Heat storage types

We have not worked with thermo-chemical storage options, only latent heat and sensible heat options.

Requirements:

We are preferably looking for solutions where we can store heat at a high temperature and at any time recover the heat to the cooker at the same high temperature.

Latent heat with Phase Change Material (PCM)

If we operate the heat storage within the phase change region, the storage is at a near constant temperature. It is then only the phase fractions which will change as we charge or discharge the storage. We have tested the use of "solar salt" (Sodium and Potassium Nitrate mixture) as the melting point is suitable for frying cases (about 220 degrees C). Latent heat systems may be less appropriate for cooking applications, as the heat transfer rate can be difficult to regulate.

A weakness with a homogeneous sensible heat storage is that the temperature increases and decreases with the heat transfer in and out of the storage. The requirement of heat out to be at the same temperature as heat in can then be approximated by oversizing the heat storage, such that the temperature changes due to heat extraction for cooking are small. The oversized heat storage must then be kept at high temperatures, as recharging from cold will be time consuming.

Sensible heat with separation of hot and cold parts
With oil as a heat storage medium, the hot and the cold part of the heat storage can be separated.
This can either be a physical separation (physical barrier or separate tanks) or natural separation with thermoclines,
from the fact that hot oil has less density than cold oil.

Natural thermal stratification	Forced stratification with barrier	Separate containers

Temperature control
When charging a heat storage with a heat transfer fluid, a temperature control is needed, in order to achieve a set temperature in the heat storage.
We have tested several options and concluded on solutions which do not depend on sensors, controllers and power.