Question

EXPERIMENT 2 Table 1: Table of Measurements FREE CONVECTION Heat Transfer Surface at Power = 90 W AIM T2 T1 Difference Ts - TIN (°C) . To compare the time taken for each surface to reach a given temperature for a fixed input power Time (seconds) Surface Ts (°C) Duct Inlet (ambient) TIN (°C) Flat Finned Pinned Flat Finned Pinned Flat Finned Pinned To understand the different thermal inertia characteristics of each heat surface for free convection 0 39.8 29.7 31.8 24.2 23.9 23.9 10 53.9 41.5 39.6 24.2 23.8 24.0 PROCEDURE 20 60.1 46.2 42.9 24.2 23.8 24.0 1. Remove the fan from the top of the duct. 2. Fit your chosen heat transfer surface. 30 66.7 51.6 45.9 24.2 23.8 24.0 40 71.4 55.2 48.3 24.2 23.8 23.9 3. Take readings of the surface and inlet temperatures. 4. Switch on the heater and set it to 90 Watts. Then start your timer. 50 78.0 59.9 51.2 24.1 23.8 23.9 60 83.1 62.7 53.6 24.1 23.8 23.9 70 88.5 66.5 56.2 24.123.8 23.9 80 92.6 69.7 58.3 24.1 23.8 23.9 5. Record the surface and inlet temperatures at intervals of 10 seconds until the surface temperature reaches approximately 70°C. 6. Switch off the heater and allow the surface to cool down to near ambient temperature. 7. Repeat the experiment for the other heat transfer surfaces. 90 97.5 72.9 60.4 24.123.8 23.9 100 100.6 | 76.0 62.3 24.1 23.8 23.9 110 106.7 79.0 64.1 24.123.8 23.9 ANALYSIS 120 110.4 81.9 65.9 24.1 23.8 23.9 130 114.6 84.6 67.8 24.1 23.7 23.8 1. The temperature difference gives a a value with respect to ambient, helping to allow for changes in local conditions 140 117.3 87.3 69.8 24.1 23.7 23.8 150 117.6 89.6 71.1 24.0 23.7 23.8 160 115.392.0 72.6 24.0 23.7 23.8 170 112.6 94.2 74.0 24.0 23.7 23.8 2. Create a chat of temperature difference against time. Add to this chart your results from all three surfaces to see the relationship and compare results. Do not use the first line. 3. Which surface took most time to reach 70°C? Look at the Technical Details for the surfaces and compare the different masses. Each surface is made of the same material and back side of each is of identical construction and mass, so do the results confirm thermal inertia theory? 4. Why can you only use this test as a general comparison? 5. What does this test tell you about the importance of waiting for equilibrium? 180 109.5 | 95.8 75.4 24.0 23.7 23.8 190 107.193.2 77 23.9 23.7 23.8 200 108.4 91.3 78.1 23.9 23.7 23.8

Answer 1

Time(s)	Difference Ts – Tin (0C)
Flat	Finned	Pinned
0	15.6	5.8	7.9
10	29.7	17.7	15.6
20	35.9	22.4	18.9
30	42.5	27.8	21.9
40	47.2	31.4	24.4
50	53.9	36.1	27.3
60	59	38.9	29.7
70	64.4	42.7	32.3
80	68.5	45.9	34.4
90	73.4	49.1	36.5
100	76.5	52.2	38.4
110	82.6	55.2	40.2
120	86.3	58.1	42
130	90.5	60.9	44
143	93.2	63.6	46
150	93.6	65.9	47.3
160	91.3	68.3	48.8
170	88.6	70.5	50.2
180	85.5	72.1	51.6
190	83.2	69.5	53.2
200	84.5	67.6	54.3

1. From th given data it is clear that the time taken to reach a particular surface temperature (say 780C ) is lower for flat and higher for pinned surfaces (tflat = 50s ,tfinn =110s,tpinn = 200s) .It is because the change in surface area.

2. If we done this experiment fo time = 200s ,from the data it is clear that the flat surface has more temperature rise as compaired to the other two surface. Also the surface area is less for flat surface . It will take more time to reach the intial surrounding conditionThe  tihermal inertia is depends on conductivity and heat capacity. the heat transfer rate is higher for pinned surface and then finned surface and lowest for flat surface. so the pinned surface take les time to reach surrounding temperature than finned and highest for flat surface.