Heat transfer heal pipes

The pipe is then lagged with a 50 mm thickness of lagging of thermal conductivity 0.1 W/m K. If the outside heat transfer coefficient is given by the same equation as for the bare pipe, by what factor is the heal loss reduced ... 

The heal transfer piping system is not simple. There were three reactors and the heat transfer system was used for both heating and C(xiling the reactor. The circulating fluid heats the reactor to several hundred degrees Fahrenheit to start the reaction. Once the ery exothermic reaction is underway, the circulating heat fluid removes heat from this reactor. (.See Figure 7-1.)... 

Z-Xl Water flows through a pipe at an average temperature of VO C. The inner and outer radii of the pipe are rf = 6 cm and rj = 6.5 cm. respectively. The outer surface of the pipe is wrapped with a thin electric heater that consumes 300 W pet m length of the pipe. The exposed surface of the heater is heavily insulated so that the entire heal generated in the heater is transferred to the pipe. Heat is transferred from the inner surface of the pipe to the water by convection with a heat transfer coefficient of h = 85 W/m K. Assuming constant thermal conductivity and one-dimensionat heat transfer, express the mathematical formulation (the differential equation and the boundary conditions) of the heal conduction in the pipe during steady operation. Do not solve. 

In steady operation, there is no change in the temperature of the pipe with time at any point. Therefore, the rate of heat transfer into the pipe must be equal to the rate of beat transfer out of it. In other words, heal transfer through tlie pipe must be constant, t cond.cyi constant. 

Therefore, the diameter of the copper rod needs to be almost 40 times that of the heat pipe to transfer heal at the same rale. Also, the rod would have a mass of 120 kg, which is impossible for an average person to lift. 

The thermal resistance network associated with this heat transfer process involves two convection and one conduction resistances, as shown in Fig. 11-7. Here the subscripts i and o represent the inner and outer surfaces of the inner tub d. For a double-pipe heal exchanger, the Ihennul resistance of the tube wall is >... 

A double-pipe parallel-flow heat exchanger is to heal water (c = 4180 I/fcg °C) from 25°C to 60°C at a rate of 0.2 kg/s. The healing is to be accomplished by geothermal water (c = 4310 J/kg °C) available at 140"C at a mass flow rale of 0.3 kg/s. The inner tube is thin-walled and has a diameter of 0.8 cm. If the overall heat transfer coefficient of the heat exchanger is 550 W/m °C, determine the length of the tube required to achieve the desired heating. 

Cold water (Cp = 4180 J/kg °C) leading to a shower enters a Ihin-wallcd double-pipe counter-flow heat exchanger at I5°C at a rate of 1.25 kg/s and is healed to 45"C by hot water (Cp = 4190 J/kg °C) that enters at 100°C at a tale of 3 kg/s. If the overall heat transfer coefficient is 880 W/ni °C, determine the rate of heat transfer and the heat transfer surface area of the heat exchanger. 

Glycerin (Cp = 2400 J/kg °C) at 20 C and 0.3 kg/s is lo be heated by ethylene glycol (Cp = 2500 J/kg C) at 60°C in a thin-walled double-pipe parallel flow heat exchanger. The temperature difference between the two fluids is 15°C at the outlet of the heat exchanger. If the overall heat transfer coefficient is 240 W/ni °C and the heal transfer surface area is 3.2 m, determine (a) the rate of heat transfer, (b) the outlet temperature of the glycerin, and (c) the mass flow rate of the ethylene glycol. 

C Consider a double-pipe counter-llow heat c.xchanger. In order to enhance heat transfer, Ihc length of the heal exchanger is now doubled. Do you think its effectiveness will also double ... 

A thin-walled double-pipe parallel-flow heal exchanger is used to heat a chemical whose specific heat is 1800 J/kg - C with hot water (c, = 4180 J/kg °C). The chemical enters at 20 C at a rate of 3 kg/s, while the water enters at 110°C at a rale of 2 kg/s. The heal transfer surface area of the heat exchanger is 7 and the overall heat transfer coefficient is 1200 W/m -"C. Delermine Ihe outlet temperatures of the chemical and the water. 

Mori, Y. and W. Nakayama, Study on Forced Convective Heat Transfer in Curved Pipes, Pt. 11 Turbulent Flow Region, Int. J. Heal Mass Transfer, 10, 37-59 (1967). 

Heat transfer from steam to pipe Heal transfer from pipe to insulation Heat transfer from insulation to air ... 

One of the simplest and cheapest types of heat exchanger is the concentric pipe arrangement known as the double-pipe heat exchanger. Such equipment can be made up from standard fittings and is useful where only a small heal transfer area is required. Several units can be connected in series to extend the capacity. ... 

Tfe A 50-m-long section of a steam pipe whose outer Wy diameter is 10 cm passes through an open space at IS C. The average temperature of the outer surface of the pipe is measured to be 150°C. If (he combined heal transfer coefficient on the outer surface of the pipe is 20 W/m C, determine (a) the rate of heat loss from the steam pipe (b) the... 

C- A. Sleicher and M. W. Rouse. A Convenient Correlation for Heal Transfer to Constant and Variable Property Fluids in Turbulent Pipe Flow. International Journal of Heat Mass Transfer 18 (1975), pp. 1429-1435. 

Hot water at 90°C enters a 15-m section ofa cast iron pipe (k = 52 W/m °C) whose inner and outer diameleis arc 4 and 4,6 cm, respectively, at an average velocity of 1.2 m/s.Tlie outer snrface of the pipe, whose emissivily is 0.7, is exposed to the cold air al 10°C in a basement, with a convection heal transfer coefficient of 12 W/ni C. Taking the walls of Ihe basement to be at 10°C also, determine (a) the rate of heat loss from tile water and (f>) the temperature at which the water leaves Uie basement. 

FIGURE 11-7 Tliermal resistance network associated with heal transfer in a double-pipe heat exchanger. 

The mass flow rate, specific heat, and inlet temperature of the tube-side stream in a double-pipe, parallel-flow heat exchanger are 2700 kg/h, 2.0 kJ/kg K, and 120°C, respectively. The mass flow rate, specific heat, and inlet temperature of the other stream are 1800 kg/h, 4.2 kJ/kg K, and 20°C, respectively. The heat Iranster area and overall heal transfer coefficient are 0.50 and 2.0 kW/m K, respectively. Find the outlet temperatures of both streams in steady operation using (a) the LMTD method and (6) the effcctivcncss-NTU method. 

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