WHITE PAPER April 2017 All that glitters… may not be an effective cargo cover in all situations
How the properties of cargo covers affect their performance in real exposure conditions.
Dr. Steve Brabbs, Dr. Srinivas S Cherukupalli, Lawrence M Knorr, Alain Weimerskirch E.I. DuPont de Nemours & Company
Background Properties important for passive thermal covers During most stages of the journey of a pharmaceutical ship- It is likely that cargo will be exposed to ambient temperatures ment, the external environment can, at least in principle, be outside the acceptable range during breaks in the cold-chain, maintained at a temperature which will not be deleterious to so it is important for a cover to separate the goods from the the efficacy of the product, be that in a temperature controlled external environment; i.e. when the temperature of the outer warehouse, a reefer truck or container, the refrigerated hold surface varies, the resulting temperature gradient across the of a ship or in the cargo hold of an aircraft. If temperature cover should not result in a significant heat flow through deviations occur in these areas, they can usually be resolved the cover. This insulation property is most usefully expressed by improvements in infrastructure, procedures, training and in terms of the thermal resistance or ‘R-value’, with units communication of handling requirements down the chain. m²K/W. R-value is the temperature difference across the Much progress has been made in improving best practice for cover which will cause a heat flow of 1 W through 1 m² of temperature controlled pharmaceutical shipments and today, surface, and it can be calculated by dividing the thickness of most would agree that while cold-chain breaks still happen, the cover (in m) by the thermal conductivity (in W/mK) of they occur more often than not during handover from one the material from which it is made. A higher R-value means controlled environment to the next. Examples would be dur- the cover can maintain a higher temperature difference and ing loading or unloading of an aircraft, charging a load into still have a low heat flow. Of course, if there is a temperature a reefer truck at a warehouse dock, or during the last mile difference, heat will always flow to equalize the temperatures, delivery to smaller pharmacies or clinics. The common factor so with any cover the load temperature will eventually reach in these handovers is that the cargo must be moved outdoors the outside temperature. However, if heat flow is low, this for a time, so the external conditions may well be outside the process is slowed, so a higher R-value translates into a longer specified range for the product in question. exposure time before the cargo temperature goes outside the Shippers use a variety of solutions to mitigate the effects of allowed range. uncontrolled external conditions, including powered contain- But how is heat transferred between the external environment ers with autonomous heating and cooling systems, or insulat- and the outer surface of the cover? One mechanism is by direct ing box systems equipped with phase change materials to help contact with the hot or cold air surrounding the cover, but maintain a stable internal temperature. For Controlled Room unless wind speeds and/or temperature differences are very Temperature (CRT) shipments, a common risk management high, this convective heat transfer is relatively weak because air solution is a cargo cover or cargo wrap fitted over the pallet to is a rather poor heat transfer fluid. isolate it from the external environment. In selecting such cov- ers, shippers must understand the specific risks of the intended A second heat transfer process is direct emission or absorption shipping route and how the covers will respond to those risks. of radiation by the outer surface of the cover. Many covers This article describes a study conducted to compare different attempt to minimize this using aluminum foil or a polymer types of covers in controlled but realistic exposure conditions, film coated with a thin layer of aluminum to provide a shiny, to better understand the relationship between cover proper- metallic surface having a low emissivity. Instruments used ties and real-world cover performance. to measure emissivity operate at wavelengths of 8000 nm or greater, so emissivity values are useful in assessing radi- clear day, direct solar radiation can easily reach a radiant flux ant absorption or emission in this far infra-red region of the of around 1200 W/m2. However, the surface temperature spectrum. The peak wavelength of thermal emission from an of the sun is of the order of 5500°C, which means that the object, λmax, may be estimated using Wien’s law: peak wavelength for its emitted radiation is about 500 nm,
λmax = b/T in the visible part of the spectrum. This is very much what is observed in the solar spectrum measured at ground level. As where T is the temperature in kelvin and b = 2.898 x 10-3 mK. For can be seen in Chart 1, the peak in radiant energy in sunlight is a CRT cargo with a temperature around 20°C the peak emis- far from the infra-red wavelengths used in emissiviometers, so sion wavelength should be about 11000 nm so a low emis- a low measured emissivity does not predict that a material will sivity cover will reduce the rate of cooling by radiation if the load is placed in a cold environment. In a hot environment, have low absorption of solar energy. For this, high reflectance incoming thermal radiation comes from the ground and in the visible and near infra-red is a more useful parameter, from nearby objects which could have temperatures as high because the more of this incident energy is reflected back into as perhaps 80°C which corresponds to a peak wavelength the surroundings, the less can be absorbed. of about 8200 nm. Again, if the cover has a low emissivity, Experimental absorption of these wavelengths coming from the surround- Reflectance was measured for electromagnetic radiation of wave- ings will be poor and the rate of heating will be reduced. lengths in the range of 400 nm – 1050 nm, covering visible and As most cold-chain breaks occur outdoors, a source of radiant near-IR wavelengths, using a Hunter Lab Ultra Scan ProD65 energy which cannot be ignored is, of course, the sun. On a instrument. ASTM E1331 standard was followed for these tests.
