A potato may be approximated as a 5.7-cm-diameter solid sphere with the properties
(a) 77kJ
(b) 483 kJ
(c) 927 kJ
(ci) 970 kJ
(e) 1012kJ
Want to see the full answer?
Check out a sample textbook solutionChapter 4 Solutions
Heat and Mass Transfer: Fundamentals and Applications
- Stainless steel ball bearings (p=8085 kg/m², kJ/kg.°C) having diameter of 1.2 cm are to k=15.1 W/m°C, and C=0.480 be quenched in water. The ball leaving the oven at a uniform temperature of 900°C and is exposed to air at 30°C and with a convection coefficient of 125W/m².°C. Determine the time necessary to reach its surface to 850°C.arrow_forwardIn a ball bearing production facility, steel balls (k=50 W/m.K, c=0.460 kJ/kg.K, ρ=7865 kg/m3) that are each of 13,99 mm in diameter are annealed by first heating them to 870 oC and then slowly cooling in air to 125 oC. If the cooling air stream temperature is 60 oC, and it has a convective heat transfer coefficient of 35 W/m2.K), determine the time [s] required for the cooling.arrow_forwardK .1 Freshly harvested berries measuring 2 cm in diameter are chilled from 18°C to 7°C in a chiller at 2°C, with a surface heat transfer coefficient of 25 W/m2 K. They are then loaded in 250 kg batches into containers and held for 12 h in a cold store operating at 2°C prior to further processing. Each container weighs 50 kg. The cold store holds an average of 2.5 t of berries and measures 3 m high by 10 m 10 m. The walls and roof are insulated with 300 mm of polyurethane foam and the floor is constructed from 450 mm of concrete. The ambient air temperature in the factory averages 12°C and the soil temperature 9°C. An operator spends an average of 45 min per day moving the containers within the store and switches on four 100W lights when inside the store. Calculate the time required to cool the berries in the chiller and determine whether a 5-kW refrigeration unit using R-717 as refrigerant would be suitable for the cold store. The outside temperature is 20°C. Design the refrigeration…arrow_forward
- 1. For heat transfer purposes, an egg can be considered to be a 4-cm diameter sphere having the properties of water. An egg that is initially at 8°C is dropped into boiling water at 100°C. The heat transfer coefficient at the surface of the egg is estimated to be 400 W/m2°C. If the egg is considered cooked when its center temperature reaches 60°C, determine how long the egg should be kept in the boiling water? Assume negligible internal resistance íarrow_forwardSteel cubes 10 mm in width are annealed by heating to 1,377 K and then slowly cooling to 469 K in an air environment for which T∞ = 301 K and h = 24 W/m2-K. Assuming the properties of the steel to be k = 24 W/m · K, ρ = 7,047 kg/m3, and c = 916 J/kg · K, estimate the time required for the cooling process.arrow_forwardA fabricated food, in the form of small spherical pellets, is to be frozen in an air-blast freezer. The air-blast freezer is operating with air at -30°C. The initial product temperature is 25°C. The pellets have a diameter of 1.2 cm, and the density of the product is 980 kg/m³ . The initial freezing temperature is -2.5°C. The latent heat of fusion for this product is 280 kJ/kg. The thermal conductivity of the frozen product is 1.9 W/(m°C). The convective heat transfer coefficient is 50 W/(m² °C). Calculate the freezing time (h)arrow_forward
- A fabricated food, in the form of small spherical pellets, is to be frozen in an air-blast freezer. The air-blast freezer is operating with air at -30°C. The initial product temperature is 25°C. The pellets have a diameter of 1.2 cm, and the density of the product is 980 kg/m3 . The initial freezing temperature is -2.5°C. The latent heat of fusion for this product is 280 kJ/kg. The thermal conductivity of the frozen product is 1.9 W/(m°C). The convective heat transfer coefficient is 50 W/(m2°C). Calculate the freezing time.arrow_forward2 (a) A short bronze cylinder of diameter 6 cm and length 12 cm is initially at 40°C and then plunged into a fluid at 200°C. The temperature at the centre of the cylinder is measured by a thermocouple to be 150°C after 5 minutes. What is the convective heat transfer coefficient between the cylinder and the fluid? The following properties of the bronze cylinder may be used: Thermal conductivity k = 26 W/m-K, density p = 8800 kg/m², and specific heat c = 420 J/kg-K. State and justify all assumptions made.arrow_forwardA glass vessel with an insulating cover with a surface area of (Z + 100) cm² and (Z + 15) mm thick is filled with ice at 0° C and placed in a second vessel maintained at a temperature of 100° C. Find the mass of the ice that melts per minute when the flow of heat becomes steady. Latent heat of ice = 3.3 x 105 J/kg and K for glass = 1.0 W /mK. %3!arrow_forward
- In a dairy operation, milk at a flow rate of 0.25m3/hr and a cow-body temperature of 38.6°C must be chilled to a safe-to- store temperature of 13°C. Cold water at 2.2°C is available at a flow rate of 0.94m3/hr. The density and specific heat of milk are 1030 kg/m3 and 3860 J/kg.K, respectively. The density and specific heat of water is 1000 kg/m3 and 4187 J/kg.K. The chilling process is done by a double pipe counter-flow exchanger with an overall heat transfer coefficient U=1000 W/m2.K. The pipe of the heat exchanger has a 50-mm diameter with negligible thickness. Determine the pipe length L required. Select one: O a. 2.28 m O b. 4.28 m O c. 3.28 m O d. 1.28 marrow_forwardA fabricated food, in the form of small spherical pellets, is to be frozen in an air-blast freezer. The air-blast freezer isoperating with air at -40°C. The initial product temperatureis 25°C. The pellets have a diameter of 0.5 cm, and the density of the product is 980 kg/m3. The initial freezing temperature is -2.5°C. The latent heat of fusion for this product is 280 kJ/kg. The thermal conductivity of the frozen productis 1.9 W/(m°C). The convective heat transfer coefficient is 50 W/(m2 °C). Calculate the freezing time.arrow_forwardA copper sphere of 18 mm diameter (density = 8960 kg/m3 and CP= 0.38 kJ/kg K) is exposed to air at 100 oC. The temperature of the sphere was observed to increase by 17 oC in 1.5 min. The initial temperature of the sphere was 25 oC. Assuming uniform system, find the heat transfer coefficient, in W/m2 K, between air and sphere.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning