Evaluation and design of downhole heat exchangers for direct application
Over 400 wells with downhole heat exchangers are in use in Klamath Falls, Oregon. Some have been in use for nearly 30 years. Despite the large number and the long experience, the exact nature of the mechanism of heat exchange and, therefore, the maximum output was not known, except that it had been theorized that convection cells were established in the well. Oregon Institute of Technology and Oregon State University are jointly involved in a project to study the heat exchange process and economics of the downhole heat exchanger system. The existence of significant convection cell circulation has been established and measured using a spinner, hot film anemometer, and by energy balance calculations. Based on these measurements, analytical models have been developed which predict heat extraction rates within 15% of actual measured values. The existence of significant mixing of new and circulating well fluid has been established and can be calculated, although at this time not accurately predicted before testing a well. Based on the analytical models, multi-tube heat exchangers have been designed and very recently tested with outputs within 15% of predicted values. Economic analysis shows that for small to moderate extraction rates, about 300 kW thermal, and shallow wells, DHEs may be more economical than pumped systems when surface discharge is not acceptable.
- Research Organization:
- Oregon Inst. of Tech., Klamath Falls (USA); Oregon State Univ., Corvallis, OR (United States)
- DOE Contract Number:
- EY-76-S-06-2429
- OSTI ID:
- 6496727
- Report Number(s):
- RLO-2429-5
- Country of Publication:
- United States
- Language:
- English
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GEOTHERMAL WELLS
HEAT EXCHANGERS
DESIGN
OPERATION
ANEMOMETERS
ECONOMIC ANALYSIS
HEAT EXTRACTION
HEAT TRANSFER
JOINTS
OREGON
ECONOMICS
ENERGY TRANSFER
MEASURING INSTRUMENTS
NORTH AMERICA
PACIFIC NORTHWEST REGION
USA
WELLS
Geothermal Legacy
151000* - Geothermal Energy- Direct Energy Utilization