CROSS-REFERENCE TO RELATED APPLICATION

[0001] Benefit is claimed of US Patent Application Ser. No. 61/308,571, filed February 26, 2010, and entitled "Refrigerated Case", the disclosure of which is incorporated by reference herein in its entirety as if set forth at length.

BACKGROUND

[0002] The disclosure relates to refrigerated cases. More particularly, the disclosure relates to cleaning of heat exchangers of refrigerated cases.

[0003] A number of refrigerated case configurations have the compressor and heat rejection heat exchanger in the base of the case below the refrigerated compartment (e.g., an open-front case, a door- front case, an open-top case, and the like). To cool the heat rejection heat exchanger, a fan drives an airflow along a flowpath through the heat rejection heat exchanger. For ease of reference, the heat rejection heat exchanger will be referred to as a "condenser" which is intended to comprehend both true condensers and gas coolers. When operated in the normal

(cooling) mode of operation, the fan drives the airflow along the flowpath. Typically, the airflow across the condenser is front-to-back with relatively cool room air entering a grille at the front of the base and passing essentially straight through and exiting the rear of the base. The proximity of the base to the floor causes this airflow to be particularly dirty (e.g., dusty). There is a tendency for such contaminants to accumulate on the condenser and decrease its

performance/efficiency. The decrease can include a combination of insulating the condenser from the airflow and blocking the airflow. This contamination or fouling occurs not merely on the tube sections of the condenser but also, and especially, on fins. An exemplary fin heat exchanger is a round tube plate fin (RTPF) heat exchanger wherein there is typically a lateral array of plates extending vertically and front-to-back. Each of the tube sections extends through and is in thermal contact with the plates.

[0004] As fouling accumulates, periodically the fan may be reversed to reverse the airflow to backflush the condenser. This may, for example, be done during the defrost cycle. However, backflushing is not fully effective and, from time to time, there must be a manual cleaning (e.g., vacuuming/brushing).

[0005] To partially address such fouling problems, anti-fouling coatings have been proposed.

Examples of such a coating are found in WO2009/039874. SUMMARY

[0006] One aspect of the disclosure involves a plate fin heat exchanger having a plurality of tube sections extending across an air flowpath. These include a first group of sections forming a leading group. The heat exchanger includes means for preferentially shielding portions of the fins ahead of the leading group against debris accumulation.

[0007] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a simplified view of a refrigerated case.

[0009] FIG. 2 is a simplified vertical front-to-back sectional view of the case of FIG. 1.

[0010] FIG. 3 is a schematic view of a refrigeration system of the case of FIG. 1.

[0011] FIG. 4 is a top side view of a heat exchanger.

[0012] FIG. 5 is a top front view of the heat exchanger of FIG. 4.

[0013] FIG. 6 is a top view of the heat exchanger of FIG. 4.

[0014] FIG. 7 is a front cutaway view of the heat exchanger of FIG. 6, taken along line 7-7.

[0015] FIG. 8 is a first side view of the heat exchanger of FIG. 6.

[0016] FIG. 9 is a second side view of the heat exchanger of FIG. 6.

[0017] FIG. 10 is a side schematic view of the heat exchanger of FIG. 6 in a cooling mode.

[0018] FIG. 11 is a side schematic view of the heat exchanger of FIG. 6 in a cleaning mode.

[0019] FIG. 12 is a side schematic view of a second heat exchanger.

[0020] FIG. 13 is a side schematic view of a third heat exchanger.

[0021] FIG. 14 is a partial top view of a fourth heat exchanger.

[0022] Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0023] FIGS. 1 and 2 show a refrigerated case 20 having a body 22 at least partially enclosing a refrigerated compartment (interior) 24. The exemplary case/body is an open- front case having a left wall 26 at a left side 28, a right wall 30 at a right side 32, a top panel (wall) 34 at a top 36, a base 38 at a bottom 40, and a rear (back) panel 42 at a back (rear end) 44. An opening 46 extends at least partially along a front of 48 of the case. In the exemplary case, a vertical array of shelves 50 is positioned within the compartment 24.

[0024] The exemplary case 20 includes a refrigeration system 60 (FIG. 3). The refrigeration system comprises a compressor 62 along a refrigerant fiowpath 64. The compressor has an inlet (suction port) 66 and an outlet (discharge port) 68. The refrigeration system includes a first refrigerant-air heat exchanger 70 and a second refrigerant-air heat exchanger 72. An expansion device 74 may be along the refrigerant fiowpath 64 between the heat exchangers 70 and 72 opposite the compressor. Fans 80 and 82 may respectively drive airflows 84 and 86 across the heat exchangers 70 and 72.

