다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

https://eva.fing.edu.uy/pluginfile.php/55828/mod_resource/content/1/kalogiru.pdf

Solar thermal collectors and applications

An introduction to heat transfer

Food systems contribute 19%–29% of global anthropogenic greenhouse gas (GHG) emissions, releasing 9,800–16,900 megatonnes of carbon dioxide equivalent (MtCO2e) in 2008. Agricultural production, including indirect emissions associated with land-cover change, contributes 80%–86% of total food system emissions, with significant regional variation. The impacts of global climate change on food systems are expected to be widespread, complex, geographically and temporally variable, and profoundly influenced by socioeconomic conditions. Historical statistical studies and integrated assessment models provide evidence that climate change will affect agricultural yields and earnings, food prices, reliability of delivery, food quality, and, notably, food safety. Low-income producers and consumers of food will be more vulnerable to climate change owing to their comparatively limited ability to invest in adaptive institutions and technologies under increasing climatic risks. Some synergies among food security, adaptati...

https://sustainabledevelopment.un.org/content/documents/881annurev.pdf

Climate Change and Food Systems

This paper presents a comprehensive analysis of heat-transfer characteristics and correlations for CO2 at supercritical pressure in the critical and pseudo-critical region. Firstly, the thermophysical properties of CO2 are discussed along with their influence on heat-transfer characteristics. This is followed by a review of existing experimental and numerical studies on heat transfer and pressure drop for different channel geometries (smooth tubes, porous tubes, concentric annular passages, micro-fin tubes, and helical coils), covering hydraulic diameters from 0.27 to 22.8 mm and bulk temperature from 0 to 120° C and pressure from 74 to 150 bar, as well as factors influencing heat transfer. The review of published works shows that the heat-transfer characteristics are influenced by the geometry configuration and operating conditions, including channel shape and dimension, mass flux, heat flux, bulk temperature and pressure, flow direction, buoyancy, and heating or cooling conditions. Detailed comparisons and analysis of available heat-transfer correlations for CO2 at supercritical pressure are discussed and the review shows that there is lack of universal correlations able to accurately describe local heat transfer and pressure drop for different channel geometries and in particular for the pseudo-critical region. The paper identifies research gaps and proposes research and development needs to fill these gaps to ensure that reliable heat transfer and pressure drop correlations are developed to cover a wider range of operating conditions and applications. 

A state-of-the-art review of heat transfer of supercritical CO2 flowing inside channels and heat exchanger tubes

Existing industrial processes are energy intensive environments with a multitude of waste heat streams at different temperature levels whose recovery would undoubtedly contribute to the enhancement of the sustainability of the industrial sites and their products. In particular, the geographical distribution and size of the available waste heat potential is very widespread with most sources being small to medium size, up to 1 MW and fewer of larger size above 1 MW. Among the waste heat to power conversion approaches, the usage of bottoming thermodynamic cycles based on carbon dioxide in supercritical phase (sCO2) provides significant advantages compared to more conventional technologies such as the Organic Rankine Cycle (ORC) systems that are nowadays commercially available even at small scale (~10 kWe). However, unlike the large sCO2 systems that are already on the market (~ MWe), medium and small size ones are still under development. In the current work, the challenges involved in the design of a small scale sCO2 system are considered through thermodynamic analysis (1 and 2 law) as well as by a preliminary turbomachinery design based on the similarity approach. With reference to a simple regenerative cycle architecture, the study provides details on the design parameters and performance trends as well as on the operational and manufacturing constraints that the compressor imposes to the theoretical values.

/pdf/design-considerations-on-a-small-scale-supercritical-co2-1jt8vduipa.pdf

Design considerations on a small scale supercritical CO2 power system for industrial high temperature waste heat to power recovery applications

There is evidence that food retail has shifted towards smaller stores and food products requiring less time for cooking Small supermarkets (<400m2) usually located within urban areas have higher energy intensity than larger supermarkets because of the high ratio of food against non-food products An energy and thermal small supermarket model was developed based on EnergyPlus using a coupling approach on the interdependence of subsystems andverifiedwith operational data Simulations ofenergy efficient retrofits indicate savings of up to 17% with integrated improvements of building design, lighting, refrigeration and HVAC systems Analysis of refrigeration type and food ratios indicates reduction of total and refrigeration energy consumption with decreasing frozen foods, but increase for the HVAC system making its choice more critical Location within the urban heat island also has a small impact on the total energy use more pronounced for the HVAC and depending on the refrigeration system

Savvas A. Tassou

Papers

A state-of-the-art review of heat transfer of supercritical CO2 flowing inside channels and heat exchanger tubes

Design considerations on a small scale supercritical CO2 power system for industrial high temperature waste heat to power recovery applications

A study of improving energy efficiency of small supermarkets by modelling interactions between building, HVAC, refrigeration and display product.

A mathematical model of the heat transfer process in a shell and tube condenser for use in refrigeration applications

Inventory control assessment for small scale sCO2 heat to power conversion systems