values of ae and kLae are observed for counter-rotation of the adjacent packing rings compared to co-rotation. The flooding and mass transfer results are compared with existing literature data on packed columns and conventional HiGee to evaluate the process intensification potential of the novel HiGee. The flooding limits are comparable to conventional HiGee, while the reported ae and kLae values are higher.

Limiting Gas Liquid Flows and Mass Transfer in a Novel Rotating Packed Bed (HiGee)

Modeling of trickle-bed reactors requires the knowledge of liquid flow texture. A dye-adsorption method was employed to study the liquid flow texture in the bed. Pictures of cross sections of the dismantled bed at different depths were taken. The texture in prewetted and nonprewetted beds of glass beads (nonporous) and alumina particles (porous) of different sizes was studied. To supplement the visual observation, exit liquid distribution and pressure drop were measured. The liquid flow texture was deduced from the visual observations and exit liquid distribution. The present study revealed several unexpected features. The behavior of a bed of porous particles was strikingly different from that of nonporous particles. The interpretation of the previous work on the hysteresis of pressure drop, gas−liquid and liquid−solid interfacial areas, and the implications of the observed liquid flow texture on modeling of trickle-bed reactors are discussed.

D.P. Rao

Papers

Process Intensification in Rotating Packed Beds (HIGEE): An Appraisal

Gas-Phase Mass Transfer in a Centrifugal Contactor

Process Intensification in HiGee Absorption and Distillation: Design Procedure and Applications

Limiting Gas Liquid Flows and Mass Transfer in a Novel Rotating Packed Bed (HiGee)

Liquid Flow Texture in Trickle-Bed Reactors: An Experimental Study