Thermohydraulic analysis of single phase heat transfer fluids in CSP solar receivers

Theoretical modelling techniques are used to compare the thermohydraulic performance and thermal storage characteristics of molten salt, liquid sodium, and lead-bismuth in a CSP solar receiver concept. For molten salt, the performance of a number of heat transfer augmentation techniques are also studied. Sodium and lead-bismuth both yield excellent receiver thermal efficiency (max ∼92%), when compared to molten salt (max ∼90%), due to high thermal conductivity values that lead to large heat transfer coefficients. A high pressure drop penalty for lead-bismuth largely offsets its thermal performance gain over molten salt, however sodium retains its advantage as a receiver working fluid with a low pumping parasitic. The implementation of heat transfer enhancement techniques can significantly improve the performance of a molten salt receiver when compared to smooth tube designs. The low specific heat capacity and high unit cost of lead-bismuth is prohibitive towards its use as a storage medium in storage-integrated plant designs, resulting in very high LCOE values. Sodium is the most economically feasible fluid for systems with low storage (<3 h), however the low per-unit cost and high specific heat capacity of molten salt means that this is the most effective working fluid in systems with larger storage requirements.