Chart 1- Solar Irradiance at Earth's Surface Source - US National Renewable Energy Laboratory 1,75
ASTM G173-03 Reference 1,50 Spectrum
1,25
1,00
0,75
0,50
0,25 VISIBLE INFRA-RED
0,00 250 500 750 1000 1250 1500 1750 2000 2250 2500 Wavelength nm
2 Thermal conductivity was measured according to ASTM so the variety of covers in use today reflects different com- C518 using a 30 cm x 30 cm sample held between the plates promises between all these aspects. The cargo covers selected of a Netzsch HFM 436/3 Lambda instrument with a tem- for this study were representative of different structures used perature gradient of 20⁰C and the top plate maintained at to protect CRT pharmaceutical shipments. They included 25⁰C. Heat flow from the hotter surface to the cooler surface a metallised film laminate, two examples of covers based on through the sample was measured until equilibrium was metallised bubble wrap, a multi-layer metallised thermal blan- attained. Thermal resistance (R-value) was then calculated ket and white, single side metallised Tyvek® non-woven covers as the sample thickness divided by its thermal conductivity. with and without an inner insulating layer. They were selected For thin samples (<3 mm thickness), a transient plane source to cover a range of R-values, reflectivities and emissivities and (TPS) in-plane thermal conductivity value was measured their measured properties and descriptions are summarized in using a Hot Disk TPS 2500S instrument with a 5465 sensor, Table 1. and the resulting R-value was calculated in the same way. Emissivity was analyzed using a Devices & Services Co., Model AE1 instrument and calibration was achieved by mea- suring emissivity of standard black and white body samples. ASTM C 1371 was used as the reference standard for these tests. Selection of cover types tested While the primary purpose of a passive thermal cover is ther- mal protection, there are other characteristics which must be considered by users. Weight, bulkiness, and flexibility will impact on ease of use, storage, and shipping. It is desirable for a cover to provide adequate protection from rain, snow, dust, and other contamination, and recycling and sustainability may also be considerations. Cost is, of course, an important factor
Table 1 – Measured properties of covers used in the trial
Reflectivity Thermal conductivity R-value Emissivity Sample 400 - 1050 nm 2 Description W/mK m K/W %
ML1 82.0 3.2* 0.0001 0.03 Metallised laminate
White Tyvek® 0.14/0.45 W20 93.4 1.2* 0.00014 non-woven, in/out metallic layer inside.
Metallised MBW1 84.6 0.0419 0.155 0.06 bubble-wrap
Metallised MBW2 79.9 0.0400 0.190 0.16 bubble-wrap
White Tyvek® non-woven, W50 91.3 0.0326 0.267 0.45 metallic layer + insulation fleece.
