Chapter 5: Problem 19

A submerged heater is used in an aquarium to keep the water above room temperature. Should it be placed near the surface of the water or near the bottom to be most effective?

Short Answer

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Answer: A submerged heater should be placed near the bottom of the aquarium to effectively maintain the water temperature above room temperature. This position allows for better heat distribution due to convection currents, minimizes heat loss through the water surface, and reduces heat loss through the aquarium walls.

Step by step solution

Understand the heat transfer mechanisms in the aquarium

First, let's understand the main heat transfer mechanisms in this problem: conduction, convection, and radiation. In an aquarium, conduction occurs when heat is transferred through the glass walls. Convection is the most significant mechanism here because the heated water will tend to rise, creating a circulation of water and distribution of heat. Radiation is minimal in this case since the heater is submerged in water.

Examine the impact of the heater position on convection in the aquarium

Heat will be transferred from the heater to the surrounding water, warming it up. The warmer water will become less dense and rise due to buoyancy effects, while colder water sinks. This creates a convection current. By placing the heater near the bottom of the aquarium, we can take advantage of this effect by allowing warm water to rise and promote heat distribution throughout the aquarium.

Analyze the impact of water surface exposure to air and heat loss

The surface of the water in the aquarium is exposed to air, and heat loss occurs mainly due to evaporation and conduction to the surrounding air. Placing the heater near the surface will cause the water to be warmer at the surface, which in turn will promote more heat loss to the surrounding air. By placing the heater at the bottom, we encourage warm water to rise from the bottom, ensuring that the topmost layer of water is not too warm and minimizes heat loss to the air.

Account for any heat loss through the aquarium walls

While the aquarium walls are usually made of either glass or acrylic, heat loss through them can occur by conduction. Positioning the heater near the bottom can help to distribute heat more effectively throughout the aquarium, creating a more uniform temperature and reducing heat loss through the walls.

Make a conclusion about heater placement

Based on the analysis of heat transfer mechanisms, convection currents, and heat loss through the water surface and aquarium walls, it is recommended to place the submerged heater near the bottom of the aquarium. This position, as opposed to near the surface, would allow for better heat distribution throughout the aquarium, minimizing heat loss and maintaining the water temperature above room temperature more effectively.

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A submerged heater is used in an aquarium to keep the water above room temperature. Should it be placed near the surface of the water or near the bottom to be most effective?

Short Answer

Step by step solution

Understand the heat transfer mechanisms in the aquarium

Examine the impact of the heater position on convection in the aquarium

Analyze the impact of water surface exposure to air and heat loss

Account for any heat loss through the aquarium walls

Make a conclusion about heater placement

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