Question

To determine thermal properties of a new material whose density and specific heat are known, the following experimentis proposed. A 5-cm-diameter cylindrical rod made of the sample material whose density and specific heat are 6500 kg/m and 900 J/kg -°C, respectively, is initially at a uniform temperature of 25°C. Temperatures of the sample at its surface and at its center are measured with two thermocouples, one welded to the surface and the other inserted and welded into a small hole drilled to the center. The sample is dropped into boiling water at 100°C. After 2 min, the surface and the center temperatures are recorded to be 93°C and 75°C, respectively. Which will be the heat transfer coefficient, h, in this experiment? Thermocouples Rod Boiling water 100°C

Answer 1

solution: Forcylinder triven, diameter of cylindex (D= 5cm = 0.05m density of cylinder material (S) = 6500 kg / m3 Specific heat of cylinder material (C) –9005lige Boiling water temperature God = 100°C initial temperature of cylinder (Ti) = 250 Surface ce temperature of cylinder tha=r)=93°C center temperature of cylinder (To-o) = 75°C = Tc (4) Time=2min = 120 sec For Cylinder

From houph 8-T - Too Vs % TETO - 95-100 =018 2 hogy o ho 0 25 L Biot Number From irraph o vs Yai To to I-Too = 75 10 20 5- 75 100 -0.33 ) Hai Ke 30125 3742 0.40 O' (Thermal diffusivity L = 0.40%² = 0.4ox (0.0522 2x60 = 2.088166 m/ &= Cp K= 28Cp =2.08X106x6500X900 = 12.168 W/moc Heat transfer co-efficient, (h) Bruk = 0.25 &h=12.168 0.28% (0.05%) =1946.88Wmzee :: Heat transfer co-efficient (W) i8 1946.88 Wm2oc.