A sphere at 120°C was being exposed to surrounding air at 30°C withconvection coefficient of 33 W/m2K. Thermocouples were attached to thesphere on the surface, in its center, and in a random point inside the sphere.The thermocouples showed readings of approximately 100°C at 40s later. Onthe next day, a fan was switched on which provided an airstream ofapproximately 10 m/s surrounding the sphere. Analyze this situation to predictthe time taken for the sphere to cool from 60°C to 40°C. The properties of thesphere material and air at the specified temperature are provided in Table 1Table 1PropertiesAir at 30°CSphere materialDensity (kg/m³)Specific heat (J/kg.K)Kinematic viscosity (m2/s)1.15180001.007 x103001.619 x10Dynamic viscosity (N.s/m)Conductivity (W/m.K)1.86 x1050.0265600Prandtl Number0.707Note: Dynamic viscosity of air at 60°C is 2.002 x10 N.s/m2

Answered: Image /qna-images/answer/abd83b9d-bcdf-48a0-bf28-27df25334177.jpg

Answered: A sphere at 120°C was being exposed to…

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.

Chapter7: Forced Convection Inside Tubes And Ducts

Section: Chapter Questions

Problem 7.50P

See similar textbooks

Similar questions

1.67 In beauty salons and in homes, a ubiquitous device is the hairdryer. The front end of a typical hairdryer is idealized as a thin-walled cylindrical duct with a 6-cm diameter with a fan at the inlet that blows air over an electric heating coil as schematically shown in the figure. The design of this appliance requires two power settings, with which the air blown over the electric heating coil is heated from the ambient temperature of to an outlet temperature of and with exit air velocities of 1.0 m/s and 1.5 m/s. Estimate the electric power required for the heating coil to meet these conditions, assuming that heat loss from the outside of the dryer duct is neglected.
An electrical transmission line of 1.2-cm diameter carries a current of 200 amps and has a resistance of 310-4 ohm per meter of length. If the air around this line is at v, determine the surface temperature on a windy day, assuming a wind blows across the line at 33 km/h.
The air-conditioning system in a Chevrolet van for use in desert climates is to be sized. The system is to maintain an interior temperature of 20C when the van travels at 100 km/h through dry air at 30C at night. If the top of the van is idealized as a flat plate 6 m long and 2 m wide and the sides as flat plates 3 m tall and 6 m long, estimate the rate at which heat must be removed from the interior to maintain the specified
Determine the rate of heat loss from the wall of a building resulting from a 16 km/h wind blowing parallel to its surface. The wall is 24 m long and 6 m high, its surface temperature is 27C, and the temperature of the ambient air is 4C.
To ensure that the balls bounce consistently, tennis balls in Wimbledon are stored at exactly 68oF. A ballboy keeps a ball in his pocket to ensure that the ball can be given to the player quickly. If the ball is observed to warm up to 70oF after one minute, how long will it take for the ball to be within 20oF of the ballboy's body temperature (98.6oF) after he puts it in his pocket? It can be assumed that the temperature in the pocket is also the normal body temperature.
A pipe 30 m long with an outer diameter of 75 mm is used to deliver steam at a rate of 2000 kg / hour. The vapor pressure is 198.53 kPa entering the pipe with a quality of 98%. The pipe needs to be insulated with a thermal conductivity of 0.2 W / (m K) so that the quality of the steam will only slightly decrease to 95%. The outer surface temperature of the insulation is assumed to be 25 ° C. Ignore resistance conductive of the pipe material and it is assumed that there is no pressure drop in the pipe. a. Determine the enthalpy of incoming vapor = AnswerkJ / kg. b. Determine the enthalpy of steam coming out = AnswerkJ / kg. c. Determine the vapor heat change / loss along the flow = Answerwatt. d. Specify the minimum required insulation thickness = Answercm.
