Patent Application
20200340765
The present disclosure relates to a heat exchanger, and more particularly to a heat exchanger for a high Prandtl number fluid.
A variety of devices are known in the heat exchanger area. However High-Viscosity/Prandtl-number fluids such as oils or glycol solutions result in poor heat transfer and high pressure drop. Surface augmentations are often used to enhance heat transfer; however, result in even higher pressure drop.
The conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for heat exchanger having improved heat transfer capabilities. There also remains a need in the art for such heat exchangers and components that are economically viable. The present disclosure may provide a solution for at least one of these remaining challenges.
A fluid heat exchanger includes a channel for passing a first fluid therethrough arranged along a primary axis including at least two segments of a first flow pattern, wherein at least one segment of the at least two segments defines a length greater than five times a hydraulic diameter of the channel, and a first pattern flow disruptor interspersed between each of the segments of the first flow pattern configured to reduce a pressure loss of the fluid flow along the channel, and a second series of channels for passing a second fluid therethrough for transferring energy to the first fluid. A first segment of the at least two segments can define a length different from a length of a second segment of the at least two segments. The length of the first segment can be defined by the equation 5Dh<L<4DhPr wherein L is the length of the first segment, Dh is the hydraulic diameter of the first segment, and Pr is the expected steady state Prandtl number of the first fluid at a location along the first segment. The length of the second segment can be defined by the equation 5Dh<L<4DhPr wherein L is the length of the second segment, Dh is the hydraulic diameter of the second segment, and Pr is the expected steady state Prandtl number of the first fluid at a location along the second segment.
The segments of the first flow pattern can be aligned in the same direction. The segments of the first flow pattern can be straight. The first pattern flow disruptor can narrow the flow channel. The first pattern flow disruptor can change a direction of flow of the first fluid. The first pattern flow disruptor can include multiple disruptors, wherein at least one of the flow disruptors includes a longer length than another disruptor.
A method of transferring heat between fluids includes directing a fluid through a heat exchanger channel and developing a thermal boundary layer between the fluid and a surface of the channel and a momentum boundary layer between the fluid and the surface of the channel, wherein the thermal boundary layer of the fluid includes a different thickness than a thickness of the momentum boundary layer, and directing a second fluid through a second channel adjacent to the first channel and transferring heat from the first fluid to the second fluid.
The fluid includes a Pradntl number greater than 1, or preferably a Prandtl number greater than 7. The thermal boundary layer of the fluid is thinner than the momentum boundary layer. A ratio of thermal boundary thickness to momentum boundary layer thickness can decrease along a flow direction of the fluid and the ratio of thermal boundary thickness to momentum boundary layer thickness can be greater than 1.
These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings.
So that those skilled in the art to which the subject invention appertains will readily understand how to make and use the devices and methods of the subject invention without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein:
Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject invention. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a heat exchanger channel in accordance with the invention is shown in
Referring to
Referring to
The segments 112, 114 of the first flow pattern are aligned in the same direction. The segments 112, 114 of the first flow pattern can be straight. As shown in
A method of transferring heat between fluids using a heat exchanger is also disclosed. The method includes directing a first fluid through a heat exchanger channel and developing a thermal boundary layer between the first fluid and a surface of the channel and a momentum boundary layer between the first fluid and the surface of the channel, wherein the thermal boundary layer of the first fluid includes a different thickness than a thickness of the momentum boundary layer. Directing a second fluid through a second channel adjacent to the first channel and transferring heat from the first fluid to the second fluid. The first fluid includes a Pradntl number greater than 1, or more specifically a Prandtl number greater than 7.
For fluids with a Prandtl number above 1, the thermal boundary layer of the first fluid is thinner than the momentum boundary layer. A ratio of thermal boundary thickness to momentum boundary layer thickness decreases along with the flow of the fluid and the ratio is always greater than 1.
The method described above is leveraged to augment heat transfer while reducing pressure drop penalty by intermittently disturbing the flow at desired intervals, where the momentum profile is allowed to recover while the thermal profile remains augmented. For fluids having a high Prandtl number the flow through the first segment (L1) result in lower pressure drop with little degradation to the enhancement in heat transfer caused by the disruptor. The optimal length the disruptors can be selected based on expected steady state conditions and fluid properties. The implementation of this method has shown an improvement of approximately 30% more heat transfer with respect to conventional methods, while keeping the pressure drop penalty unchanged.
The methods and systems of the present disclosure, as described above and shown in the drawings, provide for a heat exchanger with superior properties heat transfer. While the apparatus and methods of the subject disclosure have been showing and described with reference to embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and score of the subject disclosure.
