Newton’s Law of Cooling states that the rate of temperature change of an object is directly proportional to the difference between its internal body temperature and ambient temperature. Newton’s Law of Cooling assumes that the ambient temperature and heat transfer coefficient of a substance remain constant during the cooling process (DESAI, 2008).
Temperature change is driven by the temperature difference between the object and the surrounding. Many factors would affect the rate of temperature change, such as the temperature gradient between the object and the surroundings, velocity of object’s movement and the presence of driving forces (The Concord Consortium, 2013). Usually, when heat transfers from a hotter object to the surrounding, a thin warm vapor layer is created on the surface (Giordano, 2009) (5.årsoppgave–Med 3590, Brage Håheim, 2014). In this experiment, the effect of this warm vapor layer on the rate of temperature of an object was investigated. It was assumed that in a closed laboratory, a breeze was absent. This warm vapor layer will remain without the presence of a breeze whereas it will be turned over with the presence of a breeze.
In the situation of a beaker of hotter water in a cooler environment, when a breeze is present and a change in strength of the breeze is present respectively, how will the rate of change of water temperature relate to the difference between water temperature and ambient temperature?
To determine the relationship between the rate of change of temperature of a substance and the difference between its own temperature and ambient temperature under three conditions: Presence of a breeze, absence of a breeze and presence of a change in strength of the breeze within a given time period, where the volume of water, room temperature and distance from the breeze are kept constant.
When we walked outside in a hot humid day, at about 35oC, we would feel very hot and sweat. However, if we walked in a hot windy day, at the same atmospheric temperature, we would not perceive that the temperature was as high as 35oC. Many people might consider that wind could lower the atmospheric temperature. However, that is not the case. It is all about the removal of the warm layer of air.
In the experiment, heat transfers from the water to the glass via conduction and then transfer to the surrounding via convection. Conduction is the heat flow of the internal energy from a hotter region to a cooler region via physical contact (Boundless Learning Incorporatino, 2012). According to the kinetic theory, increase in temperature will increase the kinetic energy of particles. Greater kinetic energy results in greater frequency and strength of collision. Particles vibrate with the neighboring particles and the kinetic and potential energies of particles are transferred (Department of Physics and Astronomy, Georgia State University, 2008). In the experiment, water temperature was higher than the beaker’s. Therefore heat energy would transfer from the internal body of water to the glass through vibration of particles. Convection is the heat transfer via the movement of fluid (Boundless Learning Incorporatino, 2012). There are mainly two types of convection, natural convection and forced convection (Boundless Learning Incorporatino, 2012).
Natural convection is where hot air rises and cool air drops (Boundless Learning Incorporatino, 2012). As with reference to Charles’ Law, hot air is less dense than cool air, hot air tends to rise whereas cool air tends to sink (Department of Physics and Astronomy, Georgia State University, 2008). Convection current is resulted to transfer heat energy and this heat transfer is relatively slow. As the temperature of the beaker with hot water was higher than the ambient temperature, the hot air from the beaker would rise while the cool air in the atmosphere would drop to cool down the beaker.
In contrast, forced convection