Continuous-Flow Heater Dry-Fire Detection via Timed Re-Energizing
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Solution Overview
Problem
Existing electric water heaters are prone to dry fires due to inadequate fluid detection, leading to overheating and damage of the heating element, with existing solutions like thermal switches and fusible links often resulting in electrical bridges and costly replacements.
Innovation Solution
The method involves briefly energizing the heating block, then waiting and re-checking for current flow to determine if the safety limiter has triggered, distinguishing between low flow and dry fire conditions to prevent overheating and reheat scenarios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thermal switch and fusible link are used as safety temperature limiter, then overheating protection is provided, but the fusible link may melt and form electrical bridges requiring replacement
Solution Approach 1:
The control switches on the heating block only briefly for a first time period before switching it off, as a preliminary action to prevent the fusible link from melting. This preliminary heating phase allows the control to assess system response without reaching critical temperatures that would damage the fusible link or require replacement.
Solution Approach 2:
The control measures current flow after the first time period to determine whether the safety temperature limiter has triggered. This feedback mechanism allows the system to detect low flow conditions or dry fire scenarios and prevent further heating that would melt the fusible link, thereby avoiding the need for replacement.
2Productivity
If the heating block is continuously energized, then heating efficiency is improved, but dry fire conditions cause overheating and element destruction
Solution Approach 1:
The system performs a preliminary brief heating phase followed by a waiting period before continuous operation begins. This preliminary action ensures that flow conditions are adequate before committing to continuous heating, preventing dry fire destruction of the heating element while maintaining efficiency during normal operation.
Solution Approach 2:
The control implements periodic checking of current flow conditions by switching off the heating block after the first time period, waiting for a second time period, then switching it on again for a third time period. This periodic action allows continuous monitoring to ensure heating element integrity while maintaining overall heating productivity.
3Difficulty of detecting and measuring
If impeller-based flow detection is used, then flow monitoring is provided, but inertia delays response time and may not prevent dry fire
Solution Approach 1:
The invention replaces mechanical impeller-based flow detection with an electrical measurement system that monitors current flow through the heating block. This substitution eliminates mechanical inertia delays and provides immediate electrical signal response when flow conditions change, enabling faster protection against dry fire.
Solution Approach 2:
The control briefly energizes the heating block before continuous operation to establish baseline current flow characteristics. This preliminary action creates reference data that enables immediate detection of flow abnormalities during subsequent operation, achieving fast response without mechanical components.
4Reliability
If safety temperature limiter triggers at high temperature, then overheating is prevented, but melted material may form electrical bridges
Solution Approach 1:
The control continuously monitors current flow during and after the brief heating phase to detect whether the safety temperature limiter has triggered. This feedback allows the system to identify low flow conditions before temperatures reach levels that would melt the fusible link and create electrical bridges, preventing this harmful effect.
Solution Approach 2:
The system performs preliminary brief heating followed by a waiting period to assess system response before continuous operation. This preliminary action prevents the temperature from reaching critical levels where fusible link melting and electrical bridge formation could occur, eliminating the harmful effect while maintaining safety.
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
Effectively prevents dry fires by avoiding overheating and fusible link melting, allowing for reliable operation and reducing maintenance costs by accurately detecting fluid presence and flow issues.
Implementation Method 1
an electric heating block (10) which is connected to a control (6)
Implementation Method 2
The thermal switch is usually a bimetallic switch that opens a circuit at a predetermined temperature T s
Implementation Method 3
The fuse of the safety temperature limiter melts at a higher temperature T Sch
Data Source
Figure 1~2
Figure 3
AI summary
In a method for preventing dry burning in an electric instantaneous water heater (1) with a heating block (10) in a hydraulic circuit (3) in which there is a circulating pump (4) and with a fusible link fuse (5) and a thermal switch ( 2), which are electrically connected in series and are thermally conductively connected to the heating block (10), the thermal switch (2) opening above a specified switching temperature TS, and the fusible link fuse (5) melting at a higher, specified temperature TSch, with a current flow through the fusible link (5) and the thermal switch (2) is measured and in the event of a power failure the heating block (10) is switched off, the circulation pump (4) is switched on, then the heating block (10) is switched on for a first time period Δt1 and waiting for a second time period Δt2 after the heating block (10) has been switched off.