Chapter 2, Problem 2.32P

Determine the rate of heat transfer per meter length to a light oil flowing through a 2.5-cm-ID, 60-cm-long copper tube at a velocity of 0.03 m/s. The oil enters the tube at 16C, and the tube is heated by steam condensing on its outer surface at atmospheric pressure with a heat transfer coefficient of 11.3 kW/m K. The properties of the oil at various temperatures are listed in the following table: Temperature, T(C) 15 30 40 65 100 (kg/m3) 912 912 896 880 864 c(kJ/kgK) 1.80 1.84 1.925 2.0 2.135 k(W/mK) 0.133 0.133 0.131 0.129 0.128 (kg/ms) 0.089 0.0414 0.023 0.00786 0.0033 Pr 1204 573 338 122 55

A 300-ft-long section of a steam pipe whose outer diameter is 4 in passes through an open space at 50°F. The average temperature of the outer surface of the pipe is measured to be 280°F, and the average heat transfer coefficient on that surface is determined to be 6 Btu/h·ft2·°F. Determine (a) the rate of heat loss from the steam pipe and (b) the annual cost of this energy loss if steam is generated in a natural gas furnace having an efficiency of 86 percent, and the price of natural gas is $1.10/therm (1 therm = 100,000 Btu).

Consider a wall heated by convection on one side and cooled by convection on the other side. Show that the heat-transfer rate through the wall is q = (T1 - T2) / (1/h1A + x/kA + 1/h2A) where T1 and T2 are the fluid temperatures on each side of the wall and h1 and h2 are the corresponding heat-transfer coefficients.

Question -) Consider a stainless steel spoon (k = 15 W/m·K) partially immersed in boiling water at 95°C in a kitchen at 25°C. The handle of the spoon has a cross section of 0.2cm x 1.2 cm, and extends 18 cm in the air from the free surface of the water. If the heat transfer coefficient at the exposed surfaces of the spoon handle is 15 W/m2·°C, determine the temperature difference across the exposed surface of the spoon handle. State your assumptions.

The condenser of a steam power plant operates at a pressure of 7.38 kPa (Tsat = 40°C). Steam at this pressure condenses on the outer surfaces of horizontal pipes through which cooling water circulates. The outer diameter of the pipes is 3 cm, and the outer surfaces of the pipes are maintained at 30°C. Determine the rate of heat transfer to the cooling water circulating in the pipes.The properties of water at the saturation temperature of 40°C are: hfg = 2407 × 10^3J/kg and ρv=0.05 kg/m3. The properties of liquid water at the film temperature: ρl = 994 kg/m3, Cpl =4178 J/kg°C, µl = 0.72 × 10^-3 kg/m.s, kl = 0.623 W/m°C Select one: a. 6758W b. 5758W c. 8758W d. 7758W

Water is to be heated from 15°C to 65°C as it flows through a 3-cm-internaldiameter 5-m-long tube . The tube is equipped with an electric resistance heater that provides uniform heating throughout the surface of the tube. The outer surface of the heater is well insulated, so that in steady operation all the heat generated in the heater is transferred to the water in the tube. If the system is to provide hot water at a rate of 10 L/min, determine the power rating of the resistance heater. Also, estimate the inner surface temperature of the tube at the exit.

A 0.6-cm-diameter mild steel rod at 38°C is suddenly immersed in a liquid at 93°C with h=110 W/m2 K. Determine the time required for the rod to warm to 88°C. Thermal conductivity (k) = 43 W/(m K); Specific heat (c) = 473 J/(kg K); Density = 7801 kg/m3 Thermal diffusivity (α) = 1.172 *10–5 m2/s.

Water is heated from 2°C to 78°C at a constant pressure of 100 kPa. The initial density of water is 1000 kg/m3 and the volume expansion coefficient of water is ?=0.377×10–3K–1. The final density of the water is (a) 28.7 kg/m3 (b) 539 kg/m3 (c) 997 kg/m3 (d) 984 kg/m3 (e) 971 kg/m3

The inner and outer surfaces of a 0.5-cm-thick 2-m × 2-m window glass in winter are 15°C and 6°C, respectively. If the thermal conductivity of the glass is 0.78 W/m·°C, determine the amount of heat loss, in kJ, that occurs through the glass over a period of 10 h. What would your answer be if the glass were 1 cm thick?