Liquid droplet radiator
An advanced or future space mission must have a power source or propulsion that will require the rejection of waste heat.
Disposing large quantities of waste heat must be considered in order to realize a large-space structure (LSS) that handle high power such as a nuclear reactor or a space solar power satellite (SPS).
Liquid metal heat pipes with conventional radiators are considered ideally suited for such applications.
[5] However, the required radiator surface area is huge, hence, the system mass is very large.
The liquid droplet radiator (LDR) has an advantage in terms of the rejected heat power-weight ratio.
The results of the studies indicate that for rejection temperatures below approximately 700 K, the LDR system is significantly lighter in weight than the other advanced radiator concepts.
A LDR can be seven times lighter than conventional heat pipe radiators of similar size.
[6] The LDR is more resistant to meteorite impacts due to less critical surface or windage, and requires less storage volume.
Therefore, the LDR has attracted attention as an advanced radiator for high-power space systems.
While undergoing a reduction in pressure the saturated liquid is sprayed into space as coherent streams of tiny, discrete droplets.
[8] Spacecraft waste heat is ultimately rejected to space by radiator surfaces.
is the average gray body view factor for droplet at stream center (less than one), and
Most of the presented solutions of the equation of radiative transfer are practical simplifications by introducing assumptions.
In order to achieve high collection efficiency splashing of the droplet on the collector surface has to be minimized.
[8] As the droplet sheet is in free fall a spacecraft performing a maneuver or angular acceleration would lose coolant.
Even a magnetically focused LDR has a very limited tolerance of less than 10−3 g. A droplet generator has approximately 105 – 106 holes (orifices) per system with diameters of 50–20 μm.
[13] Liquids have been found that in the range of 300 to 900 K have a vapor pressure so low that the evaporation loss during the normal lifetime of a space system (possibly as long as 30 years) will be only a small fraction of the total mass of the radiator.
The device induces eddy currents in the metal that generate a Lorentz force with their associated magnetic fields.
The effect is the pumping of the liquid metal resulting in a simplified design with no moving parts.
[16] For example, a simple mixture of mineral oil and iron filings was found to approximate a suitable ferrofluid for several seconds, before separation of the iron filings and oil was observed in the presence of a magnetic field.
It may be possible to mine the moon for carbon and combine it with other elements to produce ionic fluid.
[15] A Liquid Sheet Radiator (LRS), adapted for planetary surfaces, is essentially a fountain enclosed in a transparent envelope.
The liquid sheet radiator concept is exceptionally stable and does not require special machining of the orifice to achieve its performance.
