# Principles of Technology

## Year End Review: Thermal Systems

### Thermal Force (1:4)

1. What is the Prime Mover in the Thermal System?

2. What causes heat?

3. Convert 57.6 deg. C to deg. F.

4. Convert 43 deg. F to deg. C.

5. Convert 12 deg. F to deg. C.

6. The temperature inside is 68 deg. F and outside it is 37 deg. C. What is delta-T ___________ , and will the heat move from outside to inside or inside to outside (circle the answer)?

### Thermal Rate (3:4)

1. What is the heat flow rate of a cooler if it moves 12.3 X 108 BTUs of heat in 2 hr 45 min?

2. How much heat energy is produced by a 3750 Btu/hour heater in 2 hr 20 min?

3. An electric pressure cooker is rated at 9500 cal/min. It requires 2.18 x 104 cal. to can baby puke. How long will it take?

4. What is the rate of heat flow through a sheet of glass 0.375 in. thick which has a surface area of 250 ft2 if k=1.99 X 10-3(Btu in) / (hr ft2 F deg.) and a temperature difference of 227 F deg.?

5. An autoclave uses 2.5 X 104 calories to sterilize instruments. If it uses 725 cal/min, how much time is required for the sterilization to be completed?

6. What is the thermal conductivity of copper if it can transfer 1227.6 cal/hour across a 60 cm2 plate which has a thickness of 2.5 cm and a temperature difference of 55C deg.?

7. A container of liquid carbon dioxide is insulated with 8.5 cm of Celetex (k= 1.17 X 10-4 (cal cm) / (hr cm2 C deg.). The surface area of one side is 63 cm2. The outside temperature is 112 deg. F while the case temperature is -196 deg. C.

7a. What is the heat flow rate out of the case through one (1) side?

7b. Assuming that the case is a cube, what is the total heat flow rate?

8. A piece of aluminum is cooled from 148 deg. C to -66 deg. C. The constant heat flow rate out of the material is 21.5 cal/sec for 12 minutes 35 seconds. Aluminum has a specific heat of 0.22 cal / (gm C deg.) and a thermal conductivity of 0.48 (cal cm) / (sec cm2 C deg.).

8a. Find the heat given up by the aluminum

8b. Find the mass of the aluminum

### Thermal resistance (4:4)

1. The outside temperature is -22 deg. F and you want to keep it at 68 deg. F inside. You need to keep your heater running at 2150 BTUs per hour. What is the overall thermal resistance of your house?

2. A store has an overall thermal resistance of 0.027 C deg. / (kcal/hr). If the difference between the inside and outside temperatures is 22 C deg., what is the building's overall heat flow rate?

3. A 0.45 cm thick aluminum plate which has 23.5 cm2 of surface area is used to transfer heat from a stove to a frying pan. What is the thermal resistance of the plate if aluminum has a thermal conductivity value of 2031 (cal cm) / (hr cm2 C deg.)?

4. Using values from #3, calculate the heat flow rate if the delta-T across the plate is 12.5 C deg.