4. ^^I_ SAN-857-1 EVALUATION OF PRACTICABILITY OF A RADIOISOTOPE THERMAL CONVERTER FOR AN ARTIFICIAL HEART DEVICE Phase 1 Final Report April 1972 TRWSystems Group Redondo Beach, California DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED* UNITED STATES ATOMIC ENERGY COMMISSION • TECHNICAL INFORMATION CENTER DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. 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NOTICE This report was prepared as an account of work sponsored by the United States Government Neither the United States nor the United States Atomic Energy Commission, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights rhis report has been reproduced directly from the best available copy. Available from the National Technical Information Service, U. S Department of Commerce, Springfield, Virginia 22151 Price Paper Copy $7 60 Microfiche $0.95 Pt nud n >h» Un lad Stoi«t o' Am^r USAEC lachn eol Inioi'Mit on Cini* SAN-857-1 Distribution Category UC-84 EVALUATION OF PRACTICABILITY OF A RADIOISOTOPE THERMAL CONVERTER FOR AN ARTIFICIAL HEART DEVICE PHASE 1 FINAL REPORT IAN R. JONES, MALCOLM G. RIDGWAY, AND D.R. SNOKE TRW SYSTEMS GHOUP ONE SPACE PARK • B E O O fM O O BEACH • CALIFORNIA DATE PUBLISHED - APRIL 1972 PREPARED FOR THE U.S. ATOMIC ENERGY COMMISSION DIVISION OF APPLIED TECHNOLOGY UNDER CONTRACT AT{04-3)-857 NOTICE This report contains information of a preliminary nature and was prepared primarily for internal use at the originating installation. It is subject to re­ vision or correction and therefore does not repre­ sent a final report. It is passed to the recipient in confidence and should not be abstracted or further disclosed without the approval of the originating installation or USAEC Technical Information Center, Oak Ridge, TN 37830 DlSTRiBL'TION 0^ THIS DOCUMENT IS UNLUv/llTED I hi CONTENTS Page INTRODUCTION AND SUMMARY 1-1 1. 1 Description of Preferred System Concept 1-4 1.1.1 Hybrid Heat Engine 1-4 1.1.2 Motor/Reciprocator Unit 1-6 1. 1.3 Automatic Actuator 1-7 1. 2 Growth Capability 1-10 1.3 Sensitivity Analysis 1-12 1.4 Conclusions 1-13 SYSTEM DESIGN CONSIDERATIONS 2-1 2. 1 Groundrules 2-1 2. 2 System Terminology 2-3 2. 3 Alternate Conceptual Approaches 2-3 2. 3. 1 System Load Characteristics 2-5 2. 4 Waste Heat Management 2-12 2.4. 1 Heat Generation Rates 2-12 2. 4. 2 Related Experimental Studies 2-14 2.4.3 Peak Heat Rejection Rates 2-17 2. 5 Packaging Considerations 2-17 2, 5. 1 Packaging Configuration 2-18 2. 5. 2 Packaging Materials 2-18 2.6 Gas Management 2-19 2. 7 Thermal Insulation 2-20 2. 7. 1 Fibrous Insulation 2-20 2. 7. 2 Foil Insulation 2-22 2. 7. 3 Thermal Insulation Selection 2-24 2.7.4 Overtemperature Protection 2-24 2. 8 Energy Storage 2-25 2. 8. 1 Thermal Energy Storage Material (TESM) 2-25 2.8. 2 Electrochemical Energy Storage 2-28 2.9 Radioisotope Capsule Design 2-32 COMPONENT SUBSYSTEMS 3-1 3. I Power Conditioning and Control 3-1 3. 1. 1 Blood Pump Interface 3-1 3. 1. 2 Blood Pump Filling Requirements 3-3 3.1.3 Actuation of the Blood Pump 3-4 3. 1. 4 Power Conditioning 3-13 3.1.5 Performance Summary 3-23 ii 7- CONTENTS (Continued) Page 3. 2 Engine Subsystems 3-27 3. 2. 1 Gas Reciprocating Engines 3-29 3. 2. 2 Linear Vapor 3-70 3. 2. 3 Rotary Vapor 3-91 3.2.4 Thermoelectrics 3-148 3. 2. 5 Hybrid 3-166 RELIABILITY OF THE CANDIDATE COMPONENTS 4-1 4. 1 Premature Failure Reliability Modeling 4-2 4. 1. 1 Vapor/Gas Bearings 4-5 4. 1. 2 Expansion Turbine 4-6 4. 1. 3 Bellow Seals and Pumps 4-7 4. 1.4 Precision Ball/Hydrodynamic Sleeve Bearings 4-8 4. 1. 5 Electronic Components and Solid State Devices 4-10 4. 1. 6 Gear Boxes/Speed Reducers 4-10 4. 1. 7 High Energy Density Batteries 4-11 4.1.8 PCCS Circular Drive Cam 4-12 4. 2 Summary of the Premature Failure Reliability Estimates for the Candidate Systems 4-13 4,2. 1 System Reliability Math Model Results 4-13 4. 2. 2 Hybrid Thermal Converter 4-13 4. 2. 3 Hybrid Thermal Converter with Battery 4-18 4.2.4 Thermoelectric/Battery Thermal Converter 4-18 4. 2. 5 Rotary Vapor Engine 4-20 4. 2. 6 Electrical PCU 4-20 4. 2. 