[0025] In a cooling mode of operation, refrigerant compressed by the compressor exits the outlet 68 and proceeds to the first heat exchanger 70 which acts as a condenser or gas cooler (heating the air flow 84 to reduce the temperature of refrigerant as it flows through the first heat exchanger 70). Refrigerant proceeds downstream along the refrigerant fiowpath 64 to the expansion device 74 where it is expanded and its temperature further reduced. The cold refrigerant enters the second heat exchanger 72 (which acts as an evaporator, absorbing heat from the airflow 86 and heating the refrigerant as it flows through the second heat exchanger 72). Refrigerant discharged from the second heat exchanger 72 returns to the compressor inlet 66. Other details, including accumulators, valves, and sensors may be present but are not shown for ease of illustration.

[0026] FIG. 2 shows further details of a base air fiowpath 98 and a recirculating cabinet/case air fiowpath 100 and exemplary positioning of components of the refrigeration system 60. In the exemplary case 20, the compressor 62 and first heat exchanger 70 are positioned within a compartment 102 of the base 38. A rear duct 104 is located between the rear wall 42 and the compartment 24. The rear duct 104 extends from a base duct 106 at a lower end of the compartment which has an inlet 108 at a lower end of the front opening. The second heat exchanger 72 is positioned within the base outlet 106. The rear duct 104 feeds a top duct 110 which has an outlet 112. The flow 86 produces a discharge flow 114 from the outlet which may initiate/form an air curtain along the opening 46. Additional branching flows 115 may branch off the flow 86 and pass into the compartment 24. At least a portion of the flow 114 and any branching flows returns to the inlet 108 as an inlet flow 116. In the exemplary embodiment, the fan 82 is positioned near the front (upstream) end of base duct 106.

[0027] In a cooling mode, moisture in the inlet flow 116 may freeze on the heat exchanger 72 and may produce a frost accumulation which may lead to a blockage. Accordingly, a defrost mode may be initiated. Exemplary defrost may be via a heating element (e.g., an electric resistance element) and/or via directing hot refrigerant to the heat exchanger 72 (instead of cold refrigerant). The defrost operation melts the frost which may flow downward as a flow 130 (e.g., of droplets) and reach a drain. An exemplary drain is formed proximate a lower end of the rear duct. The drain may include a trap (e.g., a conventional J or S trap or a more complex trap such as that shown in JP2004353909). The drain, in turn, may discharge water as one or more flows into an evaporation vessel or a drainline.

[0028] FIGS. 4 and 5 show an exemplary heat rejection heat exchanger 70 (hereinafter generically "condenser" which includes both true condensers and gas coolers). The exemplary condenser 70 is an RTPF condenser having a plurality of sections of tube (e.g., an array) spanning first and second endplates 150 and 152. At the endplates, various of the tube sections are coupled to each other (e.g., via bends or U-shaped connectors to create the refrigerant circuit/flowpath through the condenser). The exemplary condenser has a plurality of rows of tube sections (an exemplary four rows shown extending from a leading group or row 154 (shown oriented horizontally and arrayed vertically) to a trailing row 156 with two intermediate rows 158 and 160). The leading and trailing direction is defined relative to the cooling mode direction of the airflow 84 along the flowpath 98.

[0029] FIG. 6 also shows the array of individual fin plates 162 extending between the endplates 150 and 152. The plates, thus, have leading edges 164 and trailing edges 166. The exemplary fan 80 is normally a pull-through fan drawing the airflow 84 across the tube array. As heretofore described, the condenser may be otherwise a conventional condenser. The condenser may, however, have added to it a shield 170 which helps mitigate fouling problems. Such a shield may also be used with other heat exchanger constructions such as fmned-tube or other non-plate finned constructions. The shield may alternatively be defined as part of the condenser or as a separate element. It has been observed that fouling is particularly significant along/near the leading edges of the plates 162. In the backflushing mode, it has been observed that the backflushing is relatively ineffective at removing fouling from the portions of the plates immediately forward (upstream in the cooling mode direction of the airflow 84 but downstream in the backflush mode direction) of the tube sections of the leading row 154. These areas may be referred to as the "wind shadow" of such tube sections in that the tube sections block the airflow so that relatively high velocity airflow clears the fins between the tube sections but the relatively lower velocity in the shadow is less effective at cleaning. The lack of uniform cleaning caused by this effect has several consequences. First, there is a slight initial loss of efficiency relative to a fully clean condenser. Also, however, the still-fouled areas in the shadow can act as

catalysts/seeds, increasing the rapidity by which the clean areas foul. The shield 170 serves as means for reducing fouling in the wind shadow areas of the leading row of tubes (relative to accumulation in the inter-tube spaces between such areas). This compensates for the relative inability of backflushing to access/clean the wind shadow areas. The exemplary shield 170 does this by serving as a means for preferentially shielding the leading group of tube sections (and the wind shadow areas of the fins) in the cooling mode. Specifically, the airflow is directed away from the front of the tube sections and toward the inter-tube spaces. The direction is

