Infrared Transparent Visible Opaque Fabrics (ITVOF)

Technology #17390

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Theoretical results for the visible and IR wavelength range highlighting the contrast in optical properties needed for an ITVOF. These results correspond to the case of Df =1μm, Dy =30 μm, Ds =1 μm, and Dp =5 μm. For comparison, the experimentally measured reflectances and transmittances of cotton and polyester cloths are also shown.Heat transfer model was developed to analyze heat dissipation from a clothed human body to the ambient environment. Various heat transfer contributions that lead to dissipation of heat from the human body, such as radiation, heat conduction, and heat convection, are included. To model loose fitting clothing, a finite air gap is assumed between the cloth and the skin.Numerical simulation results for the IR optical properties of a polyethylene-based ITVOF illustrating the effect of reducing the fiber and yarn size. Upper row: The yarn diameter is varied (Dy = 30, 50, and 100 μm) assuming a fixed fiber diameter of Df =10 μm. Lower row: The fiber diameter is varied (Df = 1, 5, and 10 μm) assuming a fixed yarn diameter of Dy =30 μm. For all simulations, the fiber separation distance is Ds =1 μm and the yarn separation distance is Dp =5μm. The spectrally integrated transmittance (τc) and reflectance (ρc) is shown in each plot weighted by the Planck’s distribution assuming a body temperature of 33.9 °C (93 °F). For Df =10 μm, the material volume per unit depth for a single yarn is 4870 μm2 for Dy = 100 μm, 1492 μm2 for Dy =50 μm, and 550 μm2 for Dy =30 μm. For Dy =30 μm, the material volume is 373 μm2 for Df = 5 and 136 μm2 for Df =1 μm. The optical properties of the ITVOF are calculated for the wavelength range from 5.5 to 24 μm, which will provide a conservative estimate of the total transmittance and the reflectance.
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Inventors
Professor Gang Chen
Department of Mechanical Engineering, MIT
External Link (web.mit.edu)
Jonathan Tong
Department of Mechanical Engineering, MIT
Svetlana Boriskina
Department of Mechanical Engineering, MIT
External Link (www.mit.edu)
Xiaopeng Huang
Department of Mechanical Engineering, MIT
James Loomis
Department of Mechanical Engineering, MIT
Yanfei Xu
Department of Mechanical Engineering, MIT
Managed By
Christopher Noble
MIT Technology Licensing Officer - Clean and Renewable Energy
Patent Protection

Infrared transparent visible opaque fabrics

PCT Patent Application WO 2016-044609

Infrared transparent visible opaque fabrics

US Patent Pending
Publications
Infrared-Transparent Visible-Opaque Fabrics for Wearable Personal Thermal Management
ACS Photonics, 2015, 2 (6), pp 769–778

Applications

The materials in this technology have been engineered primarily for clothing . The material enables thermal radiative heat transfer to increase user comfort. These fabrics provide cooling regardless of the wearer's activity or surrounding environment. 

Problem Addressed

State-of-the-art cooling technologies have predominantly focused on clothing (e.g. moisture wicking, phase change materials, active cooling technologies) for individuals who are performing high levels of physical activity. Additionally, materials currently used for clothing fabrics (e.g. cotton and polyester) have a transmittance of 1-2% in the infrared (IR) spectrum, which doesn't allow cooling via radiation. ITVOF are transparent in the infrared spectrum and increase a person’s cooling rate by >23W. Personal cooling rate and ambient temperature affect personal thermal comfort. Therefore, increasing a person's cooling rate allows a higher ambient temperature to achieve the same level of comfort. Specifically, a >23W increase in cooling rate allows an ambient temperature increase ≥ 4oF (to ~79oF), which leads to lower air conditiong set points and significant energy savings in buildings.

Technology

A model of the system, including a person and their clothes, was created to analyze the effects of incorporating IVTOF in clothing.  It was determined that a transmittance of 34-43% in the IR spectrum is required to achieve sufficient cooling. Using polyethylene (PE), with a maximum yarn thickness of 100µm, the minimum spectrally integrated transmittance in the IR spectrum was 48.8%, which is greater than the required transmittance. The second requirement of a clothing fabric is opaqueness in the visible spectrum. Polyester and cotton cloths exhibited uniform reflectance of 40-50% in the visible spectrum and the PE sample exhibited 50-60%. Therefore, PE fabrics are one potential material for IVTOF.  Fabrication of these materials consists of three steps; extrusion of molten polymer through a spinneret into a bundle of fibers, drawing of fibers, and spooling the fibers into a yarn. The spinneret is designed to include the total number of fibers in a yarn allowing equal production rate for fibers and yarns. Once the yarns are created, they can be woven into fabric with commercially available looms. 

Advantages

  • Increased thermal comfort in clothing
  • Increased energy savings by increased air conditioning set points