Developing novel correlations for calculating natural gas thermodynamic properties

Natural gas is a mixture of 21 components and it is widely used in industries and homes. Knowledge of its thermodynamic properties is essential for designing appropriate processes and equipment. This paper presents simple but precise correlations of how to compute important thermodynamic properties of natural gas. As measuring natural gas composition is costly and may not be effective for real time process, the correlations are developed based on measurable real time properties. The real time properties are temperature, pressure and specific gravity of the natural gas. Calculations with these correlations are compared with measured values. The validations show that the average absolute percent deviation (AAPD) for compressibility factor calculations is 0.674%, for density is 2.55%, for Joule-Thomson coefficient is 4.16%. Furthermore, in this work, new correlations are presented for computing thermal properties of natural gas such as enthalpy, internal energy and entropy. Due to the lack of experimental data for these properties, the validation is done for pure methane. The validation shows that AAPD is 1.31%, 1.56% and 0.4% for enthalpy, internal energy and entropy respectively. The comparisons show that the correlations could predict natural gas properties with an error that is acceptable for most engineering applications

The effect of important parameters on the natural gas vehicles driving range

One of the most important issues regarding Natural Gas Vehicles (NGVs) is the Driving Range, chich is defi ned as capability of a NGV to travel a certain distance after each refueling. The Driving Range is a serious obstacle in the development and growth of NGVs. Thus the necessity of studying the effects of various parameters on the Driving Range could be realized. It is found that the on-board storage capacity and the natural gas heating value have the greatest effect on the Driving Range. The charge mass of NGV cylinders is varied due to the natural gas composition and the fi nal in-cylinder values (temperature and pressure). Underfi lling of NGV cylinders, during charging operations, is a result of the elevated temperature which occurs in the NGV storage cylinder, due to compression and Rother processes could be overcome by applying extensive over-pressurization of the cylinder during the fuelling operation. Here, the effects of the most important parameters on the Driving Range have been investigated. The parameters are natural gas composition, engine effi ciency and fi nal NGV on-board in-cylinder temperature and pressure. It is found that, the composition has big effects on the Driving Range. The results also show that as fi nal in-cylinder pressure decreases (or temperature increases), the Driving Range will be increased

Somatic mutations reveal asymmetric cellular dynamics in the early human embryo

Somatic cells acquire mutations throughout the course of an individual’s life. Mutations occurring early in embryogenesis are often present in a substantial proportion of, but not all, cells in postnatal humans and thus have particular characteristics and effects1. Depending on their location in the genome and the proportion of cells they are present in, these mosaic mutations can cause a wide range of genetic disease syndromes2 and predispose carriers to cancer3,4. They have a high chance of being transmitted to offspring as de novo germline mutations and, in principle, can provide insights into early human embryonic cell lineages and their contributions to adult tissues5. Although it is known that gross chromosomal abnormalities are remarkably common in early human embryos6, our understanding of early embryonic somatic mutations is very limited. Here we use whole-genome sequences of normal blood from 241 adults to identify 163 early embryonic mutations. We estimate that approximately three base substitution mutations occur per cell per cell-doubling event in early human embryogenesis and these are mainly attributable to two known mutational signatures7. We used the mutations to reconstruct developmental lineages of adult cells and demonstrate that the two daughter cells of many early embryonic cell-doubling events contribute asymmetrically to adult blood at an approximately 2:1 ratio. This study therefore provides insights into the mutation rates, mutational processes and developmental outcomes of cell dynamics that operate during early human embryogenesis