ReadiFreeze is an early-stage engineering project. A compact backpack unit uses CO₂ to chill a fluid loop, and a sleeve worn on the body carries that cold to the skin.
Concept drawing of the V2 system. Front panel cut away.Not to scale
Architecture
Backpack unit + body-worn sleeve
Cooling source
20 oz CO₂ tank
Working fluid
30% isopropyl, 70% distilled water
Current phase
V2 armband prototype, in build
01System
The cooling loop
CO₂ never touches the body. It cools a fluid inside the backpack, and only that fluid travels to the sleeve. The diagram below is the V2 architecture as designed. It is being built and tested now.
01
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Portable supply
A 20 oz CO₂ tank in the backpack is the only source of cooling.
20 oz CO₂ tankRegulatorHigh-pressure hose
02
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Flow control
A solenoid valve meters CO₂ into the chamber. The controller decides when it opens.
Solenoid valveArduino Uno R3CO₂ gas sensor
03
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Heat exchange
Expanding CO₂ pulls heat out of the working fluid, then vents out of the pack.
Cooling chamberJT-DC3W pumpVent, always open
04
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Wearable interface
Chilled fluid runs through channels against the skin and returns warm.
The pump sends chilled fluid out through the umbilical. It returns warm and is cooled again in the chamber.
Control loop
The skin probe reports temperature to the controller, which opens and closes the solenoid to hold the target.
CO₂ path
Gas expands in the chamber and leaves through a vent that is never closed, so pressure cannot build up.
02Design
What's in the backpack
Everything with weight or pressure sits in the backpack. The sleeve is just silicone channels and one temperature probe, so it stays light enough to wear on an arm.
Fig. 1Backpack unit, front section.
CO₂ tank20 oz
Regulator and solenoid valveCO₂ flow
Cooling chamberHeat exchange
PumpJT-DC3W
Controller and displayUno R3, SSD1306
VentAlways open
Umbilical port¼ in ID
Fig. 2Armband sleeve, flat pattern.
Form factor
Split into two units
An earlier design put CO₂ and phase-change material directly on the body. V2 moves the bulk into a backpack so the wearable part stays light.
Connection
Insulated umbilical
A 1 to 1.5 m silicone line with a ¼ in inner diameter, insulated so the fluid arrives cold.
Working fluid
Isopropyl and water
A 30/70 mix of isopropyl alcohol and distilled water. The alcohol lowers the freezing point so the loop keeps flowing when the chamber gets very cold.
03How it works
Step 1
The backpack
The unit carries its own cooling. There is no ice to freeze, no wall power and no hospital equipment involved.
Step 2
Inside the backpack
CO₂ flows from the tank through a valve into the cooling chamber. As it expands it takes heat from the fluid, and the controller decides how much to let through.
Step 3
The sleeve
The pump pushes chilled fluid down the umbilical and through the sleeve. A probe under the sleeve reads skin temperature and closes the loop.
04Engineering
Design decisions so far
What I had to figure out, what I chose, and what still needs testing.
Decision 01
System architecture
Question
How do you cool the body without putting the tank and electronics on the body?
Decision
A split system. The backpack handles CO₂, heat exchange and control. Only chilled fluid reaches the sleeve.
Next
Run every subsystem together on the V2 armband.
Fig. 3V2 system schematic. Not to scale.
Decision 02
Control and safety cutoffs
Question
What should the system do when something goes wrong?
Decision
Latching faults. Three conditions stop cooling, and the system stays off until a person resets it. An Arduino Uno runs the valve logic because it responds in real time, and the buzzer is treated as required, not optional.
Next
Trip each fault on purpose and confirm the cutoff.
RunningDual-loop cascade control holds the skin target.
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Any fault
Skin too cold
Probe disconnected
CO₂ building up
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Latched offSolenoid closes, buzzer sounds, event logged to SD.
Restart requires a manual reset.
Decision 03
Pressure handling
Question
Where does pressure live, and what is each line rated for?
Decision
Two pressure zones. A rated high-pressure hose runs from the tank to the regulator. Silicone tubing is used only after the regulator. The chamber vent stays open, with an opening at least ten times the inlet orifice area.
Next
Pressure-related tests happen with a mentor present.
High pressure
Tank to regulator. CGA-320 rated hose.
Low pressure
Regulator, solenoid and chamber. Silicone tubing, open vent.
Tank → regulator → solenoid → chamber → vent to air
Decision 04
Evaluation
Question
How well does it actually cool?
Status
Not measured yet. The site will not list cooling performance until it has been tested. The plan is to characterize the system on a thermal phantom before any test on a person.
Cooling power delivered at the sleevePlanned
CO₂ used per unit of coolingPlanned
Each fault cutoff, triggered on purposePlanned
Build log
Research, testing and mentor check-ins, newest first. This log is the main record of the project for the Van Eney '09 Fellows Program.
05Status
Where the project stands
ReadiFreeze is a prototype in development. It is not a medical device, and it has not been validated for clinical or field use.
Done
V2 3D modelsBackpack and armband
V2 parts ordered and received
Physical build started
In progress
Phase 1: V2 armband buildAssembling and wiring both units
Subsystem validationValve, pump, sensors and fault cutoffs
Planned
Thermal phantom testingCooling power and CO₂ efficiency
Phase 2: vestScale the loop to the torso
Phase 3: helmetBring cooling to the head
Status as of fall 2026.
Possible uses
These are areas the project is exploring. None of them is a validated use.
Traumatic brain injury and neurological emergenciesFirst response, before the hospital
School nurses, medics and first respondersOn-the-spot cooling
AthletesHeat and recovery
Military working dogsHeat stress
06Team
Jeremy Jones
Designer and builder
I'm a senior at Severn School, and I developed ReadiFreeze through the school's Van Eney '09 Fellows Program. I wanted cooling that you can carry and start right away, in the first minutes after an injury.
