Patent Description:
HVAC systems, such as chillers, use an evaporator to facilitate a thermal energy exchange between a refrigerant in the evaporator and a medium flowing in a number of evaporator tubes positioned in the evaporator. In a flooded evaporator, the tubes are submerged in a pool of refrigerant. This results in a particularly high volume of refrigerant necessary, depending on a quantity and size of evaporator tubes, for efficient system operation. Another type of evaporator used in chiller systems is a falling film evaporator. In a falling film evaporator, the evaporator tubes are positioned typically below a distribution manifold from which refrigerant is urged, forming a "falling film" on the evaporator tubes, utilizing gravity to drive the flow of refrigerant over the evaporator tubes. Evaporation is primarily accomplished through thin film evaporation on the surface of the evaporator tubes, while a small fraction of refrigerant is boiled off in a pool boiling section of the evaporator.

As regulatory & industry trends continues to drive towards replacement of conventional HFC's like R134a, of particular interest are the class of "low pressure refrigerants", i.e. refrigerants that are near or below atmospheric pressure at typical boiling temperatures in a chiller. These refrigerants can provide environmental benefits through increased cycle efficiencies, reduced global warming potential, and slower refrigerant leak rates. However, in real systems their lower vapor densities can result in a refrigerant pressure drops that can offset any performance gains.

Low pressure refrigerants offer potential for high efficiency refrigeration systems, but are very sensitive to changes in pressure, meaning that pressure losses greatly increase energy use. For this reason, velocities and flow resistances must be minimized by enlarging HX vessels and refrigerant lines. However, enlarged vessel and line sizes increase cost and physical footprint of these chiller systems, so solutions that can optimize vessel size and pressure drop are critical.

<CIT> discloses an integrated separator-distributor for a falling film evaporator. In the evaporator, a distributor is located above evaporator tubes to distribute liquid refrigerant over the evaporator tubes. A separator is located in the housing upstream of the distributor. The separator includes a refrigerant inlet for vapor and liquid refrigerant mixture to enter the separator. The separator utilizes gravity to separate the liquid refrigerant from the vapor and liquid refrigerant mixture. Liquid refrigerant leaves the separator and enters the distributor via one or more drains and a sparge channel. The vapor refrigerant and remainder of entrained liquid refrigerant flows through a vent stack with its outlet in proximity with a refrigerant pool at a bottom of the evaporator. The entrained liquid refrigerant in the vapor refrigerant exiting the vent stack is captured in the refrigerant pool thus allowing only vapor refrigerant to return to a compressor via a suction line.

<CIT> discloses a heat exchanger for a vapor compression system includes a shell with a longitudinal center axis extending generally parallel to a horizontal plane, a distributing part, a tube bundle, a trough part and a guide part. The distributing part distributes a refrigerant. The tube bundle includes a plurality of heat transfer tubes disposed below the distributing part so that the refrigerant discharged from the distributing part is supplied onto the tube bundle. The heat transfer tubes extend generally parallel to the longitudinal center axis of the shell. The trough part extends generally parallel to the longitudinal center axis of the shell under at least one of the heat transfer tubes to accumulate the refrigerant in the trough part.

<CIT> discloses a liquid refrigerant distributor for use within a heat exchanger having a body of heat exchange tubes. The distributor comprises a mesh screen and a liquid refrigerant sprayer. The liquid refrigerant sprayer is adapted to spray refrigerant on the mesh screen. The mesh screen is adapted to pass liquid and vaporous refrigerant and to direct liquid refrigerant onto the heat exchange tubes.

<CIT> discloses a heat exchanger comprising a tubular shell, a shroud mounted inside the shell, a bundle of tubes extending into the shroud, and means for charging a heat-exchange fluid to the space between the shell and the shroud and into indirect heat exchange contact with the bundle of tubes.

