1.What is the necessity and application of refrigeration system?

Now-a-days refrigeration has become an essential part of food chain- from post harvest heat
removal to processing, distribution and storage. Refrigeration has become essential for
many chemical and processing industries to improve the standard, quality, precision and
efficiency of many manufacturing processes.

Refrigerator Heat Pump Heat Engine

A refrigerator is a reversed heat engine, where Any refrigerating system is a heat pump, A heat engine is a system
heat is pumped from a body at low temperature which extracts heat from a cold body and converts Thermal energy
to a body at high temperature. delivers it to a hot body. Mechanical Energy.
The network done by the refrigerator is given The network done by the heat pump is The network done by th
by WR= Q2-Q1 given by Wp= Q2-Q1 is given by We= Q2-Q1
The C.O.P. of Refrigerator is The C.O.P. of heat pump is The C.O.P. of heat engin
(C.O.P)R = Q1/ WR = Q1 / (Q2-Q1) (C.O.P)hp = Q2/ WR = Q2 / (Q2-Q1) (C.O.P)e= (Q2-Q1)/Q2

Principle of Refrigeration:
In the process of refrigeration, the available heat, with the system to
be maintained at low temperature, is continuously removed and
transferred to the surrounding which is at high temperature.

According to the second law of thermodynamics (Clausius theorem),

the removal of heat from low temperature in order to supply heat at
high temperature is only possible by supplying external work to the
system under operation. Hence, a refrigerator needs external power for
removing heat continuously from the cabinet to maintain temperature
lower than the surrounding.

What are the Different Types of Refrigerators?

 Top Freezer Refrigerator.
 Side-by-Side Refrigerator.
 Bottom Freezer Refrigerator.
 French Door Refrigerator.
 Counter-Depth Refrigerator.
 Mini Fridge

1TR was defined as the rate of heat transfer required to make 1 short ton (2000 lbs) of ice
per day from water at 0oC.
In an open refrigeration system, the air is directly passed over the space is to be cooled,
and allowed to circulate through the cooler. The pressure of open refrigeration cycle is
limited to the atmospheric pressure.
 Closed refrigeration system / Dense air refrigeration
cycle
In closed or dense air refrigeration cycle, air refrigerant is contained within pipes and
component part of the system at all time. The circulated air does not have to direct contact
with the space to be cooled. The air is used to cool another fluid (brine), and this fluid is
circulated into the space to be cooled. So the disadvantages listed in open air refrigeration
can be eliminated. The advantages of closed air refrigeration system are

Advantages
 The suction to the compressor may be at high pressure, therefore the volume of air
handled by the compressor and expander is low when compared to an open system.
Hence the size of compressor and expander is small compared to the open air system.

Merits and Demerits of Air Cycle Refrigeration:

merits

(a) Air is non-flammable, so there is no chance of fire hazards.

(b) Air is cheaply and easily available as compared to other

refrigerants.

(c) The weight of air refrigeration system per ton of refrigeration is

much less as compared to other systems. Because of this reason, this
system is employed in aircraft applications. Weight is an important
consideration in aircrafts.

Demerits:
(a) The COP of the system is very low as compared to other systems.

(b) The amount of air required to be circulated for producing cold effect
is more as compared to other refrigerants used in other systems. In
this system, heat is carried by air in the form of sensible heats.

Explain the working principle of Bell-Coleman cycle

Working principle of the Bell Coleman air refrigeration system :

The Bell Coleman air refrigeration system is based on a reverse Joule cycle.
  The components of the Bell Coleman air refrigeration system are shown in figure (a).
In this system, the air is taken into the compressor from the atmosphere and
compressed.
 The hot compressed air is cooled in a heat exchanger up to the atmospheric
temperature (in ideal conditions). The cooled air is then expanded in an expander.
 The temperature of the air coming out from the expander is below the atmospheric
temperature due to isentropic expansion.
 The low-temperature air coming out from the expander enters into the evaporator and
absorbs the heat. The cycle is repeated again.

 What is the principle of Vapour compression refrigeration system?




 Vapor-compression uses a circulating liquid refrigerant as the medium
which absorbs and removes heat from the space to be cooled and
subsequently rejects that heat elsewhere

the main components of a refrigeration system are the condenser, the compressor, the
evaporator and the expansion valve.

