An uninsulated steam pipe passes through a room in which the air and surrounding walls are at25◦c. the outside diameter of the pipe is 70mm, and its wall temperature and emissivity are200◦cand 0.8, respectively. the heat transfer coefficient associated with the free convection heattransfer from the wall to the air is 15w/m2·k. a)what is the wall emissive power. b)what is the rate of heat loss from the wall per unit length of pipe by radiation? c)what is the total rate of heat loss from the wall per unit length of pipe by radiation and freeconvection? d)calculate an approximate radiative heat transfer coefficient based on the wall temperature. basedon this approximated radiative heat transfer coefficient what would be the approximate radiativeheat loss from the wall to the surroundings? e) repeat part (d) by calculating an approximate radatve heat transfer coefficient based on theaverage temperature, taverage= [tw+tsur]/2. any comments? note that of if we had forced convection, the forced convection heat transfer could be much largerin magnitude than the free convection and radiative heat transfer. (hint: tsur=tair=t[infinity])

Abearing is designed to a reduce friction b. support a load c.guide moving parts such as wheels, shafts and pivots d. all of the above

Aroll in a paper machine is powered by a separately excited dc machine. operating point 1 (under load): the roll typically operates at 764 rpm and must provide 301 nm of torque to oppose the load of the paper. the armature voltage is 230v for this operating point operating point 2 (no load): when the load is removed the speed of the roll increases to 900 rpm (the field characteristics are unchanged) la ea dev m (a) calculate the maximum torque (units of nm) that the motor can supply with this applied voltage (b) calculate the value of the armature resistance, ra (in ohms) (c) at operating point 1 (loaded condition), the field current, i, and the total input power (armature field), are measured to be to be 10 a and 28,600 w respectively. use this information to calculate the value of the field resistance, rf (in ohms). (d) (d) at operating point 1 (loaded condition), calculate the motor efficiency. express your answer as a percent to at least 2 significant digits. (d) if the field voltage is reduced by 1/2, calculate the new stall torque (in nm) of the motor (f). if the field voltage is reduced by 1/2, calculate the new no-load speed (in rad/sec)

Ms.hidalgo opens the door to her classroom. her classroom is 60 degrees and the air outside is 80. predict what will happen using your knowledge of how heat flows.