Chips of width
(a) If heat is rejected from the chips by radiation andnatural convection, what is the maximum operatingpower of each chip? The convection coefficientdepends on the chip-to-air temperature differenceand may be approximated as
(b) If a fan is used to maintain airflow through theenclosure and heat transfer is by forced convection, with
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Fundamentals of Heat and Mass Transfer
- Determine the power requirement of a soldering iron in which the tip is maintained at 400C. The tip is a cylinder 3 mm in diameter and 10 mm long. The surrounding air temperature is 20C, and the average convection heat transfer coefficient over the tip is 20W/m2K. The tip is highly polished initially, giving it a very low emittance.arrow_forward1.13 If the outer air temperature in Problem is –2°C, calculate the convection heat transfer coefficient between the outer surface of the window and the air, assuming radiation is negligible.arrow_forwardA long wire 0.7 mm in diameter with an emissivity of 0.9 is placed in a large quiescent air space at 270 K. If the wire is at 800 K, calculate the net rate of heat loss. Discuss your assumptions.arrow_forward
- 2. A heater is a thin vertical panel 1.0m long and 0.7m high and is used in a warehouse to keep workers warm. The heater has air circulating on each side. Assume the maximum temperature of the panel is 60°C (already above the board line that is safe for human hands to touch briefly without getting hurt). Assume the room air temperature is 18°C but the warehouse wall temperature is 5°C. Model the surface with an emittance of 0.9 and Vair = 1.57x105 m²/s. a. Determine the maximum power rating for the heater. b. Now if you run the heat by standing on its side (it will be 1.0 m high and 0.7 m long), determine the surface temperature. c. Compare case a and b and explain any differences you see.arrow_forward(25 pt) A vertical cavity wall of a house has 2.7 m height and 10 m width. The cavity space in the wall has length of 30 cm and involves quiescent air. During a winter day surface of the cavity towards indoors is 15 °C, whereas other surface towards outdoors is 5 °C. a. Calculate the natural convection heat transfer rate across the cavity? b. If the emissivity of the cavity surfaces is 0.7 what is the total heat transfer rate across the cavity? T₂ = 5 °C T₁-15 °C Indoors Cavity Quiescent air | L= 30 cm | H= 2.7 m Width of the wall is 10 m Outdoorsarrow_forwardChips of width L 15 mm on a side are mounted to a substrate that is installed in an enclosure whose walls and air are maintained at a temperature of Tsur=T»=25°C. The chips have an emissivity of E=0.60 and a maximum allowable temperature of Ts=85°C. (a) If heat is rejected from the chips by radiation and natural convection, what is the maximum operating power of each chip? The convection coefficient may be approximated as h=11.7 W/m²K. (b) If a fan is used to maintain airflow through the enclosure and heat transfer is by only forced convection, with h=250 W/m²K, what is the maximum operating power? Enclosure, Tur Substrate Air T_, h Chip (T,, e)arrow_forward
- A simple cavity wall consists of two brick layers separated by an air gap of 50 mm. If theinside air temperature is 20oC and the ambient outside temperature is 5oC, calculate theheat flux through the wall. Bricks are 100 mm thick with thermal conductivity kbrick = 1.2W/m K, hin = 10 W/m2 K, hout = 20 W/m2 K. The internal air cavity can be considered still (noconvection) with kair = 0.015 W/m K.arrow_forwardAt the end of its manufacturing process, a silicon wafer of diameter d= 258 mm , thickness & =1 mm is at an initial temperature of 325 C and is allowed to cool in quiescent, ambient air and large surroundings for which T =T= 25 C, What is the initial rate of cooling by convection (kJ/s) from the Lower surface ONLY (Watts)? 3 Silicon :p= 2330 kg/m , c̟ = 813 J/kg K, k = 87.8 W/m · K. -6 Air: v = 32.15×10 m /s, k = 0.0372 W/m· K, a = 46.8 ×10 0.686, m /s, Pr = Quiescent air T Tsur Silicon wafer D, 8, e, T Select one:arrow_forwardA spherical interplanetary probe of 0.5-m diameter contains electronics that dissipate 150 W. If the probe surface has an emissivity of 0.8 and the probe does not receive radiation from other surfaces, as, for example, from the sun, what is its surface temperature?arrow_forward
- 2 inch OD during a visit to a plastic sheet factory 60 m long section of a horizontal steam pipe passes from one end to the other without insulation is observed. While the temperature of the ambient air and its surfaces is 20 °C, the temperature measurements at several points are the average of the exposed surfaces of the steam pipe. indicates that the temperature is 160 °C. It is seen that the outer surface of the pipe is oxidized and The emissivity can be taken as 0.59. According to this; a) Calculate the heat loss in the steam pipe. b) The steam used is produced in a gas furnace operating with an efficiency of 59%. Factory 105500 It pays $1.10 per kJ of natural gas. If it is assumed that the factory works all year (365 days), for this facility Calculate the annual cost of heat losses in the steam pipe.arrow_forwardIn Gaziantep, many people use the energy of the Sun for heating their domestic water used for having shower in bathroom, for washing-machines, for kitchen stuffs, and etc. An ordinary solar collector panel is generally constructed on the roof of a house and the panels are declined approximately 60° with the horizontal line. Commonly, the total surface area of two glass panels is approximately 4.0 m² (2 panels: 1980mm x 1000mm for each) and they receive the energy from the Sun to heat the water. Although there is an inclination by 60°, it is reported that the twenty percent of the total incoming energy is reflected back to the atmosphere by well-insulated panel's glass surface. The remaining energy is used to heat the domestic water from 20°C to 50°C, and it is stored in storage tanks in a sunny day. The cold water enters from the bottom side of panel and exits from the top. It is assumed that the water passing through the solar collector has a negligible pressure drop. If the volume…arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning