In a fire-tube boiler, hot products of combustion flowing through an array of thin-walled tubes are used toboil water flowing over the tubes. At the time of installation, the overall heat transfer coefficient was
Whether the boiler should be scheduled for cleaning of the tube surfaces.
Answer to Problem 11.1P
Scheduled cleaning is essential.
Explanation of Solution
Given information:
The overall heat transfer coefficient at the time of installation:
Fouling factors of inner and outer tube surfaces after 1 year of use:
Calculations:
The overall heat transfer coefficient after one year is calculated as:
Thus, periodic cleaning is essential for efficient boiler operation.
Conclusion: The boiler should be scheduled for cleaning of the tube surfaces
Want to see more full solutions like this?
Chapter 11 Solutions
Fundamentals of Heat and Mass Transfer
Additional Engineering Textbook Solutions
Thinking Like an Engineer: An Active Learning Approach (4th Edition)
Engineering Mechanics: Statics
Degarmo's Materials And Processes In Manufacturing
Introduction To Finite Element Analysis And Design
Mechanics of Materials (10th Edition)
Statics and Mechanics of Materials (5th Edition)
- copper determine the overall heat transfer coefficient of a condenser formed of pipe when the fluid-side heat-transfer coefficient is 2000 W/m². °C and the heat-transfer coefficient on the refrigerant side is 1200 W/m². °C. The pipe has an outside diameter of 25.4 mm and an inside diameter of 19.8 mm. The thermal conductivity of steel is (410) W/m °C.arrow_forwardA heat recovery device involves transferring energy from the hot flue gases passing through an annular region to pressurized water flowing through the inner tube of the annulus. The inner tube has inner and outer diameters of 24 and 30 mm and is connected by 8 struts to an insulated outer tube of 40-mm diameter. Each strut is 3 mm thick and is integrally fabricated with the inner tube from carbon steel (k = 50W/m-K). E1 = 3 mm D. Water Gas Consider conditions for which water at 300 K flows through the inner tube at 0.161 kg/s while flue gases at 800 K flow through the annulus, maintaining a convection coefficient of 100 W/m2-K on both the struts and the outer surface of the inner tube. What is the rate of heat transfer per unit length of tube from gas to the water? Use the Dittus-Boelter equation to obtain the water-side convection coefficient. Determine the rate of heat transfer per unit length of tube from gas to the water, in W/m. i W/m Physical Properties Mathematical Functionsarrow_forwardA condenser consists of 5 horizontal pipes of 3 meters length of 1/4 sch40 arranged in 6 rows on top of each other. Cooling water with a heat transfer coefficient of 2000W / m-K flows through the pipes. As the flow rate of water is very high, the water temperature is fixed to 35C. Saturated water vapor at 2 bar pressure condenses outside the pipes. Calculate the condenser capacity in kW.arrow_forward
- Determine the length needed for a simple concentric-tube, parallel flow heat exchanger to transfer heat from hot water to cold water at a rate of 900 W. The heat exchanger consists of two Type K copper (k=386 W/m-degC) tubes. The smaller tube has an inside diameter of 49.8 mm and an outside diameter of 54.0 mm. Assume that both film coefficients are equal to 100 W/sq.m.-degC. The hot water enters at 90 degC and leaves at 50 degC, and the cold water enters at 10 degC and leaves at 40 degC.arrow_forwardYou as a Biochemical Engineer in an ezyme industries is assigned to handle a counter flow double pipe heat exchanger with A,= 9 m2 which used for cooling a fermentation broth (c, = 3.15 kJ/kg. K) at a rate of 10 kg/s with an inlet temperature of 90°C. The water used as coolant enters the heat exchanger at a rate of 8 kg/s with an inlet temperature of 10°C. The plant data gave the following equation for the overall heat transfer coefficient (in W/m².K): 600 %3D 1 2 • U.8 |m. where m. and m, are the cold and hot stream flow rates in kg/s, respectively.arrow_forwardA radiator heat exchanger is to be designed for the following specifications. Hot gas at 1145°C, Cold gas temperature 45°C, Unit surface conductance on the hot side, 230 W/m2-K, Unit surface conductance on the cold side 290 W/m2-K, Thermal conductivity of the metal wall 1115 W/m-K. Find the maximum thickness (in mm) of the metal wall between the hot gas and the cold gas so that the maximum temperature of the wall does not exceed 545°C.arrow_forward
- Task 2 A heat exchanger that is used for cooling lubricating oil is comprised of a thin-walled inner tube of 30 mm diameter carrying water and an outer tube of 50 mm diameter carrying the oil. The exchanger operates in counterflow mode with an overall heat transfer coefficient of 65 W/m² K and the tabulated average properties are given. Properties P (kg/m²) (J/kg-K) ▸ (m²/s) k (W/m K) Pr Page 6 of 8 Water 1000 4200 7 x 107 0.64 4.7 Oil 800 1900 1 x 10-5 0.134 140 Join = 100°c OiL m = 0.2kg/s To, out tr Water> mw=0-15kg, S Twin = L Tw, out 30°℃ (a) If the outlet temperature of the oil is 60°C, determine the total heat transfer and the outlet temperature of the water. (b) How long must the tube be made if the outlet temperature of the oil is 60°C? (c) Explain and discuss with the use of diagrams the difference between parallel and counter flow heat exchangers? (d)If the heat exchanger is changed to a parallel flow heat exchanger, how long must the tube be made if the outlet temperature…arrow_forwardSaturated water vapor at 100°C condenses in the shell side of a one-shell and two-tube heat exchanger with a surface area of 0.5 m2 and an overall heat transfer coefficient of 2000 W/m2·K. Cold water (cpc = 4179 J/kg·K) flowing at 0.5 kg/s enters the tube side at 15°C, determine the outlet temperature of the cold water and the heat transfer rate for the heat exchanger.arrow_forwardTask 2A heat exchanger that is used for cooling lubricating oil is comprised of a thin-walled inner tube of 30mm diameter carrying water and an outer tube of 50 mm diameter carrying the oil. The exchanger operates in counterflow mode with an overall heat transfer coefficient of 65 W/m2 K and the tabulated average properties are given. (a) If the outlet temperature of the oil is 60°C, determine the total heat transfer and the outlet temperature of the water.(b) How long must the tube be made if the outlet temperature of the oil is 60°C?(c) Explain and discuss with the use of diagrams the difference between parallel and counter flow heat exchangers?(d)If the heat exchanger is changed to a parallel flow heat exchanger, how long must the tube be made if the outlet temperature of the oil is 60°C?arrow_forward
- 5. Hot exhaust gases, which enter a finned-tube, cross-flow heat exchanger at 300 °C and leave at 100 °C, are used to heat pressurized water at a flow rate of 1 kg/s from 35 °C 125 °C. The specific heat of water at the average water temperature is 4197 J/kg. K. The overall heat transfer coefficient based on the gas-side surface area is Uh = 100 W/m².K. Determine the required gas-side surface area A₁ using the LMTD and & -NTU method.arrow_forwardA heat exchanger is to be designed to condense 8 kg/sec of an organic liquid (tsat=80°C, hfg=600 KJ/kg) with cooling water available at 15°C and at a flow rate of 60 kg/sec. The overall heat transfer coefficient is 480 W/m2 -°C calculate: a) The number of tubes required. The tubes are to be of 25 mm outer diameter, 2 mm thickness and 4.85 m length b) The number of tube passes. The velocity of the cooling water is not to exceed 2 m/sec.arrow_forwardA 15 cm bare oxidized steel (Ɛ = 0.79) pipe (16.8 cm O.D.) carrying steam at a high temperature is enclosed in a 30 x 30 cm red brick (Ɛ = 0.80) conduit having wall temperatures somewhat lower than the pipe diameter. What percentage of the heat lost by radiation from the pipe would be saved if the conduit walls were painted with aluminum paint (Ɛ = 0.52)arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning