Simultaneous Determination of Reference Free-Stream Temperature and Convective Heat Transfer Coefficient
This paper deals with the development of a new method that can obtain heat transfer coefficient and reference free stream temperature simultaneously, The method is based on transient heat transfer experiments using two narrow-band TLCs. The method is validated through error analysis in terms of the random uncertainties in the measured temperatures. It is found that the errors could be reduced more than 2 times less. The general method described in this paper is applicable to many heat transfer models with unknown free stream temperature.
Fundamental Investigations of Supercritical Water Flows for Hydrothermal Spallation Drilling
Our society has a growing demand for electricity and heat that has to be satisfied by different sources of energy. The geothermal energy stored in the deep underground can be part of this energy mix. For operation, a geothermal power plant needs at least two wells of several kilometers depth (2–10 km) in order to reach the required temperatures clearly above 100 ◦C for electricity generation. At the bottom of the wells, a system of fractures is generated to connect both wells with each other. These fractures act as a heat exchanger to transfer heat from the hot rock to the circulating working fluid. Deep geothermal wells have to be drilled with conventional rotary drilling methods in abrasive and hard rock environments. Wear of the drilling head under these conditions and therefore the required replacement results in expensive trip times during drilling. The costs associated with drilling represent the major part of the costs (up to 70%) for the construction of a geothermal power plant. In order to make deep geothermal energy competitive with respect to other sources of energy, the drilling costs need to be significantly reduced. “Thermal spallation drilling” is known as a promising technology for drilling shallow wells in hard rock formations. This drilling approach is based on the characteristics of certain rock types to disintegrate continuously into small flakes when exposed to the high thermal loads of an impinging flame jet. Enhanced drilling velocities and less wear of the drilling head are expected as major advantages that finally could help to reduce the drilling costs. Nevertheless, for drilling wells of several kilometers depth, a water-based drilling fluid is essentially required for fulfilling several important tasks in the drilling process, e.g. removal of rock cuttings. In water filled boreholes at certain depth, the pressure exceeds the critical pressure of water (220.64 bar) and therefore, supercritical water jets are of particular interest to provide the required heat for thermal rock fragmentation. This spallation
Laminar heat or mass transfer in rectangular channels and in cylindrical tubes for fully developed flow: comparison of solutions obtained for various boundary conditions
Abstract A comparison is made of results obtained with various boundary conditions at the wall of the channels. By comparing blood Sherwood numbers for finite wall resistance with those for constant concentration boundary condition only a small variation is found for various points along the blood channel.