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The north wall of an electrically heated home is 20ft long, 10ft high, and 1ft thick and is made of brick whose thermal conductivity is
On a certain winter night, the temperatures of the inner and the outer surfaces of the wall are measured to be at about
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HEAT+MASS TRANSFER:FUND.+APPL.
- What are the important modes of heat transfer for a person sitting quietly in a room? What if the person is sitting near a roaring fireplace?arrow_forwardA container used to store ice is made of wood 5.0 cm thick and has an effective area of 12,000 cm2 and thermal conductivity of 0.00027 cal/cm2-sec-°C/cm. How much ice inside the box would be melted each 24-hour day if the outside temperature is 25°C and the temperature inside the box is 5°C.arrow_forward3. A classroom that normally contains 40 people is to be air-conditioned with window air-conditioning units of 5-kW cooling capacity. A person at rest may be assumed to dissipate heat at a rate of about 360 kJ/h. There are 10 light bulbs in the room, each with a rating of 100 W. The rate of heat transfer to the classroom through the walls and the windows is estimated to be 15,000 kJ/h. If the room air is to be maintained at a constant temperature of 210C, determine the number of window air-conditioning units required. draw a figure also, and explain each step by step solution.arrow_forward
- 2.(b) The inner and outer surfaces of a 25-cm-thick wall are at 27 oC and 45 oC, respectively. The outer surface of the wall exchanges heat by radiation with surrounding surfaces at 40 oC, and convection with ambient air at 42 oC with convection heat transfer coefficient of 9.0 W/m2 K. Solar radiation incident on the surface is at a rate of 150 W/m2. If the emissivity and the solar absorptivity of the outer surface are 0.75 and 0.85, respectively: (i) write the expression of the energy balance at the outer surface; (ii) write the expression of conduction heat flux; (iii) calculate the convection heat flux; (iv) calculate the radiation heat flux; (v) calculate the effective thermal conductivity of the wall.arrow_forwardA window is replaced by a wall with thick insulation. The thermal conductivity of the same area will be decreased to 0.0039 W/m/°C and the thickness will be increased to 16 cm. Determine the rate of heat transfer through this area of 2.16 m2 when the temperature outside is 25 C and the temperature inside is 19 C. What quantity of heat is required to raise the temperature of 450 grams of water from 15°C to 85°C? The specific heat capacity of water is 4.18 J/g/°C. A 12.9 gram sample of an unknown metal at 26.5°C is placed in a Styrofoam cup containing 50.0 grams of water at 88.6°C. The water cools down and the metal warms up until thermal equilibrium is achieved at 87.1°C. Assuming all the heat lost by the water is gained by the metal and that the cup is perfectly insulated, determine the specific heat capacity of the unknown metal. The specific heat capacity of water is 4.18 J/g/°C. Elise places 48.2 grams of ice in her beverage. What quantity of energy would be absorbed by the ice (and…arrow_forwardA composite plane wall consists of a 5-in.-thick layer of insulation (k, = 0.029 Btu/h ft. °R) and a 0.75-in.-thick layer of siding (ks = 0.058 Btu/h ft. °R). The inner temperature of the insulation is 67°F. The outer temperature of the siding is -8°F. Determine at steady state (a) the temperature at the interface of the two layers, in °F, and (b) the rate of heat transfer through the wall in Btu/h.ft² of surface area.arrow_forward
- Determine the time needed to decrease the temperature of a solid cylinder from 40 C to 35 C if the ambient temperature is equal to 31 C. The cylinder has a length equals to 0.9 m and diameter equals to 100 mm. The heat convective coefficient is equal to 9 W/m^2.K. The cylinder has a conductivity equals to 2 W/m.K, a density equals to 1200 kg/m^3 and its Cp is equal to 4.700 kJ/kgK.arrow_forwardIf H is the work output of a heat engine and Q is the total heat input of an engine, then determine its thermal efficiency.arrow_forwardWhat is the difference between internal heat generation and heat transfer in any direction. Thank youarrow_forward
- A composite plane wall consists of a 3-in.-thick layer of insulation (k = 0.029 Btu/h · ft · °R) and a 0.75-in.-thick layer of siding (kg = 0.058 Btu/h · ft · °R). The inner temperature of the insulation is 67°F. The outer temperature of the siding is 8°F. Determine at steady state (a) the temperature at the interface of the two layers, in °F, and (b) the rate of heat transfer through the wall in Btu/h-ft? of surface area.arrow_forwardExample 2: The roof of an electrically heated home is 6 m long, 8 m wide, and 0.25 m thick, and is made of a flat layer of concrete whose thermal conductivity is k=0.8 W/m·°C. The temperatures of the inner and the outer surfaces of the roof one night are measured to be 15°C and 4°C, respectively, for a period of 10 hours. Determine the rate of heat loss through the roof that nightarrow_forwardQ1: An aluminum pan whose thermal conductivity is 237 W/m-°C has a flat bottom whose diameter is 20 cm and thickness 0.6 cm. Heat is transferred steadily to boiling water in the pan through its bottom at a rate of 700 W. If the inner surface of the bottom of the pan is 105°C, determine the temperature of the outer surface of the bottom of the pan.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning