It is well know that at the same outdoor air temperature a person is cooled at a faster rate under windy conditions that under calm conditions due to the higher convection heat transfer coefficients associated with windy air. The phrase wind-chill is used to relate the rate of heat loss from people under windy conditions to an equivalent air temperature for calm conditions (considered to be a wind or walking speed of 3 mph or 5 km/h). The hypothetical wind-chill temperature (WCT), called the wind-chill temperature index (WCTI), is an air temperature equivalent to the air temperature needed to produce the same temperature (WCT), called the wind-chill temperature index (WCTI), is an air temperature equivalent to the air temperature needed to produce the same cooling effect under calm conditions. A 2003 report on wind-chill temperature by the U.S. National Weather Service gives the WCTI in metric units as
Where T is the air temperature in
Where T is the air temperature in
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Heat And Mass Transfer
- Consider a 120 mm stainless steel plate (K=45w/m.°C, p=7800kg/m2, CP3500J/kg. °C) initially at a uniform temperature of 300° stainless steel plate is immersed in a fluid at temperature Tc0 = 1000 °C and is subjected to convection heat transfer from both sides with a convection coefficient of h=225W/m2.°C. The surface temperature in(°C) after 8 minutes of cooling is O 518.8 O 643.3 O 495 O 600arrow_forwardThe global average sensible heat flux is 17 W/m2. Use the following information to estimate the latent heat flux in units of W/m2. The annual global precipitation amount is about 520×1012 m3/yr. The latent heat of vaporization for water is 2.5×103 kJ/kg and the radius of the Earth is 6400 km. What is the global annual average latent heat flux?arrow_forwardTo ensure that the balls bounce consistently, tennis balls in Wimbledon are stored at exactly 68oF. 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 70oF after one minute, how long will it take for the ball to be within 20oF of the ballboy's body temperature (98.6oF) after he puts it in his pocket? It can be assumed that the temperature in the pocket is also the normal body temperature.arrow_forward
- For a water flow over a steel surface, the temperature of water at a specific location was found to change with the vertical distance from the surface (y) up to a distance of 0.015 m as T(y) = 60 + 20y + tan(y), where temperature is in °C and y is in cm. The surface temperature and ambient temperature was measured as 60°C and 105°C, respectively. The thermal conductivity of steel and water are, respectively, 48 W/m-K and 0.6 W/m-K. What is the local convection coefficient at this location?arrow_forwardCarbon steel balls (p=7833 kg/m³, k=54 W/m.°C, Cp=0.465 kJ/kg.K) 10 mm in diameter are annealed by heating then first 910 °C in a furnace and then allowing them to cool slowly to 120 °C in ambient air at 36 °C. If the average heat transfer coefficient is 80 W/m2.°C.arrow_forwardIn thermodynamics, how do you differentiate a closed system with an adiabatic system? What is the difference in the equation used for calculating heat transfer? (If you know a good book or scientific article that contains info regarding this, please include. Thank you.)arrow_forward
- Heat transfer is of critical importance in various industrial applications, including manufacturing. During machining, both the cutting tool and the workpiece will be significantly heated by friction heating. The heating of the cutting tool will reduce the tool hardness and strength, deteriorate the cutting quality, and shorten the tool life. Therefore, it is essential to prevent the overheating of the cutting tool during machining. Coolants are an instrumental part of machining to help cool the tool and the workpiece, provide lubricant, flush away chips, and prevent corrosion. The task of this project is to design the coolant to maintain the maximum machine tool temperature below 100 °C during the side milling process. As shown in the figure below, the machine tool has a diameter of 10 mm (D) and a length of 5 cm. The tool material is M2 high speed tool steel (T11302) and the workpiece is aluminum 6061. The spindle speed (w) is 2000 RPM and the cutting speed (v) is 50 mm/min. The feed…arrow_forwardIn convection heat transfer, what mechanism heat transfer where the fluid moves due to the decrease in its density caused by increase in temperature? Select the correct response: O Natural convection Forced convection Density convection Radical convectionarrow_forwardA woman informs her engineer husband that “hot water will freeze faster than cold water.” He calls this statement nonsense. She answers by saying that she has actually timed the freezing process for ice trays in the home refrigerator and found that hot water does indeed freeze faster. As a friend, you are asked to settle the argument. Is there any logical explanation for the woman’s observation?arrow_forward
- The specific heat of air under standard atmosphericpressure, in SI units, is 1003 N · m/ kg · K. The specific heatof air under standard atmospheric pressure, in U.S. Customaryunits (ft · lb /slug · 0 R), is?arrow_forwardH.W1 Consider a person standing in a room. Determine the total rate of heat transfer from this person if the exposed surface area and temperature are 1.6m² and 29°C, respectively. Assume that the convection heat transfer coefficient is 6W/m².K and the emissivity of a person is 0.95. The air temperature in the room is maintained at 22°C at all times of the year. In summer, the wall and ceiling temperatures are observed to be 25°C, while in winter, they are 10°C. Ans: Qrotal =104.4 W In Summer Qrotal =231.3 W In Winterarrow_forwardWe have a system made up of a glass container (glass) whose bottom and top have been insulated. A mass of liquid (m) is introduced inside it at a temperature T. As this mass of water transmits heat, its temperature TI decreases, without changing the ambient temperature TA. Measurements of temperature are made with water and with saline water at different times. How would you calculate the convective heat transfer coefficient (h)?arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning