Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
8th Edition
ISBN: 9781305387102
Author: Kreith, Frank; Manglik, Raj M.
Publisher: Cengage Learning
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A potato slice that is 1⁄4” inch thick is placed on a pan that is 212F. The slice has a thermal conductivity of 0.318 Btu/hr-ft-F, and an area of 4 sq in. What is the rate that it heats up if it is initially at 75F?
Consider two houses that are identical in size. House 1 has outside walls that were built using a double layer of brick. House 2 has outside walls that were built using a single layer of wood. Discuss and explain which house will be more energy efficient?
QUESTION 7 ´
Flat-plate solar collectors are often tilted up toward the sun in order to intercept a greater amount of
direct solar radiation, as shown in Figure Q2. The tilt angle from the horizontal also affects the rate
of heat loss from the collector. Consider a 2 m (height) and 3 m (width) solar collector that is tilted at
an angle 0 from the horizontal. The back side of the absorber is insulated. The absorber plate and the
glass cover, which are spaced 2.0 cm from each other, are maintained at temperatures of 75°C and
35°C, respectively. Analyse the solar collector for different angle, 0 = 0°, 20°, and 90° to select which
O gives the lowest rate of heat loss from the absorber plate by natural convection.
Absorber
| ||
Plate 750 cm
Solar
radiation,
Glass
Insulation
Cover,
Figure Q2
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- A one-story house is built over a vented crawl space. The attic is alsovented. The heating system is designed for a temperature difference of 75°F.The exterior wall of a middle bedroom is shown. The room is 10 feet 3 incheswide. The window has double pane glass. The wall is wood frame withsheathing and siding. It has 1 inch of polystyrene insulation over 31⁄2 inchesof insulation (total R-16). The ceiling has 91⁄2 inches of insulation (R-30),and the floor has 6 inches of insulation (R-19). Find the heat load for thisroom.arrow_forwardProblem 3: During summer, the temperature in Dhahran averages at 38°C for the entire day and night period. To maintain the inside of a building at the comfort level of 20°C, an Engineer suggested to use a commercial air conditioning (AC) system. The insulation and thermal design of the building is such that 28000 kJ/h of heat transfers to Inside 28000 Outside 20°C kJ/h 38°C Refrigerant loop Evaporator Condenser Compressor the building from outside. This amount of heat needs to be removed by the AC. The cost of electricity is 0.21 Ryial/kWh. Hint: 1 kWh-360OJ a. The suggested air conditioner requires a net power input to the compressor of 2 kW. Is the Engineer's suggestion valid? Calculate the coefficient of performance and the cost of electricity for one summer month. b. What is the minimum theoretical cost to operate the air conditioner? Discuss your results.arrow_forwardWhich house uses more energy. Haron's house in June or Areum's house in December? Why do you think so? Haron's House Areum's House YLEENEDGARD ** TALE Seoul, Korea Singapore 3-bedroom 2 bathrooms 4-bedroom, 3 bathrooms Well insulated Poody insulated Built 1997 Bricks and cement only Built 1925, renovated 2005 Bricks with wood siding 3 heaters 3 air-conditioning units As Uncle Areum and Uncle Haron continue to argue, you slip away to another (quieter) room. Pulling out a pad of paper, you begin to think about what factors will have an influence on how much energy is needed to heat or cool each house. AT R- R=AA 9 MMMMMM TITEarrow_forward
- The thermal conductivities of wood is kwood = 0.1W/(m°C)and air is kair = 0.0234W/(m°C). Part A If the temperature of the room is 20°C and outside is 10°C, find the rate of heat flow for a wall of wood with area = 10 m² and thickness of 5cm. O 60 W O 304 W O 34 W O 200 W O 100 W Submit Request Answer Part B The wall of wood with thickness of 5cm is now replaced with two layers of wood and a gap of air between the wood. Each layer of wood has a 2.5cm thickness and the gap is 1cm. The rate of heat flow will, decreases. increases. stay the same. Submit Request Answer Part C The temperature in the air gap will be, O 20°C, between 10°C and 20°C, O 10°C,arrow_forward1. For a steam pipe with a given diameter of 10 cm covered by two (2) layers of insulation. The first insulation has a thickness of 4 cm and a coefficient of thermal conductivity of 0.08 W/m.K. and the second insulation has a thickness of 3 cm and a thermal conductivity of 0.15 W/m.K. The steam main conveys steam at a pressure of 1.70 MPa with 25°C superheat. Outside temperature is 27°C. The pipe is 30 meters in length. (tsat @ 1.70 MPa = 204°C). Determine the following: a) The heat loss in KW b) Explain the concepts/principles that were considered and the factors that affected the condition of the above mentioned items (a & b).arrow_forwardAnswer within 10 minutes : The temperature at the inside surface of an oven is 460 oF. The inside wall of the oven is made of brick and is 8 inch thick. The thermal conductivity of the brick is 2.2 Btu/hr.ft2.(oF/ft). The outside of the oven is covered with a 3-inch layer of asbestos as insulation, which has a thermal conductivity of 0.11 Btu/hr.ft2.(oF/ft). If the outer surface of the insulation has a temperature of 100 oF , calculate the amount of heat lost through 2 ft2 of wall area in 3 hours.arrow_forward
- The fin efficiency is defined as the ratio of the actual heat transfer from the fin to a. The heat transfer from an equivalent fin which is infinitely long b. The heat transfer through the base area of the same fin c. The heat transfer from the same fin with an adiabatic tip d. The heat transfer from the same fin if the temperature along the entire length of the fin is the same as the base temperaturearrow_forwardI need a KPI for a project that consists of two partsThe first is glasses that monitor objects around them, and alert the person when an object is within the specified distanceThe second part is a glove that senses the heat from a distance. When the temperature reaches above the permissible limit, the person is alerted by means of a vibration motor.The purposes used in the first part:Spectacle shaped frame3 ultrasonic sensors2 vibration motors Arduino Pro NanoThe purposes used in the second part:The glove consists of two layers3 temperature sensorsMotor vibrationArduino Pro NanoMicro-nano charging baseWorking principle of each part:part One ::Objects that are within the distance on which the Ultrasonic has been programmed are monitored, where there is to the right of the glasses and the left of the glasses, and to the front of the Ultrasonic glasses, and there is a vibration motor on the right of the glasses and the left of the glasses. A body is monitored from the front, and this…arrow_forwardThe 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)arrow_forward
- 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?arrow_forwardThe 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…arrow_forwardYou want to heat a house on a very cold day as shown in the figure. To do this, you want to use photovoltaic panels as an energy source. It would be about using 15 panels each with an area of 1.5 m2. These panels would be connected to an electrical resistance that would heat the house as shown in the figure. The house is losing heat through the walls and ceiling as shown in the figure. The panels are receiving solar radiation at a rate of 800 W / m2 and if their efficiency is 15%. How much will the temperature of the house rise after an hour? The house is hermetically sealed. Assume that the specific heats of air, cv and cp, are constant as shown in the figure. sol = sun fuga = leakage aire = airarrow_forward
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