Initial Research
Note: It is expected that through the conclusion of ME 470, the team’s understanding of heat exchangers will be greatly expanded. Current research and idea development was done using Bergman and Levine’s Fundamentals of Heat and Mass Transfer, Eight Edition. [1]
Simple forms of heat exchangers
- Hot and cold fluids moving in parallel flow in either opposite or the same directions. Another type of HEs have fluids moving in cross flows.
- Mixed flow (11.2b) allows fluid motion in a direction transverse to the main flow direction and unmixed (11.2a) inhibits this motion.
- What is the relationship between density of two fluids? If densities are very different, you might have different volumes to account for that.
- Heat Exchangers are “Typically Classified according to flow arrangement and type of construction.”[1]
Potential Modifications
Shell and Tube Heat Exchangers-
These are most common in the process industry and are easily modifiable.
Modify with:
- Finns on the tubes to create a higher pressure drop.
- Tube Inserts are most often used with liquids to promote boiling.
- Tube deformations can also promote boiling and increase turbulence.
In CAES systems [2]
- Direct Contact Heat Exchangers
- “heat transfer occurs through a wall that separates the fluidstream”
- Indirect Heat Exchangers
- “ the heat transfer occurs via direct contact between two fluid streams or between a fluid and a solid in a packed bed regenerator.”
- A packed bed regenerator is a porous solid with very high rates of heat transfer.
- “Packed bed regenerators will allow for higher system temperatures than conventional heat exchangers as there is no requirement for a thermal fluid which must remain liquid and stable throughout the range of temperatures encountered”
This article concluded that using a direct contact method with packed beds would provide a round trip efficiency of at least 70% because “stratification of heat stored at different temperatures can be effectively preserved”. They also mentioned that in terms of efficiencies, maintaining a high compressor and expander efficiency is important for the CAES system to be comparable to existing energy storage technologies.