2. Introduction:
2.1.
Heat transfer:
Heat transfer is the science that pursues to foresee the energy transfer that may take place among material bodies as an outcome of a temperature difference.
Thermodynamics explains that this energy transfer is described as heat.
The science of heat transfer pursues not only to explain how heat energy may be transfer, but also to foresee the rate at which the exchange will take place under certain quantified conditions.
The fact that a heat-transfer rate is the desired objective of a study points out the difference among heat transfer and thermodynamics.
Thermodynamics deals with systems in equilibrium; it may be used to foresee the amount of energy required to change a system from one equilibrium state
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Heat is transferred by conduction due to motion of free electrons in metals or atoms in
Non-metals.
Conduction is quantified by Fourier’s law: the heat lux, q, is proportional to the temperature
Gradient in the direction of the outward normal. e.g. in the x-direction:
qx ≈ dT/dx qx = -K dT/dx
The constant of proportionality, k is the thermal conductivity and over an area A, the rate of heat flow in the x-direction, Qx is
Qx = -K A dT/dx
Conduction may be treated as either steady state, where the temperature at a point is constant with time, or as time dependent (or transient) where temperature varies with time.
The general, time dependent and multi-dimensional, governing equation for conduction can be derived from an energy balance on an element of dimensions δx, δy, δz.
Consider the element shown in Figure 2.1.
The statement of energy conservation applied to this element in a time period δt is that:
Heat low in + internal heat generation = heat low out + rate of increase in internal energy
Qx + Qy + Qz + Qg = Qx +ϐx + Qy +ϐy + Qz +ϐz + mC
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(1a) shows a classic example of STHE; information shown below).
Plate heat exchanger (PHE), where corrugated plates are maintained in contact and the two fluids flow separately alongside adjacent channels in the corrugation (Fig. 1b shows details of the inside of a PHE; more details are shown below).
Open-flow heat exchanger, where one of the flows is not restricted inside the equipment (or at least, like in Fig. 1c, not exclusively piped).
They created from air-cooled tube-banks, and are mostly used for final heat discharge from a liquid to ambient air, as in the car radiator, but similarly used in vaporisers and condensers in air-conditioning and refrigeration appliances, and in directly-fired home water heaters.
When gases flow alongside both sides, the total heat-transfer coefficient is very deficient, and the finest solution is to make use of heat-pipes as intermediate heat-transfer devices among the gas streams; or else, finned split up surfaces, or, better, direct contact through a solid regain, are used.
Contact heat exchanger, where the two fluids flow into direct contact (simultaneous heat and mass transfer
Thermodynamics is essentially how heat energy transfers from one substance to another. In “Joe Science vs. the Water Heater,” the temperature of water in a water heater must be found without measuring the water directly from the water heater. This problem was translated to the lab by providing heated water, fish bowl thermometers, styrofoam cups, and all other instruments found in the lab. The thermometer only reaches 45 degrees celsius; therefore, thermodynamic equations need to be applied in order to find the original temperature of the hot water. We also had access to deionized water that was approximately room temperature.
Hess’s Law is also an important concept in this lab. It states that the enthalpy of a reaction is independent of the steps it takes to go from reactant to a product. It happens because enthalpy is a state function. A state function depends on the initial and final state but not the actual process. The Hess’s Law is used to calculate the heat formation of Magnesium Oxide. The amount of heat necessary to create one more mole of a substance is called the Enthalpy of Formation.
When there is a heat exchange between two objects, the object’s temperature will change. The rate at which this change will occur happens according to Newton’s Law of heating and cooling. This law states the rate of temperature change is directly proportional between the two objects. The data in this lab will exhibit that an object will stay in a state of temperature equilibrium, unless the object comes in contact with another object of a different temperature. Newton’s Law of Heat and Cooling can be understood by using this formula:
on how long it takes to heat up. If we heat a large volume of water it
Two pistons, called the hot and cold pistons are used on the side of the cooler, regenerator and heater. These pistons move uniformly in the similar direction to provide constant-volume heating or cooling processes of the working fluid. When the entire working fluid has been transferred into one cylinder, one piston is fixed and the other piston moves to expand or compress the working fluid. The compression work is done by the cold piston and the expansion work is done by the hot piston. In the beta-configuration, a displacer and a power piston contained within the same cylinder. The cylinder moves working fluid between the cold space and the hot space of the displacer through the heater, regenerator, and cooler. The power piston placed at the cold space of the cylinder, expands the working fluid when the working fluid is in the hot space and compresses the working fluid when the working fluid is moved into the cold
good emitter of heat radiation so a lot of heat will be lost to the
The porpoise of these is to determine the Specific Heat. Also known as Heat Capacity, the specific heat is the amount of the Heat Per Unit mass required to raise the temperature by one degree Celsius. The relationship between heat and temperature changed is usually expected in the form shown. The relationship does not apply if a phase change is encountered because the heat added or removed during a phase change does not change the temperature.
