Hello Bali Youcef ,

Am I correct in assuming that when you say, "It is known that the relation between material density and its thermal conductivity is a Positive relation, ...", you mean that the thermal conductivity of a material increases with increasing mass density? If the answer is, yes, then let me direct you to Fig. 236 on p. 556 of [1], which is a graph of thermal conductivity versus temperature for 11 different materials. You will notice from this figure that, for example tungsten (ρ = 19.35 g/cm3 @ 20°C) has a lower thermal conductivity than aluminum (ρ = 2.70 g/cm3 @ 20°C) from 100°K to 1,600°K. In addition, you will see that beryllia (BeO) has a higher thermal conductivity than silver and copper from 100°K to 200°K, and a higher thermal conductivity than nickel from 100°K to 800°K, even though it (BeO) is less dense than the metals.

What do you mean when you say, "... is the relation between density and specific heat, regular?" I can tell you from [2] that even though copper (ρ = 8.96 g/cm3 @ 25°C) is less dense than silver (ρ = 10.5 g/cm3 @ 20°C), it (copper) has a higher specific heat.

[1] Eugene Ryshkewitch, David W. Richerson; Oxide Ceramics; General Ceramics; 1985; p. 556.

[2] Samuel Ruben; Handbook of the Elements; Open Court Publishing Company; 1985; pp. 23 (copper) & 83 (silver).

I am confused about what you are trying to prove.

Regards,

Tom Cuff

Hello Thomas Cuff

We're talking about building materials with small thermal conductivity, maybe it's different for metals with large thermal conductivity, I've relied on the relationship between density and thermal conductivity that the American Institute of Concrete stipulates [1] on p2.

The same is the case in reference [2] on p 131,132,133 when it comes to the thermal conductivity of a particular type of material

As for the question I ask is about the specific heat and its relation to the dry density of the material, is it regular as well Because when doing experiments measuring the conductivity and specific heat of several different materials, I found that the specific heat has an irregular relationship with the density

[1]1. 122, A.C. Guide to thermal properties of concrete and masonry systems. 2002. American Concrete Institute.

[2] Couasnet, Yves, and Gérard Blachère. Propriétés et caractéristiques des matériaux de construction. Ed. du Moniteur, 2007.‏

Hi Bali Youcef ,

Thanks for the clarification. I have looked at ACI 122R-02, and on p. 122-12, Table 4-1, it shows the mass density versus specific heat and/or heat capacity for mortar, grout, concrete, clay brick, gypsum board, and plaster and stucco. While the mass density of these material varies from 50 to 140 lbs/ft3 - almost a factor of almost 3 {2.8 to be exact} - the specific heat, for example, only varies from 0.20 to 0.26 Btu/lb•°F - a factor of 1.3. In other words, the specific heat is not a strong function of the mass density. In fact, gypsum board, the material with the lowest mass density, 50 lbs/ft3, had the highest specific heat, 0.26 Btu/lb•°F, while concrete, the material with the highest mass density, 140 lbs/ft3, had a low, but not lowest, specific heat, 0.22 Btu/lb•°F.

You might consider this behavior as irregular, but there is a fairly simple reason for this behavior. Mass density, specific heat, heat capacity, temperature and pressure are all intensive thermodynamic properties, i.e., they do not depend on the amount of material, while mass and volume are extensive properties, i.e., they depend on amount of material, see [1]. Thus, intensive properties aren't normally affected by the material's mass density because you use the same mass of material for the measurements. The slight variation in the values of the specific heat is due to the somewhat different chemical compounds and mixtures thereof that are present in each aggregate material: calcium carbonate, calcium oxide, calcium sulfate, silicon dioxide, etc. The varying mixtures, and the processing they undergo (curing in the case of mortar, grout and concrete, versus drying or firing in the case of clay bricks) will also change their specific heats slightly.

[1] Walter J. Moore; Physical Chemistry, Third Edition; Prentice-Hall, Inc.; 1962; pp. 8-9.

Regards,

Tom Cuff