What is the shape of the cross-section of the ordinary thermometer used in the laboratory, the general thermometer?

The cross-section of the thermometer used in the laboratory is round, while the cross-section of the thermometer is triangular thermometer has a scale on the side of the three prisms made in the shape of the scale, they play a role in what? On the scale line has no effect, it is mainly to enlarge the thermometer inside the mercury column, so that people can see more clearly, understand. Because the inside of the mercury column is very thin, it is difficult to see clearly without magnification. Ordinary thermometer requirements are not very high, the mercury column is relatively thick, can directly see, thermometer because to be accurate to 0.1 degrees, which is equivalent to each degree Celsius scale lengthened, the mercury column must be designed to be finer, and therefore must be enlarged by the glass prism in order to let people see. Why are ordinary thermometers cylindrical rather than square? Comparison of cylindrical and square: square and round than, the same cross-sectional area, round circumference is small, the same surface area when the cylindrical volume to be small, so that you can save materials and labor to facilitate the manufacture, especially the scale of production. The square field production of welded seams, the complexity of the process of pressing. From the perspective of fluid mechanics analysis: one is the impact of the fluid on the pipe, square pipe force is not uniform; two is the impact of the pipe on the flow of fluid, fluid viscosity, through the pipe when there is resistance to flow, to be subjected to shear stress, the shear stress and the pipe around the area of the force has a relationship. Square pipes are subject to greater shear stress, hindering fluid flow. Round resistance to be small, conducive to fluid flow, and stress distribution is relatively uniform, unlike the square stress concentrated in the four prongs, cylindrical conducive to fluid flow, both from the analysis and the form of good; from the resistance to fluid flow and stress considerations, the round tube is good for pressure, this can be used to verify the theory of strength; thermal expansion and contraction, the force of the round to be good. From the point of view of material mechanics analysis: set square tube (height to width ratio of 1) and the same cross-sectional area of the round tube, wall thickness and the same material, then the stiffness, square tube bending stiffness of about 1.7 times the round tube, torsional stiffness of about 2.9 times the round tube, the calculation of the shaped tube is very complex.