Refrigerater and Ac Repairing

What is Refrigeration cycle and and how work this cycle  "The Mechanical refrigeration is accomplished by continuously circulating, evaporating, and condensing a fixed supply of refrigerant in a closed system. Evaporation occurs at a low temperature and low pressure while condensation occurs at a high temperature and high pressure. Thus, it is possible to transfer heat from an area of low temperature (i.e., refrigerator cabinet) to an area of high temperature.' We know that the Referring to the illustration below, beginning the cycle at the evaporator inlet (1), the low-pressure liquid expands, absorbs heat, and evaporates, changing to a low-pressure gas at the evaporator outlet (2). (The compressor (4) pumps this gas from the evaporator through the accumulator (3), increases its pressure, and discharges the high-pressure gas to the condenser (5). The accumulator is designed to protect the compressor by preventing slugs of liquid refrigerant from passing directly...

AIR TEMPERATURE  Temperature and Temperature Scales  The temperature of a substance is a measure of how hot or cold it is. Two systems are said to have equal temperatures only if there is no change in any of their observable thermal characteristics when they are brought into contact with each other. Various temperature scales commonly used to measure the temperature of various substances are illustrated in Fig. 2.2. In conventional inch-pound (I-P) units, at a standard atmospheric pressure of 14.697 psia (101,325 Pa), the Fahrenheit scale has a freezing point of 32°F (0°C) at the ice point, and a boiling point of 212°F (100°C). For the triple point with a pressure of 0.08864 psia (611.2 Pa), the magnitude on the Fahrenheit scale is 32.018°F (0.01°C). There are 180 divisions, or degrees, between the boiling and freezing points in the Fahrenheit scale. In the International System of Units (SI units), the Celsius or Centigrade scale has a freezing point of 0°C and a boilin...

DALTON’S LAW AND THE GIBBS-DALTON LAW  Dalton’s law shows that for a mixture of gases occupying a given volume at a certain temperature, the total pressure of the mixture is equal to the sum of the partial pressures of the constituents of the mixture, i.e., The partial pressure exerted by each constituent in the mixture is independent of the existence of other gases in the mixture. Figure 2.1 shows the variation of mass and pressure of dry air and water vapor, at an atmospheric pressure of 14.697 psia (101,325 Pa) and a temperature of 75°F (23.9°C). The principle of conservation of mass for nonnuclea r processes gives the following relationship: Applying Dalton’s law for moist air, we have Dalton’s law is based on experimental results. It is more accurate for gases at low pressures. Dalton’s law can be further extended to state the relationship of the internal energy, enthalpy, and entropy of the gases in a mixture as the Gibbs-Dalton law: ...

DESIGN FOR AIR CONDITIONING SYSTEM System design determines the basic characteristics. After an air conditioning system is constructed according to the design, it is difficult and expensive to change the design concept. Engineering Responsibilities The normal procedure in a design-bid project includes the following steps and requirements:  1. Initiation of a construction project by owner or developer  2. Selection of design team  3. Setting of the design criteria and indoor environmental parameters  4. Selection of conceptual alternatives for systems and subsystems; preparation of schematic layouts of HVAC&R  5. Preparation of contract documents, working drawings, specifications, materials and construction methods, commissioning guidelines  6. Competitive bidding by contractors  7. Evaluation of bids; negotiations and modification of contract documents 8. Advice on awarding of contract  9. Review of shop drawings an...

PSYCHROMETRICS Psychrometrics is the study of the thermodynamic properties of moist air. It is used extensively to illustrate and analyze the characteristics of various air conditioning processes and cycles. Moist Air The surface of the earth is surrounded by a layer of air called the atmosphere, or atmospheric air. From the point of view of psychrometrics, the lower atmosphere, or homosphere, is a mixture of dry air (including various contaminants) and water vapor, often known as moist air. The composition of dry air is comparatively stable. It varies slightly according to geographic location and from time to time. The approximate composition of dry air by volume percent is the following: The amount of water vapor present in moist air at a temperature range of 0 to 100°F (17.8 to 37.8°C) varies from 0.05 to 3 percent by mass. It has a significant influence on the characteristics of moist air. Water vapor is lighter than air. A cloud in the sky is composed of microscopic ...

AIR CONDITIONING PROJECT DEVELOPMENT Basic Steps in Development The basic steps in the development and use of a large air conditioning system are the design, construction, commissioning, operation, energy efficiency upgrading, and maintenance. Figure 1.4 is a diagram which outlines the relationship between these steps and the parties involved. The owner sets the criteria and the requirements. Design professionals in mechanical engineering consulting firms design the air conditioning system and prepare the design documents. Manufacturers supply the equipment, instruments, and materials. Contractors install and construct the air conditioning system. After construction, the air conditioning system is commissioned by a team, and then it is handed over to the operation and maintenance group of the property management for daily operation. Following a certain period of operation, an energy service company (ESCO) may often be required to upgrade the energy efficiency of the HVAC&...