crossword puzzle

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Across
  1. 5. plate collectors lose more heat to environment
  2. 6. sheet absorber is surrounded with a high vacuum
  3. 8. cover is used in a flat plate collector
  4. 11. is not used as circulating fluid
  5. 12. or glass tubes are used as absorber
  6. 14. is a common problem
  7. 15. is mainly used in flat-plat collectors
Down
  1. 1. is used as circulating fluid in tropical climate
  2. 2. area is approximately equal to absorber area
  3. 3. collector is a system to collect heat
  4. 4. pipe is a heat-transfer device
  5. 7. collector is not a non-concentrating collector
  6. 9. solution is used as coolants
  7. 10. collectors operate similarly to a parabolic dish
  8. 13. and plastic are thermal insulators