Heat exchanger selection and design analyses for metal hydride heat pump systems

Abstract

This study presents a design analysis for the development of highly efficient heat exchangers within stationary metal hydride heat pumps. The design constraints and selected performance criteria are applied to three representative heat exchangers. The proposed thermal model can be applied to select the most efficient heat exchanger design and provides outcomes generally valid in a pre-design stage. Heat transfer effectiveness is the principal performance parameter guiding the selection analysis, the results of which appear to be mildly (up to 13%) affected by the specific Nusselt correlation used. The thermo-physical properties of the heat transfer medium and geometrical parameters are varied in the sensitivity analysis, suggesting that the length of independent tubes is the physical parameter that influences the performance of the heat exchangers the most. The practical operative regions for each heat exchanger are identified by finding the conditions over which the heat removal from the solid bed enables a complete and continuous hydriding reaction. The most efficient solution is a design example that achieves the target effectiveness of 95%.

The development of a computational platform to design and simulate on-board hydrogen storage systems

“…3, whereas their thermal models can be found in Ref. [13]. According to the definition of δ, in order to achieve a uniform pattern of reaction and ensure that the solid bed will achieve the target absorbed hydrogen content by the desired fueling time at any location.…”

“…For such a configuration, the results are obtained with an aspect ratio of 0.5 (see Ref. [13]). For the charging process the internal pressure of the tank is raised from the initial value, set equal to the ambient pressure, to the desired charging pressure of 300 bar in 1 minute.…”

“…5 and 7 can be obtained for coolant rates much lower than the chosen value of 20 kg•s -1 that is here selected to operate at a shell-side velocity value (i.e. 1.17 m•s -1 ) comprised between the minimum and maximum recommended values to reduce the risk of deposits and prevent the tube corrosion [13]. In addition, from Fig.…”

“…According to the thermal model described in Ref. [13] the only design parameters that influence the hydrogen stored mass are the pitch to tube diameter ratio PR for HEX2 and the aspect ratio a for HEX1. The latter is expressed as the ratio of D i to D o with respect to Fig.…”

A Comparative Assessment of Hydrogen Embrittlement: Palladium and Palladium-Silver (25 Weight% Silver) Subjected to Hydrogen Absorption/Desorption Cycling

“…M-H systems have been studied extensively for their potential use as media for the safe storage of combustible hydrogen in transportation applications [7]. M-H materials also have been looked at as possible non-mechanical refrigeration and heat pump systems owing to the exothermicity and endothermicity of the hydrogen absorption and desorption processes, respectively [8]. Also, M-H materials currently do play a very important role in the purification of hydrogen from its natural impure sources (e.g.…”