40 Lessons On Refrigeration And Air Conditioning From Iit Kharagpur PdfBy Holly J. In and pdf 29.03.2021 at 03:54 5 min read
File Name: 40 lessons on refrigeration and air conditioning from iit kharagpur .zip
Refrigeration and Air Conditioning. Instructor: Prof. This course introduces the fundamentals of refrigeration and air conditioning.
- REFRIGERATION & AIR-CONDITIONING UNIT IIT KHARAGPUR
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Objectives of the lesson:The objectives of this lesson are to introduce the student to: i. Applications of refrigeration in: a Food processing, preservation and distribution Section 3. Section 3. Applications of air conditioning, namely: a Industrial, such as in textiles, printing, manufacturing, photographic, computer rooms, power plants, vehicular etc. IntroductionAs mentioned in Lesson 1, refrigeration deals with cooling of bodies or fluids to temperatures lower than those of surroundings.
REFRIGERATION & AIR-CONDITIONING UNIT IIT KHARAGPUR
Introduction to psychrometric processes and their representation Section Figure The heat. By separating the total heat transfer transfer rate from the cooling coil into sensible and. From Fig. Hence, we can draw the cooling and dehumidification. In Fig. This process is shown in Fig. As shown in the figure, this can.
If the temperature of the water sprayed is equal to the wetbulb. This hygroscopic material can be a. Hence, the ratio of distances on the line, i. As shown in Fig. Due to this, the humidity ratio of the resulting mixture point. An air washer is a device for conditioning air. This the process that takes place in a perfectly. This is the process that takes place in a cooling tower. The air stream. The relative humidity at the exit of heater is obtained from the values of DBT 40 o C and.
Lesson 28 - nptel. Lesson 28 - nptel READ. Important psychrometric processes namely, sensible cooling and heating, cooling and dehumidification, cooling and humidification, heating and humidification, chemical dehumidification and mixing of air streams Section Representation of the above processes on psychrometric chart and equations for heat and mass transfer rates Section Principle of air washers and various psychrometric processes that can be performed using air washers Section Concept of enthalpy potential and its use Section Represent various psychrometric processes on psychrometric chart 2.
Perform calculations for various psychrometric processes using the psychrometric charts and equations 3. Define sensible heat factor, by-pass factor, contact factor and apparatus dew point temperature 4. Describe the principle of an air washer and its practical use 5. Derive equation for total heat transfer rate in terms of enthalpy potential and explain the use of enthalpy potential Introduction: In the design and analysis of air conditioning plants, the fundamental requirement is to identify the various processes being performed on air.
Once identified, the processes can be analyzed by applying the laws of conservation of mass and energy. All these processes can be plotted easily on a psychrometric chart. This is very useful for quick visualization and also for identifying the changes taking place in important properties such as temperature, humidity ratio, enthalpy etc.
The important processes that air undergoes in a typical air conditioning plant are discussed below. Important psychrometric processes: a Sensible cooling: During this process, the moisture content of air remains constant but its temperature decreases as it flows over a cooling coil. For moisture content to remain 2 Version 1 ME, IIT Kharagpur 2 constant, the surface of the cooling coil should be dry and its surface temperature should be greater than the dew point temperature of air.
However, in practice, the exit air temperature will be higher than the cooling coil temperature. DBT c Cooling and dehumidification Process O-C : When moist air is cooled below its dew-point by bringing it in contact with a cold surface as shown in Fig. This is the process air undergoes in a typical air conditioning system. Although the actual process path will vary depending upon the type of cold surface, the surface temperature, and flow conditions, for simplicity the process line is assumed to be a straight line.
The heat and mass transfer rates can be expressed in terms of the initial and final conditions by applying the conservation of mass and conservation of energy equations as given below: By applying mass balance for the water: m. A SHF of 0. Hence, we can draw the cooling and dehumidification line on psychrometric chart if the initial state and the SHF are known. In some standard psychrometric charts, a protractor with different values of SHF is provided.
The process line is drawn through the initial state point and in parallel to the given SHF line from the protractor as shown in Fig. SHF ho-hc hw-hc Fig. In an ideal situation, when all the air comes in perfect contact with the cooling coil surface, then the exit temperature of air will be same as ADP of the coil. However, in actual case the exit temperature of air will always be greater than the apparatus dew-point temperature due to boundary layer development as air flows over the cooling coil surface and also due to c Wo-Wc 6 Version 1 ME, IIT Kharagpur 6 temperature variation along the fins etc.
When BPF is 1. In practice, the by-pass factor can be increased by increasing the number of rows in a cooling coil or by decreasing the air velocity or by reducing the fin pitch. Heating coil Steam nozzles ma TO wO hO Q h mw Mass balance of water vapor for the control volume yields the rate at which steam has to be added, i. Since this process also involves simultaneous heat and mass transfer, we can define a sensible heat factor for the process in a way similar to that of a coolind and dehumidification process.
As shown in the figure, this can be achieved by spraying cool water in the air stream. Hence, the total heat transfer depends upon the water temperature. If the temperature of the water sprayed is equal to the wetbulb temperature of air, then the net transfer rate will be zero as the sensible heat transfer from air to water will be equal to latent heat transfer from water to air.
If the water temperature is greater than WBT, then there will be a net heat transfer from water to air. If the water temperature is less than WBT, then the net heat transfer will be from air to water. Under a special case when the spray water is entirely recirculated and is neither heated nor cooled, the system is perfectly insulated and the make-up water is supplied at WBT, then at steady-state, the air undergoes an adiabatic saturation process, during which its WBT remains constant.
