A solar thermal central receiver generates heat by using a...

A solar thermal central receiver generates heat by using a field of mirrors to focus sunlight on a bank of tubes through which a coolant flows. Solar energy absorbed by the tubes is transferred to the coolant, which can then deliver useful heat to a load. Consider a receiver fabricated from multiple horizontal tubes in parallel. Each tube is $1-\mathrm{cm}-\mathrm{ID}$ and $1 \mathrm{~m}$ long. The coolant is molten salt that enters the tubes at $370^{\circ} \mathrm{C}$. Under start-up conditions, the salt flow is $10 \mathrm{gm} / \mathrm{s}$ in each tube and the net solar flux absorbed by the tubes is $10^4 \mathrm{~W} / \mathrm{m}^2$. The tube-wall will tolerate temperatures up to $600^{\circ} \mathrm{C}$. Will the tubes survive start-up? What is the salt outlet temperature? Figure Can't Copy

Key Concepts

Energy Balance

It is critical to determine how the absorbed energy increases the temperature of the fluid. In any heat transfer application, the energy added to the fluid can be calculated by balancing the absorbed power with the product of the mass flow rate and the specific heat capacity. This relationship shows how much the fluid temperature rises as it picks up energy.

Absorbed Solar Flux and Surface Area Considerations

The concept involves determining the total heat input based on the solar irradiance and the effective area over which the energy is absorbed. By multiplying the net solar flux by the area of the receiver (which is defined by its geometric dimensions), one obtains the total power transferred to the working fluid.

Fluid Flow in Heat Exchanger Tubes

Proper management of fluid flow in the tubes is essential for efficient heat exchange. The mass flow rate in the tubes influences the temperature rise of the fluid as it absorbs the solar energy. Understanding flow parameters ensures that the system operates at thermal conditions that are safe and effective.

Material Thermal Limits

This involves ensuring that the temperatures reached by the device do not exceed the material’s maximum allowable temperatures. Evaluating the thermal performance includes checking that the heat absorbed does not raise the tube wall temperature above its tolerance, which is crucial for maintaining structural integrity and safety.

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