Three teenagers from Indore have developed an innovative refrigerator that uses salt and water to keep vaccines and other temperature-sensitive medical supplies cold without electricity, batteries or ice. Named Thermavault, the portable cooling device aims to address vaccine storage and transportation challenges in rural areas where reliable electricity is limited.
The invention was developed by Dhruv Chaudhary, Mithran Ladhania and Mridul Jain, who were aged 16 and 17 when they worked on the project. Inspired by the difficulties their parents, all medical professionals, faced in maintaining vaccine temperatures during the COVID-19 pandemic, the teenagers set out to develop an alternative cooling system.
Their innovation won the Asia category of the 2025 Earth Prize, an international environmental competition for teenagers, earning them $12,500 in prize money.
How Does the Salt-Powered Fridge Work?
Thermavault uses a chemical reaction to generate cooling. Certain salts absorb energy from their surroundings when dissolved in water, lowering the temperature of the solution. The device uses this principle to maintain a cool environment without conventional refrigeration.
The refrigerator features an insulated plastic outer shell and an inner copper lining. A cooling solution made from selected salts dissolved in water is placed between the two layers.
The team initially researched around 150 salts and narrowed the options to approximately 20 for testing. After conducting experiments using laboratory facilities at the Indian Institutes of Technology (IIT), they identified ammonium chloride and barium hydroxide octahydrate as suitable compounds.
Ammonium chloride alone can maintain temperatures between 2 and 6 degrees Celsius, a range suitable for storing many vaccines. Adding barium hydroxide octahydrate can bring the mixture to subzero temperatures, potentially supporting other medical applications.
Reusable Cooling Without a Freezer
One of Thermavault’s key features is its reusable cooling system. Unlike conventional vaccine carriers that depend on ice packs, the device does not require a freezer to prepare its cooling material.
Once the salt solution warms up, users can boil away the water and recover the salt in solid form. The recovered salt can then be dissolved in fresh water to restart the cooling process.
The prototype has undergone testing at hospitals around Indore. Dr Pritesh Vyas, an orthopaedic surgeon who tested the device at V One Hospital, reported that vaccines could be kept inside Thermavault for approximately 10 to 12 hours.
The team believes the technology could help healthcare workers transport vaccines and medicines to remote villages and areas with unreliable power supply. Further improvements, including a built-in temperature monitoring system, are also being considered.
200 Units Planned for Hospital Testing
The teenagers plan to use their $12,500 Earth Prize funding to manufacture 200 Thermavault units and distribute them across 120 hospitals for further testing.
They also aim to pursue Performance, Quality and Safety (PQS) certification from the World Health Organization (WHO). This could help them present the technology to Gavi, the international vaccine alliance.
The team is also exploring patent protection for its invention. While further testing and certification will be necessary before wider adoption, Thermavault offers a potential alternative for maintaining medical cold chains in locations where conventional refrigeration is difficult to access.
