Date of this Version
Transactions of the ASAE, Vol. 44(6): 1479–1488
To study the effects of mulches and crop residues on soil temperature, researchers have frequently used simulation models. In such models, quantification of heat transport within the mulch material is often weak and heat transport mechanisms are poorly understood. In this paper we describe an apparatus to quantify heat transport through dry mulch materials. In addition, heat transport mechanisms (conduction, thermal radiation, free and forced convection) can be identified and quantified using this apparatus. The apparatus consists of precisely controlled and monitored 0.9 m by 0.9 m hot and cold plates. The hot plate actually consists of three component plates: a test, a guard, and a bottom plate that are individually controlled (temperature) and monitored (temperature and power). The guard plate surrounds the test plate, minimizing undesired lateral heat flow. The bottom plate is positioned in parallel with the test and guard plates to insure that all wattage into the test plate moves off the top of the plate through the mulch. The correct functioning of the hot plate was verified using three reference materials with a known thermal resistance.
The cold plate is based on techniques using thermoelectric devices (Peltier coolers). In addition, heat sinks and fans are used to transport heat away from the cold plate. A two–dimensional numerical simulation showed that errors caused by lateral heat flow in a sample contained between the hot and the cold plate can be neglected. The thermal conductivity of air was measured using the apparatus, yielding a value of 0.026 W m–1ºC–1, exactly matching the theoretical value, thus confirming the correct functioning of the hot/cold plate combination.