WE-NET Home Page/Summary of Annual Reports 1997

5.3 Development of liquid hydrogen storage facilities

5.3.1 R & D goals

Goals of studies in the Phase I are that to make a conceptual design of large-scale liquid hydrogen facilities, and to select technical items to be developed necessary for constructing it.

In developing large-capacity liquid hydrogen storage equipment up to fiscal 1996, we have designed storage tanks by combining different modes of storage tank types and adiabatic structures, and examined and evaluated their feasibility. As a result, we found that we lack basic performance data (thermal insulation performance and mechanical strength data of insulation structures at low temperature) at the liquid hydrogen temperature regarding adiabatic structure applicable to large-capacity storage tanks.

We installed testing equipment and designed test models in order to measure thermal insulation performances and strength of insulation structures with the purpose of collecting basic data and select adiabatic structure suitable for large-capacity storage tank structure.

5.3.2 Results in fiscal year 1997

5.3.2.1 Thermal insulation Performance Test

(1) Manufacture of equipment for thermal insulation performance tests

Based on basic design of the equipment used for thermal insulation performance test conducted in fiscal 1996, we designed most suitable apparatus affecting accuracy of thermal insulation measurement and measuring system taking safety in consideration, and evaluated testing facility.

In the basic design of fiscal 1996, we initially planed to make a test model with outer diameter 900mm x thickness 300mm. However, we changed the outer diameter to 1200mm by taking exclusion of heat input from the edge into consideration, reviewed the testing device and manufactured a large-scale thermal insulation performance test equipment with following specifications:

Measuring method: Flat plate type calorimeter system

Overall size: Diameter about 1.6m x height about 3m

Testing temperature: -253°C at the liquid hydrogen side
0 °C at the heater side

Maximum size of the test model: 1,200mm in diameter x 300mm in thickness

In designing structures of the liquid hydrogen vessel to measure quantity of heat that passes through the test model and the liquid hydrogen vessel to absorb heat input from the edge, we made vessel structure with the bottom plate, a contacting face to the test model, least deformed by heat or pressure.

After installing the equipment, we conducted preparatory performance test using liquid hydrogen, and verified the performance of the testing equipment by measuring the capacity of an electric heater placed at the bottom plate of the heat quantity measurement vessel and measuring the quantity of evaporated liquid nitrogen gas.

It is scheduled to implement thermal insulation performance tests of various adiabatic structures by using this device in a joint effort with the tanker team (ST5-2) from fiscal year of 1998.

(2) Design of thermal insulation performance test model

We designed test models, which match the test equipment described above, for insulation performance test scheduled in FY1998.

Followings are the variation of test models based on adiabatic structure design of every tank type designed up to fiscal 1996:

Test models using powder insulation in vacuum With respect to the test models of vacuum adiabatic structure using powder insulation material (microsphere), we took forming a vacuum into consideration and examined the test model structure which is being evacuated in advance by putting it in an airtight polyethylene bag etc.
Test models using solid insulation in vacuum With respect to the test models of vacuum adiabatic structure using a solid insulation material (polyurethane foam), we designed four types of test model structures: two high density materials with different density applied at the bottom of the storage tank and two low density materials with and without joints used for the side walls and the roof of the tank.
Test models using multilayer insulation and powder insulation in vacuum with supporting structure.
As adiabatic structures applied to membrane type tank, we designed two types of test models with multilayer insulation structure and powder perlite in vacuum, including FRP supporting structure.
Test model using powder insulation at atmospheric pressure We designed a test model with gas filled adiabatic structure using powder insulation material (perlite). As a filling gas, we use helium gas that does not liquefy at the liquid hydrogen temperature.

5.3.2.2 Mechanical Strength Test of thermal insulation materials

In order to measure the compressive strength of thermal insulation materials for all proposed tank types at the liquid hydrogen temperature, we examined specifications of testing device and time required to cool the test model by liquid hydrogen. We made the test schedule for fiscal 1998 based on the examination. As for the testing device, we plan to use low temperature strength test device installed by "Low temperature material development subtask team (ST6)".

As thermal insulation materials for the mechanical strength test, we are planning to test 1) microsphere, 2) polyurethane foam, 3) glass fiber reinforced plastics, 4) light concrete, 5) glass foam. We checked expected technical issues for every test material and made countermeasures to cope with them.

5.3.3 Research plan for fiscal year 1998

One or two test piece(s) of thermal insulation structures out of those designed in this fiscal year will be prepared and measured its thermal conductivity, and checked its insulation performance at 20K.

In regard to mechanical strength test of the insulation materials, preliminary tests of the test pieces at the liquid nitrogen temperature examining fracture modes etc., will be conducted prior to the tests at liquid hydrogen temperature.