This invention relates to an electrical expansion valve, such as that used in a refrigeration system or an air-conditioning system.
In the prior art, refrigeration systems have used thermostatic expansion valves as an interface between a high pressure side and a low pressure side of a refrigeration system. A thermostatic expansion valve regulates the rate at which refrigerant enters into the evaporator or cooling coil based upon the amount of heat to be removed from a refrigerated space. In a typical configuration, a thermostatic expansion valve includes a valve, a valve-opening mechanism, and a spring that opposes opening of the valve by the valve-opening mechanism to control the flow of refrigerant through the opening of the valve. The valve-opening mechanism may refer to a diaphragm which is moved by a temperature sensor. The temperature sensor may include a gas charged bulb coupled to a capillary tube. The temperature sensor may be associated with an output of the evaporator. When working properly, the thermostatic expansion valve senses the pressure of the refrigerant coming into the evaporator and the temperature of the refrigerant as it leaves the evaporator to meter the proper flow of the refrigerant into the evaporator.
However, the thermostatic valve may not operate with sufficient reliability and may be too expensive for certain applications for the following reasons. The thermostatic expansion valve may require numerous mechanical parts, including the diaphragm, the spring, the valve, the housing, the temperature sensor, which need to be manufactured according to strict tolerances and assembled carefully to create a reliable thermostatic expansion valve. During operation, the thermostatic expansion valve may experience failure or operational problems caused by one or more of the following: dirt or debris that accumulates in the opening associated with the valve, mechanical or thermal stress on the spring that lowers the spring force from its original value, corrosion of the interior of the thermostatic expansion valve which prevents the proper movement of the valve, mechanical problems that impede the movement of the diaphragm, or other problems. Thus, a need exists for an expansion valve that is economical to manufacture, while providing reliable control of the rate which refrigerant enters the evaporator.
Thermostatic expansion valves may also perform more slowly than desired because of the technical design that relies upon the movement of the diaphragm or another mechanical member in response to air or gas pressure changes. For example, a temperature sensor may be configured as a gas-charged bulb that interacts with the diaphragm through a capillary tube to control the metering of the refrigerant. Thus, a need exists for an expansion valve that provides accurate and rapid control of the refrigerant expansion process in a refrigeration or air conditioning system.
In accordance with the invention, an expansion valve for regulating the flow of a refrigerant fluid to provide reliable control of a refrigeration system includes a channel for conveying the refrigerant fluid. The channel has an inlet for accepting the refrigerant fluid and an outlet for exhausting the refrigerant fluid. A heating element is disposed in a path of the fluid and associated with the inlet. Electrical terminals are coupled to the heating element for controlling thermal properties of the heating element to regulate the flow of the refrigerant fluid through the channel.