The numerical analyses of the electromagnetic field distribution proved that the most promising of the analysed variants for the microwave heating system is the one with a freeze dryer chamber equipped with a mixer - a rotary element used to change the distribution of microwave radiation during the freeze-drying of food products.
Last week in Trondheim the 15 th IIR-Gustav Lorentzen Conference on natural refrigerants took place. It was a pleasure to listen to the presentations on refrigeration, cooling, and heating and participate in inspiring discussions.
Our Ph.D. candidate, Edyta Piechnik, gave a presentation on the development of the natural working fluid-based refrigeration system for domestic scale freeze dryer. This topic is carried out as part of her PhD project under the FrostWave project.
We are pleased to announce that the prototype of the freeze dryer with a new cooling system and chamber geometry has been successfully launched. Nevertheless, the system requires further calibration, so there is still some work ahead of us. We hope to share the results soon!
Good news from the laboratory at NTNU! Work has begun on a prototype freeze dryer whose cooling system will be based on a natural refrigerant - R290. For this purpose, the type of evaporator and compressor have been changed.
This week, our PhD student Edyta Piechnik, together with Norwegian supervisors, prof. Ignat Tolstorebrov and prof. Trygve M. Eikevik, participated in the annual event Norsk Kjøleteknisk Møte 2022, organized in the far north of Norway, Tromsø. These were two intense days full of presentations on, among others, natural refrigerants, refrigeration systems and heat pumps. During the event, Edyta presented a poster devoted to the concepts of development of a refrigeration system based on a natural refrigerant in the prototype of a freeze dryer carried out as part of the FrostWave project.
The next steps towards changing the heating system in our device have been made. The currently used heating system is based on the conduction of heat through a shelf under which a heating mat is placed to the product. In the prototype device, the product drying process will be based on the application of heat by means of microwaves. Below we present the preliminary numerical results of a freeze dryer equipped with three magnetrons emitting microwaves towards the product. The magnetrons were placed on three sides of the chamber, namely the upper and side walls.
Intensive work is carried out to select an appropriate microwave system that will adequately provide heat to food products in the freeze-drying process. It is crucial to ensure even distribution of heat generation to minimize "cold spots" and "hot spots", which will minimise the risk of underheating or overheating food during freeze-drying.
Recently, the activities of the project team have focused on developing the concept of a prototype of a freeze dryer equipped with microwaves and a new cooling system.
The proposed ideas for a new device geometry are based on the following modifications:
- internal evaporator with microwave membrane
- the use of the position of the zigzag-shaped shelves
After selecting a new refrigerant, it is time to redesign the refrigeration system, i.e. select the appropriate components, including the shape and length of the evaporator. The FrostWave team decided to move from an external evaporator (coil) to a microchannel evaporator located inside the chamber. In parallel with these activities, steps relating to a method for applying microwave heating have been taken.
The FrostWave team has just started working on the concept of a new device!
The first changes will concern the cooling system. A major step will be to switch from the current synthetic refrigerant with a relatively high GWP (Global Warming Potential) to a natural working fluid. Thanks to the analysis carried out by the NTNU team, two potential substitutes for the currently used refrigerant were identified, namely R290 (propane) and R1270 (propylene).