Members' Vote of Interest - GRETh Actions 2024

Given the current energy, environmental and economic context, hydrogen has "recently" emerged as a solution for decarbonizing the world of transport and energy production. Hydrogen is also emerging as a promising future solution for energy storage (electrical or thermal). We sometimes forget that hydrogen is a very important compound in industry, for example in ammonia production (e.g. fertilizers, explosives, organic chemistry), in the chemical industry (e.g. methanol production, etc.), in oil refining operations or in the space industry, notably for spacecraft propulsion. However, by 2022, over 80% of hydrogen will be produced directly from fossil fuels, the remaining 20% being by-products of chemical reactions (naphtha reforming) in refineries [Global Hydrogen Review 2023, IEA, Sept.2023]. New uses in the transport and energy sectors (e.g. fuel cells, associated refuelling systems, steelworks, etc.) are still marginal, as existing technologies are not yet mature, despite ever-increasing demand.

From the production of hydrogen by various means (Gray Hydrogen (mainly by steam reforming), Blue Hydrogen (i.e. gray hydrogen including CO2 capture techniques during the steam reforming reaction), Green Hydrogen (biomass gasification or water electrolysis), Yellow Hydrogen (electrolysis via nuclear energy)), to its use, via various intermediate stages (transport, storage, distribution, etc.), heat exchangers are components that are both omnipresent in the entire Hydrogen vector chain, and extremely important in the context of controlling heat transfer. Heat exchangers are omnipresent components in the entire hydrogen chain, and are extremely important in the context of controlling heat exchange in processes to increase and optimize yields, and reduce the size and cost of equipment, particularly in response to new global challenges in the energy sector.

GRETh is proposing to write a report on the subject of Hydrogen, with a particular focus on heat exchangers, their roles and positions, and existing and/or developing technologies to meet current and future challenges in processes involving hydrogen.

The energy issues that have been at stake for more than a decade, whether environmental or economic, and which have been heightened by the current situation (geopolitical, economic, regulatory & environmental), are now reemerging as a major interest in energy conversion systems, whether for the recovery of waste heat, or for the production of heat or cooling using electricity, whether surplus or not. Examples of such systems are the organic Rankine cycle (ORC), the Stirling cycle, the inverted Brayton cycle, the absorption cycle, and so on. The efficiency of these cycles depends not only on operating conditions, but also on the efficiency of their component equipment, such as compressors, turbines, evaporators, condensers and absorbers.... Heat exchangers therefore play a vital role in these systems.

GRETh proposes to carry out a summary review of the main existing systems, including descriptions of the cycles associated with these functions (Power-to-Heat / Heat-to-Power), the range of uses, targets and requirements of these cycles, a brief description of the technologies of the components associated with these cycles (other than heat exchangers), a review of the current market offer and solutions under development. Naturally, GRETh will be focusing on the role of heat exchangers in these systems, including technological descriptions of heat exchangers in use or in the process of being used, performance issues, and associated design methods, particularly in the context of the search for ever-lower pinch points on these heat exchangers, in order to improve cycle efficiency.

The EchTherm modules for air/liquid heat exchangers (operating with gases at atmospheric pressure (air or flue gas)) are used by a significant number of GRETh members. As part of the validation of EchTherm calculation results, and after having tested in the past a shell-and-tube heat exchanger and a water/water gasketed plate heat exchanger, it would be interesting to be able to verify EchTherm results for these technologies, which are widely used in processes and in EchTherm. In this respect, we propose to choose between two technologies :

- Technology n°1 - Continuous finned tube heat exchanger: A omnipresent technology in industry, it consists of tubes fitted with continuous fins. This technology is widely used in applications ranging from demanding industrial environments (air heating or cooling) to standard industrial/tertiary applications (air coolers, heat dissipation) or in the HVAC field (air-conditioning coils, AHUs). Like the heat exchangers previously tested by GRETh, this is a heat exchanger that could be described as the "common denominator" in many thermal systems.

The EchTherm modules for air/liquid heat exchangers (operating with gases at atmospheric pressure (air or flue gas)) are used by a significant number of GRETh members. As part of the validation of EchTherm calculation results, and after having tested in the past a shell-and-tube heat exchanger and a water/water gasketed plate heat exchanger, it would be interesting to be able to verify EchTherm results for these technologies, which are widely used in processes and in EchTherm. In this respect, we propose to choose between two technologies :

- Technology n°2 - Microchannel heat exchangers for single-phase applications: These are all-aluminium finned microchannel coils (usually louvered fins). This technology is more commonly used and well-proven in condensing applications, but a number of products have recently been launched in single-phase for liquid cooling or heating applications. They offer a number of advantages, particularly over competing solutions based on conventional finned coils, such as reduced weight and overall dimensions, as well as reduced (at iso thermal performance) pressure drop, and therefore ultimately reduced consumption of auxiliary equipment (fans). Experimental tests will enable us to compare the performance results of these heat exchangers with the simulation/sizing module already available in EchTherm.

Brazed plate heat exchangers are omnipresent in a wide range of thermal systems: chillers, various industrial applications for heating or cooling liquids, data centers, air conditioning/heat pump systems, gas boilers, domestic hot water (DHW) applications, district heating plant substations, network separators, etc.

Through this campaign of experimental tests, GRETh aims not to produce correlation in the strict sense of the term, but to characterize the performance of such heat exchangers, particularly in refrigeration applications involving evaporation and condensation of a refrigerant and, ultimately, heating and cooling of water (or glycol water). Comparison with EchTherm simulation/dimensioning results will enable members to compare EchTherm results with experimental results. Infrared thermography analyses may be added to this test campaign to identify any distribution bias or otherwise.

Cold plates are heat exchange devices frequently used for thermal management of various components and applications, such as: cooling of electronic components, thermal management of batteries (electric vehicle applications), data center cooling, thermal management of specific equipment such as lasers, cooling of medical systems, etc.

As the name suggests, cold plates generally consist of a plate (usually metal) into which a circuit is machined or incorporated, through which a liquid circulates. The fluids usually used are water and glycol water, but applications with specific fluids (dielectric fluid, oil, etc.) are also possible.

GRETh is proposing to integrate a simplified pre-design tool for these cold plates into EchTherm.

The modeling of heat transfer and pressure drop on the outside (shell side) of shell-and-tube heat exchanger bundles is relatively well known, particularly in the case of E-type (single-pass) shell fitted with single-segment baffles. Various methods exist in the literature, and GRETh uses the well-known Bell-Delaware method to calculate the heat exchange coefficient and pressure drop of flows through such heat exchangers. This method calculates the heat exchange coefficient and the pressure drop outside the bundle of a shell-and-tube heat exchanger, and is based on the study of real heat exchangers with all the imperfections associated with the mechanical dispersions of the parts involved (shell, baffles, tubes), as well as their functional assembly clearances. However, this method can only be applied to E-type shells with single-segment baffles.

A TEMA F-type shell-and-tube heat exchanger is a shell-and-tube heat exchanger with a double pass on the shell side via a longitudinal baffle: coupled with a U-shaped tube bundle, this configuration creates a shell side heat exchanger with 2 passes on the tube side and 2 passes on the shell side, and ultimately counter-current flows for each of the passes (whereas coupling a double pass on the tube side with a single-pass type E shell results in counter-current flow for one of the two passes and co-current flow for the other pass, thus reducing heat transfer efficiency). This configuration makes for a more compact heat exchanger.

GRETh is therefore proposing to integrate into the EchTherm software a sizing tool dedicated to this type of shell and its specific features.