Conduction, convection and radiation are the three methods through which heat can be transferred from one place to another. The (www.hyperphysics.com) first method is the conduction through which heat can be transferred from one object to another object. This process is defined as the heat is transmitted from one to another by the interaction of the atoms and the molecules. The atoms and the molecules of the body are physically attached to each other and one part of the body is at higher temperature to the other part or the body, the heat begins to transfer. A simple experiment through which conduction can be understood easily is as follows. First of all, take a metallic rod of any length. Hold the rod in the hand or at any stand made up of the insulator so that the heat does not transfer to the stand. Heat up the one end of the rod with the help of the spirit lamp. After sometime, touch the other end of the end, the other end of the becomes heated too and the temperature of the other end of the rod has also increased. Although only one end of the rod is heated with the spirit lamp, but the other end of the rod has also been heated. This is represents that the heat has been transferred from one end of the rod to the other end of the rod without heating it from the other end. So, the transformation of the heat is taking place. This process is called the conduction. Conduction is a process which is lead by the free electrons. As the conduction happens occurs only in the metallic materials, the reason for it is that the metals has the free electrons and they can move freely from one part of the body to another part of the body. These electrons are not bounded by the nucleus so, they can move easily. And when the temperature of the ...
The next type of heat transfer is convection. Convection is heat transferred by a gas or liquid. Such as dumping hot water into a cold glass of water, making the water overall warmer. The last type of heat transfer is radiation.
Thermodynamics is the branch of science concerned with the nature of heat and its conversion to any form of energy. In thermodynamics, both the thermodynamic system and its environment are considered. A thermodynamic system, in general, is defined by its volume, pressure, temperature, and chemical make-up. In general, the environment will contain heat sources with unlimited heat capacity allowing it to give and receive heat without changing its temperature. Whenever the conditions change, the thermodynamic system will respond by changing its state; the temperature, volume, pressure, or chemical make-up will adjust accordingly in order to reach its original state of equilibrium. There are three laws of thermodynamics in which the changing system can follow in order to return to equilibrium.
Have you ever taken a minute to wonder how heat in your everyday life is transferred from one object to another? Well, typically any heat that one feels throughout their day is most commonly transferred in one of three ways. Those three ways include conduction, convection, and radiation. The definitions of these three heat transfers are as follows. Conduction is specifically defined as, “the heat transfer through direct contact of molecules without any of the material as a whole” (Merriam-Webster's, 1999). A heat transfer via convection is also defined as, “the transfer of heat from one place to another by the movement of mass in liquid or gas form” (Merriam-Webster's, 1999). And finally heat radiation, is defined as, “the transfer of heat,
A Heat Exchanger is a device use for the heat transfer from one fluid to another, whether the fluids are separated by a solid wall so that they never mix or the fluids are directly in contact. The heat exchanger is widely used in different industries such as process, petroleum refining, chemicals and paper, power generation, chemical processing, A.C, refrigeration, and a food processing applications. Etc. Various Enhancement methods are used to increase performance of heat exchanger such as treated surfaces, rough surfaces etc.
Again, it is the most common means of energy transfer and by understanding exactly what conduction means, we can identify it in some of the simple things we do. For instance, think of a pot placed on the stove, on a hot burner. The burner and the bottom of the pot are obviously touching, therefore the pot begins to heat up and get hot as well. As physical contact is the key element in heat transfer through conduction, we can see how important a role it plays in this situation. Now, say that your food is done, you turn the burner off and grab the handle of the pot, only to find that it is extremely hot as well. Again, we can thank conduction for this- as the heat was transferred through the bottom of the pot to the handle. Another example of conduction can be seen through ironing. We plug in and heat up the iron prior to placing it on the clothing in which we wish to smooth out. Once the iron has heated up, we place it on top of the article of clothing and it then heats up the clothing as well. Again, physical contact between the iron and the shirt show us that conduction plays the role of heat transfer in this scenario too. For a final example of heat transfer through conduction, let’s imagine a child, playing outside in the snow on a rather cold day. Once outside for a bit, he is freezing and decides to come inside. He takes off his snow gear, cuddles up to his father and begins to warm up
The boiling phenomena is modulated in these applications by leveraging different operational and systemic parameters. In addition to temperatures of the heater and the working fluid - the transport processes in boiling can be modulated by several parameters such as geometry (shape and size), morphology and orientation of the heater; orientation and magnitude of gravitational acceleration; material properties of the heater surface as well as the fluid; system pressure; exposure to electro-magnetic field; flow velocities and inter-molecular interactions at the solid-liquid interface. When external actuators are not employed to induce the flow of the working fluid during liquid-to-vapor phase change phenomena for heater temperatures exceeding the saturation temperature it is termed as pool boiling. In contrast, when external actuators are employed for inducing bulk fluid motion on a heater exposed to the working fluid it is termed as flow
turbine via interceptor valves and control valves and after expanding enters the L.P. turbine stage via 2 numbers of cross over pipes. In the L.P. stage the steam expands in axially opposite direction to counteract the trust and enters the condenser placed directly below the L.P. turbine. The cooling water flowing throughout the condenser tubes condenses the steam and the condensate collected in the hot well of the condenser. The condensate collected is pumped by means of 3*50% duty condensate pumps through L.P. heaters to deaerator from where the boiler feed pump delivers the water to boiler through H.P. heaters thus forming a closed