Heat exchange – With impeller or conveyor moving exchange material – Mechanical gas pump
Reexamination Certificate
2000-04-19
2003-12-09
Flanigan, Allen (Department: 3743)
Heat exchange
With impeller or conveyor moving exchange material
Mechanical gas pump
C165S151000
Reexamination Certificate
active
06659170
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates generally to heat exchangers and, more particularly, to a heat rejecting refrigerant-to-air finned coil heat exchanger used as a condenser in refrigeration and air conditioning devices.
2. Background Art
Heat transfer is a function of available temperature difference and of time. The larger the temperature difference, the faster the heat transfer. However, for the same degree of available temperature difference, heat transfer can be increased by allowing longer real time contact between the two heat exchanging media. Complete heat transfer can be assured at all times by allowing an appropriate duration that heat exchanging media stay in contact.
In the prior art, finned-coil heat exchangers using forced air are common. These exchangers always approached the shape of a slab, i.e., a large surface area with a very thin depth. This “slab” is often bent to form a “U-shape”. Generally, the length dimension or width dimension or both of the coil surface area is many times greater than the dimension of the depth of the coil, 4 to 20 times or higher. This decreases resistance to the air movement, but enormously reduces the actual time during which cooler air is in contact with the hotter refrigerant tube surface. The short real time contact between the air and the fins results in a much smaller temperature rise being imparted to the cooler air passing over the fins.
In a typical refrigerant cycle, the usual available temperature difference is about 30° F. including the superheat. This is the difference between the temperature of the hot refrigerant fluid entering the heat exchanger and the temperature of the same fluid leaving the exchanger. However, the temperature rise of the air passing over the fins through the heat exchanger is typically only about 10° F., about one-third of the maximum available. That means about three times as much air is being moved as the minimum needed. The larger air quantity being moved means that more energy is being expended to move air.
Another problem with prior art finned-coil heat exchangers is that the general “slab” shape necessitates larger overall volume of the unit. It therefore has a larger footprint, so it occupies more floor space. Since about three times more air is moved than needed, the unit becomes noisier. Additionally, with a large surface area of the coil relative to the sweep of the fan blades, uneven air flow over the coil is created. Because of this, excessive amounts of air pass through the coil surface that is closest to the fan, while the peripheral areas of the coil are starved. That is, no air is moved over the coil portions radially remote from the fan center. This fact means that the full heat transfer capacity of the coil is not being utilized.
In the prior art, the fin density is very high. Typically, heat rejecting condensers use a minimum of 10 fins per inch with 12 to 14 fins per inch being common and 16 fins per inch being the upper limit. The spacing between tubes carrying the fins also has a typical dimension. For instance, the distance between the center lines of tubes having an diameter of ⅜ inch is a maximum of 1 inch; ½-inch tubes, 1.25 inches; and, ⅝-inch tubes, 1.5 inches. In other words, the maximum air space between these tubes is 0.625 inch, 0.750 inch, and 0.875 inch, respectively.
Attempts have been made in the past to increase the air path by moving air along the longer dimension of the cross section of a finned coil. Andreoli U.S. Pat. No. 3,470,947 shows a convector radiator with a monobloc housing wherein ambient air enters from an open bottom, rises through tube fins and exits from the radiator at its upper front corner. Drewes Canada Patent No. 591,553 discloses fins having a large vertical dimension and a smaller depth dimension. Monroe U.S. Pat. No. 3,867,981 employs an angularly sloped flanged fin wherein air is moved across the longer dimension to generate greater heat exchange. While air is moved across the longer side of the fin, no blower is provided to increase air flow. None of these patents show counterflow between the two media needed for efficient heat transfer. These patents also do not show the use of a large number of tube paths needed to purposely create a longer air path.
Umehashi Japan Patent No. 56-3834 shows air path partially along the longer dimension of the finned cross section in an heat absorbing evaporator unit of an air conditioner. Umehashi does not show tubes having a large number of segments transversing air flow necessary to obtain a long air path and good countercurrent (or counterflow) effects. Kormso et al. U.S. Pat. No. 4,483,392 shows air drawn across rows of tubes only three deep. Neither Umehashi nor Kormso show counterflow effects.
Kritzer U.S. Pat. No. 3,151,671 shows a laterally situated blower with air moving along the longer dimension of the finned cross section of a heat radiator employed for comfort heating of indoor space. Kritzer does not show the utilization of transversely spaced multiple tubes to achieve longer path. In heat radiators used for indoor comfort heating applications, it is not essential that complete heat exchange take place by dissipating all heat available in the fluid to the space. In fact, in indoor comfort heating applications, the heat dissipated always varies and gradually lessens as room temperature approaches the thermostat setting. There is nearly always less than complete heat exchange.
Yanadori et al. U.S. Pat. No. 4,333,520 shows air moving along the longer dimension of the finned cross section of an indoor air conditioner unit. Yanadori et al. does not show need for multiple tube paths in an aligned row to obtain long air path for complete heat transfer with minimum air movement and does not show the two media—air and fluid in the tubes—flowing in counterflow directions.
As stated above, it is not essential that there be complete heat transfer between air and the fluid in the tubes of an indoor space heating unit or space cooling unit. For a heat rejecting refrigerant-to-air condenser to be efficient, it is only essential that all heat available in the refrigerant fluid with respect to the ambient temperature be rejected. In an indoor application, it is not desirable that heat transfer take place with minimum air movement. Minimum air movement can cause uncomfortably cold air to emanate from the unit or extremely hot air to blow out of the unit. In extreme situations, this can cause icing of the coil in a cooling mode or a fire hazard in a heating mode. In an indoor space heating unit or space cooling unit application, the heat transfer between the air and the fluid within the tubes continuously varies. It gradually decreases as the space being conditioned approaches the thermostat temperature setting. Air needed to deliver heat or cooling to a distant point in the room must have a small temperature difference from ambient. It can neither be too cold nor too warm so as to become uncomfortable. Both these considerations require that high volumes of air be moved. Yet, complete heat transfer from the tube media should be obtained for maximum efficiency.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming one or more of the problems as set forth above.
According to the present invention, a heat exchanger is provided with a housing having spaced front and back walls and spaced side walls defining an internal chamber area with open lower and upper ends, tubes for conducting hot fluid into the chamber area, a series of spaced fins in contact with the tubes to transfer heat from the tubes to air within the chamber area, the tube segments being spaced transverse to the air path between the two openings located at the opposite ends of the chamber area. The tubes are arranged in rows which are substantially parallel to air flow path with the hot fluid entering the chamber at the air outlet end and traveling through the rows in a counterflow direction with the air so that the multiple tube segments provide a longer air path al
Flanigan Allen
Shepard John C.
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