**6. Nomenclature**


*At* – surface area of tube between fins

Fig. 11. Temperature on fin surface and flowing air temperature for fin profile (f).

total mass that refers to the cost of the whole heat exchanger.

resistance of the body that results in a pressure drop.

*A* – total external surface area of fins and tubes

*Ak x*, – cross-sectional area as a function of *k* and *x*

*At* – surface area of tube between fins

The heat flux depends on the temperature difference between the local plate/tube and local air temperatures. In reality, these temperatures vary along the cross section of the air stream and along the fluid flow direction. All results are calculated considering the air flow and its streamline deviations caused by the plate and tube configuration and compared with the known correlation for circular fins of rectangular cross section. The model allows considering the heat transfer in three directions. This is an advantage, comparing to other optimization method, where the temperature profile is two-dimensional. The shape of the fin and tube is modified to calculate the heat transfer for different conditions, reduce the

Described phenomena modify the conditions of the heat exchange between the plate and the fluid having the effect on the heat transfer. The rate of the heat transfer does not depend only on wall surface dimensions, heat transfer coefficient and the temperature difference between the fluid that surrounds the plate and the plate surface temperature. The air velocity and the fin shape are also essential because the fin profile influences the flow direction. For heat exchangers, built with many fins and designed for real industry, it is important to pay attention to and calculate the heat transfer considering the fluid flow and

It should be also mentioned that if the fin is positioned into an air stream, the flow applies to a force from the fin tip surface in the direction of the oncoming flow (drag). The resistance of the body results in a pressure drop. The fin and tube surface orientation also modifies the

**5. Conclusion** 

flow paths.

**6. Nomenclature** 

*Af* – fin surface area


**14** 

*Lebanon* 

**Thermal Design of Cooling** 

*Mechanical Engineering Department, Faculty of Engineering,* 

The cooling and dehumidifying coil is a critical component of air conditioning. Its performance has a strong bearing on the ultimate indoor environmental conditions, which in turn, has a significant impact on the indoor air quality. Decisions made to select a cooling coil influence the initial investment as well as the costs of installing, providing, and maintaining thermal comfort. The efficient thermal design of the cooling coil leads to a crucial reduction in the coil surface heat transfer area and of course, its capital cost and its weight. On the other hand, the enhancement in the coil thermal performance will usually be established at expense of the hydraulic performance of the cooling coil and in turn, its running cost. Because the cooling coil is an integral part of the air distribution system, its geometry — size, number of rows, fin spacing, and fin profile — contributes to the airside pressure drop and affects the sound power level of the fans. (Fan power needed to circulate air through the duct system may warrant extra sound attenuation at the air handler.) Cooling coils are an integral part of the chilled water system or the refrigeration unit, too. The extent to which coils raise the chilled water temperature or the evaporation temperature dramatically affects both capital investment in the cooling coil or the pumping power. Coil performance can even influence the efficiency of the chiller or Dx-unit. The focus of this chapter is on the description of the methodology should be used in thermal design of the

Methods to design the cooling and dehumidifying coil either chilled water coil or Dx evaporator coil are usually based on log mean enthalpy or log equivalent dry-bulb temperature difference [1]. In both methods, the cooling coil is treated as a single zone/region and hence the required surface area is determined [2]. This manner of the cooling coil design could lead to an imprecise design particularly when the cooling coil is partially wet. In this chapter, the numerical calculation using a discrete technique "row-byrow method" will be presented to calculate the detailed design of the cooling coil in order to enhance the calculation accuracy and trace the air and coil surface temperature locally.

Cooling coils are classified to direct-expansion (DX) coils and chilled water coils as shown in Figure 1. Some coil manufacturers fabricate coils from 5/8 inch OD copper tubes, others

**1. Introduction** 

cooling coil either chilled water coil or Dx-coil.

**2. Types of cooling coils** 

**and Dehumidifying Coils** 

M. Khamis Mansour and M. Hassab

*Beirut Arab University,* 

*X <sup>t</sup>* – transverse tube pitch (perpendicular to the flow) tube pitch

Greek symbols

*T* – effective mean temperature difference

*T correl* \_ –difference in air temperature between inlet and outlet section calculated from correlation

*T* \_ model –difference in air temperature between inlet and outlet section received from numerical computation

*T TT Fluid IN OUT* - difference in fluid temperature between outlet and inlet section


*<sup>f</sup>* – fin efficiency


weight

– fluid density

*<sup>s</sup>* – material density of solid (tube and fin)

## **7. References**

