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太阳能热水器为什么能输出热水

新华网 2017-12-20

  太阳能热水器是一种通过吸收太阳能并将其转换成热能来给水加温的设备,主要包括集热板、保温水箱、连接管道、控制系统、主机支架等部分。其中,集热板是关键部件,按集热板构成的不同,太阳能热水器可分为平板式和真空管式。

  为什么太阳能热水器能给水加热呢?

  在许多城镇、乡村的屋顶上,经常可以看到熠熠发光的太阳能热水器的身影。太阳能热水器的安装和使用都很简单方便,既节能又环保,在很多方面都得到了广泛应用。为什么太阳能热水器能给水加热呢?

  平板式太阳能热水器的吸热过程比较简单,太阳辐射透过玻璃盖板,热能被集热板吸收后沿肋片和管壁传导给吸热管内的水。

  真空管式太阳能热水器的集热板由许多真空集热管组成,就像是许多并排的细长的暖瓶胆。真空管的内外层之间是真空的,内管外表面有一层特种材料涂层,可以有效吸收太阳辐射能,并转化为热能,传导给管内的水。利用冷水比重大、热水比重小的原理,吸热管和保温水箱之间形成了冷水下沉、热水上升的自然对流循环,使水箱中的水逐渐变热。通过保温水箱储存热水,可以保证人们随时有热水使用。通过连接管道按需要输送热水或冷水,使整套系统形成一个闭合的环路。通过控制系统显示并全自动控制水温、水位,还能防止真空管在高温空晒后又因突然注入冷水而爆裂。

  主机支架支撑着集热板与保温水箱,还用来调节集热板与地平面之间的角度,以形成一个最佳倾斜角,这是为了使太阳能热水器的集热板能获取最大限度的太阳能量。研究人员专门设计了软件来计算集热板在不同地区的最佳倾斜角,而在进行人工估算时,通常釆用在正午时太阳光垂直射入集热板采光面为最佳倾斜角。

  

  太阳能热水器

  太阳能热水温度能达多少?

  太阳能热水器水温一般为40℃~70℃,但高温天为何会飙升到99℃?专家介绍,太阳能热水器是循环加热,逐步累积水温。夏天气温高,日照时间长,水温达到99℃很正常。比如前一天水温达到50℃,如果没有使用,水会在水箱里自动保温,第二天太阳能继续加热,温度就会到70℃。如果连续几天不去用水,没有冷水加入循环,热水器的水温很容易就会达到100℃。

  这么高的水温会带来哪些问题呢?热水器的真空管可以承受400℃高温,而且水箱侧面设计有排气孔,水温达到100℃时,就会排出水蒸气散热,热水器不会损坏,但是可能会烫伤人。所以,这种情况下使用热水要小心,尤其是小孩,如果直接打开热水阀门,很容易被热水烫伤。

  专家建议,最好买一个恒温阀安装在热水器上,将水温控制在30℃~60℃之间。用遮阳布遮住部分真空管,也能有效降低水温。太阳能热水器的水管如果采用PES管,在100℃温度下可以使用50年。如果用的是铝塑管,一两年就会老化,应及时更换,防止烫伤事故发生。

  本作品为“科普中国-科学原理一点通”原创 转载时务请注明出处

  作者: 科学原理一点通

责任编辑:李阳阳

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