1. Field of the Invention: The present invention relates to a heat exchanger for thermal conditioning of one fluid medium by heat transfer with a second fluid medium in a heat transfer tube and, more particularly, to a method and apparatus for enhancing heat transfer between the flow of one heat transfer medium and a different heat transfer medium in an evaporator unit or condenser unit for diverse applications of heat transfer including water heaters and water coolers particularly, for water of swimming pools, spas, aquariums (both fresh and salt water) and as a heat exchanger for marine engines and in heat pumps.
2. Description of the Prior Art: Evaporator and condenser functions provided by a heat exchanger are commonly used for diverse applications and while not so limited, the present invention is particularly useful in one common field of used where heat transfer with one medium consists of a flow of water for a swimming pool or spa. Swimming pool water is heated or cooled depending on the climate affecting the temperature of the pool water. The present invention is particularly applicable to a heat exchanger using a tube-in-shell construction. It is known to heat a flow of water for a swimming pool in an elongated tank having an internal chamber in which an electrically resistive heating element, frequently as a coil, is housed. Water is directed in a lengthwise path through the tank chamber containing the heating element for transfer of heat from the heating element to the water. In such a device, no control over the flow of water is provided within the internal chamber of the tank and because the heat exchanger incorporates an electrically resistive heating element as opposed to a fluid heat transfer medium, the application of such a heat exchanger is limited to use as a heater for water.
It is well known in the art to provide a heat exchanger to condition a flow of water in which a fluid is used as a heat transfer medium. In a type of construction known as "shell-and-tube" design, the heat transfer fluid is carried within a tube and the flow of water to be treated is directed past the tube, or tubes, within a shell housing. In the simplest arrangement, the heat exchanger consists of a tube within a tube and the fluids move either in the same direction, known as a "parallel flow" heat exchanger, or in opposite direction, known as a "counter flow" heat exchanger. In a tube within a tube construction, there is no control over the flow of water once it has entered the shell. Such a construction, although embodying a simple arrangement of parts, is costly as to fabrication.
Other shell-and-tube heat exchanges are known in which multiple tubes, or a coiled tube, are housed within a shell. The heat transfer tube is commonly formed from a metal such as copper or copper-nickel alloy to take advantage of favorable heat transfer properties and low cost of the metal material. Because of the favorable heat transfer properties with metals as copper and copper-nickel alloy, when heating an increased water flow is necessary the requirement is met by increasing the length of copper tubing in the coiled section thereby providing a greater residence time for the water flow in the heat exchanger. Where higher BTU heat transfer is needed for a given flow of water through the shell, providing a greater length of tubing to achieve the desired BTU heat transfer is conventional and cost effective rather than direct or otherwise manage the water flow to maximize heat transfer.
There are disadvantages associated with a copper heat transfer tube in a heat exchanger for water. One example of such disadvantages is in the thermal conditioning of salt water for applications such as holding tanks and aquariums for marine life. The marine life is susceptible to a toxic reaction to chemically produce products of corrosive reaction between the salt water and the copper metal of the heat transfer tube. The toxic reacting product can be eliminated by selecting a more chemically inert metal or alloy such as titanium to form the heat transfer tube in the heat exchanger. The use of titanium for the heat transfer tube of the heat exchanger offers the benefits of strength, durability and a prolonged service life as compared with copper for the heat transfer tube of a heat exchanger. However, to be economically competitive the high cost of titanium metals as compared with the cost of copper or copper-nickel alloy poses a need to reduce the length of heat exchanged tubing. What is also needed is a heat exchanger construction in which the heat transfer between a fluid medium directed through a shell along a heat transfer tube is greatly enhanced by causing turbulence to the fluid media to maximize heat transfer thereby reducing the usage of high cost heat transfer materials, such as titanium.
Accordingly, it is an object of the present invention to provide a heat exchanger for conditioning a flow of a fluid medium within a shell along a helical pathway to maximize heat transfer between a fluid medium and heat transfer tubing.
It is a further object of the present invention to provide a heat exchanger for conditioning a flow of a fluid medium in which an internal baffle creates an arcuate chamber containing a tube coil such that the volume for the flow of a fluid medium is reduced and the fluid flow caused purposely to undergo high turbulence to maximize heat transfer between the fluid medium and the external surface of the tube coil.
It is another object of the present invention to provide a heat exchanger for conditioning a fluid medium in which the flow of the fluid medium within a shell is controlled to maximize the heat transfer capability with a heat transfer tube to make feasible a reduction to the length of coiled tubing and use of higher cost metal as the tube material such as titanium.
It is a further object of the present invention to provide a heat exchanger for conditioning a flow of a fluid medium in which an internal baffle is provided to create an arcuate chamber containing the coiled portion of a tube such that a fluid medium volume in the vicinity of the arcuate chamber is reduced and fluid flow is highly turbulent to maximize a temperature differential and thereby BTU transfer rate to a fluid medium along the coiled portion of the tube and a fluid medium.
It is still a further object of the present invention to provide a heat exchanger for conditioning a flow of a fluid medium in which the flow of the fluid medium within a shell is controlled for maximizing heat transfer by components for which assembly is relatively uncomplicated to use higher cost material for the heat exchange tube in a heat exchanger useful in a wider range of applications.