General aspects of carbon dioxide as a refrigerant

Carbon dioxide is an innocuous refrigerant for the environment. It is a substance of current interest in the refrigeration area. Its good thermodynamic and heat transfer properties have placed it in an excellent position for substituting refrigerants that contribute to global warming. This paper describes carbon dioxide as a refrigerant, the main characteristics that have made it a substance of current interest, its applications in subcritical and transcritical cycles, and a general vision of its usage at international level. Moreover, this paper presents the disadvantages of using this refrigerant and the upgrades made by the scientific community in order to improve the performance of those systems that work with this fluid. This paper is a reference for those interested in having a wider vision of frigorific technology based on carbon dioxide as a refrigerant

A high concentration of TGF-β correlates with opportunistic infection in liver and kidney transplantation

Transforming growth factor-β (TGF-β) has been associated with numerous human infections, but its role in the occurrence of opportunistic infection (OI) after solid organ transplantation remains unexplored. This study aimed to assess the utility of the TGF-β following in vitro stimulation of whole peripheral blood (WPB) as a surrogate biomarker of post-transplant OI in a cohort of liver and kidney recipients. Thirty liver and thirty-one kidney transplant recipients were recruited to be prospectively monitored for one-year post-transplantation. Enzyme-linked immunosorbent assay (ELISA) was performed to calculate IFN-γ, IL-17, IL-10 and TGF-β concentration in the supernatant from the activated WPB. Recipients showed higher TGF-β concentrations compared to IFN-γ, IL-17, IL-10 at baseline, although these differences were not significant between INF and NoINF. However, recipients who developed an OI within the first sixth months had a higher concentration of TGF-β than those without OI. A concentration of TGF-β > 363.25 pg/ml in liver and TGF-β > 808.51 pg/ml in kidney recipients were able to stratify patients at high risk of OI with a sensitivity and specificity above 70% in both types of solid organ transplantations. TGF-β could provide valuable information for the management of liver and kidney recipients at risk of post-transplant infection.Our work was possible thanks to the support and funding obtained from the “Instituto de Salud Carlos III (ISCIII)”, Spanish Ministry of Health (Grant Number PI15/01370 and P19/01194); and co-funding by the European Union from the European Regional Development Fund (ERDF) with the principle of “A manner to build Europe”

Energy and exergy analysis of an ejector-compression refrigeration cycle with double IHX

This paper shows an energy and exergy analysis of an ejector-compression refrigeration cycle, in which two heat exchangers are included to the system: 1) between the condenser and liquid separator (IHX-1) and 2) between the condenser and the evaporator (IHX-2), which is an alternative configuration proposed and this configuration is defined as ERC+IHX-1+IHX-2. The effect of evaporation temperature and the heat exchanger effectiveness on the energy and exergy efficiencies and the irreversibilities of each component of the cycle have been analyzed for refrigeration and air conditioning applications. The results show that for the alternative configuration and an effectiveness of IHX-1=80%, it results slightly with a higher COP than when the configurations work with an effectiveness of IHX-2=80%. However, the exergy efficiency increases when the evaporation temperature decreases. The components that show the highest contribution to the irreversibilities in the ERC+IHX-1+IHX-2 configuration are: the condenser, the compressor and the evaporator; whereas that the lowest contribution is due to the expansion valve and IHX-1. In addition, the alternative configuration proposed presents a higher exergetic efficiency and lower irreversibilities than the configurations ERC+IHX-1 y ERC+IHX-2 reported in the literature