Question

1. An oven chimney is made of brick with a heat transmission coefficient 1.1 W/mK 10 cm thick. Since the shaft exterior radiation beam coefficient is 0.8 and the flue gas temperature is 350°C, the external ambient temperature is 25°C and the outer ambient heat transport coefficient is 20 W/m²K;

a) Calculate the shaft exterior temperature.

b) In order to reduce the risk of burn injury that may occur in the body, the shaft is asked to be below 55°Cve of the external surface temperature of the chimney. Accordingly, what should be the minimum thickness of the chimney?

2. Initially, the aluminum sphere with a diameter of 15 cm with a temperature of 200°C was left to cool in the airflow at a temperature of 6 m/s. By making the necessary acceptances, calculate the amount of time the aluminum sphere will fall to a temperature of 50°C.

The relevant correlation for forced transport on the sphere;

Nu_D = 2 + (0.4 Re_D ^0.5+ 0.06 Re_D ^2/3) Pr ^0.6 (μo/μy)^1/4

3. The temperature of parallel plates of two infinity lengths is 575oC and 25oC, and the radiation scalpel coefficient is 0.85 and 0.75 respectively. To reduce the heat radiation between these two sheets by 5 times, find the radiation scalpel coefficient (per) of the radiation shield to be placed.

4. Two separate fins are mounted on a plate with a base temperature of 100°C and a size of 1m x 1m. The ambient temperature is 20°C and the heat transport coefficient is 35 W/m² K. The diameter of the second wing, which is fixed to the same surface, is 4 mm and the heat transmission coefficient is 90 W/mK and to give the environment the same amount of heat in both wings; length of the second wing;

a) According to the acceptance of the tip isolated fin,

b) According to the acceptance that there is a heat transport of 35W/m ² K at the end of the fins,

c) What should be according to the acceptance that there is a constant temperature of 80°C at the end of the fins?

5. We aim to hold graduation meetings with your families in the A21 classroom where we process the Pre-Pandemia Heat Transfer course. About 100 people attended the ceremony in the classroom measuring 15m x 20m x 10 m and the internal ambient temperature is 20°C due to the working air conditioning device. Let's face it, the air conditioning device malfunctions and each person in the living room gives an average temperature of 350 kJ per hour. Find the classroom temperature at the end of 30 minutes, acknowledging that the living room walls did not receive heat or pass and that the air conditioning was not working for 30 minutes.

6. Where you are now, you want to have tea while solving questions. The water, which is found in a thin steel teapot with a diameter of 12 cm, is boiling. The heat transport coefficient between the teapot base and the boiling water is 10 kW/m²K. Since the heat flow ingrair is 40 kW/m^2;

a) Find the surface temperature of the teapot base.

b) Find the heat given to the water for 30 minutes and the amount of water evaporated.

Answer 1