Abstract:
For high reliability through redundancy, in a thermal chamber, heat exchange tubes are configured in multiple parallel runs. Typically three tubes are attached side-by-side in a strip which is formed into folded-back horizontal rows to be built into or attached to the walls of the chamber. In a freezer, each tube can serve independently as an evaporator when connected to a compressor/condenser source. Versatile source interfacing is provided by two valve-manifold routing units, one at each end of the multi-tube strip, enabling easy tube substitution in case of failure, as well as facilitating source-swapping, networking, defrosting and refrigerant operations such as purging, flushing, replenishing, changing or replacement, all without interrupting the required cooling process or affecting the chamber temperature. The multi-tube strip and valve-manifolds enhance the reliability of thermal systems such as ultra-low temperature biomedical freezers entrusted with critical at-risk payloads, and assist owner-operators in maintaining such systems fully operational with minimal need for outside repair expertise.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of heat energy exchange apparatus including thermal chambers and caloric sources thereof including refrigeration, and is more particularly directed to thermal chambers with high reliability obtained by providing flow path redundance in the thermal exchange structure and versatile control of associated flow rerouting, e.g. in the evaporator tubes and associated source interconnections of an ultra-low-temperature freezer for storing critical temperature-sensitive and/or potentially harmful substances in facilities such as biomedical laboratories where high reliability is essential. 
     BACKGROUND OF THE INVENTION 
     There is an increasing demand in the field of the invention for ultra high reliability thermal apparatus, especially ultra-low-temperature freezers used for storing biomedical substances. A refrigeration failure in the commercial food field can be costly in terms of food spoilage and business disruption. However such failure could be catastrophic in the biomedical field; for example if it involved a limited supply of special vaccine, stored for emergency protection of the general public, lack of immediate repair or refrigerated transportation to another site of a cooling chamber facility pending corrective action could result in a disastrous total loss of the vaccine. Refrigeration failure involving toxic substances can cause personal damage and/or set off alarms that require immediate and total building evacuation. On-site personnel rarely have the expertise to take the corrective action, so there is a critical dependancy on prompt expert response in such failures. 
     The functional process of cooling in refrigeration takes place in the evaporator, which is typically implemented as tubing built into the walls of the low-temperature chamber. Refrigerant entering the evaporator in liquid state at an end of the tubing “boils” or evaporates, changing state from liquid to gas, thus consuming heat energy and producing the cooling effect. The gas is drawn out from the opposite end of the tubing, recompressed and condensed back to liquid state in a continuous loop process. 
     In a common evaporator failure mode, experienced frequently in automotive air-conditioners, heaters and radiators, a pinhole leak in the tubing itself, or at a fitting, causes loss of refrigerant or other fluid medium and this cumulative loss soon degrades the thermal process and leads ultimately to total failure, meanwhile possibly contributing to pollution from the escaping gas: in the automotive case, environmental air pollution, and/or, as in the cooling chamber case, exposing the valuable payload of critical protected substances to possible contamination. 
     The term “chamber” in the present disclosure is intended to mean any thermal chamber, ranging from ultra-low temperature freezers to warming/heating chambers, in which typically it is desired to maintain substantially constant internal temperature, independent of ambient temperature and variations thereof, by circulation of a fluid thermal agent through a heat-exchanger, typically tubing located in or near the walls of the chamber 
     DISCUSSION OF KNOWN ART 
     It has been known to seek improved reliability in a heat exchange type structure such as an evaporator by providing redundancy in the form of a secondary backup unit or element that can be substituted to operate in place of the primary unit or element. 
     Permanently connecting multiple runs of tubing in parallel, as practiced commonly in automobile radiators, heaters and air conditioners and the like, increases the cross-sectional area and thus reduces the probability of flow restriction, however the risk of developing leakage increases with multiplicity, reducing the overall reliability. 
     U.S. Pat. No. 5,440,894 to Schaeffer et al for STRATEGIC MODULAR COMMERCIAL REFRIGERATION discloses a commercial refrigeration network with a plurality of multiplexed compressors, condenser and associated high side and low side refrigerant delivery and suction conduits and including a remote cooling source. 
