Oxy-acetylene torches can be used to cut or weld metal .Oxygen and acetylene are fed from separate compressed gas cylinders through pressure regulators to the torch where they are mixed and combusted .To estimate the amount of metal that can be cut or welded per unit volume of gas, the composition of the gases produced by combustion and heat produced by the combustion reaction must be determined .For this problem: Define a closed system that can be used to calculate the heat produced Define an open system that can be used to calculate the heat produced List at least two intensive variables that are important in calculation List at least two extensive variables that are important in the calculation

Oxy-acetylene torches can be used to cut or weld metal .Oxygen and acetylene are fed from separate compressed gas cylinders through pressure regulators to the torch where they are mixed and combusted .To estimate the amount of metal that can be cut or welded per unit volume of gas, the composition of the gases produced by combustion and heat produced by the combustion reaction must be determined .For this problem: Define a closed system that can be used to calculate the heat produced Define an open system that can be used to calculate the heat produced List at least two intensive variables that are important in calculation List at least two extensive variables that are important in the calculation

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter7: Forced Convection Inside Tubes And Ducts

Section: Chapter Questions

Problem 7.1DP

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In the United States, energy for household heating is generally sold using English units, e.g., therm, gal, and cord. A house in Wisconsin uses 1200 therms of thermal energy during the heating season. Calculate the cost of fuel if the furnace uses (a) natural gas with an efficiency of 70%; (b) No. 2 fuel oil, efficiency 65%; (c) kerosene, efficiency 99.9% (unvented); and (d) wood with l5% moisture with an efficiency of 50%. Use the data in Tables 2.2, 2.7, and 2.13. The efficiencies are based on the HHV. Assume the cost of natural gas is $8/MBtu, the cost of No. 2 fuel oil is $3/gal, the cost of kerosene is $3.50/gal, and the cost of wood is $100/cord. Assume the bulk density of cord wood is 30 lbm/ft3 .
Steam is produced in the copper tubes (k =223 Btu/h · ft · °F) of a heat exchanger at a temperature of 250°F by another fluid condensing on the outside surfaces of the tubes at 350°F. The inner and outer diameters of the tube are 1 in. and 1.3 in., respectively. When the heat exchanger was new, the rate of heat transfer per foot length of the tube was 2x104 Btu/h. (a) Determine the rate of heat transfer per foot length of the tube when a 0.01-in.-thick layer of limestone (k =1.7 Btu/h·ft·°F) has formed on the inner surface of the tube after extended use. (b) Assuming that a 0.01-in.-thick limestone layer has formed on both the inner and outer surfaces of the tube. Answer: 1.45x104 Btu/h; 1.20x104 Btu/h
6) In a boiler installation coal is burnt at the rate of 1.9 x 10³ kg/hr and hot gases are generated at the rate of 18 kg per kg of coal burnt. Hot gases are at the temperature of 600 K and ambient air temperature is 300 K Different pressure losses in furnace grate, flues, bends and chimney are measured to be 6 mm, 5 mm, 3 mm, and 1 mm of water respectively. Hot gases leaving chimney have velocity equivalent to 1.2 mm of water column. Considering the actual natural draught to be 80% of theoretical draught determine the height and diameter of chimney.
Steam enters the superheater of a boiler at a pressure of 25 bar and dryness of 0.98 and leaves at the same pressure at a temperature of 370O |Calculate the heat energy supplied per kg of steam supplied in the superheater.
A large piece of biological tissue has to be kept at a temperature as low as possible without freezing (ice formation). The water in the tissue has several solutes dissolved in it and the effective molecular weight of the dissolved solutes is 50. The weight of all dissolved solutes combined is 10% of the weight of water. The latent heat of fusion of water is 335 kJ/kg and the molecular weight of water is 18. What is the lowest temperature that this tissue can be stored at, without ice formation?
Ethylene glycol with a mass flow rate of 0.01 kg / sec flows in a thin-walled pipe with a diameter of 3 mm. The pipe is in the form of a serpentine, and was lifted into a well-mixed water bath at 25 ° C. Calculate the heat transfer and pipe length required for the fluid to enter the pipe at 85 ° C and exit at 35 ° C?
