Heat Energy Storage for Solar Heat Engine

Heat Storage (HS)

In this implementation, the heat storage medium will be Lithium.

If something like n-pentane is used in HTB3 to collect the heat and pass it on through Cmp-P4, the temperature of HS can reach close to 200°C.

In order to accommodate such high temperatures and have maximum storage capacity, Lithium in a neutral liquid such as oil is selected as the storage medium for this storage and output stage.

Reason - Technical data of Lithium:
Specific Heat = 3.6kj/kg
Weight = Density   = 535kg/m3
Thermal Conductivity = 85 W/(m·K)
Melting Point = 180°C.
Boiling Point = 1342°C

Compared to:
Specific Heat water = 4.2kj/kg
Weight Water = 1000kg/m3

The temperature distance between the melting point and the boiling point of Lithium means that no problems are to be expected in the temperature range that is relevant for the SHE. Only it's expansion factor needs to be taken into account when it is sealed together with oil in cans.

In motor vehicle applications, space and weight are important.

With it's high specific heat and light weight, 0.535 that of water, it became the heat storage selection for HS.

This is the Heat Collection Formula that is used for the comparison:
Q=mCp?T
Where Q (W) is the heat that the fluid loses/gains, m (kgs) is the mass flow rate of the fluid, Cp (Jkg.K) is the specific heat of the fluid, and ?T (K) is the temperature difference between the outlet and the inlet.

For Comparison of Storage mediums:
KJ = KW Calculation - Temperature of the Equivalent weight in Kg of 1m3 raised 1 degree Kelvin or Celsius:
Water = 1000 * 4.2e3 * 1
Iron = 7870 * 0.45e3 * 1
Aluminum = 2700 * 0.91e3 *1
Lithium = 535 * 3.6e3 * 1

KJ = KW Calculation - Temperature of the Equivalent weight in Kg of 1m3 raised by 40 degree Kelvin or Celsius::
WaterK40 = 1000 * 4.2e3 * 40
IronK40 = 7870 * 0.45e3 * 40
AluminiumK40 = 2700 * 0.91e3 * 40
LithiumK40 = 535 * 3.6e3 * 40

The calculations show that Lithium is a good selection for HS.
Lithium can be stored in transformer oil.
That means that it can be sealed in suitable sized cans together with a little oil that keeps it isolated from substances with which it might react.
Those round cans are then placed in the small square areas and all the free space filled with oil.
That gives maximum heat conducting area and metal suppliers quite often supply such square constructions which can be used in the heat transfer blocks.
Note that the Lithium can melt while it is collecting heat, but it's boiling point is far enough away from the maximum expected temperatures.
Perlite and Perlite Vacuum are good heat insulators that works well up to 400°C and are recommended as insulating material for all SHE components that should not loose heat that has been collected.

Propellant:
The propellant that is sent through the turbine blades, should reach about 15 bar when the last heat collector is at around 3 to 10 bar.
By using a mixture whose boiling point is below that of the last heat collector in HCR-3 the function will work well.

When the Burner places heat into the system so that the correct turbine speed is achieved, most of it is extracted by the Water/Glycerol mixture, whose temperature will not exceed 120°C, depending on the system configuration, so that cooling capability remains at all times.

Select a propellant liquid for yourself. Water is the one that most people would want to select, but any mixture that will produce enough vapor pressure Kg/cm2 together with the right size inlets and outlets at the given temperature somewhere between 120°C and 180°C will do the job.
In any case you do not want it to turn into a liquid inside the turbine chamber, without producing any rotation.

Lower temperatures also mean that electronic valves are easier to make.

Do not build the turbine yourself, buy or have one made to order. Just like you would with the electric current generator and motor.

But we are talking Africa, therefore the industrial infrastructure needs are clear.

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Heat Storage (HS)

An heat storage component - As used to store heat in a solar heat engine