     U.S. Pat. No. 6,490,877 to Bash et al for MULTI-LOAD REFRIGERATION SYSTEM WITH MULTIPLE PARALLEL EVAPORATORS discloses the principle of independently metering the flow of refrigerant into each of a plurality of evaporators for the purpose of maintaining constant temperature despite heat load fluctuations. 
     U.S. Pat. No. 5,947,195 to Sasaki for MULTI-TUBE HEAT EXCHANGER AND AIR CONDITIONER HAVING THE SAME discloses a multi-tube heat exchanger including a pair of tanks and a large plurality of heat transfer tubes fluidly interconnected between the tanks for reducing the size of the heat exchanger and the associated air conditioner for vehicles, with air flow directed in either direction between a single duct and a plurality of branched ducts. 
     OBJECTS OF THE INVENTION 
     It is a primary object of the present invention to provide increased reliability in a thermal exchange structure such as a refrigeration evaporator in an ultra-low-temperature chamber of the type used for storing and preserving biomedical substances. 
     It is a further object to attain high reliability by providing redundancy and ease of substitution in the tubing structure of an evaporator in the event of leakage. 
     It is a further object to provide flexibility in deployment of redundant tubing sections in the evaporator to offer alternative configurations to satisfy differing needs and situations. 
     It is a further object to provide interface hardware units structured to facilitate manual and automatic redirection of refrigerant to redundant sections in the evaporator as well as capability of source-swapping, thus providing high system reliability through total redundancy that can be readily deployed by non-expert owner-operators without disruption or impairment of system operation. 
     SUMMARY OF THE INVENTION 
     The foregoing objects have been met in the invention of a thermal tubing structure that provides a thermal exchange system, such as an evaporator, with multi-tube redundancy for high reliability in a thermal chamber such as a freezer. 
     A cluster of parallel multiple continuous-length tubing runs, typically three tubes attached side-by-side, is formed in a manner to be built into the walls of the chamber or attached to a false plenum lining the inside walls of the chamber. The tube ends are fitted with a pair of versatile valve-manifold units, one at each end, that provide versatility for interconnecting to the associated thermal source(s) such as a compressor/condenser unit, with capability of rapid automatic rerouting to another tube in case of failure of any one of the tubes. 
     For ultra-low-temperature freezers such as those for storing bio-medical materials, the multi-tube evaporator of the present invention facilitates operations such as defrosting and refrigerant operations such as purging and replacing refrigerant, or flushing with a cleansing fluid without interrupting the required cooling process. 
     The multi-tube evaporator and valve-manifold system enhances ultimate reliability for low temperature systems entrusted with critical at-risk payloads, and enhances an inexpert owner-operators capability of keeping such systems operating within specification with a minimum of requirement for outside expert assistance, thus avoiding the costs, uncertainties and other disadvantages of reliance on outside experts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and further objects, features and advantages of the present invention will be more fully understood from the following description taken with the accompanying drawings in which: 
     FIG. 1 is an isometric representation of a triple-tube thermal exchange system of the present invention, in an illustrative embodiment thereof, deployed in a thermal chamber. 
     FIG. 2 is a functional diagram of a valve-manifold unit of the thermal exchange system of FIG.  1 . 
     FIG. 3 is a functional block diagram showing a thermal exchange system of the present invention as in FIG. 1 with the triple-tube strip deployed as an evaporator along with a pair of valve-manifolds set as in FIG. 2, in a dual-redundancy refrigeration system. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is an isometric representation of a thermal tubing structure  10  representing an illustrative embodiment of the present invention that can serve as the heat exchange element in a temperature chamber, e.g. the evaporator in the refrigeration system of an ultra-low-temperature freezer of a type utilized for bio-medical material storage. 
     A multi-tube strip  12 , in this example made from three tubes attached in parallel in a vertical row, is configured to extend in horizontal rows with U-shaped end-returns, as shown, extending around three sides of a chamber  14  whose outline is indicated in dashed lines. 
     In a typical original system installation, strip  12  would be built into the hollow walls of thermal chamber  14  and backed with thermal-insulation around the outside of strip  12 . 
