Air source heat pumps are using air as the heat source to vanish the working fluid in evaporator of the thermodynamic cycle. The working fluid eliminates the heat together with the work delivered to compressor at the essential temperature by the operational parameters. Research activities are done across the globe focusing on the development of efficient and small footprint evaporator for transferring heat from the supply of air to working fluid easy to produce. In such situation, heat transfer from air to channel walls is substantially poor from the channel wall to working fluid. Therefore, the main purpose of activities in project were concentrating on the strength of the heat transfer

Air source heat pumps are using air as the heat source to vanish the working fluid in evaporator of the thermodynamic cycle. The working fluid eliminates the heat together with the work delivered to compressor at the essential temperature by the operational parameters. Research activities are done across the globe focusing on the development of efficient and small footprint evaporator for transferring heat from the supply of air to working fluid easy to produce. In such situation, heat transfer from air to channel walls is substantially poor from the channel wall to working fluid. Therefore, the main purpose of activities in project were concentrating on the strength of the heat transfer from the air evaporator channels.

Air-source heat pumps (ASHP) are mostly based on the brazed fin and tube heat exchanger. It is the huge density of fins needing the large fan to power air with the wide heat exchanger. Additionally, ASHP are characteristically installed making them vulnerable to the formation of frost. Frost is building up the evaporator from temperature greater than 5°C. To deal with the formation of frost of main body of research for decreasing the size of evaporator by improving the air-side heat transfer coefficient. The local intensification is accomplished with the liberal decrease of the air-side cross-sectional area resulting in the rise of the mean velocity of air stream. The main disadvantage of the application of heat transfer improvement techniques is the internal rise of the irreversible and reversible components of the airside pressure drop of evaporator. Wall to mass transfer and fluid heat are encouraged by hydrodynamics and thermal boundary layers. Recently, various studies were done for better control and/ or to improve the parietal heat transfer. The main purpose is to increase the complete heat transfer coefficient and lessen the heat transfer area and results to the lowest physical heat transfer device and less cost. Heat transfer intensification is the philosophy focusing on accomplishing the decreased size of heat transfer equipment and the related advantages. The product of intensification techniques is attaining the combination of following:

• Rise in the capacity of the already present heat exchanger
• Decrease in the size of heat exchanger for the duty
• Decrease in pumping power
• Decrease in the approach of temperature difference

Strengthened heat transfer will enhance the efficiency and leads to the conservation of energy and decrease the costs.

Techniques of Air Side Enhancement

The passive heat transfer intensification techniques mostly involve:

• Rough surfaces
• Enhanced surfaces
• Swirl Flow Devices
• Displaced Enhancement Devices
• Coiled Tubes

There are various approaches in area resulting in:

• Distraction of thermal boundary layer
• Application of minichannels
• Growing heat transfer surface area
• Secondary Flow Development
• Developing fluid turbulence

Because of the low density of gases and small hydraulic diameter, the surfaces are operated in Reynold’s number ranging from around 500 to 1500. Consequently, tube-fin or plate-fin enhancement geometries are efficient in the Reynold’s number regime. For instance, the roughness of surface is displayed to encourage the heat transfer in turbulent regime and do not offer the improvement in less Reynold’s number range.

Across the world, types of heat exchangers combining fin-tubes or plate-fins are manufactured for the applications in the industrial systems and processes required to resolve and types flow is controlled in plates. Several surface extensions in the form of turbulators and fins are utilized to enhance the air side heat transfer. Different fin types are mentioned as:

• Rectangular offset strip fins
• Slit fins
• Wavy fins
• Louvered fins

Heat Pumps Evaporators

Typically, the thermal hydraulic calculation of the appropriate heat exchangers is achieved by marketable computational fluid dynamics software. The normal approach of using the CFD code is to correctly define the calculation mesh and crack the governing equations for the geometry. The set of equations needs to be supplemented by the model of turbulent kinetic energy evolution and development of the dissipation of kinetic energy.

1. Heat Pump Cycle

In the current research, R134a is selected as the working fluid for heat pump cycle. Acquired parameters of heat pump cycle are shown as the evaporator parameters are displayed with assumptions that the less temperature difference within air and the working fluid was similar to around 5K and the inlet temperature of air is equivalent to around 8°C.

1. Tube fin heat exchanger

In case of tube fin heat exchanger, the design model of heat exchanger is utilized to size the evaporator. The data for the air side heat transfer coefficient can be removed using the methods:

• Usage of the appropriate correlation to predict the two-phase flow heat transfer coefficient
• Study model geometry to acquire air ratio data and refrigerant channel
• Using the complete heat transfer coefficient equation to guess hair.

The tube fin heat exchanger fulfils the essential area and practical pressure drop limitations. Following thermal hydraulic uncertainty present in the design:

• The length of air flow is around 0.06m. It is uncertain to whether the disruption of flow is occurred by LVG efficient at length. However, it is valuable on studying the usage of LVGs with one to be found at the flow entrance and situated at the center point of flow passage.
• The air-side pressure drop is not accounting for the LVG improvement and was unable to quantify deprived of friction factor against the data of Reynold’s number. Though, the pressure drop for plain fins is low and not projected the real pressure drop will be high.

1. Microchannel Heat Exchanger

The main part of MCHE contains the set of stainless steel shims with around more than 68 electrochemically impressed the channels of length of around 18mm and width of 350µm and the depth similar to around 110µm. Many of the plates are depending on the work of proposed HX. The HX channels are distributed with the spacing of around 1.5mm. For the removal and supply of fluids that etched the supply of fluid and outlet collectors of depth similar to around 250µm and the constant width of 5mm.

Modular construction permits to enhance the capacity of HX, in simple way, by adding the area of heat transfer in the form of shim. The shim of stainless steel will be accumulated in the heat exchanger, involving the outlet/ supplying collector.

Conclusion:

The original designs of heat exchangers are produced and tested in tube-fin heat exchanger to work as evaporator and the micro channel heat exchanger comprising of diffusion bonded stainless steel shims to work as condenser. Systematic tests established the consistency with thermal-hydraulic models.