Advantages
1. Size is small when compared to an air refrigeration system for a given capacity of
refrigeration.
2. Volume of refrigerant circulated is low. Hence the running cost is low.
3. High coefficient of performance.
4. The operating temperature range is huge.
5. The temperature at the evaporator can be easily controlled by regulating expansion
valve.
6. Latent heat involved in Phase change ensures high value of heat removal, while air
refrigeration system has sensible heat only.
7. It requires smaller evaporator

Disadvantages
1. High initial cost, costly refrigerant.
2. Environmental hazardous refrigerant involved.
3. Must ensure the prevention of leakage of refrigerant..
 The function of the condenser in a refrigeration system is to transfer heat from the
refrigerant to another medium, such as air and/or water. By rejecting heat, the
gaseous refrigerant condenses to liquid inside the condenser.
List out the components of vapour compression refrigeration system and which component of the
vapour compression refrigeration system produces the refrigeration effect.
The Vapor Compression Refrigeration Cycle involves four components: compressor,
condenser, expansion valve/throttle valve and evaporator. It is a compression process, whose
aim is to raise the refrigerant pressure, as it flows from an evaporator.

What is the effect of suction pressure?

Therefore with decrease in suction pressure the net effect decreases the COP of
the system for the same amount of refrigerant flow. The refrigerating capacity of
system decreases and refrigeration cost increases.

Write the effect of discharge (condenser) pressure?

decreases the refrigerating effect from (h1 - h4) to (h1 - h4') increases the work required
for compression from (h2-h1) to (h2' - h1)

Examples of secondary refrigerants include water, air, hydrocarbons, ammonia and

carbon dioxide

A hydrocarbon is any of a class of organic chemicals made up of only the elements

carbon (C) and hydrogen (H). The carbon atoms join together to form the framework of the
compound, and the hydrogen atoms attach to them in many different configurations.

desirable Properties of an ideal Refrigerant

 Thermodynamic Properties: (i) Low boiling point. (ii) Low freezing point. ...
 Chemical Properties: (i) Non-toxicity. (ii) Non-flammable and non-explosive. ...
 Physical Properties: (i) Low specific volume of vapour. (ii) Low specific heat. ...
 Others Properties: (i) Ease of leakage location.

The greenhouse effect is the way in which heat is trapped close to Earth's surface by
“greenhouse gases.” These heat-trapping gases can be thought of as a blanket wrapped
around Earth, keeping the planet toastier than it would be without them.

Global warming is the long-term heating of Earth's climate system observed since the
pre-industrial period (between 1850 and 1900) due to human activities, primarily fossil fuel
burning, which increases heat-trapping greenhouse gas levels in Earth's atmosphere.

According to an international agreement, refrigerants are represented by

the letter R (as in Refrigerants) followed by a two- or three-digit number
and, in some cases, one or two letters. The designation Rxyz is
determined by the chemical composition of the molecule,

An isothermal process is a thermodynamic process in which the temperature of a system

remains constant. The transfer of heat into or out of the system happens so slowly that thermal
equilibrium is maintained.

What is process refrigeration?

By its basic definition, refrigeration is the process of removing heat from a material,
substance or space. With industrial processes, process chillers are used to remove heat
from a specific process or material

REFRIGERATED SPACE is a space constructed for storage or handling of products,

where mechanical refrigeration is used to maintain the space temperature at 55° F or less.

Steam jet or Ejector refrigeration system uses water as refrigerant. It uses the basic principle
of boiling of liquid at lower temperature by reducing pressure on its surface. This
system employs a steam ejector or booster instead of mechanical compressor

What is important of psychrometry

Psychrometry is the study of the thermodynamics of gas-vapor mixtures. Psychrometry

is the study of the properties of moist air and is useful to engineers concerned with heating,
cooling, and ventilating buildings. Psychrometry is the subject which deals with the
properties of gas-vapor mixtures.
 Seven properties of atmospheric air are shown on the psychrometric chart. These properties
are: dry bulb temperature, wet bulb temperature, dew point, humidity ratio, relative
humidity, specific volume, and specific enthalpy.

Define moist air.

When there is water vapour present in the atmosphere, it is called moist air.