     Alternatively, a thermal exchange unit of the present invention can be installed around the inside walls of a pre-existing thermal chamber, supported in place by a plenum structure, to function in cooperation with, or in place of, an existing built-in thermal exchange (e.g. evaporator) unit. 
     Strip  12  is typically fabricated by pre-forming the individual tubes to the required size and shape, and then fastening them together at selected intervals, e.g. by soldering, welding, brazing, strapping, adhesives and/or other fastenings. The tubing can be of selected metal such as stainless steel or copper. 
     As an alternative to pre-forming the tubes individually in a three-dimensional pattern they could be pre-attached together into a continuous two dimensional ribbon strip that can be stocked and transported in a large long roll, then later cut to total lengths and formed as required in rows for different sized chambers. For three-dimensional forming, the pre-attached ribbon strip could be readily bent as shown in FIG. 1 at the rear corners of chamber  16 , however at the front edges, due to the length variations resulting from the three different radii involved in the flat one-dimensional U-shaped bends as shown, the ribbon strip would have to be reshaped with a 180 degree twist or other viable three-dimensional reformation in the region of each of the U-shaped bends in order to accommodate the uniform tubing lengths in the pre-attached ribbon strip. 
     The three tubes making up strip  12  are connected at their respective ends to valve-manifolds  14 ′ and  14 ″, one at each end of strip  12  as shown, serving as versatile network distribution routers and shut-off interrupters which are in turn typically connected via external low and high pressure lines to at least one refrigeration source which typically includes a compressor and condenser unit that converts gas from the upper end of strip  12  of the evaporator back to liquid state for recirculation into the lower end of strip  12  in a loop process. This source unit can be remotely located. 
     FIG. 2 is a functional diagram of a valve-manifold  14 , typical of either one of the two identical valve-manifolds  14 ′ and  14 ″ shown in FIG. 1, which are connected one at each of the two opposite ends of strip  12 . 
     Valve-manifold  14  is configured with  5  ports: tube ports A, B and C, for connection to ends of the corresponding three tubes in strip  12 , and tube ports E and E, which are source ports. At least one of these source ports in each valve-manifold ( 14 ′ and  14 ″ FIG. 1) is to be connected to a corresponding source line, e.g. one to the low pressure/suction compressor intake and the other from the pressure condenser output of the primary refrigeration source unit. The other source ports, one in each valve-manifold  14 , being available for connection to a secondary source, other special function, or simply held in reserve as a standby. 
     The six valves  16 A- 16 F each provide an on/off (open/closed) function that can be implemented with a rotating ball or cylinder core in well-known fluid valve structure. They could be of a basic manually-operated type, however for automatic control and networking, such valves are available equipped with electrical, hydraulic or pneumatic actuators. As a matter of design choice in the control system, automatic operation could be allowed to override manual settings, or manual settings could be allowed to override the automatic operation. 
     Valves  16 A and  16 D are shown set to their on (open) state; valve  16  places the active tube port A in fluid communication with its source port D, and valve  16 D places tube port B in fluid communication with source port E, available for a variety of auxiliary functions such as connection to a secondary source unit. 
     Valve-manifold  14 , representing the two identical valve-manifolds  14 ′ and  14 ″, can be custom manufactured as a solid or laminated metal block machined to provide the necessary passageways and valve cavities with suitable valve cores inserted accordingly; alternatively valve-manifold  14  can be fabricated utilizing commercially available valves interconnected by tubing or pipe in a known manner. 
     FIG. 3 is a functional block diagram showing a triple-tube thermal exchanger  10  the present invention as in FIG. 1, deployed as the evaporator in a refrigeration system that benefits from the high reliability accomplished by independent triple-tube redundancy along with independent dual-source redundancy. A primary and a secondary system each utilize a corresponding single tube of the triple-tube strip  12 , leaving the third tube as a backup substitute evaporator available to either system in the event of an evaporator failure. 
