Thermal control system

Abstract

A thermal control system with new phase change material (PCM) formulations that are able to maintain the system interior in a temperature range of, for example, −15 to −40° C., for a tunable working period from several hours to approximately half a day, is provided. The composition includes the inorganic and organic materials. The inorganic materials include the inorganic salts and various functional additives; while the organic materials include fatty acids, hydrocarbons and various nanostructures.

Claims

1. A thermal control system comprising an inorganic phase change material and an organic phase change material, wherein: the organic phase change material and the inorganic phase change material are present at a ratio in a range of 1:1 by weight to 1:5 by weight; and the inorganic phase change material comprises a salt and a first additive, wherein the first additive is selected from the group consisting of carbon-based fiber, fumed silica, porous silica, aerogel, and glass sphere.

2. The thermal control system according to claim 1, wherein the inorganic phase change material and the organic phase change material are physically mixed with each other, or wherein the inorganic phase change material forms a first layer and the organic phase change material forms a second layer, whereby the first layer and the second layer are physically distinct from each other.

3. The thermal control system according to claim 1, wherein the organic phase change material and the inorganic phase change material are independently present at a thickness in the range of 5 mm to 3 cm.

4. The thermal control system according to claim 1, wherein the first layer and the second layer are separated by a layer of fluid or are in direct contact with each other, or wherein the first layer is the inner layer and the second layer is the outer layer, or the first layer is the outer layer and the second layer is the inner layer, relative to an item to be cooled, wherein the inner layer at least partially surrounds the item to be cooled, and the outer layer at least partially surrounds the inner layer, and wherein the outer layer and inner layer are of the same temperature or the outer layer is of a relatively lower temperature than the inner layer.

5. The thermal control system according to claim 1, wherein the salt comprises a first metal selected from group 1, group 2, group 7, group 8, group 9, group 10, group 12, or group 13 of the Periodic Table of Elements, and an anion, and wherein the first additive is a nano-sized material, a micro-sized material, or a mixture thereof, or wherein the thermal conductivity of the first additive is in the range of about 0.005 W/(m*K) to about 0.07 W/(m*K).

6. The thermal control system according to claim 5, wherein the inorganic phase change material comprises 5 wt. % to 35 wt. % salt.

7. The thermal control system according to claim 5, wherein the inorganic phase change material comprises: about 70 wt. % to about 80 wt. % water; about 15 wt. % to about 25 wt. % CaCl.sub.2.6H.sub.2O; about 3 wt. % to about 4 wt. % NaCl; about 0.2 wt. % to about 0.7 wt. % porous silica microstructure; and about 0.5 wt. % to about 1.5 wt. % carbon fiber nanostructure, such that the total wt. % of each component adds to 100 wt. %.

8. The thermal control system according to claim 1, wherein the organic phase change material comprises a hydrocarbon and a second additive, wherein the hydrocarbon is an optionally functionalized aliphatic and wherein the second additive is a nano-sized material, a micro-sized material, or a mixture thereof, or wherein the thermal conductivity of the second additive is in the range of about 20 W/(m*K) to 50 W/(m*K).

9. The thermal control system according to claim 8, wherein the organic phase change material comprises about 50 wt. % to about 98 wt. % hydrocarbon.

10. The thermal control system according to claim 8, wherein the organic phase change material comprises: about 65 wt. % to about 75 wt. % C.sub.11H.sub.24 hydrocarbon; about 15 wt. % to about 25 wt. % C.sub.12H.sub.26 hydrocarbon; about 2.5 wt. % to about 7.5 wt. % C.sub.13H.sub.28 hydrocarbon; about 1.5 wt. % to about 2.5 wt. % carbon nanotube; and about 2.5 wt. % to about 3.5 wt. % copper nanoparticle, such that the total wt. % of each component adds to 100 wt. %.

11. The thermal control system according to claim 8, wherein the organic phase change material comprises: about 5 wt. % to about 15 wt. % hydrocarbon selected from the group consisting of C.sub.10H.sub.22, C.sub.11H.sub.24, and C.sub.14H.sub.30; about 25 wt. % to about 35 wt. % C.sub.12H.sub.26 hydrocarbon; about 55 wt. % to about 65 wt. % C.sub.13H.sub.28 hydrocarbon; and about 0.5 wt. % to about 2 wt. % carbon nanostructure; such that the total wt. % of each component adds to 100 wt. %.

