Heat exchange – Gradated heat transfer structure
Patent
1996-12-26
1997-12-16
Flanigan, Allen J.
Heat exchange
Gradated heat transfer structure
12223523, 165DIG481, 165910, F28F 1308
Patent
active
056974353
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The subject invention relates to methods and apparatus for transferring heat among different fluids, to heat exchangers, and to water heaters.
BACKGROUND
Various methods and apparatus for transferring heat among different fluids are well known. One example is the familiar kind of heat exchanger in which one fluid in the heat exchanger flows through heat exchanger tubes while another fluid flows in heat-transfer relationship past such tubes. In many commercial units, the heat exchanger tubes are arranged in a couple of sometimes staggered rows essentially transversely to the flow of the latter other fluid.
Advantageously, the fluids participating in the heat exchange flow in a thermal counterflow. For example, in the case of gas-fired water heaters, cold water is flowed first through the row of heat exchanger tubes remote from the gas/air combustion chamber and, after having been thus heated, is last flown through the row of heat exchangers closest to the combustion chamber. In practice, this increases overall heat transfer and in particular improves heat transfer to the row of heat exchanger tubes away from the combustion chamber.
Some of such apparatus are condensing heat exchangers in which moisture in the fluid flowing past the heat exchanger tubes is condensed. In gas-fired heaters, such moisture is water vapor generated in the gas/air combustion process. A majority, of condensing heat exchanger are for heating air, but a significant number are for heating water. A familiar type of condensing water heater has a heat exchanger with two rows of finned copper tubes arranged in the above mentioned kind of thermal counterflow.
Even with thermal counterflow, by far the largest part of the heat exchange occurs in the row of heat exchanger tubes situated closest to the combustion chamber. Accordingly, flash boiling in these heat exchanger tubes must be avoided unless the objective of the particular heater is steam generation.
Conversion of water to steam eliminates the heat sink effect of the water flowing in the heat exchanger tubes. Tubes not designed for steam generation thus can be subjected to damage, including severe corrosion, melting or rupture, and failure at points where the tubes join headers and other parts of the heat exchanger.
Also high heat flux can cause precipitation of solids from the water onto the tube surface, sometimes to a degree which blocks water flow and causes overheating of the tube. This is sometimes called "liming".
Excessive velocity of the circulating heated fluid can be avoided by arranging heat exchanger tubes in parallel flow paths, which reduces pressure drop and tube erosion. However, the velocity of the circulating fluid should be high enough to avoid flash boiling and to enable circulating fluid to pull the heat exchanger tube temperature as close to that circulating fluid as possible.
These factors represent conflicting considerations in conventional heat exchanger design. Even where tradeoffs between conflicting design factors have been successfully implemented, either the efficiency of heat transfer has remained in the eighty-percent range, or higher efficiencies have come at a price of increased space and material requirements, and thereby cost.
Subjecting the flow of the cooler fluid to turbulation in the heat exchanger tubes has helped the fluid-side heat transfer, while baffles have been used to confine the flow of the hotter fluid to spaces between fins of finned heat exchanger tubes also for improved heat transfer. However, such measures have had only a modest effect on overall efficiency and have not substantially reduced space and material requirements and costs.
SUMMARY OF THE INVENTION
It is a general object of the invention to overcome the drawbacks and to meet the needs set forth above or otherwise apparent in this disclosure.
It is a germane object of the invention to provide improved methods and apparatus for transferring heat from a first fluid to a cooler second fluid.
It is a related object of the invention to provide improve
REFERENCES:
patent: 1509782 (1924-09-01), Samuelson
patent: 4784218 (1988-11-01), Holl
patent: 4957160 (1990-09-01), Raleigh
De Vuono Anthony C.
Hamos Robert E.
Raleigh William F.
Stickford, Jr. George
Flanigan Allen J.
Teledyne Industries Inc.
LandOfFree
Heat exchanger systems does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Heat exchanger systems, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Heat exchanger systems will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-198796