REFRIGERATION+AIR COND.TECH.-W/2 ACCESS
8th Edition
ISBN: 9781337370042
Author: TOMCZYK
Publisher: CENGAGE L
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Chapter 31, Problem 46RQ
An orifice is a drilled hole in a _______.
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A power transistor with three 0.8 mm diameter leads of a copper-silver alloy (k = 400 W/m-K) dissipates 3.5 Watts of
power. The printed circuit board (PCB) on which the transistor is mounted is maintained at 30 C. The air temperature is
20 C and the heat transfer coefficient for the leads is 60 W/m² K. The length of the leads from the transistor to printed
circuit board is 9.0 mm.
(a) Determine the maximum lead temperature neglecting all convection effects.
(b) Determine the maximum lead temperature if convection is present.
T=20C
h = 60 W/m²K
Air
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Lead
k = 400 W/m K
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9 mm
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not smooth. The window casement that surrounds the edge of glass pane is raised 10 mm above the surface of the glass
and adjacent wall structure. Inside the building, the air temperature and heat transfer coefficient for the interior surface
are 21 °C and 9 W/m² K respectively. The window has a uniform thermal conductivity of 1.4 W/m K. If the outdoor air
temperature is 5 °C, determine the rate of convective heat loss from the window. Develop a thermal resistance network
for the window system. Please state and justify all assumptions. Neglect any conduction through the casement.
Assume the following air properties: kair =0.0248 W/m K, v= 14.20 x 106 m²/s, Pr = 0.712.
Outside Air
u=8m/s
T=5°C
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2 m
T=21°C
h=9W/m² K
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A thin electrical heater that dissipates 2 kW of thermal energy is position between two plane walls. The thickness of
each wall is shown in the figure below. The thermal conductivities of sections A and B are 3 W/m C and 0.8 W/m C
respectively. The electrical heater is assumed to be highly conductive (k=200 W/m C). The exterior surface of each wall
experiences convective conditions as summarized below.
(a) Construct the thermal circuit representing the steady state heat transfer for the system. Label all nodes, resistances
and relevant terms.
(b) Determine the temperate of the electrical heater.
T = 50 C
h = 200 W/m² C
A
10 cm
6 cm
B
Electrical
Heater
T_ = 20 C
h = 50 W/m² C
K₁ = 3 W/m²K
0.05 cm
k₁ = 0.08 W/m² K
Chapter 31 Solutions
REFRIGERATION+AIR COND.TECH.-W/2 ACCESS
Ch. 31 - The four types of gas furnace airflow patterns are...Ch. 31 - Describe the function of a multipoise or...Ch. 31 - Describe the function of a draft safeguard switch.Ch. 31 - Where are auxiliary limit switches used in heating...Ch. 31 - The specific gravity of natural gas is A. 0.08. B....Ch. 31 - Prob. 6RQCh. 31 - The pressure at the manifold for natural gas is...Ch. 31 - Prob. 8RQCh. 31 - The typical manifold pressurefor propane gas...Ch. 31 - Why is excess air supplied to all gas-burning...
Ch. 31 - Prob. 11RQCh. 31 - True or False: All gas valves snap open and...Ch. 31 - Which of the following features does an automatic...Ch. 31 - What is the function of the servo pressure...Ch. 31 - What is a redundant gas valve?Ch. 31 - Prob. 16RQCh. 31 - Prob. 17RQCh. 31 - Prob. 18RQCh. 31 - Prob. 19RQCh. 31 - What is an integrated furnace controller (IFC)?Ch. 31 - What is meant by the warm-air blower's off-delay...Ch. 31 - What are dual-in-line-pair (DIP) switches?Ch. 31 - Prob. 23RQCh. 31 - Describe the two types of pilot lights.Ch. 31 - True or False: A thermocouple develops direct...Ch. 31 - Describe how a thermocouple flame-proving system...Ch. 31 - Prob. 27RQCh. 31 - Describe how a liquid-filled flame-proving system...Ch. 31 - Prob. 29RQCh. 31 - Describe a flame rectification flame-proving...Ch. 31 - Prob. 31RQCh. 31 - Describe the difference between a single-rod...Ch. 31 - Prob. 33RQCh. 31 - Prob. 34RQCh. 31 - Prob. 35RQCh. 31 - Prob. 36RQCh. 31 - Define the dew point temperature as it applies to...Ch. 31 - Prob. 38RQCh. 31 - Prob. 39RQCh. 31 - What are four factors that determine the...Ch. 31 - What is a 100% shutoff system?Ch. 31 - What is the difference between a hard and a soft...Ch. 31 - Prob. 43RQCh. 31 - When would a combustion blower ever interpurge a...Ch. 31 - Prob. 45RQCh. 31 - An orifice is a drilled hole in a _______.Ch. 31 - A______ distributes gas to the various burners.Ch. 31 - True or False: An orifice measures the quantity of...Ch. 31 - Prob. 49RQCh. 31 - The ________transfers heat from the hot gas to the...Ch. 31 - Name two types of fan switches.Ch. 31 - Prob. 52RQCh. 31 - Prob. 53RQCh. 31 - Describe how a two-stage furnace operates.Ch. 31 - Describe how a modulating furnace operates.Ch. 31 - What is a variable-output programmable thermostat?Ch. 31 - Why is a metal vent often preferred rather than a...Ch. 31 - Prob. 58RQCh. 31 - Describe why you should never use a flame to leak...Ch. 31 - Prob. 60RQCh. 31 - A _____________sample is taken from the flue gas...
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