The document discusses the design and thermal performance of a heat pipe heat exchanger for recovery in air conditioning systems. It presents findings on the effectiveness of the system, revealing that the temperature changes and heat transfer increase with higher fresh air inlet temperatures, achieving a heat recovery efficiency of 85% at 40°C. Additionally, the study highlights the positive impact of mass flow rate ratios on the effectiveness of the heat exchanger specifically in the evaporator section.

1. HEAT PIPE HEAT EXCHANGER for recovery
in air conditioning.
Submitted to:- Submitted by : -
Samar Singhal 2018TH02

2. Introduction
Abstract
•The heat pipe heat exchangers are used in heat recovery applications to cool
the incoming fresh air in air conditioning applications.
•Two streams of fresh and return air have been connected with heat pipe heat
exchanger to investigate the thermal performance and effectiveness of heat
recovery system.
• Ratios of mass flow rate between return and fresh air of 1, 1.5 and 2.3 have
been adapted to validate the heat transfer and the temperature change of fresh
air. Fresh air inlet temperature of 32–40 C has been controlled, while the inlet
return air temperature is kept constant at about 26 C. The results showed that
the temperature changes of fresh and return air are increased with the increase
of inlet temperature of fresh air.

3. Introduction
Abstract
•The effectiveness and heat transfer for both evaporator and condenser sections
are also increased to about 48%, when the inlet fresh air temperature is
increased to 40 C.
•The effect of mass flow rate ratio on effectiveness is positive for evaporator side
and negative for condenser side.
•The enthalpy ratio between the heat recovery and conventional air mixing is
increased to about 85% with increasing fresh air inlet temperature.
• The optimum effectiveness of heat pipe heat exchanger is estimated
and compared with the present experimental data. The results showed that the
effectiveness is close to the optimum effectiveness at fresh air inlet temperature
near the fluid operating temperature of heat pipes.

4. Introduction
Introduction
•Heat pipe heat exchanger for heat recovery equipment are aimed for recovering
sensible heat and they are recommended for systems in which inlet and return air
should not be mixed such as surgery rooms in hospitals and chemical and biological
laboratories.
•The advantages of using heat pipes over conventional methods is that large
quantities
of heat can be transported through a small cross-sectional area over a considerable
distance with no additional power input to the system, (except for the fans to drive
the air-streams) together with simplicity of design and ease of manufacture [1].
•Efforts have successfully developed a series of heat pipes equipment, such as heat
pipes gas to gas exchangers, heat pipes steam generators, high-temperature heat
pipes hot air furnaces, and progresses have been made in the fields of metallurgical,
petrochemical, chemical, power and construction material industries on the basis
of experimental and theoretical investigations [2,3].

5. Introduction
Introduction
•Also, heat pipe heat exchangers are suitable for energy recovery in air conditioning
systems in tropical countries where incoming fresh air at high ambient temperature could
be pre-cooled by the cold exhaust air stream before it enters the refrigeration equipment
[4].
•Any study of an air conditioning system in a building should be focused mainly on
indoor air quality, thermal comfort, energy saving and environmental protection [5].
• A heat pipe heat exchanger was designed, constructed and tested under low temperature
of 15–35 C, operating conditions [13]. The results showed that the minimum heat
transfer is well above the required heat transfer rate, and for increasing the effectiveness
of the heat pipe heat exchanger, the number of rows should be increased and finned pipes
should be used.
•A design method by using computational fluid dynamic simulation of the
dehumidification process with heat pipe heat exchangers was presented [14]. The that
modeling is able to predict the thermal performance and optimize the design of the heat
pipe fin stack.

6. Introduction
Introduction
•The aim of this study is to investigate the thermal performance and effectiveness of heat
pipe heat exchanger for heat recovery in air conditioning applications by measuring the
temperature difference of fresh warm and return cold air through the evaporator and
condenser side.

7. Introduction
Experimental setup
The experimental apparatus has been designed and constructed as shown in Fig. 1.

8. Introduction
Experimental setup
The test section consists of two air ducts of 0.3 · 0.22 m2 section areas connected
together by finned tubes heat pipe heat exchanger.
A square hole of 0.3 · 0.3 m2 was made in one side of the two ducts for heat pipe heat
exchanger installation.
A laboratory refrigeration machine consisting of evaporator; compressor, condenser, and
expansion device beside the measuring instrumentations were used to supply the return
cold air to the con denser side of the heat pipe heat exchanger.
The unit was equipped with a blower of variable speed installed before
the cooling coil.
The refrigeration unit was charged with R-134a and the evaporator was made from
copper-finned tubes cooling coil.

9. Introduction
Experimental setup
•The fresh air duct was equipped with a blower to supply air to the evaporator side of the
heat pipe heat exchanger.
•The return cold and fresh warm air ducts were insulated with glass wool of 50 mm
thickness to minimize the heat transfer to surrounding air.
•The flow rates of air in both two ducts were measured with Pitot-static tube.
•The fresh air was kept constant at 0.4 kg s1, while the return air was changed from 0.4,
0.6 and 0.933 kg s1.
•The ratios between return air and fresh are 1, 1.5, and 2.333.
•The air temperature and relative humidity at inlet and outlet of the two ducts were
measured with Humidity-temperature digital device and the measured data were
conducted in steady state..

