On the other hand, air conditioning systems used chemicals that are integral to the system and air from the surroundings. These two also differ in the circulation in their system. Refrigeration systems keep the low temperature of atmosphere in a unit. This is attained with the help of the compressors where the cool air is drawn to reuse the gas. While air conditioning systems release the air to cool a space or room with the fan in the unit.
Now a day’s large numbers of industries are using cooling towers to remove heat and extract cold water for condensation purposes. Hot water coming from the processes gets cool in Cooling Tower by Evaporative Cooling principle . A cooling tower is heat rejection equipment, which extracts waste heat from the water droplets to the atmosphere by cooling it to a lower temperature. This type of heat transfer or rejection in a cooling tower is termed "evaporative" in that it allows a portion of the water being cooled to provide a significantly higher quantum of cooling to the remaining stream of water. The heat from the water stream transferred to the air stream raises the air's temperature and its moisture content to 100%, and this air is discharged to the atmosphere.
In some cases, a solid wall may separate the fluids and prevent them from mixing. In other designs, the fluids may be in direct contact with each other. In the most efficient heat exchangers the surface area and to induce turbulence. There are 3 primary flow arrangements with heat exchangers: counter – flow, parallel flow and cross flow. The most common type of heat exchangers used in the process, the shell on the other hand holds the tube bundle and acts as the conduit for the fluid.
3.1 Heat Pump A heat pump as shown in Figure 3.1 is a device that provides heat energy from a source of heat to a destination called a "heat sink". Heat pumps are designed to move thermal energy opposite to the direction of spontaneous heat flow by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses some amount of external power to accomplish the work of transferring energy from the heat source to the heat sink. While air conditioners and freezers are familiar examples of heat pumps, the term "heat pump" is more general and applies to many HVAC (heating, ventilating, and air conditioning) devices used for space heating or space cooling. When a heat pump is used for heating, it employs the same basic refrigeration-type cycle used by an air conditioner or a refrigerator, but in the opposite direction - releasing heat into the conditioned space rather than the surrounding environment.
However the metallurgical consequences that are associated with the change in thermal gradient and cooling rate must be accounted for in practical situation. But we are making use of the compressed air instead of water for heat sinking process to account for the changes in metallurgical properties. III) SELECTION OF PROCESS PARAMETER:- 1. Transverse distance between welding torch & nozzle (a) 2. Longitudinal distance between arc & nozzle (b) 3.
Since heat is not conducted through the walls of the heat pipe, there are reduced chances of blockage in the arteries of the heat pipe due to vapour bubbles. Wick is placed along the interior walls so that the condensate travels along the arteries towards the evaporator. 13. INVERTED MINISCUS HEAT PIPE As shown in Figure 14, evaporation takes place in the dry region of the porous structure at the liquid-vapour interface. The heat is conducted to this interface from the heated surface through the dry region of the porous element, and the vapour flows mainly along the solid surface through this porous region towards the triangular vapour channel.
It is designed with the principle to move thermal energy opposite to the direction of spontaneous heat flow by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses some amount of external power to accomplish the work of transferring energy from the heat source to the heat sink. A diagram of the device is presented on Fig.8 Figure 8: Diagram of a water heating heat pump (stiebelelctron) Some reversible heat pumps can work in either thermal direction to provide heating or cooling. They have a reversing valve to reverse the flow of refrigerant from the compressor through the condenser and evaporation coils. • In heating mode, the outdoor coil is an evaporator, while the indoor is a condenser.
Heat exchangers are devices that provide the flow of thermal energy between two fluids at the different temperatures.  Transfer of thermal energy between two fluids at difference temperature that devices is known as heat exchanger. One can realize their usage that any process which involves cooling, heating, condensation, boiling or evaporation will require a heat exchanger for these purposes .Heat energy is transferred from one body or fluid stream to another. Different heat exchangers are named according to their applications. For example heat exchanger being used to condense are known as condensers, similarly heat exchanger for boiling purposes are called boilers.
For example, comfort conditions for human are 22 to 25°C and 40 to 60% of relative humidity (ASHRAE, 1989) . One of the most interesting functions of HPHEs is to increase the dehumidification capacity of the conventional air conditioning systems. In a conventional air conditioning system, the humidity is controlled by cooling the supply air stream below its dew point temperature. The cold air is then reheated to a temperature that is suitable for the conditioned space. Heat Pipe Heat Exchangers (HPHEs) in HVAC systems are usually used to