Unformatted text preview: th.
4–98C What is the proper storage temperature of frozen
poultry? What are the primary methods of freezing for poultry?
4–99C What are the factors that affect the quality of
frozen fish?
4–100 The chilling room of a meat plant is 15 m 18 m
5.5 m in size and has a capacity of 350 beef carcasses. The
power consumed by the fans and the lights in the chilling room
are 22 and 2 kW, respectively, and the room gains heat through
its envelope at a rate of 11 kW. The average mass of beef carcasses is 280 kg. The carcasses enter the chilling room at 35°C,
after they are washed to facilitate evaporative cooling, and are
cooled to 16°C in 12 h. The air enters the chilling room at
2.2°C and leaves at 0.5°C. Determine (a) the refrigeration
load of the chilling room and (b) the volume flow rate of air.
The average specific heats of beef carcasses and air are 3.14
and 1.0 kJ/kg · °C, respectively, and the density of air can be
taken to be 1.28 kg/m3.
4–101 Turkeys with a water content of 64 percent that are
initially at 1°C and have a mass of about 7 kg are to be frozen
by submerging them into brine at 29°C. Using Figure 4–45,
determine how long it will take to reduce the temperature of
the turkey breast at a depth of 3.8 cm to 18°C. If the temperature at a depth of 3.8 cm in the breast represents the average
Brine –29°C
Turkey
7 kg
1°C 4–91C How does (a) the air motion and (b) the relative humidity of the environment affect the growth of microorganisms
in foods?
4–92C The cooling of a beef carcass from 37°C to 5°C with
refrigerated air at 0°C in a chilling room takes about 48 h. FIGURE P4–101 cen58933_ch04.qxd 9/10/2002 9:13 AM Page 261 261
CHAPTER 4 temperature of the turkey, determine the amount of heat transfer per turkey assuming (a) the entire water content of the
turkey is frozen and (b) only 90 percent of the water content of
the turkey is frozen at 18°C. Take the specific heats of turkey
to be 2.98 and 1.65 kJ/kg · °C above and below the freezing
point of 2.8°C, respectively, and the latent heat of fusion of
Answers: (a) 1753 kJ, (b) 1617 kJ
turkey to be 214 kJ/kg.
4–102E Chickens with a water content of 74 percent, an
initial temperature of 32°F, and a mass of about 6 lbm are to be
frozen by refrigerated air at 40°F. Using Figure 4–44, determine how long it will take to reduce the inner surface
temperature of chickens to 25°F. What would your answer be if
the air temperature were 80°F?
4–103 Chickens with an average mass of 2.2 kg and average
specific heat of 3.54 kJ/kg · °C are to be cooled by chilled water that enters a continuousflowtype immersion chiller at
0.5°C. Chickens are dropped into the chiller at a uniform temperature of 15°C at a rate of 500 chickens per hour and are
cooled to an average temperature of 3°C before they are taken
out. The chiller gains heat from the surroundings at a rate of
210 kJ/min. Determine (a) the rate of heat removal from the
chicken, in kW, and (b) the mass flow rate of water, in kg/s, if
the temperature rise of water is not to exceed 2°C.
4–104 In a meat processing plant, 10cmthick beef slabs
(ρ 1090 kg/m3, Cp 3.54 kJ/kg · °C, k 0.47 W/m · °C,
and α 0.13 10–6 m2/s) initially at 15°C are to be cooled in
the racks of a large freezer that is maintained at 12°C. The
meat slabs are placed close to each other so that heat transfer
from the 10cmthick edges is negligible. The entire slab is to
be cooled below 5°C, but the temperature of the steak is not
to drop below 1°C anywhere during refrigeration to avoid
“frost bite.” The convection heat transfer coefficient and thus
the rate of heat transfer from the steak can be controlled by
varying the speed of a circulating fan inside. Determine the
heat transfer coefficient h that will enable us to meet both temperature constraints while keeping the refrigeration time to a
Answer: 9.9 W/m2 · °C.
minimum.
Air –12°C Meat 10 cm FIGURE P4–104 between the two plates has bonded them together. In an effort
to melt the ice between the plates and separate them, the
worker takes a large hairdryer and blows hot air at 50°C all
over the exposed surface of the plate on the top. The convection heat transfer coefficient at the top surface is estimated to
be 40 W/m2 · °C. Determine how long the worker must keep
blowing hot air before the two plates separate.
Answer: 482 s 4–106 Consider a curing kiln whose walls are made of
30cmthick concrete whose properties are k 0.9 W/m · °C
and
0.23 10 5 m2/s. Initially, the kiln and its walls are
in equilibrium with the surroundings at 2°C. Then all the doors
are closed and the kiln is heated by steam so that the temperature of the inner surface of the walls is raised to 42°C and is
maintained at that level for 3 h. The curing kiln is then opened
and exposed to the atmospheric air after the stream flow is
turned off. If the outer surfaces of the walls of the kiln were insulated, would it save any energy that day during the period
the kiln was used for curing for 3 h only,...
View
Full Document
 Spring '10
 Ghaz
 Heat Transfer, TI

Click to edit the document details