10. Introduction
Experimental setup
•After enough time, the temperatures and humidity of fresh and return air before and
•after heat pipe heat exchanger were recorded, when they became nearly constant.
•The ratio between return cold and fresh air mass flow rates was obtained.
•The recorded data of the air were represented on the psychrometric chart.
• In this study, the thermodynamic properties of moist air and working fluids were
obtained by using Cool Pack and NIST software [15,16].
•The enthalpy and humidity ratio for each run was calculated from the cools tool
auxiliary program using Engineering Equation Solver by knowing the dry bulb
temperature and relative humidity of air at inlet and outlet of heat pipe heat exchanger.

11. Introduction
Test section and heat pipe heat exchanger
•The heat pipe heat exchanger consists of 25 copper tubes with length of 0.5 m, and
inside and outside diameters of 10.2 and 12.7 mm respectively.
•The heat pipe consists of three parts with straight length, evaporator section of 0.2
m, adiabatic section of 0.1 m and condenser section of 0.2 m.
•Four layers of 100 mesh brass screen with wire diameter of 0.125 mm were
installed inside the tubes to assist the liquid return from the condenser section to
the evaporator section.
•The heat pipes are closed at both ends and evacuated from air and charged with R-
11 as a working medium at pressure of 0.127 MPa, which corresponds to saturation
temperature of 30 C.
•It is note that this fluid is replaced now by R-123.
•The heat pipes were arranged horizontally in staggered form as indicated in Fig. 2.

12. Introduction
Test section and heat pipe heat exchanger

13. Introduction
Test section and heat pipe heat exchanger
•The evaporator and condenser sections are finned with 50 square aluminum sheets
of 0.5 mm thickness and area of 0.29 · 0.29 m2.

14. Introduction
Air processes and data reduction
•The sensible cooling of fresh air and sensible heating of return air processes are
represented on psychrometric chart as shown in Fig. 1.
• The heat rejected from the air stream in the evaporator section can be calculated
as,
•The effectiveness of the heat exchanger is defined as the ratio of actual rate of
heat transfer by the heat exchanger to the maximum possible heat transfer rate
between the two air streams [13,17]. Assuming, there is no water
condensation in fresh air stream and also assuming the specific heat of air
passing through the evaporator and condenser sections to be constant, then
the effectiveness of heat pipe heat exchanger at evaporator side is represented
as

15. Introduction
Air processes and data reduction
The ratio of utilized heat in the heat recovery process to the utilized heat in
the conventional mixing air process defined by enthalpy ratio is:
The above procedures were conducted for each experiment at various
mass flow ratios of 1, 1.5 and 2.33 and fresh air temperatures of 32–40 C,
while the return cold air temperature was kept constant at about 26 C.

16. Introduction
3. Results and discussion
•The temperature change of fresh, hot, and return, cold, air at various inlet air
temperatures and mass flow rate ratios are illustrated in Fig. 3.
•It is observed that for fresh and return cold air, the temperature change
increases with increasing the inlet fresh air temperature.
•The increase in temperature change for fresh air with increasing mass flow
rate ratio between return and fresh air is slightly positive. But, the temperature
change of return cold air is going down with increasing mass flow rate ratio.
•The calculated results of effectiveness for fresh and return air are indicated in
Fig. 4.
•The effectiveness is increased with increasing the inlet fresh air temperature.The
effect of mass flow rate ratios on the effectiveness of the heat exchanger is
slightly positive for evaporator side and largely negative for condenser side.

17. Introduction
3. Results and discussion
•It is interesting to find that the increase in return to fresh air mass flow rate
•ratios by about two times leads to increase in the temperature change of fresh
air by about 20% and the effectiveness in the evaporator side by about 26%.
•Inlet fresh air temperature is the most dominant parameter to enhance the
heat transfer rate in the evaporator side of the heat pipe heat exchanger.
•It is found that the heat recovery increased with increasing inlet fresh air
temperature and it reached about 85% at inlet fresh air temperature of
•40 C. Also, the heat recovery is decreased by about 10% with increasing mass
flow rate ratio by about two times.

18. Introduction
3. Results and discussion

19. Introduction
3. Results and discussion

20. Introduction
3. Results and discussion

21. Introduction
Conclusions
•The temperature changes of fresh air, hot, and return air, cold, are increased
with increasing the inlet temperature of fresh air.
•The heat transfer and effectiveness for both evaporator and condenser
sections are increased with increasing the fresh air inlet temperature.
•Increasing the return to fresh air mass flow rate ratios by about two times
leads to increase the temperature change of fresh air about 20% and
effectiveness of the heat pipe heat exchanger by about 26%.
•The effect of mass flow rate ratio on effectiveness is positive for evaporator
side and negative for condenser side.
•The enthalpy ratio between the heat recovery and conventional air mixing is
increased with increasing the inlet fresh air temperature and decreased with
increasing mass flow rate of return air.

22. Introduction
Conclusions
•The heat recovery is increased with increasing inlet fresh air temperature and
attained about 85%.

23. Extension of Interpolation method to Unstructured Meshes
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