When a hydrocarbon fuel is burned, almost all of the carbon in the fuel burns completely to form CO2 (carbon dioxide). On average, 0.59 kg of CO2 is produced for each kWh of electricity generated from a power plant that burns natural gas. A typical new household refrigerator uses about 700 kWh of electricity per year. The city's refrigerators produce. 20,650 mton CO2/year. If the area of the city is 190 miles2, and if all that CO2 accumulates in the atmosphere, calculate the increase in CO2 concentration by weight in the atmosphere knowing that each cm2 of area carries a column of air that weighs 1 kg. If 1 mature tree absorbs 48 lbm of CO2 per year, what is the ratio of trees to households this city should have to counter the effect of refrigeration?
room has a floor area of 500 m2and a height of 4 m. The room is involved in a firewith a constant energy release rate of 1 MW. Calculate the time till the smoke layer is1.5 m from the floor for(a)The case where the leakage areas are at the floor level.(b) The case where the leakage areas are at the ceiling level
Design a hydrocooling unit that can cool fruits and vegetables from 30 to 5 °C at a rate of 20,000 kg/h under the following conditions:The unit will be of the flooded type, which will cool the products when they are transported in the channel filled with water. Products will be dropped into the water filled chute at one end and collected at the other end. The channel can have a width of up to 3 m and a height of up to 90 cm. The water will circulate and be cooled by the evaporator section of a refrigeration system. The temperature of the refrigerant inside the coils will be 2°C, and the temperature of the water must not fall below 1.5°C and must not exceed 7°C.Assuming reasonable values for the average density, specific heat, and porosity of the product (the fraction of the volume of air in a box), recommend reasonable values for a) the velocity of the water through the channel and b) the flow rate refrigeration system cooling (QL). Compressor efficiency 75%. For the calculation of the…
Design a hydrocooling unit that can cool fruits and vegetables from 30 to 5 °C at a rate of 20,000 kg/h under the following conditions:The unit will be of the flooded type, which will cool the products when they are transported in the channel filled with water. Products will be dropped into the water filled chute at one end and collected at the other end. The channel can have a width of up to 3 m and a height of up to 90 cm. The water will circulate and be cooled by the evaporator section of a refrigeration system. The temperature of the refrigerant inside the coils will be 2°C, and the temperature of the water must not fall below 1.5°C and must not exceed 7°C.Assuming reasonable values for the average density, specific heat, and porosity of the product (the fraction of the volume of air in a box), recommend reasonable values for a) the velocity of the water through the channel and b) the flow rate refrigeration system cooling (QL). For the calculation of the reasonable values…
Part b. MATLAB coding. Hot air for a large scale drying operation is to be produced by routing the air over a tube bank, while products of combustion are routed through the tubes. The surface area of the cross-flow heat exchanger is A = 25 m2, and for the proposed operating conditions, the manufacturer specifies and overall heat transfer coefficient of U = 35 W/(m2 K). The air and the combustion gases may each be assumed to have a specific heat of cp = 1040 J/(kg K). Consider conditions for which combustion gases flowing at 1 kg/s enter the heat exchanger at 800 K, while air at 5 kg/s has an inlet temperature of 300 K. (a) What are the air and gas outlet temperatures? (b) Explore the effect of changes in surface area and heat transfer coefficient on the air outlet temperature for UA values from 500 to 2500 W/K. Discuss the implications and back up the discussion with an appropriate plot
Steam generators are a type of heat exchanges that are used in power plants to generate steam at desired pressure and temperature (Fig. Q1.b). In a steam generator, saturated liquid water at 30°C enters a 60-mm diameter tube at the volume flow rate of 12 L/s. After exchanging heat with hot gas, the water changes to steam and leaves the generator at a pressure of 9 MPa and a temperature of 400°C. During this process, the diameter of the water/steam tube does not change.(iv) Calculate the rate of heat transfer (in MW) required tochange the phase of liquid water to steam.