12. The thermal control system according to claim 1 comprising: about 35 wt. % to about 40 wt. % water; about 7.5 wt. % to about 12.5 wt. % CaCl.sub.2.6H.sub.2O; about 1.5 wt. % to about 2 wt. % NaCl; about 0.1 wt. % to about 0.35 wt. % porous silica microstructure; about 0.25 wt. % to about 0.75 wt. % carbon fiber nanostructure, about 32.5 wt. % to about 37.5 wt. % C.sub.11H.sub.24 hydrocarbon; about 7.5 wt. % to about 12.5 wt. % C.sub.12H.sub.26 hydrocarbon; about 1.25 wt. % to about 3.75 wt. % C.sub.13H.sub.28 hydrocarbon; about 0.75 wt. % to about 1.25 wt. % carbon nanotube; and about 1.25 wt. % to about 1.75 wt. % copper nanoparticle, such that the total wt. % of each component adds to 100 wt. %.

13. The thermal control system according to claim 1 comprising: about 35 wt. % to about 40 wt. % water; about 7.5 wt. % to about 12.5 wt. % CaCl.sub.2.6H.sub.2O; about 1.5 wt. % to about 2 wt. % NaCl; about 0.1 wt. % to about 0.35 wt. % porous silica microstructure; about 0.25 wt. % to about 0.75 wt. % carbon fiber nanostructure, about 2.5 wt. % to about 7.5 wt. % hydrocarbon selected from the group consisting of C.sub.10H.sub.22, C.sub.11H.sub.24 and C.sub.14H.sub.30; about 12.5 wt. % to about 17.5 wt. % C.sub.12H.sub.26 hydrocarbon; about 27.5 wt. % to about 32.5 wt. % C.sub.13H.sub.28 hydrocarbon; and about 0.25 wt. % to about 1 wt. % carbon nanostructure, such that the total wt. % of each component adds to 100 wt. %.

14. The thermal control system according to claim 1, further comprising a thermally insulating material at least partially surrounding the inorganic phase change material and the organic phase change material.

15. The thermal control system according to claim 14, comprising an inner thermally insulating material which at least partially surrounds the inorganic and organic phase change material, and an outer thermally insulating material which at least partially surrounds the inner phase change material.

16. A method of preparing a thermal control system, the method comprising a step of contacting an inorganic phase change material with an organic phase change material, wherein: the organic phase change material and the inorganic phase change material are present at a ratio in a range of 1:1 by weight to 1:5 by weight; and the inorganic phase change material comprises a salt and a first additive, wherein the first additive is selected from the group consisting of carbon-based fiber, fumed silica, porous silica, aerogel, and glass sphere.

17. The method according to claim 16, wherein the contacting step results in direct contact between the inorganic phase change material and the organic phase change material, or wherein the contacting step comprises the step of bringing the inorganic phase change material and the organic phase change material together with a layer of fluid in between.

18. The method according to claim 16, further comprising a step of at least partially surrounding an item to be cooled with the inorganic phase change material and the organic phase change material, or further comprising a step of at least partially surrounding the inorganic phase change material and the organic phase change material with a thermally insulating material.

19. A method for maintaining a temperature of an item, the method comprising a step of providing a thermal control system comprising an inorganic phase change material and an organic phase change material, wherein: the organic phase change material and the inorganic phase change material are present at a ratio in a range of 1:1 by weight to 1:5 by weight; and the inorganic phase change material comprises a salt and a first additive, wherein the first additive is selected from the group consisting of carbon-based fiber, fumed silica, porous silica, aerogel and glass sphere.

20. The method according to claim 19, further comprising steps of pre-cooling the organic phase change material and/or the inorganic phase change material to a temperature below −15° C., and contacting or at least partially surrounding an item to be cooled with the thermal control system.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

(2) FIG. 1 is a schematic representation showing the difference between individual packing and combined packing of the organic phase change material (PCM) layer and the inorganic PCM layer.

(3) FIG. 2 is a graph showing the differential scanning calorimetry of hydrocarbons (mixture of C.sub.11-C.sub.14)+carbon additives.

(4) FIG. 3 is a graph showing the differential scanning calorimetry of hydrocarbons (mixture of C.sub.10-C.sub.14)+carbon additives.

(5) FIG. 4 is a graph showing the differential scanning calorimetry of NaCl+CaCl.sub.2)+carbon additives+silica-based micro-particles.

