Ventilated Chamber System for Continuous Recording of Both the Evaporation Rate and the Heart Balance at the Bare Soil Surface

Abstract

This paper describes the design of a new ventilated chamber system for continuous measurement of both the evaporation rate and the energy balance components at the bare soil surface with some of its principle advantages and characteristics. The influence of the used equipment on both of the temperature of the air and its relative humidity was studied and minimized. The air velocity inside the chamber has been regulated to be a logarithmic function of the height above the soil surface. The change of static pressure within the chamber compared with the ambient pressure was modeled well as a linear function of the volumetric flow rate of the air. A new method was proposed to estimate the diurnal variation of the net radiation, latent heat, sensible heat and soil heat fluxes at the bare soil surface. Twenty four hours in-situ measurement was carried out at Rokkasho Low-level Radioactive Waste Disposal Center, Aomori Prefecture, Japan, to check the operational effectiveness of the new device and the reliability of the proposed method for experimental periods of many days. Also, an accurate estimation of the evaporation rate from the soil surface for such type of places is indispensable, for evaluating safety concerning radioactive wastes. The value of the evaporation rate from the ground surface is necessary for the simulation of the ground water flow near the surface. The downward net radiation flux, the air temperature, the air relative humidity, the air velocity and the soil temperature just beneath its surface were measured continuously through the day of the field * Doctoral Student, Graduate School of Science and Engineering, Saitama University, Japan. ** Professor, Faculty of Engineering, Saitama University, Japan. *** Civil and Architectural Engineering Department, Japan Nuclear Fuel Limited, Tokyo, Japan. experiment. The evaporation rate, the latent heat flux, the sensible heat flux and the soil heat flux were calculated from the measured data. To check the accuracy of this new method, the soil heat flux was measured directly with two soil heat flux meters through a part time of the field experiment. A comparison between the measured values and those have been resulted from this method was made. Also, the transient change of the total percentage of error was calculated through the period of the soil heat flux measurement. The obtained results give a strong indicator that this method is suitable for estimating the energy balance components at the bare soil surface. This new method has the advantage of that it needs only simple data and it wears an aspect of certainty.