MTB1 75.0 0.0326 0.447 0.37 Metallised thermal blanket
*conductivity measured by TPS method
3 Chart 2 below compares the reflectivity spectrum of the white at the location of each logger, and two additional temperatures Tyvek® W20 cover compared to that of the MBW2 cover, from separate locations under the cover, with the possibility to measured over the wavelength range from 250 to 2500 nm. download data via the USB extension cable without disturbing The reflectance spectrum of MBW2 is typical of all the metal- the load or removing the covers being tested. The sensors were lised covers tested. Comparison with the solar spectrum in distributed through each pallet in identical locations shown Chart 2- Spectral Reflectivity of Cargo Covers 100
95
90
85
80
75
Reflectvity (%) 70
65
60 Tyvek® W20 MBW2 55
50 250 500 750 1000 1250 1500 1750 2000 2250 2500 Wavelength nm
Chart 2 shows that the white Tyvek® cover has higher reflectiv- in Diagram 1 below, so that temperatures were recorded from ity where the solar spectrum is most intense in the visible and fifteen separate positions within the load. During outdoor near infra-red part of the spectrum, while the silver-coloured exposure, the pallets were placed with the same face always ori- MBW2 has higher reflectivity at longer infra-red wavelengths. ented southwards as shown. Inside the boxes at ten positions Simulated CRT loads (extreme corners, the middle of the top face, and the center of the south face), a remote temperature sensor was placed in a Identical pallets were constructed to simulate a low thermal 10 ml vial of isopropanol to approximate measurement of the mass pharmaceutical load of approximately 100 kg. Eighteen product temperature. This was chosen to provide good ther- single walled, 15” cube cardboard boxes were stacked on mal contact with the temperature probe, uniform temperature standard wooden pallets in three layers of six boxes per layer. inside the vial through mixing and because isopropanol would Eleven 500 ml bottles of drinking water were placed in each remain liquid over the whole range of temperatures foreseen. box to give a total of 198 bottles, or 99 kg of water distributed Isopropanol is also relatively safe to handle and has a lower throughout the load. Onset Hobo U12-013 data loggers were specific heat capacity (2.68 J/g°C) than water-based pharma- used to record temperature and relative humidity during each ceutical formulations so is a conservative choice in this regard. trial run, and each logger was equipped with two TMC6-HD remote temperature probes and a USB interface extension cable leading to the outside of the pallet. This allowed simulta- neous recording of one temperature and air relative humidity
4 Diagram 1 - Positions of data loggers and orientation to compass directions. Corner locations 1, 2, 3, 4, 8, 9, 10, 11, top face location 6, and south face location 5 indicate temperature probes in 10 ml vials of isopropanol. Locations 7 (top center, under cover), 12 (south facing, high), 13 (south facing low), 14 (core), and 15 (north facing middle) are air temperature measurements. The following photographs illustrate the construction of the test pallets. Top Corners
Top Face
South Face Air High Bottom Corners
South Face Air Low
After building all the pallets as described, each was protected were equilibrated in a controlled, air-conditioned warehouse with a different type of cover according to the manufacturers’ having a temperature of 20-22°C. The test pallets were con- instructions. Note that in both tests discussed, no base was used structed in this warehouse and were maintained at this tem- between the boxes and pallet. perature before and between tests for a sufficient time to ensure Exposure tests all the loggers on all the pallets were at a uniform temperature, Internationally recognised standard protocols could not be fol- within a range of ±1°C. lowed as the purpose of our experiments was to explore factors For high temperature experiments without solar exposure, a not covered in such standards as exist in this area. All test pallets heated container was constructed using a Carrier Tansicold Elite 5 Chart 3 - Temperature uniformity of 40°C container during 8 hour test
Line Model 69NT40-531-01 insulated refrigerated container loading area outside the temperature controlled warehouse was connected to a loading dock of the warehouse. Data loggers used. This was located in Miami, Florida, USA (25.8°N) where were attached to the floor and walls to monitor temperature high temperatures and strong sunshine are to be expected in the stability and uniformity. The distribution of hot air through summer months, and the trials were carried out on predomi- the container was initially found to be uneven and the capacity nantly clear days in August 2016. This solar exposure area was of the heating units was insufficient to achieve the 40°C target. south-facing and not overlooked by buildings or other objects Plywood was placed on the bottom of the container