4. Estimate the rate at which heat can be conducted from the interior of the body to the surface. Assume the typical thickness of the tissue is 4 cm, that the skin surface is 34° C, that the interior is 37° C, and that the skin area is 1.5 m². Compare this to the measured value of about 230 W that must be dissipated by a person doing light work. This shows the necessity of convective cooling by the blood.

4. Estimate the rate at which heat can be conducted from the interior of the body to the surface. Assume the typical thickness of the tissue is 4 cm, that the skin surface is 34° C, that the interior is 37° C, and that the skin area is 1.5 m². Compare this to the measured value of about 230 W that must be dissipated by a person doing light work. This shows the necessity of convective cooling by the blood.

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter3: Transient Heat Conduction

Section: Chapter Questions

Problem 3.5P: 3.5 In a ball-bearing production facility, steel balls that are each of 15 mm in diameter are...

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3.5 In a ball-bearing production facility, steel balls that are each of 15 mm in diameter are annealed by first heating them to 870°C and then slowly cooling in air to 125°C. If the cooling air stream temperature is 60°C, and it has a convective heat transfer coefficient of , determine the time required for the cooling.
2.15 Suppose that a pipe carrying a hot fluid with an external temperature of and outer radius is to be insulated with an insulation material of thermal conductivity k and outer radius . Show that if the convection heat transfer coefficient on the outside of the insulation is and the environmental temperature is , the addition of insulation actually increases the rate of heat loss if , and the maximum heat loss occurs when . This radius, is often called the critical radius.
1. 4000L/hr of distillates are cooled from 21 to 12 degrees Celsius, and wax is separated 12% by weight at 15 degrees Celsius. Oil has a specific heat of 2kJ/kg C and a specific gravity of 0.87. The latent heat of fusion is 290kJ/kg, and the specific heat of wax is 2.5. Allow 10% for losses and calculate the refrigerating machine's capacity in TOR.
A vertical cylinder 6 ft tall and 1 ft in diameter might be used to approximate a man for heat-transfer purposes. Suppose the surface temperature of the cylinder is 78°F, h=2 Btu/h · ft2 . °F, the surface emissivity is 0.9, and the cylinder is placed in a large room where the air temperature is 68°F and the wall temperature is 45°F. Calculate the heat lost from the cylinder. Repeat for a wall temperature of 80°F. What do you conclude from these calculations? Known, Find, Schematic Diagram, Assumption, Properties, Analysis and Comments
A vertical cylinder 6 ft tall and 1 ft in diameter might be used to approximate a man for heat-transfer purposes. Suppose the surface temperature of the cylinder is 78°F, h=2 Btu/h · ft2 . °F, the surface emissivity is 0.9, and the cylinder is placed in a large room where the air temperature is 68°F and the wall temperature is 45°F. Calculate the heat lost from the cylinder. Repeat for a wall temperature of 80°F. What do you conclude from these calculations?
Provide the answers with clear explantion and images. Coolant flowing through a radiator at the rate of 3 kg/s are cooled from 105 0C to 81 0 The specific heat capacity of coolant and air are 4.19 kJ/kg K and 1.13 kJ/kJ/K respectively. Th overall heat transfer coefficient from gas to water is 140 W/m2 K. Calculate the surface area required for the radiation if the vehicle speed is 100 km/h. Consider the density of air as 1.225 kg/m3.
A large piece of biological tissue has to be kept at a temperature as low as possible without freezing (ice formation). The water in the tissue has several solutes dissolved in it and the effective molecular weight of the dissolved solutes is 50. The weight of all dissolved solutes combined is 10% of the weight of water. The latent heat of fusion of water is 335 kJ/kg and the molecular weight of water is 18. What is the lowest temperature that this tissue can be stored at, without ice formation?
How long should it take to boil an egg? Model the egg as a sphere with radius of 2.3 cm that has properties similar to water with a density of = 1000 kg/m3 and thermal conductivity of k = 0.606 Watts/(mC) and specific heat of c = 4182 J/(kg C). Suppose that an egg is fully cooked when the temperature at the center reaches 70 C. Initially the egg is taken out of the fridge at 4 C and placed in the boiling water at 100 C. Since the egg shell is very thin assume that it quickly reaches a temperature of 100 C. The protein in the egg effectively immobilizes the water so the heat conduction is purely conduction (no convection). Plot the temperature of the egg over time and use the data tooltip in MATLAB to make your conclusion on the time it takes to cook the egg in minutes.
Q#01: Define the following:a) Steady and Transient state of heat transfer by the help of an example.b) If the area, thickness and temperatures are same across the material. Justify whichmaterial will transfer more heat, either the material with high thermal conductivity valueor the material with low thermal conductivity value?c) If the area and temperatures are same across the material. Explain whether thermalconductivity will have any effect on thickness or not?
A square silicon chip (k = 150 W/m • K) has side width w = 5 mm and thickness z = 1 mm.The chip is mounted on a substrate so that its sides and interior surface are insulated. whilethat the front surface is exposed to a cooling fluid.If 4 W is dissipated from the circuitry mounted on the back surface of the chip, what is the difference insteady-state temperatures between the bottom and front surfaces?
(a) A circular copper ring at 24.0°C has a hole with an area of 9.97 cm2. What minimum temperature must it have so that it can be slipped onto a steel metal rod having a cross-sectional area of 10.0 cm2?_______ °C(b) Suppose the ring and the rod are heated simultaneously. What change in temperature of both will allow the ring to be slipped onto the end of the rod? (Assume no significant change in the coefficients of linear expansion over this temperature range.)________ °C
Steam is being transported in a pipe at a chemical production facility in Gebze, Kocaeli. Theouter diameter of the pipe is 8 cm, and the surrounding air temperature is 20 °C. On the surface of thepipe, the combined heat transfer coefficient is 35 W/m2*K. The surface temperature of the pipe is 150 °C.Steady-state conditions exist.(a) What is the rate of heat loss from the pipe to the surroundings?(b) The power used to generate the steam is obtained from natural gas. Perform an online search forapproximate values of the calorific value of natural gas, as well as the cost of natural gas per cubicmeter, and estimate the financial loss due to heat loss from this steam pipe within a period of oneyear. Indicate your sources clearly in your answer.