A pipe 30 m long with an outer diameter of 75 mm is used to deliver steam at a rate of 1500 kg / hour. The vapor pressure is 198.53 kPa entering the pipe with a quality of 98%. The pipe needs to be insulated with a thermal conductivity of 0.2 W / (m K) so that the quality of the steam will only slightly decrease to 95%. The outer surface temperature of the insulation is assumed to be 25 ° C. Ignore resistance conductive of the pipe material and it is assumed that there is no pressure drop in the pipe. a. Determine the enthalpy of incoming vapor = Answer kJ / kg. b. Determine the enthalpy of steam coming out = Answer kJ / kg. c. Determine the vapor heat change / loss along the flow = Answer watt. d. Specify the minimum required insulation thickness = Answer cm.
Ground turkey was made into me at balls and refrigerated at 2 ° C before being deep fried. The diameter of each meat ball is 9cm. To make sure that the meat balls are safe to be consumed, they must be cooked over 70 ° C. Assume that the cooking oil is at a constant temperature of 180 ° C and has a heat transfer coefficient of 50 W/(m 2 ∙ K). The conductivity and specific heat of the ground turkey are approximated at 2 W/( m∙K ) and 4 kJ/( kg ∙ K) respectively. The density of the ground turkey is 500kg/ m 3 . a) During the deep- frying process, do you anticipate that each meat ball has a uniform temperature distribution throughout its volume? Please show calculation to support your answer (5 pts) . b) Please calculate the minimum time required for cooking (1 5 p ts). c) When served, what are the surface and center temperatures of each meat ball ( 15 pts).
A composite wall constructed of 2.5cm of steel (k-60.5 W/m-K) and 5.0 cm of aluminum (k177W/m-K) separates two liquids. The liquid on the steel side has a film coefficient of 15W/m²-K and a temperature of 400degC. The liquid on the steel side has a film coefficient of 30W/m² and a temperature of 100degC. Assume steady state conditions, what is the temperature at the steel-aluminum interface in deg C
Solar radiation is incident on the glass cover of a solar collector at a rate of 700W/m². The glass of collector absorbs 88 percent of the incident radiation on it and has an emissivity of 0.9. The entire hot water needs of a family can be provided by a single collector of 1.2m height and 2m width. The temperature of the glass cover of the collector is measured to be 35C° on a day when the surrounding air temperature is 25C° and the wind is blowing at 30km/h. The effective sky temperature for radiation exchange between the glass cover and the open sky is -40C°. Water enters the tubes which attached to the absorber plate at a rate of 1kg/min. Assuming the back surface of the absorber plate to be heavily insulated and the only heat loss to occur through the glass cover, determine (a) the total rate of heat loss from the collector, (b) the collector efficiency, which is the ratio of the amount of heat transferred to the water to the solar energy incident on the collector, and (c) the…
8,000 kilograms of dressed poultry are blast-frozen on hand trucks each day (24 hrs) in a freezing tunnel. The poultry is to precooled to 7°C before entering the freezer where it is frozen and its temperature is lowered to -20°C for storage. The specific heat of poultry above and below freezing are 3.18 and 1.55 kJ/kg-°C, respectively. The latent heat is 246 kJ/kg and the freezing temperature is -2.75°C. Neglecting the heat load from the hand trucks, determine the amount of heat needed to be removed from the dressed poultry in kW.
A long rod of AISI 4130 steel initially at a uniform temperature of 400°C issuddenly exposed to 20°C air, where the heat transfer coefficient is 15 W/m2∙K. The rod has a diameter of 4.8 cm. How long after being exposed to the 20°C airwill the steel rod reach a temperature of 60°C? The properties of the rod arep = 7840 kg/m3, Cp = 460 J/kg.K and k = 43 W

SEE MORE QUESTIONS

Recommended textbooks for you

Principles of Heat Transfer (Activate Learning wi…

Mechanical Engineering

ISBN:

9781305387102

Author:

Kreith, Frank; Manglik, Raj M.

Publisher:

Cengage Learning