to cover which could shade any part of the test area during the test. After the floor air channels for the majority of their length in order re-conditioning at 20°C, the test pallets were moved to the out- to direct air towards the door end, and mobile, closed loop door test area shortly before noon to simulate a ramp handling controlled electrical heaters were installed to boost heating event at a tropical airport during the part of the day when solar capacity. In this way, more uniform spacial temperature distri- exposure is strongest. The pallets were placed well apart (at least bution at the target temperature was achieved. twice the pallet height) to ensure that one pallet could not cast a To conduct the trial, test pallets conditioned at 20°C in the air shadow on its neighbour during the test. After approximately 4 conditioned warehouse were moved into the heated container hours exposure, the pallets were returned to the air conditioned in an operation lasting about 10 minutes, the container doors warehouse and stored overnight. The data from the loggers was were closed and the trial was left to run for eight hours. There then downloaded using the previously installed USB exension was a dip in temperature especially near the floor when the doors cables. During the solar exposure a portable weather station were opened for loading, but this was short relative to the dura- (Onset Hobo U30 NRC with upward and downward facing tion of the test. At the end of the 40°C exposure time the pallets Kipp & Zonen SMP3-A pyranometers) was set up adjacent were returned to the air conditioned warehouse overnight and to the test area to record direct and indirect solar intensity, then the logger data was downloaded via the extension cables, wind speed and air temperature during the test. Data from the allowing the covers to remain in place and minimizing handling. weather station are summarised in Chart 4 below. For high temperature exposure with solar radiation, a concrete
6 Chart 4 - Weather station data collected during solar exposure trial
As can be seen from the chart, the sky was clear during most of the analysis presented here, all data from positions within the the trial, with only five brief dips in solar intensity when clouds pallets which showed anomalous behaviour. While the results passed in front of the sun. The peak solar intensity reached should be regarded with some caution, the overall pattern is about 1100 W/m2. The air temperture ranged between 34°C consistent and the data presented here have been selected to and 37°C and the average wind speed was below 1 m/s, with illustrate this. gusts just exceeding 4 m/s. The following charts show the results from the data loggers Results recorded during exposure of the pallets to temperatures above In the heated container trial, in many cases the top corner log- the 15-25°C CRT range, with and without solar exposure, gers recorded the highest rate of temperature incease, followed from data loggers recording air and simulated product tem- by the top centre, then the sides, then the bottom corners and perature in the top of the box in the middle of the top face, and lastly the centre of the pallet. This is what would be expected, simulated product temperature in the outer face of the box given that heat will flow most quickly to loggers which are in the middle of the south-facing side of the pallet. The data close to outside exposed surfaces and that hot air will tend to presented here were obtained using the equipment and in the rise under the pallet cover. However, some pallets displayed specific experimental conditions described above, and should anomalies in temperature distribution which we believe to not be taken as universally applicable. It is advisable for users of have been caused by air currents enterning the bottom of cargo covers to conduct their own investigations under condi- the pallet from gaps in the floor, or local air currents caused tions relevant to their particular circumstances to confirm any by the additional electric heaters used to boost the heating of the present results which may be of interest. capacity of the container. The equipment design had practical advantages in allowing tests to be carried out quickly and eco- nomically, but its limitations in local temperature uniformity should be recognised. For this reason, we have excluded from
7 B Top Air B Top Air B Top Air B Top Air B Top Air B Top Air L Top Air L Top Air L Top Air TB Top Air TB Top Air TB Top Air Top Air Top Air Temperature C Temperature C Top Air
Temperature C Top Air Top Air Top Air posure Time min posure Time min Chart - Thermal cham er no sun - air temperature top Chart - Thermal cham er no sun - air temperature top
B Top ro uct B Top ro uct B Top ro uct B Top ro uct B Top ro uct L Top ro uct L Top ro uct TB Top ro uct TB Top ro uct TB Top ro uct Top ro uct Temperature C Temperature C Top ro uct Temperature C Top ro uct Top ro uct Top ro uct posure Time min posure Time min Chart - Thermal cham er no sun - product temperature top Chart - Thermal cham er no sun - product temperature top
