Radiative heat transfer in insulations with random fibre orientation

Mathes, R.; Blumenberg, J.; Keller, Karl

doi:10.1016/0017-9310(90)90174-s

Cited by 23 publications

(4 citation statements)

References 4 publications

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“…Radiation and convection act on each surface, while conduction takes place in solid materials such as cladding and wall core. It should be noted that there are radiation and conduction through the insulation, usually modeled as apparent diffusion (Mathes, Blumenberg, and Keller 1990). However, only the effective conduction part is considered in this study for simplicity.…”

Section: Energy Balancementioning

confidence: 99%

Thermal resistance of ventilated air-spaces behind external claddings; definitions and challenges (ASHRAE 1759-RP)

Rahiminejad

Khovalyg

2021

Science and Technology for the Built Environment

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The presence of an airspace within a building envelope is known to have a varying contribution to the overall thermal performance of the wall assembly due to the combined effect of convection and radiation in the air cavity. In particular, the thermal resistance of a ventilated airspace can vary significantly depending on multiple environmental and thermo-physical parameters. Although the thermal resistance of enclosed air-spaces in the building structures has been thoroughly investigated in the literature, it has not been defined for a ventilated cavity. This paper aims to introduce the plausible definitions of the thermal resistance of a vertical ventilated airspace behind external cladding systems. Both theoretical and applied formulations are provided and compared. The energy balance method is used to model the steady-state heat transfer through two types of traditional external wall systems (i.e., brick and vinyl siding) in summer and winter conditions. A range of air exchange rates in the cavity is examined, and the effect of the presence of reflective insulation in the airspace on the thermal resistance of the air gap is analyzed. The results show that the presence of a ventilated cavity in the wall assembly can influence the thermal performance of the building envelope. In particular, the effective thermal resistance of a ventilated airspace behind a brick cladding wall could be between 0.17 and 1.85 times the thermal resistance of the cladding in the range of air change rate in the cavity from 0 to 100 1/h. The effective thermal resistance of the ventilated air gap behind vinyl siding could reach up to 9 times the thermal resistance of the cladding.

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Section: Energy Balancementioning

confidence: 99%

Thermal resistance of ventilated air-spaces behind external claddings; definitions and challenges (ASHRAE 1759-RP)

Rahiminejad

Khovalyg

2021

Science and Technology for the Built Environment

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“…Also in the case of low-density materials , radiation is of greater importance and lower density materials lead to higher values of effective the rm al conductivity [10 ,14]. At low pressures, in particular, conduction through residual gases decreases and radi ation heat transfer increases and becomes predomi nant [14] .…”

Section: Porous Structures For Mars Landers -mentioning

confidence: 99%

“…Fine fibers cover better than coarse fibers with a higher surface area-tovolume ratio and greate r amount of reflection [17]. In addition , Mathes et al demonstrated that the radiation extinction coefficients for irradiance perpendicular and oblique to the fibers , va ri es with temperature and fiber diameter [14].…”

Section: Porous Structures For Mars Landers -mentioning

confidence: 99%

Advanced Space Suit Insulation Feasibility Study

Trevino¹,

Orndoff²

2000

SAE Technical Paper Series

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For planetary applications, the space suit insulation has unique requirements because it must perform in a dynamic mode to protect humans in the harsh dust, pressure and temperature environments. Since the presence of a gaseous planetary atmosphere adds significant thermal conductance to the suit insulation, the current mu lti-layer flexible insulation designed for vacuum applications is not suitable in reduced pressure planetary environments such as that of Mars. Therefore a feasibility study has been conducted at NASA to identify the most promising insulation concepts that can be developed to provide an acceptable suit insulation. Insulation concepts surveyed include foams , microspheres , microfibers, and vacuum jackets. The feasibility study includes a literature survey of potential concepts, an evaluation of test results for initial insulation concepts , and a development philosophy to be pursued as a res ult of the initial testing and conceptual surveys . The recommended focus is on rnicrofibers due to the versatility of fiber structure configurations , the wide ch oice of fiber materials avail able , the maturity of the fiber processing ind ustry , and past experience wi h fibers in insu lation applications. INTRODUCTIONHEAT BALANCE FOR SUITED CREWMEMBERTo better understand the effect of insulation on the su ited crewmember, an overall heat balance must first be presented , along with a breakdown of the individual heat contributions. Figure 1 shows the overall heat balance terms. The heat input term is the heat generated within the crewmember enclosure, or Qgen , consisting of metabolic heat and equipment loads. Heat output terms are the heat removed by the thermal control system, or Qtes , an(:l the heat lost to the environment through the insulation and suit enclosure, or Qsuit-leak. Luis A. Trevino and Evelyne S. Orndoff NASA Johnson Space CenterThe heat loads can further be sub-divided into individual thermal environment contributions, as shown in Figure 2. Here the Qsuit-Ieak term has been replaced by three terms. The absorbed thermal radiation , or Qabs, is that due to the net solar and infrared radiation absorbed by the outer surfaces of the EMU. Of importance in this term are the solar absorption property , Ct, and the infrared absorption property , E, of the outer suit materials. A second term is the emitted radiation from the suit surface, or Qemitted, which also involves the infrared absorption property E. Finally , in a gaseous environment such as on Mars, a third term is the heat lost to the gas, or Qlost-to-gas . The gas term in tum

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“…The early radiation studies were based on semiempirical approaches of curve fitting to experimental data, which therefore, have limited applicability in analyzing insulations of different compositions [1][2][3][4][5][6][7][8][9][10][11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

An Investigation of the Radiative Heat Transfer through Nonwoven Fibrous Materials

Qashou¹,

Tafreshi

Pourdeyhimi

2009

Journal of Engineered Fibers and Fabrics

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In this study, the surface-to-surface radiation model of the Fluent CFD code is used to investigate the response of a fibrous material to the radiative heat transfer. The unsteady state heat transfer equation is solved for the temperature and heat flux in and around the fibers that constitute a nonwoven fibrous material. For a fixed fiber diameter, it was shown that the higher the fabric's Solid Volume Fraction (SVF), the slower is the material's average temperature rise. Our simulation results also indicate that for a fixed SVF, fiber diameter has a negligible influence on the unsteady transfer of heat through the media. Of particular interest in this paper is the effect of material's thickness on the heat penetration. It is shown that the transient heat transfer exponentially decreases by increasing the material's thickness for fixed SVFs and fiber diameters. The above finding is also in agreement with our experimental study. k in q ,

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Radiative heat transfer in insulations with random fibre orientation

Cited by 23 publications

References 4 publications

Thermal resistance of ventilated air-spaces behind external claddings; definitions and challenges (ASHRAE 1759-RP)

Thermal resistance of ventilated air-spaces behind external claddings; definitions and challenges (ASHRAE 1759-RP)

Advanced Space Suit Insulation Feasibility Study

An Investigation of the Radiative Heat Transfer through Nonwoven Fibrous Materials

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