Patent Application
20210015277
The present disclosure relates generally to sleeping bags, with and without hoods, with separate hoods. and variations thereof including quilts, top quilts and bottom quilts and, more particularly, to cold weather sleeping bags (all collectively referred to as sleeping bags henceforth) that in addition to providing warmth by controlling heat loss due to thermal conduction, further reduce heat loss due to evaporation and radiation.
This section provides background information related to the present disclosure which is not necessarily prior art.
Sleeping bags used in outdoor activities such as camping, backpacking and mountaineering are designed to keep a person warm while sleeping in cold environments. The purpose of the bag is to reduce the heat lost by the sleeper to a level that can result in comfortable sleep. The rate at which heat is lost by the sleeper is historically controlled by the thermal conductivity of the insulation surrounding the sleeper. Heat loss by thermal conductivity is a function of the insulation thickness, the coefficient of thermal conductivity of the insulating material, the area and the temperatures inside the bag and outside the bag. This is shown in the following heat transfer by thermal conductivity equation:
{dot over (Q)} is the amount of heat transferred per unit time
k is the coefficient of thermal conductivity of the insulation
A is the area through which the heat passes
TH is the higher temperature (temperature inside the bag)
TL is the lower temperature (temperature outside the bag)
t is the thickness of the insulation
Thus, the comfort range of sleeping bags has historically been managed by the selection of insulating material (for the coefficient of thermal conductivity) and the thickness of that insulating material. Thus, the lower temperature limit of the bag is limited by the type and thickness of the insulating material surrounding the body. This insulation allows the body to maintain warmth (by conserving heat which is internally generated by the body's metabolic process) by blocking the loss of heat by thermal conductivity through the walls of the sleeping bag.
However, in addition to conduction, heat may be also be lost by other means of heat transfer which include convection, radiation and evaporation. Products exist that are designed to manage heat loss by radiation alone, such as the well know “space blanket.” Other products exist where the sleeping bag manages evaporation by incorporating a moisture/vapor barrier lining. The subject sleeping bag addresses methods by which heat loss may be further reduced by the addition of a combined radiation and moisture/vapor barrier.
For a liquid to undergo a phase transition from the liquid state to the vapor state a significant amount of heat is required. In the case of water, while it takes only one calorie of heat to raise one gram of water one degree C., it takes 540 calories to evaporate the same one gram of water (with one dietary calorie equal to 1000 calories). That is, 540 calories must be supplied or extracted from the surroundings for each gram of water that is transformed from a liquid to a vapor (gas). This number is called the latent heat of vaporization for water. Measurements have shown that the body loses somewhere between 0.5 L to 1.0 L (with one milliliter of water having a mass of one gram) of water while sleeping outside, in a sleeping bag on a long winter night at below freezing temperatures. This moisture is lost through respiration and insensible perspiration.
Winter air at −18 degrees C. (zero degrees F.) that contains a moisture level of 50% relative humidity when heated by a sleeper's body inside the sleeping bag to 25 degrees C. (75 degrees F.) has a relative humidity of 3.4% (as established with reference to the psychometric chart). This moisture level is below that encountered in the driest desert conditions. For comparison the Sahara Desert's average relative humidity is reported to be 25% and the typical summer afternoon relative humidity on the Mojave Desert is reported to be approximately 10%. In this low humidity environment, the body loses moisture from its surface in the form of insensible perspiration. That is, perspiration that evaporates before it is perceived as moisture on the skin. This means that when using a conventional sleeping bag (without a moisture/vapor barrier) at low (below freezing) temperatures the sleeper will lose moisture without sweating and without knowing it. Still, every gram of water that is evaporated whither through respiration or insensible perspiration, takes 540 calories of heat from the sleeper's body. So to evaporate one liter of water, 540,000 calories (or 540 dietary calories) would be extracted from the person while sleeping in a sleeping bag that did not employ any type of moisture/vapor barrier. This energy would have to be supplied by the sleeper's body converting food into heat energy.
As this moisture, in the form of water vapor, moves outward from the body through the inner lining of the sleeping bag and then through the insulation it will be cooled. Once it reaches the dew point temperature it will condense from a vapor to a liquid. This condensation will take place in the insulation between the inner lining and outer shell of the sleeping bag. If there is additional cooling of the moisture, it could possibly freeze within the insulating material. Condensation of moisture in the insulating material also has a deleterious effect on the insulation ranging from increasing its thermal conductivity to causing a thickness decrease, all having a negative effect on the temperature range of the sleeping bag. Accumulation of moisture in the insulating material also adds unwanted weight to the bag.
