Thermodynamic Systems 12

Thermodynamic Systems 1
THERMODYNAMIC SYSTEMS
Name
Course
Professor
University
City/state
Date

Thermodynamic Systems 2
Thermodynamic Systems
Introduction
This assignment involves solving various problems related to thermodynamic systems and
determining the effect of energy transfer on these systems. The assignment helps in analyzing
data, choosing and applying scientific and mathematical principles related to heat transfer and
how it affects various engineering systems.
Tasks
Task 1
a) Heat energy required
The total heat is the amount of heat required is that needed to convert the 10kg of ice from solid
at -30°C to solid at 0°C and the heat needed to convert the ice from solid at 0°C to liquid (water)
at 0° . The formula for heat needed is:
Heat, Q = (m x cp x ∆T) + (m x cf)
Where Q = total heat, m = mass of ice, cp = specific heat capacity of ice, ∆T = change in
temperature, and cf = specific latent heat of fusion of ice.
Therefore
Q = (10kg x 2.1 kJ/kg°C x 30°C) + (10kg x 335 kJ/kg)
= 630 KJ + 3,350 KJ
= 3,980 KJ
= 3.98 MJ

Thermodynamic Systems 3
b) Process of refrigeration
i) The process of refrigeration as a heat exchanger
Introduction
Heat exchangers play a very crucial role in refrigeration systems. The fundamental
function of a heat exchanger is to exchange or transfer heat from one fluid to another.
Refrigeration basically involves removal of heat from a system and disposing it from the system.
This process relies on the principle of convection. The process of refrigeration in a heat
exchanger takes place by use of a compressor and refrigerant gases. A refrigerant is a stable gas
with the capacity to compress and expand, which makes it able to absorb and discharge heat.
How refrigeration works
A refrigeration system comprises of five main components. These components are: a
compressor fluid refrigerant, condenser coils, evaporator and an expansion device. The
compressor works by constricting the refrigerant vapor, which increases its pressure and
transfers it to the coils located outside the refrigeration system. The mixture of the cooler air
temperature and the hot gas present in the coils produces a liquid. This liquid is at high pressure
and this condition makes the refrigerant to cool down while flowing into the coils located inside
the refrigeration system. The refrigerant is able to absorb any heat present in the refrigeration
system thus cooling down all the air found in it. Thereafter, the refrigerant is able to evaporate
and become a gas, and flows back to the compressor for the refrigeration cycle to start over
again. This process is continuous and the refrigeration system uses a heat exchanger as an
evaporator.

Thermodynamic Systems 4
In other words, refrigeration cycle comprises of two main pressures: low side (low
pressure or evaporating side) and high side (high pressure or condensing side). These two
pressure sides are separated by the compressor and metering device. The metering device is used
to control flow of refrigerant whereas the compressor is used to compress the vapor.
How heat exchangers work
A heat exchanger refers to a device that is used to transfer thermal or heat energy
between different mediums. Heat exchangers are used in heating, ventilation and air conditioning
(HVAC) systems and also help engines and machines to work efficiently. Some of the basic
examples of heat exchangers are: evaporators, condensers and earth coils. The main focus of this
report is on how a heat exchanger is used in a refrigeration system, such as a HVAC system. The
fundamental function of a HVAC system is to remove heat from inside a building and transfer it
outside. This process largely depends on a substance known as a refrigerant. During refrigeration
process, the refrigerant works by carrying, absorbing and releasing heat while it changes state
from gaseous state to liquid state.
The refrigeration process begins with the refrigerant moving through different
components of the refrigeration system, and transferring heat as it moves. The refrigerant starts
moving from the evaporator coils as a low-pressure liquid. If it is a building, the fan inside the
building blows warm air across the coils. The refrigerant is able to absorb heat from the warm
air, which turns it from liquid to vapor. After absorbing the warm air, the refrigerant now
becomes a low-pressure warm gas and starts moving into the compressor. The compressor is
usually positioned outdoors. Inside the compressor, the refrigerant gets converted into a high-
pressure, warm gas. This high-pressure, warm gas them moves into the condenser that is also
usually located outdoors. As air moves over the condenser, it is able to absorb heat from the