Resistive liquid heater
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Solution Overview
Problem
Existing liquid heaters using resistive heating face challenges in achieving high power density and thermal control, particularly when heating liquids with varying conductivities, as they often require larger electrodes to avoid electrolysis and lack precise control over heating rates.
Innovation Solution
A liquid heater design featuring bi-directional switches that energize electrodes with alternating voltage at frequencies above 150 kHz, allowing for smaller electrodes and multiple electrode configurations with varying total electrical resistance, enabling high power density and precise thermal control through a control unit that adjusts configurations based on temperature and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrodes are energized with low-frequency AC voltage (50-60 Hz) to avoid electrolysis, then electrode size must be increased, but this reduces power density
Solution Approach 1:
The patent changes the frequency parameter of the applied voltage from conventional 50-60 Hz to high frequency (150 kHz or more). This parameter change allows the use of smaller electrodes while avoiding electrolysis, thereby achieving high power density without sacrificing reliability.
2Device complexity
If single electrode configuration is used to simplify device structure, then control precision over heating rates is reduced, but this worsens thermal fidelity
Solution Approach 1:
The patent divides the heating system into multiple electrode configurations (at least six different configurations), each with different total electrical resistance. This segmentation allows precise control over heating rates by selecting appropriate configurations, thereby achieving high thermal fidelity without excessive device complexity.
3Device complexity
If bi-directional switches are used to enable AC/AC conversion without rectification, then device complexity increases, but this improves energy efficiency
Solution Approach 1:
The patent extracts and eliminates unnecessary power conversion stages (rectification, AC-to-DC conversion, active power factor correction, energy storage) from the conventional heating system. By using bi-directional switches to directly convert AC to AC at high frequency, the system reduces energy loss while maintaining manageable device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves higher power density and finer thermal control by using smaller electrodes without electrolysis and allows for efficient heating of liquids with varying conductivities, providing a wide dynamic range of heating rates and precise temperature management.
Implementation Method 1
A liquid heater may employ resistive heating, also referred to as Joule or Ohmic heating, to provide instantaneous or on-demand heating of a liquid. As the liquid passes through the heater, electrodes apply an electric current to the liquid, causing the liquid to heat.
Implementation Method 2
By energising the electrodes with an alternating voltage, electrolysis of the electrodes may be avoided. The electrodes are energised with an alternating voltage having a frequency of at least 150 kHz.
Data Source
AI summary
A liquid heater is described including a chamber for receiving a liquid, a pair of electrodes located within the chamber for applying electric current to the liquid, input terminals for connection to a power supply, a plurality of bi-directional switches for connecting the electrodes to the input terminals, and a control unit for controlling the switches. The power supply supplies an alternating voltage having a frequency no greater than 60 Hz, and the control unit controls the switches such that the electrodes are energised with an alternating voltage having a frequency no less than 150 kHz.