Convection currents in a water calorimeter

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Fluid Dynamics

Background:

• Accurate temperature measurement is crucial for radiation dosimetry.
• Water calorimeters are standard devices for absorbed dose determination.
• Understanding heat transfer phenomena in water calorimeters is essential for precise measurements.

Purpose of the Study:

• To construct and evaluate a flexible, temperature-regulated water calorimeter.
• To investigate the influence of irradiation geometry and temperature on heat transfer.
• To identify and characterize convection currents in water during irradiation.

Main Methods:

• A novel flexible water calorimeter with dual thermistor pairs was designed and built.
• The calorimeter was irradiated with a 19 MeV electron beam at various temperatures (3-40°C) and beam orientations (vertical and horizontal).
• Temperature responses were recorded, and experiments were conducted at 30°C and 4°C to assess convection effects.

Main Results:

• Vertical beam irradiation at 30°C showed thermistor responses consistent with the depth-dose curve.
• Horizontal irradiation at 30°C induced convection currents, altering temperature patterns over time.
• Operating the calorimeter at 4°C suppressed convection, yielding temperature patterns similar to vertical irradiation, confirming convection at 30°C.

Conclusions:

• The developed water calorimeter effectively measures temperature changes under irradiation.
• Convection currents form in water at 30°C with small temperature gradients (10⁻³ °C cm⁻¹) during horizontal irradiation.
• These findings highlight the importance of accounting for convection in water calorimetry for accurate radiation dosimetry.