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Chapter 1: Problem 2

What is the driving force for \((a)\) heat transfer, \((b)\) electric current flow, and (c) fluid flow?

Short Answer

Expert verified
Answer: (a) The driving force for heat transfer is the temperature difference or gradient between two points or areas. (b) The driving force for electric current flow is the electric potential difference, also known as voltage, between two points in a circuit. (c) The driving force for fluid flow is the pressure difference between two points within a fluid or across the boundaries of a fluid system.

Step by step solution

01

(a) Driving force for heat transfer

The driving force for heat transfer is the temperature difference or, more specifically, the temperature gradient between two points or areas. Heat always flows from an area of higher temperature to an area of lower temperature, and this flow will continue until the temperature difference reaches equilibrium or becomes equal. The greater the temperature difference, the more significant the heat transfer between the two points.
02

(b) Driving force for electric current flow

The driving force for electric current flow is the electric potential difference, also known as voltage, between two points in a circuit. Electric current flows from a point of higher electric potential (higher voltage) to a point of lower electric potential (lower voltage) as the electric charges experience a force that drives them to move due to the difference in electric potential energy. The greater the potential difference, the larger the current that flows through the circuit.
03

(c) Driving force for fluid flow

The driving force for fluid flow is the pressure difference between two points within a fluid or across the boundaries of a fluid system. Fluid flow occurs from an area of higher pressure to an area of lower pressure, as the fluid particles experience a force caused by the pressure difference that pushes them to move in the direction of lower pressure. Other external forces, such as gravity, can also affect the flow of fluids, but in general, the pressure difference is the driving force behind fluid flow.

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Most popular questions from this chapter

A concrete wall with a surface area of \(20 \mathrm{~m}^{2}\) and a thickness of \(0.30 \mathrm{~m}\) separates conditioned room air from ambient air. The temperature of the inner surface of the wall \(\left(T_{1}\right)\) is maintained at \(25^{\circ} \mathrm{C}\). (a) Determine the heat loss \(\dot{Q}(\mathrm{~W})\) through the concrete wall for three thermal conductivity values of \((0.75,1\), and \(1.25 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K})\) and outer wall surface temperatures of \(T_{2}=-15,-10,-5,0,5,10,15,20,25,30\), and \(38^{\circ} \mathrm{C}\) (a total of 11 data points for each thermal conductivity value). Tabulate the results for all three cases in one table. Also provide a computer generated graph [Heat loss, \(\dot{Q}(\mathrm{~W})\) vs. Outside wall temperature, \(\left.T_{2}\left({ }^{\circ} \mathrm{C}\right)\right]\) for the display of your results. The results for all three cases should be plotted on the same graph. (b) Discuss your results for the three cases.

What is the value of the engineering software packages in ( \(a\) ) engineering education and \((b)\) engineering practice?

An AISI 316 stainless steel spherical container is used for storing chemicals undergoing exothermic reaction that provides a uniform heat flux of \(60 \mathrm{~kW} / \mathrm{m}^{2}\) to the container's inner surface. The container has an inner diameter of \(1 \mathrm{~m}\) and a wall thickness of \(5 \mathrm{~cm}\). For safety reason to prevent thermal burn on individuals working around the container, it is necessary to keep the container's outer surface temperature below \(50^{\circ} \mathrm{C}\). If the ambient temperature is \(23^{\circ} \mathrm{C}\), determine the necessary convection heat transfer coefficient to keep the container's outer surface temperature below \(50^{\circ} \mathrm{C}\). Is the necessary convection heat transfer coefficient feasible with free convection of air? If not, discuss other option to prevent the container's outer surface temperature from causing thermal burn.

Consider a person standing in a room maintained at \(20^{\circ} \mathrm{C}\) at all times. The inner surfaces of the walls, floors, and ceiling of the house are observed to be at an average temperature of \(12^{\circ} \mathrm{C}\) in winter and \(23^{\circ} \mathrm{C}\) in summer. Determine the rates of radiation heat transfer between this person and the surrounding surfaces in both summer and winter if the exposed surface area, emissivity, and the average outer surface temperature of the person are \(1.6 \mathrm{~m}^{2}, 0.95\), and \(32^{\circ} \mathrm{C}\), respectively.

A 4-m \(\times 5-\mathrm{m} \times 6-\mathrm{m}\) room is to be heated by one ton ( \(1000 \mathrm{~kg}\) ) of liquid water contained in a tank placed in the room. The room is losing heat to the outside at an average rate of \(10,000 \mathrm{~kJ} / \mathrm{h}\). The room is initially at \(20^{\circ} \mathrm{C}\) and \(100 \mathrm{kPa}\), and is maintained at an average temperature of \(20^{\circ} \mathrm{C}\) at all times. If the hot water is to meet the heating requirements of this room for a 24-h period, determine the minimum temperature of the water when it is first brought into the room. Assume constant specific heats for both air and water at room temperature. Answer: \(77.4^{\circ} \mathrm{C}\)
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