     The valves in valve-manifolds  14 ′ and  14 ″ are set as shown in FIG.  2 . In the primary system, the refrigerant flows in the following loop path as indicated by the arrows: in liquid state under pressure from condenser  18 ′ through high pressure line  20 ′ to port D of valve-manifold  14 ′, which is set to direct the liquid via source port A into the upper tube at the lower end of strip  12 ; in flowing through the evaporator tube, the liquid. state refrigerant evaporates and causes cooling. The resultant gas state refrigerant reaching valve-manifold  14 ″, at the upper end of strip  12 , is directed via tube port A, through the open top valve and via source port D into low pressure/suction line  22 ′ which conducts the gas state refrigerant into compressor  24 ′ where it is compressed and forced into condenser  18 ′ for cooling and conversion back to liquid state to complete the cycle in the continuously recirculating loop process. 
     In this example, for illustrative purposes, the secondary source is a duplicate of the primary source, utilizing the middle tube in strip  12  as the evaporator, connected in the same manner and for the same refrigerant flow direction as in the primary system, reserving the third (bottom) tube as the backup. 
     The secondary system operates in the same manner as described above for the corresponding components in the primary system, with fluid flow in the following loop path as indicated by the arrows: in liquid state under pressure, from condenser  18 ″ through high pressure line  20 ″ and source port E of valve-manifold  14 ′, through the open valve (fourth down from top) to tube port C, which is connected to the middle tube of strip  12 , wherein gas at it its upper end enters valve-manifold  14 ″ at tube port C, flowing through the open valve (fourth down), to source port E (valve-manifold  14 ″), via low pressure/suction line  22 ″ to compressor  24 ″ and back into condenser  18 ″, reconverted to liquid state. 
     The dual sources could be made identical and utilized equally, e.g. time-shared alternately for designated equal time periods, with each serving as backup for the other. Optionally, the time-sharing could be made unequal, or the primary source could be utilized continuously, reserving the secondary source as the backup for emergency or unusual demand. 
     As another option, the secondary source could be made different from the primary source for a special type of standby system, for example one that would normally not run continuously or one that is designed for a different refrigerant or temperature range. 
     In addition to the dual-source system described above, the versatility provided by the triple-tube evaporator  10  and the valve-manifolds  14 ′ and  14 ″ of the present invention enables the configuration of numerous single-source arrangements including: 
     (a) A simple single-tube normal thermal operation of any kind wherein one of the three tubes is selected as the normal operating tube and the other two tubes are held in reserve as standby so that either of them stands ready to replace the normal operating tube in the event of a leakage failure. 
     (b) As in (a) but with two tubes selected for operation in parallel while the third tube is held in reserve as replacement standby in the event of a leakage failure in either of the other two operating tubes. 
     (c) All three tubes could be operated simultaneously in parallel by setting all six valves to the on (open) state. 
     While the illustrative embodiment is shown utilizing three tubes attached side-by-side in a row, and shaped so as to remain located generally in three flat planes corresponding to chamber walls, the invention could be practiced with more than three tubes, and/or they could be arranged other than in a row, for example in a multi-tube cluster of a radial array. 
     The exemplary configuration of valve-manifold  14  shown allows any one, two or all three of the tubes in strip  12  to be connected to the high and low pressure lines  20 ′ and  24 ′ of the primary source; optionally one or two tubes, if made available, could be redirected out of the main source and connected to an auxiliary source for purposes of backup cooling/refrigeration or for other special operations that may seek to introduce temperature variations, e.g. for accelerated cooling, heating or defrosting. 
     The redirecting and control principles described above can be extended to a network of refrigeration system elements including a plurality of evaporators/chambers and/or source (compressor/condenser) units, which can be co-located or remote and can be flexibly interlinked by additional master/slave valve-manifold units under centralized control. 
     The principle of the invention can be practiced in connection with practically any thermal exchanger and/or chamber regardless of intended operating temperature range, wherein fluid is circulated through tubing to absorb or dissipate heat and/or to develop and/or maintain a desired temperature in a thermal chamber, ranging from ultra-low freezers to warming/heating chambers. 
     The invention may be embodied and practiced in other specific forms without departing from the spirit and essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description; and all variations, substitutions and changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.