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US-12618619-B2 - Optimized heat exchanger and methods for designing the same

US12618619B2US 12618619 B2US12618619 B2US 12618619B2US-12618619-B2

Abstract

A heat storage system, and systems and methods for designing a heat exchanger system included in the heat storage system are disclosed. The heat exchanger system includes a heat exchanger including a plurality of planar fins parallelly arranged between a first header and a second header, and a plurality of tubes configured to be received in axially aligned holes of the plurality of fins, the plurality of tubes being configured to allow flow of a fluid exchanger fluid. The heat storage system also includes a storage tank comprising phase change material (PCM) for at least partially submerging the heat exchanger within the PCM. A spacing between the plurality of fins is optimized using a finite particle model of the heat exchanger to achieve a performance objective of at least 75% thermal heat discharge from the PCM in about 3 hours.

Inventors

  • JOSEPH D. RENDALL
  • Som S. Shrestha
  • ZHENGLAI SHEN
  • Diana Hun
  • Achutha Tamraparni

Assignees

  • UT-BATTELLE, LLC

Dates

Publication Date
20260505
Application Date
20240322

Claims (9)

  1. 1 . A heat storage system comprising: a heat exchanger comprising: a plurality of planar fins parallelly arranged between a first header and a second header and have a plurality of holes through the fins, subsets of the plurality of holes in the fins being axially aligned; a plurality of tubes configured to be received in the axially aligned subsets of holes through the plurality of fins, the plurality of tubes being configured to allow flow of a fluid exchanger fluid; a storage tank comprising phase change material (PCM), wherein the heat exchanger is configured to be at least partially submerged within the PCM; wherein the number of tubes is less than the number of subsets of axially aligned holes, and wherein a spacing between the plurality of fins and a spacing between the plurality of tubes satisfies the following ratios: fin spacing/tube spacing=0.1 to 0.2; fin spacing/fin thickness=2.3 to 125; fin spacing/PCM conductivity=0.5 to 7.5; and fin spacing (inch)/PCM volumetric latent heat (kJ/m 3 )=0.0000047 to 0.0000006; and wherein the heat storage system discharges at least 75% thermal heat discharge from the PCM in about 3 hours.
  2. 2 . The heat storage system of claim 1 , wherein the spacing is about 0.75 inch to about 0.14 inch.
  3. 3 . The heat storage system of claim 1 , wherein a thickness of each of the plurality of fins is about 0.006 inch to about 0.06 inch.
  4. 4 . The heat storage system of claim 1 , wherein a spacing between the plurality of tubes is about 2 inches to about 4 inches.
  5. 5 . The heat storage system of claim 4 , wherein a diameter of each of the plurality of tubes is about 0.375 inch to 0.16 inch.
  6. 6 . The heat storage system of claim 1 , wherein the spacing is optimized to satisfy at least one of the following ratios: Fins ⁢ spacing tube ⁢ diameter = 0.9 to ⁢ 2 Fin ⁢ spacing ⁢ ( inch ) PCM ⁢ specific ⁢ latent ⁢ heat ⁢ ( kJ kg ) = 0.0042 to ⁢ 0.0006 .
  7. 7 . The heat storage system of claim 1 , wherein the heat exchanger is a vertical finned horizontal tube exchanger.
  8. 8 . The heat storage system of claim 1 , wherein the heat exchanger is a horizonal finned vertical tube exchanger.
  9. 9 . The heat storage system of claim 1 , wherein one or more of the plurality of tubes comprise a twisted tape insert.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application 63/541,009 filed Sep. 28, 2023, entitled “AN OPTIMIZED HEAT EXCHANGER AND METHODS FOR DESIGNING THE SAME”, the entire disclosure of which incorporated herein by reference. