An Apparatus to Measure Thermophysical Properties of Heavy Crudes
The main purpose of this work was to develop an apparatus to measure thermophysical properties of a special group of “new” substances: heavy crudes from the Orinoco Belt in Venezuela. These crudes are highly viscous and in many cases contain sand, heavy metals and water. They have to be heated up to 80°C and more to assist in their extraction and transportation from the well to a location where they can be processed and utilized. Thus, it is important to know the thermophysical properties of these substances to design the transport systems that will handle them. Small errors in the estimation of these properties could mean kilometers of misused pipes.
The Hot Wire Transient Technique was chosen among many others because of its simplicity and accuracy. The apparatus was designed and built in accordance with its intended use for routine measurements in the laboratory.
The apparatus consists of a metallic cylindrical cell inside a constant-temperature bath. The top cover and bottom of the cell have electric connectors and pipe fittings to allow measuring and constant cleaning of the cell. A frame holds the “wire” and other important connections inside the cell. The thermal conductivity of the sample can be measured at pressures up to 17 bars and at temperatures up to 250°C.
Several crudes were examined in a range of temperatures between 180°C and 20°C. An important effect of volatile concentration was detected. Also the effect of moisture was measured for one of the samples. These effects are discussed in the light of existing theories.
A slight modification of the original circuit improved both the accuracy of the thermal conductivity measurement and also the ability to determine the thermal diffusivity of the sample. An effort is now being made to automate the measuring process with a microcomputer.