| 摘要 |
PURPOSE:To widen the range of regulating flow rate, lower the surface temperature of a heat-transmitting surface of a heat exchanger and enhance reliability, by a method wherein a bypass passage provided with a pressure relief valve connecting an intermediate part of a heat exchanger and an inflow port or an outflow port to each other is fitted to a water heating passage. CONSTITUTION:In using a heater, when a flow rate regulating valve 4 is opened, a fluid to be heated starts to flow through a heating passage 1b, and when the flow rate exceeds a predetermined value, the pressure P in a heating passage 1 between a valve 4 and a heat exchanger 5 is raised to close a pressure switch 9. Then, an electric current is passed to a heating means 8, and the heat exchanger 5 is heated. When said pressure P is reached, the pressure relief valve 10 in a bypass passage 11 starts to open so that a part of the fluid is diverted into the passage 11. The quantity of the fluid diverted is markedly increased by only a small rise in the pressure P by the action of the relief valve 10. Accordingly, the overall flow rate through the heating passage 1b can be increased while maintaining the minimum rate of the flow to the heat exchanger, and a wide range of regulating the flow rate can be obtained. |
