Heat sterilization of lumber, timbers, and pallets is used to kill insects to prevent their transfer between countries in international trade. This is analogous to food sterilization by heat. A typical requirement here is that the slowest heating point of any wood configuration be held at 56 °C for 30 minutes. Consider hot air heating of wooden boards that maintains their surface temperature at 70 °C. The boards are stacked outside and in the winter time they can be considered to be at 0 °C when they are brought in for heating. The thermal diffusivity of the wood is 9*10-8 m?/s. •Calculate the time from the start of heating for a 2.5 cm thick board to reach a sterilization temperature of 56 °C at its slowest heating point.

Heat sterilization of lumber, timbers, and pallets is used to kill insects to prevent their transfer between countries in international trade. This is analogous to food sterilization by heat. A typical requirement here is that the slowest heating point of any wood configuration be held at 56 °C for 30 minutes. Consider hot air heating of wooden boards that maintains their surface temperature at 70 °C. The boards are stacked outside and in the winter time they can be considered to be at 0 °C when they are brought in for heating. The thermal diffusivity of the wood is 9*10-8 m?/s. •Calculate the time from the start of heating for a 2.5 cm thick board to reach a sterilization temperature of 56 °C at its slowest heating point.

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter6: Forced Convection Over Exterior Surfaces

Section: Chapter Questions

Problem 6.28P

See similar textbooks

Similar questions

Don’t use Heissler charts to answer this question Heat sterilization of lumber, timbers, and pallets is used to kill insects to prevent their transfer between countries in international trade. This is analogous to food sterilization by heat. A typical requirement here is that the slowest heating point of any woodconfiguration be held at 56 °C for 30 minutes. Consider hot air heating of wooden boards that maintains their surface temperature at 70 °C. The boards are stacked outside and in the winter time they can be considered to be at 0 °Cwhen theyare brought in for heating. The thermal diffusivity of the wood is 9*10-8m2/s. a.Calculate the time from the start of heating for a 2.5 cm thick board to reach a sterilization temperature of 56 °C at its slowest heating point .b.Calculate the heating time when four such boards are stacked together. c.Calculate the ratio of the two heating times (for a single board versus when they are stacked), and explain the ratio. Note: You’re free to…
Recent studies show that the major energy consumption in Fijian villages is wood which is used for cooking on open fires. Typical consumption of wood is 1 kg/person/day. (a) Estimate the heat energy required to boil a 2 litre pot full of water. Assuming this to be the cooking requirement of each person, compare this with the heat content of the wood, and thus estimate the thermal efficiency of the open fire. (b) How much timber has to be felled each year to cook for a village of 200 people ? Assuming systematic replanting, what area of crop must the village therefore set aside for fuel use if it is not to make a net deforestation ?
Heat sterilization of lumber, timbers, and pallets is used to kill insects to prevent their transfer between countries in international trade. This is analogous to food sterilization by heat. A typical requirement here is that the slowest heating point of any wood configuration be held at 56 °C for 30 minutes. Consider hot air heating of wooden boards that maintains their surface temperature at 70 °C. The boards are stacked outside and in the winter time they can be considered to be at 0 °C when they are brought in for heating. The thermal diffusivity of the wood is 9*10-8 m2/s. Calculate the time from the start of heating for a 2.5 cm thick board to reach a sterilization temperature of 56 °C at its slowest heating point. Calculate the heating time when four such boards are stacked together. Calculate the ratio of the two heating times (for a single board versus when they are stacked), and explain the ratio. Note: You’re free to make assumptions regarding any value you…
Heat sterilization of lumber, timbers, and pallets is used to kill insects to prevent their transfer between countries in international trade. This is analogous to food sterilization by heat. A typical requirement here is that the slowest heating point of any wood configuration be held at 56 °C for 30 minutes. Consider hot air heating of wooden boards that maintains their surface temperature at 70 °C. The boards are stacked outside and in the winter time they can be considered to be at 0 °C when they are brought in for heating. The thermal diffusivity of the wood is 9*10-8 m2/s. Calculate the time from the start of heating for a 2.5 cm thick board to reach a sterilization temperature of 56 °C at its slowest heating point. Calculate the heating time when four such boards are stacked together. Calculate the ratio of the two heating times (for a single board versus when they are stacked), and explain the ratio. Note: You’re free to make assumptions regarding any value you think…