According to claim <NUM>, a falling film evaporator includes an evaporator vessel, a plurality of evaporator tubes disposed in the evaporator vessel through which a volume of thermal energy transfer medium is flowed and a suction port extending through the evaporator vessel to remove vapor refrigerant from the evaporator vessel. A refrigerant distribution system is located in the evaporator vessel to distribute a flow of liquid refrigerant over the plurality of evaporator tubes. The refrigerant distribution system includes a distributor disposed in the evaporator vessel above the plurality of evaporator tubes to distribute a flow of liquid refrigerant over the plurality of evaporator tubes, and a vapor-liquid separator disposed in the evaporator vessel to separate the vapor refrigerant from a vapor and liquid refrigerant mixture. The vapor-liquid separator is configured such that the vapor-liquid separator has a first height at the suction port and a second height greater than the first height at a longitudinal location other than at the suction port. The first height transitions to the second height via a plurality of vertical steps.

Optionally, the first height is a minimum height of the refrigerant distribution system.

Optionally, the suction port is located at a first longitudinal end of the evaporator vessel.

Optionally, the second height is located at a second longitudinal end of the evaporator vessel opposite the first longitudinal end.

Optionally, the suction port is located between a first longitudinal end of the evaporator vessel and a second longitudinal end of the evaporator vessel and the first height is a minimum vapor-liquid separator height.

Optionally, the second height is at one or more of the first longitudinal end or the second longitudinal end and is a maximum height of the refrigerant distribution system.

In another embodiment, a heating, ventilation and air conditioning (HVAC) system according to claim <NUM> includes a condenser flowing a flow of refrigerant therethrough and a falling film evaporator according to claim <NUM> in flow communication with the condenser.

Optionally, the first height is a minimum height of the vapor-liquid separator.

Optionally, the second height is at one or more of the first longitudinal end or the second longitudinal end.

Optionally, the second height is a maximum height of the vapor-liquid separator.

Shown in <FIG> is a schematic view an embodiment of a heating, ventilation and air conditioning (HVAC) unit, for example, a chiller <NUM> utilizing a falling film evaporator <NUM> according to claim <NUM>.

A flow of vapor refrigerant <NUM> is directed into a compressor <NUM> and then to a condenser <NUM> that outputs a flow of liquid refrigerant <NUM> to an expansion valve <NUM>. The expansion valve <NUM> outputs a vapor and liquid refrigerant mixture <NUM> toward the evaporator <NUM>. The evaporator <NUM> includes a plurality of evaporator tubes <NUM> located therein, through which a heat transfer fluid <NUM> is circulated. The heat transfer fluid <NUM> is cooled via thermal energy transfer with the flow of refrigerant at the evaporator <NUM>.

Referring now to <FIG>, as stated above, the evaporator <NUM> according to claim <NUM> is a falling film evaporator. The evaporator <NUM> includes an evaporator vessel <NUM> in which a refrigerant distribution system of the evaporator <NUM> is located. The distribution system includes a distributor <NUM> and a vapor liquid separator <NUM>, as well as other components. An inlet port <NUM> extends through the evaporator vessel <NUM> to admit the vapor and liquid refrigerant mixture <NUM> into the evaporator <NUM>. The vapor and liquid refrigerant mixture <NUM> is directed from the inlet port <NUM> into the vapor-liquid separator <NUM> in which liquid refrigerant <NUM> is separated from the vapor and liquid refrigerant mixture <NUM>. The liquid refrigerant <NUM> is flowed from the vapor-liquid separator <NUM> into the distributor <NUM>, while vapor refrigerant <NUM> exits the vapor-liquid separator <NUM> through a vapor vent <NUM> and flows toward a suction port <NUM> extending through the evaporator vessel <NUM> which directs the vapor refrigerant <NUM> toward the compressor <NUM>.

The distributor <NUM> is located above the evaporator tubes <NUM> to distribute the liquid refrigerant <NUM> over the evaporator tubes <NUM> via one or more distributor ports (not shown). A thermal energy exchange occurs between a flow of heat transfer medium <NUM> (shown in <FIG>) flowing through the evaporator tubes <NUM> into and out of the evaporator <NUM> and the liquid refrigerant <NUM>. As the liquid refrigerant <NUM> is boiled off in the evaporator <NUM>, the resulting vapor refrigerant <NUM> is directed to the compressor <NUM> via the suction port <NUM>. While the evaporator <NUM> shown is rectangular in cross-section, one skilled in the art will appreciate that the evaporator <NUM> may be a variety of shapes, including spherical, cylindrical, rectilinear or any combination of shapes such as these.

