Introduction to Heat Transfer
6th Edition
ISBN: 9780470501962
Author: Frank P. Incropera, David P. DeWitt, Theodore L. Bergman, Adrienne S. Lavine
Publisher: Wiley, John & Sons, Incorporated
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Chapter 7, Problem 7.56P
a.
To determine
The cost of lost heat.
b).
To determine
Savings associated with
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A 6 kg/s of hot liquid flow continuously without leaking in a 40 mm inside diameter with thickness of 7 mm pipe with temperature of 50℃. Thermal conductivity of pipe is 10W/(m℃) and surface conductance of liquid is 9W/(m^2℃). The outer fluid has temperature of 25℃ and surface conductance of 6W/(m^2℃). Cp of hot liquid = 4.2KJ/(Kg℃). Find the minimum length of pipe in meters just to cool down the hot liquid as much as possible if the maximum heat transfer is the constant heat transfer throughout the pipe.
Water at an average temperature of 23 deg C flows through a 10-cm diameter pipe that is 2.5 m long. The pipe wall is heated by steam and is held at 100 deg C. The convective heat transfer coefficient is 2.25 x 10^4 W/m^2K. Find the heat flow in W.
Consider the same problem in which an
axial compressor with a mean diameter of
0.8 m is being designed to run at 3000
rpm. The whirl velocities at the inlet and
outlet are 5m/s and 30 m/s, respectively.
The air mass flow rate through the
compressor is 2 kg/s at a temperature of
27 °C.
Assume C, of air equal to 1000 J/kg-K
and Cy = 718 J/kg-K.
%3D
The temperature change is equal to
O 3.14 K
5.28 K
7.42 K
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Chapter 7 Solutions
Introduction to Heat Transfer
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- Consider the same problem in which an axial compressor with a mean diameter of 0.8 m is being designed to run at 3000 rpm. The whirl velocities at the inlet and outlet are 5m/s and 30 m/s, respectively. The air mass flow rate through the compressor is 2 kg/s at a temperature of 27 °C. Assume C, of air equal to 1000 J/kg-K and Cy = 718 J/kg-K. The pressure ratio is equal to O 1.037 O 1.065 O 1.370 O 1.873arrow_forward3:10 < Back 1. Ch. 8 An 8-m-long, uninsulated square duct of cross section 0.2 m x 0.2 m and relative roughness 10³ passes through the attic space of a house. Hot air enters the duct at 1 atm and 80°C at a volume flow rate of 0.15 m³/s. The duct surface is nearly isothermal at 60°C. Determine the rate of heat loss from the duct to the attic space and the pressure difference between the inlet and outlet sections of the duct. Evaluate air properties at a bulk mean temperature of 80°C. Is this a good assumption? (Use the Moody chart if you need a friction factor.) Water 2. Ch 8 Liquid water flows at a mass flow rate of 0.7 kg/s through a concentric annulus tube with the inlet and outlet mean temperatures of 20°C and 80°C, respectively. The concentric annulus tube has inner and outer diameters of 10 mm and 100 mm, respectively. The inner tube wall is maintained with a constant surface temperature of 120°C, while the outer tube surface is insulated. Determine the length of the concentric…arrow_forward30°C, 10m/s 2m Electronic components inside D= 20cm Figure 5 You are designing components of an electronic systems that needs to be inside a 2 m long horizontal duct. The components are sensitive so the cooling mechanism is only done by air flowing over the duct at 30°C and 10 m/s. Initially you proposed a square cross-section with 20-cm length for the duct but is rejected by your client because they said a circular cross- section is better. If the surface temperature of the duct cannot exceed 60°C, find the maximum power rating in kW of the electronics devices that can be located inside the circular cross-section duct. Is it true that circular cross-section is better than a square one for this application?arrow_forward
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- An oil-fired thermal plant uses 0.002m^3/s of bunker oil whose relative density at 23.9C is 0.905. The specific enthalpy of steam in kJ/kg are as follows: boiler outlet = 3530.9, condenser inlet3 2289.5, pump inlet = 251. 96, boiler inlet = 259.05. The boiler of this plant is 90% effective in transferring the energy chargeable to the water. Using the ASME formula to compute the fuel's higher heating value, compute the possible steam consumption of this power plant in kg/s. a.) 22.1194 b.) 22.1933 c.) 22.2045 d.) 22.1412 Note: Use 4 decimal places in all computation.arrow_forwardWater at 33 °C flows in a straight horizontal pipe in which there is no exchange of either heat or work with the surroundings. Its velocity is 9 m/s in a pipe with an internal diameter of 1.5 inch until it flows into a section where the pipe diameter abruptly increases. What is the temperature change of the water if the downstream diameter is 2 inches?arrow_forwardAutomobile air-conditioner gives up 18 kW at 65 km/h if the outside temperature is 35°C. The refrigerant temperature is constant at 65°C under these conditions, and the air rises 6°C in temperature as it flows across the heat exchanger tubes. The heat exchanger is of the finned-tube type shown in Fig. 3.6b, with U? 200 W/m°K. If U? (Air velocity) 0.7 and the mass flow rate increases directly with the velocity, plot the percentage reduction of heat transfer in the condenser as a function of air velocity between 15 and 65 km/h. b. A section of an automotive air condition- tall wavy fins is allowed to mix with itself while unmixedarrow_forward
- Q1: (5pt) In a cylindrical fuel element for a gas-cooled nuclear reactor, the generation rate of thermal energy within the fuel element due to fission can be approximated by the relation q(1) W/m³ %3D where a is the radius of the fuel element and is constant.The boundary surface at r = a is maintained at a uniform temperature Tɔ. (a) Assuming one-dimensional, steady-state heat flow, develop a relation for the temperature drop from the centreline to the surface of the fuel element. (b) For a radius of a = 30 mm, the thermal conductivity k = 10 W/(m °C) and qo = 2 x 107 W/m³, calculate the temperature drop from the centreline to the surface. 02: (5pt)arrow_forwardSteam is supplied to a turbine at 407.1 inHg (abs) with the following initial conditions: u = 1163.3 Btu/lb, density = 0.3774 Ib/ft^3 and intake velocity of 400 fps. Exhaust conditions are at 2 inHg (abs) and u = 925 Btu/lb, specific volume = 294 ft^3/lb and exit velocity of 335.26 mps. The heat loss form the steam in the turbine is 10 Btu/lb. Determine the work in hp for 10 Ib/min of steam. * 50 hp 60 hp 55 hp 65 hparrow_forward4. An experimental test rig is used to examine two-phase flow regimes in horizontal pipelines. A particular experiment involved uses air and water at a temperature of 25°C, which flow through a horizontal glass tube with an internal diameter of 25.4 mm and a length of 40 m. Water is admitted at a controlled rate of 0.026 kgs-¹ at one end and air at a rate of 5 x 104 kgs¹ in the same direction. The density of water is 1000 kgm3, and the density of air is 1.2 kgm-³. Determine the mass flow rate, the mean density, gas void fraction, and the superficial velocities of the air and water. Answer: 0.02605 kgs-1, 61.1 kgm ³, 0.94, 0.822 ms-1, 0.051 ms-1arrow_forward
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