ADVANTAGES AND DISADVANTAGES OF SHELL & SPIRAL COIL HEAT EXCHANGER

Advantages of Shell & Coil Heat Exchangers: -

The shell and coil design is the perfect choice whenever high heat transfer rates, compact design and low maintenance costs are high priorities. Other benefits include:

·        Compact and lightweight: closely packed tubes make our shell and coil exchangers compact and lightweights. Makes it install is limited and hard to access.

·        High Efficiency: The large number of tightly packed tubes increases the heat transfer area providing a high heat transfer coefficient.

·        Low Installation Costs: Because of its compact size. lightweight and unique vertical shape, the shell and coil heat exchanger takes up less space and will cost less to install.

·        Flexible Designs: With many model types and configurations, the shell and coil heat exchanger can be used with a wide range pressures, temperatures and flows.

·        Low Maintenance: The helically corrugated tubes promote turbulent fluid flow reducing the amount of scale buildup and fouling. Can be easily removed from piping system and flushed if necessary

·        Low Pressure Drop: In the Shell and coil heat exchanger pressure drop is low.

Disadvantages of Shell & Coil Heat Exchangers: -

1.         A heat exchanger comprising:

a shell having: a tubular outer wall having a first and second end, a tubular inner wall having a first and second end coaxial with said outer wall, and first and second end plates attached to the first and second ends of the outer and inner walls to form an enclosed tubular shell cavity there between having a first and second end; means for admitting a first fluid into said shell cavity; means for removing the first fluid from the shell cavity; a spiral coil of tubing having a first and second end sealingly exiting through the shell cavity wall for carrying a second fluid there between, said spiral coil lying within the shell cavity and having a plurality of spiral windings formed about the axis thereof, the spiral coil sized to fit between the inner and outer shell wall with limited radial clearance to allow limited axial flow of the first fluid, said winding axially spaced from one another to define a spiral flow path there between for the first fluid, said radial clearance and axial spacing relatively sized to induce the first fluid to travel in a substantially spiral motion to enhance the heat transfer between the first and second fluids; an auxiliary coil of tubing having a first and second end sealing extending through the shell cavity for carrying a third fluid there between, said auxiliary coil lying within the shell cavity and having a plurality of windings formed about the axis thereof and axially spaced apart from the spiral coil, for transferring heat between the first and third fluids; and a divider plate dividing the shell cavity into two coaxial cylindrical regions, a primary region in which lies the spiral coil and an auxiliary region in which lies the auxiliary coil, and means to admit and means to remove a fourth fluid from the auxiliary region.

2.         Wherein the shell cavity provides a path for the flow of the first fluid, said path has an axial flow area when viewed parallel to the axis and a spiral flow area when viewed parallel to a line tangent to the coil tube, where said axial flow area divided by the spiral flow area defines an axial clearance ratio which is less than 1.0.

3.         Wherein the axial clearance ratio is greater than 0.05.

4.          Wherein the axial clearance ratio falls within a range of 0.25 to 0.60.

5.         Wherein said spiral coil is formed of a tube having at least one augmented wall surface to maximize surface area and heat transfer.

6.            Wherein said tube is formed of copper.

7.         Further comprising a fluid receiver formed within the volume bounded by the shell inner tube wall and the first and second end plates, said receiver further provided with means for admitting and means for removing fluid from the enclosed receiver volume.

8.         Further comprising a fluid receiver formed within the volume bounded by the shell inner tube wall and the first and second end plates, said receiver further provided with means for admitting and means for removing fluid from the enclosed receiver volume.

Shell and Coil Applications:

            The shell and coil design were designed specifically for the hydraulic markets including:

·                    Heating Systems:

·                    Chilled Water Systems

·                    Ground Water Systems

·                    Residential Use

Use Of Heat Exchanger In Dual Mode Heat Pump:

The heat exchanger described in the first embodiment works quite satisfactorily in a water source heat pump which can be used for both heating and cooling. Schematic diagram of a heat pump in the heating mode and in the cooling mode are shown in FIGS. 7 and 8, respectively. The heat exchanger is depicted by box 20 and is provided with water inlet 60 and water outlet 62. The water circulates through the tubular coil in the heat exchanger unit. In the shell of the heat exchanger is circulated a refrigerant such as Freon.RTM. 22. In the heating mode, refrigerant enters in the outlet 64 and exits the shell cavity through inlet/outlet 66 as the refrigerant is circulated by pump 68, which circulates the Freon.RTM. in a closed loop path through tube and shell heat exchanger 20, tube and fin heat exchanger 70. Heat exchanger 70 transmits energy between the Freon.RTM. and air which is circulated through the heat exchanger by a blower which is not shown in the heating mode and reversing valve 72 and is oriented such that the output of the pump is connected to the tubing vent heat exchanger 70 and the suction side of the pump is connected to a shell and coil heat exchanger.

In the heating mode the shell and coil heat exchanger acts as an evaporator and the tube and fin heat exchanger 70 acts as a condenser. The hot high pressure output of pump 68 flows to tube and fin heat exchanger 70 and is cooled by the flow of air there through. Pressure is maintained relatively high and the tube and fin exchanger 70 by expansion valve 74. When the refrigerant flows through expansion valve 74, pressure drops substantially. As a low-pressure refrigerant flows into the heat exchanger 20, it absorbs heat from the water circulating through the coils and evaporates. Refrigerant exits the heat exchanger through outlets 66 and passes through reversing valve 72 to the inlet of pump 60 to complete the heating cycle.

Pump 60 is driven by conventional mechanical means such as an electrical motor. Since heat energy is being added or removed from the water circulating through the coil of the heat exchanger, the energy output to the air substantially exceeds the energy consumed by the pump 68 in the heating and cooling modes. In the cooling mode, the reversing valve switches as shown in FIG. 8 so the suction side of the pump is connected to the tube and fin heat exchanger 70 and the outlet of the pump is connected to the shell and coil heat exchanger 20. In the cooling mode the heat exchanger 20 acts as a condenser. The water circulating through the coil cools the refrigerant circulating through the shell cavity. The refrigerant flows through expansion valve 74 and evaporates in the tube and fin heat exchanger 74 to cool the air flowing there through.

It has been determined that the heat exchanger of the present design performs quite well in a reverse cycle water source heat pump and is capable of achieving very high efficiency levels in both the heating and cooling modes. Previous heat pump designs tended to optimize performance in one mode that was used most frequently and accepting a lower coefficient of performance in the lesser-used mode.