(6) FIG. 5 refers to a thermogravimetric analysis image of paraffin wax.

(7) FIG. 6 refers to a thermogravimetric analysis image of tetracosane.

(8) FIG. 7 refers to a photograph image showing the set up for the reliability test for the thermal control system comprising NaCl+CaCl.sub.2)+carbon additives+silica-based micro-particles.

(9) FIG. 8 refers to a graph showing the temperature profile for the thermal control system comprising NaCl+CaCl.sub.2)+carbon additives+silica-based micro-particles.

(10) FIG. 9 refers to a graph showing the temperature profile of hydrocarbons (mixture of C.sub.11-C.sub.14)+carbon additives.

(11) FIG. 10 refers to a graph showing the temperature profile of hydrocarbons (mixture of C.sub.10-C.sub.14)+carbon additives.

(12) FIG. 11 refers to a graph showing the temperature profile of NaCl+CaCl.sub.2)+carbon additives+silica-based micro-particles.

(13) FIG. 12 refers to a graph showing the temperature profile of PCM1+PCM3 thermal control system, where PCM1:PCM3=1:1.

(14) FIG. 13 refers to a graph showing the temperature profile of PCM1+PCM3 thermal control system, where PCM1:PCM3=7:3.

EXAMPLES

(15) Non-limiting examples of the invention will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Example 1: Materials and Methods

(16) NaCl, MgCl.sub.2, KCl, CaCl.sub.2), Na.sub.2SO.sub.4, MgSO.sub.4, K.sub.2SO.sub.4, CaSO.sub.4, NaNO.sub.3, Mg(NO.sub.3).sub.2, KNO.sub.B, and Ca(NO.sub.3).sub.2 were purchased from Sigma Aldrich (St. Paul, Minneapolis, USA) and fatty acids including carboxylic acids of the short-(C.sub.2 to C.sub.12) and long-(C.sub.13 to C.sub.24) alkyl chains were purchased from TCI (Tokyo, Japan). Waxes of short-(C.sub.6 to C.sub.12) and long-(C.sub.13 to C.sub.24) chained hydrocarbons were purchased from Alfa Aesar (Ward Hill, Mass., USA).

(17) Differential Scanning calorimetry (DSC)

(18) Photo differential scanning calorimeter (DSC Q100), TA instruments was used to measure phase change temperature (e.g. melting point) and heat capacity.

(19) DSC measurements were taken as follows: measure out sample between 4 mg-7 mg and place in DSC pan seal pan with the sample encapsulating press place sealed pan into machine key in weight to programme, temperature range (−60° C. to −10° C.), number of cycles (3) run sample analyse generated data to get melting point and heat capacity
Thermogravimetry Analysis (TGA)

(20) Thermogravimetric analyser (TGA Q500), TA Instruments was used to measure the thermal stability of a material (decomposition temperature of the material).

(21) TGA measurements were taken as follows: torch TGA pan tare weight on machine weigh 10-20 mg sample into the pan, by reading off the weight via the computer monitor (means must take out and hang back the pan to check weight until weight is within range) key in temperature range (25° C. to 400° C.) and ram (10-20° C./min) run sample analyse generated data to get decomposition temperature
Datalogger with PT-100 Sensor

(22) Datalogger: GL-840M, Graphtec PT100 sensors: PT-100-5-T, ESEL Pte. Ltd. were used to measure the temperature change during prototype testing.

(23) Datalogger and sensor measurements were taken as follows: connect sensor to datalogger fit sensor to positions to be tested start datalogger stop when desired duration has been tested convert and analyse data

Example 2: Formulations

(24) Inorganic Phase Change Material (PCM) Formulation

(25) In order to enhance the performance of overall cool box system, an inorganic-based phase change material was developed. It comprises an aqueous solution of one or two or multiple salts and different functional additives. The salt concentration was in the range of 10-30% using salts including NaCl, MgCl.sub.2, KCl, CaCl.sub.2), Na.sub.2SO.sub.4, MgSO.sub.4, K.sub.2SO.sub.4, CaSO.sub.4, NaNO.sub.3, Mg(NO.sub.3).sub.2, KNO.sub.B, and Ca(NO.sub.3).sub.2. The functional additives included carbon-based fibers, silica-based nano-sized or micro-sized materials, such as fumed silica, aerogel, glass spheres or others at 0.1%-3% concentration. These ingredients were mixed at different ratios to tune the working temperature or working duration of the phase change material.

