Air Recirculation Through a Duct-Room System

Air Recirculation Through a Duct-Room System
Abstract
The purpose of this laboratory was to examine air flow into a room and analyze the heat losses
during heating and cooling and the power consumed by the pre-heaters during operation and
explain the possible causes for the phenomena above. Two test A and B were conducted. In test
A, air was allowed to flow into the room via a duct and into the outlet whereas in test B. air was
allowed to flow into the room via a recirculated system. In test A, the inlet and the outlet louvres
were open while the recycle louvre was closed. On the other hand, in test B the inlet and the
outlet louvres were closed and only the recycle louvre was operational. The velocity of air
flowing into the room and the temperatures were measured using velocity meters and
temperature sensors respectively. It was observed that the temperatures were higher for test B
where a recirculated system was used compared to test A for there was no recirculation.
Nomenclature
Contents
Abstract..........................................................................................................................................1
Nomenclature.................................................................................................................................1
Introduction....................................................................................................................................1
Methodology...................................................................................................................................3
Equipment’s Used......................................................................................................................3
Experimental Set-up..................................................................................................................4
Assumptions................................................................................................................................5

Procedure....................................................................................................................................5
Test A..........................................................................................................................................6
Test B...........................................................................................................................................6
Results and Analysis......................................................................................................................6
Conclusion......................................................................................................................................8
List of Tables
List of Figures
Introduction
Heat transfer is the process by which energy is transferred from a medium of low temperature to
a medium of high temperature. The various forms of heat transfer are conduction, convection,
and radiation. The study of heat transfer aids in the analysis of thermodynamic processes such as
flow of air in a room and its efficiency.
In this experiment, heat flow from one end to the other end of an enclosed assembled system is
determined to simulate what would happen in a real environment. Heat transfer between two
surfaces is determined using the following equation:
∆ QAB =m(CpB T B−C pA T A )
The mass flow rate “m” is determined as follows:
m=ρV = ρ Ac V avg ( Kgm−3)

The specific heat is determined by the equation;
C p= 28.11+ 0.1967 x 10−2 T + 0.4802 x 10−5 T 2−0.1966 x 10−9 T 3
28.97
Where T is the temperature in Kelvin and Cp is in KJ/Kg.K.
Air density is determined using the formula below;
P
ρ =RT
The power produced by the pre-heater is determined using the equation below:
Power=mC p (T 1−T2 )
In this experiment two tests A and B were conducted. In test A, an inlet and outlet louvre were
open whereas the recycle louvre was closed to ensure that no air got back into the system and
that all the air that came in via the inlet went out via the outlet. On the other hand, in test B, the
inlet and outlet were shut and the recycle louvre left open to ensure that instead of the air leaving
the room, it was just circulated inside.
Methodology
Equipment’s Used
To combination of equipment’s used to successful completion of the experiment were; the
velocity meters, the temperatures sensors, the fan, the pre-heaters, recirculation duct. All this
equipment’s were assembled into a single unit that was controlled by RA3-360 computer
software that read the values from the temperature and velocity sensors. The speed of the fan and
the power to pre-heaters were also adjusted by the computer software. A side view of the entire
system is as shown below: