Gas and liquid contact apparatus – Contact devices – Wet baffle
Reexamination Certificate
1999-02-17
2001-01-30
Barry, Chester T. (Department: 1724)
Gas and liquid contact apparatus
Contact devices
Wet baffle
C165S133000, C165SDIG004, C165S010000
Reexamination Certificate
active
06179276
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to assemblies of heat and mass transfer plates which provide improved levels of transfer compared to any increase in pressure drop. More particularly, the assemblies have a gas stream flowing in the spaces between adjacent plates whereby heat is transferred between the plates and the fluid and/or the fluid is acted upon by the plates such as a catalytic action to effect mass transfer within the fluid. Most particularly the assemblies are used for heat transfer in rotary regenerative air preheaters or for a substrate for supporting a catalyst for the reduction of No, in a flue gas stream flowing over the plates.
One type of heat exchange apparatus to which the present invention has particular application is the well-known rotary regenerative heater. A typical rotary regenerative heater has a cylindrical rotor divided into compartments in which are disposed and supported spaced heat transfer plates which, as the rotor turns, are alternately exposed to a stream of heating gas and then upon rotation of the rotor to a stream of cooler air or other gaseous fluid to be heated. As the heat transfer plates are exposed to the heating gas, they absorb heat therefrom and then when exposed to the cool air or other gaseous fluid to be heated, the heat absorbed from the heating gas by the heat transfer plates is transferred to the cooler gas. Most heat exchangers of this type have their heat transfer plates closely stacked in spaced relationship to provide a plurality of passageways between adjacent plates for flowing the heat exchange fluid therebetween.
In such a heat exchanger, the heat transfer capability of a heat exchanger of a given size is a function of the rate of heat transfer between the heat exchange fluid and the plate structure. However for commercial devices, the utility of a device is determined not alone by the coefficient of heat transfer obtained, but also by other factors such as cost and weight of the plate structure. Ideally, the heat transfer plates will induce a highly turbulent flow through the passages therebetween in order to increase heat transfer from the heat exchange fluid to the plates while at the same time providing relatively low resistance to flow between the passages and also presenting a surface configuration which is readily cleanable.
To clean the heat transfer plates, it has been customary to provide soot blowers which deliver a blast of high pressure air or steam through the passages between the stacked heat transfer plates to dislodge any particulate deposits from the surface thereof and carry them away leaving a relatively clean surface. One problem encountered with this method of cleaning is that the force of the high pressure blowing medium on the relatively thin heat transfer plates can lead to cracking of the plates unless a certain amount of structural rigidity is designed into the stack assembly of heat transfer plates.
One solution to this problem is to crimp the individual heat transfer plates at frequent intervals to provide double-lobed notches which have one lobe extending away from the plate in one direction and the other lobe extending away from the plate in the opposite direction. Then when the plates are stacked together to form the heat transfer element assembly, these notches serve to maintain adjacent plates so that forces placed on the plates during the soot blowing operation can be equilibrated between the various plates making up the heat transfer element assembly.
A heat transfer element assembly of this type is disclosed in U.S. Pat. No. 4,396,058. In the patent, the notches extend in the direction of the general heat exchange fluid flow, i.e., axially through the rotor. In addition to the notches, the plates are corrugated to provide a series of oblique furrows or undulations extending between the notches at an acute angle to the flow of heat exchange fluid. The undulations on adjacent plates extend obliquely to the line of flow either in an aligned manner or oppositely to each other. Although such heat transfer element assemblies exhibit favorable heat transfer rates, the results can vary rather widely depending upon the specific design and relationship of the notches and undulations.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved heat transfer element assembly wherein the thermal performance is optimized to provide a desired level of heat transfer and pressure drop with assemblies having a reduced volume and weight. In accordance with the invention, the heat transfer plates of the heat transfer element assembly have means, such as longitudinal bibbed notches, spacing the plates apart to form the flow passages. The plates have multiple V-shaped ribs on each side in the flow passages aligned to produce longitudinal vortices which, together with specific ranges for the plate spacing in relation to rib parameters produce the optimum thermal performance.
REFERENCES:
patent: 4396058 (1983-08-01), Kurschner
Papers 4, 5 and 6 of thesis entitled “Thermal and Hydraulic Performance of Enhanced Rectangular Tubes for Compact Heat Exchangers” by Carl-Olof Olsson, published Mar. 14, 1997 (ISBN 91-7197-457-1).
Thesis entitled “Thermal and Hydraulic Performance of Enhanced Rectangular Tubes for Compact Heat Exchangers” by Carl-Olof Olsson, published Mar. 14, 1997 (ISBN 91-7197-457-1).
Chen Michael M.
Olsson Carl-Olof Erik
ABB Air Preheater Inc.
Alix Yale & Ristas, LLP
Barry Chester T.
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