3. For the same composite in Question 2, air temperature on the left side is 20°C, and on the right side is 80°C. Convection coefficient is h = 15W/m²K on both sides. What is the rate of heat transfer through the composite? (Answer: 17.177W) 4. A steam pipe 8m long has an external diameter of 100mm and it is covered by lagging 50mm thick. The pipe contains steam at 198°C and the temperature of the atmosphere surrounding the pipe is 18°C. The thermal conductivity of the lagging is 0.15W/mK. The surface heat transfer coefficient is 10W/m²K. Assuming the pipe has the same uniform temperature as the steam, calculate the heat loss and the surface temperature of the lagging. (Answer: 1609 W, 50°C) 5. A spherical tank 2m diameter contains liquefied fuel gas. It is covered in insulation 120mm thick with a thermal conductivity of 0.025W/mK. The surface heat transfer coefficient between the lagging and the surrounding air is 30W/m²K. The air is at 25°C and the liquid is -125°C. Assume the inner surface temperature is the same as the liquid. Calculate the heat transfer rate required to keep the liquid at a constant temperature and surface temperature of the insulation. (Answer: 437.32 W, 24.1°C) 6. A nylon pipe has a bore of 50mm and a wall thickness of 5mm. It is covered with insulation 10mm thick. The thermal conductivity of the nylon is 0.25W/mK and for the insulation it is 0.1 W/mK. The inside of the pipe carries hot water at 50°C and the outer surface of the pipe is at 10°C. Calculate the heat loss per metre length and the temperature between the two materials. (Answer: 70 W/m, 41.9°C) Assessment 4 PMAOPS511 Determine Energy Transfer Loads Radiated Heat Transfer and Radiated Surface Heat Transfer Coefficient & Comparing heat transfer rates for different fluids and determine appropriate fluid for the application Assessment instructions: You are provided following engineering/or daily life scenarios. Use the acquired knowledge and skills to find the unknown parameter(s) • ⋅ Draw a neat clean diagram Show Thermal circuit . Show all the variable that are known and unknown before attempting to substitute values in equations Make sure you are using appropriate units for all the variables before the values are put in respective correct equations Remember a numerical value doesn't have any significance if units are not mentioned (unless the measured quantity is dimensionless) 1. Determine the heat radiated from an electric radiator consisting of a coil wound from 2.8 m of 0.8 mm wire when the surface temperature of the wire is 1100°C and the surface emissivity 0.75. (1.06kW) 2. A grey iron casting has a surface area of 6.5m². It is stripped from the mould when the surface temperature is 400°C. Determine the rate at which heat is radiated from the casting if the temperature in the foundry is 30°C and emissivity of the grey cast iron is 0.31 (22.5KW) 3. The flame in a steam generator furnace has a temperature of 1250°C and the surrounding surface of the furnace is at a temperature of 220°C. What is the maximum possible rate of heat transfer by radiation per m² of wall area? (301708.7 W) If the actual surface emissivity is 0.7, what is the actual radiation heat transfer rate per m² of wall area? (211196.09 W) A radiator may be treated as a block body with a true surface area of 10m² and an envelope area of 6m². It has a surface temperature of 40°C and is situated in a dark room at 20°C. The surface heat transfer coefficient is 4W/m²K. Calculate ACERT the radiation heat transfer rate (Qadation), convection heat transfer rate (qconvection) (757.9 W, 800W & 1557.9W) and total heat transfer rate Calculate the radiated surface heat transfer coefficient (hr) and obtain the same result for heat transfer by radiation (q.) using it. (6.31W/m²K) 5. The roof of a truck at a mine site in a parking lot absorbs a solar radiant flux of 650 W/m². While the underside perfectly insulated. The convection coefficient between the roof and the ambient air is 12 W/m²K. (a) Neglect the radiation exchange with the surroundings; calculate the temperature of the roof under steady state conditions if the ambient air temperature is 20°C. (74.2°C) (b)For the same ambient air temperature calculate the temperature of the roof if the surface emissivity is 0.8 (Note: include heat transfer by radiation in your energy balance equation for this part. You need to adopt trial and error solution to obtain the final temperature) 6. (a )A cartridge electrical heater is shaped as a cylinder of length L = 200 mm and outer diameter D = 20 mm. Under normal operating conditions the heater dissipates 2 kW, while submerged in a water flow that is at 20°C and provides a convection heat transfer coefficient of h =5000 W/m2.K. Neglecting heat transfer from the ends of the heater, determine its surface temperature Ts. Smont yvizeime doute (51.8°C) (b) If the water flow is inadvertently terminated while the heater continues to operate, the heater surface is exposed to air that is also at 20°C but for which h= 50W/m²K.What is the corresponding surface temperature? (c) What are the consequences of such an event? (3203°C) (d) Out of the two fluid (water and air) which one would you recommend to have a controlled heat transfer rate and ensuring the integrity of the heater? WOIBLES