To block this moisture loss from insensible perspiration, a vapor barrier liner can be used inside the sleeping bag. In this case the person sleeping surrounds himself with a material that is impervious to moisture in either it's liquid or vapor form. This can be anything from a garbage bag to a special sleeping bag liner. The air inside the vapor barrier will have a low humidity at first, however, as the body gives off moisture the humidity inside the vapor barrier will rise until it is very high, approaching 100% relative humidity, at which point evaporation from the body ceases, and thus heat loss by evaporation ceases. For this to occur it is essential that the vapor barrier encapsulate the sleeper so that the enclosed air within the encapsulated volume can achieve the higher levels of humidity. Use of vapor barrier mechanisms to reduce heat transfer have been considered and recognized as prior art.
Heat loss by radiation automatically occurs between a warmer body and a colder body through electromagnetic radiation. No transfer medium is required for heat transfer by radiation. Radiation heat transfer occurs in the vacuum of space. The warming of the earth by the sun is an everyday example of heat transfer by radiation with this type of heat transfer is described by the Stefan-Boltzmann equation:
{dot over (Q)}=εσAT4
{dot over (Q)} is the amount of heat transferred per unit time
ε is the emissivity of the surface of the body loosing or gaining heat energy
σ is the Stefan-Boltzmann Constant
A is the surface area radiating to/from
T is the temperature of the radiating or absorbing body
If a hot object is radiating to cooler surroundings the heat loss rate can be expressed:
{dot over (Q)}=εσA(Th4−Tl4)
Th is the temperature of the warmer body
Tl is the temperature of the colder body
The heat loss is driven by the differences in temperature to the fourth power but is controlled by the emissivity of the surface. Thus, if the emissivity, ε, can be reduced, then the heat transferred by radiation can be minimized. Since dark, rough surfaces have a high value of emissivity (0.94 for flat black paint), and shiny, silvered surfaces have low values of emissivity, (0.03 for aluminum foil), then by using an aluminized (or other low emissivity coating, less than 0.1) inner liner, heat loss by radiation can be greatly reduced. For example, if the nylon lining of a sleeping bag had an emissivity of 0.85, then replacing it with an aluminized surface having an emissivity of 0.03 would reduce heat loss by radiation by 96%.
It is an aspect of the present teachings to provide a sleeping bag that incorporates an inner shell material that affects the warmth of the sleeping bag by reducing heat loss due to both heat transfer mechanisms, evaporation and radiation.
An additional aspect of the present teaching is that a total sleep system weight savings is achieved for any temperature range, since the combined vapor-radiation barrier lining weight is less than the additional insulation required to achieve an equivalent lower temperature range extension, thus resulting in a superior warmth to weight ratio compared with prior art.
In accordance with this and other aspects, the present disclosure is directed to a sleeping bag that has an inner shell that has been fabricated using materials that are impervious to water in either its liquid or a vapor states, and exhibit the property of low emissivity (emissivity less than 0.1).
Further areas of applicability will become apparent from the description and claims herein. The description and specific examples in the disclosure and summary are intended for purposes of illustration only and are not intended to limit the scope of the present invention.
The drawings described herein are for illustrative purposes only for selected exemplary embodiments and are not intended to limit the scope of the present disclosure in any way. Similar or identical elements are given consistent reference numerals throughout the various figures.
Reference now will be made to the accompanying drawings in which:
The following exemplary embodiments are provided so that the present disclosure will be thorough and fully convey the scope to those skilled in the art. Numerous specific details are set forth such as examples of specific components, devices and schematic configurations to provide a thorough understanding of exemplary embodiments of the present disclosure. However, it will be apparent to those skilled in the art that these specific details need not be employed, that the exemplary embodiments may be embodied in many different forms, and that neither should be construed to limit the scope of the present disclosure.
Referring to
Elaboration on the inner shell 14 materials and function as it pertains to this disclosure are to follow. The sleeping bag 10 has a first half 15 and a second half 17 arranged in opposing facing relation so that first half 15 and second half 17 are configured to define a sleeping compartment therebetween when the zipper assembly 16 is closed. A draft tube 22, filled with insulating material, backs the zipper assembly 16 to maintain insulating thickness the length of the zipper. A drawstring 23 can be used in conjunction with a pair of draw hems 20 to adjustably vary an opening at the top of sleeping bag 10 once zipper assembly 16 has been drawn to its closed position. A drawstring lock 21 is also provided to maintain the drawstring 23 in a preferred cinched or partially cinched position.
The sleeping bag 10 has incorporated an inner shell material 14 that affects the warmth of the sleeping bag by reducing heat loss due to evaporation and radiation,
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/876,159 filed on Jul. 19, 2019, the entire disclosure of which is hereby incorporated by reference
| Number | Date | Country | |
|---|---|---|---|
| 62876159 | Jul 2019 | US |
