| What is a Low Temperature Application? Generally speaking a low temperature application is one where a perishable product needs to be kept at or below 0° C (or 32° F) for a specified shipment period. What Distinguishes Airliner from Other Modes of Packaging Insulation? There are three distinct modes of heat transfer: Conduction, Convection, and Radiation. Alternate insulation materials commonly used in the marketplace such as polystyrene (eps), polyurethane, and high-density fiberglass rely upon their solid mass to restrict heat flow by the physics of conduction. Airliner, on the other hand, is an inflatable insulating liner that converts a corrugated shipper into a cooler. It is manufactured from HDPE and LDPE inner and outer poly films with interior baffle films made from metalized poly film. An inflated AirLiner has a very low conductive rate and inhibits heat flow with this internal radiant barrier technology. Therefore, its mass consists mainly of the gas used for inflation. Low Temperature Thermodynamics The patented technology and geometry inside of AirLiner products forces the mode of heat transfer to be predominantly radiant heat flow. AirLiner, when inflated, has a structure composed of internal radiant barriers to inhibit heat flow. This radiant heat transfer across the baffles of AirLiner is calculated using a standard version of the Stefan-Boltzman Law for two infinite planes with σ = 5.669 x 10-8. Q = σ[(T2 + ΔT1,2)4 iV (T2)4]  (1/£`1 + 1/£`2) Where: Q = Heat Flow A = Area of the baffle cavity £`1 = emissivity of the hot face £`2 = emissivity of the cold face T1 = temperature of the hot face T2 = temperature of the cold face |
Dry Ice Usage and Reduction!
In most low temperature shipment applications, the Stefan Boltzman Law effectively explains why AirLiner reacts to dry ice differently than alternate packaging methods. In order to minimize this effect, when packaging with dry ice, Cold Pack System recommends that the dry ice be wrapped or bagged in a simple bubble wrap pouch prior to its placement in the AirLiner. Because the bubble wrap acts as an insulator, this effectively reduces the ΔT inside of the AirLiner while extending the duration of the dry ice. The use of the bubble wrap bag also has the added safety benefit of protecting your customers from the extreme cold temperature of the dry ice. In several instances, low temperature application AirLiner customers have successfully reduced the amount of dry ice used in their packaging protocol! Alternate Refrigerants AirLiner can be used with all types of frozen refrigerants. These consist mainly of dry ice and frozen gel packs. While dry ice remains the standard refrigerant for shipping frozen or low temperature products, Cold Pack System has several customers that prefer to use gel packs. Because of the radiant barrier insulation of AirLiner products, our customers can use low eutectic (-12° C / +10°F) gel packs. These same customers found that by switching to a smaller quantity of low eutectic gel packs (from the typical +30° F gel packs) they gained a cost and convenience advantage of longer transit while still maintaining the ideal temperature. The amount of refrigerant to use in a package is dependent upon the mass of the product, duration of the transit and the temperature range of the product. Testing with AirLiner can precisely determine the optimum amount of gel packs. Cold Pack System now offers a variety of gel packs. Please see our gel pack options or contact your representative for more details. Insulated Package Testing Recommendations When testing AirLiner there are several key parameters to ensure a valid test: 1. The control box (current packaging) and the AirLiner must be as similar as possible in size, amount of product, amount of refrigerant and amount of void space. 2. Temperature-recording devices should be used and can be provided to you by Cold Pack System. When using such devices it is imperative that they are placed on or in the product being tested, not on the packaging. 3. Each test package should be placed in the same ambient environment. The ambient temperature should be recorded as well. 4. Each package should be loaded the same way; we suggest that the refrigerant always be placed on the top. When using dry ice we have found, by thorough testing, that the best results are achieved when dry ice is first placed in a bubble pouch to achieve a slower rate of sublimation (link to Dry Ice Usage and Reduction). Use of this pouch may allow you to use less dry ice in AirLiner due to its radiant barrier technology and insulation. 5. AirLiner should be filled to proper pressure prior to beginning the test. 6. The test duration should be equal to the normal shipping time for your product. Following these simple testing protocols will help ensure that you achieve the most accurate test results. |