{"id":16314,"date":"2018-01-02T13:21:28","date_gmt":"2018-01-02T13:21:28","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=16314"},"modified":"2022-11-18T12:11:47","modified_gmt":"2022-11-18T12:11:47","slug":"what-is-density-physics","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-engineering\/thermodynamics\/thermodynamic-properties\/what-is-density-physics\/","title":{"rendered":"What is Density – Physics"},"content":{"rendered":"
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Density<\/strong> is defined as the mass per unit volume<\/strong>. It is an intensive property<\/strong><\/a>, which is mathematically defined as mass divided by volume:<\/p>\n

\u03c1 = m\/V<\/strong><\/p>\n

In other words, the density (\u03c1) of a substance is the total mass (m) of that substance divided by the total volume (V) occupied by that substance. The standard SI unit is kilograms per cubic meter<\/strong> (kg\/m3<\/sup><\/strong>). The Standard English unit is pounds mass per cubic foot<\/strong> (lbm\/ft3<\/sup><\/strong>).<\/p>\n<\/div><\/div>\n

\"Density<\/a>
Typical densities of various substances at atmospheric pressure.<\/figcaption><\/figure>\n

The density (\u03c1) of a substance is the reciprocal of its specific volume<\/strong> (\u03bd).<\/p>\n

\u03c1 = m\/V = 1\/\u03c1<\/strong><\/p>\n

Specific volume<\/strong> is an intensive variable<\/strong>, whereas volume is an extensive variable.<\/p>\n

The SI system\u2019s standard unit for specific volumes is cubic meters per kilogram (m3<\/sup>\/kg). The standard unit in the English system is cubic feet per pound-mass (ft3<\/sup>\/lbm).<\/p>\n

<\/span>Changes of Density<\/div>
In general, density<\/strong> can be changed<\/strong> by changing either the pressure<\/strong> or the temperature<\/strong>. Increasing the pressure always increases<\/strong> the density<\/strong> of a material. The effect of pressure on the densities of liquids<\/strong> and solids<\/strong> is very, very small. On the other hand, the density of gases is strongly affected by pressure. This is expressed by compressibility<\/strong>. Compressibility<\/strong> measures the relative volume change of a fluid or solid as a response to a pressure change.<\/p>\n

The effect of temperature<\/strong> on the densities of liquids and solids is also very important. Most substances expand when heated<\/strong> and contract when cooled<\/strong>. However, the amount of expansion or contraction varies, depending on the material. This phenomenon is known as thermal expansion<\/strong>. The following relation gives the change in volume of a material that undergoes a temperature change:<\/p>\n

\"thermal-expansion\"<\/a><\/p>\n

where \u2206T is the temperature change, V is the original volume, \u2206V is the volume change, and \u03b1V<\/sub><\/strong> is the coefficient of volume expansion<\/strong>.<\/p>\n

We must note that there are exceptions to this rule. For example, water<\/strong> differs from most liquids in that it becomes less dense as it freezes<\/strong>. It has a maximum density of 3.98 \u00b0C (1000 kg\/m3<\/sup>), whereas the density of ice is 917 kg\/m3<\/sup>. It differs by about 9% and therefore ice floats<\/strong> on liquid water<\/div><\/div>

<\/span>Coolant acceleration in a reactor core<\/div>
See also: Fluid Acceleration – Pressure Loss<\/a><\/p>\n

It is an illustrative example. The following data do not correspond to any reactor design.<\/span><\/p>\n

\"Continuity<\/a>
Example of flow rates in a reactor. It is an illustrative example, and the data do not represent any reactor design.<\/figcaption><\/figure>\n

Pressurized water reactors<\/b><\/a> are cooled and moderated<\/a> by high-pressure liquid water (e.g.,, 16MPa). <\/span>At this pressure, water boils at approximately 350\u00b0C (662\u00b0F).\u00a0 The inlet temperature of the water is about 290\u00b0C (\u2374 ~ 720 kg\/m3<\/sup>). The water (coolant) is heated in the reactor core<\/a> to approximately 325\u00b0C (\u2374 ~ 654 kg\/m3<\/sup>) as the water flows through the core.<\/p>\n

The primary circuit of typical PWRs is divided into four independent loops (piping diameter ~ 700mm). Each loop comprises a steam generator<\/a> and one main coolant pump<\/a>. Inside the reactor pressure vessel (RPV), the coolant first flows down outside the reactor core (through the downcomer). The flow is reversed up through the core from the bottom of the pressure vessel, where the coolant temperature increases<\/strong> as it passes through the fuel rods and the assemblies formed by them.<\/p>\n

Calculate:<\/strong><\/p>\n