A Geothermal Measurement of the Shizukuishi No. 2 Tunnel (a Hot Tunnel) and Consideration on Heat Budget of Fluid Passing through the Tunnel

Abstract

The Shizukuishi No. 2 tunnel is a hot tunnel penetrating through a shallow hot dry rock. In the tunnel, after completion, construction of a pipeline is scheduled to transport geothermal water produced from wells in the Kakkonda Geothermal Power Plant to the heat-exchanger-site for a demonstration project on direct use of geothermal energy. On 20 and 21 April 1983, just after the hot tunnel of a total length of 940 m has been dug through, temperatures and heat flow on the wall surface of the tunnel, some thermal properties of the rock samples, the temperature profiles in slender, short pitholes drilled in the rock matrix, the dry- and wet-bulb air temperatures and wind speed in the tunnel and the mass and temperature of the discharged water from the tunnel were measured in all-round. Based upon the results summarized in several figures and tables, heat budget is computed on the fluid passing through the tunnel. The heat losses by air and water are 38.6 and 45.5 kcal sec^-1, respectively. The total heat loss of 84.1 kcal sec^-1 is compared with heat-exchange between fluid and rock matrix. Finally, heat transfer coefficient or Newtonian cooling factor determined from the measurement is discussed by means of Taylor-Prandtl analogy on turbulent-forced convection.