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Chapter 1: Problem 93

We often turn the fan on in summer to help us cool. Explain how a fan makes us feel cooler in the summer. Also explain why some people use ceiling fans also in winter.

Short Answer

Expert verified
Answer: A fan helps us cool down in the summer by circulating air, creating a breeze, which increases the evaporation rate of our sweat, ultimately cooling us down. In the winter, ceiling fans can redistribute warm air, improve air quality, and reduce energy consumption by enhancing the performance of heating systems.

Step by step solution

01

Understanding the role of fans

Fans work by circulating air, which helps create a breeze. The moving air helps with our body's natural cooling process by increasing the rate of evaporation of perspiration on the skin. This creates a cooling sensation.
02

How a fan cools us down during summer

In summer months, the following steps explain how a fan helps us cool down: 1. The fan circulates the air in the room, creating a breeze. 2. The breeze increases the evaporation rate of our sweat. 3. The evaporation of sweat absorbs heat from our bodies, cooling us down. 4. As a result, we feel more comfortable and cooler.
03

Benefits of using a ceiling fan during winter

In winter months, some people use ceiling fans for the following reasons: 1. To redistribute warm air: Warm air rises to the ceiling due to its lower density. A ceiling fan, when operated at a low speed and in a clockwise direction, helps push the warm air downwards, redistributing it evenly around the room. This helps maintain a comfortable temperature and reduces the need for additional heating. 2. Energy efficiency: Ceiling fans use significantly less energy compared to heating systems. By redistributing warm air and maintaining a consistent room temperature, using a ceiling fan in conjunction with a heating system can help reduce energy consumption and lower heating bills. 3. Improved air quality: During winter, indoor spaces tend to have stagnant air. The circulation provided by a ceiling fan can help improve indoor air quality by reducing dust and allergens buildup. In conclusion, the primary reason a fan makes us feel cooler in the summer is by increasing the rate of sweat evaporation, which helps our bodies cool down. Additionally, using a ceiling fan during winter can help redistribute warm air, improve air quality, and reduce energy consumption by enhancing the performance of heating systems.

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Key Concepts

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

Evaporation Cooling
When we sweat, our body's natural way of regulating temperature, it releases moisture onto the skin. This sweat needs to evaporate to cool us down effectively. Fans play a crucial role in speeding up this evaporation process, thereby enhancing cooling.

By circulating air, fans create a breeze that accelerates the evaporation of sweat. This action absorbs heat from our skin as the sweat changes from a liquid to a vapor. The result? We feel cooler.

This process is a simple yet effective way to use our body's natural mechanisms to feel more comfortable on hot days.
Ceiling Fan Benefits
Ceiling fans offer numerous advantages throughout the year, not just during the summer. In the winter, using a ceiling fan can help in several ways:
  • Redistributing Warm Air: Heat naturally rises, so warm air accumulates near the ceiling. By running a ceiling fan in a clockwise direction at low speed, it pushes this warm air back down into the room. This can help maintain a uniform temperature throughout the space.
  • Improving Air Quality: Fresh air circulation can help remove dust and reduce allergens. Fans help in achieving this by keeping the air moving, which is essential for a healthier indoor environment.
  • Reducing Humidity: Even in colder months, controlling indoor humidity is beneficial, and fans can help reduce excess moisture through air movement.

These benefits make ceiling fans valuable tools in both summer and winter, offering comfort and environmental improvements.
Energy Efficiency
Ceiling fans are champions of energy efficiency, offering great benefits at low power consumption. Unlike expensive heating systems, fans operate with only minimal energy.

Running a ceiling fan allows you to set your thermostat a few degrees lower in the winter because the fan helps distribute warm air more efficiently across the room. This results in reduced reliance on heating systems, leading to significant energy savings and lower electricity bills.

The efficient function of fans not only helps preserve our environment by lowering energy demands but also provides a cost-effective solution for maintaining consistent indoor comfort.

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Most popular questions from this chapter

A hair dryer is basically a duct in which a few layers of electric resistors are placed. A small fan pulls the air in and forces it to flow over the resistors where it is heated. Air enters a \(900-\mathrm{W}\) hair dryer at \(100 \mathrm{kPa}\) and \(25^{\circ} \mathrm{C}\), and leaves at \(50^{\circ} \mathrm{C}\). The cross-sectional area of the hair dryer at the exit is \(60 \mathrm{~cm}^{2}\). Neglecting the power consumed by the fan and the heat losses through the walls of the hair dryer, determine \((a)\) the volume flow rate of air at the inlet and \((b)\) the velocity of the air at the exit.

How do rating problems in heat transfer differ from the sizing problems?

The deep human body temperature of a healthy person remains constant at \(37^{\circ} \mathrm{C}\) while the temperature and the humidity of the environment change with time. Discuss the heat transfer mechanisms between the human body and the environment both in summer and winter, and explain how a person can keep cooler in summer and warmer in winter.

Liquid ethanol is a flammable fluid and can release vapors that form explosive mixtures at temperatures above its flashpoint at \(16.6^{\circ} \mathrm{C}\). In a chemical plant, liquid ethanol \(\left(c_{p}=2.44 \mathrm{~kJ} / \mathrm{kg} \cdot \mathrm{K}, \rho=789 \mathrm{~kg} / \mathrm{m}^{3}\right)\) is being transported in a pipe with an inside diameter of \(5 \mathrm{~cm}\). The pipe is located in a hot area with the presence of ignition source, where an estimated \(20 \mathrm{~kW}\) of heat is added to the ethanol. Your task, as an engineer, is to design a pumping system to transport the ethanol safely and to prevent fire hazard. If the inlet temperature of the ethanol is \(10^{\circ} \mathrm{C}\), determine the volume flow rate that is necessary to keep the temperature of the ethanol in the pipe below its flashpoint.

Consider a person standing in a room at \(18^{\circ} \mathrm{C}\). Determine the total rate of heat transfer from this person if the exposed surface area and the skin temperature of the person are \(1.7 \mathrm{~m}^{2}\) and \(32^{\circ} \mathrm{C}\), respectively, and the convection heat transfer coefficient is \(5 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\). Take the emissivity of the skin and the clothes to be \(0.9\), and assume the temperature of the inner surfaces of the room to be the same as the air temperature.
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