The highest vapor velocities in an evaporator <NUM> occur near the suction port <NUM> where the vapor refrigerant <NUM> exits the evaporator vessel <NUM>. The relatively high velocities in this region make it especially prone to pressure and efficiency loss. This is especially challenging in a falling film evaporator, in which refrigerant distribution systems occupy space near the top of the heat exchanger and relatively close to the suction port <NUM>.

To optimize the efficiency, cost, and physical space of the evaporator <NUM>, the height of the vapor-liquid separator <NUM> is varied along the length of the evaporator vessel <NUM>. In the vicinity of the suction port <NUM>, a vapor-liquid separator height <NUM> is reduced, providing an increased space between the vapor-liquid separator <NUM> and the suction port <NUM> for vapor refrigerant flow. Conversely, the vapor-liquid separator height <NUM> is increased at locations further from the suction port <NUM> area where vapor refrigerant flow velocities are lower and efficiency impacts are less critical. The larger cross section of the vapor-liquid separator <NUM> in the regions further from the suction port <NUM> improves vapor-liquid separation and refrigerant distribution functionality than would be possible with a smaller evaporator <NUM>. The net effect of the configuration is that the evaporator <NUM> can have a more compact diameter and lower cost for a given efficiency and cooling capacity.

In some embodiments, such as shown in <FIG>, the suction port <NUM> is located at a first longitudinal end <NUM> of the evaporator <NUM>. As such, the vapor-liquid separator height <NUM> is at a minimum at the first longitudinal end <NUM>, or at the suction port <NUM>. In some embodiments, the vapor-liquid separator height <NUM> is at a maximum at a second longitudinal end <NUM>, opposite the first longitudinal end <NUM>. In the embodiment of <FIG> the vapor-liquid separator height <NUM> is stepped, with a first separator height 46a at the first longitudinal end <NUM>, a second separator height 46b greater than the first separator height 46a, and a third separator height 46c greater than the second separator height 46b at the second longitudinal end <NUM>. While three separator heights 46a-46c are shown in the embodiment of <FIG>, one skilled in the art will readily appreciate that other quantities of separator heights may be utilized in other embodiments.

In some embodiments the suction port <NUM> is not located at either of the first longitudinal end <NUM> or the second longitudinal end <NUM>, but between the first longitudinal end <NUM> and the second longitudinal end <NUM>. For example, in some embodiments the suction port <NUM> is located midway between the first longitudinal end <NUM> and the second longitudinal end <NUM>. In such embodiments, the vapor-liquid separator height <NUM> is at a minimum at the suction port <NUM> and increases with increasing distance from the suction port <NUM> toward either or both of the first longitudinal end <NUM> and the second longitudinal end <NUM>. In some embodiments, the vapor-liquid separator height <NUM> is at a maximum at either or both of the first longitudinal end <NUM> and the second longitudinal end <NUM>.

Claim 1:
A falling film evaporator comprising:
an evaporator vessel (<NUM>);
a plurality of evaporator tubes (<NUM>) disposed in the evaporator vessel through which a volume of thermal energy transfer medium is flowed;
a suction port (<NUM>) extending through the evaporator vessel to remove vapor refrigerant (<NUM>) from the evaporator vessel (<NUM>); and
a refrigerant distribution system (<NUM>, <NUM>) disposed in the evaporator vessel to distribute a flow of liquid refrigerant (<NUM>) over the plurality of evaporator tubes (<NUM>), the refrigerant distribution system including:
a distributor (<NUM>) disposed in the evaporator vessel (<NUM>) above the plurality of evaporator tubes (<NUM>) to distribute a flow of liquid refrigerant (<NUM>) over the plurality of evaporator tubes (<NUM>), and
a vapor-liquid separator (<NUM>) disposed in the evaporator vessel (<NUM>) to separate the vapor refrigerant (<NUM>) from a vapor and liquid refrigerant mixture,
characterised in that the vapor-liquid separator (<NUM>) is configured such that the vapor-liquid separator (<NUM>) has a first height (46a) at the suction port (<NUM>) and a second height (46b, 46c) greater than the first height at a longitudinal location other than at the suction port,
and in that the first height (46a) transitions to the second height (46b, 46c) via a plurality of vertical steps.