The design of a concentric cylinder calorimeter for measuring the apparent thermal conductivity of MLI blankets is presented. Unlike similar devices where a liquid cryogen is used to control the cold boundary temperature and the cryogen boil-off rate is used to obtain the heat transfer through blanket, the design presented in this paper utilizes mechanical refrigerators to control the boundary temperatures and a heat rate meter to determine the heat load. This approach ensures two unique features of the apparatus. First, the use of cryocoolers enables the user to set the boundary temperatures anywhere within the operating range of the refrigerators and therefore permits a wide range of temperature and temperature differences with the measurement. The other unique feature is that the total heat transfer through the blanket is obtained by measuring the heat conducted along a cold cylinder support rod of known thermal conductivity. To determine the absolute thermal conductivity, a calibration is needed to eliminate the temperature related effects on the support rod.
This research and development project exemplifies a shared public/private commitment to advance the development of energy efficient industrial technologies that will reduce the U.S. dependence upon foreign oil, provide energy savings, and reduce greenhouse gas emissions. This project developed and demonstrated a Direct Evaporator for the Organic Rankine Cycle (ORC) for the conversion of waste heat from gas turbine exhaust to electricity. In conventional ORCs, the heat from the exhaust stream is transferred indirectly to a hydrocarbon-based working fluid by means of an intermediate thermal oil loop. The Direct Evaporator accomplishes preheating, evaporation and superheating of the working fluid by a heat exchanger placed within the exhaust gas stream. Direct Evaporation is simpler and up to 15% less expensive than conventional ORCs, since the secondary oil loop and associated equipment can be eliminated. However, in the past, Direct Evaporation has been avoided due to technical challenges imposed by decomposition and flammability of the working fluid. The purpose of this project was to retire key risks and overcome the technical barriers to implementing an ORC with Direct Evaporation. R&D was conducted through a partnership between Idaho National Laboratory (INL) and General Electric (GE) Global Research Center (GRC). The project consisted of four research tasks: (1) Detailed Design & Modeling of the ORC Direct Evaporator, (2) Design and Construction of Partial Prototype Direct Evaporator Test Facility, (3) Working Fluid Decomposition Chemical Analyses, and (4) Prototype Evaluation. Issues pertinent to the selection of an ORC working fluid, along with thermodynamic and design considerations of the direct evaporator, were identified. The failure modes and effects analysis (FMEA) and hazards and operability analysis (HazOp) safety studies performed to mitigate risks are described, followed by a discussion of the flammability analysis of the direct evaporator. A testbed was constructed and the prototype demonstrated at the GE GRC-Niskayuna facility. v vi
One of the steps in the manufacture of a superconducting MRI magnet involves cool down of the magnet cryostat from room temperature to 4.2 K before it can be filled with liquid helium. The primary source for refrigeration in this process is cryogenic temperature helium gas that is injected into an inlet port in the cryostat and recovered at the outlet port. During normal clinical use, the electromagnetic forces generated by the magnet are extremely high. The design of the cryostat is therefore aimed at supporting the structural and electromagnetic requirements of the magnet at the expense of heat transfer efficiency during cool down. As a result, the cool down process may be inefficient leading to loss and expense of cryogenic helium. The aim of this work is to evaluate this potential inefficiency by experimentally measuring temperature distribution and heat transfer characteristics of a typical GE 1.5 T magnet to refine and validate a CFD model of the cryostat.
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