ISSN:
1089-7623
Source:
AIP Digital Archive
Topics:
Physics
,
Electrical Engineering, Measurement and Control Technology
Notes:
This article discusses the design and construction of guarded hot plate instruments for measuring the heat flow through an evacuated space between plane-parallel glass surfaces. In this structure, the insulating region is surrounded by two pieces of relatively highly conducting material. High resolution measurements of heat flow using these instruments therefore requires the detection of quite small temperature differences (10−4 K) between the metering piece and the guard. The instruments are calibrated, and the linearity evaluated, by measuring radiative heat transfer through the evacuated space between uncoated soda lime glass sheets; this is because this heat flow can be calculated to high accuracy from the infrared optical properties of the glass. The level of parasitic heat flow in the instruments is estimated by measuring radiative heat flow between glass surfaces coated with very low emittance layers, such as evaporated gold. These instruments operate over a range of temperatures from 0 to about 70 °C. It is shown that the heat flow between evacuated glass surfaces can be measured with these instruments to high resolution (∼10 μW) and high accuracy (∼1%) over an area of ∼1 cm2. The departures from linearity, and the level of parasitic heat flow, are within the measurement resolution. For a temperature difference across the sample of 20 K, the measurement resolution corresponds to an uncertainty in the thermal conductance of the sample of ∼0.005 W m−2 K−1. © 1998 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1149038
