Q6) A 50-cm-long, 800-W electric resistance heating element cm and surface temperature 120°C is immersed in 60 kg of water Determine how long it will take for this heater to raise the wat 80°C. Also, determine the convection heat transfer coefficients and at the end of the heating process. Take Cp =4180 J/kg °C

Q6) A 50-cm-long, 800-W electric resistance heating element cm and surface temperature 120°C is immersed in 60 kg of water Determine how long it will take for this heater to raise the wat 80°C. Also, determine the convection heat transfer coefficients and at the end of the heating process. Take Cp =4180 J/kg °C

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.

Chapter3: Transient Heat Conduction

Section: Chapter Questions

Problem 3.12P

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1.60 Two electric resistance heaters with a 20 cm length and a 2 cm diameter are inserted into a well-insulated 40-L tank of water that is initially at 300 K. If each heater dissipates 500 W, what is the time required for bringing the water temperature in the tank to 340 K? State your assumption for your analysis.
Q5 c) Water is to be heated from 10°C to 80°C as it flows through a 2-cm-internal-diameter, 7-m- long tube. The tube is equipped with an electric resistance heater, which provides uniform heating throughout the surface of the tube. The outer surface of the heater is well insulated, so that in steady operation all the heat from the heater is transferred to the water in the tube. If the system is to provide hot water at a rate of 8 L/min, determine the convection heat transfer coefficient and temperature at the inner surface of the pipe at the exit. d) Hot air at atmospheric pressure and 85°C enters a 10-m long uninsulated square duct of cross section 0.15m x 0.15m that passes through the attic of a house at a rate of 0.1 m/s. The duct is observed to be nearly isothermal at 60°C. Determine the rate of heat loss from the duct to the air space in the attic.
Example: 0.5 kg of water per minute is heated from 20° to 40°C when passed through a tube of 2.5 cm diameter steel pipe. The pipe surface temperature is maintained at 110°C by condensing steam on its surface. Find out the length of the pipe required. The properties of water at mean temperature of 70°C are given below: p = 978 kg/m² k= 0.575 W/m. K Cp = 4200 J/kg. K v = 0.415 x 10-6 m²/sec
4- Carbon steel balls 8 mm in diameter are annealed by heating them first to 900°C in a furnace and then allowing them to cool slowly to 100°C in ambient air at 35°C. If the average heat transfer coefficient is 75 W/m -°C, determine how long the annealing process will take. If 2500 balls are to be annealed per hour Given: Carbon steel [k = 54 W/m.°C, p = 7833 kg/m, and C,= 0.465 kJ/kg. °C. and a= 1.474x 10* m²/s] Air, 35°C Fumace Steel ball 100°C 900°C
H.W. Q: An aluminum pan whose thermal conductivity is 237 W/m-°C has a flat bottom with diameter 20 cm and thickness 0.4 cm. Heat is transferred steadily to boiling water in the pan through its bottom at a rate of 800 W. If the inner surface of the bottom of the pan is at 105°C, determine the temperature of the outer surface of the bottom of the pan. 105°C 0.4 cm Answer: T= 105.43 °C 800 W 7
Ball bearing ro=4 mm leaving the oven at a uniform temperature of 900 oC are exposed to air for a while before they are dropped in to the water for quenching . Determine the time they can stand the air before their temperature falls below 850 oC also find the total rate of heat transfer .Take for the balls k = 54 W/m .oC , ρ= 7833 kg/m3 , Cp=0.456 kJ/kg.oC
High-pressure steam condenses at 400 K on the outer surface of a thin-walled tube of 50 mm diameter. The overall heat transfer coefficient between steam and air on the inside of the tube is 200 W/m?. If the air enters the tube at 25 m/s, 150 kPa and 280 K, find the length of the tube required for the air to be heated to 350 K.
2 (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.
Most automobiles have a coolant reservoir to catch radiator fluid that may overflow when the engine is hot. Such a radiator, made of copper, is filled to its 12-L capacity when at 10.0°C. -What volume of radiator fluid, in liters, will overflow when the radiator and fluid reach their 99.5°C operating temperature, given that the fluid’s thermal coefficient of volume expansion is 400.0 × 10-6 / °C? The coefficient of volume expansion for copper is 5.1 × 10-5 /°C.
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 í
4-31 The temperature of a gas stream is to be measured by a thermocouple whose junction can be approximated as a 1.2-mm-diameter sphere. The properties of the junction are k 35 W/m K, p = 8500 kg/m3, and c, = 320 J/kg-K, and the heat transfer coefficient between the junction and the gas is h = 110 W/m2-K. Determine how long it will take for the thermocouple to read 99 percent of the initial temperature difference. Answer: 22.8 s
In determining the average rate of heating of a tank of 20% sugar syrup, thetemperature at the beginning was 20°C and it took 30 min to heat to 80°C. Thevolume of the sugar syrup was 50 ft3 and its density 66.9 lb/ft3. The specific heat ofthe sugar syrup is 0.9 Btu lb-1°F-1.(a) Convert the specific heat to kJ kg-1°C-1.(b) Determine the rate of heating, that is the heat energy transferred in unit time, in SI units (kJ s-1)