Question

Homework 7 heat transfer 2018-20 1) A horizontal tube of 12.5-mm dimeter with an outer srface temperature of 240°C is placed in a room with an air temperature of 20°C. Estimate the heat transfer rate per unit length of the tube due to free convection. 2) Air at -10°C flows at 10 m/s over the roof plate of two 5m length rooms whose air is at Too-200C. The roof plate is 0.20-m thick concrete (k = 0.6 w/ m. K). a) determine the heat transfer rate from each room to the external air per width-room unit and b) now assume that the rooms are insulated with a 0.20-m layer of fiberglass (k 0.043 W/m2. K), sticking to the inside surface of the plate concrete, and determine as the heat transfer rate changes 3) Water enters a horizontal thin-walled, 50-mm diameter long tube at 0.2 kg/s and 90°C The tube is placed in a room with quiet air at 10°C . a) Estimate the pipe length required to cool the water to 30°C. b) Now estimate the water outlet temperature (Tma, the average surface temperature of the tube (T:), and the heat transfer rate if the tube length is 8 m. 4)A drying oven consists of a long semicircular duct of diameter 1 m. Materials to be drying cover the base of the oven, while the wall is maintained at 1200 K. What is the drying per unit length of the oven (kg/s) if the water-coated layer of material is maintained at 325 K during the drying process? Assume balk-body behavior of the surfaces. 5) Consider the two very long parallel plates. The upper plate is black and is at 1000 K, while the lower is gray with an emissivity of 0.8 and a temperature of 500 K. Determine the irradiation and radiosity for the upper plate and the radiosity for the lower plate. What is the net radiation exchange between the plates per unit area of the plates? 6) Determine the net radiation heat transfer from each surface of the following room, assuming that: i) the surface 1 has a emissivity of 0.8 and is maintained at 40°C by embedded electrical heating element, i) heaters are also used to maintain the surface 2 of emissivity 0.9 at 50°C, ili) the wall 3 of emissivity 0.7 is at 15°C, and iv) the walls 5A and 5B are very well insulated. 10 m 6 m

Answer 1

Please refer the following image for the solution.

D Soluhom Given dato Tube lian, eter, d: 12.5mm-0.0)25m Outside ait temperetue o 20 Propevtes o ain T 240120 130C 240+20 130 C 2. 0.8824 (13o 12735 2.4813313 2 2 153フ3.35421 Ga 1D) O188 Nu 4.86S Nu ho Nuxk 4863.36S x162 Ο, 012S .: Heat tromsfen cte per unit tenth, x o. 0125 R1n (240-2o 13.0967% 113.147W