A USB-powered coffee cup warmer advertised on Amazon claims to have a heating plate that reaches 85°C when there is no cup placed on it. What is the electrical power required for this? Assume the device is 100% efficient at converting electrical power to heat in the plate and that heat from the plate is lost to air from the top surface of the heating plate only. Take ambient temperature to be 20.0°C, the diameter of the plate to be 10.0 cm, the convection coefficient from the plate to air to be 7.1 W/(m2.K), and take the emissivity of the plate to be 1.0. 7.0 W 9.8 W 12 W 3.6 W 7.7 W 5.5 W

A USB-powered coffee cup warmer advertised on Amazon claims to have a heating plate that reaches 85°C when there is no cup placed on it. What is the electrical power required for this? Assume the device is 100% efficient at converting electrical power to heat in the plate and that heat from the plate is lost to air from the top surface of the heating plate only. Take ambient temperature to be 20.0°C, the diameter of the plate to be 10.0 cm, the convection coefficient from the plate to air to be 7.1 W/(m2.K), and take the emissivity of the plate to be 1.0. 7.0 W 9.8 W 12 W 3.6 W 7.7 W 5.5 W

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.

Chapter1: Basic Modes Of Heat Transfer

Section: Chapter Questions

Problem 1.67P: 1.67 In beauty salons and in homes, a ubiquitous device is the hairdryer. The front end of a typical...

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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.
Thermodynamics: Can you show me how to solve for the answer that is written below? Please show it in step by step solution Thank you!
The inside wall of a furnace is at 2100oF and the outside wall is at 300oF. The wall of a furnace must be designed to transmit no more than 220 Btu/hr-ft2. Two types of bricks are available for construction:TYPE A: k = 0.38 Btu/ hr-ft-R with an allowable maximum temperature of 1400oFTYPE B: k = 0.98 Btu/ hr-ft-R with an allowable maximum temperature of 2300oF Both types of bricks have the same dimensions (9” x 4.5” x 3”) but the cost for Type B brick is twice the cost of Type A brick. Illustrate the order of arrangement of bricks A and B in the furnace wall (with thickness, estimated temperatures at the interface between walls A and B and at the interior and exterior surface, the transport area and direction of transfer included)
The inside wall of a furnace is at 2100oF and the outside wall is at 300oF. The wall of a furnace must be designed to transmit no more than 220 Btu/hr-ft2. Two types of bricks are available for construction:TYPE A: k = 0.38 Btu/ hr-ft-R with an allowable maximum temperature of 1400oFTYPE B: k = 0.98 Btu/ hr-ft-R with an allowable maximum temperature of 2300oF Both types of bricks have the same dimensions (9” x 4.5” x 3”) but the cost for Type B brick is twice the cost of Type A brick. If a 15 ft2 wall is to be constructed, how many bricks will be used? how many brick A and how many brick B?
The inside wall of a furnace is at 2100oF and the outside wall is at 300oF. The wall of a furnace must be designed to transmit no more than 220 Btu/hr-ft2. Two types of bricks are available for construction:TYPE A: k = 0.38 Btu/ hr-ft-R with an allowable maximum temperature of 1400oFTYPE B: k = 0.98 Btu/ hr-ft-R with an allowable maximum temperature of 2300oF Both types of bricks have the same dimensions (9” x 4.5” x 3”) but the cost for Type B brick is twice the cost of Type A brick. Model the wall as one-dimensional and determine the most economical arrangement of the bricks. Include:a drawing labeled with all given informationthe variables used in the appropriate places on the drawing (along with values and units, if provided)a thermal circuit showing the paths for heat transmissionequations and calculationsCalculations that show that the maximum temperature for Type A brick does not exceed 1400oFA recommendation for the number and orientation of the bricks. The inside temp is 2100f…
The inside wall of a furnace is at 2100oF and the outside wall is at 300oF. The wall of a furnace must be designed to transmit no more than 220 Btu/hr-ft2. Two types of bricks are available for construction:TYPE A: k = 0.38 Btu/ hr-ft-R with an allowable maximum temperature of 1400oFTYPE B: k = 0.98 Btu/ hr-ft-R with an allowable maximum temperature of 2300oF Both types of bricks have the same dimensions (9” x 4.5” x 3”) but the cost for Type B brick is twice the cost of Type A brick. What is the rate of heat conduction through wall A? If a 15 ft2 wall is to be constructed, how many bricks will be used? how many brick A and how many brick B?
6. a. The heat flux applied to the walls of the biomass combustion furnace is 20 W/m2. The furnace walls have a thickness of 10 mm and a thermal conductivity of 12 W/m.K. If the wall surface temperature is measured to be 50oC on the left and 30oC on the right, prove that conduction heat transfer occurs at a steady state!b. Heating the iron cylinder on the bottom side is done by placing the iron on the hotplate. This iron has a length of 20 cm. The surface temperature of the hotplate is set at 300oC while the top side of the iron is in contact with the still outside air. To reach the desired hotplate temperature, it takes 5 minutes. Then it takes 15 minutes to measure the temperature of the upper side of the iron cylinder at 300oC. Show 3 proofs that heat transfer occurs transiently
A metal cube of 0.1 m sides is being cooled down uniformly from 300°C to 30°C by placing it in cold water at 10°C. The convection coefficient of water around the cube is 40 W/m².K. The properties of the cube material are as follows - thermal conductivity: 137 W/m-K, density: 1600 kg/m³; specific heat: 800 J/kg.K. Neglect radiation. Find the time required for coo cooling. 1426-2
2. A steel plate of k=50w/mk and thickness 10cm passes a heat flux by conduction of 25kW/m² . If the temperature of hot surface of plate is 100C, then what is the temperature of the cooler side of plate?
Question 6: Find the required length of a 5 cm-diameter tube to heat water from an inlet temperature of 30 °C to an outlet temperature of 100 °C using either: a) Constant temperature of 200 °C, or b) Constant heat flux of 10,000 W/m?. The mass flow rate of the water is 0.5 kg/s, its thermal conductivity is 0.04 W/m.K and its specific heat is 4190 kJ/kg.K. Assume a fully-developed flow.
A rectangular glass window pane on a house has a width of 1.4 m, a height of 2.2 m, and a thickness of 0.49 cm. Find the energy transferred through the window by conduction in 12 hours on a day when the inside temperature of the house is 22°C and the outside temperature is 2.0°C. Take surface air layers into consideration. J
A solar collector and storage tank, shown in Figure (a) below, is to be optimized to achieve minimum first cost. During the day the temperature of water in the storage vessel is elevated from 25 °C (the minimum useful temperature) to tmax, as shown in Figure (b). The collector receives 260 W/m² of solar energy, but there is heat loss from the collector to ambient air by convection. The convection coefficient is 2 W/(m²*K), and the average temperature difference during the 10-hour day is (25 + tmax)/2 minus the ambient temperature of 10 °C. The energy above the minimum useful temperature of 25 °C that is to be stored in the vessel during the day is 200,000 kJ. The density of water is 1000 kg/m³, and its specific heat is 4.19 kJ/(kg*K). The cost of the solar collector in dollars is 20A, where A is the area in square meters, and the cost of the storage vessel in dollars is 101.5V, where V is the volume in cubic meters. Storage tank Collector (a) Temperature, °C tmax conforte 25°C, lowest…