Experimental and analytical study of a boiling collector in thermal siphon operation
The purpose of this study is to analytically and experimentally evaluate the performance of a boiling solar collector in thermal siphon operation so that, in future work, solar collectors can be optimized for boiling operation. A new procedure, based on boiling heat transfer fundamentals, is developed to estimate the rate of energy gain in the collector. The temperature of the absorber plate is determined from the simultaneous solution of the rate of energy absorbed by the collector and the rate of energy used in boiling as a function of vapor bubble density, the energy required for bubble formation, and the volumetric flow rate through the collector. Since the volumetric flow rate could not be predicted theoretically, experimentally estimated values are used in the numerical calculation. This model is an improvement over previous models which assume that the total mass flow rate that flows through the collector boils, when in reality just a small percent of this mass flow boils and most of it is recirculated. To validate the analytical model, the thermal efficiency and the absorber plate temperature of two collector-condenser systems are experimentally determined. Measurements with both a conventional sheet with tube and a waffled flat plate collector indicate the importance of collector geometry. The two-phase thermal siphon system operates at practically the same thermal efficiency as the hydronic single-phase system, but it uses one less pump, the net rate of useful energy transfer in the two-phase system is higher than in the single-phase system. When boiling collectors are designed for two-phase operation, they may out-perform hydronic collectors.
- Research Organization:
- Colorado State Univ., Fort Collins, CO (United States)
- OSTI ID:
- 5901824
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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