(26) In an exemplary formulation, the respective weight of each component as indicated below was mixed and a mechanical stirrer was used to mix the mixture until it was homogeneously blended. Water 100 g NaCl 5 g CaCl.sub.2) 20 g Carbon Nanotube (nanoparticle) 50 mg CaCO.sub.3 10 mg SiO.sub.2 30 mg
Organic Phase Change Material (PCM) Formulation

(27) The organic-based phase change material (PCM) formulations contained fatty acids, wax, or a mixture of both in different portions and other functional nanoparticles. The fatty acids included carboxylic acids of the short-(C.sub.2 to C.sub.12) and long-(C.sub.13 to C.sub.24) alkyl chains. The waxes contained short-(C.sub.6 to C.sub.12) and long-(C.sub.13 to C.sub.24) chained hydrocarbons; the functional nanoparticles was selected from copper-based nanostructures or carbon-based nanostructures. The nanostructures were in the form of nanoparticles, nanotubes or nanorods or a combination thereof. The nano-structures were used to manage thermal regulation. Similar to the inorganic PMC, these ingredients can be mixed at different ratios of each different component to tune the working temperature or working duration.

(28) In an exemplary formulation, the respective weight of each component as indicated below was mixed, heated to 100° C. and a mechanical stirrer was used to mix the mixture for about 1 hour until it was homogeneously blended. C.sub.10H.sub.22, 3.5 kg C.sub.11H.sub.24, 1 kg C.sub.12H.sub.26, 470 g Copper nanoparticle, 5 g Carbon nano fibre 25 g

Example 3: Design of Device

(29) The above PCM mixtures were transferred to a container or bag and tightly sealed. The container or bag was subsequently placed in a freezer which was set to a temperature based on the working temperature range of the PCM. For example, for a working temperature range of −10° C., and if the freezing point of the PCM as tested by DSC (see below) was around −11° C. to −9° C., then the PCM was placed in a −20° C. freezer to freeze.

(30) An appropriate number of containers or bags of frozen PCM were placed in a prototype test box, and the box was closed for testing in a temperature range of: −24° C. to −20° C.; or −18° C.

(31) These testing temperatures were selected based on the temperature ranges that are commonly used in grocery and pharmaceutical logistics.

(32) To achieve better performance, a combination of different phase change material (PCM) formulations can be used, either physically mixed or packed separately as seen in FIG. 1. In FIG. 1, 101 refers to an individual packing design and 102 refers to a combined packing design. In each case, an organic PCM layer (103) which is the top or outer layer (105) in relation to the item to be cooled, acts as a thermal insulation barrier, while the inorganic PCM layer (104) which is the bottom or inner layer (106) in relation to the item to be cooled, acts as a cold sink to maintain interior temperature. The difference between individual packing (101) and combined packing (102) is that in individual packing (101), there is an air gap (107) between the PCM packs which result in heat penetration, which effectively lowers efficiency, whereas in combined packing (102), there is no air gap (108) between the PCM layers, reducing heat penetration and effectively increasing efficiency.

(33) Different types of PCM, for example organic and inorganic PCMs, which may also be eutectic PCMs, may be used in different ratios to produce cold boxes of different working temperature and duration. In fact, for PCMs that are physically mixed together in the packaging, the heat penetration which would be present if PCMs were individually packed are theoretically reduced. The design principle of a dual PCM system having an inner layer and an outer layer relative to the item to be cooled, is that the dual-PCM system can enhance the performance of the thermal control system than any single layer PCM system, as the inner layer stabilizes the temperature so that temperature fluctuation of the system can be further minimized. At the same time, the outer layer is used as a “cold sink” to quench the heat penetration from the outside environment into the inner layer, effectively acting as a thermal-insulation barrier. This dual-PCM design enhances the performance of the thermal control system significantly, especially at an extremely low-temperature range.

Example 4: Performance Evaluation

(34) To determine which PCM is suitable for the thermal control system, the respective PCMs were subjected to the following tests:

(35) Differential Scanning calorimetry (DSC): to determine the melting temperature range and heat capacity of the PCM. The melting temperature range should be within or below the working temperature range of the thermal control system to be considered.

(36) Thermal Gravimetric Analysis (TGA): to determine the decomposition temperature and therefore thermal stability of a material.

