## 1 Introduction  
In construction machinery, the heat-dissipating components always include an engine radiator, intercooler, hydraulic oil radiator, and torque converter radiator, and these share about 30 percent of the total engine power [1]. Take an ordinary loading machine for instance; total heat dissipating capacity is about 100 kW, which may even be up to 200 kW in some very large loaders [2, 3]. The stricter fuel consumption and emission regulations put the worldwide carmakers and suppliers under pressure to develop more efficient thermal management systems. [PERSON] built up simulation-based vehicle thermal management system concept and methodology [4], whereas [PERSON] designed a high-precision performance test bench to study the automotive cooling system [5]. [PERSON] focused on the warm-up period performance of the cooling system [6], but [PERSON] focused on the radiator of system key component [7]. All researches are aiming at the strong, but efficient, cooling project to ensure all radiators operate in good conditions, so that a key issue for a construction machinery plant is matching a suitable and reliable cooling system in the machine design program. In the traditional cooling case, there is usually one fan responsible for heat transfer and airflow for all radiators [8]. However, this seems to be inappropriate, or even insufficient, for modern construction machinery [9; 10]. Due to energy savings and emission reduction, the machine tends to be lightweight and small in size, with the same power. Consequently, its overall heat flow density is increasing but its thermal distribution is becoming uneven [11]. If just one fan is still adopted, the fan should be of a large size and high rotating speed for supporting a large amount of cool air across the radiators for heat dissipation. This will lead to two new problems. One is that a large fan goes against the demand of light weight for modern machines. Another is that a high rotating-speed fan will greatly increase noise emission, while many national decrees are promulgated to restrict equipment noise for environment and operator health protection [12]. Therefore, in the requirements of increased power density, uneven thermal problems, engine compartment constraints, and working demands, the challenge now is how to ensure sufficient air flow, but maintain low noise emission for a cooling system. There are different ways, such as using electric coolant pump [13], or using integrated configuration [14], and one of the ways is adopting multiple fans. The cooling system with multiple fans has some advantages. First, it can enhance heat dissipation, since it benefits from the independent design of each radiator, such as its power, rotating speed, cross-section, size, and so on. Second, as each fan can be different in size and working parameters, it can improve thermal unevenness problem. Third, as not all radiators are arranged together anymore, they can be flexible configurations to satisfy various engine compartments. [PERSON] studied heat exchanger flow interactions of multiple fans and found that it, indeed, performed well [15]. [PERSON] used two fans in a tracked vehicle and each fan can be controlled independently. The fan speed reached a maximum 5200 rpm on a hot summer day, while the fan usually worked at a speed of 3000 rpm [16]. [PERSON] used multiple fans with an auto temperature-controlled system in a large bus and decreased fuel consumption by 8% per hundred kilometers, both in null and full loads [17]. [PERSON] imported a multiple fan scheme into a meter-rail motor train and found it was useful in a limited engine compartment situation [18]. [PERSON] found that adopting multiple fans could not achieve a good heat transfer effect in the old cooling system with all of the radiators together and, thus, it should alter its original configuration and separate the fans into different parts as well as radiators [19]. As described above, multi-fan designs have been used in many fields, and proved to be a good strategy for system cooling.