A 9-cm-diameter potato
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Heat and Mass Transfer: Fundamentals and Applications
- A food product with 82% moisture content is being frozen. Estimate the specific heat of the product at -8°C when 82% of the water is in a frozen state. The specific heat of dry product solid is 2.5 kJ/(kg °C). Assume specific heat of water at -10°C is similar to specific heat of water at 0°C.arrow_forwardTo ensure that the balls bounce consistently, tennis balls in Wimbledon are stored at exactly 68°F. A ballboy keeps a ball in his pocket to ensure that the ball can be given to the player quickly. If the ball is observed to warm up to 70°F after one minute, how long will it take for the ball to be within 20°F of the ballboy's body temperature (98.6°F) after he puts it in his pocket? It can be assumed that the temperature in the pocket is also the normal body temperature. O 14.3 min O 8.48 min O 5.3 min O 6.29 minarrow_forwardThree tons of fish is to be stored at a temperature of -10°C for 24hrs. The product enters the chiller at a temperature of 8°C. The specific heat below and above freezing is 0.41 kcal/kg-C and 0.76 kcal/kg-C respectively and its latent heat of fusion is 51 kcal/kg. If the freezing temperature of the product is -2.2 °C, determine the product load in kcal/hr.arrow_forward
- Humans are able to control their rates of heat production and heat loss to maintain a nearly constant core temperature of Tc = 37°C under a wide range of environmental conditions. This process is called thermoregulation. From the perspective of calculating heat transfer between a human body and its surroundings, we focus on a layer of skin and fat, with its outer surface exposed to the environment and its inner surface at a temperature slightly less than the core temperature, Ti = 35°C = 308 K. Consider a person with a skin/fat layer of thickness L = 2 mm and effective thermal conductivity k = 0.3 Wm ⋅ K. The person has a surface area A = 1.8 m2 and is dressed in a bathing suit. The emissivity of the skin is ε = 0.95.a). When the person is in still air at T∞ = 308 K, what is the skin surface temperature and rate of heat loss to the environment? Convection heat transfer to the air is characterized by a free convection coefficient of h = 2 W?2 ⋅ Kb). When the person is in water at T∞ =…arrow_forwardNewton's Law of Cooling - Differential Equations The rate at which a body cools is proportional to the difference in temperature between the body and its surroundings. If a body in air at 0°C will cool from 200°C to 100°C in 40 minutes, how many more minutes will it take the body to cool from 100°C to 50°C?arrow_forwardProblem #2: A mass of ice at -4°C is needed to cool 115 kg of vegetables in a bunker for 24 hours. The initial temperature of the vegetables is assumed to be 29°C. It is also assumed that, within the 24-hr period, the average temperature inside the bunker is 7°C. If the heat gained per hour in the bunker is 30% of the heat removed to cool the vegetables from 29°C to 7°C, what would be the required mass of ice in kg? Use: Specific heat of water 4.2292 kJ/kg-°C • Specific heat of ice 1.9387 kJ/kg-°C Specific heat of vegetables 3.35 kJ/kg-°Carrow_forward
- In a double-glazed window, the panes of glass are separated by 1.0 cm and the space is filled with a gas with thermal conductivity 24 mW K−1 m−1. What is the rate of transfer of heat by conduction from the warm room (28 °C) to the cold exterior (−15 °C) through a window of area 1.0 m2? You may assume that one pane of glass is at the same temperature as the inside and the other as the outside. What power of heater is required to make good the loss of heat?arrow_forwardQI/The top surface of the passenger car of a train moving at a velocity of 70 km/h is 2.8 m wide and 8 m long. The top surface is absorbing solar radiation at a rate of 200 W/m2, and the temperature of the ambient air is 30°C. Assuming the roof of the car to be perfectly insulated and the radiation heat exchange with the surroundings to be small relative to convection, determine the equilibrium temperature of the top surface of the car. Ans =35.1 carrow_forward3. A well-mixed cement-lined storage tank contains water initially at 50°C. The water loses energy to its surroundings via conduction through the tank's concrete-lined walls. The tank sits in an unheated warehouse with an air temperature of 0°C. A diagram of the storage tank is shown below. The cement lining is 1.5-cm thick and has a thermal conductivity (htc) of 2.0 W/(m K). height = 1.5 m diameter = 2.0 m a. How long will it take (in minutes) for the water to cool to 40°C? b. Why might you be over- or underestimating the time it will take to cool the contents of the reactor?arrow_forward
- Measuring the temperature of very cold substances can be challenging. Here is one way of measuring the temperature of liquid nitrogen. A 50g flake of aluminum is submerged in liquid nitrogen and left immersed until it is in thermal equilibrium. The flake is then removed and placed in a well-insulated container with 500ml of water at 30°C. When water and flake attain thermal equilibrium, the temperature of the water is found to be 25°C. What was the temperature of the liquid nitrogen?arrow_forwardA father and son conducted the following simple experiment on a hot dog which measured 12.5 cm in length and 2.2 cm in diameter. They inserted one food thermometer into the midpoint of the hot dog and another one was placed just under the skin of the hot dog. The temperatures of the thermometers were monitored until both thermometers read 20°C, which is the ambient temperature. The hot dog was then placed in 94°C boiling water and after exactly 2 min they recorded the center temperature and the skin temperature of the hot dog to be 59°C and 88°C, respectively. Assuming the following properties for the hot dog: r = 980 kg/m3 and cp = 3900 J/kg·K and using transient temperature charts, determine (a) the thermal diffusivity of the hot dog, (b) the thermal conductivity of the hot dog, and (c) the convection heat transfer coefficient.arrow_forwardA small copper wire with a diameter of 0.792 mm and initially at 366.5 K is suddenly immersed in a liquid held constant at 311 K. The convection coefficient h = 85.2 W/m2 · K. The physical properties can be assumed constant and are k = 374 W/m · K, cp = 0.389 kJ/kg · K, and ρ = 8890 kg/m3. Determine the time in seconds for the average temperature of the wire to drop to 338.8 K (one-half the initial temperature difference). Do the same but for h=11.36W/m2·K. Forpart(b),calculate the total amount of heat removed for a wire 1.0 m long.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning