Metal Hydride Heat Pump System Research Articles

Lumped model for a quasi-continuously operating open metal hydride heat pump system

Hydrogen as a potential future fuel for fuel cell vehicles is mostly stored in high-pressure tanks at 350 or 700 bar, which requires energy-intense compression of typically 15 % of the lower heating value. For the recovery of parts of the compression work, a promising possibility is the usage of an open metal hydride heat pump. Similarly to other sorption-based heat pump systems, in order to reach high specific thermal power, it is crucial to find a trade-off in the design and operation of the reactor between two main factors: enabling fast reaction dynamics and reducing losses due to temperature switches. The present work introduces a steady-state model with lumped metal hydride and reactor mass considering one-dimensional heat and mass transfer, which is able to quickly predict the corresponding specific thermal power and efficiency. A special focus is on the calculation of the non-complete conversion due to an operation at constant gas flow. The model is validated with existing experimental data over a broad range of operation conditions in terms of metal hydride specific hydrogen mass flow (1.6–7.6 gH2 min−1 kgMH-1) and temperature boundary conditions (cold side temperature: 13–25 °C, hot side temperature: 24–42 °C). It is capable of describing the specific thermal power and the efficiency as the two main performance indicators with a suitable accuracy. To give an example of the applicability of the developed tool, a generic discussion of the performance limitations of the selected reactor design is carried out, indicating that the reactor of the validation experiment is mainly mass transport limited.

Compressor driven metal hydride heat pumps using an adsorptive slurry and isothermal compression

Metal hydrides have been investigated for use in environmentally friendly heat pumps. These systems operate using reversible adsorption and desorption of hydrogen from metallic compounds and can be incorporated in a cycle having a work input (compressor) or thermal energy input (generator). Some challenges faced by compressor driven metal hydride heat pumps are poor heat transfer in the metal hydride beds and high compressor discharge temperatures. To overcome these challenges, this article investigates the use of a metal-hydride slurry in conjunction with various isothermal compression techniques. Liquid-flooded, electrochemical, and liquid piston compressors were modeled and integrated into a system model in order to assess their impact on the performance of the slurry-based metal hydride heat pump system.

Electrochemical compressor driven metal hydride heat pump

In this study, a new metal hydride heat pump system driven by an electrochemical compressor was proposed. The system uses the electrochemical compressor to generate absorption heating and desorption cooling in two identical LaNi5 reactors operating at different pressure levels. A thermodynamic model was developed to predict the system performance in terms of various parameters. Modeling shows EC compression efficiency has a great impact on system performance. The system is suitable for cooling application less than 200 W where mechanical compressors are the most inefficient. The high compression efficiency of electrochemical compressor could potentially make the cooling system more competitive than existing metal hydride heat pump systems.

G0600605 MHシートの有効熱伝導率とMHヒートポンプシステムへの適用に関する研究

G0600605 MHシートの有効熱伝導率とMHヒートポンプシステムへの適用に関する研究

A comprehensive approach for alloy selection in metal hydride thermal systems

Metal hydride thermal systems can be used in a variety of applications, but the selection of hydrides for such systems is often limited to a narrow set of materials. In this work, we present the methods and accompanying property database to conduct a comprehensive material selection analysis for a metal hydride thermal system using a database of over 300 hydrides from the open literature. To use this data effectively, we developed a robust thermodynamic equilibrium model that can be applied to a wide range of hydride types, a set of generic reaction rate expressions, and a set of relevant thermophysical property models. The combination of these features—distributed as a freely available object-oriented MATLAB® Toolbox—allows consideration of over 100,000 possible hydride pairs for a given two-hydride thermal system and shows trends otherwise unavailable from an analysis of only a few hydride pairs. We use a metal hydride heat pump system to demonstrate this capability and to identify trends of system coefficient of performance (COP) and the fraction of hydrogen transferred between hydrides. Using the simulation results from the 3999 hydride pairs which have suitable thermodynamics to work in the metal hydride heat pump system, we show that the system COP calculated only from material parameters is not a reliable predictor of the dynamic system COP.