B South ro uct B South ro uct B South ro uct B South ro uct B South ro uct B South ro uct L South ro uct L South ro uct L South ro uct TB South ro uct TB South ro uct TB South ro uct South ro uct
Temperature C South ro uct Temperature C South ro uct Temperature C South ro uct South ro uct posure Time min posure Time min Chart - Thermal cham er no sun - product temperature south Chart - Thermal cham er no sun - product temperature south 8
B Top Air B Top Air B Top Air B Top Air B Top Air L Top Air L Top Air TB Top Air TB Top Air TB Top Air Top Air
Temperature C Temperature C Top Air Temperature C Top Air Top Air posure Time min posure Time min Chart 8 - olar exposure - air temperature top Chart 8 - olar exposure - air temperature top
B Top ro uct B Top ro uct B Top ro uct B Top ro uct B Top ro uct L Top ro uct L Top ro uct TB Top ro uct TB Top ro uct Top ro uct
Temperature C Top ro uct Temperature C Top ro uct Temperature C Top ro uct Top ro uct posure Time min posure Time min Chart - olar exposure - product temperature top Chart - olar exposure - product temperature top
B South ro uct B South ro uct B South ro uct B South ro uct B South ro uct L South ro uct L South ro uct TB South ro uct TB South ro uct South ro uct
Temperature C South ro uct
Temperature C South ro uct Temperature C South ro uct South ro uct posure Time min posure Time min Chart 0 - olar exposure - product temperature south Chart 0 - olar exposure - product temperature south
TB Top ro uct TB Top ro uct TB Top ro uct
Top ro uct Temperature C Top ro uct Temperature C Top ro uct Temperature C
posure Time min posure Time min Chart - olar exposure - degree-hours a o e °C Chart - olar exposure - degree-hours a o e °C B Top Air B Top Air B Top Air B Top Air B Top Air L Top Air L Top Air TB L Top Top Air Air TB Top Air TB Top Air Top Air Top Air Temperature C Temperature C Top Air Temperature C Top Air Top Air posure Time min posure Time min Chart - Thermal cham er no sun posure - air temperature Time min top Chart - Thermal cham er no sun - air temperature top B Top ro uct B Top ro uct B Top ro uct B Top ro uct L B Top Top ro uct ro uct L Top ro uct TB L Top Top ro uct ro uct TB Top ro uct TB Top Top ro uct ro uct Top ro uct Temperature C
Temperature C Top ro uct Temperature C Top ro uct Top ro uct posure Time min posure Time min Chart - Thermal cham er no sun posure - product Time temperature min top Chart - Thermal cham er no sun - product temperature top B South ro uct B South ro uct B South ro uct B South ro uct B South ro uct L South ro uct L South ro uct L South ro uct TB South ro uct TB South ro uct TB South South ro uct ro uct Temperature C South ro uct Temperature C South ro uct
Temperature C South ro uct South ro uct South ro uct posure Time min Chart - Thermal cham er no sun posure - product Time temperature min south Chart - Thermal cham er no sun - product temperature south
B Top Air B Top Air B Top Air B Top Air B Top Air B Top Air L Top Air L Top Air L Top Air TB Top Air TB Top Air TB Top Air Top Air Top Air Temperature C Temperature C Top Air Top Air Temperature C Top Air Top Air posure Time min Chart 8 - olar exposure - air temperature posure Time top min Chart 8 - olar exposure - air temperature top
B Top ro uct B Top ro uct B Top ro uct B Top ro uct L B Top Top ro uct ro uct L Top ro uct TB L Top Top ro uct ro uct TB Top ro uct TB Top Top ro uct ro uct Top ro uct
Temperature C Temperature C Top ro uct Top ro uct Temperature C Top ro uct posure Time min Chart - olar exposure - product posure temperature Time min top Chart - olar exposure - product temperature top
B South ro uct B South ro uct B South ro uct B South ro uct B South ro uct B South ro uct L South ro uct L South ro uct L South ro uct TB South ro uct TB South ro uct TB South ro uct South ro uct Temperature C South ro uct Temperature C South ro uct Temperature C South ro uct South ro uct South ro uct posure Time min Chart 0 - olar exposure - product posure temperature Time min south Chart 0 - olar exposure - product temperature south 9 TB Top ro uct TB Top ro uct TB Top ro uct Top ro uct Temperature C Top ro uct Temperature C Top ro uct Temperature C posure Time min Chart - olar exposure - degree-hours posure a o eTime min °C Chart - olar exposure - degree-hours a o e °C Discussion and conclulsions was most directly exposed to solar radiation. In these circum- Comparing the air temperature with the simulated product stances, high solar reflectivity appears to play a greater role than temperature during exposure both with and without sun, the R-value in determining the performance of the covers. Indeed, air temperatures shown in Charts 5 and 8 were observed to rise even the white Tyvek® W20 cover, which has high solar reflec- faster and to reach higher levels than the product temperatures tivity but very low R-value, performed equally as well as thicker shown in Charts 6 and 9. This may be due to a combination