/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 133 Water \(\left(\mu=9.0 \times 10^... [FREE SOLUTION] | 91影视

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Water \(\left(\mu=9.0 \times 10^{-4} \mathrm{~kg} / \mathrm{m} \cdot \mathrm{s}, \rho=1000 \mathrm{~kg} / \mathrm{m}^{3}\right)\) enters a 2-cm- diameter and 3-m-long tube whose walls are maintained at \(100^{\circ} \mathrm{C}\). The water enters this tube with a bulk temperature of \(25^{\circ} \mathrm{C}\) and a volume flow rate of \(3 \mathrm{~m}^{3} / \mathrm{h}\). The Reynolds number for this internal flow is (a) 59,000 (b) 105,000 (d) 236,000 (e) 342,000 (c) 178,000

Short Answer

Expert verified
Based on the given information, the Reynolds number for internal flow of water in the tube is 236,000. This value is essential in determining the type of flow (laminar, transitional, or turbulent) and can be calculated using the formula Re = (蟻VD) / 渭.

Step by step solution

01

Calculating the flow velocity (V)

We will first convert the volume flow rate of water from cubic meters per hour(m^3/h) to cubic meters per second(m^3/s). $$ Q = 3 \frac{\mathrm{m}^3}{\mathrm{h}} \cdot \frac{1\mathrm{h}}{3600\mathrm{s}} = 8.33\times 10^{-4}\frac{\mathrm{m}^3}{\mathrm{s}} $$ The flow velocity can be determined using the equation: $$ V = \frac{Q}{A} $$ Where V is the flow velocity, Q is the volume flow rate, and A is the cross-sectional area of the tube. The area A of the tube can be calculated using the formula for the area of a circle: $$ A = \pi\left(\frac{D}{2}\right)^2 $$ Where D is the diameter of the tube (2 cm).
02

Calculating the cross-sectional area (A)

Let's first convert the diameter from centimeters to meters, and then calculate the area of the tube. $$ D = 2 \mathrm{cm} \cdot \frac{1 \mathrm{m}}{100 \mathrm{cm}} = 0.02 \mathrm{m} $$ $$ A = \pi\left(\frac{0.02 \mathrm{m}}{2}\right)^2 = 3.14 \times 10^{-4} \mathrm{m}^2 $$
03

Calculating the flow velocity (V)

Now we can calculate the flow velocity using the volume flow rate (Q) and the cross-sectional area (A). $$ V = \frac{8.33\times 10^{-4}\frac{\mathrm{m}^3}{\mathrm{s}}}{3.14 \times 10^{-4} \mathrm{m}^2} = 2.65 \frac{\mathrm{m}}{\mathrm{s}} $$
04

Calculating the Reynolds number (Re)

Finally, we can calculate the Reynolds number(Re) using the formula: $$ \begin{aligned} \operatorname{Re} &=\frac{\rho \mathrm{V} \cdot{\mathrm{D}}}{\mu} \\ &=\frac{1000 \frac{\mathrm{kg}}{\mathrm{m}^{3}} \times 2.65 \frac{\mathrm{m}}{\mathrm{s}} \times 0.02 \mathrm{m}}{9.0 \times 10^{-4} \frac{\mathrm{kg}}{\mathrm{m} \cdot \mathrm{s}}} \\ &=236000 \end{aligned} $$ The correct answer is (d) 236,000.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Fluid Mechanics
Fluid mechanics is a branch of physics that studies the behavior of fluids (liquids, gases, and plasmas) and the forces on them. One of its central concepts is the Reynolds number, which is a dimensionless quantity used to predict flow patterns in different fluid flow situations. The Reynolds number helps to determine whether the flow will be laminar or turbulent.

In the case of the exercise, water flowing through a tube constitutes an internal flow problem in fluid mechanics. By calculating the Reynolds number, we can infer the characteristics of the flow within the tube, which is crucial for tasks such as selecting the proper equipment for fluid transport systems, predicting heat transfer rates, and designing piping systems.
Internal Flow
Internal flow refers to the study of fluid motion within a confined boundary, such as pipes, tubes, or any channel. Unlike external flow where fluid streams over a body, internal flow is confined by the physical boundaries of the conduit. This feature critically impacts the distribution of velocity, pressure, and other properties of the fluid within it.

In our solved problem, we analyzed the water movement inside a tube, which is a classic internal flow scenario. Knowing the flow velocity and tube dimensions, we've utilized these to comprehend the behavior of the water as affected by the tube's walls and the heat transfer occurring due to the water's contact with these walls.
Engineering Education
Engineering education combines theoretical knowledge with practical skills to equip individuals with the competencies required to solve complex real-world problems. It's crucial for engineering students to learn how to apply principles of fluid mechanics, like calculation of the Reynolds number, to ascertain the performance of systems involving fluid flow.

Exercises such as the one provided help bridge the gap between theory and application. The step-by-step solution demonstrates how to perform essential calculations that will be common in many engineering tasks, ensuring students understand the underlying principles and can replicate similar computations independently.
Heat Transfer
Heat transfer is an area of thermal engineering that involves the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into three basic types: conduction, convection, and radiation. In the context of internal flow, convection is the main mode of heat transfer, happening between the fluid (water in this case) and the tube wall.

In the solution, the water enters a tube that is maintained at a higher temperature, and this temperature difference drives the heat to transfer from the tube walls to the cooler water. Understanding this interaction and being able to quantify it using principles of fluid mechanics and heat transfer is crucial for designing efficient thermal systems, such as heating, ventilation, and air conditioning (HVAC) systems, and for analyzing energy conversion processes.

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Most popular questions from this chapter

A geothermal district heating system involves the transport of geothermal water at \(110^{\circ} \mathrm{C}\) from a geothermal well to a city at about the same elevation for a distance of \(12 \mathrm{~km}\) at a rate of \(1.5 \mathrm{~m}^{3} / \mathrm{s}\) in \(60-\mathrm{cm}\)-diameter stainless steel pipes. The fluid pressures at the wellhead and the arrival point in the city are to be the same. The minor losses are negligible because of the large length-to-diameter ratio and the relatively small number of components that cause minor losses. (a) Assuming the pump-motor efficiency to be 65 percent, determine the electric power consumption of the system for pumping. \((b)\) Determine the daily cost of power consumption of the system if the unit cost of electricity is $$\$ 0.06 / \mathrm{kWh}$$. (c) The temperature of geothermal water is estimated to drop \(0.5^{\circ} \mathrm{C}\) during this long flow. Determine if the frictional heating during flow can make up for this drop in temperature.

Combustion gases passing through a 3-cm-internaldiameter circular tube are used to vaporize waste water at atmospheric pressure. Hot gases enter the tube at \(115 \mathrm{kPa}\) and \(250^{\circ} \mathrm{C}\) at a mean velocity of \(5 \mathrm{~m} / \mathrm{s}\), and leave at \(150^{\circ} \mathrm{C}\). If the average heat transfer coefficient is \(120 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\) and the inner surface temperature of the tube is \(110^{\circ} \mathrm{C}\), determine \((a)\) the tube length and (b) the rate of evaporation of water.

Consider a fluid with a Prandtl number of 7 flowing through a smooth circular tube. Using the Colburn, Petukhov, and Gnielinski equations, determine the Nusselt numbers for Reynolds numbers at \(3500,10^{4}\), and \(5 \times 10^{5}\). Compare and discuss the results.

Water at \(15^{\circ} \mathrm{C}\) is flowing through a 5 -cm-diameter smooth tube with a length of \(200 \mathrm{~m}\). Determine the Darcy friction factor and pressure loss associated with the tube for (a) mass flow rate of \(0.02 \mathrm{~kg} / \mathrm{s}\) and \((b)\) mass flow rate of \(0.5 \mathrm{~kg} / \mathrm{s}\).

Hot air at \(60^{\circ} \mathrm{C}\) leaving the furnace of a house enters a 12-m-long section of a sheet metal duct of rectangular cross section \(20 \mathrm{~cm} \times 20 \mathrm{~cm}\) at an average velocity of \(4 \mathrm{~m} / \mathrm{s}\). The thermal resistance of the duct is negligible, and the outer surface of the duct, whose emissivity is \(0.3\), is exposed to the cold air at \(10^{\circ} \mathrm{C}\) in the basement, with a convection heat transfer coefficient of \(10 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\). Taking the walls of the basement to be at \(10^{\circ} \mathrm{C}\) also, determine \((a)\) the temperature at which the hot air will leave the basement and \((b)\) the rate of heat loss from the hot air in the duct to the basement. Evaluate air properties at a bulk mean temperature of \(50^{\circ} \mathrm{C}\). Is this a good assumption?

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