Saturated air is the moist air where the partial pressure of water-vapour equals the saturation
pressure of steam corresponding to the temperature of air.

specific humidity, mass of water vapour in a unit mass of moist air,

usually expressed as grams of vapour per kilogram of air, or, in air
conditioning, as grains per pound. The specific humidity is an extremely
useful quantity in meteorology.

Latent and sensible heat are types of energy released or absorbed in the atmosphere. Latent heat is
related to changes in phase between liquids, gases, and solids. Sensible heat is related to changes in
temperature of a gas or object with no change in phase.

PSYCHROMETRIC PROCESSES: –
 Sensible heating,
 Sensible cooling,
 Humidification and dehumidification,
 Cooling and adiabatic humidification,
 Cooling and humidification by water injection,
 Heating and humidification,

In heating and humidification psychrometric process of

the air, the dry bulb temperature as well as the humidity
of the air increases. The heating and humidification
process is carried out by passing the air over spray of
water, which is maintained at temperature higher than
 the dry bulb temperature of air or by mixing air and the
steam.

Dehumidification is a highly energy intensive process, especially in humid climates and for
building typologies that require strict space humidity setpoints. Sub-cooling of air to
condense out moisture using chilled water or refrigerant is the most common method
for dehumidifying.
Sensible heat factor is the ratio of sensible heat and Total heat. Sensible heat is the heat
which increases or decreases the temperature of the body.

Bypass factor (BPF):

It is defined as the ratio of loss in cooling or heating to the ideal cooling or
heating.

This is termed as dynamic loss.

 3)Pressure loss due to Enlargement in area. ...
 4)Pressure loss due to Contraction in area. ...
 5)Pressure Loss at Suction and Discharge of Duct. ...
 6) Pressure Loss due to Obstruction in duct Pressure losses also occur due to
various obstructions in path of air flow from fan to outlet

Constant air volume (CAV) is a type of heating, ventilating, and air-conditioning (HVAC)
system. In a simple CAV system, the supply air flow rate is constant, but the supply air
temperature is varied to meet the thermal loads of a space.

Dual duct variable air volume (DDVAV)) systems are used to obtain zone temperature
control by mixing the cold and warm air in various volume combinations.
Variable air volume (VAV) is a type of heating, ventilating, and/or air-conditioning (HVAC)
system. Unlike constant air volume (CAV) systems, which supply a constant airflow at a variable
temperature, VAV systems vary the airflow at a constant temperature. The advantages of VAV
systems over constant-volume systems include more precise temperature control, reduced
compressor wear, lower energy consumption by system fans, less fan noise, and additional
passive dehumidification.[1]

An Air Handling Unit (AHU) is used to re-condition and circulate air as part of a heating,
ventilating and air-conditioning system. The basic function of the AHU is to take in
outside air, re-condition it and supply it as fresh air to a building.
The most common air conditioning systems include window air conditioners, portable air
conditioners, wall hung split or multi head split systems, and ducted air conditioners.

According to ASHRAE, 'Human comfort is that condition of mind, which expresses

satisfaction with the thermal environment'

The effective temperature is the temperature of the saturated environment at which

motionless saturated air would induce same level of comfort as experienced in a normal
environment in a sedentary worker wearing ordinary indoor clothing.

Which are the factors governing effective temperature? The degree of warmth or cold felt by
a human body depends mainly on following three factors: (a) Dry bulb temperature (b)
Relative humidity (c) Air velocity.

This system consists of heating and cooling equipments with automatic controls to
produce comfortable conditions throughout the year. ... Year round air conditioning fulfils the
requirement of comfort i.e. “heating and humidifying in winter” and “cooling and
dehumidifying in summer

Room Sensible Heat Factor - RSHF - is defined as the sensible heat load divided by the
total heat load in a room.
The Great Sensible Heat Factor is the ratio sensible to total heat in a cooling coil.

Unitary air conditioner means an air conditioning equipment with one or more factory-
made assemblies that includes evaporator, compressor, condenser, cooling or heating coil,
air re-circulation fan section, and regulator controls, with single or multiple indoor units,
which serves to supply cooled or heated air.

In year-round air conditioning system, the outside air flows through the damper and
mixed with the recirculated air (which is obtained from the conditioned space). The mixed
air passes through a filter to remove dirt, dust and impurities.
District cooling system (DCS) distributes thermal energy in the form of chilled water
from a central source to multiple buildings through a network of underground pipes
for use in space cooling.