Study of integrated metal hydrides heat pump and cascade utilization of liquefied natural gas cold energy recovery system

The traditional cold energy utilization of the liquefied natural gas system needs a higher temperature heat source to improve exergy efficiency, which barricades the application of the common low quality thermal energy. The adoption of a metal hydride heat pump system powered by low quality energy could provide the necessary high temperature heat and reduce the overall energy consumption. Thus, an LNG cold energy recovery system integrating metal hydride heat pump was proposed, and the exergy analysis method was applied to study the case. The performance of the proposed integration system was evaluated. Moreover, some key factors were also theoretically investigated about their influences on the system performance. According to the results of the analysis, some optimization directions of the integrated system were also pointed out.

Determination and analysis of site selection for introducing Metal Hydride Heat Pump System based on the spatial and eco-efficiency analysis in the Kanto of Japan

Determination and analysis of site selection for introducing Metal Hydride Heat Pump System based on the spatial and eco-efficiency analysis in the Kanto of Japan

The operating characteristics of the compressor-driven metal hydride heat pump system

Metal hydrides can be utilized advantageously as working materials in a number of systems that can significantly contribute to an environmentally clean technology. Among such systems, there is a CDMHHP (compressor-driven metal hydride heat pump). This CDMHHP is expected to generate higher cooling power than that of conventional MHHP driven by waste heat. In this work, extensive investigation was carried out to find the operating characteristics of a CDMHHP system. In the system, the Zr 0.9Ti 0.1Cr 0.55Fe 1.45 Laves phase metal hydride was selected as a suitable alloy for a given compressor. The maximum cooling power of this system is 251 kcal/ kg alloy h .

Simulation of the metal hydride heat pump system with the single and double reactors

The main obstacles for the practical use of a metal hydride heat pump (MHHP) system are a low-heat transport rate of the metal hydride and a relatively large irreversible heat loss during the hydriding and dehydriding processes. Very extensive investigations are required to overcome these obstacles, which are both time-consuming and costly. In order to save both time and cost, computer simulation can be introduced in the development of such MHHP systems. In particular, simulation can provide useful technical knowledge for improving the system by optimum reactor construction and identification of optimum operational parameters. In this work, a simulation method for the MHHP system, based on the three-vector equilibrium space of temperature, concentration and enthalpy, is proposed and tested practically. Using a computer simulation program for a single reactor MHHP system driven by a given pressure or flow rate of hydrogen, it was possible to describe equilibrium properties of hydride as they are changed by variations in temperature and concentration. Simulation of the MHHP system with two reactors, i.e. one metal hydride pair, allowed the thermodynamics of a conventional system to be described theoretically.

Compressor-driven metal-hydride heat pumps

Analysis and experiments are presented for a compressor-driven hydrogen metal-hydride heat-pump system. Such a system, utilizing fast hydride reactors, has the potential to achieve higher efficiency and competitive life-cycle costs with conventional refrigeration systems. Fast reactors utilizing copper-coated LaNi 5 hydride compacts were designed with improved thermal conductivity. Reactors were built and tested and the results evaluated. The potential for hydride heat pumps is also described.

Compression-Type Metal Hydride Heat Pump System.

A compression-type metal hydride heat pump system has been constructed which utilizes the exothermic and endothermic characteristics of hydrogen storage alloy during its absorbing and desorbing reaction with hydrogen. The system is composed of two identical heat exchanger units, a hydrogen compressor, a cooling/heating fluid circulating system, and a control unit. Four effects on the system performance were examined: (1) hydrogen mass in the system, (2) fluid mass in the reservoir, (3) switch-cycle timing, (4) flow rate of the fluid. Under the optimal parameters, the output of the system was 1.65kW and the coefficient of performance (COP) was 3.7