This is the process of adiabatic saturation discussed in Chapter The process of cooling and humidification is encountered in a wide variety of devices such as evaporative coolers, cooling towers etc. If this process is thermally isolated, then the enthalpy of air remains constant, as a result the temperature of air increases as its moisture content decreases as shown in Fig.
This hygroscopic material can be a solid or a liquid. In general, the absorption of water by the hygroscopic material is an exothermic reaction, as a result heat is released during this process, which is transferred to air and the enthalpy of air increases.
Hygroscopic material O F g Mixing of air streams: Fig. Chemical de-humidification process O F TO TF Mixing of air streams at different states is commonly encountered in many processes, including in air conditioning. Depending upon the state of the individual streams, the mixing process can take place with or without condensation of moisture.
As shown in the figure, when two air streams at state points 1 and 2 mix, the resulting mixture condition 3 can be obtained from mass and energy balance.
With this approximation, the point on the psychrometric chart representing the mixture lies on a straight line connecting the two inlet states. The resulting error due to the assumption that the humid specific heats being constant is usually less than 1 percent. Mixing of two air streams without condensation As shown in Fig. Due to this, the humidity ratio of the resulting mixture point 3 will be less than that at point 4.
Corresponding to this will be an increase in temperature of air due to the release of latent heat of condensation. This process rarely occurs in an air conditioning system, but this is the phenomenon which results in the formation of fog or frost if the mixture temperature is below 0 o C. This happens in winter when the cold air near the earth mixes with the humid and warm air, which develops towards the evening or after rains.
Air Washers: An air washer is a device for conditioning air. The outlet condition of air depends upon the temperature of water sprayed in the air washer. Hence, by controlling the water temperature externally, it is possible to control the outlet conditions of air, which then can be used for air conditioning purposes. As a consequence of the 2 nd law, the heat transfer between air and water droplets will be in the direction of decreasing temperature gradient.
Similarly, the mass transfer will be in the direction of decreasing vapor pressure gradient. For example, a Cooling and dehumidification: tw inlet value, from energy balance it can be shown that there is a transfer of total energy from air to water. Hence to continue the process, water has to be externally cooled.
Here both latent and sensible heat transfers are from air to water. This is shown by Process O-A in Fig. Here the sensible heat transfer from air to water is exactly equal to latent heat transfer from water to air. Hence, no external cooling or heating of water is required.
That is this is a case of pure water recirculation. This the process that takes place in a perfectly insulated evaporative cooler. This is shown by Process O-C in Fig. This is shown by Process O-D in Fig. The air stream extracts heat from the hot water coming from the condenser, and the cooled water is sent back to the condenser.
Here both sensible and latent heat transfers are from water to air, hence, water has to be heated externally. This is shown by Process O-E in Fig. Thus, it can be seen that an air washer works as a year-round air conditioning system. Though air washer is a and extremely useful simple device, it is not commonly used for comfort air conditioning applications due to concerns about health resulting from bacterial or fungal growth on the wetted surfaces.
However, it can be used in industrial applications. Enthalpy potential: As shown in case of an air washer, whenever water or a wetted surface and air contact each other, there is possibility of heat and moisture transfer between them. The directions of heat and moisture transfer depend upon the temperature and vapor pressure differences between air and water.
As a result, the direction of the total heat transfer rate, which is a sum of sensible heat transfer and latent heat transfers also depends upon water and air conditions.
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Explain the working principle of a centrifugal compressor Section Present the analysis of centrifugal compressors Section Discuss the selection of impeller diameter and speed of a centrifugal. Discuss the effect of blade width on the capacity of centrifugal compressor. Compare the performance of a centrifugal compressor with a reciprocating. Analyse the performance of a centrifugal compressor using steady flow energy equation and velocity diagrams.
The time and venue for opening the bids will be notified separately to the bidders. As the commercial bids of only the technically qualified bidders shall be opened, the bidders must clearly indicate technical and commercial on the envelops. The Institute reserves the right to accept or reject any bid, postpone or cancel the bidding process without assigning any reason whatsoever. Air handling units are installed on the roof tops 2 nos. Starter panels are located near the AHU s. The following supporting documents must be supplied along with the bid: a.
EE IIT, Kharagpur, India 4O LESSONS ON REFRIGERATION AND AIR The subject of refrigeration and air conditioning has evolved out of human need for In steady state, pump temperature is T M = 40 o C and the surroundings is at.
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Introduction to psychrometric processes and their representation Section Figure The heat. By separating the total heat transfer transfer rate from the cooling coil into sensible and. From Fig. Hence, we can draw the cooling and dehumidification.
40 Lessons On Air Conditioning And Refrigeration From IIT Kharagpur. Lesson Page. Lesson 1 History Of Refrigeration [Natural Refrigeration.
Лейтенант следил за его взглядом. - Ужасное уродство, правда. Но не искалеченная рука привлекла внимание Беккера. Он увидел кое-что другое.
Как они этого сразу не заметили. Северная Дакота - вовсе не отсылка к названию американского штата, это соль, которой он посыпал их раны. Он даже предупредил АНБ, подбросив ключ, что NDAKOTA - он. Это имя так просто превращается в Танкадо. И лучшие в мире специалисты-криптографы этого не поняли, прошли мимо, на что он и рассчитывал.