7 Mechanical Actuator for Electrical Systems 4-20 4. 2. 8 Gas Reciprocating Engine 4-22 4. 2. 9 TESM 4-22 4.2. 10 Gas Reciprocating Engine PCU 4-22 4.2. 11 Gas Reciprocating Engine Actuators 4-22 4. 2. 12 Linear Vapor Engine and PCU 4-26 4. 2. 13 Linear Vapor Engine Actuator 4-26 4. 3 Reliability Against Wearout 4-26 4. 4 Confidence in the Reliability Estimates 4-29 CANDIDATE SYSTEM DESCRIPTION 5-1 iii CONTENTS (Continued) Pag EVALUATION CRITERIA AND SCORING METHODOLOGY 6-1 CANDIDATE SCORING 7-1 SENSITIVITY ANALYSIS 8-1 8, 1 Introduction 8-1 8. 2 Distribution of Criteria by Category 8-2 8, 3 Effects of Criteria Scoring Revisions 8-4 8. 4 Alternate Scoring Techniques 8-7 8. 5 Conclusions 8-9 REFERENCES 9-1 APPENDIX A-I Acknowledgments Of the many TRW personnel who contributed to the Phase I Project, the following deserve separate mention: J. P. Aha, R. D. Baggenstoss, J. E. Boretz, D. J. Dunivin, K. E. Green, A. R. Halpern, L. M. Osborne, S. R. Rocklin, G. D. Shaw, and B. A. Snoke. In addition, two of our consultants merit special mention: Dr. Y. Nose of the Cleveland Clinic Foundation, and Dr. T. Finkelstein of Trans Computer Associates. ^ r Abstract The objective of the program was to determine the practicability of developing a radioisotope thermal converter for an artificial heart device. The thermal converter, including the radioisotope heat source, and all associated power conditioning and control systems are to be fully implantable and capable of functioning for ten years with high reliability. The device must supply the necessary mechanical, hydraulic, or pneumatic power for a blood pump which provides 100% of the left ventricular pumping function. The principal design groundrules included a daily average power level of 2.8 watts delivered to the blood pump and the following design maxima: 60-watt heat source, 1. 5-liter volume, 3.0-kilogram weight, and peak power level of 4. 44 watts. The concepts evaluated included various mechanizations of gas reciprocating, vapor reciprocating, vapor rotary, and thermoelectric cycles, as well as various combinations of these devices. A total of eight different thermal converter systems were found capable of meeting all the design groundrules. These eight systems were compared using previously-defined evaluation criteria and scoring procedures. The preferred concept is an all-electric-output hybrid engine which consists of a thermo­ electric stage operated thermally in series and electrically in parallel with an organic vapor turbogenerator. The hybrid engine powers a motor/reciprocator unit which in turn mechanically actuates a Kwan- Gett-type blood pump. The weight and volume of the entire thermal converter (exclusive of the blood pump) are 1. 83 kg and 1. 33 liters. The thermal converter requires a 49-watt heat source and has an overall heat-to-mechanical conversion efficiency of a little over nine percent. vi 1. INTRODUCTION AND SUMMARY The overall objective of the program is to determine the practica- bilitv of developing a fully implantable radioisotope thermal converter to power a heart-assist pump that is capable of assuming 100 percent of the left-ventricular pumping function, and has a high probabilitv of operating acceptably for 10 years. The objective of this first phase of the study was to evaluate all the possible concepts and recommend a preferred system for more detailed evaluation in Phase II. The Phase I practicability evaluation of a radioisotope thermal con­ verter was carried out under the design groundrules listed in Table 1-1, In addition to these physical and performance specifications, we imposed the requirement that all candidate systems utilize fibrous thermal insulation Table 1-1. l^rinu' I')csign Groundrules Power supply to support blood pump in 1 00"'(i-assist left ventricular functional replacement mode (i.e., to take over 100";) of left ventricular work not simply capture 100'^', of cardiac output) Nominal average output power 2.81 watts (to 60% efficient Kwan-Gett- type of blood pump) Maximum heat source 60 watts (thermal) Output power range 2.