A 12-by-12 inches ingot iron casting 60-in high is stripped from its moldwhile its temperature is 1740 °F. If it stands on end on the floor of a largefoundry having wall, floor, and roof temperatures of 80°F, what is the rate ofradiant-heat exchange between the casting and the roof wall, and floorsurfaces?
For a specified heat input and a given volume which material will have the smallest tempera- ture rise (Use data book if necessary) (a) steel (b) aluminium (c) water (d) copper. When a hot metal piece is left to cool in air the time rate of cooling of the outer layer will be (a) slower at start and faster near the end (b) faster at start and slower near the end (c) both rates will be the same (d) this will depend on the material. (viii) A thin black plate at temperature T receives radiation from a surface at Temperature T1 and radiates to a surface at T2. If all surfaces are black at steady state (a) (T1 – T) > (T – T2) (b) (T1 – T) < (T – T2) (c) (T1 – T) = (T – T2) (d) can be any one of a, b or c. (ix) The temperature profile (in) a slab initially at a constant temperature and then allowed to cool by convection for a short time will be as shown in Fig : (a) E1.2a (b) E1.2b (c) E1.2c (d) E1.2d. Ti
Trasient Cooling What are some of the factors and assumptions that would casue a different between the experimential convection coefficient, hexp, and the theorectical htheo?
Air has a very low thermal conductivity. This explains whywe feel comfortable wearing short sleeves in a 20°C environment eventhough our body temperature is 37°C. Material objects feel cooler to ourimmediate touch than the air, owing to relatively high thermal conductivities.(a) Touch a few surfaces in a room-temperature environment andrank them in order of which feel the coolest to which feel the warmest.Objects that feel cooler have larger thermal conductivities. Consider awood surface, a metallic surface, and a glass surface, and rank these inorder from coolest to warmest
Question : Studies show that the major energy consumption in Fijian villages is wood which is used for cooking over open fires. Typical consumption of wood is 1 kg person–1day–1. (a) Estimate the heat energy required to boil a 2-liter pot full of water. Assuming this to be the cooking requirement of each person, compare this with the heat content of the wood, and thus estimate the thermal efficiency of the open fire. (b) How much timber has to be felled each year to cook for a village of 200 people?Assuming systematic replanting, what area of crop must the village therefore set aside for fuel use if it is not to make a net deforestation? Hint: refer to Table 10.4. (c) Comment on the realism of the assumptions made, and revise your estimates accordingly. Answer: (a) mcDT ≈ 0.6 MJ (heat losses from pot imply actual requirement is higher). h ≈ 3%. (b) 70 tonnes; 7 ha.
In a quiescent hot summer day, you are walking under the sunlight. Suddenly, you remember heat transfer lecture that you have successfully failed. Explain the mechanisms of heat transfer that are falling on you? Which one is dominant and why? b) Hot air at 50 C does not cause a lethal burn on our skin, but water with the same temperature is dangerous and it can burn our skin. Explain the reason? Any SAME answer from the internet sources or your friends will give you ZERO (0) point. *
You are asked to design a metal hot dog holder for roasting hot dogs over an opencampfire. The holder is to be designed such that while the end holding the hot dogbecomes cherry red (1400oF), the other end can still be held without using aninsulated handle or glove (~95oF). Design it such that it can be used even on awarm, still day, Tf = 90oF (Assume the convective heat transfer coefficient, h, fora horizontal cylinder is uniform over the whole cylinder and equal to 4.0Btu/hrft2oF)
An underwater sonar that maps the ocean bathymetry is encapsulated in a sphere with a diameter of 85 mm. During operation, the sonar generates heat at a rate of 300W. What is the sonar surface temperature when it’s located in a water column where the temperature is 15o C and the water current is 1 m/sec? The sonar was pulled out of the water without turning it off, thus, it was still working. The air temperature was 15o C and the air speed was 3 m/sec. What was the sonar surface temperature? Was there any reason for concern?