Hydrogen could play an important role as an energy vector in the coming decades in the framework of Sustainable Development. It is the universe's most abundant element and thus a never-ending source of energy. Hydrogen can be directly converted into electric energy by using fuel cells without producing toxic gases. It can also be produced by renewable sources such as biomass, solar and wind energies with no impact for the environment. However, although hydrogen represents a promising eco-friendly solution for energy transition, several issues related to its storage and delivery remain to be solved if it is to be widely used in both stationary and automotive applications. Hydrogen has the lowest volumetric energy density among the commonly used fuels, i.e., 0.01079 MJ/L at atmospheric pressure. Compression is the direct solution to overcome this obstacle. High pressure levels can give satisfying energy densities. The present review summarises the state of the art of the most classical hydrogen compression technologies. We shall present the technical and design features of mechanical compressors, i.e., reciprocating, diaphragm, linear and ionic liquid compressors, as well as of innovative non-mechanical technologies specifically conceived for hydrogen applications, such as cryogenic, metal hydride, electrochemical and adsorption compressors. The basic operating principles and the potential performance levels for each compression technology are analysed. Specifically, their current uses in hydrogen applications and their technological limits are described along with proposals of possible ways of improving their performance levels.

/pdf/review-of-the-current-technologies-and-performances-of-4iffocw39m.pdf

Review of the current technologies and performances of hydrogen compression for stationary and automotive applications

A review is presented for the research development of Stirling cycle engines for recovering low and moderate temperature heat. The Stirling cycle engines are categorized into four types, including kinetic, thermoacoustic, free-piston, and liquid piston types. The working characteristics, features, technological details, and performances of the related Stirling cycle engines are summarized. Upon comparing the available experimental results and the technology potentials, the research directions and the possible applications of different Stirling cycle engines are further discussed and identified. It is concluded that kinetic Stirling engines and thermoacoustic engines have the greatest application prospect in low and moderate temperature heat recoveries in terms of output power scale, conversion efficiency, and costs. In particular, kinetic Stirling engines should be oriented toward two directions for practical applications, including providing low-cost solutions for low temperatures, and moderate efficient solutions with moderate costs for medium temperatures. Thermoacoustic engines for low temperature applications are especially attractive due to their low costs, high efficiencies, superior reliabilities, and simplicities over the other mechanical Stirling engines. This work indicates that a cost effective Stirling cycle engine is practical for recovering small-scale distributed low-grade thermal energy from various sources.

/pdf/stirling-cycle-engines-for-recovering-low-and-moderate-4i8vuhf5zt.pdf

Stirling cycle engines for recovering low and moderate temperature heat: A review

Potassium (K+) is an important macronutrient for plant growth and productivity. It fulfills important functions and it is widely included in fertilization management strategies to increase crop production. Although K+ is one of the most abundant elements of the earth crust, its availability to plants is usually limited leading to severe reduction in plant growth and yield. In plants, K+ shortage induces several responses at different levels: morphological, physiological, biochemical, and molecular. Activation of signaling cascades including reactive oxygen species, phytohormones (ethylene, auxin, and jasmonic acid), Ca2+, and phosphatidic acid is also triggered. In this review, we summarize the main of these adaptive responses evolved by plants to cope with K+ deficiency in the rhizosphere.

Potassium deficiency in plants: effects and signaling cascades

An empirical equation of state correlation is proposed for the Lennard-Jones model fluid. The equation in terms of the Helmholtz energy is based on a large molecular simulation data set and thermal virial coefficients. The underlying data set consists of directly simulated residual Helmholtz energy derivatives with respect to temperature and density in the canonical ensemble. Using these data introduces a new methodology for developing equations of state from molecular simulation. The correlation is valid for temperatures 0.5 < T/Tc < 7 and pressures up to p/pc = 500. Extensive comparisons to simulation data from the literature are made. The accuracy and extrapolation behavior are better than for existing equations of state.

Equation of State for the Lennard-Jones Fluid

Waste thermal energy harvesting from a convection-driven Rijke–Zhao thermo-acoustic-piezo system

Experimental study on a double-orifice two-stage pulse tube refrigerator

The Gruneisen parameter has long been used in equations of state for solids to relate thermodynamic properties to lattice vibrational spectra [1]. A few papers have extended the concept to studies of liquid structure. Knopoff and Shapiro [2] have evaluated a Gruneisen parameter for water and for mercury, attempting to relate its temperature dependence in a limited range to atomic clustering within the liquid. Sharma [3], in a series of papers, has evaluated a pseudo-Gruneisen parameter in mercury and liquefied gases and related it to internal pressures, a solubility parameter, and clustering phenomena. In this paper we evaluate the Gruneisen parameter for a variety of fluids, and show how it occurs in many problems in compressible fluid hydrodynamics, without reference to concepts of liquid structure. The work extends that reported in an earlier paper for the special case of steady state, single phase flow [4].

Guobang Chen

Papers

Experimental study on a double-orifice two-stage pulse tube refrigerator

The Grüneisen Parameter in Fluids

Influence of resonance tube length on performance of thermoacoustically driven pulse tube refrigerator

Investigation on a thermoacoustically driven pulse tube cooler working at 80 K

Investigation on traveling wave thermoacoustic heat engine with high pressure amplitude