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT This invention was made with government support under Contract No. DE-AC05-00OR22725 awarded by the U.S. Department of Energy. The government has certain rights in this invention. FIELD OF INVENTION This application relates to tube and fin heat exchangers, and in particular, to novel fin design for tube and fin heat exchangers and methods of designing the same. BACKGROUND In 2021, US residential buildings consumed 20.8 quadrillion Btu, and commercial buildings consumed 17.0 quadrillion Btu, accounting for 21.8% and 17.9%, respectively, of the total US primary energy use that year. To reduce building energy consumption, building thermal energy loads can be stored to reduce the burden on the electrical grid. These thermal energy storage (TES) systems need to reduce the building energy consumption during peak periods, which are often up to 4 hours long. Building thermal storage has several benefits, including offsetting peak heating and cooling loads, increasing energy efficiency by reducing the mismatch between supply and demand for heating and cooling, and increasing resilience during heat waves. In buildings, cost and footprint are major concerns for the building owners, and the TES systems need to be optimized accordingly. TES systems based on solid/liquid phase change materials (PCMs) have large volumetric latent heat energy storage values, suitable phase change temperatures, and low volumetric changes between phase transitions. However, the energy charge and discharge rates of PCM-based TES systems are severely limited because of their relatively low thermal conductivity. Additionally, even though PCMs have a high energy density, heat transfer in PCMs is complex because the melting and freezing fronts change as functions of stored or released heat, location, and time. PCMs may be used in conjunction with heat exchange systems in order to optimize PCM-based TES systems. However, prior attempts to optimize heat exchangers in one or two dimensions by maximizing the melt and freeze front area often yield fractal geometry which is often difficult to model/optimize, and hence the heat exchangers are expensive to construct. This document describes methods and systems that are directed to addressing the problems described above, and/or other issues. SUMMARY In various scenarios, a heat storage system is disclosed. The heat exchanger system may include a heat exchanger including a plurality of planar fins parallelly arranged between a first header and a second header, and a plurality of tubes configured to be received in axially aligned holes of the plurality of fins, the plurality of tubes being configured to allow flow of a fluid exchanger fluid. The heat storage system may also include a storage tank comprising phase change material (PCM) for at least partially submerging the heat exchanger within the PCM. A spacing between the plurality of fins is optimized using a finite particle model of the heat exchanger to achieve a performance objective of at least 75% thermal heat discharge from the PCM in about 3 hours. Optionally, the spacing is about 0.75 inch to about 0.14 inch. In some implementations, a thickness of each of the plurality of fins is about 0.006 inch to about 0.06 inch. A spacing between the plurality of tubes may also be optimized using the finite particle model of the heat exchanger and, optionally, may be about 2 inches to about 4 inches. Optionally, a diameter of each of the plurality of tubes may be about 0.375 inch to 0.16 inch. In various implementations, the spacing can be optimized to satisfy one or more of the following ratios: i.Fin⁢ spacingtube⁢ space=0.1 to 0.2 ii.Fin⁢ spacingfin⁢ thickness=2.3 to⁢ 125 iii.Fins⁢ spacingtube⁢ diameter=0.9 to⁢ 2 iv.Fin⁢ spacingPCM⁢ conductivty=0.5 to 7.5 v.Fin⁢ spacing⁢ (inch)PCM⁢ specific⁢ latent⁢ heat⁢ (kJkg)=0.0042 to 0. 0006 vi.Fin⁢ spacing⁢ (inch)PCM⁢ volumetric⁢ latent⁢ heat⁢ (kJm3)=0.0000047 to 0. 0000006 The heat exchanger can be a vertical finned horizontal tube exchanger or a horizontal finned vertical tube exchanger. Optionally, one or more of the plurality of fins are perforated. Optionally, one or more of the plurality of tubes may include a twisted tape insert. In various scenarios, systems and methods for optimizing a heat exchanger design for use as heat storage by charging or discharging heat from a PCM are also disclosed. The systems may include a processor and a non-transitory computer readable medium including instructions that can be executed by the processor to perform the methods. The methods may include generating a finite e