metalised bubble wrap covers having much higher R-values. of the very low heat capacity of air, and the fact that hot air can The shiny, metallic surfaces of the metallised covers were not, in rise and accumulate in the top of the load where these measure- fact, reflecting solar radiation effectively. ments were taken. A further point to note in all these experiments is the differ- ent rates of cooling observed when the pallets were returned The air temperture was also seen to be very sensitive to short to the CRT warehouse. In this case, the metallised covers, and term changes in outside conditions. During the thermal cham- especially the metallised thermal blanket MTB1, showed a ber experiment, a periodic fluctuation was seen in the air tem- slow rate of temperature decrease relative to the white Tyvek® perature (Chart 5) recorded in most test pallets from about covers. High R-values will slow down the escape of heat which 100 minutes onward, and this correlates well with an observed has accumulated during the exposure phase, and a metallised chamber temperature oscillation having an amplitude of about outer surface with a low emissivity is also expected to reduce 1°C (Chart 3). Similarly during the solar exposure test, rapid radiant heat loss from the load. Additionally, the higher air fluctuations in air temperature were visible from about 50 permeability of the Tyvek® W20 and W50 covers may further minutes onwards (Chart 8) and these can be attributed to fluc- enhance their ability to shed undesired heat when brought back tuating solar irradiation, external temperature and wind speed into CRT conditions. The stability budget of pharmaceutical as recorded in Chart 4. The product temperatures shown in products is consumed by both the extent of any deviation above Charts 6 and 9 at the same locations were much more stable the maximum temperature allowed (in °C), and the duration so it appears that even a small mass of fluid has much higher of that deviation (in hours) so the stability budget in some way heat capacity than the air in a box, and provides sufficient tem- correlates with the area under the temperature curves shown in perature ‘inertia’ to smooth out such short term changes. This the charts above, measured in “degree-hours”. To calculate this underlines the importance of measuring product temperature relative to a 25°C upper CRT limit, for each data point above in studies of passive thermal protection systems – air temperture that limit we multiply the difference between the measured meaurements may give misleading results as they are so sensitive temperature and that limit by the recording interval, and sum to random changes in external conditions. those values over the duration of the trial. This yields a measure The only passive thermal protection systems which appeared of the total exposure for the whole trial in “degree hours” above to provide a more stable air temperature under the cover were the CRT limit. This is illustrated in Chart 11 and the calculated the thicker metallised thermal blanket MTB1 and white Tyvek® degree-hours above 25°C are shown below in Table 2 for the W50 covers which have the highest R-values of the covers tested top face product temperature in the trials conducted with and (Charts 5 and 8). High R-value can be understood to damp out without solar exposure. rapid changes in the external conditions. If a temperature excursion takes place, the faster the tem- Looking at the performance of the different covers in the ther- perature of the product can be brought back below the critical mal chamber test in Charts 6 and 7, the slowest temperature limit, the less of the stability budget of the pharmaceutical rise was observed with the metallised thermal blanket MTB1, product will be consumed. The differing abilities of the cov- with white Tyvek® W50 slightly faster and the remaining cov- ers to allow the load to recover once it is brought back into a ers clustering after that and showing broadly similar behaviour. CRT environment had a strong impact on the net exposure As expected, the covers with the highest R-values provided the experienced as measured in °hr > 25°C. highest level of protection in these circumstances. As can be seen from the data in Table 2, Tyvek® covers having However, in the solar exposure experiment (Charts 9 and 10), high reflectivity in the visible and near infra-red provided the relative performance of the covers was quite different from the lowest degree-hours of exposure of all the covers tested that observed in the thermal chamber test. The white Tyvek® outdoors in the sun . Additionally, when recovery is taken W50 now showed the lowest temperature rise and the metal- into account, the Tyvek® W50 cover also provided the low- lised thermal blanket MTB1 the highest, even though it has the est degree-hours of exposure, even when testing in a thermal highest R-value. This was especially true for the top face which chamber where its high solar reflectivity is not a factor.