(37) Reliability Test: Datalogger with PT100 sensor was used for measurement of temperature change during prototype testing to test how long the frozen PCM takes to reach room temperature. A longer duration would be better.

(38) Simulation Test: packing all contents in the thermal control system and monitoring the temperature profile. This simulates a realistic thermal control system, something that may be used in real-life, and thus would help to assess the feasibility of the PCM system design and assembly.

(39) Differential Scanning Calorimetry (DSC)

(40) DSC was conducted to determine the latent heat and melting point of the PCM. Below are examples of three short listed PCMs:

(41) a) Hydrocarbons (mixture of C.sub.11-C.sub.14)+Carbon additives The formulation was made by stirring a mixture of C.sub.11H.sub.24 hydrocarbons (70%), C.sub.12H.sub.26 hydrocarbons (20%), C.sub.13H.sub.28 hydrocarbons (5%), carbon nanotube (CNT) (2%), and copper nanoparticle (3%) for 20 minutes.

(42) b) Hydrocarbons (mixture of C.sub.10-C.sub.14)+Carbon additives; The formulation was made by stirring a mixture of C.sub.10H.sub.22, C.sub.11H.sub.24 and C.sub.14H.sub.30 hydrocarbons (8-9.5%), C.sub.12H.sub.26 hydrocarbons (30%) and C.sub.13H.sub.28 hydrocarbons (60%), and carbon nanostructure (0.5-2%) for 20 minutes.

(43) c) Sodium chloride+Calcium chloride+carbon additive+silica-based micro-materials. The formulation was made by stirring a mixture of water (75%), CaCl.sub.2*6H.sub.2O (20%), K.sub.2SO.sub.4 (3.5%), porous silica microstructure (0.5%) and carbon fiber nanostructure (1%) for 20 minutes. During this process, a chemical reaction to generate CaSO.sub.4 occurs, which is important for the sustainable performance of the formulation.

(44) The DSC spectrum can be seen in FIG. 2, FIG. 3 and FIG. 4, respectively. The respective phase change temperatures were all found to be within a tolerable temperature range in different containers for the purposes of the thermal control system.

(45) Thermal Gravimetric Analysis (TGA)

(46) From the TGA images of paraffin wax and tetracosane (FIGS. 5 and 6), it can be seen that the decomposition temperature was approximately 200° C. or above, which was significantly higher than the working temperature range of the PCMs. This shows that the PCMs are safe to use without decomposition within the working temperature.

(47) Reliability Test

(48) A reliability test is conducted by freezing a PT100 thermocouple with the PCM in a centrifuge tube, and logging the temperature as the PCM melts at room temperature as seen in FIG. 7 conducted for NaCl. The temperature profile of the melting cycle is as seen in FIG. 8 where it takes about half an hour to reach −8° C.

(49) From the reliability test, it can be seen that the inventive formulation with NaCl takes a longer time to reach room temperature compared to pure water when starting from the frozen state. Thus it is evident that the inventive formulation has better properties than pure ice packs for maintaining low temperature.

(50) Simulation Test

(51) For performance evaluation, various PCMs were placed in a container for the real-life simulated tests. More specifically, several types of PCMs were tested: a) Hydrocarbons (mixture of C.sub.11-C.sub.14)+Carbon additives b) Hydrocarbons (mixture of C.sub.10-C.sub.14)+Carbon additives c) NaCl+CaCl.sub.2+carbon additives+silica-based micro-materials I d) PCM1+PCM3 system

(52) The formulation was made by mixing formulation (a) and formulation (c) for a dual-PCM thermal control system.

(53) The temperature profile can be seen in FIG. 9, FIG. 10, FIG. 11, FIG. 12 and FIG. 13.

(54) It was therefore shown that the inventive formulations can act as PCM coolants at a working temperature in the range of −20 to −24° C. and for a duration in the range of 3 to 10 hours.

INDUSTRIAL APPLICABILITY

(55) The thermal control system may be useful in cold chain transport, especially in the pharmaceutical industry. The thermal control system may be useful in expanded polystyrene boxes or polyurethane boxes for maintaining the temperature of the item to be cooled below a desired temperature. The thermal control system may be useful in transporting agricultural produce, seafood, frozen food, photographic film, chemical reagent, enzyme, protein, and pharmaceutical drugs that require cold chain transport. The thermal control system may also have potential applications in green buildings, electronic cooling devices and heat sinks.

(56) It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.