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An unsteady-state method for determining overall coefficient of heat transfer (k-value) of insulated bodies at variable external temperatures

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Abstract

A method for determining k-value of insulated bodies at variable external temperatures is proposed, theoretically described and results of experimental verification are presented in this paper. Theoretical analyses include descriptions of both physical and mathematical models and definition of the extrapolation formula. The method is tested in laboratory conditions on a simple model of insulated chamber and compliance with all testing conditions prescribed by Agreement on Transport of Perishables. The advantage of this method in comparison to any other unsteady- or steady-state method is that it enables k-value determination out of the specialized test stations. This further makes it possible to carry out cheaper and more frequent k-value measurements/control in insulated bodies. Also, the proposed method can be used for testing the k-value of stationary insulated chambers which cannot be objectively tested by means of stationary methods.

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Abbreviations

k:

Overall coefficient of heat transfer (k-value) (W m−2 K−1)

Q:

Heat flux (W)

T:

Temperature (K)

t, τ:

Time (h)

S:

Mean surface (the geometric mean of external and internal surface) (m2)

x:

Coordinate (m)

L:

Insulation thickness (m)

cp :

Isobaric specific heat (kJ kg−1 K−1)

ρ:

Density (kg m−3)

λ:

Heat conduction coefficient (W m−1 K−1)

a:

Thermal diffusion coefficient (m2 h−1)

1,e:

External

2,i:

Internal

m:

Mean

∞:

For t = ∞

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  1. Faculty of Technical Sciences, 21125, Novi Sad, Serbia

    Dušan Gvozdenac

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  1. Dušan Gvozdenac
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Correspondence to Dušan Gvozdenac.

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Gvozdenac, D. An unsteady-state method for determining overall coefficient of heat transfer (k-value) of insulated bodies at variable external temperatures. Heat Mass Transfer 51, 171–180 (2015). https://doi.org/10.1007/s00231-014-1393-2

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  • DOI: https://doi.org/10.1007/s00231-014-1393-2

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