10 B Top Air B Top Air L Top Air TB Top Air Top Air Temperature C Top Air posure Time min Chart - Thermal cham er no sun - air temperature top
B Top ro uct B Top ro uct L Top ro uct TB Top ro uct Top ro uct Temperature C Top ro uct posure Time min Chart - Thermal cham er no sun - product temperature top
B South ro uct B South ro uct
L South ro uct
TB South ro uct
South ro uct Temperature C
South ro uct
posure Time min Chart - Thermal cham er no sun - product temperature south
B Top Air B Top Air L Top Air TB Top Air
Top Air Temperature C Top Air
posure Time min Chart 8 - olar exposure - air temperature top
B Top ro uct
B Top ro uct L Top ro uct TB Top ro uct Top ro uct Temperature C Top ro uct
posure Time min Chart - olar exposure - product temperature top
B South ro uct
B South ro uct L South ro uct
TB South ro uct
South ro uct Temperature C
South ro uct posure Time min Chart 0 - olar exposure - product temperature south
TB Top ro uct
Top ro uct Temperature C
posure Time min Chart - olar exposure - degree-hours a o e °C
Table 2 – total exposure above 25°C for top face product temperature Solar and Hot Chamber tests. Cover Type Solar Test: (°hr >25°C) Hot Chamber Test: (°hr >25°C)
Tyvek ® W50 16.0 53.1
Tyvek ® W20 26.7 67.4
ML1 27.2 72.3
MTB1 31.2 59.3
MBW2 31.2 72.3
MBW1 33.8 74.9
Summary in our specific experimental set-up, so users of cargo covers should still conduct tests appropriate for their particular This study has shown that high R-value and low emissivity shipping routes to understand how these effects may apply in metallised covers can be effective in reducing temperature their own circumstances. However, R-value, emissivity AND excursions when a cargo is exposed to high temperatures in visible/near infra-red reflectivity should all be considered when a thermal chamber. However, it has also shown that R-value selecting passive protection systems to protect pharmaceutical and emissivity alone are not good predictors of performance products during shipment. Depending on the type of threat when loads are heated by exposure to the sun, and that in this which can be expected on the shipping route in question, all case, visible and near infra-red reflectivity become important. that glitters (i.e. shiny, metallised materials) may not be the Indeed, in real-life cold-chain breaks where outdoor solar best choice if time at temperature is taken into consideration. exposure is often significant, the high R-values and low emissivity of metallised systems may have an overall negative impact by helping to retain heat gained during an excursion “All that glitters is not gold; Often have you heard that told;” The and extending the duration of product exposure to high Merchant of Venice, William Shakespeare, 1596 temperatures even after the ambient conditions return to normal. These conclusions are derived from results obtained
11 All technical information set out herein is provided free of charge and is based on technical data which DuPont believes to be reliable and may be subject to revision as new knowledge becomes available. It is intended for use by persons having skill, at their own discretion and risk. It is your responsibility to investigate other sources of information on this issue that more appropriately addresses your product and its intended use. Since conditions of product use are outside of our control DUPONT MAKES NO WARRANTIES OF ANY KIND REGARDING THIS INFORMATION AND ASSUMES NO LIABILITY WHATSOEVER IN CONNECTION WITH ANY USE OF THIS INFORMATION. This information is not intended for use by you or others in advertising, promotion, publication or any other commercial use, AND is not a license to operate under, or intended to suggest infringement of, any existing trademarks or patents. Not for use in the Peoples Republic of China.
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