Temperature variations in cycle of an internal combustion engine.

- An internal combustion engine undergoes a series of processes in a cycle, including intake, compression, combustion, and exhaust.
- These processes result in changes in temperature within the engine.
- During the intake stroke, the air-fuel mixture enters the combustion chamber, causing a decrease in temperature.
- In the compression stroke, the mixture is compressed, leading to an increase in temperature.
- The combustion of the mixture during the power stroke produces high temperatures.
- Finally, during the exhaust stroke, the combustion products are expelled, leading to a decrease in temperature.
- This cycle repeats continuously as the engine operates.

Cooling of bars, blanks and metal billets in steel works.

- When bars, blanks, and metal billets are produced in steel works, they are often heated to high temperatures for shaping and processing.
- After the shaping process, these metal components need to be cooled down to ambient temperature for further handling or storage.
- The cooling process involves transferring heat from the hot metal to the surrounding environment.
- However, this cooling process is typically not periodic but rather a continuous and gradual decrease in temperature.
- The rate of cooling depends on various factors such as the initial temperature of the metal, the ambient temperature, and the surface area-to-volume ratio of the metal.
- The cooling rate can be controlled by adjusting the cooling medium, such as air or water, and their flow rates.
- While the temperature of the metal may change over time during the cooling process, it does not exhibit a periodic variation.

Variation of temperature of a building during a full day period of 24 hours.

- The temperature of a building can vary throughout the day due to various factors such as solar radiation, outdoor temperature, and HVAC system operation.
- During the day, when the sun is up, the building may experience an increase in temperature due to solar heat gain.
- As the sun sets and the outdoor temperature drops, the building may start to lose heat and the temperature may decrease.
- However, this temperature variation is not periodic as it is influenced by external factors such as weather conditions and the time of year.
- The temperature of the building may also be affected by the operation of heating, ventilation, and air conditioning (HVAC) systems.
- The HVAC system may be programmed to maintain a constant temperature or to follow a specific temperature schedule, but this schedule is typically not a perfect periodic variation.

Heat processing of regenerators whose packings are alternately heated by flue gases and cooled by air.

- Regenerators are heat exchangers used in various industrial processes, including combustion systems.
- In some regenerators, the packings or beds are designed to alternate between being heated by hot flue gases and cooled by air.
- This alternating heating and cooling process can result in a periodic variation of temperature within the regenerator.
- When the packings are exposed to flue gases, they absorb heat and their temperature increases.
- After a certain period, the flow is switched, and the packings are exposed to cooling air, causing their temperature to decrease.
- This alternating heating and cooling cycle repeats, resulting in a periodic variation of temperature within the regenerator.
- The purpose of this process is to efficiently transfer heat between the flue gases and the air, maximizing the energy efficiency of the system.

Therefore, among the given options