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Heat and Mass Transfer - Introduction to Fire Hazard in Buildings

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The SI unit for thermal conductivity, k is watt per meter kelvin (W/m.K)

ii. W/m.K is not same with W/m. °C. Even though both of the units have same dimensional equation which is M1L1T-3ϴ-1. However, the temperature unit used for k is difference which is kelvin and Celsius. Kelvin (K) is one of the basic unit in the International System of Units (SI) while Celsius (°C) is a derivation from SI unit. In Kelvin scale, it do not have negative value while Celsius scale have negative values.

iii. There are many experimental ways to find the thermal conductivity, k, of material nowadays. Few example of experimental ways are transient plane source method, transient line source method, laser flash method, Searle’s bar method, Lees’ disk method and 3ω-method. The chosen method that will be describe in this question is Lee’s Disc Method. Lee’s Disc method is used to determine an approximate value of the thermal conductivity, k, of a poor conductor (non-metal) of heat such as glass [1]. In this method, the apparatus of Lee’s Disc was set up (refer figure 1). The list of the apparatus are steam chamber, 2 Lee’s disc, thermometers, steam generator.

Figure 1

List of equation used in this experiment;

K=(mcd(dT/dt)_(T_2 ))/(A(T_1-T_2))

Where; thickness of the tested material, d (m)

Cross sectional area of disc, A (m)

Metallic disc temperature, T1 ( 0C)

Brass disc temperature, T2 ( 0C)

The slope of graph, (dT/dt)_(T_2 )

Mass of brass disc, m (kg)

C is constant

The SI unit for heat transfer coefficient h used in convection is W/m2.K.

Absolute zero is the lowest temperature possible. Absolute zero occur at 0 degrees Kelvin or at -273.15 degrees Celsius or at -460 degrees Fahrenheit. At this temperature there is no motion and no heat. That’s mean all atomic and molecular motion stops. Object with 0 degrees Celsius still can radiate energy this is because the atomic and molecular motion still exist at 0 degrees Celsius. An object still radiate energy although the molecular motion is slow. The motion of atomic and molecular only stop at absolute zero that is at 0 degrees kelvin. So, 0 degrees Celsius is above the absolute zero and an object still can radiate heat [4].


Introduction to fire hazard in buildings.

With the development of science and technology, building industry is growing rapidly. Many kinds of buildings come out. As the building gathers the enormous wealth and population, the society is faced with serious security issues and fire accidents occur frequently. The building fire accidents involve in many hazard factors and are difficult to manage.

The only recorded structural failures in tall buildings in the last 30 years are earthquake and fire related, and in the case of mechanical failure resulting from earthquakes, it was failure to adhere to building code requirements or accepted engineering practices that ended with the undesired result. Where strong code enforcement and / or adequate engineering is prominent, major earthquakes have resulted in no significant damage to tall structures, thus there is a strong feeling that structural design, in particular with respect to seismic loading, is evolving in step with the transformation of tall buildings. The case of fire failures is clearly different with the last decade or so seeing the collapses of tall buildings of different structural forms as a result of fire.

Nowadays, with the high amount of the tall buildings, the fire hazard risks are higher too. Buildings need to have fire safety system, so the risks will be decreased. Performance based-design has been introduced in many places and the determination of design fire is one of the most important steps in the design process [5]

The important inputs we need to predict and calculate are Fire Load and Heat Release Rate. Heat Release Rate must be known in order to estimate the fire hazard. It will give information such as fire size, rate of smoke production, and the possible fire environment. The main factors that control the fire environment at growth stage and fully developed stage are different.

Heat release rate in the growth stage

In the fire growth stage, there is sufficient oxygen for combustion and the fire is so-called fuel-controlled. The characteristics, distribution and arrangement

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