"preferential" in that it is towards certain areas (the "preferred" inter-tube areas) relative to the wind shadow areas. Thus, the leading tubes and their wind shadow areas are preferentially shielded.

[0030] FIG. 10 shows the shield 170 as having an array of bars 180 directly and immediately (no intervening structures) in front of and respectively associated with individual ones of the tube sections of the leading group 154. The bars 180 tend to block contaminants from accumulating in the wind shadow areas 182 while relatively freely allowing contaminants/fouling 184 to reach the inter-tube areas 186 between the wind shadow areas 182.

[0031] FIG. 11 shows the backflushing ejecting the fouling. Exemplary bars 180 are formed as V-sectioned members having a leading end 190 at the vertex of the V and a trailing end 192 formed by the opposite ends of the legs of the V. The exemplary bar height H is close to the tube height (diameter D for a round tube). Exemplary trailing ends 192 have a spacing Si ahead of the associated tubes and S ₂ ahead of the fins. Exemplary S ₂ is up to about 30mm (more narrowly, 2- 10mm, or 3-6mm, or about 5mm). As discussed below, this dimension can technically become negative if the fins are recessed into the bars. Exemplary H is 80-120% of D (e.g., about 1.0 x D). Exemplary tube outer diameter OD is 7.2mm or 3/8 of an inch. The exemplary bars are registered with the associated tube sections (e.g., at the same height and not out-of-phase). For example, exemplary bars may extend no more than 15% of D above or below the associated tubes, more narrowly, no more than 10% or 5% above or below.

[0032] Other shapes of bar cross-section are possible. For example, other generally divergent (in the cooling mode flow direction) shapes such as C-shaped or paraboloid may be used.

Alternatively, ellipsoid, rhomboid, or other shapes may be used (whether hollow or solid).

Exemplary bar materials are plastic (such as polyethylene, polypropylene, acrylonitrile styrene acrylate (ASA), or ABS-PMMA) or metal (e.g., aluminum or lacquered steel). It is desirable that the surface of the bar material be relatively smooth so as to hinder dust accumulation on the bars. The bars may be secured in any of several ways. FIGS. 4 and 5 show the bars mounted to endplates which are secured as extensions of the existing condenser endplates (sideplates).

However, in a production environment this might be made by merely using larger condenser endplates. FIG. 12 shows the bars mounted on a structure which is secured to the bottom of the base compartment ahead of the condenser. FIG. 3 shows the bars (or a frame structure holding the bars) registered to the condenser via brackets 200 to engage one or more of the leading tube sections. FIG. 14 shows recesses 220 in the bars which accommodate the fins (and thus the negative value of S ₂ previously mentioned).

[0033] In operation, there may be several advantages to such a system. The relative cleanliness of the condenser post-backflushing may yield relatively higher efficiencies post back-flushing. Reduction in the catalyst/seed effect may delay further loss of efficiency. Most significantly, the frequency of needed manual cleaning may be reduced.

[0034] The system may be implemented with conventional manufacturing techniques and materials (e.g., brazing or welding metal bars to associated endplates or gripping or gluing metal or plastic bars). The bar material may be stock angle material (e.g., right angle). Use parameters may be essentially unchanged. For example, the backflushing may still occur in the defrost mode (e.g., under fully automated or semi-automated control). The manual cleaning may still be performed via vacuuming. Depending upon the situation, the bars may be made removable (e.g., as a unit) for access to the fins. However, it is likely that the bars will merely be left in place during normal vacuuming.

[0035] The fins, tubes, and/or bars may have protective coatings such as that shown in WO2009/039874. Yet other variations are possible.

[0036] Although an embodiment is described above in detail, such description is not intended for limiting the scope of the present disclosure. It will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, when implemented in the reengineering of an existing system configuration, details of the existing configuration may influence or dictate details of any particular implementation. Accordingly, other embodiments are within the scope of the following claims.