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Chapter 1: Problem 120

What is asymmetric thermal radiation? How does it cause thermal discomfort in the occupants of a room?

Short Answer

Expert verified
Answer: Asymmetric thermal radiation is the significant difference in temperature across various surfaces in a room, leading to an uneven distribution of heat. It can cause thermal discomfort for occupants by creating hot and cold spots due to factors like large windows, unequally distributed heat sources, poor insulation, and different building materials. Discomfort arises from differences in skin temperature, increased likelihood of drafts, individuals' personal preferences, and health issues exacerbated by uneven heating.

Step by step solution

01

Definition of Asymmetric Thermal Radiation

Asymmetric thermal radiation occurs when there is a significant difference in the temperature of different surfaces in a room. This leads to an uneven distribution of heat in the space, with some areas receiving more heat than others. When occupants of the room are exposed to these varying temperatures, it can lead to thermal discomfort.
02

Causes of Asymmetric Thermal Radiation

There are several factors that can cause asymmetric thermal radiation in a room. These include: 1. Large windows or doors: If a room has large windows or doors, it can let in more sunlight on one side, creating warmer areas. 2. Radiators or other heat sources: Unequally distributed heat sources, such as radiators on one side of the room, can create hot spots near them and cooler areas further away. 3. Insulation: Poor insulation in certain areas of the room can lead to heat loss, creating cold spots. 4. Building materials: Different building materials can absorb and release heat at different rates, contributing to an uneven distribution of temperature.
03

Thermal Discomfort in Occupants

Asymmetric thermal radiation can cause thermal discomfort for the occupants of a room. When they are exposed to uneven heat distribution, their bodies can't adapt to the temperature easily, leading to the following issues: 1. Differences in skin temperature: The human body is sensitive to differences in skin temperature between various body parts. Asymmetric thermal radiation can create an uneven warming effect on the skin, causing discomfort. 2. Increased likelihood of drafts: With hot and cold spots in a room, there is a higher chance of air movement and drafts, which can make the room uncomfortable. 3. Personal preference: Everyone has a different preference for the temperature they find comfortable. In a room with asymmetric thermal radiation, it may be challenging to find a temperature that suits all occupants. 4. Health issues: Some health issues, such as joint pain or respiratory problems, may be exacerbated by exposure to uneven heating in a room. Understanding asymmetric thermal radiation can help address these issues, leading to more comfortable environments for occupants of a room.

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Most popular questions from this chapter

A series of experiments were conducted by passing \(40^{\circ} \mathrm{C}\) air over a long \(25 \mathrm{~mm}\) diameter cylinder with an embedded electrical heater. The objective of these experiments was to determine the power per unit length required \((\dot{W} / L)\) to maintain the surface temperature of the cylinder at \(300^{\circ} \mathrm{C}\) for different air velocities \((V)\). The results of these experiments are given in the following table: $$ \begin{array}{lccccc} \hline V(\mathrm{~m} / \mathrm{s}) & 1 & 2 & 4 & 8 & 12 \\ \dot{W} / L(\mathrm{~W} / \mathrm{m}) & 450 & 658 & 983 & 1507 & 1963 \\ \hline \end{array} $$ (a) Assuming a uniform temperature over the cylinder, negligible radiation between the cylinder surface and surroundings, and steady state conditions, determine the convection heat transfer coefficient \((h)\) for each velocity \((V)\). Plot the results in terms of \(h\left(\mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\right)\) vs. \(V(\mathrm{~m} / \mathrm{s})\). Provide a computer generated graph for the display of your results and tabulate the data used for the graph. (b) Assume that the heat transfer coefficient and velocity can be expressed in the form of \(h=C V^{m}\). Determine the values of the constants \(C\) and \(n\) from the results of part (a) by plotting \(h\) vs. \(V\) on log-log coordinates and choosing a \(C\) value that assures a match at \(V=1 \mathrm{~m} / \mathrm{s}\) and then varying \(n\) to get the best fit.

A person standing in a room loses heat to the air in the room by convection and to the surrounding surfaces by radiation. Both the air in the room and the surrounding surfaces are at \(20^{\circ} \mathrm{C}\). The exposed surface of the person is \(1.5 \mathrm{~m}^{2}\) and has an average temperature of \(32^{\circ} \mathrm{C}\), and an emissivity of \(0.90\). If the rates of heat transfer from the person by convection and by radiation are equal, the combined heat transfer coefficient is (a) \(0.008 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\) (b) \(3.0 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\) (c) \(5.5 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\) (d) \(8.3 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\) (e) \(10.9 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\)

A 300-ft-long section of a steam pipe whose outer diameter is 4 in passes through an open space at \(50^{\circ} \mathrm{F}\). The average temperature of the outer surface of the pipe is measured to be \(280^{\circ} \mathrm{F}\), and the average heat transfer coefficient on that surface is determined to be \(6 \mathrm{Btu} / \mathrm{h} \cdot \mathrm{ft}^{2} \cdot{ }^{\circ} \mathrm{F}\). Determine \((a)\) the rate of heat loss from the steam pipe and (b) the annual cost of this energy loss if steam is generated in a natural gas furnace having an efficiency of 86 percent, and the price of natural gas is $$\$ 1.10 /$$ therm ( 1 therm \(=100,000\) Btu).

Eggs with a mass of \(0.15 \mathrm{~kg}\) per egg and a specific heat of \(3.32 \mathrm{~kJ} / \mathrm{kg} \cdot{ }^{\circ} \mathrm{C}\) are cooled from \(32^{\circ} \mathrm{C}\) to \(10^{\circ} \mathrm{C}\) at a rate of 200 eggs per minute. The rate of heat removal from the eggs is (a) \(7.3 \mathrm{~kW}\) (b) \(53 \mathrm{~kW}\) (c) \(17 \mathrm{~kW}\) (d) \(438 \mathrm{~kW}\) (e) \(37 \mathrm{~kW}\)

Solve this system of two equations with two unknowns using EES: $$ \begin{aligned} x^{3}-y^{2} &=10.5 \\ 3 x y+y &=4.6 \end{aligned} $$
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